Abstract
The Diyab Reservoir is an unconventional prospect in Abu Dhabi where previous exploration efforts revealed thin low permeability targets, unsuccessful stimulation, and poor well placement. This early field experience coupled with limited knowledge about local in situ stress and the impact of faults and subseismic fractures to affect hydrofracs led to a concentrated field data acquisition program together with a fully integrated 3D reservoir simulation approach to assess Producibility, Fracability and Geohazards in the Diyab.
The fit-for-purpose field data acquisition program, 3D hydraulic fracture simulation, and reservoir flow modeling helped establish a baseline understanding of the relationship between 3D reservoir characterization and proppant transport. Seismic data was interpreted to understand structural components and natural fracture characterization. Elastic inversions were performed on this data using petrophysical models to populate high-resolution 3D geological and geomechanical models calibrated against log derived rock properties and in situ tests. A detailed analysis of core identified bitumen layers and thinly laminated mudstones that have the ability to undermine completions by causing horizontal hydraulic fracture growth and undesirable proppant migration. Physics-driven frac simulation of this fully integrated geomodel was performed to determine design completion and fracking strategies for the target reservoirs.
Post frac analysis for three Diyab wells reveals that the ISIP varied significantly among the stages and the largest post frac pressure drops occurred at stages intersected by small-scale faults or natural fracture zones, particularly when they are well oriented for shear slip.
Results of high-resolution 3D simulation of frac stages on earlier wells showed proppant distribution closely followed reservoir property distributions of low stress and similar Young’s Modulus values. Wells were landed in specific target reservoirs, however, the simulation demonstrated that proppant from some stages was inadvertently placed in overlying reservoirs. The natural fractures play a significant role in stage efficiency indicating the need to utilize non-geometric completion design. Simulating the role of natural fractures to create reservoir access indicated significant differences in propped height and length within naturally fractured stages. Dual permeability pre-frac reservoir modeling based on frac simulation results predicted cumulative gas rates for the new wells.
