Evaluation Of Fracture Reservoir For Yanchang Formation In Mahuang Mountain Of The West Ordos Basin

The reservoir of low porosity and permeability is controlled by the lithology or the structure- lithology in the Mesozoic of the West Ordos Basin and it's hard to explorative and develops. The oil-gas productivity is greatly depending on the developing degree of natural fracture in the reservoir. The petroleum shift poly reservoir formation is awfully controlled by the formation condition and development regularity of natural fracture. Studing on the distrbution of reservoir fracture can afford the scientific reference for the exploration arrangement and making Oil field development and implementation the measures in region of interest in the future.Based on research and analysis of the fracture in the outcrops and cores, we judge the lithology, the bed thickness and the tectonism are dominant factors to control the development of fracture, and the multiphase tectonic activity is principal factor in the difference of fracture development in the region of interest. With the decreasing of rock particles and porosity, the rock will become compaction and easily to create the fracture; the bed thickness and the fracture development are inverse relation; there is more development of fracture in the stronger tectonic deformation. Based on analysis of the relation with the fracture in the core and the characteristic of logging electric response, we calculate the fracture width and the fracture porosity, and then establish the discriminant function about the fracture, and use the R/S analysis to identify the fracture in single well. At last to comprehensive evaluate the fracture in single well, judge in the Triassic the more development of fracture in Chang 3 of Yanchang Formation and Chang 5 of Yanchang Formation than in Chang 5 of Yanchang Formation, and the more development of fracture in the northeast in the whole region of interest. With experiment of acoustic emission and combination relations of the fracture in the outcrops and cores, we judge there were 3 breakup phases by the tectonic stress in Yanchang Formation of the Triassic. And using the established achievements it experienced the early period of Yanshan Mountain tectonic movement, late period of Yanshan Mountain tectonic movement and the early period of Himalayan tectonic movements. We evaluated the distribution of fracture by ways of the main curvature method; thin-plate-buckling method and directional-Filter method in Yanchang Formation of the Triassic. And then using the expert system to comprehensive evaluate the distribution of fracture by these methods. The coincidence rate is 86.36%, and we think the result is good conformity, and there is more development of fracture in the east than the west in whole region of interest. There is also more development of fracture in the north of the region.Based on the analysis of the distribution of fracture and the established achievements of oil-gas accumulation, we judge the favorable exploration area is the north of the Quanwanzi convex belt in the Yanchang Formation of the Triassic.