Considering local constraints such as, prevailing currents, tide and climate


Offshore drilling has been around for a long time and there are many precautions in place to keep workers safe, protect the environment, and reduce the impact on the sea life.  Though of course there will always be some disruption to the environment when people enter the picture (recreation, development, etc.), but when the offshore drilling regulations are followed, it is kept to a minimum. Recently the oil spill in the Gulf has made many people reconsider the risks and safety of offshore drilling.

There are risks to the environment include the following:
•    Explosions and fire
•    Sonar disrupts communication of some sea life communication
•    The ocean floor
•    Water temperature
•    Oil spills and seepage
•    Faulty pipe lines
•    Drilling rig exhaust
•    Hazard material waste

There are risks to workers as was seen with the explosion on the oil-drilling rig in the Gulf. Explosions, fire, and equipment malfunctions put workers at risk. When precautions and regulations are followed it reduces the risk of injury and death to workers on an oil-drilling rig.
Some feel the risks that are associated with offshore drilling are worth it because it reduces the dependency on foreign oil. The dependency on foreign oil comes with its own risks that are permanent and long lasting.
Some of the regulations that are in place include restricting the use of sonar during times that it can affect the reproduction activities of whales and dolphins that use sonar for navigation in the ocean. Exhaust from oil drilling rigs is restricted. The restrictions are fairly broad to accommodate an emergency when the rigs must run full power for extended periods of time.
The current offshore drilling precautions would be more effective if they were enforced and followed. It is expected that there will be additional regulations and restrictions on offshore drilling due to the results of the recent events in the Gulf of Mexico. It is expected that offshore oil drilling will resume as the push to become less dependent on foreign oil continues. Onshore drilling will most likely increase during the current halt on offshore oil drilling.


Deepwater drilling operations are sensitive to ocean currents due to the length of the
riser and the large top tensions required to support the riser string . If severe

•  Riser installation may be disrupted;
•  Drilling downtime may be incurred;
•  Survival envelopes for drift-off events may be reduced;
•  Fatigue due to Vortex Induced Vibration (VIV) may become excessive

Alternatives to Conventional Deepwater Drilling Risers

Conventional deepwater drilling risers have a number of problems during operations which can seriously hinder efficient working of the risers and drilling of a well. Various factors can result in the riser being retrieved, e.g. failure of seals on the joint flanges, control pod issues in the lower stack and environmental events such as hurricanes and loop currents. The trip times involved in the riser being
retrieved and then redeployed under such conditions run into several days in deepwater.

During recent years, alternatives to conventional deepwater drilling risers have been proposed to address these issues. These also address the problem of 5th generation rig availability.

Free Standing Drilling Riser (FSDR)

A FSDR has the ability to disengage at an interface component, called a Near Surface Disconnect Package (NSDP), located a short distance below the water surface. The lower riser section is left freestanding and held up by a buoyancy can system. This significantly reduces installation and retrieval time, as well as it also allows the rig to park the free-standing riser on a temporary wellhead and move off location for other non-drilling activities. The FSDR, thus, provides a beneficial alternative
to deep water drilling operations where weather windows regularly suspend drilling activities.


Artificial Buoyant Seabed (ABS) Drilling Solution

The ABS system allows for a conventional shallow water drilling riser and its subsea BOP to be run to the ABS. An ABS is installed at shallow depth below the rig, with a well casing acting as a tether to anchor it to the actual seabed. As a result, no equipment remains on the real seabed. On approach of bad weather, the shallow water riser can be disconnected and retrieved, leaving the BOP behind on the ABS for well control.

Subsea Mudlift Drilling (SMD)

In conventional deepwater drilling systems, problems are often encountered during mud circulation. One major concern is to keep the wellbore annulus pressure above the pore pressure so that the well does not “kick” and below the fracture pressure so  that the well does not hydraulically fracture and lose circulation. This pressure range can be increased by reducing annular pressure to that of seawater. This can be achieved by providing mud pumps on the seafloor to pump mud via, smaller return lines changing the pressure gradient in the wellbore to a more favorable one. One benefit of such a system is that it facilitates the use of an older generation rig with a lower tension capacity than that required for a conventional deepwater drilling riser as the main 21” riser can be filled with seawater for the entire drilling program.


Bad Weather


Hangoff Procedures During Bad Weather

Whilst 'Waiting on Weather' it might be necessary to hang the drill string off from the wellhead or BOPs. In severe cases, it might also be necessary to disconnect the riser from the BOP stack. The decision to 'hang-off should be taken to allow sufficient time for the bit to be pulled safely into the casing shoe. A natural tendency for the driller to pull up too quickly could perhaps induce swabbing and a possible kick situation later.

