chapter -2 offshore & land rigs

7/30/2019 Chapter -2 Offshore & Land Rigs

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Chapter- 2

Land & Offshore Rigs



2.1 Introduction

Operations proceed in accordance with terms of a permit

issued by the regulatory agency with jurisdiction. Normally, a

drilling location is graded, a conductor pipe is set to support

subsequent casing strings, blowout control equipment is

installed and tested for well safety, the drilling rig and

auxiliary equipment is moved in and set up, and drilling

operations are underway.

2.2 Steps to drilling a well

Before drilling commences, certain arrangements and decisions

have to be made. These may include:

1. Leasing of the land.

2. Building of roads.

3. Moving the equipment in.

4. Drilling method.

5. Depth and size of well.



2.3 Drill-site selection

The selection of the drill site is based largely on the geological

evidence indicating the possible accumulation of petroleum. The

exploration company will want to drill the well at the most

advantageous location for the discovery of oil or gas. Surface

conditions, however, must also be taken into consideration

when selecting the drill site. There must be a nearly level area

of sufficient size on which to erect the drilling rig, excavate

reserve pits, and provide storage for all of the materials and

equipment that will be required for the drilling program. All of

the required legal matters need to have been attended to, such

as acquiring a drilling permit, surveying of the drill site, and so

on. When all of these matters have been resolved, the work on

site preparation will begin.

2.4 Drill-site preparation

Once the drill site has been selected and surveyed, a

contractor or contractors will move in with equipment to

prepare the location. If necessary, the site will be cleared and

leveled. A large pit will be constructed to contain water for

drilling operations and for the disposal of drill cuttings and

other waste. A large-diameter hole will be drilled to a shallow

depth and lined with conductor pipe.



A large, rectangular cellar is excavated under the rig floor,

dug before drilling to provide space for equipment at the top

of the wellbore. The cellar serves to collect drainage water andother fluids which are jetted at intervals.

A smaller-diameter hole called a "rat hole" is drilled near the

main bore hole. The rat hole is lined with pipe and is used for

the temporary storage of a piece of drilling equipment called

the "kelly." When all of this work has been completed, the

drilling contractor will move in with the large drilling rig and all

the equipment required for the drilling of the well. After those

actual drilling operations on the well is started. Start of the

actual drilling usually called spud-in. The term is handed down

from cable tool operations in the early days of the oil industry.

2-5 The Rig Crew



Drilling is usually done by a service company or drilling

contractor . The drilling crew is composed of a toolpusher , a

driller , a derrick man, and several roughnecks. The toolpusher



manages the drilling operation. The driller operates the rig. The

derrick man helps with the drilling mud and in removing pipe from

the hole. Roughnecks help with the drilling operation and

maintaining the drilling equipment.

2-6 Rotary Drilling rigs

Drilling rig is a machine used to drill a wellbore. In onshore

operations, the rig includes virtually everything except living

quarters. Major components of the rig include the mud tanks,

the mud pumps, the derrick or mast, the drawworks, the rotary

table or topdrive, the drillstring, the power generation

equipment and auxiliary equipment.

Rotary drilling rigs are used for almost all drilling done today.

The hole is drilled by rotating a bit to which a downward force

is applied. The bit is turned by rotating the entire drill string,

which consists of drill pipe and heavy, thick-walled pipe, called

drill collars, which supply the downward force. The cuttingsare lifted to the surface by circulating a fluid down the drill

string, through the bit, and up the annular space between the

hole and the drill string. The cuttings are filtered from the

drilling mud at the surface by a device called a “shale shaker.”



A blowout prevention system is used to shut in the well in case

of an emergency condition. Most rigs are powered electrically;

diesel engines are used to generate the electrical power.



Figure 2-1 : Rotary drilling rig

Generally drilling rig classified to two types, onshore and

offshore rigs. Onshore rigs are different tan that offshore

one. Figure 2-2 shows the classifications of rotary drilling rigs.

Figure 2-2: Classifications of rotary drilling rigs



2.6.1 Land (onshore) Rigs

Figure 2-3 land drilling rig



2-6-2 Offshore Rigs

Onshore rigs are different tan that offshore one as general

layout. Both types (offshore and onshore) perform the same

principles of operations (hoisting, circulating and rotating. A

power system is required to perform those operations). There

are different types of offshore rigs.

A swamp barge is used in water depths of less than 20 feet.

It is towed to the location and sunk in place.

A jacket rig with tender is also used in shallow waters. The

platform is fixed, and the drilling package is lifted onto the

platform by the tender.

For water depth less than 350 feet, a jack-up rig is often

used. The rig is towed to the location with the legs elevated.

On location, the legs are lowered and the rig is “jacked-up”

above the wave action by means of hydraulic jacks.

For deeper waters, a semi-submersible rig is used. The rig is

towed to the location, and is partially submerged for stability.

The rig is usually anchored over the hole.

Once a large field has been discovered offshore, a large fixed

platform may be employed to drill development wells.



Drill ships are used to drill in very deep waters. However, they

are limited to areas where wave action is not severe.

Figure 2-4: different types of offshore rigs

Swampbarge

Jacketwith

tender Jack-up

Semi-sub

FixedPlatfor

mDrillship

chapter -2 offshore & land rigs

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