23-06-2012, 02:39 PM
OIL EXPLORATION & DRILLING USING EXTREME OIL RIG
Extreme oil rig.docx (Size: 2.66 MB / Downloads: 64)
. Introduction
Oil drilling is the process by which tubing is bored through the Earth's surface and a
well is established. After drilling the well flows by its self pressure or a pump is connected
to the tube and the petroleum under the surface is forcibly recovered from underground. Oil
drilling is a highly-specialized business that grew into the largest industry on the planet by
the early 21st century
Offshore oil rigs work round the clock, enabling the uninterrupted production of oil.
Different types of offshore oil rigs can drill wells in shallow coastal waters or in waters
thousands of feet deep, with offshore drilling technology advancing each year
A rig is the 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 and
mast, the draw works, the
rotary table or topdrive, the
drillstring, the power
generation equipment and
auxiliary equipment.
Offshore, the rig includes the same components as onshore, but mounted in special floating
platform or installed in a drill ship. The floating platform could be a submersible type or a
jack up type. Offshore rigs can be of various types depending on the water depth.
Oil drilling commences with the insertion of a hole that is normally 36 inches in diameter.
This hole is made with an equipment called a drilling rig, and a drilling string is attached to
the rig. After the hole is created, a section of tubing, made out of steel, is inserted in the
hole. At this point, a drill bit, which can either compress the rock or just cut and threw it,
moves through the rock. Fluid is used both to help wear down the rock and to fetch up bits
of rock that have already been sheared from the surface
A lot of additional operations are performed during drilling including logging
(measurement versus depth or time, or both, of one or more physical quantities in or around
a well) testing, completion etc.
History
Over five thousand years ago, oil that had come up through the ground was being
used in medication, lighting, paints and for waterproofing boats. Lighting in many homes
was made possible by whale oil until the whale numbers dropped and increased the price of
this oil. The demand for oil increased and many companies began looking for ways to find
other sources or an alternative to oil. Coal oil was then found and used until a process for
drilling for crude oil was developed. At first land oil wells were drilled then with the
increased demand people began to look to drilling beneath the sea for this black gold.
Over the years the oil industry has further developed and has expanded oil fields into deeper
water and further away from land. Safety has become a serious issue that has improved over
the years and now enables all employees to be safe and well prepared in case of disaster with
full training provided by employers.
Crude oil or Petroleum is created by the formation of animal and plant remains that become
buried deep into the seabed as the years progress. The material will then decompose into
petroleum and seep into the layers in the rocks. As the tectonic plates of the earth move the
oil is then gathered into pools then drained through oil wells.
What is Petroleum?
Oil is commonly formed in rock or in sealed pockets under
the seabed / at subsurface and it is from the Latin for ‘rock
oil’ that the word ‘Petroleum’ is derived, though this name
also covers natural gas as well as oil. Chemically it is a
complex mixture of hydrogen and carbon with slight amount
of other organics, thus called hydro-carbon. The term crude
oil is commonly used for the product which is not undergone
refining process. The crude oil is classified as sweet if it has
very little sulphur in it, and is classified as sour if it has a
great deal of sulfur in it. So a crude oil will usually be called
something like a sweet, light oil, or a sour, heavy oil. The
color of crude oil can range from pure black or dark brown to
greenish or yellowish, depending on the composition.
How Hydrocarbons are formed?
Petroleum was formed from the remains of marine plant and animal life which existed many
millions of years ago (hence it is known as a fossil fuel). Some of these remains were
deposited along with rock-forming sediments under the sea where they were decomposed
anaerobically (without oxygen) by bacteria which changed the fats in the sediments into
fatty acids which were then changed into an asphaltic material called kerogen. This was then
converted over millions of years into petroleum by the combined action of heat and pressure.
At an early stage the organic material was squeezed out of its original sedimentary mud into
adjacent sandstones. Small globules of oil collected together in the pores of the rock and
eventually migrated upwards through layers of porous rock by the action of the oil's own surface tension (capillary action), by the force of water movement within the rock, and by
gas pressure. This migration ended either when the petroleum emerged through a fissure as a
seepage of gas or oil onto the earth's surface, or when it was trapped in porous reservoir
rocks, such as sandstone or limestone, in anticlines and other traps below impervious rock
layers.
Locating Oil
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 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. 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.
Siesmic Survey
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)
A seismic wave is energy that moves through the earth as a result of an earthquake /
artificially made by
exploding dynamite
or made by special
vibrators. When a
seismic survey is
conducted, seismic
waves are usually
generated by
dynamite or by
special vibrators
mounted on trucks.
These vibroseis
trucks, as they are
known, are often
used if the use of
dynamite could
cause serious
damage to the surroundings. The trucks use heavy metal plates weighing in at over 3
tons that are placed in contact with the ground, and which are then struck with heavy
hammers.At offshore, seismic surveys are being conducted by special ships equipped with air guns
to produce shock waves and reflections are captured by hydrophones (geophone).
As the seismic waves pass through the earth and encounter different materials, some of
their energy is reflected off the boundaries between the different strata while other waves
will pass through. The reflected energy returns to the surface, where its speed and
strength is measured by special detectors, known as geophones. The geophones convert
the movement of the ground into electrical signals, which are then digitized by
seismometers. These signals are then processed by computers. The speed and strength of
the reflected waves depends on the density of the strata they encounter. Rock becomes
denser the deeper underground it is located, but pockets of gas and oil have a much
lower density. The denser the material is, the faster the waves will be reflected. As the
seismic waves encounter lower density materials, more of their energy passes through.
By analyzing the time it takes for the waves to be reflected, geologists can build an
accurate image of the subsoil by using 3D seismic interpretation software.
