Mechanical stratigraphy of Mississippian strata using machine learning and seismic-based reservoir characterization and modeling, Anadarko Basin, Oklahoma

Abstract

The Sooner Trend in the Anadarko (Basin) in Canadian and Kingfisher counties play primarily produces oil and gas from Mississippian strata. The interval consists of interbedded argillaceous mudstones and calcareous siltstones. Such a contrast in rock composition is linked directly to the mechanical stratigraphy of the strata. Brittle (calcareous siltstones) and ductile beds (argillaceous mudstones) are related to the sequence-stratigraphic framework at different scales. We have used seismic and well-log data to estimate and map the geomechanical properties’ distribution and interpret the mechanical stratigraphy of rocks within the Mississippian strata. First, we defined the parasequences that form the main reservoir zones of the Meramecian-Mississippian strata. Once we established the stratigraphic framework, we estimated and compared rock brittleness index (BI) using two independent laboratory-based measurements from the core. The first method, the mineralogical-derived BI, uses mineralogical composition inverted from Fourier-transform infrared spectroscopy analyses, whereas the second method, the mechanical-derived BI, involves measurements of compressional and shear velocities from core plugs. We use the data from core-plug velocity measurements along with well logs and an artificial neural network approach to establish relationships among the geomechanical properties, well logs, and acoustic impedance values. We then applied these relationships to generate 3D geomechanical models constrained to seismic volumes. The resulting grid distributions illustrate the stratigraphic variability of the properties at the parasequence scale. Overall, brittle strata decrease in thickness and abundance basinward as the frequency of interbedded brittle and ductile zones increases and gradually transitions into thin calcite-cemented siltstones and clay-rich mudstones. Analysis of the production performance of selected horizontal wells drilled within the Mississippian strata indicates that the proportion of brittle and ductile rocks along the well path drilled and the drilled area vertical stacking pattern play a significant role in hydrocarbon production for these Mississippian units.