OIL DRILLING

By Craig Freudenrich, Ph.D. and Jonathan Strickland

(Compiled by Ejaz Ahmed ; ejazahmedbhatti@yahoo.com)

Inside this Article

1. Introduction to How Oil Drilling Works

2. Forming Oil

3. Locating Oil

4. Oil Drilling Preparation

5. Oil Rig Systems

6. The Oil Drilling Process

7. Testing for Oil

8. Extracting Oil

9. Offshore Oil Drilling

Introduction to Oil Drilling

Oil Field Image Gallery

Photo courtesy ConocoPhillips Offshore oil rig. See more oil field pictures.

In 2008 alone, the United States produced an estimated 4.9 million barrels of

crude oil per day and imported 9.8 million barrels per day from other countries

[source: U.S. Energy Information Administration]. This oil gets refined into

gasoline, kerosene, heating oil and other products. To keep up with our

consumption, oil companies must constantly look for new sources of petroleum,

as well as improve the production of existing wells.

How does a company go about finding oil and pumping it from the ground? You

may have seen images of black crude oil gushing out of the ground, or seen an

oil well in movies and television shows like "Giant," "Oklahoma Crude,"

"Armageddon" and "Beverly Hillbillies." But modern oil production is quite

different from the way it's portrayed in the movies.

In this article, we'll examine how modern oil exploration and drilling works.

We'll discuss how oil is formed, found and extracted from the ground.

Forming Oil

Oil comes from the remains of tiny plants and animals (plankton) that died in

ancient seas between 10 million and 600 million years ago. After the organisms

died, they sank into the sand and mud at the bottom of the sea.

Over the years, the organisms decayed in the sedimentary layers. In these

layers, there was little or no oxygen present. So microorganisms broke the

remains into carbon-rich compounds that formed organic layers. The organic

material mixed with the sediments, forming fine-grained shale, or source rock. As

new sedimentary layers were deposited, they exerted intense pressure and heat

on the source rock. The heat and pressure distilled the organic material into

crude oil and natural gas. The oil flowed from the source rock and accumulated

in thicker, more porous limestone or sandstone, called reservoir rock.

Movements in the Earth trapped the oil and natural gas in the reservoir rocks

between layers of impermeable rock, or cap rock, such as granite or marble.

These movements of the Earth include:

Folding - Horizontal movements press inward and move the rock layers

upward into a fold or anticline.

Faulting - The layers of rock crack, and one side shifts upward or

downward.

Pinching out - A layer of impermeable rock is squeezed upward into the

reservoir rock.

Locating Oil

Photo courtesy the Energy Institute

Searching for oil over water using seismology

Whether employed directly by an oil company or under contract from a private

firm, geologists are the ones responsible for finding oil. Their task is to find the

right conditions for an oil trap -- the right source rock, reservoir rock and

entrapment. Many years ago, geologists interpreted surface features, surface

rock and soil types, and perhaps some small core samples obtained by shallow

drilling. Modern oil geologists also examine surface rocks and terrain, with the

additional help of satellite images. However, they also use a variety of other

methods to find oil. They can use sensitive gravity meters to measure tiny

changes in the Earth's gravitational field that could indicate flowing oil, as well as

sensitive magnetometers to measure tiny changes in the Earth's magnetic field

caused by flowing oil. They can detect the smell of hydrocarbons using sensitive

electronic noses called sniffers. Finally, and most commonly, they

use seismology, creating shock waves that pass through hidden rock layers and

interpreting the waves that are reflected back to the surface.

In seismic surveys, a shock wave is created by the following:

Compressed-air gun - shoots pulses of air into the water (for

exploration over water)

Thumper truck - slams heavy plates into the ground (for exploration

over land)

Explosives - detonated after being drilled into the ground (for

exploration over land) or thrown overboard (for exploration over water)

The shock waves travel beneath the surface of the Earth and are reflected back

by the various rock layers. The reflections travel at different speeds depending

upon the type or density of rock layers through which they must pass. Sensitive

microphones or vibration detectors detect the reflections of the shock waves

-- hydrophones over water, seismometers over land. Seismologists interpret the

readings for signs of oil and gas traps.

Once geologists find a prospective oil strike, they mark the location

using GPS coordinates on land or by marker buoys on water.

Oil Drilling Preparation

Once the site has been selected, scientists survey the area to determine its

boundaries, and conduct environmental impact studies if necessary. The oil

company may need lease agreements, titles and right-of way accesses before

drilling the land. For off-shore sites, legal jurisdiction must be determined.

