Seismic-constrained Lithology Prediction and Reservoir-quality Modeling using Pre-stack Inversion and Bayesian Classification, Mississippian Meramec strata, eastern Anadarko Basin, Oklahoma

Abstract

The Mississippian Meramec strata within the STACK (Sooner Trend in the Anadarko [Basin] in Canadian and Kingfisher counties) play of central Oklahoma is primarily a fine-grained mixed siliciclastic-carbonate system composed of mudstones, argillaceous siltstones, argillaceous-calcareous siltstones, and silty limestones. The Meramec interval within the study area ranges in thickness from 300 – 400 ft (91 – 122 m) and stratigraphically consists of seven parasequences, Meramec 1-7. The Meramec dips structurally to the southwest and is offset by several faults with varying throw that ranges from 50 to 150 ft (15 – 46 m). Five lithologies and three petrophysics-based rock types are classified in non-cored wells using a supervised Artificial Neural Network (ANN) based on well-log and core data. Elastic seismic attributes are derived from a pre-stack inversion to produce P-impedance, S-impedance, and density volumes. Elastic properties, P-impedance and S-impedance, are used to create lithology probability volumes for each lithology and a single lithology classification volume. Three-dimensional lithology and rock-type models illustrate the spatial distribution of stacked parasequences grading upward from argillaceous siltstone to calcareous siltstone. Petrophysical (porosity and water saturation) and geomechanical (Poisson’s Ratio and Young’s Modulus) property models show that lower values of porosity and higher value of water saturation are associated with brittle, calcareous-rich lithologies and rock types, and higher values of porosity and lower values of water saturation are associated with ductile, argillaceous-rich lithologies and rock types. Comparisons to oil production suggest that higher reservoir productivity is associated with the mixed argillaceous and calcareous-rich rock type 2 and relatively more brittle rocks. The distribution of optimal reservoir quality parameters including geomechanical and petrophysical properties are associated with the stratigraphically controlled stacking pattern and distribution of lithologies and rock types. Meramec parasequences 3 and 4, at the turnaround from retrogradational to progradational units, have the combination of depositional, petrophysical, and geomechanical characteristics associated with better reservoir quality and favorable drilling and hydraulic fracturing conditions.