Once formed in source rock, oil and natural gas, being lighter than water, begin to migrate laterally and vertically through migratory rock. Oil and gas pass through the pore space within the sedimentary rock structure and through fractures in rock layers. This migration may extend as far as 200 miles from source rock. The rate of migration depends on the porosity and permeability of the migratory rock. Porosity is a measure of the spaces within the rock that can be filled with fluids and permeability is a measure of the ease with which a fluid can pass from one pore to the next. Both are critical in determining the flow of hydrocarbons into a well; generally speaking, the greater the porosity, the greater the permeability.
Oil and gas migration continues until interrupted by an intervening rock formation shaped like an inverted bowl or a fault made of a well-cemented rock with no spaces between the grains. Once migrating oil and gas are trapped in reservoir rock, natural gas, the lightest, rises to the top of the reservoir and forms a gas cap; saltwater, the heaviest, sinks to the bottom, leaving oil in the middle. In some reservoirs, a small concentration of natural gas may remain mixed with crude oil without forming a gas cap; in still others, there is no associated natural gas. The subsurface water that makes up the water table is fresh, produced by rain percolating through the soil; but the water beneath the water table is more or less as saline as ocean water.
Contrary to a popular conception the originated with the dawn of the oil age, an oil reservoir does not consist of a void space filled with a pool of oil; rather, it is migratory rock turned reservoir rock, saturated with oil and gas, that has been prevented from continuing its journey to the earth’s surface. The geometry of a trap is one determinant of the size of an oil field; the larger the dome or fault of caprock and the greater the distance from the top of the trap to the spill point the larger the size of the potential oil field. Other determinants are porosity, which determines the quantity of oil and gas contained in reservoir rock, its permeability, which determines the flow of the oil and gas to a well and its potential recoverability, and, of course, the concentration of oil and natural gas in the reservoir rock.
Heartland Energy Colorado is one of the top hydrocarbon-based energy providers in the USA. They have many drilling locations throughout the country and remain one of the top producers of US oil & gas companies. For more information on Heartland Energy Colorado, see Heartland Energy Development Corporation online.
(Source: "Energy for the 21st Century," Nersesian)
Very interesting how fossil fuels form over time. Good Article. I also read up on some similar information on the creation of domestic oil in the American West. I found that article at Heartland Energy Colorado
ReplyDelete