An Integrated Approach to Constrain In-Situ Stress Field: Comprehensive Geomechanical Analysis

Abstract

The in-situ stress field could govern the mechanical response of a formation to drilling, stimulation, and depletion. Therefore, the in-situ stresses are essential input parameters for all geomechanical analyses, regardless of the complexity of the problem. The determination of in-situ stresses should include both the magnitude and direction of all the principal stress components. An accurate estimation of the in-situ stress field is a prerequisite for a robust and reliable geomechanical analysis.

In this work, an integrated approach is used to constrain both minimum and maximum horizontal stresses (including both magnitude and direction) by using the data from a single well. Within the framework, the combination of fracture injection test and image log analysis is used to constrain and calibrate the in-situ stress components and minimize uncertainties.

Using the proposed workflow, a series of geomechanical analyses is performed to quantify the impact of in-situ stress uncertainty in geomechanical modeling and analysis used in different design applications. The geomechanical analyses include critically stressed fracture analysis, hydraulic fracture modeling (i.e., near wellbore initiation and far-field propagation), and discrete fracture network reactivation (i.e., induced micro-seismicity).

The analysis confirms that by using the integrated stress-field-determination approach, the uncertainty of in-situ stress magnitude and direction can be reduced and the reliability of geomechanical model predictions can be enhanced. The accurately constrained in-situ stress field could be utilized in different geomechanical models and analysis—including wellbore stability, hydraulic fracturing, wellbore placement, depletion-/injection-induced stress changes, and corresponding production forecast—to improve the overall efficiency of the field operations and development.

1. INTRODUCTION

During exploration, stimulation and production, in-situ stress field is routinely monitored, measured and used in the oil and gas industry. The in-situ stress field is composed of three principal components (vertical and two horizontal components). The vertical stress is generated by the gravity of the overburden rock. The two horizontal components are caused by the Poisson effect and poroelastic deformation of the confined formation upon the overburden loading acting on top of the target layer or zone. The tectonic forces acting on the perimeter of the formation could change and even make the in-situ stress condition more complex. As a result of the regional tectonic activities and reservoir heterogeneity, the magnitudes of the two horizontal components are usually unequal, the difference between which is termed as stress anisotropy in horizontal direction.