After the legal issues are settled, the crew goes about preparing the land:

1. The land must be cleared and leveled, and access roads may be built.

2. Because water is used in drilling, there must be a source of water nearby.

If there is no natural source, the crew drills a water well.

3. The crew digs a reserve pit, which is used to dispose of rock cuttings and

drilling mud during the drilling process, and lines it with plastic to protect

the environment. If the site is an ecologically sensitive area, such as a

marsh or wilderness, then the cuttings and mud must be disposed of

offsite -- trucked away instead of placed in a pit.

Once the land has been prepared, the crew digs several holes to make way

for the rig and the main hole. A rectangular pit called a cellar is dug around the

location of the actual drilling hole. The cellar provides a work space around the

hole for the workers and drilling accessories. The crew then begins drilling the

main hole, often with a small drill truck rather than the main rig. The first part of

the hole is larger and shallower than the main portion, and is lined with a large-

diameter conductor pipe. The crew digs additional holes off to the side to

temporarily store equipment -- when these holes are finished, the rig equipment

can be brought in and set up.

Depending upon the remoteness of the drill site and its access, it may be

necessary to bring in equipment by truck, helicopter or barge (raft). Some rigs

are built on ships or barges for work on inland water where there is no foundation

to support a rig (as in marshes or lakes).

Oil Rig Systems

Anatomy of an oil rig

Once the equipment is at the site, the crew sets the rig up. Here are the major

systems of a land oil rig:

Power system

o large diesel engines - burn diesel-fuel oil to provide the main

source of power

o electrical generators - powered by the diesel engines to provide

electrical power

Mechanical system - driven by electric motors

o hoisting system - used for lifting heavy loads; consists of a

mechanical winch (drawworks) with a large steel cable spool,

a block-and-tackle pulley and a receiving storage reel for the cable

o turntable - part of the drilling apparatus

Rotating equipment - used for rotary drilling

o swivel - large handle that holds the weight of the drill string; allows

the string to rotate and makes a pressure-tight seal on the hole

o kelly - four- or six-sided pipe that transfers rotary motion to the

turntable and drill string

o turntable or rotary table - drives the rotating motion using power

from electric motors

o drill string - consists of drill pipe (connected sections of about 30

feet (10 meters) and drill collars (larger diameter, heavier pipe that

fits around the drill pipe and places weight on the drill bit)

o drill bit(s) - end of the drill that actually cuts up the rock; comes in

many shapes and materials (tungsten carbide steel, diamond) that

are specialized for various drilling tasks and rock formations

Casing - large-diameter concrete pipe that lines the drill hole, prevents the

hole from collapsing, and allows drilling mud to circulate

Photo courtesy the Energy Institute

Mud circulation in the hole

Circulation system - pumps drilling mud (mixture of water, clay,

weighting material and chemicals, used to lift rock cuttings from the drill bit

to the surface) under pressure through the kelly, rotary table, drill pipes

and drill collars

o pump - sucks mud from the mud pits and pumps it to the drilling

apparatus

o pipes and hoses - connects pump to drilling apparatus

o mud-return line - returns mud from the hole

o shale shaker - shaker/sieve that separates rock cuttings from the

mud

o shale slide - conveys cuttings to the reserve pit

o reserve pit - collects rock cuttings separated from the mud

o mud pits - where drilling mud is mixed and recycled

o mud-mixing hopper - where new mud is mixed and then sent to

the mud pits

Derrick - support structure that holds the drilling apparatus; tall enough to

allow new sections of drill pipe to be added to the drilling apparatus as

drilling progresses

Blowout preventer - high-pressure valves (located under the land rig or

on the sea floor) that seal the high-pressure drill lines and relieve pressure

when necessary to prevent a blowout (uncontrolled gush of gas or oil to

the surface, often associated with fire)

The Oil Drilling Process

Photo courtesy ConocoPhillips

Rotary workers trip drill pipe.

The crew sets up the rig and starts the drilling operations. First, from the starter

hole, the team drills a surface hole down to a pre-set depth, which is somewhere

above where they think the oil trap is located. There are five basic steps to

drilling the surface hole:

1. Place the drill bit, collar and drill pipe in the hole.

2. Attach the kelly and turntable, and begin drilling.

3. As drilling progresses, circulate mud through the pipe and out of the bit to

float the rock cuttings out of the hole.

4. Add new sections (joints) of drill pipes as the hole gets deeper.

5. Remove (trip out) the drill pipe, collar and bit when the pre-set depth

(anywhere from a few hundred to a couple-thousand feet) is reached.

