This paper describes the workflow used to assess modeling the impact of fractures (and faults) on the dynamic performance of a Lower Cretaceous reservoir located offshore Abu Dhabi. The reservoir is not highly fractured and the modeling challenge is to identify a practical method to incorporate their impact in a geologic and simulation model. The work plans developed to address these issues consist of four elements of a conceptual fault and fracture model - these are: two groups of diffuse fractures in specified layers; seismic scale faults; and fracture corridors. This paper focuses on learnings from the study of the first two elements of the developed work plans - i.e., modeling the impact of diffuse fractures on water movement.
The workflow began by modelling diffuse fractures at mini-sector scale (single geo-model grid-cell with layers and properties). Fracture parameters have been defined for low-side, most likely and high-side cases based on core data from 80 wells. By preparation of discrete fracture network (DFN) models for these cases and calibration to well test permeability, we are able to define a permissible range of fracture parameter values; and also to define the sensitivity of each fracture parameter. Dual media mini-sector simulation models are then used to compare water breakthrough time and evolution for different DFN models. The mini-sector models are also used to estimate the range of possible behaviours given the uncertainty in fracture data and other key factors like matrix-fracture transfer.
The results of this modeling work were used to formulate plans and recommendations for full-field modeling. A key conclusion derived from this study was that an effective single medium model would be adequate for full-field modeling of the subject reservoir. Work on the effective single medium full-field model is currently underway and the results-to-date are promising in terms of modeling reservoir behavior.