超深层致密砂岩储层构造裂缝分布特征及其成因 ——以塔里木盆地库车前陆冲断带克深气田为例

综合采用岩心、薄片及成像测井等资料,对塔里木盆地克深气田巴什基奇克组超深层致密砂岩储层构造裂缝的基本特征与形成序列进行了分析,在此基础上讨论了裂缝产状、力学性质、密度、开度、充填性和充填物的差异性分布及其成因,最后探讨了不同气藏应采取的储层改造措施和有利勘探目标.结果表明:克深气田主要发育3期构造裂缝,各个气藏之间构造...

Distribution and origin of tectonic fractures in ultra-deep tight sandstone reservoirs: A case study of Keshen gas field,Kuqa foreland thrust belt,Tarim Basin

Observations of cores and thin sections combined with logging data interpretation were used to analyze the basic properties and forming sequence of tectonic fractures in the ultra-deep tight sandstone reservoirs of the Bashijiqike Formation in Keshen gas field.The differences in the fracture properties, including occurrence, mechanical characteristics, density, aperture, filling and fills, were then studied and the causes for the differences were also investigated to select suitable reservoir stimulation measures and determine exploration targets for the field.The results show that the fractures were developed in 3 stages (early, middle and late) in Keshen gas field and constitute reservoirs of distinctive characteristics due to the control of tectonic deformation stage and aqueous diagenesis environment.The Keshen-5 and -6 gas reservoirs in the north of the field are dominated by vertical fractures or high-angle tensile fractures which are nearly parallel to the long axis of the anticline under the effect of slow tectonic deformation at the early stage; the Keshen-2 gas reservoir in the center was under the influence of the middle deformation stage and contains both near NS-trending shearing fractures and near EW-trending tensile fractures with the former being relatively superior in number; the Keshen-8 and -9 gas reservoirs in the south of the field is dominated by vertical shearing fractures of nearly NS trending under deformation of the late stage.In general, from the north to the south, both the major differential stress to rock compressive strength ratios and the fracture density show a rise-fall tendency; meanwhile, the dominant strike of fractures gradually runs parallel to the present major principal stress from a high-angle intersection along with shrinking facture forming time, which in turn reduces filling rate and results in greater effective aperture.In addition, the Bashijiqike Formation (K₁bs) was deposited in a saline water as a whole: the Keshen-5, -6, and -2 blocks in the north of the field were formed in a fresh-brackish setting with fractures mainly filled by calcites, making acidification a suitable reservoir stimulation choice; and the Keshen-8, and -9 blocks in the south of the field were formed in a alkaline-prone water setting with fractures primarily filled with anhydrite and dolomite, making fracturing a more applicable stimulation option.The Keshen-8 block ranks first in terms of tectonic fracture effectiveness, followed by the Keshen-2 and -9 blocks, and then by the Keshen-5 and -6 gas pools.The Keshen-18, -19, -20, and -24 blocks are suggested to have well-developed tectonic fractures and shall be targeted in future exploration.