The Mississippian-age Meramec Series is one of the primary producing intervals of the Sooner Trend in the Anadarko Basin of Canadian and Kingfisher (STACK) counties, Oklahoma and is currently among the most sought-after hydrocarbon plays in the US. It is a low permeability and low porosity play; therefore, understanding reservoir limits, fluid characterization, and petrophysical characterization are critical to development planning of these reservoirs.

In this study, we establish an integrated workflow for multi-component fluid characterization, stimulation-region limits and hydraulic-fracture-dimension estimation, and apply the workflow to a study area of the Meramec interval in the STACK play of Oklahoma. First, rate transient analysis (RTA) is used to characterize porosity, permeability, fracture dimensions and drainage areas. Subsequently, an Equation-of-State (EOS) model is established for the study area spanning the liquids-rich zone to high Gas-Oil Ratio (GOR) region. The EOS model is refined via compositional reservoir simulation by matching initial producing GORs field-wide and imposing compositional variations that would be observed due to thermal maturity. Reservoir parameters are then refined using the enhanced fluid model, and the integrated workflow is repeated until convergence.

This approach has yielded an initial integrated fluid and petrophysical characterization and completion evaluation across an area of 1,000 mi2 within the STACK play. We have used production data from 2014 to 2017 for 20 wells in this area. A 15-component EOS model with 4 plus-fraction components is calibrated for the study area. Compositional gradients for methane and the first plus-fraction component are found to be 0.082 and 0.037 mole-fraction per 1,000 ft, respectively. Initial pressure gradient ranged within 0.42-0.65 psi/ft. GOR varied from 0.8 MSCF/STB in the liquids-rich zone to 1,500 MSCF/STB in gas zone. Formation volume factors of oil vary between 1.35-6.50 RB/STB. With regards to stimulated-region characterization, fracture half-length, fracture height, and drainage area ranged from 540-900 ft, 200-300 ft, and 315-505 acres, respectively. Integration of the various data allows for representative in-place volume estimates, as well as aiding in planning of optimal development and completion strategies.

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