中国海相地层水文地质地球化学与油气保存条件研究

我国海相地层的油气藏被构造运动改造的强度较大,油气保存条件较差.地下水动力场的分布特征在油气藏的形成与演化过程中起着重要的作用.本文通过对比研究四川盆地、塔里木盆地、鄂尔多斯盆地已知海相油田与南方海相地层的水文地质地球化学特征,揭示了水文地质地球化学性质与油气保存条件的密切关系.沉积埋藏阶段是油气生成运移、聚集的主要时期;抬升剥蚀时期水文地质的最大特点是地层压实排水作用停止,沉积埋藏水被大气水驱替、淡化.不整合面附近的封存大气水可能是油气藏被破坏和保存条件差的标志,也可能是有机质尚未进入二次生烃的重要指标.通常水文地质开启程度随着深度的增加而减弱.交替停滞带是不受地表水影响的水文地质带,有利于油气保存;自由交替带受地表水强烈影响,不利于油气保存.并且初步总结了一套比较系统的油气保存条件的水文地质地球化学综合判别指标体系.

Hydrogeological and Hydrogeochemical Characteristics and Hydrocarbon Preservation Conditions for Marine Strata in China

Reconstructed by several tectonic activities,the preservation conditions for oil and gas reservoirs of marine strata in southern China is severely disturbed.The distribution characteristics of hydrodynamic fields are of great importance to the formation and evolution of the oil-gas reservoirs.Through the analysis on hydrogeological/hydrogeochemical characteristics of several exploration areas of China,a close relationship between the hydrogeological/hydrogeochemical characteristics and the hydrocarbon preservation conditions is discussed in this paper.In the uplift and denudation stage,the formation compaction stopped,buried sedimentary water was driven out by meteoric water,therefore,the deposition and burial stage becomes the main period during which the formation,migration and accumulation of hydrocarbon occurred.The preserved meteoric water occurring near unconformable surfaces can be an indicator of the reservoir's being damaged and poor preservation conditions,and also can be an important indicator that the organic material has not yet began secondary hydrocarbon generation.As the buried depth increases,stratal open extent decreases.The exchanging-retarded zone is favorable to the preservation of oil and gas as it is not influenced by surface water,while the free exchanging zone,strongly affected by surface water,offers a poor environment for petroleum preservation.Based upon above,a relatively systematical hydrogeochemical index system is established for distinguishing hydrocarbon preservation conditions in this paper.