Distribution of the fracture within the low permeability sandstone reservoir of Baka oilfield, Tuha Basin, Northwest China

Sandstone reservoir of Middle Jurassic in Baka oil field is of lowest permeability, which is fracture and pore, and the average permeability is only 0.3×10 -3 μm 2 on the ground. According to a test, the matrix permeability is 0.16×10 -3 μm 2 and matrix porosity is 7.4% in the underground basement. There are 6 styles main fractures, i.e., normal orthogonal fracture,diagonal orthogonal fracture,tectonic bedding fracture and plumose fracture. Generally, the wide of fracture is 0.3 3.2 mm,and long is 0.1 0.8m in vertical direction, 0.2 2.1 m in horizon. Most of fractures are semi filled,whose distribution are controlled by lithology,thickness of strata and tectonic characters, moreover, the fraction presents banded vertically. Fracture growth relates to tectonic setting. The size of matrix rock is decided by the fracture frequency. Most matrix rocks distributed in a NWW trend, which is identical with tectonic axes.