柴西地区基岩油藏形成的石油地质条件分析

Geological Conditions of Basement Oil Pools in Western Qaidam Basin

柴达木盆地基岩风化壳油藏普遍发育,在昆北等区已形成油田。然而,目前对基岩油藏的成藏背景认识不清,制约了勘探步伐。利用钻井、测井、试油和分析化验等资料对基岩油藏基本特征及成藏条件进行分析,认为该区油藏是受岩性及构造多重因素控制的复合油藏,成藏需紧邻富烃凹陷、具有良好的储盖组合和油源断裂3个基本条件。通过油藏解剖发现,基岩油藏属于源外次生成藏,根据油气侧向运移方式、远近不同建立2种成藏模式:1油源断裂+裂缝输导的近源成藏模式;2油源断裂+不整合面侧向运移+次级断裂辅助运移的远源成藏模式。研究以期对柴达木盆地基岩风化壳油气藏的勘探提供地质理论依据。

Oil reservoirs in top of weathering crust are widespread in Qaidam Basin,which have formed oilfield in areas such as Kunbei.However,the formation background of basement oil pools is unclear,which restricts the pace of exploration.This paper analyzed the basic characteristics and formation conditions of basement oil pools by using well drilling,earthquake,oil production testing and chemical analysis data.The bedrock reservoirs are mostly the composite reservoirs which are controlled by lithology and tectonic in western Qaidam Basin.There are three basic conditions which control the formation of oil pool,i.e.,close to the hydrocarbon-enriched depression,good reservoir-sealing assemblage,and oil-migrating fault which connects the source and reservoir providing mainly longitudinal channel system to form reservoirs.According to oil reservoir analysis,the oil reservoir in bedrock belongs to external source secondary reservoir.Therefore,two reservoir formation models are established according to the oil migration mode and distance,near-source box-type gas accumulation model which includes oil-migratingfault and fracture migration and far-source box-type gas accumulation model which includes oil-migrating fault,lateral migration on the unconformity surface and secondary fault migration.The aim of this research is to provide geological theory basis for exploration of the oil reservoirs of bedrock in western Qaidam Basin.