Research On Remaining Oil Distribution And Short Horizontal Well Infill In Ultra Low Permeability Reservoir

This paper takes the ultra low permeability reservoir in Ansai Oilfield as the research object.Based on the systematic study of reservoir geology,the fracture development and its distribution law,and the distribution law of remaining oil are studied.The well placement orientation and the optimal horizontal section length for short horizontal well infilling are optimized.According to the well spacing change,dynamic fracture distribution,and water line width,reasonable reservoir reconstruction parameters and methods are explored,and the infilling effect is evaluated.Through the study of this paper,the following four research results are obtained:1.Delta front subfacies are developed in Chang 6 oil layer of the study area,the sand body is developed from northeast to southwest,in strip distribution,and four single sand bodies are developed in Chang6₁^1-2 small layer of the main layer,which belongs to medium heterogeneous reservoir;2.Natural microfractures are developed,with an inclination of about 80°.The artificial fractures are consistent with the direction of the maximum horizontal principal stress NE76°.The dynamic fractures of water injection include the natural fractures closed in the early stage,the artificial pressure fractures and the new fractures generated by the later rock fracture,and their extension direction is consistent with the direction of the current maximum horizontal principal stress;3.The remaining oil is distributed in strips on both sides of the water line on the plane.The width of the strong water washing zone is about 60-80 m,and the remaining oil enrichment area is above 100 m;The high water flooded layer and low water washed section are alternately distributed on the profile,and the strong water washed section accounts for only about 30%;4.The horizontal well densification is relatively effective in the way of not crossing the waterline and crossing 30-60°with the main stress.The reasonable horizontal section length is 120-200m.Large flow rate,middle reinforcement and control at both ends are used.The average fracturing is 3-5 sections,with interval of 30-40m,single section sand adding of 30-35m³,and underground fluid of 1150-1350m³.It has a high initial production and stable production capacity.The research results of this paper can be used to determine the reasonable well spacing,well layout and reconstruction parameters of infilled short horizontal wells in Ansai Oilfield,provide theoretical guidance for infilling technology of short horizontal wells,and have important significance for the efficient development of ultra-low permeability reservoirs in Ansai Oilfield.