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贵州中岭-坪山区块多煤层煤层气可采性评价

Recoverability evaluation on coalbed methane of multiple coal seams in Zhongling-Pingshan Block of Guizhou Province

  • 摘要: 煤层气资源可采性评价是煤层气勘探开发的前提和基础,是各种地质因素有效配置的结果。多煤层发育的黔西地区具有丰富的煤层气资源,其可采性值得关注,为了评价黔西地区煤层气资源的开发潜力,以中岭-坪山为研究区块,在分析构造特征、多煤层发育基本特征、煤层含气量、煤层吸附性的基础上,采用水头高度等效煤储层压力-等温吸附法,评价了等效储层压力、临界解吸压力、含气饱和度及采收率。
    研究表明,区内上二叠统龙潭组薄—中厚煤层发育,煤层数量多达50余层,可采煤层10~12层;煤层含气量较高,为8.25~15.44 m3/t,平均11.71 m3/t;等效储层压力梯度较低,为0.59~0.95 MPa/hm,平均为0.80 MPa/hm;临界解吸压力分布在1.07~1.87 MPa,平均为1.56 MPa;含气饱和度较高为62%~82%,平均为72%;计算得出煤层气理论采收率分布在27.54%~48.66%,平均40.4%,高于全国平均水平,表现出较好的煤层气可采性特点,资源开发潜力大。
    含气量、储层压力等值线图及计算结果显示,含气量、储层压力、临界解吸压力、含气饱和度在平面上分布具有一致性,即高含气量区,等效储层压力高,临界解吸压力高,含气饱和度也高。煤层气富集区是未来开发的首选区域,由于区内煤层发育具有多且薄的特点,多煤层合采是大幅提高气井产量及资源采收率的有效途径,可作为贵州省煤层气开发的首选开发方式。

     

    Abstract: The recoverability evaluation plays an important role in exploration and development of coalbed methane (CBM), which depends on a number of geological parameters. The Qianxi area is abundant in coalbed methane in multiple coal seams, the recoverability of which deserves attention greatly. In this paper, Zhongling-Pingshan in Guizhou is selected as the research object to evaluate the development potential of coalbed methane resources in Qianxi area. Based on analysis of the tectonic characteristics, multi-seams development characteristics, gas content, and adsorptivity, the equivalent reservoir pressure, critical desorption pressure, gas saturation, and recoverability were evaluated using equivalent coal reservoir pressure isothermal adsorption method. The results show that the thin to medium thick seams were developed in the upper Permian Longtan formation which contains as many as over 50 layers. Among all the layers, 10 to 12 layers are recoverable, with gas content 8.25 to 15.44 m3/t and an average of 11.71 m3/t. The equivalent reservoir pressure gradient was 0.59~0.95 MPa/hm with an average of 0.80 MPa/hm. The critical desorption pressure is 1.07~1.87 MPa with an average of 1.56 MPa and the gas saturation is 62%~82%with an average of 72%. The calculated recoverability is favorable which is 27.54%~48.66%, with an average of 40.4%, higher than the national average. The isoline maps of gas contents, pressure and calculated results show that the distributions of gas content, reservoir pressure, critical desorption pressure and gas saturation is consistent. In high gas content area, all the equivalent reservoir pressure, critical desorption pressure, and the gas saturation have high values. Since mining multiple coal seams is an effective way to greatly improve coalbed methane production and recoverability, it will be the first choice for coalbed methane development method for Guizhou.

     

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