Accumulation conditions and exploration orientation of coal measure gas in the Upper Paleozoic in Huanghua Depression
In Huanghua Depression,coal seams in Shanxi-Taiyuan formations have wide distribution area,great thickness,and large burial depth,showing good conditions for coal measure gas exploration.However,some geological parameters should urgently be clarified such as the main coal seam distribution,sealing capacity of cap rocks,gas bearing property,and resource amount.Based on drilling,wireline logging,mud logging and geochemical data from wells encountering coal seams in the depression,the preliminary assessment has been conducted on coal seam distribution,coal measure gas accumulation conditions,gas content,and resource amount in Taiyuan Formation.The study results indicate that two main coal accumulation areas of Shanxi-Taiyuan coal seams were developed in Kongdian-Guanjiabao and Botou-Yanshan areas in the southern and northern parts,with the main burial depth range of 1500-4500 m,multi set thin coal seams,single coal seam thickness of 0.5-6.2 m and mostly of 1-3 m,and cumulative thicknesses reaching up to 32.7 m;Due to deeply burying and volcanic heating,the vitrinite reflectance(Ro)of Taiyuan Formation coal measure rocks are generally greater than 0.85％,indicating a moderate thermal evolution stage;In the study area,there are three types of lithologic combinations between coal seam and cap rock,i.e.,coal-mudstone,coal-limestone,and coal-sandstone,among which the extensively developed coal-mudstone combination provides favorable sealing conditions;By using methods such as multivariate regression analysis of well logging parameters,gas content of Ⅳ、Ⅴ,and Ⅵ coal groups in Taiyuan Formation has been predicted,and the preliminarily estimated coal measure gas resources of 1.1×1012m3.In addition,Wangguantun slope in Wumaying area has optimally been selected as a favorable orientation to study the coal measure gas accumulation pattern of"coexistence of conventional and unconventional reservoirs,and cooccurrence of adsorbed and free gas".
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