塔里木盆地库车坳陷克深地区白垩系低孔砂岩储层“三重介质特征”

Tri-media reservoir characteristic of fractured tight gas reservoir of gasfield A,Kuqa Depression,Tarim Basin

塔里木盆地库车坳陷克深气田巴什基奇克组属于低孔裂缝性砂岩储层,储层埋藏深度大,基质致密,裂缝发育。由于该气田储层孔喉细小、结构复杂,传统孔喉表征技术难以定量系统表征,综合激光共聚焦扫描、场发射扫描电镜、微米CT、氮气吸附和核磁共振等先进孔喉表征技术,首次发现库车坳陷克深气田储层基质微观呈"三重介质"特征,即大孔喉介质、小孔喉介质和裂缝,其中大孔喉介质和小孔喉介质所占储集空间比重相当,但大孔喉介质对基质渗透率贡献率达95%以上;储层孔喉配置关系以大孔隙—粗喉道、小孔隙—细喉道配置为主,其次为小孔隙—粗喉道。研究区裂缝孔隙度仅占储集空间的1.8%~2.8%,但裂缝性砂岩岩心渗透率比基质渗透率高1~2个数量级。基于此建立了研究区砂岩储层"三重介质"概念模型,该模型可以很好解释储层渗流特征。

The reservoir of gasfield A, which located in Kuqa Depression of Tarim Basin, has features of large burial depth, and belongs to fractured tight gas reservoir. As the pore-throat is small and the pore structure is complex, it＇s difficult to do the pore throat structure characterization by conventional methods. In this paper, lots of advanced technologies, such as LSCM, FESEM, Micro-CT, Nitrogen adsorption and NMR,are used to do the pore throat structure characterization.It＇s found for the first time that,the reservoir of gasfield A has microscopic characteristic of tri-media, which contain large pore-throat medium, small pore-throat medium and fractures. The volume of large pore-throat medium approximately equals to the volume of small pore-throat medium, but large pore-throat medium＇s contribution to the matrix permeabil- ity accounted for 95%.The pore and throat collocations are mainly big pore-coarse throat, small pore-fine throat, and small pore-coarse throat are secondary.Absolute fracture porosity is only about 0.01 %-0.5 %, 1.8%-2.8% of total reservoir porosity,but fracture is main seepage channel of reservoir,the permeability of fractured samples is about 10 times or 100 times of samples without fracture.Based on the research of reservoir characteristics above,the conceptual model of tri-media reservoir is established, which can interpret the reservoir seepage characteristics well. The research idea in this paper will be helpful to other similar reservoir.