Schlumberger Carbon Services (SCS) and partners have identified leaky wellbores as an important risk to storage integrity that warrants further study to develop methods to quantify the risk of leakage in active and abandoned wellbores. This three-year project is working to develop methods for risk quantification that can be directly applied to individual wells using measurements from borehole logging tools. Models for leakage risk of wells can be developed that use collected data to establish the overall probability of leakage of a given well. Logging information is input into a model to evaluate the probability of leakage for specific zones in the well, e.g., the casing, cement, cemen tcasing interface, cement-formation interface, and any existing defects (Figure 1).
Through its core research and development program administered by the National Energy Technology Laboratory (NETL), the U.S. Department of Energy (DOE) emphasizes monitoring, verification, and accounting (MVA), as well as computer simulation and risk assessment, of possible carbon dioxide (CO2) leakage at CO2 geologic storage sites. MVA efforts focus on the development and deployment of technologies that can provide an accurate accounting of stored CO2, with a high level of confidence that the CO2 will remain stored underground permanently. Effective application of these MVA technologies will ensure the safety of geologic storage projects with respect to both human health and the environment, and can provide the basis for establishing carbon credit trading markets for geologically storing CO2. Computer simulation can be used to estimate CO2 plume and pressure movement within the storage formation as well as aid in determining safe operational parameters; results from computer simulations can be used to refine and update a given site’s MVA plan. Risk assessment research focuses on identifying and quantifying potential risks to humans and the environment associated with geologic storage of CO2, and helping to ensure that these risks remain low.
It will be necessary to improve existing monitoring technologies, develop novel systems, and protocols to satisfy regulations to track the fate of subsurface CO2 and quantify any emissions from reservoirs. The Carbon Storage Program is sponsoring the development of technologies and protocols by 2020 that are broadly applicable in different geologic storage classes and have sufficient accuracy to account for greater than 99 percent of all injected CO2. If necessary, the tools will support project developers to help quantify emissions from carbon capture, utilization, and storage (CCUS) projects in the unlikely event that CO2 migrates out of the injection zone. Finally, coupled with our increased understanding of these systems and reservoir models, MVA tools will help in the development of one of DOE’s goals to quantify storage capacity within ± 30 percent accuracy.
In anticipation of a large number of carbon storage sites starting in the next several years, it is important to understand the risk of CO2 leakage through existing wells. This project is leading to the development of a rigorous data set that can be used to understand well leakage probability and risk. In addition, this project may lead to the development of a down-hole tool and analytical method to determine the risk of well-bore leakage. This would improve the ability to assess the integrity of well-bores within mature oil and gas fields as part of any CO2 storage efforts. Model validation and calibration resulting in quantitative risk of leakage will have a significant impact on both the quality and uncertainty in site performance and risk models. A reduction in uncertainty will allow for better decisions on the use of resources to repair wells and determine appropriate MVA technologies.
The primary objective of the DOE’s Carbon Storage Program is to develop technologies to safely and permanently store CO2 and reduce Greenhouse Gas (GHG) emissions without adversely affecting energy use or hindering economic growth. The Programmatic goals of Carbon Storage research are: (1) estimating CO2 storage capacity in geologic formations; (2) demonstrating that 99 percent of injected CO2 remains in the injection zone(s); (3) improving efficiency of storage operations; and (4) developing Best Practices Manuals (BPMs).
The main goal for this project is to develop a new method to relate the risk of leakage of existing wells at CO2 geologic storage sites to data collected by tools used to non-destructively determine well cement integrity. This goal will help to demonstrate and ensure CO2 permanence in the subsurface. The data will be taken from existing wells that have not been exposed to CO2 in order to quantify the risk of leakage at the start of a project (prior to injection) and populate risk models. Supporting objectives include the following:
Develop methods to establish the average flow parameters (porosity and permeability or mobility) from individual measurements of the material properties and potential defects in a well.
Develop a correlation between field flow-property data and cement logs that can be used to establish the flow-properties of well materials and well features using cement mapping tools.
Establish a method that uses the flow-property model (previous objective) to analyze the statistical uncertainties associated with potential individual well leakage that can provide a basis for uncertainty in risk calculations.
Click to view Presentations, Papers, and Publications