A STUDY ON THE MICROFLOW CHARACTERISTICS OF DIFFERENT FLOW UNITS——Taking Hua-152 Block of Chang 3 Reservoir in the Huachi OilfieLd as an ExampLe

A physical simulation experimental study on the micro-flow characteristics of different flow units has been conducted by using the natural sandstone micromodels with the aim to provide a scientific basis for improving exploitation effect.The flow units in Hua-152 block of Chang 3 reservoir in the Huachi oilfield,the Ordos Basin can be classified into 3 types,e.g type A,type B and type C,with the reservoir properties and the permeability properties changing from superior to inferior.The study shows that the microflow characteristics of different flow units are significantly different in the aspects of the entry order of the fluid,the displacement pattern of the fluid,and the type of the residual oil.The fluid always enters into type A flow unit preferentially,then type B flow unit,and is always difficult to enter into type C flow unit.The injection water during oil displacement cannot enter into type C flow unit.As for the difference in the displacement pattern of the fluid,the pattern of oil displacing water is non-piston displacement in type A flow unit,while in type B and type C flow units,the pattern of oil displacing water is piston-like displacement.The types of the residual oils in different flow units are also different after being displaced by water.The residual oils in type A flow unit are mainly small clustered oil block and thick filmlike oils caused by the injection water going around small pore spaces,whereas the residual oils in type B flow unit are mainly larger clustered oil block and spherical or drop-like oils caused by the injection water going around larger pore spaces.The difference in the pore structure and the wettability between different flow units is the main reason leading to the above differences in the microflow characteristics.The experimental study also indicates that type C and type B flow units is the main areas for the residual oil to accumulate,where more exploration efforts should be made.