introduction to mwd

g

GE Power Systems

Introduction to MWD IInnttrroodduuccttiioonn ttoo MMWWDD

SERIAL NUMBER: Client Company:

THIS MANUAL CONTAINS PROPRIETARY INFORMATION THAT MAY NOT BE DISCLOSED TO OTHERS, REPRODUCED OR USED WITHOUT WRITTEN AUTHORITY FROM GE POWER SYSTEMS 1840 ROYSTON LANE ROUND ROCK, TEXAS 78664

This document is an unpublished work. Copyrinformation and expression contained herein confidence on a need to know basis. Yourrequiring the information contained herein. Yo

ight 2003 GE Power Systems. All rights reserved. This document and allare the property of GE Power Systems and is provided to the recipient in use of this document is strictly limited to a legitimate business purposeur use of this document constitutes acceptance of these terms.

g

GE Power Systems

NOTE: The PDF version of this document requires Adobe Acrobat version 5.0 or higher to correctly display the special characters such as math symbols.

Page 2 of 127 09/11/03 Introduction to MWD

g

GE Power Systems

Table of Contents CHAPTER 1: THE FOUNDATION: BASIC SKILLS AND KNOWLEDGE ...........7

1.1 Mathematics Review................................................................................................... 8 1.1.1 Arithmetic .............................................................................................................. 8

1.1.1.1 Basic Operations of Arithmetic ...................................................................... 8 1.1.1.2 Commutative Property .................................................................................... 9 1.1.1.3 Associative Property ..................................................................................... 10 1.1.1.4 Distributive Property..................................................................................... 10

1.1.2 Algebra................................................................................................................. 10 1.1.2.1 Lines and Graphs .......................................................................................... 10 1.1.2.2 Working With Variables ............................................................................... 15 1.1.2.3 Balancing an Equation .................................................................................. 15 1.1.2.4 Solving Quadratic Equations ........................................................................ 17

1.1.3 Trigonometry ....................................................................................................... 21 1.1.3.1 Triangles ....................................................................................................... 21 1.1.3.2 Sine, Cosine, Tangent ................................................................................... 23 1.1.3.3 Practical Application..................................................................................... 24

1.2 Basic Hydraulics........................................................................................................ 26 1.2.1 System Pressures.................................................................................................. 26 1.2.2 Bernoullis Principle ............................................................................................ 28 1.2.3 Annular Velocity.................................................................................................. 28 1.2.4 Pressure Pulses..................................................................................................... 31 1.2.5 Drilling Fluid ....................................................................................................... 33

1.3 The Drilling Rig......................................................................................................... 33 1.3.1 Different Types of Drilling Rigs.......................................................................... 33

1.3.1.1 Offshore ........................................................................................................ 34 1.3.1.2 Land .............................................................................................................. 38

1.3.2 Parts of a Drilling Rig .......................................................................................... 38 1.3.2.1 Rig Floor ....................................................................................................... 38 1.3.2.2 Mud Pumps ................................................................................................... 39 1.3.2.3 Standpipe....................................................................................................... 40 1.3.2.4 Draw Works .................................................................................................. 41 1.3.2.5 Kelly.............................................................................................................. 42

1.4 Bottom Hole Assemblies ........................................................................................... 42 1.4.1 Drill Collars ......................................................................................................... 42 1.4.2 Universal Bottom Hole Orienting Subs ............................................................... 43 1.4.3 Stabilizers............................................................................................................. 44

Introduction to MWD 09/11/03 Page 3 of 127

g

GE Power Systems

1.4.4 Crossovers............................................................................................................ 45 1.4.5 Heavyweight Drill Pipe........................................................................................ 45 1.4.6 Jars ....................................................................................................................... 46 1.4.7 Drillpipe Configuration........................................................................................ 46 1.4.8 Positive Displacement Mud Motors..................................................................... 46

1.5 MWD Tools................................................................................................................ 47 1.5.1 What is an MWD Tool?....................................................................................... 47 1.5.2 Different Types of MWD Tools .......................................................................... 47

1.5.2.1 Retrievable MWD Tools............................................................................... 47 1.5.2.2 Non-Retrievable MWD Tools....................................................................... 48 1.5.2.3 Logging Tools............................................................................................... 48

1.5.3 The Role of the MWD Operator .......................................................................... 49

CHAPTER 2: FIELD OPERATIONS ..................................................................51

2.1 Recommended Paperwork ....................................................................................... 51 2.1.1 Equipment Inventory ........................................................................................... 51 2.1.2 MWD Job Sheet................................................................................................... 51 2.1.3 Environmental/Job Site Information.................................................................... 51 2.1.4 Paperwork List ..................................................................................................... 51 2.1.5 Job Charge sheet .................................................................................................. 51 2.1.6 MWD Insurance sheet.......................................................................................... 51 2.1.7 Magnetic Declination/Tool Face Offset............................................................... 51 2.1.8 Survey Tie-in Information sheet .......................................................................... 52 2.1.9 Electro-Magnetic Error Report sheet ................................................................... 52

2.2 Well Site Responsibilities ......................................................................................... 52 2.2.1 Arrival at Rig Site ................................................................................................ 52 2.2.2 Before Rigging Up............................................................................................... 53

2.3 Rigging Up Surface equipment................................................................................ 53 2.3.1 Lines and Cables .................................................................................................. 53

2.4 Directional-Only Service .......................................................................................... 53 2.4.1 Safe Area Rig-Up................................................................................................. 53

2.4.1.1 Set Up in the Safe Area................................................................................. 53 2.4.1.2 Use the UPS (Uninterruptible Power Supply) .............................................. 53 2.4.1.3 Set Up Computer........................................................................................... 54 2.4.1.4 Connect RS-232 Cable.................................................................................. 54 2.4.1.5 Connect Programming Cable........................................................................ 54

2.4.2 Rig Floor Area Equipment................................................................................... 54 2.4.2.1 Set Up Terminal............................................................................................ 54 2.4.2.2 Connect 10-Pin Cable ................................................................................... 55


g GE Power Systems

2.4.2.3 Connect Power/Communications Cable(s) ................................................... 55 2.4.3 Rig Floor Area Equipment................................................................................... 56

2.4.3.1 Protect the Standpipe Pressure Transducer................................................... 56 2.4.3.2 Install the Standpipe Pressure Transducer .................................................... 56

CHAPTER 3: INTRODUCTION TO SURVEYING..............................................57

3.1 Reference Points........................................................................................................ 57 3.1.1 Magnetic North .................................................................................................... 58 3.1.2 True North............................................................................................................ 60 3.1.3 Grid North............................................................................................................ 61

3.2 Corrections ................................................................................................................ 65 3.2.1 Magnetic Declination........................................................................................... 66 3.2.2 Grid Correction .................................................................................................... 70

3.3 Quality Factors.......................................................................................................... 72 3.3.1 Magnetic Dip Angle............................................................................................. 72 3.3.2 Total Magnetic Field............................................................................................ 74 3.3.3 Total Gravity Field............................................................................................... 76

CHAPTER 4: TRANSFORMING INFLUENCES ................................................79

4.1 Magnetic Interference From BHA .......................................................................... 79 4.1.1 Hole Angle ........................................................................................................... 81 4.1.2 Hole Direction...................................................................................................... 83 4.1.3 Latitude ................................................................................................................ 84 4.1.4 Not Enough Non-magnetic Material.................................................................... 85 4.1.5 Hot Spots.............................................................................................................. 88

4.2 Magnetic Interference From Formation................................................................. 88 4.2.1 Formation Constituents........................................................................................ 88 4.2.2 Steel Components in the Hole.............................................................................. 89

4.3 Magnetic Interference From Solar Flares .............................................................. 89

4.4 Incorrect Operator Input ......................................................................................... 89

4.5 Incorrect Calibration................................................................................................ 89

4.6 Survey Technique...................................................................................................... 90 4.6.1 Drill String Movement......................................................................................... 90 4.6.2 Bad Detection....................................................................................................... 90 4.6.3 Stored Surveys ..................................................................................................... 90


g

GE Power Systems

4.6.4 Incorrect Survey Depth ........................................................................................ 91

CHAPTER 5: CALCULATING BOTTOM HOLE LOCATION.............................93

5.1 Calculating Bottom Hole Location .......................................................................... 94 5.1.1 Average Angle ..................................................................................................... 99 5.1.2 Radius of Curvature ........................................................................................... 102 5.1.3 Minimum Radius of Curvature .......................................................................... 105

5.2 Plotting Bottom Hole Location .............................................................................. 109

CHAPTER 6: GEOMETRICAL STEERING......................................................111

6.1 Toolfaces .................................................................................................................. 111 6.1.1 Magnetic Toolfaces (mTF) ................................................................................ 113 6.1.2 Gravity or Highside Toolfaces (gTF) ................................................................ 114 6.1.3 Orienting MWD Tools to Steering Tools .......................................................... 116

6.1.3.1 Orienting Retrievable Tools........................................................................ 117 6.1.3.2 Orienting Fixed Collar Tools ...................................................................... 119

INDEX...............................................................................................................123


g

GE Power Systems

Chapter 1: The Foundation: Basic Skills and Knowledge

MWD stands for Measurements While Drilling. The measurements considered for the purposes of this manual are directional measurements. An MWD Operator must have certain basic skills to perform at an optimum level. Among the skills necessary is a working knowledge of Mathematics, which encompasses simple arithmetic to trigonometry.

