--> 1D Mechanical Earth Model In A Carbonate Reservoir Of The Abadan Plain, Southwestern Iran: Implications For Wellbore Stability

AAPG Asia Pacific Region GTW, Pore Pressure & Geomechanics: From Exploration to Abandonment

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1D Mechanical Earth Model In A Carbonate Reservoir Of The Abadan Plain, Southwestern Iran: Implications For Wellbore Stability

Abstract

Knowledge of the rock mechanical properties and stress tensor including orientation and magnitude of in-situ stresses has numerous implications in different aspects of petroleum exploration and production. In particular, these geomechanical parameters control fluid flow in naturally-fractured reservoirs, hydraulic fracture stimulation, seal breach by fault reactivation, wellbore stability and reduce non-productive time in drilling operations. Knowledge of the in-situ stress state is particularly important in Iran, which has an extensive and mature petroleum exploration and production industry, and is also prone to stress-related geohazards such as earthquakes. Yet, the 2016 release of the World Stress Map project contains very little in-situ stress information for Iran.

In this study, we present a comprehensive one dimensional mechanical earth model in an appraisal well in a carbonate oil-bearing reservoir in southwestern Iran. Different rock mechanical tests including Brazilian, Uniaxial compressive strength, and tri-axial compressive tests are applied on the core samples to determine rock strength and elastic properties such as tensile strength, UCS, cohesion, friction angle, young modulus, Poisson’s ratio. These static rock mechanical properties then provide a reference to calibrate the well-log derived or dynamic rock mechanical properties. We use different sets of data such as pressure tests, leak off tests, borehole image log and wireline data to estimate the continuous profile of vertical and horizontal stresses and pore pressure in different lithological layers of the studied well. Analysis of borehole breakouts and drilling induced tensile fractures suggest a NE-SW orientation for the maximum horizontal stress orientation which is consistent with deep earthquake focal mechanism solutions in the study area, derived from the World Stress Map database. The results also indicate a prevailing strike-slip tectonic stress regime which is consistent with the published data in the Abadan Plain. The constructed 1D MEM was calibrated by wellbore stability analysis of the current drilled well. The results indicated the instable borehole in some intervals which was consistent with borehole image and caliper logs. Finally, we use the constructed 1D mechanical earth model in this study for sensitivity analysis of different wellbore trajectories and mud weight window for future well planning and safe drilling in this under-development oil field. The results of study indicate a horizontal well in direction of NE-SW would be the most stable path for future safe drilling in this under-development field.