Research On Mechanism And Controlling Methods Of Cutting Plug Pipe Sticking In Shale Gas Horizontal Wells

Shale gas is an essential fuel resource of China,while horizontal drilling is the key technology of developing shale gas.Pipe sticking accidents due to cutting plugs have occurred repeatly in shale gas horizotal drilling practices,seriously impeding the progress of drilling engineering and resulting in massive economical loss.At present,the mechanism of cutting plug pipe sticking is ambiguous in the drilling industry.Methods of evaluating and controlling cutting plug pipe sticking risk are nearly all experimental.In this work,systematic research about cutting plug pipe sticking and related risk controlling was conducted to reveal the mechanism,predict and prevent the risk of cutting plug pipe sticking.(1)For tripping out process(pulling out or back reaming),the formation of a cutting plug was studied under the bulldozer effect of the drilling string and the avalanche effect of the cutting bed.The calculation models of cutting plug volume were derived.According to the granular mechincal property of the cutting plug,the sticking force model was established for both permeable and impermeable cutting plugs.Combining the torque and drag model of a drilling string,the mechanism of cutting plug pipe sticking in tripping out process was revealed.(2)For tripping in process(running in or reaming),considering the differences of cutting plug geometry and relative location with the drilling string,the calculation models of cutting plugs formed under the bulldozer effect and the avalanche effect were established.The pipe sticking force model was established for both permeable and impermeable cutting plugs in the tripping in process.Combining the torque and drag model of a drilling string,the mechanism of cutting plug pipe sticking in tripping in and reaming processes was revealed.(3)With the mechanism of cutting plug pipe sticking in tripping in and tripping out,processes,the abnormal signs of logging parameters like the hook load,the top drive torque,the drilling fluid level at the surface and the pump pressure were quantitatively analyzed.Based on the decision tree model,considering the effect of data imbalance,a pipe sticking evaluation method was established targeting at the minimum misclassification cost expectation.(4)Considering the restrict of formation fracturing pressure,with the calculation method of wellbore circulating pressure drops,the allowable maximum flow rate for transporting a cutting plug and the critical pump pressure of removing the cutting plug were derived.Taking the mechanical cutting bed removing tool as the example,according to the settling principle of cutting particles in the Herschel-Bulkley fluid,the optimal installation spacing of the tool was proposed.(5)With the case study of a pipe sticking well in Sichuan province,the feasibility of the cutting plug pipe sticking mechanism and the intelligent risk evaluation method was verified.