松辽盆地北部中央古隆起带天然气成藏条件与勘探方向

中央古隆起带是松辽盆地的重要勘探领域之一,其中,昌德凸起LP1井和LT2井获得的勘探发现展示出中央古隆起带具有良好的勘探前景。通过分析松辽盆地中央古隆起带深层天然气的构造特征、气源条件、储层特征、盖层条件和成藏方式,以期重新认识中央古隆起带的天然气成藏条件,指出有利勘探区带和勘探方向。研究表明,徐家围子断陷沙河子组烃源岩的生烃强度大、气源条件充足、供烃窗口大,天然气成藏模式为"新生古储"型。早期强烈挤压和后期持续拉张构造背景下所发育的大型构造为天然气的运移和聚集提供了良好的圈闭条件;中央古隆起带遭受长期剥蚀所形成的大面积分布的风化壳储层具有较好的储集性能;中央古隆起带上部覆盖的下白垩统登娄库组泥岩为区域性盖层。中央古隆起带发育披覆型、基岩风化壳型和基岩内幕裂缝型3种构造气藏。肇州凸起、昌德凸起、汪家屯凸起为中央古隆起带内的3个有利勘探区带。

Accumulation condition and exploration direction of natural gas in the central paleo-uplift belt of the northern Songliao Basin

The central paleo-uplift belt is one of the important exploration fields in Songliao Basin. The exploration discoveries of Well LP1 and Well LT2 in the Changde uplift show that the central paleo-uplift belt has good exploration prospects. By analyzing the structural characteristics, gas source conditions, reservoir characteristics, caprock conditions and accumulation pattern of deep gas in the central paleo-uplift belt of Songliao Basin, this paper expects to re-understand the accumulation conditions of gas in the central paleo-uplift belt and points out favorable exploration zones and exploration directions. The study shows that the source rocks of Shahezi Formation in the Xujiaweizi fault depression are characterized by large hydrocarbon generation intensity, sufficient gas source, and large hydrocarbon-supplying window. The gas accumulation pattern is shown as a "late gas generation in old reservoir" type. Large-scale structures developed under the tectonic setting of intense compression in the early period and continuous extension in the later period provide good trap conditions for the migration and accumulation of gas. A large area of weathering crust reservoir formed by long-term denudation of the central paleo-uplift belt has good reservoir property. The Lower Cretaceous Denglouku Formation mudstone covering the upper part of the central paleo-uplift belt is a regional caprock. The central paleo-uplift belt has developed three types of structural gas reservoirs:overlying type, bedrock weathering crust type and inner bedrock fracture type. The Zhaozhou uplift, Changde uplift and Wangjiatun uplift are three favorable exploration zones within the central paleo-uplift belt.