海相碳酸盐岩烃源岩有效性探讨——以川西坳陷中三叠统雷口坡组为例

Effectiveness of marine carbonate source rocks: a case study of Middle Triassic Leikoupo Formation in Western Sichuan Depression

缪九军 吴小奇 宋晓波 郑伦举 陈迎宾 曾华盛

MIAO Jiujun WU Xiaoqi SONG Xiaobo ZHENG Lunju CHEN Yingbin ZENG Huasheng

中国石化 石油勘探开发研究院 无锡石油地质研究所, 江苏 无锡 214126 中国石化 石油勘探开发研究院 四川地区勘探开发研究中心, 成都 610041 中国石化 西南油气分公司 勘探开发研究院, 成都 610041

Wuxi Research Institute of Petroleum Geology, SINOPEC, Wuxi, Jiangsu 214126, China Research Center of Exploration and Development in Sichuan Basin, Petroleum Exploration and Production Research Institute, SINOPEC, Chengdu, Sichuan 610041, China Research Institute of Exploration and Development, Southwest Oil & Gas Branch, SINOPEC, Chengdu, Sichuan 610041, China

中三叠统雷口坡组是近年来四川盆地川西坳陷天然气勘探的热点层系，对其海相碳酸盐岩烃源岩有效性认识的分歧制约了对主力气源和勘探方向的认识。对川西坳陷雷口坡组有机岩石学和有机地球化学等方面进行了综合研究，结果表明雷口坡组碳酸盐岩中干酪根显微组分以腐泥无定形体为主；藻纹层与非纹层部分有机碳含量没有明显差异；雷口坡组三段有机碳含量与黏土矿物含量呈正相关，与碳酸盐矿物含量呈负相关；与常规方法测得的有机碳含量相比，包含有机酸盐在内的总有机碳含量略高，但差值多小于0.2%。雷口坡组碳酸盐岩有机质丰度和生烃潜力整体偏低，有效烃源岩达标率仅为6.13%，相对富有机质层段的分布具有较强的局限性。雷口坡组碳酸盐岩单独难以构成主力烃源岩，对气藏的贡献较为有限。因此，气源输导条件是川西坳陷雷口坡组勘探的重要影响因素，寻找规模性的天然气聚集，应重点关注连通下伏上二叠统烃源岩的通源断裂发育区。

The Middle Triassic Leikoupo Formation (T2l) has been regarded as one of the most important strata for natural gas exploration in the Western Sichuan Depression of the Sichuan Basin. The main gas source has not been determined due to the controversy on the effectiveness of the T2l marine carbonate source rocks and exploration direction is breezing. Integrated studies on organic petrology and organic geochemistry indicate that, the organic macerals of kerogen in the T2l carbonate rocks in the Western Sichuan Depression are mainly consisted of sapropelic amorphous bodies. The total organic carbon (TOC) contents of both algal laminae and non-laminae sections insignificantly varied. The TOC content of the 3rd member of T2l is positively correlated with the content of clay minerals and negatively correlated with the content of carbonate minerals. If carboxylate is included to be calculated for these carbonates, the TOC content show increments no more than 0.2%. The T2l carbonate rocks in the Western Sichuan Depression mainly display low organic abundance and hydrocarbon potential, and only6.13% of the studied samples reach the standard values of effective source rocks, moreover, relative organic-rich layers are limitedly distributed. It is concluded that T2l marine carbonate rocks in the Western Sichuan Depression is unlikely to be main source rocks solely, and they can only contribute to the gas accumulation with a limited amount. Therefore, the migrating conditions is an important controlling factor to be considered for the T2l gas exploration, and the exploration of large-scale gas accumulation should focus on the areas with developed faults connecting the underlying Upper Permian source rocks.

国家自然科学基金项目 41872122;国家自然科学基金项目 42172149;中国科学院A类战略性先导科技专项 XDA14010402

https://doi.org/10.11781/sysydz202202241