四川盆地震旦系构造-沉积格局和天然气差异聚集OA

Based on comprehensive geological,geophysical,and geochemical data of Sichuan Basin,we conducted an in-depth investigation on two critical geological issues related to Sinian petroleum exploration:(1)the Sinian tectonic-sedimentary framework,and(2)the transformation from Sinian paleo-gas reservoirs to current reservoirs,based on their distribution patterns.Our results are summarized as follows:(1)The NE-trending Xuanhan-Suining-Emei paleo-uplift formed during Doushantuo Formation sedimentation in Sichuan Basin,influenced by pre-Sinian NE-trending arc basement structures.Dengying Formation inherited this tectonic framework but with reduced uplift dimensions,resulting in the NE-trending Xuanhan-Kaijiang paleo-uplift.During the depositional period of Doushantuo Formation and Dengying Formation in the Sinian System,Sichuan Basin was predominantly in a weakly compressional or tectonically neutral setting,representing a stage of paleo-uplift formation and evolution.Consequently,the likelihood that high-quality source rocks or reservoir rocks within the pre-Sinian and Sinian Doushantuo Formation are present in the present-day Sichuan Basin is minimal.Therefore,the petroleum exploration potential of the Pre-Sinian System in this region is limited.(2)The rapid tectonic uplift of Sichuan Basin during the Late Cretaceous governed basin-scale differential gas entrapment along the top unconformity of Dengying Formation,while the preservation-compromised zones(e.g.,gas chimneys)at the basin's periphery and interior acted as a critical switch for dynamic basin-wide readjustment of the natural gas.Structural lows within the basin developed gas-divergent valleys,and natural gas from both sides of these valleys migrated toward structural highs(gas-convergent ridges or gas chimneys)and orogenic belts at the basin's periphery(also gas chimneys).Associated contiguous traps along migration pathways accumulated gas,forming structural-lithological reservoirs.Tectonically induced gas chimneys,gas-convergent ridges,and gas-divergent valleys collectively govern the present-day gas distribution in Dengying Formation.Consequently,Sinian gas exploration should prioritize structural traps,focusing on the western areas of Huaying Mountains.