柯坪地区下志留统储层性质及控制因素

野外露头浅钻取样分析发现,柯坪地区志留系下统柯坪塔格组的储层性质与塔北及塔中地区差别较大。柯坪地区的砂岩储层以粉细粒岩屑砂岩为主,处于晚成岩A2期,孔隙度主要为2%~6%,平均4.47%,渗透率主要为(0.01~0.1)×10-3μm2,平均0.06×10-3μm2,属于特低孔特低渗储层,而塔北及塔中地区以低孔低渗和中孔中渗为主。研究表明柯坪地区成岩压实、石英次生加大是储层物性的主控因素,储层经历长期深埋藏和短期浅埋藏,使成岩压实减孔率达30.4%;胶结作用所减少的孔隙量一般为1.5%~8%,致密胶结段可达10%~11%,石英次生加大所减少的孔隙量一般2%~4%,致密胶结段可达6%~8%;溶蚀作用及次生裂缝对储层物性改善不大,一般增孔量4%左右;成岩中后期强烈挤压构造运动对储层性质有重要影响。储层演化史表明晚二叠世、晚白垩世—早第三纪是油气聚集成藏期,随后遭后期构造运动破坏,油气逸散或发生氧化作用,柯坪塔格组含沥青砂岩即是这一过程的产物。

Properties and Controlling Factors of Lower Silurian Reservoir in Kalpin Area, Tarim Basin

Based on the result of measured data of Lower Silurian Kalpintag sandstone reservoir samples from crops in Kalpin Area, Tarim Basin, it is shown that very fine-grained lithic sandstone is common in the reservoir with very low porosity (2%~6%, average of 4.4%) and very low permeability (0.01~0.1×10-3μm2, average of 0.06×10-3μm2)of due to being whin late diagenetic stage (Stage A2), which are worse than those with low porosity and low permeability in Tabei Area and those with medium porosity and medium permeability in Tazhong Area. Diagenetic compaction and secondary enlargement of quartz are the dominantly controlling factors. Having undergone long-term deep burial and short-term shallow burial, the porosity of reservoir is heavily reduced as much as 30.4% by diagenetic compaction, 1.5%~8% by cementation (even 2%~4% in tightly cemented beds), and 10%~11% by secondary enlargement of quartz (even 6%~8% in tightly cemented beds) but a small amount of porosity, only about 4%, is increased by contribution of solution and microfracturing. Intensively extrusion tectonism had an important effect to the reservoir during the middle-late diagenetic stage. Evolution history of the reservoir indicates that hydrocarbon was accumulated during Late Permian and Late Cretaceous-Early Tertiary epochs and then the accumulated hydrocarbon was oxidated or even escaped with the result of late destroying tectonism. The Kalpintag asphaltic sandstone is just a fact of this diagenesis.