赵庄区块松软低渗煤层煤层气低产机理研究

Low Production Mechanism of Coalbed Methane in Soft and Low Permeability Coal Seam of Zhaozhuang Block

为探究沁水盆地南部赵庄区块松软低渗煤层煤层气井低产原因,以3号煤层为研究对象,采用液氮吸附、扫描电镜及X衍射等手段,对目的煤层的孔-裂隙发育特征、黏土矿物组成等进行分析,查明松软低渗储层的物性特征。通过水敏性伤害实验,进一步分析松软低渗储层煤层气低产的机理。研究结果表明:赵庄3号煤层多数为开放型孔,少量发育一端封闭的不透气型孔;孔隙发育较密,孔径以小、中孔为主;微裂隙较宽,延伸距离远,但密度低,孔-裂隙中矿物填充显著;黏土矿物成分为铵伊利石/蒙皂石间层,水敏性强。因此,赵庄3号煤层水力压裂后渗透率差,难以获得理想的增透效果。

In order to explore the cause of coalbed methane wells with low production in soft and low permeability coal seam of Zhaozhuang block in southern Qinshui Basin,taking No.3 coal seam as the research object.The pore-fracture development characteristic and clay mineral composition of the target coal seam and so on were analyzed by means of liquid nitrogen adsorption(BET),scanning electron microscopy(SEM)and X-ray diffraction(XRD),to ascertain the physical characteristic of soft and low permeability reservoir.The mechanism of low production of CBM in soft and low permeability reservoir was further analyzed by water sensitive injury experiment.The results showed that Zhaozhuang No.3 coal seam was mostly open-type pores,a small number of closed and impermeable pores were developed.The No.3 coal had dense pore development and the pore size was mainly small and medium.The micro-fracture was wide and long extension distance,but the density was low.The mineral filling of pore and fracture was obvious.The clay mineral composition was ammonium-bearing illite-smectite interlayer with strong water sensitivity.Therefore,Zhaozhuang No.3 coal seam resulted in poor permeability after hydraulic fracturing,and was difficult to achieve ideal permeability enhancement effect.