The mathematical skills will be necessary when dealing with problems involving hydraulics. While computer programs solve many of the problems for the operator, the operator must be able to calculate hydraulic problems when the need arises. The same may be said of survey calculations. The operator may occasionally need to calculate a survey without the benefit of a computer.

The MWD operator must know how a drilling rig operates. Rig operations affect many aspects of the MWD tool operation. The best MWD operators are those who know not only their job but also how the rig runs.

Knowledge of rig operations includes knowing what a Bottom Hole Assembly (BHA) is and how it works. The MWD tool is part of the Bottom Hole Assembly. An operator should know as much as possible about this and all other components of the drill string.

MWD operators should know the different types of MWD tools available and their basic components. An operator should know how the components work and how they contribute to the drilling process.

The MWD operator has an important job in ensuring that problems and rig downtime are kept to a minimum. This job is difficult, demanding and requires many different types of skills.

The sum of the skills and knowledge presented in this chapter will be the foundation for a successful career in the MWD field.


g

GE Power Systems

1.1 Mathematics Review An MWD operators duties require an understanding of mathematics from arithmetic through trigonometry. This section provides a review of basic mathematical concepts and tests the understanding of those concepts.

1.1.1 Arithmetic

1.1.1.1 Basic Operations of Arithmetic

+ means add or put two things together. 5 + 2 indicates that 5 and 2 should be joined together to make 7.

means subtract or take something away. 3 means take 3 away from 6 leaving 3

* means to multiply something. This is another way of adding. 5 * 6 means add 6 to itself 5 times such as: 6 + 6 = 12 (first and second additions), 6 + 12 = 18 (third addition) 6 + 18 = 24 (fourth addition) and 6 + 24 = 30 (fifth addition). Since 6 was added to itself 5 times, multiplication is often stated as 5 times 6.

/ or means divide. Division is another means of multiplying. 12/3 means find out how many times 3 fits into 12 This is another way of saying 12 * . The result of multiplying any number by a fraction is division.

Xn means multiply something by itself the number of times shown by the little number (the exponent) next to the big number (the base). Just as multiplication indicates how many times to perform an addition, the exponent indicates how many times to perform a multiplication. In this case, the number


g

GE Power Systems

indicated by X must be multiplied by itself the number of times specified by the little number to the upper right. If X is 6 and n is 3, it means multiply 6 by itself 3 times: 6 * 6 = 36 (first and second multiplication) 6 * 36 = 216 (third multiplication).

X means square root, that is, find the number which,

multiplied by itself, equals the number represented by X. For example: 16 asks, Which number, times itself, equals 16? The answer is 4, because 4 * 4 = 16, or 42 = 16.

1.1.1.2 Commutative Property

Most of Mathematics is plain common sense. For instance, the order in which numbers are added is unimportant. The following equation illustrates this point:

2 + 4 equals 4 + 2 Eq. 1

Note that it does not matter how many numbers are added. The order in which they are added remains unimportant. This fact is called the Commutative Property.

However, when multiplication or division are mixed with addition or subtraction, the order in which operations are performed is important. For example,

4 + 2 * 10 is not the same as 2 + 4 * 10 Eq. 2

because the answer depends upon which operation is performed first. If the addition is done first, the answer is 60 in both cases. But if the multiplication is done first, the answer is 24 in the first case and 42 in the second.

One of the rules of Mathematics is to perform multiplication and division first, then addition and subtraction.

The order in which numbers are subtracted is also important:

8 2 is not the same as 2 8 Eq. 3


g

GE Power Systems

Since eight minus two equals six, it is not the same as two minus eight, which equals negative six.

1.1.1.3 Associative Property

This property is much like the Commutative Property but it involves adding three or more numbers in groups. The parentheses are used to indicate which numbers should be added first.

Adding (5 + 6) + 7 is the same as adding 5 + (6 + 7). In the first case five plus six equals eleven and seven plus eleven equals eighteen. For the second case, five added to the sum of six and seven (which is thirteen) also equals eighteen.

1.1.1.4 Distributive Property

The Distributive Property or Distributive Law is a very important and powerful concept. The Distributive Property states that:

A * (B + C) = (A * B) + (A * C) Eq. 5

5 * (10 + 2) is the same as (5 * 10) + (5 * 2) Eq. 6

Remember, always do the multiplication before the addition. In this example, five times twelve (ten plus two) equals sixty and is the same as five times ten (fifty) plus five times two (ten). Fifty plus ten equals sixty.

Application of The Distributive Property permits the solution of most algebra problems.

1.1.2 Algebra

1.1.2.1 Lines and Graphs

If you were to take four steps to your right, you would then be four steps from your starting point. Measuring your steps on a number line like the one in figure 1.1.2.1.a, you would be a distance of four from the starting point or origin. The origin is the number zero. Positive numbers are expressed as steps to the right of zero.


g

GE Power Systems

Steps to the left of zero represent negative numbers. Negative numbers are identified with a minus in front of them. Adding a negative number is like subtracting a positive number:

4 + (2) is the same as 4 2 Eq. 7

Both methods give the same answer: go four steps to the right, then two steps to the left. No matter how it is stated, you still end up at the number two.

-4 -3 -2 -1 4 3210

Figure 1.1.2.1.a Number line

If we add a second number line perpendicular to the first, passing it through the first number lines origin, we create a rectangular coordinate system, as in figure 1.1.2.1.b.

c) Intersection of lines a and b

Originb) Two spaces

to the right of the origin

a) Two spaces above the origin

Figure 1.1.2.1b Rectangular Coordinate System

The rectangular coordinate system allows the location of points not only on the number lines but also in the spaces, or quadrants, between the lines. With two lines for reference, each point gets


g

GE Power Systems

two numbers, or coordinates, to define its location. The two numbers are expressed in parentheses with a comma after the first number, for example, (2, 2).

The first number, called the X coordinate, tells the points horizontal distance from the origin. The second number, called the Y coordinate, tells the points vertical distance from the origin.

Both coordinates can be used in an equation to determine a points straight-line distance from the origin:

a2 + b2 = c2. Eq. 8

(Where a represents the X coordinate (the first number), b represents the Y coordinate (the second number) and c represents the points distance from the origin.)

So: a + b = c Eq. 9 Using this method, the distance from the origin is:

22 + 22 = c2 or 4 + 4 = c2

8 = c2 or c2 = 8 Now take the square root (the symbol means square root) of both sides of the equation c = 8 or approximately 2.8284 The slope of the line that goes from the origin through point c is calculated by dividing how many spaces go up or down by how many go right or left. This is called dividing the rise (up or down) by the run (left or right).

Calculate the slope of the line in Figure 1.1.2.1.a. by:

Slope = 2 (the rise) 2 (the run) so Slope = 1


g

GE Power Systems

A slope of one means that for every space that goes up or down, one space goes to the right or left. (See figure 1.1.2.1.b.)

For every one space moving up there is one space moving to the right.

2

1

21

Figure 1.1.2.1.b Slope of 1

As the position of the line changes, the slope changes. Suppose that for every space up, there are two spaces to the right. Dividing the rise by the run yields a slope of one half. On the other hand, if there are two spaces up and one to the right the slope is two. See Figure 1.1.2.1.c.

