introduction to petroleum engineering - lecture 8

7/27/2019 Introduction to Petroleum Engineering - Lecture 8

1/41

BEng (Hons) Petroleum Engineering

Course:

Introduction To Petroleum Engineering

Instructor

Dr. Tarek Darwich


2/41

Course Outlines: What is Petroleum Engineering?

The Life Cycle of Oil and Gas projects,

Origin, formation and accumulation of Petroleum,

Oil & Gas Exploration,

Appraisal of Oil & Gas Discoveries,

Development of Oil & Gas Discoveries,

Producing Oil & Gas Fields, Transportation of Oil & Gas,

The Petroleum Industry & the Environment,

Petroleum Economics.

I ntroduction to Petroleum Engineer ing

Year 2012 - 2013


3/41

Well Drilling

Organisational Structure


Year 2012 - 2013


4/41

UK Gas News

December 2012


Year 2012 - 2013


5/41

Main Components of Drilling Rigs


Year 2012 - 2013

- Power System

- Hoisting System

- Rotary System

- Circulating System- Well Control and Monitoring System


6/41

Drilling Rig Circulation System It is the closed hydraulic circuit which allows the mud to flow from the

surface to the bottom of the hole, inside the drill string, and subsequentlyback to the surface, in the drill string-borehole annulus.

The Circulation System consists of the following main components:

Mud pumps

Distribution lines

The mud cleaning and accumulation system

The mud from the hole has to have the cuttings removed before beingreinjected to the bottom of the hole.


Year 2012 - 2013


7/41

Drilling Rig Circulating System


Year 2012 - 2013


8/41

The Mud Cycle The flow of circulated drilling mud can

be described as from the mud pit via:

the mud mixing hopper, wherevarious additives like weightingmaterial etc. can be mixed into the

mud,

or the suction line to the mudpumps.

At the mud pumps the mud is pressuredup to the required mud pressure value.


Year 2012 - 2013


9/41

The Mud Cycle(continued)

From the mud pumps the mud is pushedthrough the stand pipe (a pipe fixedmounted at the derrick), the rotary hose(flexible connection that allows the fedof the mud into the vertically moving

drillstring), via the swivel into thedrillstring.

Inside the drillstring (kelly, drillpipe, drillcollar) the mud flows down to the bitwhere it is forced through the nozzles to

act against the bottom of the hole.

From the bottom of the well the mudrises up the annuli (drill collar, drillpipe)and the mud line (mud return line)which is located above the BOP.


Year 2012 - 2013


10/41


From the mud line the mud is fed to themud cleaning system consisting of shaleshakers, settlement tank, de-sander andde-silter. After cleaning the mud, thecirculation circle is closed when the mud

returns to the mud pit.


Year 2012 - 2013


11/41



Year 2012 - 2013

Mud mixing Hooper

Mud Pit and Mud Pump


12/41

The Mud Pumps

The mud pumps supply the energynecessary for circulation.

They are generally positive-displacement piston pumps, becauseof the greater head these providecompared with other types of pump,e.g. centrifugal pumps.

In a rig there are always at least twomud pumps, connected in parallel,

both for safety reasons and forflexibility of operation.


Year 2012 - 2013


13/41

The Shale Shakers

The shale shaker is designed toremove these rock cuttings and othersolid materials from the drilling mudso that it can be safely reused overand over again.

The shale shakers consist of avibrating tray lined with a wire meshscreen.

Rocks and other solid materials

remain on top of the screen whileliquid passes through.

The vibrating action of the screenhelps to facilitate this process.


Year 2012 - 2013


14/41

The Shale Shakers with Cuttings


Year 2012 - 2013


15/41



Year 2012 - 2013
http://localhost/var/www/apps/conversion/tmp/scratch_6//upload.wikimedia.org/wikipedia/commons/5/5f/Desander_%26_Desilter.jpg


16/41

The Shale Shakers

The choice of shale shaker screen is critical to successful removal ofsolid materials.

The size of the holes on the screen should be matched to the size ofthe rock being extracted from each bore hole.

It is also important to choose corrosion-resistant screen materialslike galvanized steel to hold up against the extreme conditions on adrilling site.

