Hasdrubal Field, Tunisia: geomechanical integrity study

Abstract

Hasdrubal is a naturally fractured carbonate reservoir field located in offshore Tunisia. Over the last decade, the field has manifested serious integrity and water coning production issues. The extended network of discontinuities in addition to the impact of reservoir depletion renders the stability of the reservoir a major concern for the field operator. An integrity study of the field was necessary to accurately determine the ever-changing stress settings (magnitudes and orientation of stresses tensors) in order to accordingly adjust the design of well trajectory while properly assimilate their impact on the production trend. An elaborated workflow was initiated to fine-tune mechanical properties of rock basing on geological information, drilling event, and field logs. The one-dimensional mechanical earth model (MEM) was then built to validate wellbore failure and explain drilling incidences reported. The stress regime was also confirmed and matches the geological history of the area with an alteration between normal faulting and strike-slip regimes. The mechanical earth model was in position to explain the drilling events for all the vertical wells and so providing reasonable guide design for the wells under development. The shear stability of faults encountered by horizontal well Hasdrubal-A1 was also appraised using the Fracture Stability Advisor software. The results show that at initial reservoir pressures, the fractures in Hasdrubal field are stable and do not exceed the failure criterion. Previous interpretation is applicable to any major discrete discontinuity that is present in the same stress field and depicts similar rock-related properties strength. A predictive and robust three-dimensional model to represent the complex environment of reservoir is necessary to explain production profile induced from pressure depletion, especially alteration at fractures and faults network, and so improving well planning and long-term field development. The mechanical earth model described herewith has represented an indispensable foundation of the three-dimensional model that has been built to address the classical 1D-MEM limitations and so to properly assimilate the presence of fractures and their impacts on the geomechanical behaviour of the field.