Changes

Conventional recovery methods (primary and secondary) typically extract approximately one-third of the original oil-in-place in a reservoir. Estimates (made in the late 1970s) of worldwide oil in-place range up to 1.5 trillion barrels; using that figure, it is estimated that the oil remaining as a residual oil saturation after conventional recovery would be approximately 1.0 trillion barrels.<ref name=pt10r24>National Petroleum Council, 1976, An analysis of the potential for enhanced oil recovery from known fields in the United States—1976–2000: NPC, Dec.</ref> Several enhanced oil recovery (EOR) techniques—generally grouped together as tertiary production schemes—have targeted this huge unexploited reserve.

Conventional recovery methods (primary and secondary) typically extract approximately one-third of the original oil-in-place in a reservoir. Estimates (made in the late 1970s) of worldwide oil in-place range up to 1.5 trillion barrels; using that figure, it is estimated that the oil remaining as a residual oil saturation after conventional recovery would be approximately 1.0 trillion barrels.<ref name=pt10r24>National Petroleum Council, 1976, An analysis of the potential for enhanced oil recovery from known fields in the United States—1976–2000: NPC, Dec.</ref> Several enhanced oil recovery (EOR) techniques—generally grouped together as tertiary production schemes—have targeted this huge unexploited reserve.

In the past, chemical, thermal, and miscible techniques have been used by the industry on a commercial scale. EOR techniques require the injection of chemical compounds dissolved in water, the injection of steam, or the injection of a gas that is miscible with the oil in place. As a result, all current EOR techniques are much more expensive to implement than normal secondary water injection projects. Therefore, the amount of oil that can ultimately be recovered by existing EOR techniques is directly related to the price of crude oil.

In the past, chemical, thermal, and miscible techniques have been used by the industry on a commercial scale. EOR techniques require the injection of chemical compounds dissolved in water, the injection of steam, or the injection of a gas that is miscible with the oil in place. As a result, all current EOR techniques are much more expensive to implement than normal secondary water injection projects. Therefore, the amount of oil that can ultimately be recovered by existing EOR techniques is directly related to the price of [[crude oil]].

All EOR projects begin with an analysis of the nature, location, and causes of residual oil saturations (''S''_or) that remain after primary and/or secondary recovery operations. The main factors that control the value of ''S''_or are pore geometry, rock [[wettability]], and the properties of the displaced (oil) and displacing (injected) fluids. Fluid properties of particular interest are interfacial tension, viscosity, and density. In combination with the heterogeneity of the reservoir, these properties result in the overall recovery (''E''_R) for any recovery scheme.

All EOR projects begin with an analysis of the nature, location, and causes of residual oil saturations (''S''_or) that remain after primary and/or secondary recovery operations. The main factors that control the value of ''S''_or are pore geometry, rock [[wettability]], and the properties of the displaced (oil) and displacing (injected) fluids. Fluid properties of particular interest are interfacial tension, viscosity, and density. In combination with the heterogeneity of the reservoir, these properties result in the overall recovery (''E''_R) for any recovery scheme.