Buckling Analysis Of Drillstring In Extended Reach Wells And The Maximum Drilling Limit Prediction

Extended reach well is widely used as a kind of economic and effective drilling methodin our country. Drilling4000meters horizontal displacement is start in foreign extended reachdrilling wells, and the success is a result of many facets which include technologybreakthroughs and drilling equipment ability. But in our country no extended reach wellrecord has overcome10000meters horizontal displacement. So, using the extended reachwell drill, how far can we drill using an existing rig and what determines the difficulty ofdrilling an ERD well? The paper attempts to study extended limit of extended reach well,which can provide certain theoretical guidance for predicting future drilling performance,engineering design and reducing drilling risk.The drilling constraints such as well profile, hole cleaning, bottom hole assembly,drilling fluid property, drillability of rock are emerging which constraint the drilling limit. Sothe extended reach well has its objective extended limit and affected by many constraints.While any changes of hole conditions can be shown in the way of friction changes, such ashole cleaning, hole smoothness, lithological changes. So the extend limit of extended reachwell depends on the solve degree of friction, and extended reach well drilling technologyultimately is the process of how to overcome the friction to finish all kinds of professionalwork.So, to predict extended capability exactly, we should analyze the torque and drag ofdrillstring, but buckling of drillstring is an important part of torque/drag calculation, itdetermines calculation accuracy to a great extent, and buckling drillstring may be locked up,which limit the extended capability of wellbore. So accurately predict the actual workingcondition of drillstring, judge whether the drill string buckling, determine mechanicalproperties of buckling drillstring is very important. The paper obtains some researchachievements.First, considering the effect of friction and gravity, the paper studies the bucklingbehavior of drillstring in curved three-dimensional wellbore, and the buckling equation isestablished.Second, the different solutions in three different states, critical buckling load, and theload distribution are obtained. And the computing method of normal pressure, torque anddrag of buckling drillsting is derived, which provides a method for accurately frictionprediction. Third, from rock broken theory, strength and stability condition limit, the drilling limitprediction model of extended reach well is established considering the buckling of drillstring,torque and drag. And the influence law of the influence factors is analyzed.Finally, the study of this paper is applied in two horizontal wells. The results show thatthe calculation method and research can meet the drilling design and constructionrequirements. The studies in paper can provide theoretical reference for extended capabilityin extended reach well, and has important guiding significance for stretching the drilling limitof extended reach well.