The preferred method to hang-off the string is to use a special hang-off tool which supports the pipe in the wellhead. It consists of a fluted hanger that is designed to land on the wear bushing, casing hanger or seal assembly, a slick joint around which the pipe ram(s) can be closed and an upper sub containing both a coarse left hand thread and a drill pipe thread box. Each hang-off assembly should be appropriate to the particular wellhead (BOP) in use so that once it is in place and disconnected the pipe ram(s) can be closed round the slick joint and the shear rams can be closed above the top sub.
For some wellhead systems, only one fluted hanger is needed and can be run whatever size wear bushing or casing hanger is in the wellhead. Other systems require the hanger to be changed according to the size of the last casing string run. Various spacer subs appropriate to the distance between the hang-off point and the shear rams might also be required.
In order to provide additional safety, it is usual practice to install an inside BOP (or inside BOP with an open Kelly cock underneath it) one joint below the fluted hanger.


How oil drilling works



Finding Oil

The task of finding oil is assigned to geologists, whether employed directly by an oil company or under contract from a private firm. 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 - drilled into the ground (for exploration over land) or thrown overboard (for exploration over water), and detonated
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. The reflections of the shock waves are detected by sensitive microphones or vibration detectors -- hydrophones over water, seismometers over land. The readings are interpreted by seismologists for signs of oil and gas traps.
Although modern oil-exploration methods are better than previous ones, they still may have only a 10-percent success rate for finding new oil fields. Once a prospective oil strike is found, the location is marked by GPS coordinates on land or by marker buoys on water.
Preparing to Drill
Once the site has been selected, it must be surveyed to determine its boundaries, and environmental impact studies may be done. Lease agreements, titles and right-of way accesses for the land must be obtained and evaluated legally. For off-shore sites, legal jurisdiction must be determined.
Once the legal issues have been settled, the crew goes about preparing the land:
1.    The land is 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, they drill a water well.
3.    They dig a reserve pit, which is used to dispose of rock cuttings and drilling mud during the drilling process, and line 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 offsite -- trucked away instead of placed in a pit. 

Once the land has been prepared, several holes must be dug 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. Additional holes are dug off to the side to temporarily store equipment -- when these holes are finished, the rig equipment can be brought in and set up.

Setting Up the Rig
Depending upon the remoteness of the drill site and its access, equipment may be transported to the site 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). Once the equipment is at the site, the rig is set up. Here are the major systems of a land oil rig:
Anatomy of an oil rig
•    Power system
    large diesel engines - burn diesel-fuel oil to provide the main source of power
    electrical generators - powered by the diesel engines to provide electrical power
•    Mechanical system - driven by electric motors
    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
    turntable - part of the drilling apparatus
•    Rotating equipment - used for rotary drilling
    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
    kelly - four- or six-sided pipe that transfers rotary motion to the turntable and drill string
    turntable or rotary table - drives the rotating motion using power from electric motors
    drill string - consists of drill pipe (connected sections of about 30 ft / 10 m) and drill collars (larger diameter, heavier pipe that fits around the drill pipe and places weight on the drill bit)
    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
•    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
    pump - sucks mud from the mud pits and pumps it to the drilling apparatus
    pipes and hoses - connects pump to drilling apparatus
    mud-return line - returns mud from hole
    shale shaker - shaker/sieve that separates rock cuttings from the mud
    shale slide - conveys cuttings to the reserve pit
    reserve pit - collects rock cuttings separated from the mud
    mud pits - where drilling mud is mixed and recycled
    mud-mixing hopper - where new mud is mixed and then sent to the mud pits




Photo courtesy Institute of Petroleum
Mud circulation in the hole

Drill-mud circulation system
•    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)


Offshore oil drilling inspection
Photo courtesy Phillips Petroleum Co.
Rotary workers trip drill pipe
The crew sets up the rig and starts the drilling operations. First, from the starter hole, they drill 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.
Drilling continues in stages: They drill, then run and cement new casings, then drill again. When the rock cuttings from the mud reveal the oil sand from the reservoir rock, they may have reached the final depth. At this point, they 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 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 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 is 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.
Once the well is completed, they 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 the Oil
After the rig is removed, a pump is placed on the well head.
Photo courtesy California Department of Conservation
Pump on an oil well
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. A second hole is then drilled into the reservoir and steam is injected 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.
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.
Photo courtesy California Department of Conservation
Enhanced oil recovery