Exploration is the process of trying to find accumulations of oil and natural gas trapped under the Earth’s surface. Production is the process of recovering those hidden resources for processing, marketing and use.
To understand the challenges the oil and natural gas industry faces in exploration and production, it helps to understand how oil and gas accumulations – often called “reservoirs” – develop in the first place:
Oil and natural gas are formed when decaying plants and micro-organisms are trapped in layers of sediment and – over the course of millions of years – become buried deep within the earth, where underground heat and pressure turn them into useful hydrocarbons, such as oil and natural gas.
The layers of rock in which hydrocarbons are formed are called source rocks. High pressures underground tend to squeeze hydrocarbons out of source rocks into what are called reservoir rocks. These are rocks, such as sandstone, which feature pores large enough to permit fluids like oil, natural gas, and water to pass through them. Since oil and natural gas are less dense than water, they will float upward toward the surface. If nothing stops this migration, the oil and natural gas may reach daylight through what is called a surface seep.
More often, however, hydrocarbons’ path upward is blocked by a layer of impermeable rock, such as shale, or by some other geologic formation. These trap the oil and natural gas, either in an underground pocket or in a layer of reservoir rock, so that it may be recovered only by drilling a well.»next