1 1

2

1 2 1

Figure 1.1.2.1.c Two different slopes

The graph on the left has a slope of while the graph on the right has a slope of 2.

Suppose that two points along the line are known. Each point is defined by two values, the distance along the x or horizontal axis and the distance along the y or vertical axis. See Figure 1.1.2.1.d. Whenever the x and y values are given they look like


g

GE Power Systems

(3, 2). The x value is always given first. Values for Point 2 are presented as (6, 3).

3

X

Chapt

Point 2: X = 6, Y = 3

Point 1: X = 3, Y = 2

3 6

2

Figure 1.1.2.1.d Two points on the line are known.

If two points are known, the difference between their y values divided by the difference between their x values determines the slope of the line:

Y value of Point 2 minus Y value of point 1

Divided by

X value of point 2 minus X value of point 1

Therefore, the slope of the line in Figure 1.1.2.1.d. is determined in the following manner:

(3 2) (6 3) = 1 3 = 1/3 The slope is 1/3: the line goes one space up for every three spaces to the right.


g

GE Power Systems

1.1.2.2 Working With Variables

Sometimes a variable is used to represent the unknown information in a problem. Typically, a letter is used for the variable, as in the following formula:

5n + 3 = 18 Eq. 10

The letter n is a variable standing for an unknown value. To identify the value, solve the equation for n.

To solve for n, we will isolate the variable on one side of the equation (normally the left side) with everything else on the other side of the equal sign.

Start the process of isolating n by subtracting three from both sides of the equation.

5n + 3 3 = 18 3

By subtracting three from both sides, the values remain equivalent. Now the equation looks like:

5n = 15

Dividing both sides by 5 completes the process.

5n / 5 = 15 / 5

Since 5n divided by 5 is n and 15 divided by 5 is 3, the solution for n is that n equals 3.

n = 3

To identify the value of a variable, isolate the variable on one side of the equation by applying identical operations to both sides of the equation.

1.1.2.3 Balancing an Equation

Solving an equation for an unknown, as covered in section 1.1.2.2, involves balancing an equation. Balancing means keeping each side equivalent while you solve for the unknown.

In the following example, the equivalence of each side of the equation is preserved.


g

GE Power Systems

5n + 3 = 8n 6

Add a negative three to the left side to isolate 5n. Also add a negative three to the right side to preserve equivalence.

5n + 3 3 = 8n 6 3

5n = 8n 9

Now add 8n to the left side to remove n from the left. Add the same to the right side to preserve the balance.

3n = 9

Multiply both sides by 1

3n = 9

Divide both sides by 3

n = 3

Notice that all the operations performed maintained the equivalence of both sides. To maintain the equivalence while solving for the unknown is to balancing the equation.

Units of measure are also multiplied and divided, just like numbers, to balance equations.

Suppose you need to convert 10,000 feet-per-second into miles-per-hour. Ask the question like this: If you can go 10,000 feet in one second, how many miles can you go in one hour (3,600 seconds)? Now put it equation form:

10,000 feet = n miles 1 second 1 hour

Convert feet-per-second to feet-per-hour:

10,000 feet * 3,600 seconds = n miles 1 second 1 hour 1 hour

10,000 feet * 3,600 seconds = n miles 1 second 1 hour 1 hour


g

GE Power Systems

36,000,000 feet = n miles 1 hour 1 hour

Note: You can multiply just one side of an equation by a factor only when that factor is equal to 1.

The factor 3,600 seconds 1 hour

is equal to 1 because 3,600 seconds equals 1 hour. 3,600 seconds / 1 hour equals 1/1 or 1.

Now convert feet-per-hour to miles-per-hour:

36,000,000 feet * 1 mile = n miles 1 hour 5,280 feet 1 hour

36,000,000 feet * 1 mile = n miles 1 hour 5,280 feet 1 hour

(36,000,000 5,280) miles = n miles 1 hour 1 hour

36,000,000 5,280 6,818.2 miles per hour. Note: The symbol means, is approximately equal to. In this

case, if the decimal point were carried out to four places the answer would be 6,818.1818. The decimal portion is rounded off to .2.

6818.2 miles = n miles 1 hour 1 hour

So the answer is, if you can go 10,000 feet per second, you can go approximately 6818.2 miles per hour.

1.1.2.4 Solving Quadratic Equations

Quadratic equations contain a squared variable, that is, a variable with an exponent of 2, such as x2. An example of a quadratic equation is 3x2 + 2x + 5 = 21.


g

GE Power Systems

Many strategies can be used to simplifying these equations so they are not so intimidating. In the above example, 3x2, 2x, 5 and 21 are all terms of the equation. A term, in an equation, is anything that is separated by an operation sign, or operator, such as + , , * , , or = . Think of terms as packages that can be moved around or opened and repacked.

To begin solving this equation for x, reduce one side of the equation to zero by subtracting 21 from each side.

3x2 + 2x + 5 21 = 21 21

3x2 + 2x 16 = 0

Now apply the simplifying strategy of grouping. In grouping, you divide the non-zero side of the quadratic equation into two smaller equations, in accordance with the distributive property. Each of the smaller equations will contain the variable adding or subtracting a number. If the term containing the squared variable also has a number, such as the 3 in 3x2, place the number with the variable in the first smaller equation

Once you have reduced one side of the equation to zero (and arranged the terms on the non-zero side from greatest to least factors of the variable) you can use the terms and operators as clues to find the smaller equations.

You can determine the operation signs of the smaller equations from the signs in the quadratic equation. The fact that the second operation sign is minus tells you that the two smaller equations will have different operation signs. One will be plus, the other will be minus.

So far, we know the smaller equations look like this:

(3x + __ ) (x __ ) = 0

Note: When terms are enclosed in parentheses and put close together, it indicates that the terms must be multiplied. ( c ) ( b ) means multiply c times b.

You can determine the numbers to add or subtract in the smaller equations from the terms of the quadratic equation. These two numbers, when multiplied by each other, equal the last term in the quadratic equation, in this case 16. They will also equal the


g

GE Power Systems

numerical portion of the middle term when added or subtracted according to the operators in the two smaller equations.

However, when the first term in the quadratic equation also has a numerical portion, you must also account for this number in finding the second terms for the smaller equations.

Two questions will help you find the missing two numbers.

First question: Which sets of two numbers each multiply to equal 16?

Answer: The sets 1 and 16, 2 and 8, and 4 and 4. Each of these pairs, when multiplied, equals 16.

Second question, Which of these pairs of numbers, when one of its numbers is multiplied by 3, add or subtract to make 2 (the numerical portion of the equations middle term)?

Does 16 (3 * 1) equal 2? How about (3 * 4) 4?

No, but 8 (3 * 2) does equal 2. So use 8 and 2 as the second terms in the smaller equations.

Now we know the smaller equations will be:

(3x + 8) (x 2) = 0

Lets verify: use the FOIL (First, Outside, Inside, Last) method to multiply the smaller equations.

First, multiply the first terms of each smaller equation:

3x * x = 3x2

Second, multiply the outside terms:

3x * 2 = 6x

Note that you include the minus sign with the term.

Third, multiply the inside terms:

8 * x = 8x

Fourth, multiply the last terms:


g

GE Power Systems

8 * 2 = 16

Now add the results of the FOIL method:

3x2 6x + 8x 16 = 0

and simplify:

3x2 + 2x 16 = 0

So (3x + 8) (x 2) does equal our quadratic equation.

With the correct combination of terms, we can now solve the equation for x. We have used the distributive property to restate the quadratic equation as:

(3x + 8) (x 2) = 0

With the right side of the equation set to zero, we can know that at least one of the factors on the left side equals zero. The only way a product can equal zero is if at least one of the factors equals zero. So we know that either (3x + 8) = 0 or (x 2) = 0

Solve (3x + 8) = 0 for x.

Subtract 8 from both sides of the equation:

3x = 8

Divide both sides by 3.

x = 8/3

Substitute 8/3 for x in the original equation:

3x2 + 2x + 5 = 21

3 * (8/3) 2 + 2 * 8/3 + 5 = 21

3 * (64/9) + 16/3 + 5 = 21

64/3 16/3 + 5 = 21

21 1/3 5 1/3 + 5 =21

16 + 5 = 21


g

GE Power Systems

21 = 21

So one value of X is 8/3.

Now solve (x 2) = 0 for x.

