Experimental Study on Water Injection Response Differences Between Oil and Non-Oil Formations of Chang-8 Tight Oil Reservoir of Xifeng Oilfield

Chang-8reservoir of Xifeng Oilfield is characterized with thick oil formations interbedded with many dry layers and water layers,but it is difficult to perforate individual layers separately and so in reality all layers are perforated all together and commingled water injection.To understand the differences in water injection profiles among the oil layers,water layers and dry layers,30 cores were selected to conduct the parallel commingled waterflood flow experiments.The results show that when the oil and water layers have similar permeability and the waterflood injection pressure is low,water first produced is from the water layer and later from both the water layer and the oil layer.For the commingled waterflood of the oil layer and dry layer,when permeability of the oil layer is larger than that of the dry layer,water first produced is from the oil layer and the majority of the produced water remains to be from the oil layer even after water breaks-through from the dry layer.For the commingled waterflood of the oil/water/dry layers,when k_oil=k_water>k_dry,water first produced is from the water layer and later from the dry layer and the oil layer.When k_oil>k_water>k_dry and the injection pressure is low,first produced water comes from both the oil layer and the water layer,and later the dry layer.These results are important for understanding waterflood sweep mechanisms and the remaining oil distribution under the conditions of commingled injection for the oil/water/dry layers,and they can be utilized to guide the development strategy of tight oil reservoirs with interbedded layers.