New Mexico Geological Society Annual Spring Meeting — Abstracts

This study presents a field scale reservoir characterization of 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 CO₂, storage and enhanced oil recovery (EOR) project conducted by Chaparral Energy (LLC) and the Southwest Regional Partnership on Carbon Sequestration (SWP). The target unit is the upper most Morrow sandstone bed (Morrow B Sand). The objective of the current study was to utilize extensive data acquired from FWU to improve previously constructed static and dynamic geologic models used for simulation and prediction of reservoir behavior.

Legacy data included wire-line logs from 151 wells, including 48 with associated cores and 10 with thin sections. Depth converted 3D seismic data in conjunction with the abundant well control was used to define stratigraphic surfaces and structural features within the static model. Three new characterization wells were drilled for the project. Cores and advanced wire-line logs from these wells were analyzed for stratigraphic context, sedimentological character and depositional setting to gain a better understanding of the reservoir. Porosity and permeability trends were sought in order to model flow within the reservoir, an important aspect of the EOR and CO₂ storage efforts at the field.

The Morrow B reservoir was deposited as fluvial low-stand to transgressive clastic fill within an incised valley. It is a subarkosic, brown to grey, sub-angular to sub-rounded, poorly sorted, planar to massively bedded, upper medium to very coarse sand and fine gravel sandstone. Gallagher (2014) demonstrated that primary depositional fabrics have less effect than post depositional diagenetic features do on reservoir performance.

Because of the initial difficulty in describing reservoir heterogeneity using traditional methods the Winland R35 hydraulic flow unit methodology (HFU) was used to characterize and refine porosity permeability relationships within the field. This methodology involves calculating R35 values, an empirically derived estimate of pore throat aperture radius when core samples are 35% saturated during a mercury porosimetry test. The R35 value is believed to be the point at which pores form interconnected networks responsible for flow and often provides an excellent means for correlating porosity and permeability. At FWU using R35 values not only provided a means of categorizing porosity as a function of permeability but also helped illuminate some of the underlying geologic underpinnings of flow characteristics within the reservoir.

It is shown at FWU that low HFU's correspond to areas with occluded intergranular space and only minor intragranular microporosity, whereas increasing HFU's have increasing amounts of intergranular space that is better able to form interconnected flow paths.

The integrated 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.

Future work will focus on tying HFU to associated controls such as clay content and degree cementation, then defining a geologic reason for their abundance and distribution in order to further enhance the geologic modeling process.