Abstract: In recent years, oil and gas exploration in Songliao Basin has gradually shifted from shallow to medium-deep strata. The breakthroughs in the fields of deep volcanic rocks and tight gas are critical challenges restricting the increase of hydrocarbon reserves and production. This paper involves a case study of Changling fault sag in southern Songliao Basin, aiming to explore the main controlling factors for oil and gas enrichment in different areas of the faulted lake basin in Songliao Basin. Based on exploitation methods supported by the Whole Petroleum System theory, the paper comprehensive analyzes the hydrocarbon accumulation conditions including fault basin-forming background, source rocks, reservoirs, caprocks, and hydrocarbon transport systems. The results show that Changling fault sag possesses basic petroleum geological conditions involving favorable source-reservoir-cap assembles. It developed an atypical extensional fault basin under the influence of volcanic landform, where the hydrocarbon source conditions are controlled by the quality and thermal evolution degree of primary source rocks in Shahezi Formation of the deep sag. The distribution of favorable sandbodies is controlled by the dominant sedimentary microfacies of clastic rocks, while the development of high quality volcanic reservoirs is jointly controlled by the factors such as volcanism, acidic fluids, weathering, and tectonic processes. The hydrocarbon migration pathways are determined by the connectivity patterns of four types of transport layers in volcanic rocks. The combination of stable mudstone caps and late-stage faults both controls the preservation conditions, playing a decisive role in the formation of major hydrocarbon-rich reservoir intervals. The results suggest that Changling fault sag develops three favorable hydrocarbon accumulation assemblages, i.e., sub-source volcanic rock reservoirs, intra-source tight sandstone reservoirs, and supra-source conventional sandstone reservoirs, which provide a material basis for forming large-to-medium gas fields. Specifically, the sub-source volcanic rock reservoirs exhibit a natural gas accumulation mode characterized by near-source overpressure charging, accumulation along paleo-structural ridges, fault-fracture composite transport system, and high-quality reservoir enrichment. These findings provide a reference for deep gas exploration in Songliao Basin.

Key words: volcanic landform, atypical extension, sub-source volcanic rock, intra-source tight sandstone, supra-source conventional sandstone

摘要： 近年来,松辽盆地的油气勘探逐渐由浅层迈入中—深层,如何实现深层火山岩和致密气等领域的突破是制约油气增储上产的关键。为探索松辽盆地断陷湖盆不同领域的油气富集主控因素,基于全油气系统勘探理论的勘探方法,以松辽盆地南部长岭断陷为例,综合分析了断陷的成盆背景、烃源岩、储层、盖层及输导体系等成藏条件。研究结果认为:长岭断陷具备良好的生、储、盖等基本石油地质条件,发育火山地貌背景控制下的非典型拉张断陷湖盆,深洼区沙河子组主力烃源岩的质量及热演化程度控制了油气源条件;碎屑岩优势沉积微相控制了有利砂体分布,而火山岩优质储层受火山作用、酸性流体、风化作用和构造作用等因素共同控制;火山岩内部4类输导层的连通形式控制了油气的运移方向;稳定的泥岩盖层与晚期断裂的组合控制了保存条件,决定了油气的主要富集层系。研究结果表明,长岭断陷发育源下火山岩油气藏、源内致密砂岩油气藏、源上常规砂岩油气藏3套有利成藏组合,具有形成大—中型气田的资源条件。其中,源下火山岩领域具有"近源超压充注、古构造脊汇聚、断缝复合输导、优质储层富集"的天然气成藏模式。研究成果可为松辽盆地深层的天然气勘探提供参考。

关键词: 火山地貌, 非典型拉张作用, 源下火山岩, 源内致密砂岩, 源上常规砂岩