ME4105 NUS Offshore Oil and Gas Technology Lecture 3

8/11/2019 ME4105 NUS Offshore Oil and Gas Technology Lecture 3

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Fluid Circulating System The fluid circulating systemis necessary to pump a

drilling fluid down the hole to aid in the drilling process. The drilling fluid is called the drilling mud because of its

physical appearance.

Drilling mud is usually a mixture of water, clay (bentonite),weighing element (barite), and various special chemicals.

The surface portion of the fluid circulating system consistsof a mud pump, which forces the mud from the mud pitsup through the standpipe, into the kelly and down the drillstring through to the bit. The mud passes through the

bottom of the bit and returns up through the annulus(thespace between the drill pipe and the wall of the borehole).

Mud pumps in the 1970s have rating up to 1750 inputhorsepower and higher. They capable of pumping largevolumes of fluid at pressure exceeding 3000 psi.


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Fluid circulating system

Source: Giuliano, Introduction to Oil and Gas Technology


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Back at the surface, the mud exits the hole through the

mud-return lineand flows over a vibrating screen calledthe shale shaker, which filters the rock cuttings out of theliquid mud.

The rock cuttings are dumped into earthern excavations,

or reserve pits, where such material is stored. The mud is often further filtered by desanders anddesilters, which remove fine-grained solids from the mud.

The mud is then put into tanks, where it is recirculatedback through the pump and down the hole.

As the drilling mud plays an indispensable role in theprocess of drilling a well, the properties are carefullymonitored by a mud engineer during the drillingoperations to make sure that the mud has the properweight and chemicals to perform its various functions.

Fluid Circulating System


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Fluid circulating system

Source: Gerding, Fundamentals of Petroleum, 3rdEd.


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Drilling Mud A Drilling mud is used to carry out the following functions:

Carry cuttings and broken rock fragment out of the hole without

it the hole will become clogged with rock cuttings

Cool the drill bit and lubricate its teeth

Lubricate and cool the bit, drill pipe and drill collar

control formation pressure or subsurface pressure the mud

helps counterbalance any high pressure oil, gas or water zonesencountered in the formation being drilled

Clean the bottom of the hole

Stabilise the well bore to prevent it from caving in

Help in the evaluation and interpretation of well log

Partial aid in supporting the weight of the drill string and casing.

Prevent corrosion fatigue of drill pipe.

Transmission of the surface-available hydraulic horsepower to the

bit

Act as medium for settling out of cuttings in the surface pit


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Drilling Mud As drilling mud plays an indispensable role in the

process of drilling a well, it is important that the mud iscarefully designed and engineered, since theconsequence of not maintaining good mud propertiesmay result in drilling problems which will take a greatdeal of time and therefore money to resolve.

In view of the high cost of not maintaining good mudproperties, an operating company will usually hire aservice company to provide a mud engineer, a drillingfluid specialist, on the rig to formulate, continuouslymonitor and it necessary treat the mud.

Drilling muds may be defined as a suspension of solidsin a liquid phase; the liquid can be water or oil.

The two most common types of drilling fluid used are:

Water-base muds

Oil-base muds


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Drilling Mud

Source: Dawe, Modern Petroleum Technology, Vol 1, Upstream


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Gas-liquid mixture (foam) are most often used where the

formation pressures are so low that massive losses

occur when even water is used as the drilling fluid. Thiscan occur in mature fields where depletion of reservoir

fluids has resulted in low bore pressure.

Water based muds are relatively inexpensive because of

the ready supply of water. They consist of a mixture ofsolids, liquids and chemicals.

The main disadvantage of using water-based muds is

that the water in these muds caused instability in shales.

Shale is composed primarily of clays and instability islargely caused by hydration of the clays by the water in

the mud. Shales are the most common rock types

encountered while drilling for oil and gas and give rise to

more problems per metre drilled any other type of

formation.

Drilling Mud


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Power System & Rotary All the equipment in the rotary drilling rig is powered by

the power system, which is the heart of the entire rig. The central power plant powers the rotary table, hoisting

system, and the fluid circulating system.

A typical large rig usually has more than 2000 hp

available for operating all the rig equipment.

Powered by the prime mover, the rotaryis the device

that turns the drill string, and ultimately the bit.

The rotary drivetransmits power to the rotary table,which is set in the rig deck, and through which the drill

string is run.


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Rotary System

Source: Berger, Anderson, Modern Petroleum - A Basic Primer of the industry, 3rdEd.


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Power Swivel

(or Top Drive system)

An innovation in rotary drilling is a device called a powerswivel(also know as a top drive system).

The top drive system replaces the functions of the rotary

table and kelly.

This allows the drill string to be rotated from the topusing a power swivel, eliminating the need of a kelly and

a rotary table.

A heavy duty motor (e.g. 1,000 hp) incorporated into the

swivel can deliver over 30,000 ft-lbs torque and canoperate at over 200 rpm.

The power swivel is remotely controlled from the drillers

console, and can be set back if necessary to allow

conventional operations to be carried out.


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Power swivel (or top dr ive system)

Source: Gerding, Fundamentals of Petroleum, 3rdEd.


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Top Drive System

The top drive system has the following advantages: It enables complete 90 ft stands to be added to the

drill string rather then the conventional 30 ft singles.

This saves rig time since two out of every three

connections are eliminated. It also makes coringoperations more efficient.

When tripping out of the hole the power swivel can be

easily stabbed into the string to ream back if

necessary (e.g. to prevent stuck pipe).

When tripping into the hole the power swivel can be

connected to allow any bridges to be drilled out

without having to pick up the kelly.

ME4105 NUS Offshore Oil and Gas Technology Lecture 3

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