四川盆地震旦系、寒武系烃源岩特征、资源潜力与勘探方向

Characteristics of source rocks,resource potential and exploration direction of Sinian and Cambrian in Sichuan Basin

2013年四川盆地川中地区震旦系—寒武系发现了安岳特大型气田,储量规模达万亿立方米,在全球古老地层天然气勘探中尚属首次。气源研究认为,震旦系天然气来源于震旦系和寒武系烃源岩,开展震旦系及寒武系古老烃源岩系统研究,对全球古老地层油气地质领域具有重要的科学和实践意义。通过对四川盆地震旦系、寒武系钻井资料和野外剖面观察,利用28 000km地震资料解释结果和新钻井资料,结合2 315样次烃源岩地球化学分析,系统研究了下寒武统优质烃源岩中心,主要沿绵竹—长宁克拉通内裂陷分布,累计厚度可达200~450m,其他地区烃源岩厚度为50~100m,裂陷范围内烃源岩对震旦系—寒武系天然气资源贡献约占全盆地的56%~63%;系统评价了震旦系灯影组灯三段泥质烃源岩及其分布,TOC含量介于0.04%~4.73%之间,平均为0.65%,川中地区厚度在10~30m之间;首次系统研究了能够形成大气田的中国最古老震旦系烃源岩,大川中地区震旦系烃源岩总生气强度为(15~28)×10~8 m^3/km^2,具备形成大气田的气源条件。采用成因法、类比法重新评价全盆地震旦系、寒武系天然气资源量为(4.65~5.58)×10^(12) m^3,天然气资源潜力巨大。川中区块天然气资源量约占全盆地总资源量的66%,是当前勘探的首选。

The Anyue giant gasfield was discovered in the Sinian-Cambrian Central Sichuan region of the Si- chuan Basin in 2013 ,with geological reserves up to 1×10^12m^3 ,which is the first time for the exploration of natural gas paleo-reservoirs in the world.The gas source studies suggest that the Sinian natural gas is origi- nated from the Sinian and Cambrian hydrocarbon source rocks, and the systematical study on the Sinian and Cambrian ancient source rocks has important scientific and practical significance for the global oil and gas geologic domain of the ancient stratum.Based on the drilling data and field profile observation of Sinian and Cambrian in Siehuan Basin, with adoption of the interpretation data of 28 000 kin-seismic and new drilling data, combined with geochemical analysis of source rocks of 2 315 samples,this paper systematical- ly studied the high quality hydrocarbon source rock center, where the source rocks are mainly distributed a- long the Mianzhu-Changning eraton inner rift, with a accumulative thickness reaching 200-450m, and 50- 100m for the thickness of source rocks in other areas.The hydrocarbon source rocks of the Sinian-Cambrian contributed about 56%-63% of natural gas resources of the whole basin.Systematical evaluations have been conducted to the mudstone source rocks and their distribution in the Ill-section of Sinian Dengying Forma- tion,where TOC value is ranging from 0.04% to 4.73% ,with an average of 0.65%.The thickness of the source rocks in central Sichuan region is ranging from 10 to 30 re.The oldest Sinian source rocks that can form large gasfields in China were systematically studied for the first time,and the total gas production in- tensity of the Sinian source rocks in the great central Sichuan region is （15-28）×10^8m^3/km^2 ,where the gas source conditions for the formation of large gasfields are available.By using the genetic method and analogy method,the amount of natural gas resources of the Sinian-Cambrian in the basin are re-evaluated as （4.65- 5.58）× 10^12ma ,and the resources potential of natural gas is huge.The amount of natural gas resources in the central Sichuan block accounts for about 66% of the total basin resources,which is the preferred selec- tion for current exploration.