曲靖盆地生物气成藏条件及主控因素分析

The Analysis of Elements of Biogas Accumulation in Qujing Basin

曲靖盆地新近系茨营组第三段的晚期生物气藏是新近系沉积之后,喜山运动时期各种成藏条件有效的时空配置的结果。在讨论曲靖盆地构造和沉积演化的基础上,综合分析了生物气源、储集层和盖层、圈闭形成以及天然气输导等成藏条件,阐述了生物气晚期聚集成藏条件的时空匹配关系。指出自第四纪以来,生物气源岩持续高效的产气作用是生物气成藏的物质保障,气藏的形成是生物气连续的补充大于逸散动态平衡的产物;背斜构造、砂岩上倾尖灭和砂岩透镜体圈闭是该区主要的圈闭类型;断裂和不整合面是沟通生物气源岩到圈闭的垂向和侧向输导通道,茨营组的连通砂岩体是生物气近距离运移的输导层。蔡家冲组大套湖相暗色泥岩的生物产气效率、断裂的垂向输导能力和圈闭的保存条件及其在时空上的动态配置是生物气晚期成藏的主控因素。

The late-stage accumulation of biogas within the Lower part of the Ciying Formation in Qujing Basin occurred due to effective biogas accumulation of the essential elements in time and space during Himalayan Orogeny. This article discusses the tectonic and depositional evolution of the basin, and analyzes the accumulating elements, the gas source-rocks, reservoirs and cap-beds, and the processes of trap formation and biogas generation-migration. It is suggested that the continuous-effective biogenie gas formation plays an important role for the biogas accumulations since Quaternary, and the Biogenic gas reservoirs must have been formed through a dynamic balance process between the loss of gas and the compensation of biogas uninterruptedly. This study indicates that the major types of traps include fault nose, fault-anticlines, lithologic upelined pinch-out, and sand lens, and that the pathway system of vertical and longitudinal migration from gas source to trap forms by faults, the uniformity between the Oligocene and Neogene strata, and interconnected sandstone bodies. The study proposes that the efficiency of biogas generation from the large-scale dark mudstone of Caijiachong Formation, capability of fault conduits, preserving conditions of traps, and their dynamic matching could be the key factors for the late-stage biogas accumulation in the basin.