古近系油气初次运移有效性的主控因素——以珠江口盆地西江A和西江B构造圈闭油气勘探效果对比为例

通过珠江口盆地西江主洼地区古近系油气勘探实例，提出了油气初次运移有效性与初次运移有效区的概念。初次运移是否有效取决于烃源岩排出之油气进入邻近砂体后能否顺利二次分配。初次运移有效性的主控因素取决于2点：一是发育与烃源岩接触面积较大的规模性砂体；二是砂体中粗孔喉相对发育。前者可为初次运移有效性、提高运聚充注效率奠定基础；后者则决定了油气优先充注的运聚方向，其是决定初次运移最终有效的直接条件。据此，对比分析了西江A构造圈闭与西江B构造圈闭的钻探结果，并对西江A构造钻探失利进行了深入解剖，进而深化了该区古近系油气成藏规律的认识，且为进一步勘探寻找类似油气藏提供了参考和借鉴。

THE MAIN CONTROL FACTORS ON EFFECTIVE PALEOGENE PRIMARY OIL AND GAS MIGRATION:A COMPARATIVE STUDY OF EXPLORATION RESULTS FROM XIJIANG A AND XIJIANG B STRUCTURAL TRAPS,ZHUJIANGKOU BASIN

Based upon the exploration data from the major Xijiang depression, we put forward in this paper the two concepts of effective primary migration and effective primary migration area.The effective primary migration of oil and gas depends upon the capability of remigration or secondary migration of oil and gas after charging into the sand body close to the source rocks.The effectiveness is depending on two main factors:one is the occurrence of large-scale sand body near the hydrocarbon source rock and the other is the availability of coarse pore throats within the sand body.The former will decide if there is enough oil and gas for effective primary migration, the latter determines the priority of filling direction of oil and gas.Based on this working hypothesis, we made a comparison between the Xijiang A and Xijiang B structural traps with the exploration results available and discussed the failure of exploration in the Xijiang A region.The conclusion may help further understanding the Paleogene hydrocarbon accumulation in this region and provide a case for the endeavor to look for similar reservoirs.