关键词: 低渗透储层, 低角度裂缝, 逆冲构造带, 分布特征, 成因, 地质意义

Abstract:

Fractures in the low-permeability reservoirs are usually high dip-angles. But there exist low dip-angle fractures formed by tectonism in the thrust zones of the western basins of China. These low dip-angle fractures are mainly distributed in the medium-granular sandstones and grit stones nearby the thrust or sliding layers. These fractures are often oblique to bedding plane with tiny angle and have equal spacing. Some fractures are filled with calcite, quartz and asphalt.Some fractures are characterized by dissolution and cut by the high dip-angle fractures. The geological analysis and numerical simulation show that the low dip-angle fractures are mainly formed by shearing due to thrusting or interlayer gliding under tectonic compression. These low dip-angle fractures are widely distributed along the thrust or sliding layer and have good lateral connectivity and high permeability in the horizontal direction. They can be also connected with high dip-angle fractures to form a good network system,which is advantageous to the enrichment for oil and gas in the low-permeability formation and to generation of high production wells.

Key words: low-permeability reservoir, low dip-angle fracture, thrust zone, distribution characteristics, origin, geological significance