山西省海陆过渡相页岩气地质评价及有利区优选

GEOLOGICAL EVALUATION OF MARINE-CONTINENTAL TRANSITIONAL-FACIES SHALE GAS AND OPTIMAL SELECTION OF FAVORABLE AREAS, SHANXI PROVINCE

我国含气页岩分布广泛、类型较多,其中海陆过渡相页岩由于具有沉积环境不稳定、区域分布不稳定、垂向岩性变化大、有机质类型差异较大、有机质含量变化大等特点,评价工作相对较难。为此,以山西省石炭系—二叠系地层为研究对象,通过分析整理煤田钻孔资料,钻孔泥页岩样品、岩石学、有机地球化学等方面的实验测试分析数据,系统研究了山西省海陆过渡相页岩气富集特征。结果表明:1山西省富有机质泥页岩厚度大,分布面积广,埋藏深度适中;2源岩、储层条件好,有利区面积广,页岩气资源量大;3与煤层气、致密砂岩气叠置成藏。针对其地质特征,同时参考海相页岩的评价体系,将富有机质泥页岩厚度超过30 m、埋深超过1 000 m、TOC≥2.0%、R_o≥1.0%、气含量超过1 m^3/t等条件作为山西省页岩气有利区的选区标准,优选山西省页岩气有利区,为下一步山西省页岩气勘探开发提供了指导性方向。

In China, gas shales have wide distribution and various kinds. However, marinecontinental transitional-facies shale gas is characterized by unstable sedimentary environment and unstable regional distribution, large variation of vertical lithology, big difference among organic-matter types, and great change of organic-matter content, which may bring about more difficulty in its evaluation. In this study, some previous drilling data and samples from the Carboniferous-Permian coal-bearing strata in shanxi province were analyzed and tested in terms of petrology and organic geochemistry; and the shale-gas accumulation was systematically explored. Results show that in Shanxi province,(1) the shales are well developed with rich organic matter, large thickness,wide distribution, and moderate burial depth;(2)better assemblage of both source rock and reservoir leads to forming large amount of shale-gas resources or extensively favorable area; and(3)it is always superimposed with CBM, tight sandstone gas. In addition, with an evaluation system of marine shale for reference, some standards to select a favorable shale-gas area are summed up for Shanxi province, including thickness more than 30 m, burial depth more than 1 000 m, TOC more than 2.0%, Romore than 1.0%, and gas content more than 1m^3/t. Based on these standards, favorable shale-gas areas have been selected, which is conducive to next exploration and development.