涠西南凹陷流沙港组二段优质烃源岩判别及其控油作用

Organic geochemistry identification of high-quality source rocks in the 2nd member of Liushagang Fm and its controls on petroleum occurrence in the Weixi'nan Sag, Beibuwan Basin

高岗 徐新德 刘诗局 甘军 胡晨晖 赵建宇

Gang Gao Xinde Xu Shiju Liu Jun Gan Chenhui Hu Jianyu Zhao

针对北部湾盆地涠西南凹陷流沙港组湖相优质烃源岩发育特征及其控油作用不清的实际，基于烃源岩生、排烃基本原理，利用有机地化方法建立判别优质烃源岩的方法，并确定了其分布和对油气分布的控制作用。流沙港组泥岩是涠西南凹陷的主要烃源岩，从下到上分为流三段、流二段和流一段，流二段为主力烃源岩。依据生、排烃基本原理，利用烃源岩含量与热解、氯仿沥青“A”含量的关系确定的流沙港组湖相优质烃源岩的含量界限值为2%左右。流二段底部黑色页岩含量均大于2%，母质类型好，生烃潜力高，均属于优质烃源岩；部分暗色泥岩属于优质烃源岩。与流二段底部黑色页岩有亲缘关系的原油既可在黑色页岩层段之下近源运移、聚集，也可沿流二段之下的流三段砂体长距离侧向运移而在构造高部位聚集；与暗色泥岩有亲缘关系的原油主要在凹陷内部优质烃源岩层之上的流一段—涠洲组聚集，断裂为近距离垂向运移通道，源控特征显著。

In the Weixi'nan Sag of the Beibuwan Basin, the high-quality lacustrine source rock in the Liushagang Fm has been poorly understood in terms of its characteristics and its controls on hydrocarbon distribution.To this end, we establish an organic geochemical method to identify quality source rocks, and reveal the source rock distribution pattern and its controls on hydrocarbon distribution, based on the fundamental mechanisms of hydrocarbon generation and expulsion for source rocks.Among others, the major source rocks for the Weixi'nan Sag are the Liushagang Fm shale, which can be divided into three intervals, namely the Liu 3, Liu 2 and Liu 1 members downwardly, with the Liu 2 member as the major zone.Based on the principle of hydrocarbon generation and expulsion for source rocks as well as relations between the content, and the pyrolysis and chloroform bitumen "A" content of mature source rocks, we identify the lower limit value of content of the high-quality lacustrine source rocks in the Liushagang Fm is about 2%.The black shale at the bottom of the Liu 2 member (E) with a content higher than 2%, contains oil-prone organic matters with high hydrocarbon-generating potential, and is high-quality source rocks.Part of the dark mudstone is also high-quality source rocks.The crude oil expelled from the black shale at the bottom of Liu 2 member could migrate in short distance and accumulate under the black shale interval, or could migrate laterally in long distance along the sand bodies in the Liu 3 member and accumulate at higher structures.However, the crude oil expelled from the dark mudstone mainly accumulates in the Liu 1 member and Weizhou Fm, which are vertically above the quality source rocks inside the sag, with faults as the vertical pathway for migration and thus the accumulation is directly characterized by source rock distribution.

10.11743/ogg20200210