鄂尔多斯盆地南缘泾河油田长7段烃源岩生、排烃期与油气成藏期对比

Comparison of hydrocarbon generation,expulsion periods,and accumulation periods of source rocks in Member 7 of the Yanchang Formation in the Jinghe Oilfield,southern Ordos Basin

泾河油田位于鄂尔多斯盆地西南部,目前已发现的油气主要位于研究区东北部,前人研究表明原油主要来自延长组长7段油页岩,然而原油到底来自研究区还是其东北部盆地中心的烃源岩还未有定论,从而制约了泾河油田的下一步勘探。利用盆地模拟方法,模拟了研究区和盆地中心长7段烃源岩生、排烃史,确定了泾河油田不同构造部位长7段烃源岩的生、排烃时间,并结合流体包裹体技术厘定了延长组储层原油成藏期次。烃源岩生、排烃时间和储层原油成藏时间以及生、排烃量的计算结果显示,泾河油田长7段烃源岩对本区油气成藏贡献有限,而盆地中心烃源岩生、排烃时间与研究区油气成藏时间具有很好的对应关系,并且本区油气明显具有由东北部向西南部运移的特点。因此与普遍认为的延长组储层以近源短距离垂向运移为主的成藏特征不同,本区已发现油藏可能主要来源于其东北部盆地中心优势生、排烃区,沿走滑断裂带经历了一定距离的侧向运移后聚集成藏。研究结果可为下一步研究区有利运聚方向及成藏区带预测提供重要参考。

[Objective]Commercial oil accumulation in the Jinghe Oilfield of the Southwest Ordos Basin was primarily found in the Northeast area.Previous studies have shown that oil mainly sourced from the oil shale in Member 7 of the Yanchang Formation.However,whether the oil comes from the source rocks spatially located in the Jinghe Oilfield or the basin center has not been determined,which inhibits further exploration of the Jinghe Oilfield.[Methods]In this paper,the hydrocarbon generation and expulsion history of source rocks in Member 7 of the Yanchang Formation in different tectonic parts of the Jinghe Oilfield and in the basin center have been reconstructed through basin simulation.Then,the accumulation periods of oil in the Yanchang Formation reservoir have been identified using fluid inclusion technology.[Results]The time window comparison of the oil accumulation in reservoir and the hydrocarbon generation and expulsion of source rocks show that oil in the Jinghe Oilfield limitedly came from the source rocks beneath the Jinghe Oilfield but more widely came from source rocks in the basin center.The oil in the Jinghe Oilfield generally shows the migration direction from Northeast to Southwest.[Conclusion]Therefore,unlike the traditional model of short-distance vertical migration,a new model can be established as that,the oil in the Jinghe Oilfield mainly laterally migrated from the hydrocarbon kitchen in the basin center along the strike-slip fault belt.The research results can provide an important reference for the prediction of hydrocarbon accumulation zones in the Jinghe Oilfield.