Leveraging 3-D Seismic Attributes for Constructing Geocellular Models of Complexly Stratified Icehouse Reservoirs

For legacy fields, geologists are too often reluctant to revise the stratigraphy once the reservoir zonation has become fully entrenched in spite of advancements in depositional models and 3-D seismic. This study disregards the reservoir zonation established in the mid-20th century for the Carboniferous–Permian Horseshoe Atoll of West Texas, (USA) and instead relies upon mutually supportive observations from core descriptions, PSDM seismic, fusulinid biostratigraphy, and stratal configurations from outcrop analogs to build a seismically guided and geologically sensible dual-permeability sector model (16 sq km) for Occidental’s Sharon Ridge Unit. Many fields within this 4+ BBBL trend are undergoing capital-intensive tertiary recovery and increasingly rely upon reservoir simulations to optimize CO2 pattern floods, forecast production, and prioritize CO2 allocation.

The Horseshoe Atoll was deposited during peak eustatic amplitude fluctuations and records complex and variably dipping stratal patterns consisting of phylloid-crinoid mounds, bank-top ooid bars, and slope debrites and turbidites that are overprinted by syndepositional faults/fractures and karst. Presented here, is a new internal reservoir zonation built from 3-D seismic interpretation of zero crossings from the amplitude volume combined with six Missourian–Wolfcampian fusulinid zones identified during core descriptions. Facies models were constructed using multi-point simulation of seismically sculpted geobodies and probability relationships based on facies proportions and cell-distance from mound core. The petrophysical models are spatially constrained by the facies model and an inversion-based seismic porosity attribute. Simulation models derived from these fine-scale seismically guided geocellular models reduced history matching studies from 1 year to 2-months providing production-based validation of seismically constrained geobodies.