陆域天然气水合物厚覆盖层跟管取心技术研究

CORING WITH CASING BEHIND APPLIED IN ONSHORE NATURAL GAS HYDRATE COVERED FORMATIONS

针对陆域天然气水合物厚覆盖层取心钻进中存在的采取率低、孔壁不稳定等技术难题,制定了“隔水式单动双管取心、低温钻井液护心护壁、孔底扩眼跟管钻进”的钻进方法。隔水式单动双管取心是湿式钻进,相比于干钻取心,钻井液能起到良好的护壁作用;采用近钻头冷却,钻井液不会直接冲刷、冲散岩心,松散沉积地层能够进入岩心管;单动双管钻具,内管不回转,有效保护岩心的原位性。低温钻井液能够抑制水合物分解,有利于钻获水合物实物样品,通过室内试验确定了低温钻井液配方,研制了新型的翅片管式钻井液冷却装置,具有启动电流小、换热效率高等突出优点。跟管护壁是单动双管取心、液推式扩眼器扩孔的同时将套管下入孔内,起到护壁作用,根本上解决成孔问题。

The drilling method adopting water insulate one-tube-rotating double tube core drilling tool,low temperature mud to protect the core and wellbore,bottom hole reaming with casing behind is developed to overcome the problems of low core recovery rate and instable wellbore during core drilling through natural gas hydrate covered formations onshore.The water insulate one-tube-rotating double tube core drilling is wet drilling.The circling mud can enhance the wellbore compared with the dry core drilling.Near bit cooling adopted will not directly scour and disperse the core,allowing the loose core entering the core tube.Only the outer tube of the double tube drilling tool rotates,the inner tube without turning can effectively keep the core in place.Low temperature mud can also restrain the resolution of the hydrate which is advantageous to obtain the hydrate sample.Through laboratory tests the low temperature mud formula has been determined,a new type mud cooling finned tube device is developed,which has the advantages of small starting current and high heat exchange efficiency.Together with double tube coring,the hydraulic reamer is enlarging downhole and casing is run in to protect the wellbore,and the hole is successfully constructed.