الفهرس 
Chapter 1 - IntroductionOnly 14 pages are availabe for public view
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Abstract
Wellbore instability is one of the main problems that engineers meet during drilling. The causes of wellbore instability are often classified into either mechanical induced instability for example, failure of rock around the hole because of high stresses, low rock strength , or inappropriate drilling practiced or chemical effects which arise from damaging interaction between the rock and the drilling fluid. Theses problems might cause serious complication in well and in some causes can lead to expensive cost operational problems. To contribute the solutions of these issues, an integrated wellbore instability study was implemented to effectively plan the future drilling operations in karama oil field, to minimize the drilling merging for the future wells drilled, and to optimize the future field development. So, the main aim of this research is to developed a geo-mechanical analytical model to investigate the stability analysis around the wellbore hole. However the mechanical instability is mainly related to incorrect mud weight and or well trajectory. So, the mud pressure should be designed accurately to prevent onset borehole shear failure, manifested by the collapse of borehole wall and borehole tensile failure, represented by hydraulic fracturing. The main aspect of the wellbore stability analysis is to mitigate the drilling problems. This is typically investigated by a constitutive model to estimate stress around the wellbore, coupled with a failure criterion. Then, for stability analysis a linear elastic model, was presented, in conjunction with linear failure criteria like Mohr – Coulomb .But, the Mohr – Coulomb failure criterion only involves σ1 and σ3 and therefore assumes that σ2 has no influence on rock strength. Then, a model for the mud weight window determination, using Mogi – coulomb failure criterion was also developed. This is based on hypothesis that, σ2 plays an important role on rock strength. However, this study indicates that, whereas using analytical solutions of the Mogi – Coulomb and Mohr – Coulomb failure criteria. The boreholes with various inclination (i) and azimuth(φ), the best drilling directions are vertical and deviated one. The predicted maximum inclination angle by the Mohr – coulomb criterion is 30° and by Mogi – Coulomb criterion is 50°, that is, well drilling with inclination angles lower than that predicted ones are safe. And by increasing well inclination, the pressure should be increased. Also, the stability of the horizontal borehole (i= 90°) is lower than vertical one. The well can be drilled with inclination angle lower than 50° indirection parallel to the minimum in-situ stress (i.e σh ). When the difference between in-situ horizontal stresses is high, low inclination wells are more stable than highly inclined boreholes is obtained. In general, the higher azimuth, the more stable wellbore. In the case of high difference between in-situ stresses, the optimum path for a well is a low inclination and an intermediate azimuth. Also, from this study; it has been concluded that the overbalanced mud pressure, at a depth = 7906ft, is 3900 psi using φ =90° and i=90°. For the anisotropic horizontal stresses, it is found that with the analysis based on Mogi – coulomb criterion and equals 4200 psi, when the analysis is based on Mohr – Coulomb criterion under the same conditions. But where φ = 0.0° and i=0.0° for isotropic case, the overbalance mud pressure is nearly the same for the two failure criteria. At last, it is recommended that the results of this study could be benefit to the mitigation and/or prevention of wellbore stability issues in the karama oil field.