库车坳陷迪那2气田古近系砂岩储层孔隙构造-成岩演化

Tectonic-Diagenetic Evolution of Paleocene Tight Sandstone Reservoir Pores in the DN2 Gas Field of Kuqa Depression

以岩芯观察和薄片鉴定为基础,辅以扫描电镜、黏土矿物X衍射、流体包裹体、油层物性分析等技术手段,结合区域油气地质研究成果,系统研究塔里木盆地库车坳陷迪那2气田古近系砂岩储层孔隙构造-成岩演化与致密化过程。结果表明:研究区砂岩储层经历了同生期碳酸盐、岩盐胶结—早成岩期压实作用、胶结作用和低熟烃类充注—中成岩期有机酸溶蚀、液态烃类充注—构造挤压、构造破裂、天然气充注和晚期碳酸盐胶结等构造-成岩序列和两次致密化过程。储层原始孔隙度平均仅为31.7%,沉积作用是其致密的内因;孔隙度演化至现今约5.8%。压实作用造成了20.8%的孔隙度损失,是储层初次致密的决定性因素;胶结作用减孔约6.59%,加剧了储层致密化程度;溶蚀作用和各种成缝作用增孔约4.28%,使初次致密的储层孔隙度最高可达11%以上。从12~5Ma的康村期储层孔隙度从14.5%减少至8.0%,完成初次致密化过程,且与迪那低幅构造油藏形成大致同步,即"边致密边成藏"。5Ma以来迪那油气藏构造幅度增大,强烈构造挤压减孔2.76%,是储层再次致密的主要因素,该时期侏罗系烃源岩大规模气侵形成现今气藏,亦为"边致密边成藏"。

Tectonic-diagenetic evolution and compaction history of tight sandstone reservoir of Paleogene in the DN2 gas field of Kuqa Depression were studied through core observation,thin-section analysis,scanning electron microscope observation,X-ray diffraction,fluid inclusion and reservoir physical parameters analysis,in combination with regional geological research results,such as burial thermal,organic matter revolution and accumulation history.The results show that the sandstone reservoir in the study area underwent a tectonic-diagenetic series and two densification.The tectonic-diagenetic series includes：contemporaneous cementation of carbonate minerals and halite-compaction,cementation and low-maturity hydrocarbon charging in the early diagentic stage-organic dissolution and liquid hydrocarbon charging in the middle diagenetic stage-tectonic compression and fracturing,natural gas charging,and late carbonatic cementation.The mean primary porosity of sandstone reservoir of the DN2 gas field was only 31.7%,with sedimentation being the internal cause of densification.Evolution of the reservoir caused the porosity of the reservoir to the current 5.8%.Compaction being responsible for 20.8%of loss in porosity is the key factor for initial compaction of the reservoir,and cementation reducing 6.59% porosity intensified the compaction degree of the reservoir.Corrosion and various fracturing increased porosity by 4.28%,which improved the porosity of reservoir up to 11%.The porosity of reservoir during the Kangcun stage（12~5Ma）decreased from 14.5% to 8.0% and completed the first densification process,which is roughly synchronous to densification and the formation of the low anticline structural reservoir.During the past 5Ma years,the low anticline reservoir underwent strong tectonic compression in Pliocene and reduced the porosity of the reservoir by 2.76%.This is the most important cause of the second compaction process of the reservoir.Migration of large amount of gas generated by Jurassic hydrocarbon source rock formed the current gas reservoir,which is so-called densification coupled with reservoir formation.