Many projects include multiple shale shakers so that the drilling mudmust pass through several layers of cleaning and refinement.


Year 2012 - 2013


17/41

Drilling Rig Circulation System

The principal functions of the drilling fluids are

1. Subsurface pressure control

2. Cuttings removal and transport

3. Suspension of solid particles

4. Sealing of permeable formations

5. Stabilizing the wellbore

6. Preventing formation damage

7. Cooling and lubricating the bit and drill string

8. Transmitting hydraulic horsepower to the bit

9. Facilitating the collection of formation data


Year 2012 - 2013


18/41

Drilling Fluids Functions:

- Cuttings Removals & Transport:


Year 2012 - 2013
http://localhost/var/www/apps/conversion/tmp/scratch_6//upload.wikimedia.org/wikipedia/commons/1/11/Drill_cuttings_-_Annotated_-_2004.jpg


19/41


- Cuttings Removals & Transport:

- Efficient cuttings removal requires circulating rates that are sufficientto override the force of gravity acting upon the cuttings.

- Other factors affecting the cuttings removal include drilling fluid

density and rheology, annular velocity, hole angle, and cuttings-slipvelocity.

- In most cases, the rig hydraulics program provides for an annularvelocity sufficient to result in a net upward movement of the cuttings.

- Annular velocity is determined by the cross-sectional area of the

annulus and the pump output


Year 2012 - 2013


20/41



Year 2012 - 2013
http://localhost/var/www/apps/conversion/tmp/scratch_6//upload.wikimedia.org/wikipedia/commons/5/5f/Desander_%26_Desilter.jpg


21/41


- Suspension Of Solid Particles:

- When the rig's mud pumps are shut down and circulation is halted(e.g., during connections, trips or downtime), cuttings that have notbeen removed from the hole must be held in suspension.

- The rate of fall of a particle through a column of drilling fluid dependson the density of the particle and the fluid, the size of the particle, theviscosity of the fluid, and the thixotropic (gel-strength)propertiesof the fluid.

- The controlled gelling of the fluid prevents the solid particles fromsettling, or at least reduces their rate of fall.

- In some cases, it may be necessary to circulate for several hoursbefore a trip in order to clean the hole of cuttings and to prevent fill inthe bottom of the hole from occurring during a round trip.


Year 2012 - 2013


22/41


- Viscosity:

- Viscosity (m), by definition, is the ratio of shear stress (t) to shearrate (g):

- In the most general sense, viscosity describes a substances

resistance to flow.

- Unit: PaS, NS/m2, kg/ms, cp, dyneS/cm2, lbfS/100ft2

- A high-viscosity drilling mud may be characterized as "thick," while alow-viscosity mud may be described as "thin."


Year 2012 - 2013


23/41


- Sealing of Permeable Formations:

- As the drill bit penetrates a permeable formation, the liquid portion ofthe drilling fluid filters into the formation and the solids form arelatively impermeable "cake" on the borehole wall.

- The quality of this filter cake governs the rate of filtrate loss to theformation.

- Drilling fluid systems should be designed to deposit a thin, lowpermeability filter cake on the formation to limit the invasion of mudfiltrate.

- Potential problems related to thick filter cake and excessive filtrationinclude tight hole conditions, poor log quality, increased torque anddrag, stuck pipe, lost circulation and formation damage.

- Bentonite is the best base material from which to build a tough, low-permeability filter cake. Polymers are also used for this purpose.


Year 2012 - 2013


24/41


- Stabilising the wellbore:

- The borehole walls are normally competent immediately after the bitpenetrates a section.

- Wellbore stability is a complex balance of mechanical and chemical

factors.

- The chemical composition and mud properties must combine to providea stable wellbore until casing can be run and cemented.

- The weight of the mud must be within the necessary range to balancethe mechanical forces acting on the wellbore.

- The other cause of borehole instability is a chemical reaction betweenthe drilling fluid and the formations drilled. In most cases, thisinstability is a result of water absorption by the shale.

- Inhibitive fluids (calcium, sodium, potassium, and oil-base fluids) aid inpreventing formation swelling.


Year 2012 - 2013


25/41


- Presventing Formation damage:

- Any reduction in a producing formations natural porosity orpermeability is considered to be formation damage.

