Fracture and gas potential in tight sandstone reservoirs in the eastern part of Sulige Gas Field, Ordos basin (China)

摘要

Sulige gas field in Ordos Basin is the largest discovered gas field in China. But tight sandstone reservoirs is becoming the main limitation of natural gas exploration and exploitation in Sulige gas field. Intensively analysis on micro-pore structure of sandstone reservoirs in Shan_1 member of Shanxi formation and He_8 member of Shihexizi formation in Permian system in the eastern part of Sulige gas field are conducted by means of drill core observation, slice identification, SEM analysis, casting slice and mercury injection etc. analytical methods. Result shows that fracture is well developed in sandstone reservoirs in the northern part of the interest area, by which petrophysical property of tight sandstone reservoir is improved distinctly. Types of fracture are dominated by diaclase and the diagenesis cracks. Main direction of the fractures is NE and NW, and the angle of the two groups fractures is nearly 90°.But one set of the conjugate shear fractures would develop well and the other was rest rained by the influenced of strong anisotropism of sandbodies. Diaclase and the diagenesis cracks developed along the boundery of tectonic divisions. Fracture is one of the important reasons for improvement of permeability in tight sandstone reservoirs. Gas potential of sandstone in fracture-developed section is much better than that of non-fracture section. Consequently, it is signaficant for all of reservoir forecasting, high productivity gas pool seeking, design and construction of natural gas exploitation to grasp distribution laws of fracture.