Three-dimensional geological modelling of the lithofacies of Caddo Limestone in Stephens County, North-Central Texas

Abstract

The Pennsylvanian (early Desmoinesian) Caddo Limestone in Stephens County, Texas hosts important reservoirs and hydrocarbon resources. Therefore, constructing a three-dimensional geological model of the Caddo Limestone is of great significance. The Caddo Limestone Formation comprises shelf carbonate build-ups in which the major allochems are phylloid algal and Komia. This study focuses on the uppermost two cycles of the Caddo Limestone. This study integrated geological, geophysical and petrophysical analysis to build a three-dimensional geological model of the Caddo Limestone. The model is based on 18 cores (totalling 700 ft long), wireline logs from 173 wells and 3-dimensional seismic data. A 3D structure model derived from 3D seismic data and 3D geocellular model of lithofacies are the two key products of this study. Five lithofacies have been differentiated: (1) Komia wackestone and mud-dominated packstone, (2) Phylloid-algal wackestone and packstone, (3) Bioclastic wackestone to packstone, (4) Komia grainstone and grain-dominated packstone, and (5) Komia boundstone. An artificial Neutral Network (ANN) algorithm was applied to predict lithofacies in wells without core samples. The lithofacies were extrapolated within the geocellular model using indicator Kriging. This work demonstrated a viable workflow to build 3D reservoir models of Paleozoic carbonate mound reservoirs.