High vertical and horizontal conformance viscous oil recovery method

Abstract

Disclosed is an oil recovery method especially useful for recovering viscous oil from thick formations including tar sand deposits. The method comprises several phases which accomplish efficient recovery of the viscous oil from the formation with good vertical and horizontal sweep conformance or effectiveness. The first phase may utilize as few as two spaced apart wells, one for fluid injection and one for oil production and an oil recovery method such as injecting steam or a mixture of air and steam for low temperature, controlled oxidation is a preferred fluid for use in the first phase. After fluid breakthrough at the production well occurs, the producer of the first phase is converted to an injection well and one or more new production wells outside of the pattern swept by the injected fluid are completed in the oil formation. Thermal recovery fluids are then injected into two wells with the displacement moving in the direction of the new production wells. The oil displacement process of the second phase may be air or oxygen for high temperature in situ combustion. In thick formations, if the wells utilized in the first phase are completed low in the formation, the new production wells should be completed high in the formation to expand the recovery zone vertically to encompass more of the formation. A third phase employs a well located centrally to the four previous wells for production with air injection being into all four wells utilized in the first two cycles to further expand the three-dimensional extent of the swept zone within the pattern defined by the wells.