松辽盆地北部中央古隆起带古潜山天然气成藏条件

松辽盆地中央古隆起带是该盆地深层油气勘探的重要领域,但天然气成藏条件复杂,储层分布、成藏规律等方面认识不足制约了其油气勘探进程。为了给中央古隆起带的油气高效勘探提供技术支持,综合运用钻井、三维地震及实验测试等资料,针对其气源条件、储层条件、成藏模式等开展了系统研究,归纳总结了油气勘探实践所取得的认识,明确了该区天然气成藏的模式。研究结果表明:(1)该古隆起带紧邻徐家围子断陷生烃中心,下白垩统沙河子组烃源岩生烃强度大,供烃窗口宽,气源充足;(2)该古隆起带受早期强烈挤压和后期持续拉张作用,发育大型构造,具备良好的构造背景,为天然气运聚提供了良好的圈闭条件;(3)该古隆起带遭受了长期的暴露剥蚀,形成了大面积分布的风化壳,具有较好的储集性能;(4)该古隆起带上部覆盖下白垩统登娄库组二段泥岩,形成了区域性盖层。结论认为,该古隆起带为构造控制下的大面积风化壳、内幕成藏模式,采用水平井+大规模体积压裂工艺有望实现该区大面积致密储层天然气产能的突破。

Hydrocarbon accumulation conditions ofthe buried hills in the central paleo-uplift belt of the northern Songliao Basin

The central paleo-uplift belt is an important deep-seated oil and gas exploration area of the Songliao Basin, but its oil and gas exploration process is restricted due to its complex gas accumulation conditions and for lack of the understanding of its reservoir distribution and hydrocarbon accumulation laws. In order to provide technical support for the efficient oil and gas exploration in this central paleo-uplift belt, this paper carried out systematical studies in terms of gas source conditions, reservoir conditions and hydrocarbon accumulation models by using the drilling, 3D seismic and test data comprehensively. Then, the understandings obtained in the oil and gas exploration practice were summarized and the hydrocarbon accumulation models of the natural gas in this area were confirmed. And the following research results were obtained. First, this paleo-uplift belt is adjacent to the hydrocarbon generation center of Xujiaweizi fault depression and the source rocks of Lower Cretaceous Shahezi Formation have high hydrocarbon generation intensity, wide hydrocarbon supply window, and sufficient gas source. Second, under the effect of early intense extrusion and late tensile extension, a large-scale structure is developed in this paleo-uplift belt, and it has a good structural background and provides good trap conditions for natural gas migration and accumulation. Third, this central paleo-uplift belt suffered long-term exposure and erosion, and a weathering crust of large-area distribution is formed with good reservoir properties. Fourth, the upper part of this central paleo-uplift belt is overlain by the mudstone of the second Member of Denglouku Formation of Lower Cretaceous, which acts as the regional caprock. In conclusion, this central paleo-uplift belt is in the internal hydrocarbon accumulation model of large-area weathering crust under the structural control. By adopting the technology of "horizontal well + large-scale stimulated reservoir volume (SRV)", it is expected to realize a breakthrough in gas productivity of large-area tight gas reservoir in this area.