Study On Enhanced Oil Recovery By Unsteady Water Injection In SH Oilfield

Most water injection oilfields in China now have been presenting in the stage of extra-high watercut after many years waterflooding. The efficiency of exploitation by conventional waterflooding and the oil production rate have become shrinked, also the rate of water is very high, as well as that the adjustment level of pattern well has happened to be smaller and smaller. Despite that these old oilfields which are in the stage of extra-high watercut still have a certain amount of remaining oil; it is not allowed to put a large investment for improving the exploitation because of the premise of ensuring the economic benefit maximization. Therefore, it is necessary to find a suitable method which can enhance the oil recovery of those oilfields. Unstable-waterflooding is a substitutable method which has many advantages, like low investment requirement, easy implementation, convenient management, high effect, and environmentally friendly, etc.Based on literature investigation, theoretical research and numerical reservoir simulation, this paper studied the mechanisms of unstable-waterflooding, plan of enhancing oil recovery, as well as applicable condition of SH oilfield which was in its extra-high watercut stage. According to the predecessors’ geological model and production performance data of SH oilfield, this paper completed the production history matching and got residual oil distribution law for SH oilfield. Then selected three typical well groups which were in the stage of extra-high watercut on the matched geological model to verify the elastic and capillary force during the unstable-waterflooding process, on the basis of these found that the effect of elastic force slightly larger than the effect of capillary force.And analysed the influence factors including capillary force, elastic force, oil viscosity, reservoir wettability and reservoir heterogeneity. Compared the development effect of conventional waterflooding and unstable-waterflooding for the three typical well groups to verify that unstable-waterflooding can be used for SH oilfield. Finally, put forward the different unstable-waterflooding plans to enhance oil recovery on the basis of residual oil study and water injection parameter optimization. The prediction results indicated that the effect of asynchronous unstable-waterflooding is better than the effect of synchronous unstable-waterflooding. Our research results have a significant meaning for those oilfields which are in the stage of extra-high watercut to use unstable-waterflooding to enhance their oil recovery.