ME4105 NUS Offshore Oil and Gas Technology Lecture 4

8/11/2019 ME4105 NUS Offshore Oil and Gas Technology Lecture 4

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Offshore Oil & Gas Technology


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Hoisting System The derrick(which is more than 150 ft tall) is a part of

the hoisting system. Because the drill pipe, drill collars, and the drill bit need

to be lifted in and out of the hole, a hoisting system must

be designed to lift loads which often weight several

hundred thousand pounds.

The drawworksis a large spool of cable driven by the

rigs engines to raise and lower the pulley system that is

hung in the derrick. The drawworks also contains heavy-

duty brakes to restrict the speed of lowering heavy

strings of pipe into the hole.

The crown blockis the upper set of stationary pulley

mounted at the top of the derrick. The lower set, the

traveling block, is moveable and is suspended in the

derrick by a wire rope called the drilling line.


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Hoisting System

Source: Gerding, Fundamentals of Petroleum, 3rdEd.


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The drilling lineis usually threaded six or eight times

(depending on the weight if needs to support) around thecrown block and through the traveling block.

The fast lineis the part of the drilling line which runs

from the drawworks to the crown block, and which

moves as the traveling block is lowered or raised. The deadlineruns from the crown block to the storage

reeland is secured by the deadline anchor. Extra line is

kept on the storage reel by the side of the rig.

The hoisting system is used to suspend the drill string inthe hole, maintaining the proper weight on the bit. It is

also used to pull the drill string out of the hole and to

lower it back to bottom the process is called tripping

or a tripping operating.

Hoisting System


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Tripping

Tripping is the process of removing and/or replacing thedrill string when it is necessary to change the bit or other

piece of the drill string, or perform some other operation

in the borehole or wellbore, e.g. coring, etc.

Tripping outor making a tripis the process of pullingthe drill string and bit out of the hole

Tripping inis the process of reassembling the drill string

and its replacement in the wellbore.


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Tripping out the drill string

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


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Adding a new joint of pipe



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Fishing Fishingrefers to the attempt to recover tools or pipe lost

in the hole during drilling operations.

Anything which in the hole is known as a fish.

Drill pipe or drill collar are the most common type of fish

lost in the hole because they occasionally break during

drilling

Source: Giuliano, Introduction to Oil and Gas Technology


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Blowout Prevention System A blowoutcan be defined as an uncontrolled influx of

formation fluid which has sufficient pressure to causedamage to rig equipment and injury to rig personnel.

A kickis an unwanted flow of formation fluids into the

well bore hole which may (if not controlled) develop into

a blowout. Well kickoccurs when the hydrostatic pressure

exerted by the mud in the hole is below the formation

pressureexerted by the well fluids in the formation.

A blowout preventer (BOP)is a device placed on top ofa well to prevent high pressure fluids from flowing out of

the well in the event of a well kick.

BOPs must be installed on the top of the well before

drilling commences.


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Annular surface blowout preventer



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Annular blowout preventer

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


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Ram-type blowout preventer



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Ram-type blowout preventer



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A BOP is basically high pressure valves which seal off

the top of the well in the event of an influx.

There are two types of BOP

Annular preventer made up of rubber elements,

which, when compressed vertically, will seal off the

annular space between the preventer and the drillstring.

Ram-type preventer made of hydraulic rams,

which, when required, are driven across the wellbore

to seal off the annular space. Normally, both types of preventers are used on a well

and are stacked up, one on top of the other, to form a

BOP stack.

Blowout Prevention System


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BOP Stack


BOP St k


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BOP Stack



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Sort out legal aspects of drilling a well leases, drilling

contracts, contracts, etc.

Well design process a drilling engineer will design the

process to drill the well on the basis of the following

information:

Objective of the well

Depth (onshore or subsea) and location (longitude

and latitude) of target formations

Geological cross section

Pore pressure profile prediction

The drilling programme contains all of the information

that is required to safely and efficiently drill the well.

Drilling Operations


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Drill ing Programme The drilling programme is used by various parties

involved in the drilling operation to select the appropriatetools to drill the well, order the required equipment and

schedule the operation.

