Analysis On Main Controlling Factors Of Productivity Of Chang-7 Shale Oil Horizontal Well In Qingcheng And Optimization Of Favorable Areas

Chang 7 reservoir in Qingcheng area,southwest Ordos Basin is a typical shale oil reservoir.Affected by petrological characteristics,physical properties,oil content,crude oil properties and engineering mechanical properties,the productivity of Chang 7 reservoir in this area after fracturing is unstable,and the main controlling factors affecting the productivity are not clear,making it difficult to develop on a large scale.Multiple vertical reservoirs are superimposed,but the single sand body is thin,the reservoir lithology changes quickly,the transverse continuity of sand body is poor,the difference of oil content is large,and the heterogeneity is strong.Therefore,it is difficult to select the high-quality favorable area with weak transverse continuity of reservoir,and the deployment of horizontal well location is difficult,which seriously restricts the large-scale and effective development of shale oil in Qingcheng area.Based on seismic,core analysis and well logging data in the study area,the characteristics of sedimentary microfacies and sand body distribution are defined.The core physical properties and pore structures of different target strata were analyzed by casting thin sections and scanning electron microscopy,and the brittleness and physical properties of rocks were clarified.Based on the oil content,formation pressure,fluid property characteristics and fracturing engineering factors in the study area,single-factor analysis,multi-factor analysis and big data analysis methods were used to distinguish the main controlling factors of productivity.Combined with the classification standard of reservoir sweet spot,the favorable target area of production and construction is selected.Finally,the following main achievements and understandings were obtained:(1)Channel-lobe sublacustrine fan deposits are developed in the target layer of the study area.(2)The total sand body thickness,the maximum single sand body thickness and the overall sand-to-ground ratio of class Ⅰ and Class Ⅱ sandy clastic flow reservoirs are larger.However,the total thickness of turbidity sedimentary facies is small,the maximum thickness of single sand body and the total sand-ground ratio are small,and the continuity of sand body is relatively poor.(3)Reservoir porosity,fluid properties and oil saturation have a great influence on the cumulative oil production of a single well in the first year.The number of fracturing stages,the amount of fluid into the ground and the amount of sand added are the main controlling factors of horizontal well productivity.(4)17 favorable target areas were finally selected,and the average oil production per well in the first year was predicted to be 4167 t and the average daily oil production per well was 11.6 t/d.The research results can provide scientific basis for rapid production construction and efficient development of Chang 7 shale reservoir in Qingcheng area.