The Calculation Model Of Cutting Particles Settling Drag And Its Reciprocation Angle

In horizontal and other wells drilling projects,the drilling fluid will stop circulating and the cuttings will stop coming back when the pump is stopped.Because of the density difference between cuttings and drilling fluid,the cuttings in the vertical section will settle due to gravity.If the operation under pump shutdown condition couldn't be completed in time,the cuttings will deposit continuously in the highly inclined section and form cuttings bed.When the cuttings bed reaches a certain thickness,the cuttings bed may slide down or even be consolidated due to the partial force of the cuttings gravity along the inclined direction of the well.Body collapse eventually leads to underground accidents such as buried wellbore,sticking and so on.To study the final settling velocity of cuttings particles in the vertical section under pump shutdown condition,and then predict the thickness of cuttings bed deposited in the highly inclined section,so as to complete pump shutdown operation as soon as possible and avoid the decline of cuttings bed thickness at the bottom of the well.At the same time,once the cuttings bed of the bottom of the well slides down and buries the borehole,resulting in sand jamming and other downhole accidents,it is necessary to carry out deblocking operations.The static equilibrium condition in the wellbore after the formation of the cuttings bed in the section,i.e.the angle of repose of the cuttings bed,is helpful to predict the location of sand jamming.Firstly,the parameters that characterize the characteristics of particles are described.By comparing the expression methods of equivalent diameter and shape coefficient of irregular particles,and comparing the settling conditions of cuttings in actual drilling,it is considered that when studying the settling of cuttings in drilling fluid,the screening average diameter and triaxial diameter are used as the equivalent diameter of cuttings settling,and the Corey shape factor is used to characterize the irregular degree of cuttings.Then,based on Stokes resistance equation and Newton-Redding formula,the settlement resistance equation of debris particles is deduced to calculate the final settlement velocity of debris in each flow regime.Because the proportion coefficient of viscous resistance and pressure difference resistance of cuttings subsidence are defined,it is considered that the proportion coefficient of resistance is a function of Reynolds number of particles by dimensional analysis method.In order to obtain the functional relationship between the proportion coefficient of resistance and Reynolds number of particles,a large number of experimental data are obtained through settling experiments of cuttings particles in saturated brine and polyacrylamide solution.This function relation can be obtained from the established particle resistance settlement equation.Studying the angle of repose of cuttings bed is of great significance for wellbore cleaning.By analyzing the intergranular force between cuttings on average cuttings bed surface and from the point of view of force balance,the theoretical models of the angle of repose of cuttings with two shapes of particle sliding and rolling are established and perfected.According to the wedge accumulation model and considering the relevant knowledge of soil mechanics,the formula for calculating friction coefficient is obtained.When discussing the wedge packing model,the liquid film thickness of particles is taken into account.Because the nature of drilling fluid is different from that of water,the liquid film thickness on the cuttings surface is different from that on the sediment surface.The liquid film thickness on the cuttings surface is obtained from the experimental values of the angle of repose of cuttings in polyacrylamide solutions with different concentrations.The effect of solution concentration on the angle of repose of cuttings is also studied.The range of repose angle of cuttings bed is obtained,which can provide theoretical reference for related wellbore cleaning.