焦作马厂勘查区煤层气富集规律及主控因素研究
Research on law of coalbed methane enrichment and main controlling factors in Jiaozuo Machang exploration area
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摘要: 为了查明马厂勘查区煤层气富集规律及主控因素,采用了现场调研、取样和实验室测试的方法,结合煤炭资源勘查阶段的资料,深入总结了该区二1煤层含气性分布特征,系统分析了影响该区煤层含气量的内在和外在因素。结果表明:马厂勘查区实测煤层含气量13.77~27.30 cm3/g,平均20.26 cm3/g,整体呈现出由西到东、由南到北减小的趋势,西南部最高。这种分布首先受4种内在因素控制:①二1煤镜质组含量较高,具有较强的生气能力,有利于煤层气的生成;②二1煤灰分和水分含量较低,煤层吸附能力较强,有利于煤层气的赋存;③二1煤层主要由微孔组成,能够为煤层气吸附提供较大的比表面积,有利于煤层气的赋存;④软煤在构造应力的作用下,煤的分子和晶体结构发生变化,孔隙度和比表面积有所增加,使得其亲甲烷能力有所增强,煤层含气量增高。然后受2种外在因素控制:①随着上覆基岩厚度的增加,封存能力逐渐增强,煤层含气量逐渐增大;②因断层的作用使得北部断块中二1煤层与奥陶系石灰岩直接对接,形成相对导水边界,地下水的径流不可避免地带走一定量的煤层气,引起煤层含气量降低。中部断块中因凤凰岭强径流带的作用,煤层气以水流为载体进行运移,导致煤层含气量降低,但相对高于北部断块;南部断块中二1煤层与二叠系弱透水岩层对接,对煤层气的保存有利,煤层含气量较高,形成马厂勘查区煤层气最有利富集区。Abstract: The paper is devoted to explore the rules and main control factors of coalbed methane enrichment in Machang exploration area.Field research,sampling,laboratory testing,and analysis of coal exploration data were used in this study.The distribution characteristics of coal seam gas content in Machang area were summarized and the intrinsic and extrinsic factors affecting coal seam gas content were analyzed systematically.The results show that the measured coalbed methane content in the Machang exploration area is 13.77~27.30 cm3/g,with an average of 20.26 cm3/g.The gas content is decreasing from west to east and south to north,with the highest in the southwest.The gas content distribution is controlled by four intrinsic factors.First,Ⅱ1 vitrinite group has a high content and has strong gas generating capacity,which is conducive to the formation of coalbed methane.Second,the coal ash content and moisture content of Ⅱ1 are low,and the adsorption capacity of is strong,which is conducive to the occurrence of coalbed methane.Third,Ⅱ1 coal seam is mainly composed of mi-cropores,which can provide a large specific surface area for coalbed methane adsorption and is conducive to the occurrence of coalbed methane.Fourth,under the action of tectonic stress,the soft coal has a change in the molecular and crystal structure of the coal,and the porosity and specific surface area have increased,which has enhanced the affinity of the methane and increased the gas content of the coal seam.Meanwhile,the gas content distribution is controlled by two extrinsic factors.First,with the increase of overlying bedrock thickness,the storage capacity is gradually enhanced,and the gas content of coal seam is gradually increased.Second,due to the effect of faults,theⅡ1 coal seam in the northern fault block is directly connected with Ordovician limestone,forming a relatively water-conducting boundary.The runoff of the groundwater will inevitably take a certain amount of coalbed methane,causing the gas content of the coal seam to decrease.Due to the action of the Fenghuangling strong runoff zone in the central fault block,the coalbed methane migrates with the water flow as the carrier,resulting in a decrease in the gas content of the coal seam,but relatively higher than the northern fault block.Ⅱ1 coal seam in the southern fault block is connected with the Permian weakly permeable rock stratum,which is beneficial to the preservation of coalbed methane,and the gas content of the coal seam is relatively high,forming the most favorable enrichment area of coalbed methane in Machang exploration area.