Analysis of the seismic data provides vital information on petroleum geology of the area
of interest. This information can tell us the possibility of hydrocarbon reserve
availability, its depth from surface etc. Once these data are available, the company /
government decide to explore further for oil or abandon the project, if found
economically / technically not feasible.
The land may be leased to oil operating companies for a particular period, receiving a
profit from the oil produced, or the land owner arrange to drill and produce the oil.
Whatever it may be, the drilling contractor has to start to drill a well. An oil / gas well is
drilled from earth’s surface to the depth indicated by seismologists. This could be
thousands of feet deeper.
Preparation for oil drilling
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 producing 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 onshore rig is moved to location. As the rig is moved
part by part in many trucks, it needed to be assembled together at the site. This preparation is known as rigging up. 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.
Depending upon the remoteness of the drill site and its access, it may be necessary to bring
in equipment by truck, helicopter or barge. 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).
Drilling a well
Normally drilling of a new well may take few weeks, and there will be cementing,
perforation, well stimulation, well testing, well logging etc, before they hand over the well to
production. Mostly new wells will take about 2-3 months to complete. For exploration wells,
as the reservoir conditions are not known, every moment the program is expected to change,
though the entire drilling process will be done according to
the standard drilling manual of the operating company.
Once the drilling to a particular depth is over, a steel casing
(large OD pipe) is lowered and cemented, this will avoid any
caving in. Then a little smaller diameter hole is drilled and at
a particular depth it is again cased and cemented. The drilling
continues with smaller diameter hole and a tubing is lowered
with or without special locks (nipples) sliding doors (SSD),
gas lifting valves (GLM), safety valves etc. The preparation,
allocation, testing and lowering of these items with steel tubing are called well completion.
Just after the drilling is over, the test completion string is run in hole to test the well to find
out its characteristics. Perforation of pay zone, well stimulation etc are may be required,
according to the well drilling and testing program. Once the well testing is over, the final
completion is run and the well will be handed over to production. The entire procedure is
depended on the objective of the well, the reservoir under study, and the method of lifting
the oil. The oil operating company will have a guide line for the complete drilling, testing
and completion of the particular well.
Once the well is completed as per the program, company has to wait for the pipe lines to be
installed for transferring the crude oil / gas to the separating / processing stations. In the case
of onshore wells, the pipe lines are connected directly to well head.
For offshore, to install the well head and associated equipment, a platform may have to
build. The pipe lines are connected to well head and will be laid down at sea-bed. Typically
a well head platform will accommodate 6-20 wells. This will reduce the investment spend on
building a platform at sea. Though the well heads installed in an array on the platform, the
wells will be drilled in different angles, by employing directional drilling techniques.
Oil Drilling Rig – Parts and Functions
Once the equipment is at the site, the crew sets the rig up. Here are the major systems of a
land oil rig:
Engine - Device converting the combustion of fuel and air into mechanical energy, used to
drive the drilling mechanism of rig.
Substructure - Metal infrastructure that supports the derrick, engines and auxiliary
equipment.
Vibrating mudscreen (shale shaker) - Perforated vibrating tray that is used to filter mud as
it exits the well to remove debris and recycle the mud. Samples are collected for analysis by
mud engineer.
Lifting hook - Steel part that is attached to the traveling block; it is used to support the
swivel and the drill pipes.
Derrick - Metal
structure erected
over an oil well;
tools for drilling
through rock are
raised and
lowered through
it. While drill
pipes are running
in hole, the
derrick man
engages the pipes
to lifting hook.
Crown block -
is the Mechanical
device that is
mounted on top of
the derrick; it has
several pulleys
and, with the
traveling block, it
supports the drill
pipes.
Drilling Mud – Is the chemical mixture pumping down to the well being drilled. The
major role of mud is to counter-act and over balance the well pressure during drilling. Also
mud acts as a coolant and as a media to bring the drill cuttings to surface. These cuttings will
be inspected by the well site mud engineer and geologist to find the presence of hydrocarbon
and to get any other useful information related to the rock / area being drilled.
Mud pump - Device that circulates the mud in the drilling rig.
Mud injection hose - Flexible hose that introduces the drilling mud into the swivel.
Mud pit - Pit that contains mud (a mixture of water, clay and chemical products) used to
counter-act the pressure from the area being drilled.
Drilling draw-works - Device that consists of a cylinder on which hoisting cables are
wound, it is used to lower the drill pipes and bit into the well and to lift them out.
Swivel - Piece attached to the lifting hook and the kelly; it is used to introduce mud into the
drill pipe to cool and lubricate the bit.
Traveling block - Movable mechanical device with pulleys; it is attached by cable to the
crown block and fitted with a lifting hook.
Drill pipe - Hollow steel rods that are joined together according to the depth of the well;
their rotation activates the bit.
Drill collar - Heavy steel tube immediately
above the bit that applies a certain weight to
the bit to help it cut into the rock. This will
work as a connection from drill bit to drill
pipe.
Bit - Rotating drill bit with toothed steel or
diamond wheels; it bores into rock to break it
up and drill a hole. Depend on the rock being
drilled, and the hole size, the bits are selected.
Rotary table - Circular table that is moved by
powerful motors; it transmits its rotational
movement to the drill pipes by means of the
kelly.
Kelly -Special square rod that is screwed to
the top of the drill pipes and driven by the
rotary table.
Testing Oil
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 drill
pipe from the hole and perform several tests to confirm this finding:
Well logging - lowering complex electronic sensors interfaced to computers into the
hole to take measurements of the rock.
Drill-stem testing - lowering a mechanicsl device into the hole to study the integrity
of cementing, study of reservoir
Core samples - taking samples of rock to look for characteristics of reservoir rock.
Once they have 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.
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.