Once they reach the pre-set depth, they must run and cement the casing -- place

casing-pipe sections into the hole to prevent it from collapsing in on itself. The

casing pipe has spacers around the outside to keep it centered in the hole.

The casing crew puts the casing pipe in the hole. The cement crew pumps

cement down the casing pipe using a bottom plug, a cement slurry, a top plug

and drill mud. The pressure from the drill mud causes the cement slurry to move

through the casing and fill the space between the outside of the casing and the

hole. Finally, the cement is allowed to harden and then tested for such properties

as hardness, alignment and a proper seal.

Testing for Oil

Blowouts and Fires

In the movies, you see oil gushing (a blowout), and perhaps even a fire, when drillers

reach the final depth. These are actually dangerous conditions, and are (hopefully)

prevented by the blowout preventer and the pressure of the drilling mud. In most wells,

the oil flow must be started by acidizing or fracturing the well.

Drilling continues in stages: The crew drills, then runs and cements new

casings, then drills again. When the rock cuttings from the mud reveal the oil

sand from the reservoir rock, the crew may have reached the well's final depth.

At this point, crew members remove the drilling apparatus from the hole and

perform several tests to confirm this finding:

Well logging - lowering electrical and gas sensors into the hole to take

measurements of the rock formations there

Drill-stem testing - lowering a device into the hole to measure the

pressures, which will reveal whether reservoir rock has been reached

Core samples - taking samples of rock to look for characteristics of

reservoir rock

Once they've reached the final depth, the crew completes the well to allow oil to

flow into the casing in a controlled manner. First, they lower a perforating

gun into the well to the production depth. The gun has explosive charges to

create holes in the casing through which oil can flow. After the casing has been

perforated, they run a small-diameter pipe (tubing) into the hole as a conduit for

oil and gas to flow up through the well. A device called a packer is run down the

outside of the tubing. When the packer is set at the production level, it's

expanded to form a seal around the outside of the tubing. Finally, they connect a

multi-valved structure called a Christmas tree to the top of the tubing and

cement it to the top of the casing. The Christmas tree allows them to control the

flow of oil from the well.

After the well is completed, the crew must start the flow of oil into the well. For

limestone reservoir rock, acid is pumped down the well and out the perforations.

The acid dissolves channels in the limestone that lead oil into the well. For

sandstone reservoir rock, a specially blended fluid containing proppants (sand,

walnut shells, aluminum pellets) is pumped down the well and out the

perforations. The pressure from this fluid makes small fractures in the sandstone

that allow oil to flow into the well, while the proppants hold these fractures open.

Once the oil is flowing, the oil rig is removed from the site and production

equipment is set up to extract the oil from the well.

Extracting Oil

After the rig is removed, the crew puts a pump on the well head.

In the pump system, an electric motor drives a gear box that moves a lever. The

lever pushes and pulls a polishing rod up and down. The polishing rod is

attached to a sucker rod, which is attached to a pump. This system forces the

pump up and down, creating a suction that draws oil up through the well.

In some cases, the oil may be too heavy to flow. In these cases, the crew drills a

second hole into the reservoir and injects steam under pressure. The heat from

the steam thins the oil in the reservoir, and the pressure helps push it up the well.

This process is called enhanced oil recovery.

Recently, another type of oil drilling has made the news: offshore oil drilling.

Offshore Oil Drilling

Not all oil is accessible on land or in shallow waters. You can find some oil

deposits buried deep under the ocean floor. Reaching these oil deposits is

dangerous, but if done correctly, it can also be rewarding. If things go wrong,

however, the results can be deadly both for oil workers and the surrounding

environment.

Using sonic equipment, oil companies determine the drilling sites most likely to

produce oil. Then they use a mobile offshore drilling unit (MODU) to dig

the initial well. Some units are converted into production rigs, meaning they

switch from drilling for oil to capturing oil once it's found. Most of the time, the oil

company will replace the MODU with a more permanent oil production rig to

capture oil.

There are four main types of MODUs:

A submersible MODU usually consists of a barge that rests on the sea

floor at depths of around 30 to 35 feet (9.1 to 10.7 meters). On the barge's

deck are steel posts that extend above the water line. A drilling platform

rests on top of the steel posts. These rigs are typically used in areas with

calm water.

