吐哈盆地巴喀油田特低渗砂岩油层裂缝分布特征

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

巴喀油田中侏罗统砂岩属特低渗透裂缝 孔隙型储集层 ,平均渗透率为 0 .3× 10 - 3μm2 ;地下基质岩块孔隙度为7.4%,渗透率为 0 .16× 10 - 3μm2 。砂岩储集层发育的主要裂缝类型有构造层理缝、正向正交缝、斜向正交缝和羽裂等 ,裂缝宽度一般为 0 .3～ 3 .2mm ,纵向切深为 0 .1～ 0 .8m ,水平延伸长度为 0 .2～ 2 .1m。裂缝以半充填为主 ,其分布受岩性、层厚和构造位置的影响 ,纵向、横向均呈带状分布 ,被裂缝切割而成的基质岩块尺寸取决于裂缝频率 ,岩块长轴方向以北西西向为主 ,与构造轴向基本一致。图 3表 4参

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.