We present an integrated approach to monitoring long-term wellbore integrity based on measurement of passive and active seismo-acoustic signals and stress changes in the near-wellbore region. Our goal is the development of an autonomous system that can be deployed in wells for long- term (e.g., decades), unattended monitoring both wellbore integrity and associated stress changes. Our signal target is threefold: (i) small seismo-acoustic signals associated with moving (leaking) fluids; (ii) the stress field along the wellbore where changes in stress may presage damage and leakage; (iii) nonlinear properties in the near-wellbore region that arise when damage develops and progresses. We envision an autonomous system consisting of both wellhead and downhole components based on the combined signals of piezoelectric and/or optical sensors integrated with innovative strategies for both source generation and data analysis. Our approach is based on our extensive work in four areas: (i) the physics of time reversal (TR) to focus acoustic energy, allowing interrogation of material properties locally; (ii) nonlinear elastic wave spectroscopy to probe damage in materials; (iii) the measurement and interpretation of seismo-acoustic signals, including recent work focused on extracting very small signals; and (iv) the characterization of in situ strains and stresses. The final system would entail autonomous, passive monitoring for changes in the local characteristics of both stress/strain field and seismo-acoustic noise, with periodic use of active monitoring (TR NEWS) to probe local changes in elastic properties tied to damage.
