沁南潘河煤层气田空气钻井和固井技术

Air drilling and cementing in the Panhe CBM Gas Field,southern Qinshui Basin

沁水盆地南部潘庄区块位于沁水盆地东南缘,该区总体为单斜构造,倾向西北,煤层稳定、埋藏浅且渗透性较好,大量区域地质调查资料和煤田勘探成果表明,区内断层稀少,以发育次级褶皱为主。该区钻井类型主要为钻井液钻井(煤层段清水钻进)和空气钻井。通过对比分析空气钻井、水钻井井身质量与时效平均值可知:①空气钻井在井身质量方面略优于水钻井,但相差不大,均达到设计及规范要求;②空气钻井在时效方面比水钻井效率高,其机械钻速是水钻井机械钻速的3倍多,因此,空气钻井周期短,综合经济效益较好。而微珠低密度固井技术采用优质微珠为减轻材料,水泥浆密度为1.60 g/cm3,抗压强度在15 MPa以上,满足了在确保固井强度的基础上减轻水泥浆正压差对储层污染的要求。采用上述技术使潘河煤层气田示范工程固井合格率达到100%,其中优良率为84%。

With its main monoclinal structures in the northwest direction,the Panzhuang Block is situated at the southeastern marginal area of the Qinshui Basin,where coal seams are steadily buried in shallow beds with a high permeability.A great number of geological survey data and coal field exploration practices have demonstrated that faults can hardly be found but secondary folding is only found to dominate in this block.Air(or air foam),water,or solid free polymer are commonly used as drilling fluids here to achieve underbalanced or near-balanced drilling and to prevent the formation from damage.Through a comparison analysis of wellbore quality and drilling efficiency between air drilling and water drilling,it is concluded that(1) the wellbore quality of both can meet the design and standard requirement but that of air drilling is a little bit better;and(2) the drilling efficiency of air drilling is higher than that of water drilling and the ROP of air drilling is even three times that of water drilling.Therefore,air drilling has a better performance with a short cycle and favorable economic profit.Premium microspheres are used in hollow microspheres low-density cement to reduce the hydrostatic pressure on weak formations and to cement lost circulation zones.After the formula of the cement slurry is optimized with the density of the cement slurry 1.60 g/cm3 and the compressive strength more than 15 MPa,the cement quality is well guaranteed and the formation damage by the positive differential pressure of cement slurry is mitigated.With all those above drilling and cementing technologies,the acceptance rate reaches up to 100% and the excellent rate up to 84% of well cementing in the Panhe CBM Gas Field as one of the CBM demonstration projects.