An approach to well bore wall stability analysis by MATLAB and FLAC3D software for Salman oil field

Instability in wellbore wall is one of the most serious difficulties in drilling, because this problem can ultimately delay the drilling operations, increase cost of drilling and in some cases lead to the wellbore becoming abandoned. Now a day, with consideration of physical and chemical characteristics of mud we can apply the necessary changes to the composition of mud and make the wellbore wall more stable. With the help of the science of rock mechanics and the full knowledge of the characteristics of formation, the optimum path to drilling wellbore and the mud window can be calculated. In this research, first stability of the shale layer in wellbore 2SK5 in Salman oil field using analytical method (MATLAB software) and numerical method (FALC3D software) with the use of three criteria of failure of Mohr Coulomb, Mogi Coulomb and Drucker Prager will be studied and at the same time comparisons of applications of above criteria in stability of wellbore and comparisons of occurred difficulties in drilling this wellbore will be studied, and recommendations concerning drilling wellbore in the mentioned oil field will be presented, also at the same time some research work will be carried out in assessing drilling deviational wellbores in oil fields and effect of different stress regimes for calculating optimum direction and angle of deviation. Therefore, we conclude that stability of the wellbore with the increase in angle of deviation of wellbore does not necessarily decrease from that of its right angled one (90 degrees) , unless in a case when stress is normal or the principal horizontal stresses are equal. Also, when stress regime is normal, drilling in the direction of minimum horizontal stress and decrease in angle of deviation of the wellbore from that of right angled one will be most stabilizing for the wellbore, but drilling in this direction in the other two stress regimes will result maximum instability