A Comprehensive Geomechanical Study for Deep-Water Field Development Planning: A Case Study from Southeast Asia

Abstract

Abstract Several concerns arise at the field development planning stage which may be only answered by geomechanical studies, such as wellbore stability analyses, sanding risk assessments, and studies of compaction and subsidence during the life of the field. These issues can be very important in large projects in deep-water environments. A comprehensive geomechanical study was conducted for an offshore deep-water gas field in Southeast Asia as part of the field development planning. The study covered a wide range of geomechanical studies from drilling to production stages for the entire life of the field. The geomechanical model was built based on the available logs and data from the exploration and appraisal wells drilled in the field. The model was then used for several geomechanical applications; a) wellbore and fault stability analysis to investigate the effect of the well trajectories on mud weight recommendations and casing design, b) sand production prediction analysis to study the risk of sanding for different completion scenarios, and c) compaction and subsidence analysis to study the impact of depletion on the platform and subsurface designs. A wellbore stability analysis was conducted to investigate the effect of wellbore trajectory on the safe mud weight window. The analysis suggested that the collapse pressure for any well in the field is dependent on the deviation of wells rather than their azimuths. The impact of the stability of the natural fractures and faults on the upper bound of the safe mud weight window was investigated in detail. The analysis showed that the mud weight required to reactivate the natural fracture and fault intersecting the wells is above the upper bound of the safe mud weight window defined by the wellbore stability analysis. The sand production prediction analysis showed that sanding is expected from the early stages of production for both open-hole and cased and perforated completions. The analysis suggested that selective and oriented perforations may only delay or reduce the risk of sanding and cannot eliminate it entirely. The compaction analysis showed that the maximum compaction is less than 1% for all reservoirs. This is significantly lower than the general criteria of 3% – 5% which may cause problems for casing and completion systems. Moreover, the maximum total calculated subsidence at the seabed is expected to be below the engineering design limits. All the methodologies and approaches used to conduct the above mentioned geomechanical analyses, and interpretation of the results are thoroughly explained in this paper. This study highlights the importance of the geomechanical studies for decision making in deep-water field development planning.