Experimental Studyof Waterfloodingfrom Layered Sandstone

Water flooding of oilfield development faces three contradictions:the contradictions of planes, inter layers and interior layers, for layered reservoirs are mainly contradictions of interior layers, which caused by intraformational heterogeneity. And the water flooding of layered reservoir development faces some adverse conditions like low recovery degree, invalid water cycle, and uncertain of distribution of remaining oil and etc al, which would cause much difficulty to the tertiary oil recovery.Physical simulation method is an important way to explore the law of water flooding. Traditional experiments using small core column simulate water flooding experiment to get the endpoint value such as residual oil saturation, recovery degree, which cannot simulate the intrafomational heterogeneity of layered reservoir. Subsequent researchers use layered sand-pack models to simulate the intraformational heterogeneity of layered reservoir, inside which a series of probe were embedded to detect the stress and/or saturation distribution. There’s also some problems like model complexity, the lack of precision of test results and they have no idea of how to detect the crossflow between the adjacent layers, although it makes a big step forward of the study. So in this research, some real core from LASAXING oilfield were used to simulate the layered reservoir and with the help of CT scanning technology, a whole new simulation method was build. Systematic research was made by7groups of water flooding experiments to study the recovery degree and its influence factors, the rules of flow distribution, the mechanism of invalid water cycle, the quantification and visualization of remaining oil distribution, and methods to enhance the oil recovery.Research results show that water flooding recovery degree of the layered reservoir are affected mostly by water phase permeability differential, and even with same heterogeneity coefficient, layered sandstone models with different rhythms would behave very differently during the water flooding; crossflow phenomenon exists in the process of water flooding of layered reservoirs and follows some certain rules:the stronger the reservoir heterogeneity is, the more serious the crossflow behaves, and crossflow mainly happened during a specific period after the breakthrough of the layer with highest permeability, meanwhile crossflow would be more serious in inverted layered reservoir than in positive rhythm reservoir; to the late period of high water cut, invalid water circulation would appear in positive and inverted rhythm reservoir, and the reason of which is water phase crossflow of low permeability layer to high permeability layer after the breakthrough of high permeability layer; after water flooding, remaining oil would disperse overall the layered reservoir, but would also concentrate in some local position, and with different heterogeneity, the remaining oil’s position and distribution of different layered reservoir would be different, which need different methods to enhance the oil recovery.