A jackup is a rig that sits on top of a floating barge. A ship tows the barge

to the drilling site. Once positioned, the jackup can extend legs down to

the sea floor. The legs are loaded in such a way that they don't penetrate

the floor. Once each leg is secure, the jackup continues to ratchet the legs

so that the platform rises above the water level. This keeps the rig safe

from tidal motions and waves. Jackups can operate in depths of up to 525

feet (160 meters).

Drill ships are ships that have a drilling rig on the top deck. The drill

operates through a hole in the hull. Drill ships can pilot to the drill site and

then use a combination of anchors and propellers to correct for drift as the

rig drills for oil. They can operate in deep water conditions.

Semisubmersibles float on the surface of the ocean on top of huge,

submerged pontoons. Some have propulsion systems, which allow them

to navigate to drilling sites under their own power while others require a

second vessel to tow them to the right location. Most use several anchors

-- up to a dozen -- that help maintain the structure's orientation.

Computers control the tension on each anchor chain to correct for drift.

Some can convert from drilling rigs to production rigs, reducing the need

for a second rig to take its place once oil is found.

The MODU's job is to drill down into the ocean's floor to find oil deposits. The

part of the drill that extends below the deck and through the water is called the

riser. The riser allows for drilling fluids to move between the floor and the rig.

Engineers lower a drill string -- a series of pipes designed to drill down to the oil

deposit -- through the riser.

At the sea floor is the blowout preventer (BOP). The blowout preventer has a

pair of hydraulically-powered clamps that can close off the pipe leading up to the

rig in the case of a blowout. As the rig drills down, engineers must add more pipe

to the drill string. Each section of pipe is about 30 feet long (9.1 meters).

To add stability to the well, the engineers use metal casings, much as they do

with land-based oil rigs. These casings help keep the well from collapsing in on

itself. Each casing is lined with cement walls. Casings get narrower as the well

gets deeper. Oil companies use progressively smaller drill bits as the well's depth

increases. At each annulus -- the spot where a narrower casing joins with a

wider one -- engineers use a liner hanger O-ring to seal the two sections

together.

When the MODU hits oil, engineers must seal the well to prepare it for a

production rig. The engineers will use a pair of plugs to seal off the well bore. The

bottom plug sits near the oil deposit. Drilling mud or seawater provides the

pressure to hold the plug in place while the engineers place a top plug to cap the

oil well. Then the well is ready for a production rig to take over. Offshore

production rigs work in a similar way to land-based oil rigs.

General Categories of Human Capital at work

Following are the general categories of Human Capital at work on any Oil Rig

Site:

 

Essential personnel

 

Not all of the following personnel are present on every platform. On smaller

platforms, one worker can perform a number of different jobs. The following also

are not names officially recognized in the industry:

OIM (offshore installation manager) who is the ultimate authority

during his/her shift and makes the essential decisions regarding the

operation of the platform;

Operations team leader (OTL);

Offshore operations engineer (OOE) who is the senior technical

authority on the platform;

PSTL or operations coordinator for managing crew changes;

Dynamic positioning operator, navigation, ship or vessel maneuvering

(MODU), station keeping, fire and gas systems operations in the

event of incident;

Second mate to meet manning requirements of flag state, operates

fast rescue craft, cargo operations, fire team leader;

Third mate to meet manning requirements of flag state, operate fast

rescue craft, cargo operations, fire team leader;

Ballast control operator to operate fire and gas systems;

Crane operators to operate the cranes for lifting cargo around the

platform and between boats;

Scaffolders to rig up scaffolding for when it is required for workers to

work at height;

Coxswains to maintain the lifeboats and manning them if necessary;

Control room operators, especially FPSO or production platforms;

Catering crew, including people tasked with performing essential

functions such as Cooking, laundry and cleaning the accommodation;

Production techs to run the production plant;

Helicopter pilot(s) living on some platforms that have a helicopter

based offshore and transporting workers to other platforms or to

shore on crew changes;

Maintenance technicians (instrument, electrical or mechanic)

Incidental personnel

 

Drill crew will be on board if the installation is performing drilling operations. A

drill crew will normally comprise:

Tool pusher

Driller

Roughnecks

Roustabouts

Company man

Mud engineer

Derrick hand

Geologist

Well services

 

Well services crew will be on board for well work. The crew will normally

comprise:

Well services supervisor

Wire line or coiled tubing operators

Pump operator

The Terminal Thought

With all of this oil-drilling technology in use, and new methods in development,

the question remains: Will we have enough oil to meet our needs? Current

estimates suggest that we have enough oil for about 63 to 95 years to come,

based on current and future finds and present demands.