云南曲靖盆地构造演化及其对生物气成藏条件的控制

Tectonic Evolution and Its Effect on the Accumulation Elements of Biogas in Qujing Basin,Yunnan

曲靖盆地是在云南省发现的具有工业价值生物气藏的第三系沉积盆地之一。利用二维地震测线结合地质和钻井等资料开展了详细的构造和沉积解释,对曲靖盆地的构造特征、盆地形成和演化进行了较为系统的综合研究,分析了构造演化对生物气成藏条件的控制作用。曲靖盆地的早—中渐新世的断陷阶段为大套湖相暗色泥岩(蔡家冲组)形成时期;渐新世晚期—上新世早期为盆地整体抬升萎缩阶段,避免了蔡家冲组有机质的大量消耗,保存了第四纪以来生物气成藏的有机物质;晚上新世的盆地坳陷阶段为茨营组含煤层系(次要气源岩)、储集层、盖层和岩性圈闭形成的主要时期;上新世末的压扭抬升萎缩阶段是断背斜和断鼻等构造圈闭和构造—岩性复合圈闭发育时期;第四纪盆地稳定沉降阶段为生物气聚集成藏时期。

Qujing Basin is one of several Tertiary sedimentary basins with the discovered biogenic gas resources in Yunnan Province. Through tectonic and sedimentary interpretation using two-dimensional seismic lines combining with geological data and well logs, this article discusses the tectonic characteristics and evolution of this basin, and analyzes the effect of tectonic evolution on the accumulation elements of biogenic gas. During the subsidence of faulting stage within the Early to Mid Oligocene, the major gas source-rocks of the large-scale dark mudstone of Caijiachong Formation were deposited. From the Late Oligocene to the Early Pliocene, as a result of cooling due to the entire uplift and erosion of this basin, the over-consumption of the organic matters in Caijiachong Formation by organic maturation and hydrocarbon generation or biogas generation significantly was avoided. In the period of down-warping stage of the Late Pliocene, the secondary gas source rocks of the coalbearing, sandstone reservoirs, mudstone cap-beds and lithological traps in Ciying Formation were formed. In the end of Pliocene, the basin underwent the stage of compression-shearing uplift and shrink, structural traps of fault nose and fault-anticlines as well as structural-lithological combination traps were formed; The steady subsidence stage of the Quaternary was the period of biogas accumulation.