Wells used to inject CO2 and monitor carbon storage sites are completed with cement and steel piping that is designed to seal the wellbore and eliminate pathways for the CO2 to migrate out of the storage formation. These seals can be compromised if voids are present or the steel or cement degrades and cracks, necessitating methods to repair leakage pathways that can potentially facilitate migration of CO2. Researchers at the University of New Mexico (UNM) are examining ways to repair leakage pathways by modifying polymer cements with various nanomaterials to produce polymer-cement nanocomposites that have superior repair characteristics compared to conventional materials. The first phase of this research effort involves modifying polymer-cement slurries with various nanomaterials to increase their long-term performance in preventing CO2 leakage through the wellbore. Bond strength and fracture toughness testing will be conducted on the repair material bonded to the steel and cement. The slurries will be evaluated at the macroscale to determine their rheological properties, bond strength, fracture toughness, permeability, and durability against CO2 and brine water containing CO2 (Figure 1). Microstructural investigations of these nanocomposites will beconducted using nuclear magnetic resonance, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, and nanoscratch tests. The second phase involves testing the ability of select nanocomposite materials developed in the first phase to repair simulated flawed seal systems (Figure 2). Seal systems, composed of a casing (well pipe) set into a sheath of conventional well cement, will be created and various flaws (voids and fractures) will be incorporated into the cement and the cement-casing interface (corroded casing and artificially de-bonded interfacial regions). The samples will be placed in a pressure cell that mimics the pressures and temperatures found at CO2 storage depths and repair effectiveness will be measured. Post-test samples also will be examined for repair effectiveness and bond testing. The outcome will be an evaluation of the ability of the nanocomposite materials to repair flaws within the wellbore. The ability of the repair material to withstand supercritical CO2 will also be tested using a specialized system capable of delivering mixtures of CO2 and water at high pressures and specified flow rates.
The overall goal of the Department of Energy’s (DOE) Carbon Storage Program is to develop and advance technologies that will significantly improve the effectiveness of geologic carbon storage, reduce the cost of implementation, and prepare for widespread commercial deployment between 2020 and 2030. Research conducted to develop these technologies will ensure safe and permanent storage of carbon dioxide (CO2) to reduce greenhouse gas (GHG) emissions without adversely affecting energy use or hindering economic growth. Geologic carbon storage involves the injection of CO2 into underground formations that have the ability to securely contain the CO2 permanently. Technologies being developed for geologic carbon storage are focused on five storage types: oil and gas reservoirs, saline formations, unmineable coal seams, basalts, and organic-rich shales. Technologies being developed will work towards meeting carbon storage programmatic goals of (1) estimating CO2 storage capacity +/- 30 percent in geologic formations; (2) ensuring 99 percent storage permanence; (3) improving efficiency of storage operations;and (4) developing Best Practices Manuals. These technologies will lead to future CO2 management for coal-based electric power generating facilities and other industrial CO2 emitters by enabling the storage and utilization of CO2 in all storage types. The DOE Carbon Storage Program encompasses five Technology Areas: (1) Geologic Storage and Simulation and Risk Assessment (GSRA), (2) Monitoring, Verification, Accounting (MVA) and Assessment, (3) CO2 Use and Re-Use, (4) Regional Carbon Sequestration Partnerships (RCSP), and (5) Focus Area for Sequestration Science. The first three Technology Areas comprise the Core Research and Development (R&D) that includes studies ranging from applied laboratory to pilot-scale research focused on developing new technologies and systems for GHG mitigation through carbon storage. This project is part of the Core R&D GSRA Technology Area and works to develop technologies and simulation tools to ensure secure geologic storage of CO2. It is critical that these technologies are available to aid in characterizing geologic formations before CO2-injection takes place in order to predict the CO2 storage resource and develop CO2 injection techniques that achieve optimal use of the pore space in the reservoir and avoid fracturing the confining zone (caprock). The program’s R&D strategy includes adapting and applying existing technologies that can be utilized in the next five years, while concurrently developing innovative and advanced technologies that will be deployed in the decade beyond. For this project, researchers are developing and testing new materials to repair flaws (voids, fractures, degraded interfaces) in seal systems in wellbores penetrating formations used for the geologic storage of CO2. The project is making a vital contribution to the scientific, technical, and institutional knowledge base needed to establish frameworks for the development of commercial-scale carbon capture and storage (CCS). Maintaining the seal integrity of abandoned wellbores is central to ensuring permanent storage of CO2 in geologic formations. This project will identify repair materials that improve upon conventional wellbore repair materials. This will help to ensure hydraulic isolation of the wellbore, reducing the risk of release of CO2 around the well casing and cement. Permanent storage of CO2 within the identified formation is one of the key goals of the CO2 storage research efforts. The technologies developed in this project will contribute to the DOE’s effort to ensure that 99 percent storage permanence.
Objectives The objective of this project is to develop and test new materials for repairing flaws and restoring seal integrity to wellbores that penetrate formations used for CO2 storage. Polymer cement slurries will be modified with various nanomaterials to produce nanocomposites that have superior seal repair characteristics—particularly for sealing the cement-casing interface—compared to conventional materials. The objectives of this project will be achieved through a combined research and analysis effort that includes:
Developing seal repair materials suitable for the expected wellbore environments that have acceptable viscosity and setup time, high bond strength to casing and cement, low permeability, and high ductility and fracture toughness (resistance to crack growth). The project will focus on the development of new polymer-cement nanocomposites and the evaluation of their rheological properties.
Evaluating the effectiveness of these materials to repair flaws in large lab-scale annular seal systems (casing set inside a sheath of cement) that are subjected to the temperatures, pressures, and fluids expected under CO2 storage conditions. The project will compare the bond strength, fracture toughness, and durability of these improved repair materials with that of conventional repair materials.
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