四川盆地二叠系烃源岩及其天然气勘探潜力(一)——烃源岩空间分布特征

二叠系—中下三叠统是四川盆地天然气勘探的主要目的层系之一,已发现的许多大中型气田的天然气都来源于二叠系烃源岩,但目前对于该层系烃源岩的主要类型与空间分布规律尚缺乏系统完整的认识。为此,通过对该盆地典型井/剖面二叠系烃源岩发育层位的精细地球化学标定,结合钻井、录井资料,探讨了二叠系烃源岩的类型及其空间展布特征。研究结果表明:(1)该盆地二叠系普遍发育中二叠统碳酸盐岩和上二叠统泥质岩两套烃源岩,局部发育上二叠统大隆组海相泥岩烃源岩;(2)上二叠统龙潭组泥质岩类烃源岩厚度大,有机质丰度高且广泛分布于全盆地,是二叠系中最主要的烃源岩,其中盆地北部的苍溪—云阳地区厚度最大(80~140 m),南部的成都—重庆—泸州地区厚度次之(60~100 m),而中部地区则相对较薄(40~80 m);(3)龙潭组煤层也是该盆地非常重要的烃源岩之一,盆地中部—东南部的南充—綦江—泸州地区煤层厚度最大(5~15 m),川东北地区煤层厚度次之(2~5 m);(4)上二叠统长兴组烃源岩发育程度差,但大隆组烃源岩分布于盆地北部开江—广元一线,厚度介于5~25 m,是盆地北部地区重要的烃源岩;(5)中二叠统碳酸盐岩烃源岩广泛分布于全盆地,其中东北部和东南部厚度介于50~150 m,其他地区的厚度则一般小于50 m,是二叠系中次要的烃源岩。

The Permian source rocks in the Sichuan Basin and its natural gas exploration potential (Part 1): Spatial distribution of source rocks

The Permian–Middle-Lower Triassic strata belong to the major gas payzones in the Sichuan Basin. Natural gas in many large and medium-sized gas fields discovered is derived from the Permian source rocks, but the main types an spatial distribution of which, so far, however, have not been understood systematically and completely. In this paper, fine geochemical calibration was conducted on the horizons of Permian source rocks in typical wells/sections of the Sichuan Basin. Then, the types and spatial distribution of the Permian source rocks were analyzed using well drilling and logging data. The following results were obtained. First, in the Sichuan Basin, two sets of source rocks (i.e., the Middle Permian carbonate rocks and the Upper Permian mudstone rocks) are developed in the Permian, and the Upper Permian Dalong Fm marine mudstone source rocks are locally developed. Second, the mudstone source rocks of Longtan Fm, Upper Permian, are characterized by large thickness, high organic matter abundance and wide distribution in the whole basin, and it is the most important set of source rocks in the Permian. The Longtan Fm mudstone source rocks are 80-140 m thick in the Cangxi–Yunyang area in the northern Sichuan Basin, 60-100 m thick in the Chengdu–Chongqing–Luzhou area in the southern Sichuan Basin, and 40-80 m thick in central Sichuan Basin. Third, the Longtan Fm coal is also an important source rock in the Sichuan Basin. It is 5-15 m thick in the Nanchong–Qijiang–Luzhou area in the central–SE Sichuan Basin and 2-5 m thick in the NE Sichuan Basin. Fourth, the Upper Permian Changxing Fm source rocks are poorly developed, while the Dalong Fm source rocks are distributed with a thickness of 5-25 m in the Kaijiang–Guangyuan area in the northern Sichuan Basin, acting as important source rocks in the northern Sichuan Basin. Fifth, the Middle Permian carbonate source rocks are widely distributed in the whole Sichuan Basin, acting as secondary source rocks in the Permian, and their thickness is 50-150 m in the NE and SE Sichuan Basin and generally less than 50 m in other areas.