Predicting Lithology-Controlled Stress Variations in the Woodford Shale from Well Log Data via Viscoplastic Relaxation

Abstract

Summary We report here a study of lithology-controlled stress variations observed in the Woodford shale (WDFD) in north-central Oklahoma. In a previous study, we showed that the magnitude of the minimum horizontal stress Shmin systematically varied with the abundance of clay plus kerogen in three distinct WDFD lithofacies. In this study, we demonstrate that it is possible to quantitatively estimate the observed stress variations using elastic properties determined from well logs as proxies for laboratory-inferred parameters via a relatively simple viscoplastic constitutive relationship. The modeled variations of Shmin along the two horizontal wells that encounter the three lithofacies along their respective well trajectory are in good agreement with measured values obtained from multistage hydraulic fracturing (HF). We believe that the application of the workflow described here in the context of viscoplastic stress relaxation can facilitate the understanding of layer-to-layer stress variations with lithology and thus contribute to improved HF effectiveness.