影响致密砂岩储层裂缝分布的主控因素分析--以库车前陆盆地侏罗系-新近系为例

Controlling factors on fracture development in the tight sandstone reservoirs:A case study of Jurassic-Neogene in the Kuqa foreland basin

系统阐明致密砂岩储层裂缝发育的控制因素,是准确预测裂缝分布规律的重要基础。在对裂缝精细定量表征的基础上,系统分析了库车地区致密砂岩中裂缝分布的控制因素。研究区主要发育构造裂缝,裂缝发育程度除受岩性、岩石力学层、沉积微相及成岩相等内因控制以外,还受构造部位和异常高压等外因的控制。脆性矿物含量高、粒度细、孔隙度低、分选好的岩石有利于裂缝的发育;裂缝往往发育在能干性强的岩石中,其高度受岩石力学层厚度控制;单层厚度薄、累积厚度大、粒度细的沉积微相更有利于裂缝的发育;强压实强胶结致密型成岩相是裂缝发育的有利区;断裂附近及褶皱转折端是局部应力集中区,裂缝发育程度明显升高;异常高压降低了有效应力,促进岩石发生破裂。

Systematically illuminating the controlling factors on fracture development in the tight sandstone reservoirs is the key basis to accurately predict the fracture distribution. Fractures in the tight sandstone reservoirs of Kuqa foreland basin are quantitatively characterized,and a systematic research on the fracture distribution and controlling factors is carried out. Tectonic fractures are dominant in the tight sandstone reservoirs, and their development was controlled by inherent （e.g., lithology, mechanical stratigraphy, sedimentary micro-facies and diagenesis facies） and external （structural position and overpressure） factors. Rocks with high content of brittle minerals ,fine grain size, low porosity and well sorting are conducive to the development of fractures.Fractures often develop in the competent rocks and their height is equivalent to the thickness of mechanical layer.Sedimentary micro-facies with thick cumulative deposition thickness, thin single layer and fine granularity are the favorable area for fracture development.Diagenesis facies with dense compaction and cementation are also areas favorable for fracture development. Vicinity of fault and hinge of fold are area of local stress concentration,thus the fracture density increased significantly.The existence of overpressure promotes the failure of rocks.