Drilling programmes for an underground gas storage with ultra-low pressure,Tuha oilfield:Optimization and application
Wenxiyi Underground Gas Storage(UGS)is the first ultra-low pressure one in Tuha oilfield rebuild from depleted gas reser-voirs with the Jurassic Xishanyao Formation as the target.Xishanyao gas reservoirs are characterized by the pressure coefficient only from 0.2 to 0.22,well-developed vertical fractures,massive shale which is stretched into or above caprocks very easy to be hydrated and peeled off,leading to coexistence of lost circulation and well collapse.The optimal and fast drilling is confronted with great chal-lenges.So,for the ultra-low pressure reservoirs,their geological,drilling and completion conditions were evaluated to make clear design requirements on this UGS.In addition,three drilling programmes were optimized for injection and production wells.First,a third-spud casing program is adopted,running the intermediate casing about 1 m to 2 m above top reservoirs.Second,following the liner hanging and casing tie-back,the production casing is cemented with ductile micro-expansion cement slurry.Third,the polyam-ine drilling-fluid system is combined with gel composite pressure plugging in this spud.After the application of these programmes to Wenxiyi UGS,the lost circulation is reduced by above 50%than before,the cementing qualification exceeding 70%,and the quality cementing in continuous caprocks over 40 m,respectively,meeting the demand of wellbore integrity throughout a life cycle of the storage,which may provide technical reference for similar kinds of UGS construction in China.
Ultra-low pressure gas reservoirUnderground gas storageCasing programDuctile cement slurryPolyamine drilling fluidPlugging
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