Stress Inversion via Borehole Image Log and Fracturing Data: Integrated Approach

Abstract

The mechanical behavior of geological formations impacts the exploration, development, production, and storage of oil and gas in the subsurface via wellbore and reservoir scale phenomena such as wellbore stability, compaction and subsidence, fault reactivation, sand production, and hydraulic fracturing. The behavior can be represented in a geomechanical model whose requirements depend on the complexity of the problem to be solved. However, regardless of whether the problem is addressed with a simple quick-look analysis or more complex and advanced analysis, the in-situ stress state is a common input requirement. More specifically, accurate estimation of in-situ stress magnitude and direction is a prerequisite for robust and reliable geomechanical analysis. A variety of methodologies have been proposed for determining the in-situ stress field. Nevertheless, some limitations need to be addressed for a successful application. For example, some methods require data from different wellbores in the same area at the same depth, and some methods either do not address the non-uniqueness of the solution altogether or do so within a limited context.

The focus of this study is to eliminate the solution limitations by combining fracturing and image log data for determining the complete stress field using data from a single wellbore. Fracturing data (e.g., leak-off tests) and image log information (i.e., tensile fracture characteristics) are utilized to determine the in-situ stress field using a novel inversion algorithm capable of efficiently sampling from the complete in-situ stress solution set conforming to the input data and satisfying a priori domain constraints.

Introduction

Geomechanical models quantify mechanical behavior of geologic formations which, in turn, influences the exploration, development, production, and storage of oil and gas in the subsurface. This includes wellbore and/or reservoir scale phenomena such as wellbore stability, wellbore strengthening, hydraulic fracturing, compaction/subsidence, fault reactivation, discrete network stimulation, sand production and proppant embedment, among others. Each geomechanical model is unique, and model requirements depend on the complexity of the problem. For example, geomechanical models can involve simple and quick-look techniques (e.g., 1D log analysis) or more complex and advanced analysis (e.g., 3D mechanical earth models). Regardless of the complexity of the analysis, in-situ stress state is a common input parameter to all geomechanical models. That is, an accurate estimation of the in-situ stress magnitude and direction is a prerequisite for a robust and reliable geomechanical analysis.