- If a large volume of drilling-fluid filtrate invades a formation, it may

damage the formation and hinder hydrocarbon production.

- There are several factors to consider when selecting a drilling fluid:

- Fluid compatibility with the producing reservoir

- Presence of swelling formation clays

- Fractured formations

- The possible reduction of permeability by invasion of nonacidsoluble materials into the formation


Year 2012 - 2013


26/41


- Cooling and Lubricating the bit:

- Friction at the bit, and between the drillstring and wellbore, generatesa considerable amount of heat.

- The circulating drilling fluid transports the heat away from these

frictional sites by absorbing it into the liquid phase of the fluid andcarrying it away.

- The amount of lubrication provided by a drilling fluid varies widely anddepends on

- the type and quantity of drill solids and weight material, and

- also on the chemical composition of the system as expressed interms of pH, salinity and hardness.

- Indications of poor lubrication are high torque and drag, abnormalwear, and heat checking of drillstring components.


Year 2012 - 2013


27/41


- Transmitting the horsepower to the bit:

- During circulation, the rate of fluid flow should be regulated so that themud pumps deliver the optimal amount of hydraulic energy to cleanthe hole ahead of the bit.

- Hydraulic energy also provides power for mud motors to rotate the bitand for Measurement While Drilling (MWD) and Logging While Drilling(LWD) tools.

- Hydraulics programs are based on sizing the bit nozzles to maximizethe hydraulic horsepower.


Year 2012 - 2013


28/41


- Facilitating the collection of formation data:

- The drilling fluid program and formation evaluation program areclosely related. As drilling proceeds, for example, mud loggers monitormud returns and drilled cuttings for signs of oil and gas.

- This information is recorded on a mud log that shows lithology,penetration rate, gas detection and oil-stained cuttings, plus otherimportant geological and drilling parameters.

- Measurement-While-Drilling (MWD) and Logging-While-Drilling(LWD) procedures are influenced by the mud program, as is theselection of wireline logging tools for post-drilling evaluation.


Year 2012 - 2013


29/41


- Pasrtial Support of Drilling String and Casing Weights:

- With average well depths increasing, the weight supported by thesurface wellhead equipment is becoming an increasingly crucial factorin drilling.

- Both drillpipe and casing are buoyed by a force equal to the weight ofthe drilling fluid that they displace.

- When the drilling fluid density is increased, the total weight supportedby the surface equipment is reduced considerably.


Year 2012 - 2013


30/41


- Assisting in Cementing and Completion:

- To cement casing properly, the mud must be completely displaced bythe spacers, flushes and cement.

- Effective mud displacement requires that the hole be near-gauge and

that the mud have low viscosity and low, non-progressive gelstrengths.

- Completion operations such as perforating and gravel packing alsorequire a near-gauge wellbore and may be affected by mudcharacteristics.


Year 2012 - 2013


31/41

MUD INGREDIENTS


32/41

Mud Ingredients:

- Various materials may be added at the surface to change or modify the characteristicsof the mud:

- Weighting agents (usually barite) are added to increase the density ofthe mud, which helps to control subsurface pressures and build thewallcake.

- Viscosifying agents (clays, polymers, and emulsified liquids) areadded to thicken the mud and increase its hole-cleaning ability.

- Dispersants or deflocculants may be added to thin the mud, whichhelps to reduce surge, swab, and circulating-pressure problems.

- Clays, polymers, starches, dispersants, and asphaltic materials may beadded to reduce filtration of the mud through the borehole wall. Thisreduces formation damage, differential sticking, and problems in loginterpretation.

- Salts are sometimes added to protect downhole formations or toprotect the mud against future contamination, as well as to increase

density.


Year 2012 - 2013


33/41

Mud Ingredients (continued):

- Various materials may be added at the surface to change or modify the characteristicsof the mud:

- Other mud additives may include lubricants, corrosion inhibitors,chemicals that tie up calcium ions, and flocculants to aid in the removalof cuttings at the surface.

- Caustic soda is often added to increase the pH of the mud, whichimproves the performance of dispersants and reduces corrosion.

- Preservatives, bactericides, emulsifiers, and temperature extendersmay all be added to make other additives work better.