A typical drilling programme contains the following

information: Drill rig to be used to drill the well

Proposed location for the drilling rig

Casing size, specifications and setting depths

Drilling fluid specifications

Directional drilling information

Well control equipment and procedure


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Drilling Procedures A survey crew goes into the field and surveys precisely

the location selected by the geologist or geophysicist.For offshore, a survey ship uses instruments to take

bearings from orbiting satellites, GPS, etc to locate the

well site.

The location is prepared for the drilling rig. Onshore

the land is leveled, earthen pits are excavated and lined

with plastic to serve as reserve pits, and an excess road

is constructed so that equipment can be brought to the

site. If the location is in a swamp, it is often necessary to

dredge out a canal into the area where the well is beingdrilled.

The drilling rig is then rigged up.


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Spudding In & Casing When drilling is ready to begin, the hole is ready for

spudding in. Spudding in involves drilling a usually shallow, large

diameter hole (often several hundred feet deep) and

lining it with conductor casing set in cement. The depth

of the conductor will depend upon the nature of the soil

at the drill site.

Once the required surface casing depth is reached, the

drill string is tripped out and a special casing crew moves

in to run the surface casing. The surface casing (a string

of large diameter steel pipes usually in 30 to 40 ft lengthand screwed together as it is run into the hole) is

inserted into the hole. Casing accessories include

centralisers, scratcher, a guide shoe, a float collar, and

plugs.


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Casing

cementing



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Surface Casing Once the surface is place, cement is pumped down the

inside of the pipe, followed by a plug used to wipe thecement from the inside of the casing.

Drilling mud is pumped in on top of the plug to displacethe cement to bottom and out into the annular spacebetween the casing and the wellbore.

Once the surface pipe has been set, deeper drillingbegins. A smaller bit is run down the inside of the casingthrough the plug and the guide shoeat the bottom ofthe casing.

The surface casing serves as an attachment point theBOPs.

Routine drilling then continues to the desired depth.

Sometimes it is necessary to set intermediate casing, i.e.drilling into a high pressure zone.


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Cementing casing


Casing strings cemented in hole


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Casing strings cemented in hole



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Casing There are many reason to having to casing off formations:

To prevent unstable formations from caving in. To protect weak formation from the high mud-weights

that may be required in subsequent hole section thesehigh mud weights may fracture the weaker zones.

To isolate zones with abnormally high pressure fromdeeper or shallower zones which may be lowerpressured.

To seal off lost circulation zones.

And when set across the production interval:

To allow selective access for production/injection/controlof the flow of fluids from, or into the reservoir(s).

One of the casing strings will also be required to providestructural support for the wellhead and BOP.


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Offshore Drilling Offshore operation in the petroleum industry began as

extensions to land operations. The first offshore well in the USA was drill in 1897 off the

coast of southern California a wooden pier that extended300 ft into the Pacific Ocean was built from the shore.Near the end of the pier a drilling rig was erected, and a

well was drilled to tap oil and gas that lay in a sub-surfacereservoir below the water.

In the 1930s, offshore drilling of exploratory wells (orwildcats) in coastal marshlands, bayous, and shallowbays in the Coast of Mexico involved first dredging achannel of 4 to 8 ft deep in the marshes and bays andthen towing a barge into the channel. The barge was thensubmerged and secured in place by wooden pilings, and arig was erected on the deck of the barge, which remainedabove the waterline.

Drilling barge


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Drilling barge



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Another method of drilling wildcats in shallow bays in the1930s involved building wooden platform on timber piles

and erecting a rig on the platform. The first mobile offshore drilling rig was designed in

1948. Several steel beams, or posts were attached tothe deck of a barge, an upper deck was laid on top of theposts, and drilling equipment was placed on the upperdeck. The rig was floated out to the drill site to enter themouth of Mississippi River (in 18 ft of water), and waterwas allowed to enter the barge hull at a controlled rateso that the unit slowly submerged and came to rest on

the seafloor, while the posts extended the drilling deskwell above the waterline, providing a stable platform forthe drilling operation. After the first well was successfullydrilled, the water in the barge hull was pumped out, andonce again the entire unit floated on the waters surface.

It can then be towed to a second location.

Offshore Drilling


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Drilling Rigs Dril ling bargesare useful for shallow protected water

such as lagoons and canals up to about 25 ft. Bargesdiffer from ship in that they are not self-propelled, but

must be towed to and from the well location by a tug.