Add 2 to both sides of the equation:

x = 2

Substitute 2 for x in the original equation:

3x2 + 2x + 5 = 21

3 * ( 4 ) + 4 + 5 = 21

12 + 9 = 21

21 = 21

So the other value of x is 2.

Using the strategies of balancing equations, grouping and the distributive property, we have identified the possible values of x and solved the quadratic equation.

1.1.3 Trigonometry 1.1.3.1 Triangles

Triangles have several interesting properties. The three angles of any triangle in a single plane must add up to 180 degrees. All Right Triangles, like the ones shown in Figure 1.1.3.1, have one angle that is 90 degrees. That means that the other two angles must equal 90 degrees when added together.

Another property of triangles is that the ratio of sides is always the same for similar triangles (two triangles with identical angle measurements), even if they are of different sizes.

In Figure 1.1.3.1, assuming the two triangles are similar, the ratios of the sides for triangle A are the same as for those of triangle B. For instance, the ratio of sides c and a on triangle A is the same as the ratio of sides c and a on triangle B.


g

GE Power Systems

B

c

a

c

A

a

b b

Figure 1.1.3.1 Two Right Triangles

Another property of Right Triangles that is extremely useful is that the length of any side can be determined if the lengths of the other two sides are known.

In Figure 1.1.3.1, the sides are labeled a, b and c. Side c is the hypotenuse. The hypotenuse is the side opposite the right angle (90 degree angle) in a Right Triangle.

For any Right Triangle, the sides have the following relationship:

c2 = a2 + b2

This means that if you know the length of any two sides, the length of the other side can be calculated. For example, suppose that the length of side a is 10 and side c is 15, the length of side b is:

b2 = c2 a2 b = (c2 a2) b = (152 102) b = (225 100) b = (125)

b 11.1803


g

GE Power Systems

1.1.3.2 Sine, Cosine, Tangent

The ratios of the sides of a triangle have peculiar names. An example is the cosine. The cosine is the ratio of the side adjacent an angle to the hypotenuse. See Figure 1.1.3.2 for an example of the cosine function.

c

a

b

Figure 1.1.3.2 Right Triangle with angles and sides labeled

The cosine of angle is the ratio of side b to side c or in other words, the length of the adjacent side b divided by the length of the hypotenuse c. Suppose angle is sixty degrees. The cosine of 60 degrees is 0.5, so the ratio of side b to c is 0.5. If side b is 10 feet, side c must be 20 feet

0.5 = 10 side c side c * 0.5 = 10

side c = 10 0.5 side c = 20

As long as the angle is 60 degrees, the ratio of the adjacent side to the hypotenuse will be 0.5, even if the Right Triangle is sized or oriented differently from the one presented in Figure 1.1.3.2.

If one angle in Figure 1.1.3.2 is 60 degrees and the right angle is always 90 degrees, then the remaining angle must be 30 degrees:


g

GE Power Systems

180 (60 + 90) = 30

180 150 = 30.

If angle is 30 degrees, the length of side b can be determined by using the cosine of angle : Cosine = length of side b hypotenuse Cosine 30 = a 20 0.86602 = a 20 a = 20 * 0.86602

a = 17.32

Rules for sine, cosine and tangent are:

Sine = the length of the side opposite the angle divided by the length of the hypotenuse

Cosine = the length of the side adjacent the angle divided by the length of the hypotenuse.

Tangent = the length of the side opposite the angle divided by the length of the side adjacent the angle.

The sine, cosine and tangent values for all angles are found in tables or are available on most scientific calculators.

1.1.3.3 Practical Application

Trigonometry is used extensively in drilling a directional well. Directional wells are those not drilled vertically, that is, not drilled straight down. Chapter 2 discusses directional wells in more detail. Chapter 3 discusses the surveying of directional wells.

Suppose a well is drilled at a 50-degree angle instead of straight down (see Figure 1.1.3.3. for a theoretical directional well). While the depth of the hole from the surface to the drill bit can be measured directly, the vertical depth cannot. No sensor measures vertical depth. However, vertical depth is important because it establishes a comparison point between a vertical well


g

GE Power Systems

and a directional well. It also allows comparison between two directional wells.

Well angle measured

from vertical plane

MeasuredDepth

Offset of well bottomfrom vertical planeor vertical section

Vertical Depth

Figure 1.1.3.3 Directional well

Notice that the measured depth looks like the hypotenuse of a triangle and the vertical depth is the adjacent side to the angle of offset from vertical. To calculate the vertical depth, you must know two things:

1) The angle of the offset from vertical, called the hole angle and

2) The measured depth of the hole.

With a hole angle of 50 degrees and a measured depth of 1,000 feet the vertical depth is calculated by:

Cosine 50 0.6428 Cosine 50 vertical depth 1,000 Cosine 50 * 1,000 vertical depth 0.6428 * 1,000 642.8 feet.


g

GE Power Systems

Using the same hole angle and measured depth, the offset from vertical (vertical section) can be calculated by taking the sine of the hole angle. Remember that the sine is defined as dividing the opposite side, the vertical section, by the hypotenuse, the measured depth. So,

Sine 50 0.7660 Sine 50 vertical section 1000 Sine 50 * 1,000 vertical section 0.7660 766.0 feet In a typical directional well, surveys are calculated at regular intervals with the vertical depth and vertical section part of the survey calculation.

1.2 Basic Hydraulics 1.2.1 System Pressures

One of the most important concepts when dealing with hydraulics as it applies to MWD service is that pressure is felt equally throughout a system. While this may seem too sensible to even state formally, it is very important to keep it in mind. When drilling a well, the cuttings, or drilling residue, must be removed from the well bore by some means. The means may be a flow of water, weighted mud, foam, steam or air. Most wells are drilled with either water or some type of weighted mud. The column of water or mud will be called a drilling fluid. Drilling fluids exert hydraulic pressure against the formation. Remember that this pressure is exerted in all directions. The pressure is called the hydrostatic head or hydrostatic pressure. It can be calculated by using the formula: Pressure = 0.052 * Weight of the drilling fluid * Vertical depth Hydrostatic pressure is normally measured in pounds per square inch or psi. In Europe, Asia and some parts of Latin America, the pressure may be measured in Bars. For the purposes of this manual, pounds per square inch will be used. Similarly, Weight of the drilling fluid in the United States is normally stated in pounds per gallon. In parts of


g

GE Power Systems

Europe, Asia and Latin America, it may be stated as grams per cubic centimeter. The example in this manual will use pounds per gallon. When calculating the hydrostatic pressure (also called the Bottom Hole Pressure, or BHP) it is important to remember to multiply by the Vertical Depth if the hole is a directional well. The following example shows how to calculate bottom hole pressure (BHP):

Vertical Depth = 10,000 feet Weight of the Drilling Fluid = 10 pounds per gallon BHP = 0.052 * 10 * 10,000 BHP = 0.052 * 100,000 BHP = 5,200 psi

The reason it is important to remember that pressure is felt equally throughout the system for a particular depth is that MWD tools are limited to a maximum system pressure, typically 20,000 psi. If the maximum mud weight to be used is 18 pounds per gallon (ppg), what is the maximum vertical hole depth before the system pressure exceeds the tools maximum pressure rating?

20,000 psi = 0.052 * 18 * Max_Vertical_Depth

Max_Vertical_Depth = 20,000 (0.052 * 18) Max_Vertical_Depth = 20,000 0.936 Max_Vertical_Depth = 18,720 feet

Once the tool depth exceeds 18,720 feet, there is a possibility that one or more systems will fail due to excessive pressure.


g

GE Power Systems

1.2.2 Bernoullis Principle Squeeze a water hose near the end. Water shoots out of the hose at a high rate. Why? Ask Bernoulli, the person who first explained this phenomenon. In the pinched region of the hose, the cross sectional area of the hose is reduced, an area of low pressure is created and the velocity of the water is greatly increased. The increased velocity causes the water to shoot out of the hose. Figure 1.2.2 illustrates three separate areas with different pressure regions. The pressure is higher before the restriction than in or past the restriction. In the area of restriction, the pressure is relatively low. After the restricted area, the pressure returns to normal.

