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临兴地区下二叠统太原组页岩气地质特征及勘探潜力

Shale gas geological characteristics and exploration potential of lower permian Taiyuan Formation in Linxing Area

  • 摘要: 为揭示鄂尔多斯盆地东缘临兴地区太原组页岩气地质特征及勘探潜力,以富含有机质泥页岩为研究对象,基于野外钻孔和测井基础地质资料,查明了泥页岩累计厚度和单层最大厚度分布规律;针对泥页岩开展了有机地化、物性特征、X射线衍射和等温吸附等试验测试分析,对页岩气聚集成藏条件及勘探潜力进行了研究。结果表明:临兴地区太原组泥页岩分布稳定,累计厚度为10~50 m,平均为30 m,单层最大厚度为5~25 m。有机质丰度较高,TOC含量介于0.26%~12%,平均为3.81%,有机质类型以II、III型干酪根为主,最高热解峰温介于443~576 ℃,在紫金山岩体附近泥页岩热成熟度明显增大。泥页岩发育纳米级-微米级的孔裂隙,有机质孔多呈圆形、椭圆形和蜂窝状,碎屑矿物溶蚀孔等其它类型孔隙均有发育,矿物颗粒内部、碎屑颗粒边缘和有机质内部的微裂隙较为发育。石英、长石等脆性矿物含量占45%~65%,黏土矿物含量介于28%~62%,多为非膨胀类矿物。泥页岩含气量变化范围大,介于0.08~7.3 m3/t,平均为1.41 m3/t,含气量与TOC呈明显的正相关关系。综合考虑泥页岩厚度、有机质丰度、热演化程度等因素,临兴地区的中北部泥页岩厚度大、TOC含量高,矿物组合有利于储层改造,为页岩气勘探有利区。与四川盆地海相页岩气勘探区相比,临兴地区太原组泥页岩具有埋深浅、含气量偏低的特点,在油气资源勘探开发中宜注意与煤系地层的砂岩气和煤层气的联合勘探开发。

     

    Abstract: In order to reveal the geological characteristics and exploration potential of shale gas in Taiyuan Formation in Linxing area, eastern Ordos Basin, taking organic-rich mud shale as the research object, the distribution rules of mud shale cumulative thickness and single layer maximum thickness were found out based on field drilling and logging geological data. The organic geochemistry, physical properties, X-ray diffraction and isothermal adsorption experiments were carried out for shales, and the accumulation conditions and exploration potential of shale gas were studied. The results show that the distribution of mud shale in Taiyuan Formation in Linxing area is stable, the cumulative thickness is 10-50 m, the average thickness is 30 m, and the maximum thickness of single layer is 5−25 m. The Organic matter abundance is high, TOC content is 0.26%-12%, with an average value of 3.81%. Organic matter type is mainly II and III kerogen, and peak temperature of pyrolysis is between 443 ℃ and 576 ℃. The thermal maturity of shale near zijinshan rock mass increases obviously. The pores and fissures of nanoscale–micron scale are developed in shales. The pores of organic matter are mostly round, oval and honeycomb. Other types of pores such as the dissolution pores of clastic minerals are developed. The microcracks in mineral particles, the edge of clastic particles and the internal organic matter are relatively developed. The content of brittle minerals such as quartz and feldspar are 45%-65%, and the content of clay minerals is 28%-62%, which are mostly non-expansive minerals. The variation range of gas content in shale is large, ranging from 0.08 m3/t to 7.3 m3/t, with an average value of 1.41 m3/t. There is a significant positive correlation between gas content and TOC. Considering the factors such as shale thickness, organic matter abundance and thermal evolution degree, the central and northern shale in Linxing area has large thickness and high TOC content. The mineral assemblage is conducive to reservoir reconstruction and is a favorable area for shale gas exploration. Compared with marine shale gas exploration area in Sichuan Basin, Taiyuan Formation shale in Linxing area has the characteristics of shallow burial depth and low gas content. In the exploration and development of oil and gas resources, it is necessary to pay attention to the joint exploration and development of sandstone gas and coalbed methane in coal measure strata.

     

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