Research On Swab And Surge Pressure In The Well Considering Cutting Bed

When drilling the layer of narrow safety density window,the borehole's instantaneous surge and swab pressure may lead some safety accidents,such as wellbore instability,the well leakage and well blowout.so it is critical to predict the correctiy Surge and swab pressure in the process of well control,MPD,drilling parameter optimization.In the process of drilling horizontal well and directional well,It is easy to form the cutting bed in the highly deviated eccentric annulus,it will not only increase the friction torque,but also have a greater impact on annular flow.In order to realize the accurate and convenient prediction of the Surge and swab pressure in the eccentric annulus,this paper based on the fluid mechanics' theory,firstly,for the yield power law fluid,the numerical model of eccentric annular Surge and swab pressure,a fitting model of concentric annular surge and swab pressure and eccentric annular pressure ratio fitting model were presented,secendly the computational fluid dynamics technique(Ansys-fluent)was using to carry out the simulation experiment about the concentric annulus and eccentric annulus pressure wave of considering the influence of the cutting bed.Finally,on the fundation of introduction the equivalent hydraulic diameter,using the simulation results of CFD,the fitting model of the Surge and swab pressure in concentric annulus and eccentric annulus were established.The main research achievements are as follows:(1)Analysis results of surge and swab pressures model shown that:surge pressure shown linear or quasi-linear change with changing of inner pipe velocity,fluid yield stress and consistency index,and shown index change with changing of fluid behavior index,diameter rate and dimensionless eccentricity.New regression models for predicting surge and swab pressures for closed-ended pipe was established based on numerical model in concentric and eccentric annulus,respectively.The regression models shown high accuracy and only within 0?+10%and±5%error bands,respectively.(2)Computational grid(mesh)near the inner and outer walls has been refined and coarse grids are used in the central part of the annulus,and is used for predicting surge and swab pressures consindering cutting bed.the surge and swab pressures for concentric and eccentric annulus based on CFD simulations first increases and then decrease with increasing of cutting bed's height.and when the cutting bed's height is similar,the pressures increase with increasing of inner pipe velocity,fluid yield value,consistency index and behavior index.(3)Average cutting bed shear stress for concentric and eccentric annulus increase with increasing of inner pipe velocity,fluid yield value,consistency index and behavior index.In concentric annulus,cutting bed is most easy to be removed when cutting bed's height is less than annular clearance,while cutting bed's height nearly close to the inner walls is most difficult to be removed.In eccentric annulus,cutting bed is most difficult to be removed when cutting bed's height is less than annular clearance,while cutting bed's height nearly close to the inner walls is most easy to be removed.(4)Bying the meaning of introducing the effective hydraulic diameter,A simple and accurate method for predicting the Surge and swab pressure of concentric annulus and eccentric annulus considering the influence of cuttings bed were presented,comparing with the simulated result of computational fluid dynamics(CFD)technique,The prediction accuracy of the fitting model which is modified equivalent hydraulic diameter can be greatly improved,Concentric annulus error range is about 5%?10%,The eccentricity error range is about +11%.