Higher Pressure Area

Pressure is reduced and

velocity is increased in this area

Pressure returns to normal in this area

Direction Of

Flow

Figure 1.2.2 Hydraulic system with a restriction

1.2.3 Annular Velocity Annular velocity (AV) is the speed of a fluid traveling in a closed pressure system such as in the annulus (the ring-shaped space) between the drill pipe and the hole. Erosion on the metal surfaces of the MWD tool as well as around areas where restrictions occur are directly related to annular velocity and the amount of solid material in the mud system. Two types of mud flow will be considered in this manual, turbulent flow and laminar flow. Turbulent flow occurs when the annular velocity reaches a critical point called critical velocity. Below the critical velocity mud flow is laminar (flowing smoothly). Above the critical flow value mud flow is turbulent.


g

GE Power Systems

Turbulent mud flow describes a situation in which the fluid column has eddy currents. See Figure 1.2.3.a.

Restriction in this region creates turbulent flow

below

Area of turbulent flow

Figure 1.2.3.a Restrictions create turbulence at critical velocity

The area of erosion in Figure 1.2.3.a is right below the two blades on either side of the drill pipe. Laminar flow causes less damage. In the laminar flow region, particles are moving parallel with the object in the hole and very little damage due to erosion occurs. See Figure 1.2.3.b.


g

GE Power Systems

Figure 1.2.3.b Laminar flow creates very little erosion

Fluid velocity, or as it is commonly called, annular velocity, is usually expressed in units of feet per minute. Use the following formula to calculate fluid velocity:

Pump Output * Strokes Per Minute Annular Capacity

Pump Output is in Barrels per Stroke bbls/stk Strokes Per Minute spm Annular Capacity is in Barrels per Foot bbl/ft Remember to treat the units as if they were numbers. That is they are added, subtracted, multiplied and divided. Annular capacity is the diameter of the larger cylinder squared minus the diameter of the smaller cylinder squared divided by 1029. Calculate the annular capacity using the following formula:

Inside Diameter2 Outside Diameter2 1029


g

GE Power Systems

If the hole diameter is 9.5 inches and the drill pipe is 5 inches, then the calculation is:

9.52 52 1029

90.25 25 1029

65.25 1029

0.06341 Assume the pump output is 0.107 barrels per stroke and the pump is operating at 100 strokes per minute:

0.107 bbls/stk * 100 stks/min 0.6341 bbls/ft.

10.7 bbls/min 0.6341 bbls/ft

16.87 ft/min

The annular velocity in this case is approximately 16.87 feet per minute.

1.2.4 Pressure Pulses Most of the MWD tools in service today use Bernoullis principle to communicate between the tool and the surface computer. The data from the tool are encoded into a series of pressure pulses and decoded at the surface. Figure 1.2.4 shows how the pressure pulses are created.


g

GE Power Systems

Normal state: no restriction

High Pressure Pulse = 500 psi

2000 psi

Restriction creates

high pressure

Pressure returns to

normal

P R E S S U R E

3000 psi

1500 psi

0 psi

TIME

Figure 1.2.4 Pressure Pulse Creation

High-pressure pulses are created by a momentary restriction of the hydraulic system (see Figure 1.2.4.). Data are arranged into a series of restrictions. A sensor at the surface converts the mechanical pressure of the pulse to an electrical signal. The electrical signal is sent to a signal converter and then to a computer. The surface computer decodes the data and displays the information on the computer screen.


g

GE Power Systems

1.2.5 Drilling Fluid In the oil and gas industry drilling fluids are collectively called mud. Some exceptions are areas where wells are drilled with foam or air. However, the majority of wells drilled in the United States are drilled with mud. For the Tensor MWD system the fluid column of a well acts as part of the communications system or communications bus, also called the qbus. Instead of communicating with electrical pulses, the system uses changes in fluid pressure to send data. The fluid or mud system then becomes part of the qbus, essentially a mud bus. The mud system controls the quality of the mud and is critical to successfully transmitting MWD data through the mud bus. Thicker or more viscous muds affect pulses by creating less sharp peaks. Imagine swimming through molasses compared to swimming through clear water. Just as a swimmer would lose energy more quickly while trying to swim through molasses, the pulse loses energy when transmitted through a viscous fluid. Sometimes gas or air will get into the mud. Both will cause symptoms that look like pulse failures.

1.3 The Drilling Rig The several different types of drilling rigs can be organized into two basic categories:

1) drilling rigs that operate on land and 2) drilling rigs that operate over water, including offshore rigs.

Most rigs have some basic parts in common. Learning the names of the basic parts is extremely important since the oil field has developed its own vocabulary. Once the names are mastered, working on a drilling rig will be considerably easier.

1.3.1 Different Types of Drilling Rigs Although the types of drilling rigs are confined to two major categories, the types of rigs that operate in very shallow water in inland lakes, marshes and swamps deserve their own category. These are inland barges. For the purposes of this manual the inland barges will be considered offshore rigs.


g

GE Power Systems

1.3.1.1 Offshore

1.3.1.1.1 Inland Barge

As noted in the introduction to this section, the inland barge exists somewhere between land rigs and offshore rigs. They are included in the offshore section because they work over water.

An inland barge is a drilling rig that has been mounted on a barge. It is not self-propelled and must be moved by special push boats to the drilling site.

It is very rare for an inland barge to drill in more than fifty feet of water. Normally the water depth is less than thirty feet. See Figure 1.3.1.1.1

Figure 1.3.1.1.1 Inland barge

1.3.1.1.2 Platform

As the name suggests, the drilling rig sits on a platform. The platform has very long legs on each corner that stand on the bottom of the ocean floor.

Generally, the platform rig is involved with production rather than drilling. However, at some platform rigs, new wells are


g

GE Power Systems

being drilled horizontally out from existing wells to increase production.

Some platform rigs do not have legs but are anchored to the ocean floor with huge wire cables called tension legs. These type platform rigs are used to drill the initial holes and can be quite large. See Figure 1.3.1.1.2.

Figure 1.3.1.1.2 Platform rig

The depths at which platform rigs operate vary. The tension leg platform rigs can be used in very deep water. Traditional steel leg type platform rigs are usually found in water depths of less than two thousand feet.

1.3.1.1.3 Jack Up

Jack up drilling rigs are literally jacked up. They have three or four large legs that are affixed to pontoons. To prepare the rig for transit, the pontoons are filled with air and jacked up to the surface by shortening the rig legs. Tugboats then tow the rig. At the new location, the pontoons are filled with water and jacked down by lengthening the rig legs.

The largest jack up rigs may drill in water depths between four hundred and one thousand feet of water. However, the length of their legs limits this type of rig to shallower water. See Figure 1.3.1.1.3.


g

GE Power Systems

Figure 1.3.1.1.3 Jack up Rig

1.3.1.1.4 Semi-Submersible

Semi-submersible drilling rigs operate in the deeper waters. These rigs are able to operate in water depths greater than two thousand feet.

This type of rig rests on pontoons. Unlike the jack ups the semi-submersible drilling rigs actually float on the pontoons. They are held in position by eight large anchors, with two anchors at each corner of the drilling rig.

At one time, the semi-submersible drilling rigs were used only for exploration drilling. Now, the rigs are also used as floating production platforms, especially in the deep water off the coast of Brazil. See Figure 1.3.1.1.4.


g

GE Power Systems

Figure 1.3.1.1.4 Semi-submersible rig

1.3.1.1.5 Drill Ships

As the name implies, these ships have been developed specifically for drilling. They operate in very deep water, generally from two thousand to seven thousand feet. See Figure 1.3.1.1.5.

Figure 1.3.1.1.5 Drill ship


g

GE Power Systems

1.3.1.2 Land

Land rigs vary less than offshore rigs. The major difference in land rigs is how deep the rigs can drill.

No matter what type of drilling rig, land or offshore, the majority of rigs have several parts in common. With few exceptions, the parts will only differ in size. See Figure 1.3.1.2.

Figure 1.3.1.2 Land drilling rig

1.3.2 Parts of a Drilling Rig

1.3.2.1 Rig Floor

The rig floor is where the business of drilling a hole takes place. The draw works, traveling block, kelly, rotary table, standpipe and drillers console are all on the rig floor.

Because the majority of work occurs on the rig floor, it is the place where most accidents happen. While on the floor, it is necessary to be alert to avoid being seriously injured. See Figure 1.3.2.1.


g

GE Power Systems

Figure 1.3.2.1 Rig Floor

1.3.2.2 Mud Pumps

When the term mud is used, it should be understood to mean a heavier drilling fluid, such as water. Although air or foam may be used to drill a well, the vast majority of wells are drilled with a heavier type of drilling fluid. The muds function is to remove the drilling residue (the drilled formation) from the hole.

