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 stress tensors) in order to, accordingly, adjust the design of the well trajectory while properly assimilate their impact on the production trend. An elaborated workflow was initiated to fine-tune the mechanical proprieties of rock basing on geological information, drilling data, 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. It matches the geological history of the area with an alteration between Normal Faulting and Strike slip regimes (Albukhari et al. in First international conference on advances in rock mechanics. Hammamet, Tunisia 2018; Wendt et al. in Geomechanical study—Hasdrubal field 2005). The MEM was in a position to explain the drilling events for all the vertical wells, thus, providing a reasonable guide design for the wells under development. The shear stability of faults encountered by the horizontal well HAS-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. The previous interpretation is applicable to any major discrete discontinuity that is present in the same stress field and depicts similar rock-related strength properties.