鄂尔多斯盆地姬塬地区延长组长82储层沉积成岩作用

鄂尔多斯盆地姬塬地区延长组长8²沉积期,构造相对稳定,发育浅水三角洲沉积体系,湖岸线在东南部小规模迁移,分流河道及水下分流河道构成了该区沉积骨架。在对大量薄片和岩心分析的基础上,运用扫描电镜、X-衍射、阴极发光等实验手段,对长8²储层的成岩作用进行了研究。研究结果表明,成岩作用对储层的影响具有双重性。早期绿泥石膜的发育对抵抗压实作用具有一定积极作用,早期方解石易与有机酸发生溶解反应,形成次生孔隙,改善储层物性,溶蚀作用极大程度地改造了储层物性,是次生孔隙形成的主要途径;压实作用破坏了成岩早期原生孔隙,晚期铁方解石堵塞孔隙,形成局部强钙质胶结区。沉积成岩作用对油气的分布具有决定性作用,分流河道及水下分流河道砂体厚度高值区决定了储层发育的形态及规模,在此基础上,受后期成岩作用改造的绿泥石胶结剩余粒间孔相和长石溶蚀+剩余粒间孔相是该区油气聚集的重要场所。

Sedimentation and diagenesis of Chang 82 reservoir in the Yanchang Formation in Jiyuan region,Ordos Basin

The structure of Jiyuan region in the Ordos Basin was relatively stable during the deposition of Chang 8².In this period,a shallow water delta depositional system was developed,the lake shore line slightly migrated in the southeast,and distributary channel and underwater distributary channel constituted the deposition framework.This paper studied the diagenesis of Chang 8² reservoir based on large amount of thin sections,core observation,SEM samples,X-ray analysis,and Cathodoluminescence analysis.The study shows that the diagenesis has double effects on the reservoir.On one hand,early development of chlorite film has a positive effect on anti-compaction.The early calcite is easy to be dissolved by organic acid,resulting in secondary pores and improving poroperm characteristics.Dissolution is the major mechanism of secondary pore formation and can greatly improve reservoir poroperm characteristics.On the other hand,compaction destroys the primary porosity formed in early digenetic process,and late ferrocalcite fills pores,resulting in local strong calcareous cementation zone.In general,the sedimentary facies and diagenetic facies control the distribution of oil and gas.The former determines the reservoir shape and dimensions.While the later modifies reservoir pore space.Late diagenesis-modified chlorite-cemented sedimentary facies with residual inter-granular pores and that with feldspar-dissolution plus residual inter-granular pores are the major reservoir spaces for hydrocarbon accumulation.