大宁-吉县区块深层煤层气井酸化压裂产气效果影响因素分析

Influencing factors on gas production effect of acid fractured CBM Wells in deep coal seam of Daning-Jixian Block

大宁-吉县区块深层8号煤层面积大、厚度大、分布广、煤层气资源富集,体积酸压后试采获得突破,但试采井产能差异大,产能主控因素不明确,严重制约煤层气开发进程。针对大宁-吉县区块2 000 m以深的上石炭统本溪组8号煤层试采井,从地质条件、酸压施工和排采制度中选取28个典型评价指标,运用灰色关联方法对煤层气井酸压后产能进行敏感性分析并提出相应技术对策。结果表明:酸压施工因素对产能的影响高于地质因素和排采因素;砂量、酸量、见气前产水指数、泥质含量和阵列感应电阻率是影响该区块气井产能的主控因素,可将阵列感应电阻率和泥质含量作为筛选有利区的重要指标;提出采用低密度、低粒径支撑剂提高支撑剂运移距离与支撑裂缝长度;控制排采速度不超过200 m^(3)/d,以保证深层煤层气平稳连续产出。该研究可为深层煤层气有利区筛选、施工参数优化以及排采制度调整提供参考。

The No.8 deep coal seam in Daning-Jixian Block is large, thick, widely distributed, and rich in coalbed methane(CBM) resources. After volume acid fracturing, a breakthrough has been achieved in the producing test. However,the productivity of the testing wells varies greatly, and the major controlling factors of productivity are not clear,severely restricting the CBM development. In this paper, the testing wells in the No.8 coal seam with a buried depth of more than 2 000 m of the Upper Carboniferous Benxi Formation in Daning-Jixian Block were taken as the research object, and 28 typical evaluation indicators were selected from geological conditions, acid fracturing construction and drainage technology. The grey correlation method was applied to analyze the production sensitivity of CBM wells after acid fracturing, and corresponding technical measures were presented. The results show that factors of acid fracturing construction have a greater impact on productivity than geological factors and drainage factors. Sand volume, acid dosage, water production index before CBM breakthrough, mud content and array induction resistivity(M2RX) are the main controlling factors of productivity. The M2RX and mud content can be used as important indicators to screen out favorable areas. Low density and small particle size proppants are proposed to increase the migration distance of proppants and the propped fracture length. Gas production rate is controlled below 200 m^(3)/d to ensure the smooth and continuous production of deep CBM. This research could provide reference for the selection of favorable areas, optimization of construction parameters and adjustment of drainage and production systems.