Reconciling Core Derived Permeabilities and Well Test Using A Fracture Network: A Field Case Example

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractIt is a common observation that well test permeability values do not match with thickness weighted core permeability averages. This is not a surprise because of the differences in the measurement scales where, unlike well test measurements, core samples represent a very small portion of the reservoir around the well bore. In addition, the presence of fractures and/or high permeability channels will further enhance the difference between the two sources of data. Therefore, reservoir descriptions based on core measurements alone cannot honor well test results. They need to be modified properly without violating the underlying geological and geostatistical information.In this paper, we present a methodology to properly enhance permeability fields that also accounts for fracture distribution in the reservoir. The basic idea is that radial upscaling around a wellbore within a given investigation radius should match the permeability obtained from well tests. The enhancement is caused by two factors: microfractures, which cannot be explicitly represented in the reservoir description, and macro-fractures, which can be interpreted using 3-D seismic data. To account for these two different types of fractures, we calculate two different enhancement factors, one for the base level (microfractures) and one for the higher level (macro-fractures). The base level, after appropriate interpolation, is applied across the entire reservoir, whereas the higher level is applied only to locations where macro-fractures are interpreted from 3-D seismic data.The technique was successfully applied to a Middle Eastern carbonate reservoir. A significant correlation is observed between the enhancement required to match the well test data and the fracture density (macro-fractures obtained from 3-D seismic data) within a given investigation area. A correlation function is then obtained between the enhancement factor and the fracture density for a given grid block, which in turn is used to apply enhancement to interwell locations. Thus, the resulting permeability field did not only honor the well test results but also the fracture distribution and the underlying geological and geostatistical descriptions. In a later stage, a tensorial approach was used to upscale permeability to account for the anisotropy in permeability distribution. Using this approach, a proper anisotropy of permeability distribution, matching the fracture orientation, has been obtained.

Fully Integrated 3D-Reservoir Characterization and Flow Simulation Study: A Field Case Example

“…The details of the procedure in reconciling the well test permeability and the core-derived permeability for this study are presented in another paper. 4 Ranking of Multiple Realizations. Recently, it has become a common practice to generate large number of realizations of reservoir models to assess the uncertainty in reservoir descriptions and performance predictions.…”

Fully Integrated 3D-Reservoir Characterization and Flow Simulation Study: A Field Case Example

“…The detail of this calculation is beyond the scope of this paper and can be found in Ref. 4. Due to the limitation of the simulator being used (ECLIPSE-100), the diagonal terms of permeability tensor was ignored and the effective x-and-y permeability were calculated accordingly.…”

“…These differences were attributed to the fracture that was observed from the core and/or FMS/FMI logs. 4 In order to quantify the influence of fracture in the permeability distribution, fracture study was conducted to estimate the spatial locations of the fracture. These locations were determined using seismic curvature analysis.…”