北部湾盆地涠西南凹陷涠洲组二段油气成藏特征分析

摘要

南海北部湾盆地涠西南凹陷是一个富生烃凹陷,但目前涠洲组二段发现的油气资源规模有限,其成藏特征和规律不清,制约了下一步的勘探方向.通过分析化验、钻井资料和地震资料,对涠洲组二段油气成藏主控因素和成藏规律进行研究,分析表明涠洲组原油主要来自于流沙港组二段中上部厚层优质油页岩,涠洲组二段上层序湖相泥岩是区域上良好盖层.油气主要分布在2号断裂带的沟源断裂附近,沟源断裂是其成藏关键因素;反向断层遮挡的屋脊构造,同时断层断面处断层泥比率(SGR)大于0.64、泥岩涂抹系数(SSF)小于1.70的断块圈闭成藏概率高,是下一步比较有利的勘探目标和方向.%The Weixinan Sag in the Beibu Gulf Basin of the South China Sea is a hydrocarbon-rich sag. However, currently limited oil and gas were found in the 2nd member of Weizhou Formation,and the hydrocarbon accumulation characteristics and laws were unclear, which restricted next exploration direction. The main controlling factors and accumulation rules of oil and gas in the 2nd member of Weizhou Formation were studied based on laboratory tests and drilling and seismic data. The crude oil of Weizhou Formation was mainly originated from the thick oil shale in the central and upper parts of the 2nd member of Liushagang Formation.The lacustrine mudstones in the upper part of the 2nd member of Weizhou Formation provided regional cap rocks.Oil and gas were mainly distributed close to the source rock connected faults of the no.2 fault zone,which were the keys for hydrocarbon accumulation.Fault block traps with roof ridge structures generated by reverse faults and SGR>0.64 and SSF<1.70 at fault sections were favorable for hydrocarbon accumulation,providing an exploration target and direction for the next step.