Downhole Drag Analysis And Control Techniques For Casing Running Operations In Horizontal Well For Shale Gas

Horizontal well technology is widespread when it comes to the development of shale gas plays.By using horizontal wells,the cost of shale gas development can be largely reduced.However,most shale gas horizontal wells have complicated wellbore profile,for example,long horizontal section.In fact,most of these wells have already evolved into extended-reach wells(ERWs).Drags in these wells are often excessively high,drastically increasing the difficulty in running casing.Hence,to construct a shale gas horizontal well,the ability to run a very long casing is indispensable.In this paper,the influence of adhesive force on running casing is studied first.Reasons contributing to adhesive force are analyzed and discussed.Then,an adhesive force calculation model is established by studying mud cake deformation and effective stress in mud cake.The model is capable to predict adhesive force on casing string in permeable formation when casing sting is stopped during circulation.Moreover,in this paper,the method of multi-segment friction factors inversion is proposed to obtain more accurate friction factors during casing running operation in ERW.In this method,the entire wellbore of ERW is divided into several well sections based on wellbore geometry.Then,the same number of friction factors are introduced to characterize the drag in each of those well sections respectively.To calculate these multi-segment friction factors,an inversion model of high efficiency and high accuracy is built.The model is mainly based on Particle Swarm Optimization(PSO)and,at the same time,assimilates Tabu Search(TS)and Orthogonal Array Test Strategy(OATS).A case study is present in this paper and calculation results prove the high efficiency and high accuracy of the inversion model.Multi-segment friction factors obtained by the inversion model can be used to analyze drags in current well or serve as reference for construction of next well.Finally,the paper also studied the operation of aggressively working casing string in ERW.Aggressively working casing string is a special casing running operation to help casing string overcome high drags in ERW.During the operation,casing string is first picked up to a certain height and then is slacked off rapidly so that casing string seems to “fall” from that height with relatively high speed.In this manner,casing string can acquire extra kinetic energy,thus increasing casing string's capability to overcome high drags.A new drag model is developed to fully study the operation.The model is derived from soft string model but assumes dynamic state motion of casing string as its calculation basis.Eventually,the model is able to compute forces and motions of casing string in falling process of the operation.In addition,in this paper,the difficulties in running casing in ERW are specially classified into two situations.The first situation is that running casing is hindered by “large-scale high drags” and the second is that running casing is stopped by tight spot.Casing string will have different mechanical behavior when aggressively worked in the two different situations.Two case studies concerning both situations are present.The effectiveness and safety of aggressively working casing string in each situation are discussed.