BASIC CHARACTERISTICS AND QUANTITATIVE PREDICTION OF NATURAL FRACTURE SYSTEM IN THE UPPER PALEOZOIC TIGHT SAND RESERVOIRS IN TABAMIAO AREA,NORTH ORDOS BASIN

It is very hard to explore and develop the Upper Paleozoic low pressure tight sand gas reservoir effectively in north ordos basin.However,the existence of natural fractures in tight gas sand will change the situation dramatically by providing good conditions for gas migration and accumulation.The Tabamiao block is located in the north of ordos basin,and its tectonic setting is monoclinal structure,which stratigraphic dip is only 1 degree and is not commonly deemed good conditions for natural fracture growth.However,many vertical fractures and high-angle fractures have been found through core analysis and thin-section analysis as well as well testing and imaging logging interpretation.Further investigation in building the tectonic fracture system has been conducted on the drilling cores with paleomagnetic method and sound wave imaging technology.The result reveals that the NWW-EW oriented tectonic fractures are primary,the NEE,NE and NW NNW-SE ones are subsidiary,respectively.The local and regional fractures,which are respectively related to flexibility deformation and regional stress field,are two types of natural fractures in Tabamiao area.Based on the analysis of tectonic fractures/geometry,kinematics and dynamics,and the causes of formation of regional fracture system and its major function of gas migration and accumulation,we properly predict and evaluate the fracture distribution law and development degree for major layer(He 2+3 segment)in this area by use of detailed three-dimensions fracture predictive simulation methods.It makes clear that a majority of high producing gas wells in this area are commendably corresponding to predictive fracture development regions.