ABSTRACT:

Mechanical rock properties affect borehole pressure and permeability during production. The objective of this paper is to estimate and predict potential borehole failures and form a geomechanical model detailing the most likely areas to fail under drilling, completion or borehole collapse stress. A model of the fracture patterns of the area will be made and compared with the structural geology of the zone. This project uses data found in petrophysical logs for the study of geomechanical properties, later assisting in geomechanical correlations throughout the reservoir. The elastic and mechanical constants ofYoung modulus (E), Poisson ratio (v), Shear modulus (G), and Bulk modulus (K) were derived to determine weak and strong zones. The fracture initiations were then predicted and compared for each weak and strong zone using the Mohr-Coulomb criterion. It was also found that an increase of vertical stress (σv) induced due to drilling causes failure by 200MPa in the strong zones. The results also show how the reduction in the σmin (minimum horizontal stress) between 0.47MPa and 25MPa causes normal failure. Geomechanical failure risk can be linked to the thickness and pattern of the fractured zone. The fractured zone thickness is larger in the northern part of the field compared to the south-east. In conclusion, geomechanical failure risk related to fracture is reduced to the south of the structure.

1 INTRODUCTION

This paper focuses on a carbonate reservoir of the Middle East. As the work is being done on a limestone reservoir it is predicted to encounter mostly brittle and fractured rocks that are classified as strong zones (SZ); while more ductile rocks are in zones called weak zones (WZ). Therefore knowing the zone properties, as well as the stresses required to cause failure can allow more secure drilling operations in the future.

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