ANALYSIS OF GEOMECHANICAL PROPERTIES IN WELL DESIGN AND WELL OPTIMIZATION

Abstract

Abstract -Main aspect in wellbore instability is the selection of an appropriate rock failure criterion. This criterion involves only the maximum and minimum principal stresses and  and therefore assumes that the intermediate stress  has no influence on the rock strength. When Mohr-Coulomb criterion was developed it justified by experimental evidence from conventional triaxial test (>). Based on triaxal failure machine the Mohr-Coulomb criterion has been extensively used to represent rock failure under the polyaxial stress state (>).  In contrast to the prediction of redistribution Mohr-Coulomb much evidence has been accumulating to suggest that  thus indeed have a strengthening effect. This research shown that Mohr-Coulomb failure criterion only represent, that triaxial stress state (=) which only occasionally encountered in-situ.The linear failure criterion has been justified by experimental evidence from triaxial tests as well as polyaxial test. It is natural extension of the classical Mohr-Coulomb criterion into three dimensions. As the Mohr-Coulomb criterion only represents rock failure under triaxial stress state, it is expected to be conservative in predicting well bore instability. The 3D analytical model employed by Mogi-Coulomb has been achieved by using linear elasticity theory to calculate the stresses.

A model was developed used in analyzing shale intrusion, at depth 6100ft the well bore pressure of the formation is found to be 0.9180psi/ft and decreases to 0.420psi/ft at depth 7300ft.  The membrane efficiency of the formation increases from 0.698 to 0.719 at the depth considered above.

Keywords:formation,coulomb,triaxial,

Stress,polyaxial,elasticity,modulii