The mud pumps pump the mud downhole and back to the surface where it flows over the shakers. Shale shakers remove the drilled cuttings from the mud. From the shakers, the mud goes to the return pit. It is then sent back to the suction pit where it is pumped back downhole. See Figure 1.3.2.2.


g

GE Power Systems

Figure 1.3.2.2 Mud Pump

If the mud pumps run smoothly, the signal from the MWD tool will be clear and easy to decode. When the mud pumps have problems, the signal from the MWD tool may be compromised.

The mud pumps have pulsation dampers that smooth the noise created by the action of the pumps. The pulsation dampers must be set to correct operating pressure for good detection of the MWD pulse signal.

Mud pumps come in two varieties, a duplex pump which pumps fluid on the forward and backward stroke of the pump piston and a triplex pump which pumps fluid only on the forward stroke of the piston.

Duplex pumps are noisier than triplex pumps and create pulsations that interfere with the MWD signal.

1.3.2.3 Standpipe

The mud travels from the mud pumps, through the standpipe, into the kelly, down through the drill string and out the drilling bit. The standpipe is located next to the derrick and is about forty feet tall.

Mud goes through a standpipe manifold on the drill floor before traveling up through the standpipe. The pressure transducer, that converts the physical energy of the pulse into an electrical


g

GE Power Systems

signal, is located on the standpipe manifold. It is called the Standpipe Pressure Transducer (SPT).

1.3.2.4 Draw Works

Also on the drill floor is a large spool wound with thick wire rope. This is the draw works. It works in conjunction with a huge winch system containing the traveling block and the crown block.

The wire rope, called the drill line, comes off the spool or draw works, is routed to the crown block, goes from the crown block to the traveling block and then to an anchor called the dead line.

Both the crown block and the traveling block have a series of pulleys that the drilling line winds around. The crown block is located at the top of the derrick and is stationary while the traveling block moves up and down. See Figure 1.3.2.3.

Figure 1.3.2.3 Typical draw works, land rig example

The drill string is lengthened by picking up a thirty-foot section of drill pipe and screwing it into the pipe already in the hole. The crown block and traveling block hold the weight of the drill pipe while a brake on the draw works controls the release of the weight. Since the drill string is very heavy, the weight of the string pushes the bit into the formation, allowing it to drill. The most common type drill bit has a series of chisel-like teeth on three rollers. The draw works is rotated and as the weight is released, the hole is drilled deeper.


g

GE Power Systems

1.3.2.5 Kelly

The kelly is a part of the drilling process, not a persons name. It is the drive connector at the top of the drill string. Most new rigs use top drives so that fewer connections are necessary to drill the well.

Sections of drill pipe are called joints. Joints are usually thirty feet long. Once a joint is drilled down, the kelly is raised and detached from the drill string. The new joint is put in the drill string below the kelly.

A typical kelly is about 45 feet long. About 40 feet of the kelly is extended below the surface with the drill string. So the total depth of the hole (called the measured depth) equals the length of the drill string plus the part of the kelly extended below the surface.

Putting a new joint into the drill string is called making a connection. Directional surveys are often taken when a connection is made. These surveys allow the directional driller to make necessary corrections and keep the hole on the correct course.

Much of what the directional driller does involves manipulating the Bottom Hole Assembly to cause the hole to be drilled in the desired direction. Bottom Hole Assemblies are discussed in the next section.

1.4 Bottom Hole Assemblies Bottom Hole Assemblies consist of many different types of specialized drill pipe. These special function pieces are grouped together at the bottom of the drill string, hence the name Bottom Hole Assembly (BHA). The directional driller sometimes needs to change the Bottom Hole Assembly to effect the necessary changes in course direction or angle.

1.4.1 Drill Collars To drill into the formation (the selected volume of earth), the drill bit requires weight, much like a hand drill and drill bit require pressure to drill through wood. Without pressure, the bit will not drill the hole. Pressure on a drill bit is supplied by the weight of very heavy drill pipe called drill collars. The more drill collars in the Bottom Hole Assembly, the more weight that can be imposed on the drill bit. Because drill


g

GE Power Systems

collars are larger than normal drill pipe, the number of drill collars that can be used in the Bottom Hole Assembly is limited.

1.4.2 Universal Bottom Hole Orienting Subs Universal Bottom Hole Orienting (UBHO) subs are also called muleshoe subs. A sleeve is inserted into the UBHO sub for the alignment of directional components. See Figure 1.4.2. Names for this sleeve include the muleshoe, the insert, and the orienting sleeve. At the bottom of the MWD tool is a cutaway that mates to a key in the muleshoe insert. This keyed connection orients the directional module to the bend in the Mud Motor (refer to section 1.4.8).


g

GE Power Systems

Orientation sleeve inserted in the

UBHO

Orientation sleeve

Orientation Key

UBHO Orientation

Sleeve Orientation

Key

Top View: Orientation sleeve inserted

in the UBHO

Figure 1.4.2 Orientation sleeve, key and UBHO

1.4.3 Stabilizers Stabilizers are aptly named. They provide stiffness to the Bottom Hole Assembly (BHA). These specialized pieces have blades on them that are almost the same diameter as the hole being drilled. Putting more stabilizers in the hole creates a stiffer Bottom Hole Assembly. The stiffer the Bottom Hole Assembly, the less the hole will stray from the desired direction. The stabilizer blades outside diameter and their placement in the BHA control how the BHA performs while drilling. Additional, smaller


g

GE Power Systems

stabilizers, called under-gauge stabilizers are used to either build angle or lose angle, depending on their location in the BHA.

1.4.4 Crossovers Drill pipe, drill collar and other specialized drill string items do not have standardized threads. In order to assemble two drill string elements having different connections, a crossover is used (see Figure 1.4.4).

Box-by-Pin Crossover

Box-by-Box Crossover

Pin-by-Pin Crossover

Figure 1.4.4 Different types of crossover subs

A drill string component may have either a protruding, threaded connector, called a pin, or a recessed, threaded connector, called a box. Some drill string components have a box at both. If the end of the piece that it screws into also has a box, a pin-by-pin crossover is used to attach the two pieces. Conversely, the drill string elements may have a pin at both ends of the pipe. To attach this item to another pipe that also has a pin, a box-by-box crossover is used.

1.4.5 Heavyweight Drill Pipe As the name implies, heavyweight drill pipe is heavier than normal drill pipe. Like drill collars, heavyweight drill pipe adds weight to the Bottom Hole Assembly. There is a limit to how much heavyweight drill pipe can be used in the drill string. Too many sections of heavyweight drill pipe make it difficult to adequately control the amount of weight


g

GE Power Systems

transferred to the drill bit. Heavyweight drill pipe is also more expensive than normal drill pipe, so its use may also be limited by cost.

1.4.6 Jars Sometimes the drill string becomes stuck in the formation. It is the job of the jars to help free the drill string. Jars operate by creating a very strong shock in the drill string. This is why the name is appropriate: it jars the drill string loose.

1.4.7 Drillpipe Configuration The drill string is normally configured with the drill collars on the bottom, the heavyweight pipe above the drill collars and drillpipe from the heavyweight to the surface. The mud pumped downhole goes through the kelly then through the drillpipe, the heavyweight, the drill collars and out through nozzles in the drill bit.

1.4.8 Positive Displacement Mud Motors A mud motor rotates the drill bit. It uses the Moineau principle to create rotation. A positive displacement mud motor consists of a molded rubber stator and a steel rotor. The rotor and stator have a helix shape. Rotation results from forcing the mud down through the area between the rotor and stator. A drill string configuration that includes a mud motor allows rotation of the drill bit without rotation of the drill string. Such a configuration therefore allows the drill string to be oriented in new directions. The use of a mud motor to influence drilling direction pre-dates MWD tools. MWD tools complement the mud motor with two critical functions:

1) they tell in which direction the hole is being drilled and 2) they enable the directional driller to orient the mud motor

to the desired angle and direction.


g

GE Power Systems

1.5 MWD Tools 1.5.1 What is an MWD Tool?

Guiding the hole to its final destination is the job of the MWD tool. It is like a pair of downhole eyes for the directional driller. The MWD tool shows not only how the mud motor is oriented while drilling, but also how successful the orientation has been. MWD stands for Measurements While Drilling. It is part of the Bottom Hole Assembly, typically located right above the mud motor. If no mud motor is installed, the MWD tool is placed as close to the bit as possible. At the most basic level, the MWD tool provides readout of tool facing (how the mud motor is oriented), hole direction and hole angle. MWD tools may also supply a variety of services beyond the basic level. The most revolutionary advance in MWD technology has been the addition of sensors that provide data about hole characteristics while drilling. This advanced level of service is called Logging While Drilling (LWD). It is now common practice to refer to directional-only capable tools as DMWD or Directional Measurements While Drilling. For the purposes of this manual, DMWD tools will be referred to as MWD tools.

