煤层气直井开发概要——以鄂尔多斯盆地韩城地区煤层气开发为例

Outlines of vertical well development for CBM: A case study of CBM gas development in the Hancheng District of the Ordos Basin

煤层气钻井方式中,直井技术(包括丛式井)最为成熟,费用较低,操作简单,没有太大的使用限制,无论在前期开发评价,还是后期的增产改造和规模开发中,其作用都不可替代,是国内煤层气开发普遍采用的方式。为此,论述了其开发要点:①煤层气的选区、选井及选层主要依靠地震勘探技术结合基础地质技术完成;②单井评价通常以测井评价为主,录井技术和试井技术为辅,而测井记录的数据常需使用经过选择的煤心和试井数据标定,这样才能提高储层评价参数及单井评价的可靠性,进而确定射孔压裂层段;③直井的增产改造方法除水力压裂外,还可考虑裸眼完井和筛管完井技术,裸眼完井需考虑煤层适应性,而筛管完井除了应用于水平井外,也可以用于裸眼完井的直井中;④煤层气排采需紧密结合排采装备,初期以最小的强度稳定缓慢排采,然后根据地层实际供液能力调整工作制度,尽量使地层供液与排液量保持一致,稳定持续缓慢降液,尽可能地扩大压降范围。

Among the CBM gas drilling methods,vertical wells including the cluster wells need the lowest cost with the most mature drilling techniques and the involved operations are quite simple.As the most popular method of CBM gas development in China,their role is irreplaceable whether in the development assessment in the earlier period or in the stimulation treatment and commercial production in the later period.In view of this,the features of vertical well development for CBM are discussed.(1) The selection of well blocks,types,and pay zones is done through the fundamental geological techniques combined with seismic exploration techniques.(2) The per-well performance assessment relies on logging evaluation,assisted by mud logs and well tests,while the logging data is often calibrated by use of the selected coal samples from core and well test information,the purpose of which is to improve the reliability of both reservoir evaluation parameters and per-well performance evaluation,thereby to determine the layers operated by perforation and fracturing treatment.(3) Apart from hydraulic fracturing treatment,open-hole and liner completion will be also considered as the EOR stimulation measures for such vertical wells.However,the adaptability of coal seams should be taken into account in open-hole well completion whereas liner completion can be used for vertical wells besides horizontal wells.(4) The CBM gas recovery by liquid drainage is kept steady and slow at the lowest rate in the preliminary period,then the working system can be adjusted by the actual fluid supply capacity of formations,the level of which should be kept in balance with the liquid drainage by reducing the liquid volume slowly and continuously and expanding the range of pressure drop to the highest degree.