An Improved Approach for Sandstone Reservoir Characterization

Abstract

Abstract This paper presents a field scale reservoir characterization for a late Pennsylvanian clastic reservoir at the Farnsworth Unit (FWU), located in the northeast Texas Panhandle on the northwest shelf of the Anadarko basin. The characterization is undertaken as part of a Phase III project conducted by the Southwest Regional Partnership on Carbon Sequestration (SWP). The target unit is the upper most Morrow sandstone bed (Morrow B Sand). Extensive data acquired from FWU was used to improve previously constructed static and dynamic models. The Morrow B reservoir was deposited as fluvial low-stand to transgressive clastic fill within an incised valley. It is predominantly, subarkosic, brown to grey, upper medium to very coarse sands and fine gravels with sub-angular, to sub-rounded poorly sorted grains either planar to massively bedded. It was shown that primary depositional fabrics have less effect than post depositional diagenetic features do on reservoir performance, although subtle variations in deposition may have had some effect on later diagenetic pathways. Three new wells were drilled for the purpose of field infilling and characterization. Cores and advanced wire-line logs from these wells were analyzed for stratigraphic context, sedimentological character and depositional setting in order to better predict porosity and permeability trends within the reservoir. Structural modeling was conducted through the integration of depth-converted 3D seismic data with well log data to create the framework stratigraphic intervals. This information, together with additional core, UBI image logs and an improved hydraulic flow unit methodology (HFU) was used to characterize and subsequently create a fine scale lithofacies based geological model of the field. Core and log analysis allowed subdivision of the target interval into Hydraulic Flow Units (HFUs). The HFU approach enhanced core analysis and was used to elucidate porosity–permeability correlations. This methodology proved to be an exceptional approach to assigning permeability as a function of porosity during petrophysical modeling. The integrated approach of combining seismic attributes with core calibrated facies and the HFU methodology was able to better constrain uncertainty within inter-well spacing and accurately quantify reservoir heterogeneity within FWU. The approach illustrated in this study presents an improved methodology in characterizing heterogeneous and complex reservoirs that can be applied to reservoirs with similar geological features.