河套盆地厚层砂砾岩油藏特征及成藏主控因素:以临河坳陷吉华2X油藏为例

河套盆地为中-新生代叠合盆地,早期钻井仅见到油气显示,未取得实质性突破。吉华2X厚层砂砾岩油藏的发现,展现了该区广阔的勘探前景。为进一步深化河套盆地油气成藏特征认识及明确有利勘探方向,对吉华2X油藏开展精细油藏解剖和成藏主控因素分析。结果表明:吉华2X油藏是受狼山分支断裂控制形成的继承性鼻状构造,储油层为古近系临河组及白垩系固阳组的扇三角洲平原砂体,油藏富集程度高、开发效果好;洼槽区固阳组高排烃动力的成熟烃源岩是吉华2X圈闭富集成藏的必要条件,砂地比极高的扇三角洲相储集体配套继承性发育鼻状构造与畅通无阻的运聚通道是吉华2X圈闭富集成藏的关键。研究结果对指导河套盆地下步油气勘探具有重要的指导和借鉴意义。

Controlling Factors of Thick Glutenite Reservoir Accumulation in Hetao Basin: A Case Study of Jihua-2X Reservoir,Linhe Sag

In the Meso-Cenozoic Hetao Basin, the early-stage wells have oil and gas shows but there is no substantial exploration breakthrough. The discovery of thick glutenite reservoir layer of Jihua-2X indicates good exploration prospect in the basin. To understand the hydrocarbon accumulation characteristics and delineate favorable exploration targets in the basin, we took the Jihua-2X reservoir as a research target. The major controlling factors on the accumulation of thick glutenite reservoir layers was clarified by analyzing the Jihua-2X reservoir, which is located in the eastern wing of the Jilantai tectonic belt (west of the Linhe depression). It is an inherited nose structure controlled by the Langshan branch fault. The oil-bearing sandstone is the fan delta sandbody in the Paleogene Linhe Formation and Cretaceous Guyang Formation. The Jihua-2X reservoir is well-developed and has high degree of enrichment. Matured source rocks of the Guyang Formation in the sub-sag area with high hydrocarbon expulsion power is necessary for hydrocarbon accumulation in the Jihua-2X trap. Furthermore, fan delta reservoir with high sand-strata ratio and successive nose structure, and interconnected migration pathway was likely the key for hydrocarbon accumulation in the Jihua-2X trap. Our results can provide a geological foundation for future exploration in the Hetao basin.