Oil and Gas Drilling Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Drilling is the method by which earth is penetrated for the purpose of exploration or production of oil and gas. Exploration wells are intended to gather information about the sedimentary formations that exist beneath the surface, and their structural configuration. Production wells are intended to hit a specific target, or pool, in a place where the production of oil and or gas can be maximized. Drilling is not used exclusively for oil and gas, but is a common method of subsurface exploration and production of groundwater, or even solid mineral resources.

Oil and gas are fluid hydrocarbons that commonly occur in the pore spaces of sedimentary rocks. These hydrocarbons form as the result of organic material, commonly derived from marine plankton, transformed into hydrocarbons. This transformation requires burial, pressure, temperature and time. The pressure and temperature is commonly the result of deep burial beneath successive layers of accumulating sediments. Thicker sediments and deeper burial usually results from longer history of sedimentation and/or higher sedimentation rates in areas that commonly become sedimentary basins. Common sedimentary basins include the Appalachian, Illinois, Michigan, Williston and Gulf Coast basins, to name a few. These basins, and others like them, contain many of the oil and gas fields of the petroleum provinces of the United States.

Once hydrocarbons form, they may migrate from the stratum in which they form (source rock), through or into other strata. The higher the permeability (connected pore space) of a stratum, the more likely hydrocarbons will migrate into or through that stratum. Migration is driven by density. The strata in which hydrocarbons are generated, or through which they migrate, also contain water. Oil and gas are immiscible with water and with each other. Water has a higher density than hydrocarbons, and the hydrocarbons therefore migrate upward relative to water.

An oil or gas pool is formed where the upward-migrating oil and/or gas is trapped by some type of barrier. Barriers are usually impermeable layers that have a geometry that can trap the upward-migrating fluids. There are several possible trap configurations. In an anticline or dome, strata occur in a convex-upward shape, and oil and gas is trapped in a permeable stratum (reservoir rock) that is overlain by an impermeable stratum (cap rock). Oil and gas can be trapped by a fault that superimposes an impermeable stratum against a permeable one. Oil or gas can be trapped by the pinchout or termination of a tilted permeable layer that is underlain and overlain by impermeable strata. Oil or gas can be trapped by the lateral (facies) change within a stratum from permeable to impermeable conditions, and if the stratum is overlain by an impermeable stratum. If a trapping mechanism occurs, and water, oil, and gas are present in a subsurface pool, the gas generally occurs on top (the oil below that) and the water on the bottom. Because the pools have a very specific geometry and location, drill holes must be carefully placed to maximize extraction of the oil and gas.

The environmental effects of drilling can be numerous and varied. Drilling on land requires that an area be cleared of trees and vegetation to allow the transportation and setup of the drill rig. The drilling process itself produces the spillage of drilling mud over the ground surface. Some oil usually leaks out of the hole, but this is usually kept to a minimum. Some of the worst environmental hazards are the result of oil or gas well fires. These are like huge natural torches that are difficult to extinguish. A well fire releases large amounts of carbon dioxide into the atmosphere.

Offshore drilling is usually accomplished from a ship (usually for exploration) or a drilling platform (for production wells). Many consider drilling platforms unsightly. The main environmental concern, however, is seepage or leakage of oil from the drill rig or the producing well.

Despite its adverse effects, drilling is necessary as long as society is dependent on oil and gas as an energy source.

Bibliography:

William D. McCain, The Properties of Petroleum Fluids (PennWell Books, 1989);
William Leffler and Martin Raymond, Oil & Gas Production in Nontechnical Language (PennWell Books, 1995);
I. Levorsen, Geology of Petroleum (Freeman, 1967);
Armando Navarro, Environmentally Safe Drilling Practices (PennWell Books, 1995).