Study Of Relation Between In-situ Stress And Borehole Stability

Drilling engineering is underground works, involved in the complex and volatileunderground conditions, and borehole instability will lead to a series of underground accident,have done great harm to the drilling engineering. Borehole stability problems become theproblems which troubled the engineering and technical personnel and under great concern ofthe world’s drilling engineering sector.A long time, drilling engineering staff is committed to research and exploration of thewellbore stability technology, and has made great progress. However, due to borehole stabilityproblem is very complex, influenced by many factors, there are many technical issues to beresolved. The predecessors obtain the result do not fundamentally solve the borehole stabilityproblems. Therefore, wellbore stability problems are also more in-depth study.Borehole instability mainly expressed as compression shear failure and tensile failure ofthe sidewall surrounding rock. Compression shear failure of rock is because of the drilling fluid densityis too low that stress concentration exceed rock compressive strength Tensile failure or fractures is thereason of lost circulation，well leakage serious causes the annulus pressure decreased, and may causeblowout。In this paper， analysis the wellbore stability problem with the Pinggu situ stress measurementand monitoring hole, the work as follows:1、 Measuring the in situ stress of the Pinggu drilling and take rock mechanics experiment.2、Establish wellbore stability analysis model to calculate the formation collapse and fracturepressure, analysis to the impact of stress on the borehole stability.3、Using ANSYS finite element software, make numerical simulation to Pinggu drilling.Through theoretical analysis and numerical simulation obtain the following conclusions:1、Obtain the impact of the size and heterogeneity of in-situ stress on borehole collapse pressureand fracture pressure curve.2、By choosing the Mohr-Coulomb strength criterion, the Drucker-Prager strength criterion and theMogi-Coulomb criterion, come to the intermediate principal stress strengthen the boreholestability, and the Mogi-Coulomb criterion has better applicability.3、Obtained by numerical simulation that use water got into the need to meet the wellbore stability,continue to increase the density of the drilling fluid is no further benefits to wellbore stability.