柴达木盆地石泉滩地区下侏罗统小煤沟组砂岩储层演化特征

Evolution of sandstone reservoirs in the Lower Jurassic Xiaomeigou Formation,Shiquantan area,Qaidam basin

姚根顺 寿建峰 王少依 陈子炓

Yao Genshun Shou Jianfeng Wang Shaoyi Chen Ziliao

近几年柴达木盆地石泉滩地区下侏罗统小煤沟组厚层砂岩储层中油气的发现使人们对其储层特征和成因机理引起重视。通过该区7口井的储层岩石学研究,认为小煤沟组砂岩储层主要为大气水淋滤溶蚀形成的次生孔隙储层,溶蚀作用的程度决定了储集性质的优劣。储层经历了早侏罗世的弱压实阶段、中侏罗世至白垩纪的大气水淋溶阶段、古近纪的强压实阶段和新近纪的抬升保持阶段。弱压实阶段的成岩压实量约5.5%～6.5%;大气水淋溶阶段形成发育的溶蚀孔隙,其增孔量在4.6%～16.5%,同时伴随蒙脱石矿物的形成;强压实阶段使砂岩的成岩压实量达到19.0%～21.5%,此外有少量方解石析出,该阶段是砂岩原生孔隙的主要消失时期;新近纪储层发生抬升,储层特征基本保持不变。中侏罗世至白垩纪的大气水淋滤溶蚀和古近纪的强烈压实是该区储层成岩演化的两个重要阶段,它决定了储层的成因类型及储集性质。

Recent oil and gas discoveries in the thick sandstone reservoirs in the Lower Jurassic Xiaomeigou Formation in Shiquantan area,Qaidam basin,attract attentions to their reservoir characteristics and genetic mechanisms.Detailed petrological study of the reservoirs of 7 wells in the area reveals that the sandstone reservoirs in the Xiaomeigou Formation are dominated by secondary pores dissolved by the leaching atmospheric water and that the intensity of leaching determine the poroperm characteristics of the reservoirs.The reservoirs went through the following stages: weak compaction during the Early Jurassic(with diagenetic compaction rate of 5.5%-6.5%),atmospheric water leaching during the Middle Jurassic and Cretaceous(with pore increase rate of 4.6%-16.5% and the generation of montmoirillonite),strong compaction during the Paleogene(with diagenetic compaction rate at 19.0%-21.5%,precipitation of small amount of calcite,and disappearance of primary pores),and uplifting and preservation during the Neogene with no significant changes in reservoir characteristics.The atmospheric water leaching during the Middle Jurassic and Cretaceous and the intensive compaction in the Paleogene are the two major stages in the evolution of the reservoirs,and determine the genetic types and characteristics of the reservoirs.

10.11743/ogg20070311