沁水盆地南部山西组致密砂岩古构造应力场模拟及裂缝预测

Paleotectonic stress field simulation and fracture prediction of tight sandstone in the Shanxi Formation,southern Qinshui Basin,China

以沁水盆地南部地区山西组为例,系统研究了煤系致密砂岩的裂缝发育特征,并对其古构造应力场进行了模拟,在此基础上,对裂缝发育区进行了预测。研究结果表明,山西组致密砂岩中发育不同级序的裂缝,主要为构造缝,其含量大于90%。构造缝主要为张性缝、剪切缝及挤压缝;非构造缝主要为溶蚀缝。目的层致密砂岩的裂缝充填类型主要为未充填及半充填,裂缝的有效性好。利用三维有限元法对山西组Ⅱ砂组进行了精细地质建模及古构造应力场模拟,恢复了目的层在喜马拉雅期最大一幕挤压应力环境下的古地应力场。考虑到目的层主要发育张性缝和剪切缝,同时还含少量挤压缝,构建了综合破裂率参数来定量预测裂缝的发育程度,预测结果与实际地质情况吻合较好。该方法可以实现复杂构造区致密气储层裂缝甜点的有效预测。

In this papers using the Shanxi Formation in the southern Qinshui Basin as an example,the fracture development charac teristics in tight sandstones in a coal system were studied^and the palaeotectonic stress field was simulated.Based on the findings,the fracture development area was predicted.The results showed that fractures of different scales were developed in the tight sand stone of the Shanxi Formation,of which more than 90%were tectonic fractures.The tectonic fractures mostly included tensile frac-tures shear fractures,and extrusion fractures,and the non-tectonic fractures were primarily dissolution fractures.The fracture-filling type in the tight sandstone of the target layer was mainly unfilled and semi-filled.Fine geological modeling and paleostress simulations were conducted on No.II sand group of the Shanxi Formation,using the 3D finite element method(FEM).The palaeo-geostress field of the target layer in the Himalayan area was restored.Considering that tensile and shear fractures were both well developed in the target layer,and also a small amount of extrusion fractures were developed^we constructed a comprehensive rup-ture rate(ⅠF)to quantitatively predict the development of fractures.The prediction results agreed with actual geological conditions.Therefore,this method can effectively predict the fracture sweet spots of tight gas reservoirs in complex structural areas.