Geomechanical Evaluation of Mud Losses and Wellbore Instability in Mumbai High North Field – Implications to Infill Drilling and Reservoir Development

Abstract

Abstract Mumbai High North (MHN), an Indian Offshore oil field is a multilayered carbonate reservoir. This field has been producing for the last 35 years and there exists differential pressure depletion across the field. Mud losses while drilling the carbonate reservoirs in this field is a known serious problem and there is a direct impact on non productive time (NPT) and well cost adversely. Loss circulation during drilling appears to have become more severe with increased directional drilling activity and reservoir depletion in this field. There are also number of wellbore instability incidents like stuckpipe, tight hole and cavings evidenced at shale intervals especially when there was a drop in hydrostatic head of wellbore annulus due to mud losses in carbonate reservoirs. At present, a comprehensive in-fill drilling campaign is under implementation with significant capital investment to enhance oil production from this field. This campaign covers mostly the Northern area of the field. A variety of drilling and completion problems have been encountered in the recent wells in this area which are attributed mainly due to mud losses while drilling. In order to study the underlying mechanisms behind mud losses and wellbore instability, a geomechanical study was initiated using representative offset well data around one of planned in-fill drilling areas. The study includes constraining in-situ stresses, pore pressure and rock mechanical properties from available limited data set and reconciliation of results with relevant drilling experiences from offset wells. This paper mainly discusses how the mud loss experience was analyzed and related with possible mechanisms with help of geomechanics. Based on this study, a risk matrix was generated to drill in-fill wells with appropriate mud weights and drilling practices. The study results also provided insights on possibilities of optimizing reservoir development strategy for future production.