Wellbore monitoring tools are designed to monitor the condition of the wellbore itself in hydraulically isolating formations. For injection wells, wellbore conditions must be monitored in order to meet the Environmental Protection Agency’s standards for well integrity, and proper and safe well operation.1National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf The most common causes of well integrity issues are poor casing or cementing. Selection of high-quality cement, and proper well cleaning prior to the cement job support the important role of the casing in preventing potential migration of fluids.
Demonstrations of mechanical integrity are the most common means of demonstrating that there is no movement of fluids into or between underground sources of drinking water associated with injection wells. A mechanical integrity test or MIT is required before an injection well is put into service, and at specified time intervals thereafter. The testing frequency depends on federal and state regulatory requirements. The purpose of the MIT is to assure that the mechanical components of the well are functioning to protect the environment and human health.
An MIT consists of evaluating the internal and external integrity of the well. External mechanical integrity means there is no significant fluid movement through vertical channels adjacent to the injection well bore. A well has internal mechanical integrity, if there are no significant leaks in the well, and the mechanical components of the well function properly. This is typically tested by pressurizing the well under controlled conditions. In most states, tests must be witnessed by regulatory agency staff.
MIT Summary
- Description: Mechanical Integrity Tests monitor the condition of the wellbore to assure good well integrity.
- Benefits: Many tests are easy to interpret and inexpensive to perform. Tests such as the radioactive tracer survey can locate the depth of the leak within the wellbore.
- Challenges: Depending on the type of test, may only provide a demonstration at a single point in time. Some tests are expensive relative to others and may require long periods of investigation.
Application
The Archer Daniels Midland Company’s carbon storage project in Illinois involved application for two Class VI wells under the jurisdiction of the Environmental Protection Agency. As part of obtaining the permits for these wells, the company was required to include their plans to document and demonstrate well integrity before and during CO2-injection operations. During injection the company must continuously observe and record injection pressure, flow rate and volume, and the pressure on the annulus to determine if there are any leaks in the casing, tubing or packer. These activities are part of MIT requirements for these regulated Class VI injection wells.
