Calculation and Optimization of Drill String Friction in Coalbed Methane Horizontal Wells
The development methods of coalbed methane(CBM)are mainly multi-lateral horizontal wells and cluster horizontal wells.The problems of friction in the drilling process have always been the research focus in the industry,and so far,the problems have not been effectively solved.Therefore,this paper takes deep coalbed meth-ane horizontal wells in the Daji-Jixian area as example,and studies and summarizes the friction problem of hori-zontal wells by establishing the dynamic model for the whole drilling string system and applying the numerical simulation method.The research results show that:the design weight on bit(WOB)has a great influence on the friction of the build-up section of CBM horizontal wells,the friction drag in the low inclination section is inversely proportional to WOB,while that in the high inclination section is proportional to WOB.The friction is not sensi-tive to the variation of WOB in the tangent section.Under the influence of drill string buckling,the horizontal drill string friction increases by 10.2％.The total friction of CBM horizontal wells is directly proportional to WOB as a whole because of the long high inclination section and horizontal section.This paper reveals the sensitivity of the friction to WOB in each section of deep CBM horizontal wells,and optimizes the well trajectory under different WOB conditions through modeling and numerical simulation,which can provide guidance for field operation,re-duce downhole friction and improve rate of penetration.
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