鄂尔多斯盆地东南部延长组长7致密油成藏机制及主控因素

Mechanism of Hydrocarbon Accumulation Formation and Main Controlling Factors in Chang-7 Tight Oil of Yanchang Formation, Southeastern Ordos Basin

鄂尔多斯盆地东南部延长组长7致密砂岩储层非均质性极强,受岩性、物性、沉积相影响严重,成藏机制复杂,油藏最终采收率低。因此,为制定针对性的深度勘探方案,必须弄清其储层特征、沉积相变规律及成藏主控因素。在调研致密油藏成藏机制及与油气分布关系的基础上,利用钻井、录井、测井、室内测试分析等资料,就成藏要素的内在联系进行分析。研究表明:优质烃源岩展布控制了致密油分布范围;沉积相密切控制着有利储层的分布和物性条件;长7内部良好的源储关系为有利成藏条件。其中“近油源”“优势相”“异常压力”“微裂缝”和“泥岩遮挡”是致密油成藏的主要控制因素。该研究成果可为延长组长7致密油及其他具类似特征的层位勘探起到一定的指导作用。

There are three characteristics in terrestrial tight sandstone reservoir in Chang-7 member of Yanchang formation, southeastern Ordos basin, which include strong heterogeneity, large differences in crude oil properties and low ultimate recovery of oil. Its spatial distribution is seriously affected by lithology, physical properties and sedimentary facies. The mechanism of hydrocarbon accumulation is complex. Therefore, it is necessary to clarify its reservoir characteristics, sedimentary phase transition rules and main controlling factors of reservoir formation to develop a targeted in-depth exploration program. In response to this problem, based on the investigation of the mechanism for hydrocarbon accumulation in tight sandstone reservoirs and the relationship with oil distribution, the data of drilling, mud logging, well logging, well test and production test, laboratory analysis and test, were used to analyze the internal connection between the elements of the hydrocarbon accumulation, which include source, reservoir, cap, trap, migration and conservation in the region. The research shows that the distribution of high-quality hydrocarbon source rocks control the distribution of tight oil;abnormal pressure generated from hydrocarbon generation is the main driving force for oil migration;cracks and micro-fractures are important channels for oil migration;sedimentary facies closely control the distribution of favorable reservoirs and physical conditions, good source-reservoir relationship is favorable for hydrocarbon accumulation conditions in Chang-7 member. Consequently, near oil source, advantageous sedimentary facies, abnormal pressure, micro-fracture and mudstone barrier are the main controlling factors of tight oil accumulation in this area. The results of this study can be used as a guide for tight oil exploration in Chang-7 tight oil and even other Yanchang formation which have similar characteristics in Ordos basin.