鄂尔多斯盆地东缘煤层气成藏地质模型

The Geological Model of Coalbed Methane(CBM)Reservoir in the Eastern Ordos Basin

鄂尔多斯盆地东缘煤层气勘探开发有20余年历史,近年来在保德、柳林等区块规模化开发迅速发展,但总体上全区产业化发展并不均衡。除工程因素外,对煤层气地质条件的认识仍然存在分歧,煤层气成藏地质模型可以为勘探选区提供借鉴。通过对鄂尔多斯盆地东缘构造格架、地层层序、水动力条件及气体成因的研究,构建了研究区北段单斜式低煤级煤层气成藏地质模型、中段基底上拱式中煤级煤层气成藏地质模型、南段边缘推覆式高煤级煤层气成藏地质模型,典型代表区域分别在府谷、吴堡—柳林和韩城。其中,单斜式低煤级煤层气成藏地质模型中,煤层气相对富集于地下水滞留区上部;在基底上拱式中煤级煤层气成藏地质模型中,煤层气高渗富集区位于拉张型鼻状隆起带;在边缘推覆式高煤级煤层气成藏地质模型中,气体富集于挤压型构造转折端。研究结果表明:吴堡—柳林基底上拱式中煤级煤层气成藏地质模型各成藏要素匹配良好,气体储集和渗流条件最好,建议作为优先开发区域;府谷单斜式低煤级的含气性相对差,渗透率高;韩城地区尽管气体保存条件好,但边浅部受边缘逆冲推覆构造的影响,煤体结构破坏严重,煤层气可采性差。

With over 20 year history,although the CBM development succeeded in some areas in the eastern Ordos Basin,such as Baode,Liulin,etc.,the overall industrialization isn′t balanced.Besides the engineering factors,the divergence of the CBM geology still exists and the building of CBM reservoir model will help to select favorable areas.The Upper Paleozoic CBM reservoir geological model in the eastern Ordos Basin is established.By analyzing the tectonic dynamic condition,sequence stratigraphy,ground water dynamics condition and gas origin,three geological models of CBM reservoir-formation in the eastern Ordos Basin are constructed,including the monocline and low coal rank model,raised arch of the basements and medium coal rank model,and thrust and high coal rank model.The typical areas are Fugu,Wubao-Liulin and Hancheng.The relatively sweet block lies near the stagnant area of the ground water in the monocline and low coal rank model,the tensile nose-shaped uplifted zone in the raised arch of the basements and medium coal rank model,and the compressed tectonic regime in the thrust and high coal rank model.There is good matching to the key elements of CBM reservoir-formation dynamic system in the Wubao-Liulin,which is proposed as the preferred developmental areas in the eastern Ordos Basin,with the best gas storage capacity and permeability;in the monocline and low coal rank model in the Fugu,although the permeability is high,the gas content is low;in the thrust and high coal rank model in Hancheng,the preservation condition is excellent,however,influenced by the thrust belts,the coal structure is destroyed strongly,and the gas recovery declines.