Abstract: Dual-Porosity Reservoir Modeling of the Fractured Hanifa Reservoir, Abqaiq Field, Saudi Arabia

Luthy, Stephen T.

Fractures play a significant role in the transmissibility of the Hanifa reservoir at Abqaiq Field. The Hanifa is a Type 2 fractured reservoir characterized by a finely-crystalline carbonate matrix which contains most of the reservoir storage porosity, and a stylolitic fracture system which provides essential permeability. Integration of borehole imaging data with available open-hole log, core, and well-test data from horizontal and vertical wells allowed for the distribution of fracture parameters, including fracture density, aperture, porosity, and permeability throughout a geocellular model. Analysis of over 5000 fractures showed that changes in lithology, grain size, and/or bed thickness do not correlate with changes in fracture densities. Review of P- and S-wave log d ta showed that porosity is negatively correlated with fracture density and mechanical rock strength. From these relationships, it was possible to utilize additional wells where porosity log data was available to calculate fracture densities. These wells were used to generate matrix porosity and permeability as well as fracture density attributes in a 12-sequence, 29-layer geocellular model. The effect of structural curvature on fracture intensity in the reservoir was estimated by mapping the derivative of structural dip. Incorporation of structural curvature explained variations in well test behavior not predicted by initial estimates of fracture density from porosity alone. By using average well-test derived permeabilities and average modeled fracture densities, a theoretical average fr cture aperture value of 0.0142 mm was obtained. This value was applied against the fracture density model to derive fracture permeability and porosity model attributes. Fracture permeabilities compare favorably with well-test derived productivity indices. Three-dimensional visualization of model attributes showed that a monotonous and low (<10 md) distribution of matrix-related permeability contrasts sharply with highly variable and relatively high (>50 md) permeabilities of the fracture system. Reliability of the geocellular model to predict fracture densities and associated permeabilities has been confirmed by subsequent drilling of high cost horizontal wells, and is being used in reservoir engineering and development drilling planning efforts.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France