Stochastic 3D Modelling In Complex Reservoir Geometries

The uncertainties associated with reservoir continuity yielded to major operational problems at El Guadal Sur Field. Overpressure on certain reservoirs due to unbalanced water injection contributed to the reactivation of fault systems with the subsequent collapse of 60 wells. Since the mechanical failures affected well integrity at the main reservoirs level, the implemented and planned water injection programs therefore had to be suspended with consequent production deferrals. An integrated reservoir study was conducted in order to investigate further development alternatives to regain operational integrity of the asset. This effort included the integration of a variety of data from different sources and support volumes and concluded that the lack of understanding of reservoir heterogeneity was the main contributor to the inconsistencies between the injected water volumes and the field liquids deliverability. The unbalanced injection yielded to overpressure over critical areas of tectonic incidence modifying the in-situ regional stress generating reactivation of major fault systems. Outcrops studies suggested that lateral continuity of the Bajo Barreal Formation in the area were smaller than well separation distance. Therefore, special emphasis was put on building a geological model that could avoid overestimation of reservoir continuity as obtained by conventional interpolation methods. A consistent 3D stochastic model was obtained that reproduced the reservoir geometries observed at the outcropping sections and derived detailed volumetrics were the basis for the reservoir simulation. Finally a comprehensive field development plan was formulated establishing the phasing of activities that would yield to field reactivation.