Year 2012 - 2013


34/41

Drilling Fluids Classification:

- Water-based drilling fluids.

- Oil-based drilling fluids.

- Pneumatic Fluids: Air, gas,mist, foams, gasified fluids.


Year 2012 - 2013


35/41

Water-based Drilling Fluids

- A water-base fluid is one that uses water for the liquid phase and commercial claysfor viscosity.

- The continuous phase may be fresh water, brackish water, seawater, or concentratedbrines containing any soluble salt.

- The commercial clays used may be bentonite, attapulgite, sepiolite, or polymer. ater-based drilling fluids.

- The use of other components such as thinners, filtration-control additives, lubricants,or inhibiting salts in formulating a particular drilling fluid is determined by the type ofsystem required to drill the formations safely and economically.


Year 2012 - 2013


36/41

Oil-based Drilling Fluids

- An oil-base drilling fluid is one in which the continuous phase is oil.

- The terms oil-base mud and inverted or invert-emulsion mud sometimes are used todistinguish among the different types of oil-base drilling fluids.

- Traditionally, an oil-base mud is a fluid with 0 to 5% by volume of water , while aninvert-emulsion mud contains more than 5% by volume of water.

- In many areas, diesels were used to formulate and maintain OBMs. Today, mineraloils and new synthetic fluids replace diesel and crude due to their lower toxicity.


Year 2012 - 2013


37/41

Oil-based Drilling Fluids

- Advantages of oil-based muds are:

- Shale stability: OBMs are most suited for drilling water sensitive shales. Thewhole mud results non reactive towards shales.

- ROP: allowing to drill faster than WBMs, still providing excellent shale stability

- High Temperature: can drill where bottom hole temperature exceeds WBMstolerances; can handle up to 550 0F.

- Lubricity: OBMs has a thin filter cake and the friction between the pipe and thewellbore is minimized, thus reducing the risk of differential sticking.

- Low pore pressure formation: Mud weight of OBMs can be maintained less than

that of water (as low as 7.5 PPG)

- Corrosion control: corrosion of pipe is controlled Since oil is the external phase.

- Re-use: OBMs are well-suited to be used over and over again. They can bestored for long periods of time since bacterial growth is suppressed.


Year 2012 - 2013


38/41

Pneumatic Fluids

- Air drilling is used primarily in hard-rock areas, and in special cases to preventformation damage while drilling into production zones or to circumvent severe lost-circulation problems.

- Air drilling includes dry air drilling, mist or foam drilling, and aerated-mud drilling.

- In dry air drilling, dry air or gas is injected into the standpipe at a volume and ratesufficient to achieve the annular velocities needed to clean the hole of cuttings.

- Aerated muds are used when it is impossible to drill with air alone because of watersands and/or lost-circulation situations.


Year 2012 - 2013


39/41

Mud Logging

- Mud logging entails gathering qualitative and semi-quantitative data fromhydrocarbon gas detectors that record the level of natural gas brought up in themud.

- Chromatographs are used to determine the chemical makeup of the gas.

- Other properties such as drilling rate, mud weight, flowline temperature, oilindicators, pump pressure, pump rate, lithology (rock type) of the drilled cuttings,and other data are recorded.

- Sampling the drilled cuttings, usually under the direction of the wellsitegeologist, must be performed at predetermined intervals.

- The main purpose is to identify all hydrocarbon indications from the rock samples

and from the oil and gas entrained in the drilling mud.

- Gas detected in the mud can be interpreted to be: liberated gas, recycled gas,produced gas, contamination gas and trip gas.

- Only liberated gas indicates a possible prospect; the others merely confuse theanalyst.

- .


Year 2012 - 2013


40/41

Mud Logging

- Total gas in the mud is measured in units of parts per million, but does not representthe actual quantity of oil or gas in the reservoir.

- The most common gas component is methane (C1). Heavier hydrocarbons, suchas C2 (ethane), C3 (propane), and C4 (butane) may indicate an oil or a "wet" gaszone. Heavier molecules, up to C7 may be recorded.


Year 2012 - 2013


41/41

Mud Logging


introduction to petroleum engineering - lecture 8

Documents