Offshore Drilling

Worldwide daily consumption of oil generally exceeeds 80-85 million barrels thereby driving the petroleum industry to continually search the planet for new reserves. Since the world’s oceans comprise almost 75 percent of the earth’s surface, it stands to reason that much of the world’s future new oil reserves will be discovered underwater.

Underwater exploration, drilling, and transportation of crude oil requires special equipment and processes to first, deal with the inherent challenges of work in lightless and deep areas, and second, to do so without the risk of polluting the environment. This article will focus on the methods of exploration and extraction of crude oil in the deep ocean environment.

Locating Fossil Fuels

Most of the world’s petroleum lies between 500 and 25,000 feet in depth below ground. Petroleum products are generally believed to have begun as plankton between 10 and 600 million years ago. Over millenia this decaying matter of tiny plants and animals drifted to the bottom of the ocean, was covered with sand and mud, and with the help of heat and pressure evolved into deposits of liquid oil, gas, and petroleum materials. This organic material, settling in traps under thick layers of rock, has taken a number of forms:

• Liquid petroleum (oil)
• Gaseous petroleum (natural gas)
• Petroleum deposits (oil shale or tar sands)

Locating these deposits is the first obvious challenge; geologists have traditionally studied surface features and satellite maps, taken soil and rock samples, and used gravity meters to identify gravitational fluctuations that could indicate a subterranean flow of oil. These options are viable in the exploration of land and relatively shallow water but are ineffective when working at ocean depths of thousands of feet amidst rough seas. There are a number of methods available to deal with this challenge:

• Sniffer equipment, which is used to detect traces of natural gas in seawater, aids in locating seeping deposits.
• Magnetic survey equipment can be used to identify magnetic anomolies that might serve as indicators of underground traps.
• Seismic surveying (referred to as sparking) analyzes information from sending shock waves down through the water to locate possible traps in the ocean floor. Seismic surveying is somewhat controversial with the environmentalists as the shock waves cause what some term “acoustic pollution,” viewed as a threat to the more seismically aware sea life (e.g. blue whales).

Once undersea oil deposits are detected, the survey teams typically note the GPS coordinates, plant a buoy, and apply for a government lease to perform exploratory drilling. Only through exploratory drilling can the true potential of a specific area to provide significant and commercially feasible amounts of petroleum based products be quantified.

Exploratory Off shore Drilling

Exploratory drilling involves the use of a mobile drilling platform (ship-based or towed), where the oil companies typically drill 4 temporary exploratory wells over the area in question, each drilling taking 60 to 90 days to complete. The goal is to obtain a core sample which is used to look for signs of petroleum (termed a show). Once a show occurs, the drilling is terminated and the additional tests are performed to assess the quality and quantity of the sample. If determined is determined to adequate and commercially feasible, then the oil company will drill additional wells to verify the initial findings.

Production Offshore Drilling

Production wells are anticipated to last 10 to 20 years before they are no longer profitable and  are fixed directly to the ocean floor using foundations or tethering cables. The design of these structures is critical as the actual platform must remain steady which is not an easy task given the realities of ocean effects particularly amidst storms. With the platform in place, there are a number of factors to consider:

• Coverage area: By using a process termed directional drilling, platforms can reach deposits miles away from the actual drill site.
• Efficiency: Through use of a subsea drilling template, high levels of drilling accuracy can be achieved, thereby ensuring the anticipated quantities are obtained.
• Effectiveness: Oil companies have perfected a 3-phased drilling process to ensure the oil and gas is transported to storage in tact without polluting the ocean.

Transport of Oil and Gas

Once a petroleum source is hit, the focus shifts to measures to control the flow of pressurized oil and gas up to the surface. These measures include:

• The use of a production casing, initially closing off the well from the surrounding petroleum reservoir and then perforated at different depths using well-targeted explosives, provides for the surfacing of oil and gas at less than that of a blasting geyser.
• With the gradual decline of natural pressure, injection systems providing water, compressed air, or steam are used to boost the pressure or add heat and allow for the flow the remaining petroleum.

The liquid that is removed from a well is typically a mixture of crude oil, natural gas, water, and sediments. A necessary step before refinement is the removal of unwanted substances from the oil. These production facilities are typically part of the drilling platforms themselves. As most oil refinement takes place onshore (and in some instances on converted tanker ships), the job of the drilling facility is to provide oil and natural gas to storage and treatment plants free of these pollutants.

Closing of a Well

Once a well runs dry or more typically when the costs of further development outweighs the potential future profits, the oil company will plug and abandon a well. Depending on specific geographic, political, and economic factors, the platforms will either be removed from their moorings and  relocated (or scrapped) or they will remain and slowly deteriorate from the gradual erosion and corrosion caused by the sea.

1. energyauthority says:

   October 7, 2010 at 6:08 pm

   sure