OIL PRODUCTION

Once an accumulation of oil has been found in a porous and permeable reservoir, a series of wells are drilled in a predetermined pattern to effectively drain this "oil pool". Wells may be drilled as close as one to each 10 aces (660 ft. between wells) or as far apart as one to each 640 acres (1 mile between wells) depending on the type of reservoir and the depth to the "pay" horizon. For economic reasons, spacing is usually determined by the distance the reservoir energy will move commercial quantities of oil to individual wells. The rate of production is highest at the start when all of the energy from the dissolved gas or water drive is still available. As this energy is used up, production rates drop until it becomes uneconomical to operate although significant amounts of oil still remain in the reservoir. Experience has shown that only about 12 to 15 percent of the oil in a reservoir can be produced by the expansion of the dissolved gas or existing water.