1.5.2 Different Types of MWD Tools MWD tools are grouped according to their capabilities and characteristics into two types: retrievable and non-retrievable (also called fixed collar type).

1.5.2.1 Retrievable MWD Tools

Retrievable MWD tools are those that may be removed from the drill string in the event the tool fails to function or the drill string becomes stuck. This type of tool has been improved over the years so that it is now comparable in reliability to the non-retrievable type.

Retrievable MWD tools tend to have only directional capability. They are used in situations where it is important to control the cost of drilling a hole.


g

GE Power Systems

1.5.2.2 Non-Retrievable MWD Tools

The traditional advantage of non-retrievable MWD tools was that they were more reliable than retrievable tools. This is no longer the case.

If the tool fails to function downhole, all the drill string must be brought to the surface and the tool replaced. This is an expensive and time-consuming procedure.

With a few exceptions, the non-retrievable MWD tools are used for higher-level capabilities.

1.5.2.3 Logging Tools

Before the advent of Logging While Drilling, the drilling process had to be stopped and logging tools run in the hole on a wire line in order to obtain both quantitative and qualitative data about the formation through which the hole was drilled. Adding sensors that previously were reserved for wire line operations saved operating companies money and in many cases supplies superior data.

The most common type of data supplied by the Logging While Drilling tools are gamma ray activity and formation resistivity. Gamma ray data give an indication of the type of formation being drilled. Resistivity data impart quantitative information about the presence of hydrocarbons.

Other developments in Logging While Drilling include providing downhole pressure readings, downhole temperature, formation density, formation porosity, downhole weight on bit and downhole torque on the BHA.


g

GE Power Systems

1.5.3 The Role of the MWD Operator While the primary role of the MWD operator on location is to ensure that the tool works properly, the MWD operator also has a number of supplemental or collateral duties. It is vitally important that the directional driller receive correct data. If a problem occurs with the data, decisions relating to the data will be faulty, causing lost rig time and money. All values relating to the accuracy of directional data must be thoroughly checked. In addition to providing data, the MWD operator on location is the last person in the supply line capable of preventing a defective part or incorrect information from lowering the quality of service provided. The MWD operator must check the equipment to assure that problems are non-existent or minimal. Establishing good communications and having a good working relationship with the directional driller and company man are vitally important. Problems, limitations and requirements for the MWD tools must be communicated to the responsible person(s) in order to plan the work effectively. In a sense, the MWD operator runs a small business at the rig site. Tools and equipment must be kept in good running order. All items sent to the rig or sent from the rig must be accounted for. In some cases, keeping track of daily costs is required. Reports and forms must be filled out in a timely manner and given to the person(s) requesting them with a minimum of delay. An MWD operator represents the MWD service company at the rig site. Unacceptable conduct by the engineer reflects negatively on the service provider. Professional behavior and demeanor are important.


g

GE Power Systems


g

GE Power Systems

Chapter 2: Field Operations 2.1 Recommended Paperwork

2.1.1 Equipment Inventory A Tensor MWD Equipment Inventory Form accompanies all deployed equipment. The field engineer should fill out this form before returning the equipment box from a job.

2.1.2 MWD Job Sheet Operations provides an M/LWD Job sheet which contains basic job information such as Job Number, operating company, well information and directions to the rig.

2.1.3 Environmental/Job Site Information This sheet contains job site magnetic field information including magnetic declination, grid correction and total magnetic field.

2.1.4 Paperwork List This page lists the names of all the forms included in the folder and their locations in the folder.

2.1.5 Job Charge sheet Operations fills out this sheet which details the charges for services provided on the job.

2.1.6 MWD Insurance sheet This form must be filled out before the tool goes downhole. The company man must sign the insurance Form. This form allows the MWD company to provide and charge for insurance on the tool when it is downhole.

2.1.7 Magnetic Declination/Tool Face Offset The company man, directional driller and MWD operator must all sign the Magnetic Declination/Tool Face Offset form to verify that the


g

GE Power Systems

operating company, the directional drillers and the MWD company all agree on the magnetic declination parameter being used.

2.1.8 Survey Tie-in Information sheet The directional driller and MWD operator must both sign the Survey Tie-In Information sheet to verify that the tie-in used by the directional driller agrees with the tie-in used by the MWD company.

2.1.9 Electro-Magnetic Error Report sheet The company man and the directional driller must both review the Electro-Magnetic Error Report sheet to verify the amount of non-magnetic material required above and below the MWD tool.

2.2 Well Site Responsibilities 2.2.1 Arrival at Rig Site

Upon arrival at the rig site, check in with the company man and find out whether any special operating procedures are necessary when providing service. Also, meet with the directional driller to determine the following specifications: the flow rate to be used while the tool is in the drill string how often tool face updates are required magnetic declination used by the directional drilling company non-magnetic material required above and below the MWD tool current rig activity

For offshore rigs, contact the rig electrician to provide the correct power to the unit and to determine where to run the power line. Contact the tool pusher to check for any special instructions for running cables and installing sensor(s). Land rigs and some inland barges do not have a rig electrician. In such cases, contact the tool pusher to provide the correct power and to determine where to run the power cable and how to connect to rig power.


g

GE Power Systems

2.2.2 Before Rigging Up Quickly check the equipment box inventory. Make sure everything necessary to run the job is available and proper subs and monel drill collars are on location. Call the office immediately if an important piece of equipment is missing.

2.3 Rigging Up Surface equipment Once power to the unit is provided the tool can be programmed and highsided. If power to the unit is not available and time is limited, find a safe area where the SAPS OR SAI and surface computer can be located temporarily, then program and highside the tool from the safe area. Once power is provided to the unit, the SAPS OR SAI and surface computer can be moved to the unit.

2.3.1 Lines and Cables Run all lines and cables so that they are protected from falling objects. This precaution is especially important when running the power cable. Be sure to keep lines away from areas where others might trip over them or where standing water will accumulate. Avoid running sensor cables alongside rig power cables or any other cables that may carry high voltage, as such a layout can interfere with signal detection. Cable connections exposed to weather or moisture should be taped.

2.4 Directional-Only Service 2.4.1 Safe Area Rig-Up

2.4.1.1 Set Up in the Safe Area

Set up the SAPS or SAI inside the unit, trailer or other safe area. If offshore, the area should conform to the MMS regulations for a Safe Area (see Appendix A, MMS regulations for Safe Area Rig Up).

2.4.1.2 Use the UPS (Uninterruptible Power Supply)

Route power to the SAPS OR SAI through the UPS (Uninterruptible Power Supply) power conditioner to eliminate power spikes.


g

GE Power Systems

2.4.1.3 Set Up Computer

Set up both the Surface Computer and the Offline Computer.

2.4.1.4 Connect RS-232 Cable

Connect the RS-232 cable (a) to the Surface Computer and to the SAPS or SAI. See Figure 2.4.2.1.

2.4.1.5 Connect Programming Cable

Connect the programming cable (b) to the tool and to the SAPS or SAI. See Figure 2.4.2.1.

2.4.2 Rig Floor Area Equipment 2.4.2.1 Set Up Terminal

Locate an area in the drillers console to set up the Remote Drillers Terminal or Rig Floor Display. Use rope, chain or wire to hang the Remote Drillers Terminal or Rig Floor Display in a visible but unobtrusive location.


g

GE Power Systems

Remote Drillers Terminal Surface Computer

Standpipe Pressure

Transducer

d

c

Outside Unit

a

b

PowerOn / Off Switch

Drill Floor

SAPS

Safe Area or Unit

Figure 2.4.2.1 Safe area rig up

2.4.2.2 Connect 10-Pin Cable

Connect the 10-pin cable from the Standpipe Pressure Transducer (SPT) to the Remote Drillers Terminal (c). Always connect this cable before connecting the cables on either side of it. This cable is difficult to connect after the other two cables. (See Diagram 3.5.2.).

