Research on Water-Washing Characteristics in Different Flooding Modes of Dominant Reservoir in LaSaXing Oilfield

Abstract

LaSaXing oilfield has entered the late ultra-high water cut stage after 60-year development, the dominant oil reservoirs are exploited in 3 flooding modes - water flooding, polymer flooding and ASP flooding. Fine recognition of residual oil distribution under different flooding conditions is the key to make precise adjustment and tapping oil potential. Based on stratum division and correlation, a comparison analysis was taken on the water-washing characteristics and residual oil distribution of dominant reservoirs according to the 68 core wells analysis data in LaSaXing oilfield. The results show that the degree of water-washing is aggravated in dominant reservoir and the strong and medium water-washing distribution proportion is high, where only 20% of sandstone thickness is not water-washed. The residual oil in the dominant reservoir after water flooding development is mainly distributed at the top of the positive rhythm reservoir, and some plane residual oil stagnant areas are formed due to the non-controlled water pattern. The residual oil in the dominant reservoir after polymer flooding development is mainly distributed in the medium and low water-washing area controlled by rhythm and inter-layers, and the plane residual oil stagnant area is mainly on both sides away from the main stream line of injection wells. The residual oil in the dominant reservoir after ASP flooding development is mainly distributed in the upper part of thick layer and the top of rhythm section longitudinally, and the plane residual oil stagnant area is mainly distributed near the production end. The comprehensive research on the water-washing characteristics of different flooding modes shows that even if the main reservoir of old oilfield has been developed and adjusted for many cycles over a long period, it still has oil potential for further enhanced oil recovery, and the main geological factors that control the distribution of residual oil have changed from sedimentary micro-facies to various micro-scale geological interfaces.KeywordsLaSaXing oilfieldWater-washing characteristicsDominant reservoirDifferent flooding modes