They are not suitable for deep water or for areas where

high waves might occur. Barges also house supplies andprovide quarters for the crew.

There are four main types of mobile offshore drilling rigs

used to drill wildcats or exploration wells: Submersibles,

Jackups,Semi-submersibles andDrillships.

Submersibles and Jackups are bottom-supported rigs.

Offshore drilling operations and equipment are similar to

those on land. The major difference is a top driveand

the platform upon which the rig is mounted.


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Wave Caused Motion All floating structures (drill rig, drill ship, or production

facility, etc) are subject to current, wave and wind action.

Winds, waves and current all give rise to steady

components of forces or moment, tending to displace or

overturn the system.

A floating structure has six degrees of freedom of motion

three displacement and three rotation.

The displacements are

surge,

sway,

heave.

The rotations are

pitch,

roll,

yaw.


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Six degrees of freedom of motion


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Six degrees of freedom of motion


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Posted barge a drilling barge for shallow water and also

the earliest submersibles. It is designed to be sunk andrested on the bottom while drilling. The drilling deck ismounted on posts to keep it above the surface of the water.

Bott le-types submersibles an early design that hasseveral steel cylinders, or bottles, on top of which a deck is

laid for drilling equipment. When the bottles are floodedwith water, the rig submerges and comes to rest at theseabed. To move the rig to the next, water is pumped out ofthe bottles until the unit floats on the surface and thentowed to the next site.

Arctic submersibles They are unique in that they have asteel or concrete caisson that rests on the seafloor and aredesigned to withstand impact from large floating icebergs incold arctic water. Arctic submersibles can drill in waterdepths of up to about 150 ft.

Submersible Drill Rigs


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Jack-up rigsare more widely used than submersibles,suitable for use in a large lake where many sites are tobe drilled, or in shallow offshore areas.

Jack-up rigs have watertight barge hulls that can float onthe surface of the water while the unit is being towed tothe drill site. Once the site is reached, three or four legs

are jacked down until they rest on the sea bottom,leaving the working platform well above the sea level.

With a sufficient air gap between the hull and the surfaceof the water, operations can be carried out unhamperedby tides and waves.

Jack-up rigs can also have two barge-like hulls, thebottom hull sits on the seabed and is floated with water.

Jack-up rigs are generally used to drill in water depthsup to 350 ft.

Jack-up Drill Rigs


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A jack-up drilling rig


Jack-up rig


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p g


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Semi-submersible For deeper water drilling, a floater, i.e. drill ship, and

semi-submersible, is used.

A semi-submersibleis a floating, rectangular-shapeddrilling platform, also known as a column-stabilized unit.

Semi-submersibles consists of two of more pontoon shapedhulls to which are attached several vertical columns. Thedeck is laid across the top of the columns, where the derrick

and other drilling equipment are placed. The pontoons are partially flooded so that some buoyancy

remains such that the pontoons are below the watersurface and drill deck is above the water.

Because most of the flotation is below sea level in the

pontoons, the rig is very stable even during high seas andwinds. They can drill to water depth up to 10,000 ft.

In relatively shallow water, the semi-submersible isanchored on station with a mooring pattern of anchors andchain radiating out of the rig. In deeper waters, it uses

dynamic positioningto keep it in station.


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Offshore drill rigs


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Semi-Submersible

drilling rig



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Drill ship Essentially, a drill shipis a ship with a drilling rig mounted

in the centre and drills through a hole in the hull called themoon pool. The ship floated over the drill site.

A drill shipis differs from a ship-shaped barge in that thedrill ship is self-propelled and uses dynamic positioningto stop it from drifting off the drill site by constantly

recalculating the drill ships location via navigationalsatellites or GPS.

Some drill ships have the capability of drilling in waterdepth of 10,000 ft.

Drill ships are very expensive. For efficiency, some

modern drill ships have the equipment and ability to drilltwo wells at the same time from the derrick the derrickcontain two traveling blocks and top drives, and the shiphas two independent drillers and drillers assistancestations and two set-back areas to rack the pipe.


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A drillship



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Drill ship

DeepwaterDiscovery

Documents

ME4105 NUS Offshore Oil and Gas Technology Lecture 4