晋东南沁水盆地石炭二叠纪含煤岩系古地理及聚煤作用研究

Palaeogeography and coal accumulation for coal measures of the Carboniferous -Permian in Qinshui Basin, southeastern Shanxi Province

晋东南沁水盆地是目前我国进行煤层气勘探开发的主要地区之一,煤层气储层主要分布在石炭系和二叠系,其厚度明显受沉积古地理控制。本文通过对露头及钻井剖面的岩石学和沉积相特征研究,对该区主要含煤岩系-山西组和太原组进行了岩相古地理和煤层气储层聚集控制因素分析。太原组以石灰岩、铝土质泥岩、粉砂岩、粉砂质泥岩及砂岩为主,厚度44．90-193．48 m,含多层可采煤层,厚度0-16．89 m,平均 7．19 m。在太原组沉积期,研究区北部发育下三角洲平原相,煤层相对较厚,中部和南部为潟湖相,煤层相对较薄,东南部主要为滨外碳酸盐陆棚相,在晋城一带为障壁砂坝相分布区,煤层亦较厚;山西组以砂岩、粉砂岩、泥岩为主,石灰岩仅在局部地区见到,该组厚18．60-213．25 m,含可采煤层1-2层,厚度0-10．0 m, 平均4．20 m。在山西组沉积期,北部以下三角洲平原分流河道相为主,中部和南部以分流间湾相为主,东南部则以河口砂坝相为主,厚煤带都位于中部和南部的三角洲分流间湾地区。总之,太原组富煤地带多与砂岩富集带相吻合,位于北部下三角洲平原和南部障壁砂坝地区,而山西组厚煤带大都位于南部三角洲分流间湾地区。

The Qinshui Basin in southeastern Shanxi Province is an important base for coalbed methane exploration and production in China. The methane reservoirs in this area are mainly the Carboniferous and Permian coals and their thicknesses are strongly controlled by the depositional environments and palaeogeography. In this paper, petrological and sedimentary facies researches are conducted on the Taiyuan and Shanxi formations in the Qinshui Basin based on the outcrop and borehole data and the basin-wide lithofacies palaeogeographic maps for these two formations have been reconstructed. The Taiyuan Formation is composed of limestones, aluminous mudstones, siltstones, silty mudstones, sandstones, and mineable coal seams, with a total thickness varying from 44.9 m to 193.48 m. The coal seams have a thickness ranging between 0 and 16.89 m, averaging 7.19 m. During the deposition of the Taiyuan Formation, the northern part of the study area was dominated by a lower deltaic plain environment, the central and southern parts were dominated by the lagoon environment, the southeastern corner was occupied by the barrier sand bar and carbonate platform setting. Coal is relatively thick in the northern part and the southeastern corner. The Shanxi Formation consists of sandstones, siltstones, mudstones and coals, with the limestones being locally developed. The thickness of the Shanxi Formation is from 18.6 m to 213.25 m, with the thicknesses of coal seams being from 0 to 10 m and averaging 4.2 m. During the deposition of the Shanxi Formation, the northern part of the Qinshui Basin was mainly dominated by lower deltaic plain distributary channel environment, the central and southern parts were mainly the inter-distributary bay environment, and the southeastern part was occupied by the delta front mouth bar environment. The thick coals are distributed in the central and southern parts where the inter-distributary bay dominated. It is evident that the distribution of thick coal zones of the Taiyuan Formation coincides with the distribution of sand rich belts, mainly located in the areas of northern lower deltaic plain and southeastern barrier bar environments, while the distribution of the thick coal zones of the Shanxi Formation coincides with the distribution of mudstone-rich belts, located in the areas of the central and southern inter-distributary bay environments.