Research On Wellbore Stabilization Model Considering Weak Planes And Its Application

Borehole stability analysis has been the key problem of drilling engineering,and the damage caused by the instability of the shaft wall is very serious.Drilling engineering problems are often encountered in complex geological conditions,especially the soft stratum with bedding planes and natural fractures,so it's necessary to consider the influence of the geological weak planes in the analysis of the wellbore stability.In this paper,a semi-analytical model of borehole stability is established,which is based on the stress coordinate transformation relation and both the strength criterions of weak planes and the rock mass.It can provide theoretical basis for fully understanding the influence of geological weak surface and the influence of formation parameters on the stability of shaft wall,which can guide the safe drilling.The main work carried out in this paper is:1.The uniaxial compression and ultrasonic tests of rock samples with different structures of weak structure are carried out to verify the weakening characteristics of the weak rocks.The experimental basis is provided for the subsequent theoretical analysis.2?This paper introduces the general method of obtaining the formation parameters from the logging data,including the general formula for obtaining the basic parameters of physical and mechanical properties of the rock mass.The method of obtaining the formation parameters of the wellbore stability model is described.3?The stability model for wellbore in complex formation with weak planes is established,and the program is obtained by programming software.The reliability of the solution is verified and the influence of different strength criterion on the calculation result is compared.4?Considering the general nature of the ground stress level and the influence of the weak structure in the rock mass on the strength of the surrounding rock wall,the stability of the horizontal and inclined shafts under specific working conditions is calculated.The factors influencing the stability of the borehole wall are analyzed synthetically,which provides the guiding suggestions for reasonable construction under complex conditions.5?In this paper,the method of in-situ stress inversion in complex strata is explored,and the method can be used as an effective complement to the present situation to provide richer ground stress inversion data...