جستجوی مقالات مرتبط با کلیدواژه « failure criterion » در نشریات گروه « مهندسی شیمی، نفت و پلیمر »

During drilling operation, a volume of formation rocks which have been effected by far field stress is removed. Thus induced stress field redistributes around the borehole wall. While this induced stress field exceeds the resistance of the rocks around borehole wall, borehole breakout will take place. As a result a plastic zone around borehole wall can be observed. Hence, accurate understanding of state of plastic zone around the borehole wall can lead to figure out the behavior of the borehole circumferential environment. The analysis plastic zone around the borehole wall is valuable to determine safe mud window and optimize well trajectory to mitigate well instability problems. On the other hand, analysis the wellbore stability based on the critical pressure may be unreasonable, because the critical pressure can only reflect the degree of difficulty for the initiation of damage at the wellbore rather than the extent of the wellbore damage. Therefore, the results of wellbore stability analysis based on the analysis of plastic zone around the borehole wall are more realistic. In this study, using an elasto-plastic analysis incorporating three commonly used failure criteria as Mohr-Coulomb, Mogi-Coulomb and modified Lade, the extent of plastic zone around a vertical oil well and the condition of stability with specific mud weight in southwest of Iran was investigated. Results showed that according to the Mogi-Coulomb and modified Lade failure criteria which have been confirmed by FMI data the probability of occurrence of plastic zone around the borehole wall was negligible and borehole was in the stable condition. On the other hand, the discrepancy between the results of Mohr-Coulomb criterion and the set of modified Lade and Mogi-Coulomb criteria can be due to the negligence of the effect of averaged main stress.

Wellbore instability is one of the main or principal problems during drilling. Instability’s issues may cost lots of money and time for companies. Therefore, immense efforts have been devoted to solve it. In this article, using a Mechanical Earth Model and various failure criteria, this problem has been analyzed, and the best stable trajectory has been determined in order to avoid drilling induced wellbore failures. On this purpose, first, the mechanical properties of rock have been specified through log and core data altogether. By the help of (1) density log, (2) Stress Polygon, (3) drilling reports and (4) wall failure data, the magnitude and azimuth of stresses in the region have been calculated. Then to find the stable well path and examine the effect of choosing failure criteria on this procedure, three failure criteria applied to determine safe mud window for all of the possible trajectories. Mohr – Coulomb, as the prevalent criteria, and Mogi - Coulomb and Modified Lade, as criteria that include effect of intermediate stress, are utilized. The results show that, a trajectory characterized by 60 degree inclination from a vertical well and 70-80 degree Azimuth is optimum orientation. Also it is founded out that various failure criteria give same results.