不整合面的结构与油气聚集

以准噶尔盆地白垩系底部不整合面为例,剖析了不整合面的结构特征。若不整合面之上无风化黏土层而为砂岩,不整合面多为流体输导体;发育风化黏土层时不整合面多形成圈闭。不整合面、断层和输导体构成优势运移网络,在断陷盆地表现为“近源”油气运聚,有陡坡带断层运移-不整合面分配和缓坡带不整合面运移-断层调整分配2种成藏模式;坳陷盆地多为“远源”油气运聚,不整合面与断裂构成的输导体系呈阶梯状逐渐升高,导致油气呈阶梯状运移聚集;前陆盆地冲断带主要为“源上”油气成藏,断层沟通上、下不整合面“系统”,油气呈“之”字形运移。不整合面的结构对油气运移和聚集有较强的控制作用,且随时间而逐渐演变。图8表1参62

Structure of unconformity and its control on hydrocarbon accumulation

The structural characteristics of unconformities are analyzed with the Cretaceous base unconformity in Junggar Basin as an example.Unconformity surfaces are the carrier beds in most cases if sandstones develop on them.If weathering clay zones develop,the unconformities usually form traps.The unconformity surface,the fault,and the carrier bed constitute an efficient migration net.In faulted basins,hydrocarbons migrate and accumulate "near-source" in two ways,vertically migrating along the fault and adjusting along the unconformity in a steep slope,and horizontally migrating along the unconformity and vertically adjusting along the fault in a shallow slope.In depression basins,hydrocarbons accumulate "far from the source",pools are distributed step-like as a result of the step-like rising of the migration pathway net composed of faults and unconformity surfaces.Hydrocarbons accumulate "over the source" in fold-and-thrust belts of foreland basins,and the faults connect the above and below unconformities leading to the hydrocarbons being migrated in a zigzag style.The unconformity structures control the hydrocarbon migration and accumulation,and vary with time.