Test On Wear Rule And Prediction On Wear Degree Of Casing In Deep Wells And Extended Reach Wells

During drilling process of a great number of deep wells, super-deep wells, highlydeviated wells and extended reach wells, casing pipe wear problem exists in differentdegree. After casing pipes are worn, their bearing capacity gets reduced, causing asignificant impact on subsequently drilling wells, extracting oil and repairing wells.Sometimes it can make an almost finished well discarded. Accurately predicting weardegree of casing pipes is of important significance on design of deep wells and extendedreach wells as well as drilling construction. The subject planed to adopt the research inwear rule of casing pipes as foundation and adopt prediction of wear degree of casingpipes and calculation of residual intensity as research objectives as for the wear predictionof casing pipes home and abroad along with major problems that relevant technologiesmet. Details are as follow:By integrating analyzing results of simulation experiments of casing wear wellcondition, well site monitoring and working condition in the well, mechanism of casingpipe abrasion was preliminarily discussed and concluded that casing wear was based onstatic load and was a kind of abrasion mechanism coexisting with cutting wear, adhesionwear, abrasive wear and contact fatigue wear etc. In non-weighted drilling fluid medium,cutting wear was the main form of casing pipe's wearing; In weighted drilling fluidmedium,abrasive wear and fatigue wear were main forms of casting pipe's wearing;Heavy weight additive could reduce drill stem's direct cutting effects on the casing pipe,while it would increase fatigue wear; Compared with barite heavy weight additive, highload of hematite powder would also increase casing pipe's adhesion wear.Drill rod/casing pipe frictional wear testing machine was utilized to analyze the effectrule which made by contact force, drilling fluid heavy weight additive and casing pipequality on casing pipe wear. It was concluded that wear rate of casing pipe and contactforce took on approximate linear relation. When contact force strengthened, frictionalcoefficient tended to increase; drilling fluid medium containing barite aggravating agenthad evident wear decreasing effect on casing pipe, mixture of barite and hematite power at proper ratio of 2:1 could reduce casing pipe's wear to its lowest level; at the premise ofhigh hardness, improving casing pipe's tensile strength could benefit the reduction of itswear. Based on that, parameter data and empirical formula were reached through statistics.On the basis of taking stiffness and buckling of drill column into account,tension—torque equation of drill column in deep well and extended reach well wasobtained; prediction model of wear degree of casing pipe based on energy principle wasestablished and forecast software was prepared. Wearing capacity of casing pipecorresponding to different well depths in all well sections could be predicted under suchcircumstances as layer of different casing strings, combination of drilling tools, well boretrack, type of drilling fluid and drilling parameter etc, including such operation process asdrilling and pulling out drilling tools etc. The calculated result through examples denotedthat software reduces artificial error of estimation, and predicted value was accurate andreliable.The residual collapsing strength of worn casing pipe was researched by thefinite-element analysis and verification of tests. It concluded that the yielding occurredfirst at the gravest worn part of the casing pipe, developing into"plastic hinge"gradually,and causing the instable overall structure at last. The collapsing strength respectivelypresented changes of indexes, power function and linear trend with wear wall thickness,wear radius and axial load of the casing pipe. A computation model of collapsing strengthof worn casing pipe was established based on collapsing strength calculation of non-wearcasing pipe and eccentric cylinder. Internal pressure strength of worn casing pipe wasanalyzed in"slot cutting"analysis method.Research result of the thesis has practical application value in strength optimizationdesign of casing string, wear-reducing design of casing pipe and safety assessment underwells etc, and provides references for further analyzing wear mechanism of casing pipes.