2.4.2.3 Connect Power/Communications Cable(s)

Connect the power and communication cable(s) (d) from the Remote Drillers Terminal: two cables to the SAPS or one cable to the SAI.


g

GE Power Systems

2.4.3 Rig Floor Area Equipment

2.4.3.1 Protect the Standpipe Pressure Transducer

Although the Standpipe Pressure Transducer looks rugged, it contains a very sensitive strain gauge element. Be careful when handling the Standpipe Pressure Transducer.

Always remove the Standpipe Pressure Transducer before leaving the rig for any reason. Try to position the transducer vertically to prevent mud solids from packing around its base. Mud or debris packed around the transducer can cause signal distortion. Make sure that the transducer is on the pressure side of any valves. Check to make sure that valves in-line with the transducer are open.

2.4.3.2 Install the Standpipe Pressure Transducer

2.4.3.2.1 Locate 2 NPT Female Fitting

Find a location on the standpipe that has an available 2 NPT female fitting.

2.4.3.2.2 Connect SPT

Insert the Standpipe Pressure Transducer adapter into the available fitting and screw in until hand-tight.

2.4.3.2.3 Tighten SPT

Carefully torque the Standpipe Pressure Transducer with a 36 pipe wrench.


g

GE Power Systems

Chapter 3: Introduction to Surveying Surveying is the process of obtaining information about the location of the well bore at multiple depths. The two components of any survey are Inclination (also called angle) and Azimuth (also called direction). Azimuth readings may require correction to fixed reference points. Inclination or hole angle does not require correction.

Azimuth and Inclination are both measured in degrees. For Azimuth, the scale is zero to three-hundred-and-sixty degrees. For inclination, the scale is zero to one-hundred-and-eighty degrees, but inclination rarely goes over one hundred degrees.

Azimuth and compass direction are not identical. Where azimuth direction is measured from 0 degrees at due north and proceeds clockwise to 359 degrees, compass direction can start at either 0 degrees north or 0 degrees south, and proceed to 90 degrees east or west. Compass direction is an older method of identifying direction but is still used in some cases.

Whether compass or azimuth is used, the raw azimuth readings must be corrected from Magnetic North to True North and may be corrected to Grid North. Magnetic North, True North and Grid North serve as reference points. They serve as familiar objects to help locate one point in relation to another.

It is important to know whether a survey is correct or flawed. Some indicators that help make that determination are Magnetic Dip Angle, Total Magnetic Field and Total Gravity Field. These indicators serve as quality factors when evaluating a survey.

3.1 Reference Points Look around you. How do you know where you are? In a featureless landscape you would have difficulty determining your position. Now suppose you see a tree fifty feet south of a house and thirty feet west of a barn. You are standing half way between the house and the tree and ten feet from the barn. You can now determine your position very precisely. The same principle works with surveying. It is important to establish reference points. Unfortunately, several different reference systems are used in well surveying. The system used depends upon the wells location. However, all of these reference systems relate to Magnetic North.


g

GE Power Systems

3.1.1 Magnetic North Magnetic North is the most important reference point in directional surveying. In the absence of magnetic interference, magnetometers point to Magnetic North. The earth has a magnetic field like that of a magnet. See Figure 3.1.1.a.

Figure 3.1.1.a The Earth is like a giant magnet.

Magnetic North changes with time on a cyclical basis. Changes in Magnetic North can be modeled using sophisticated computer programs and accounted for when taking surveys. True North and Magnetic North are not perfectly aligned. Survey azimuths must be corrected for the difference between the two. Azimuth is the direction of the hole in relation to north. An azimuth reading is given in degrees from 0 for north, 90 for east, 180 for south, 270 for west and back to 0. Both 0 and 360 degrees signify north.


g

GE Power Systems

N North is 0 Azimuth

W West is

270 Azimuth

EEast is

90 Azimuth

S South is 180 Azimuth

Figure 3.1.1.b Azimuth is measured in circular degrees from north.

Direction is also presented in compass form, especially when using older survey instruments such as a magnetic single shot. In the compass system the circle is divided into quadrants or four equal parts. Compass directions start at zero at north and south and increase to ninety degrees going east or west. Compass quadrants are northeast, southeast, southwest and northwest. When giving direction with compass quadrant, north or south is always stated first, then the degrees from north or south and finally the east or west direction. Direction is in degrees from north or south, so north 30 east (or N30E) is thirty degrees east of north, while south 70 west (or S70W) is seventy degrees west of south. See Figure 3.1.1.b.


g

GE Power Systems

East

North

North East

South EastSouth West

West

North West

South 70 West (S70W)

North 30 East (N30E)

South

Figure 3.1.1.c Compass Direction

3.1.2 True North Geographic North or True North is one end of a line drawn through the center of the earths rotational axis. Magnetic North is one end of a line drawn through the center of the earths magnetic field. The lines lie near one another and both extend through Antarctica, but they are not aligned. They diverge and provide two different points of reference. See Figure 3.1.2.

Figure 3.1.2 Geographic or True North


g

GE Power Systems

In Louisiana the difference between True North and Magnetic North is about 1 to 3 degrees. Going west from Louisiana, the correction becomes larger. Corrections are always made from Magnetic North to True North.

3.1.3 Grid North Map North or Grid North is another north reference used in surveying. Several different Grid North systems are used, depending upon rig location. This manual will cover Lambert Projection and Universal Transverse of Mercator or UTM. Both systems convert the earths curved surface onto a flat plane but use different methods. The Lambert Projection projects the earths surface onto a cone. The point or vertex of the cone can be over geographic north or south, depending on which hemisphere is to be mapped. See Figure 3.1.3.a.

Dashed lines are conic lines projected

onto a flat plane Arrows Point to

geographic north

These grid lines are projected

onto a flat plane

Figure 3.1.3.a Lambert Projection


g

GE Power Systems

Geographic north and Map North are different. The difference between them will be greater or smaller depending on where the rig is located on the earths surface. Where Lambert Projection uses a conic section, UTM takes points along the earths surface and presents it on a cylindrical plane laid flat. To visualize how this is done, assume that the earth is transparent with a light in the center. Now roll a sheet of photographic film in a cylinder around the earth as shown in Figure 3.1.3.b. Light rays travel from the center outward striking the cylindrical film, projecting a flat image of the earths curved surface.

P: A projection from the center of the earth contacts the earths surface.

Central Meridian: Any projection on this line points to geographical north.

Q1: The projection touches theoutside of the cylinder.

P1: The projection touches theoutside of the cylinder.

Q: A projection from the center of the earth contacts the earths surface.

Figure 3.1.3.b Universal Transverse Mercator

Points along the Central Meridian have correct scale values while those to the east or west have distorted scale values. Remember that the earth is divided along lines of Latitude and Longitude. Latitude measures a points distance north or south from the Equator. Longitude, also called departure, measures how many


g

GE Power Systems

degrees east or west a point on the earth is from a reference line called the Greenwich Meridian. The Greenwich Meridian goes through Greenwich, England and is Longitude 0. Latitude and Longitude are both measured in degrees. The UTM system maps the earths surface as 60, six-degree-wide, north-south sections, or zones, each centered on a reference meridian. The zones are numbered from one to sixty, starting at 180 degrees west longitude. The UTM zones introduce no scale distortion.

Magnified Section

0 12 12 6 6

WEST EAST

Figure 3.1.3.c UTM maps the earths surface as sixty, 6 sections.

Each UTM zone is also divided horizontally in 8 increments of latitude starting at the Equator. The latitude divisions are lettered for identification. For instance, the section covering the Louisiana Gulf coast is Zone 15R. See Figure 3.1.3.d. Zones extend from 80 Latitude south to 84 Latitude north. The location of any point within a zone is stated in meters from the reference meridian and meters from the equator. See Figure 3.1.3.d. The distance above the horizontal lines is called Northing while the distance from a zones central meridian is called Easting. UTM has


g

GE Power Systems

assigned starting values for the central meridians and equator to make location values more convenient. The zones are divided into squares of 100 by 100 kil

introduction to mwd

Documents

property of ge power

g ge power systemsnote

commutative property

associative property

distributive property

basic skills

basic hydraulics

basic operations of