库车坳陷迪北地区侏罗系致密储层裂缝发育特征及控藏模式

Development characteristics of fractures in Jurassic tight reservoir in Dibei area of Kuqa depression and its reservoir-controlling mode

库车坳陷迪北地区侏罗系致密砂岩储层中裂缝普遍发育,裂缝对致密砂岩气藏具有重要控制作用。利用露头、岩心和薄片等资料,明确裂缝发育特征和形成机理,探讨裂缝对致密砂岩气藏的控制作用。结果表明:研究区裂缝主要为构造裂缝,其次为成岩裂缝,构造裂缝较为发育,非均质性强,大部分未被充填,有效性较好。构造裂缝分为3期,分别在喜马拉雅早期、中期和晚期3期构造挤压作用下形成。第3期构造裂缝发育程度最高且基本未被充填,是最重要的一期构造裂缝;其发育期晚于天然气大量充注期,且构造裂缝形成之后天然气仍持续充注。裂缝对侏罗系致密砂岩气藏的控制作用主要表现在:发育在构造低凹或斜坡部位的小开度裂缝,可改善储层物性,有利于形成甜点(迪西1井区);发育在迪北地区构造高部位的大开度裂缝可对致密砂岩气藏进行调整、改造和破坏(依深4井区)。

Fractures are widely developed in Jurassic tight sandstone reservoir in Dibei area of Kuqa depression,which has an important control effect on tight sandstone gas reservoir.The outcrop,core,thin section,and other data are used to identify characteristics and forming mechanism of fractures,and examine control of fractures on the tight sandstone gas reservoir.The results show that in the study area,the majority are structural fractures,followed by diagenetic fractures.The structural fractures are developed with strong heterogeneity,and mostly unfilled,showing better efficiency.They are formed under the tectonic compression in early,middle and late Himalayan period,respectively.In the third period,the structural fractures are extremely developed,not filled basically,and considered as the most important ones.Their development period is later than natural gas charging period;charging of natural gas was continuous after formation of structural fractures.Control of fractures on the Jurassic tight sandstone gas reservoir is mainly reflected in the following aspects:(1)The small-aperture fracture developed in the tectonic depression and slope can improve reservoir physical properties,which is favorable to formation of sweet spots(Well Dixi-1).(2)The large-aperture fractures developed in the structural high point in Dibei area can adjust,transform and damage tight sandstone gas reservoir(Well Yishen-4).