Civil Engineering ETDs

Publication Date

Summer 8-1-2023

Abstract

Leakage from wellbores has been a major challenge in the energy industry, leading to groundwater contamination, reduced productivity, safety hazards, and increased operating costs. Cemented annulus fractures are a common type of leakage pathway in wellbores that can form due to various physical and chemical conditions. The number of wellbore leaks continues to increase globally, making it imperative to develop a better understanding of the complex mechanisms governing fluid flow through fractured wellbore cement. Understanding the behavior of fluid flow through a leaky cemented annulus is crucial for evaluating the leakage potential and risk assessments in wellbore systems, as well as designing effective repair methods. This research aims to provide a comprehensive investigation of fluid flow through leaky cemented annulus and the impact of various factors, including visco-inertial flow, effective stress, and shear displacement on the permeability of wellbore cement fractures and the resulting leakage behavior. The study addresses specific aspects of fluid flow through fractured wellbore cement using laboratory experiments and numerical simulations which are presented in Chapters 2, 3 and 4. Each of these chapters represents a standalone manuscript which is prepared for publication as a journal article.

Chapter 2 investigates the conditions that require considering visco-inertial flow for describing fluid flow through wellbore cement fractures. Through a series of gas flow experiments on fractured cement samples under varying pressure conditions and flow rates in a triaxial cell, it was shown that at higher flow rates the data significantly deviated from viscous flow and was more accurately described by visco-inertial flow.

Chapter 3 evaluates the permeability of a wellbore cement fracture under different combinations of confining stress and pore pressure. The results showed a mode of fracture permeability change, which is the propping open of the fracture due to pore pressure increase. Results from Chapter 3 show the significance of accounting for effective stress in evaluating the effective permeability of fractured cemented annulus and predicting the leakage.

Experiments described in Chapter 4 show another mechanism of fracture change, which is shear slip under increased pore pressure in favorably oriented wellbore cement fractures. The fracture permeability was found to decrease with shear displacements due to accumulation of wear products in the fracture. Findings from each chapter’s experiments were incorporated into numerical simulations of a field-scale fractured wellbore system to estimate the impact of these factors on fluid flow under practical conditions of external stress and internal pressure. The results emphasize the importance of considering visco-inertial flow, effective stress and shear slip when describing fluid flow through a fractured cemented annulus and evaluating the effective permeability of the leaky wellbore.

Keywords

Underground storage, Wellbore leakage, Cement fracture, Fluid flow

Sponsors

Sandia National Laboratories

Document Type

Dissertation

Language

English

Level of Degree

Doctoral

Department Name

Civil Engineering

First Committee Member (Chair)

John C. Stormont

Second Committee Member

Mahmoud Reda Taha

Third Committee Member

Svetlana Poroseva

Fourth Committee Member

David L. Lord

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