Geomechanical Modeling to Predict Wellbore Stresses and Strains for the Design of Wellbore Seal Repair Materials for Use at a CO₂ Injection Site

Abstract

This paper presents results of three models simulating the hydrological-mechanical behavior of a CO₂ injection reservoir and the resulting effects on wellbore system (cement and casing) and seal repair materials. A critical aspect of designing effective wellbore seal repair materials is predicting thermo-mechanical perturbations that can compromise seal integrity. Three distinct computational models comprise the current modeling effort. The first model depicts bench-top experiments of an integrated seal system in an idealized scaled wellbore mock-up being used to test candidate seal repair materials. This model will be used to gain an understanding of the wellbore microannulus compressibility and permeability. The second is a field scale model that uses the stratigraphy, material properties, and injection history from a pilot CO₂ injection operation to develop stress-strain histories for wellbore locations from 100 to 400 meters from an injection well. The results from these models are used as input to a more detailed model of a wellbore system. The 3D wellbore model examines the impacts of various loading scenarios on a wellbore system . The results from these models will be used to estimate the necessary thermal-mechanical properties needed for a successful repair material.

1. INTRODUCTION

A critical aspect of designing effective wellbore seal repair materials is predicting thermo-mechanical perturbations in local stress that can compromise seal integrity. For applications associated with CO₂ sequestration, the stress-strain history of abandoned wells, as well as changes in local pressure, stress, and temperature conditions that accompany carbon dioxide injection or brine extraction are of interest. Building on existing thermo-hydro-mechanical (THM) finite element modeling of wellbore casings subject to significant tensile and shear loads, we have been developing advancements to a conceptual and numerical methodology to assess responses of annulus cement and casing. The experimental component utilizes bench-top experiments of an integrated seal system in an idealized scaled wellbore mock-up to test candidate seal repair materials [1, 2]. These bench-top experiments have been modeled with bench-scale numerical models to identify and evaluate the essential hydrologic and mechanical properties of the candidate sealants. Field scale models using the stratigraphy from a pilot CO₂ injection operation can be used to estimate the necessary mechanical properties needed for a successful repair material [2, 3].