Published December 20, 2022
By Christine Reed
The Center for Economic Geology Research (CEGR) in the School of Energy Resources (SER) completed mechanical testing at the Wyoming CarbonSAFE Project site located next to Basin Electric Power Cooperative’s Dry Fork Station near Gillette, Wyo.
Over the course of nine days, a collaborative team conducted Step Rate Testing (SRT) and Mechanical Integrity Testing (MIT) between two wells that were previously drilled to Class VI Carbon Capture, Utilization and Storage (CCUS) standards at the site, and have the potential to serve as Wyoming’s first commercial scale carbon dioxide (CO2) injection wells for permanent underground storage. The two wells are currently permitted as Class I wells and will need to be converted to Class VI prior to any CO2 being injected.
The testing is part of phase III of the project to fully characterize the site and increase the safety assurances associated with geologic sequestration.
SRT and MIT were conducted by injecting water into three targeted storage formations, namely the Minnelusa Formation, Hulett Sandstone, and Lakota Sandstone, from one of the wells, while monitoring the pressure response from the sensor installed in the other well. The resulting information established the fracture pressure, regional stress, and formation connectivity of each zone.
“One of the concerns about any sort of injection well is the possibility of triggering seismic activity or fracturing the formation, thereby compromising its integrity,” says CEGR Project Manager Zunsheng Jiao. “Through the mechanical testing we are injecting water at different injection rates to see how high the pressure could build up before it breaks the rock in order to determine the maximum injection pressure that we can later apply to CO2 injection.”
According to Jiao, water is used in the testing because it mirrors the behavior of super critical CO2 in its fluid state, so it provides an accurate simulation of both pressure response and fluid migration within the target reservoirs.
In addition to establishing a threshold for injection pressure, a second objective of the testing is to rule out any possibility of contaminating underground drinking water sources. Both are requirements by the Wyoming Department of Environmental Qualify (DEQ) for the approval of a Class VI permit.
“We start at a low injection rate and slowly increase the pressure, but we have to get approval from a DEQ representative before each incremental increase of pressure,” he says. “Additionally, we added an element to the solution that serves as a tracer within the injectant to provide us with data about the connectivity between the targeted storage reservoir and the lowest underground source of drinking water (USDW). That way we can see how it moves in the formation and be sure that it will not leak or interfere with the USDW aquifers.”
Tyler Harris, the Groundwater Program Principal in the Division of Water Quality at DEQ was either present or able to remotely monitor every step of the testing.
“This type of well testing, with two wells in such close proximity, allows a great opportunity for academia, industry, and the regulatory body to work together to gather data and knowledge that is not only pertinent to this project, but will also be useful for future projects and education regarding the subsurface geology of the Powder River Basin, Harris says.”
Step rate and mechanical integrity testing are important in determining the strength of the formation, but also assess that the mechanical components of the well function in a way that is protective of public health and the environment.
In order to do that, the team brought in experts from the Energy & Environmental Research Center (EERC) in North Dakota, and Carbon GeoCycle, Inc. to help oversee the testing and process implementation. Mechanical Engineer Larry Pekot of the EERC and Wade Bard, the Director of Subsurface Development with Carbon GeoCycle, worked to assess the equipment and mechanical performances, oversee the test procedure, and monitor the safety of the wells.
“The Wyoming CarbonSAFE project has been, and remains to be, a collaborative effort,” says CEGR Director Fred McLaughlin. “This was our first experience with MIT in storage wells and it only makes sense to bring in specialists. Our friends at the EERC provided substantial expertise and Wade has played an integral role in the success of this project from day one.”
One final exciting outcome from the testing is that the team simultaneously observed the efficacy of the surface monitoring system that was previously installed to detect any seismic activity below ground.
“Since we had already installed a geophone network around the two wells, any perforation activities in the well or break in the rock from the water test was recorded from the surface monitoring point,” explains Jiao. “This is very positive moving forward because we know that our long-term surface monitoring system functions well and we can differentiate between what is normal activity and what is an anomaly.”
The complete test results now mean that the team can start geomechanical modeling and ensure that any future injected CO2 will remain confined in the designated area as it moves within the reservoir. The team will also use the data collected to reduce seismicity and increase safety.
“Completing this testing was a massive undertaking and we are incredible grateful for all of the additional help that we had in accomplishing this milestone,” says Jiao. “We are now looking forward to providing an updated model of the subsurface that will eliminate any lingering gaps and increase the likelihood of success for large-scale, underground carbon storage in Wyoming.”