Single-well diagnostics and increased oil recovery by oil injection and sequential waterflooding

Abstract

A method for residual oil recovery from oil reservoirs, and diagnostic tests for determining its efficiency using a single well are described. The method includes injecting oil into a well in a reservoir that has been previously waterflooded or an oil reservoir or zone of an oil reservoir which contains immobile oil at the time of discovery, and extracting the oil by waterflooding the charged zones by placing the injection well in production. The target zone from which oil is recovered may be increased by following injection of oil with injection of water to push an oil bank which grows in volume as a function of distance of propagation, because of the effect of waterflooding on residual oil. The well may then be placed in production and the oil bank volume will continue to increase in volume as it returns to the well, again because of the waterflooding effect. The oil bank is then produced at the surface. The double-sweep waterflooding process using a single well can be repeated by again charging with oil followed by waterflooding. Sequential injection of oil and water to generate more than one oil bank may also be used to increase oil recovery by multiple sequential waterfloods. Combinations of oil injection and sequential waterflooding also have application to reservoir diagnostics.