| Title | Results of the Vertical Electromagnetic Profiler (VEMP) Survey at the Utah FORGE Site |
|---|---|
| Authors | David ALUMBAUGH, Michael WILT, Edward NICHOLS, Evan UM, Kasumi OSATO, Takashi OKABE, Masami HYODO, Keith PICKET, and Noah PERKOVICH |
| Year | 2025 |
| Conference | Stanford Geothermal Workshop |
| Keywords | electromagnetic, geophysics, logging |
| Abstract | This paper will discuss the recent deployment of the three-component Vertical ElectroMagnetic Profiling (VEMP) borehole magnetic field measurement tool at the Utah FORGE site, the goal of which was characterizing the size and porosity of the stimulated geothermal reservoir. The VEMP tool contains a three-component magnetic field sensor with primary sensitivity between 1 and 128 Hz, and was specifically designed for high temperature borehole deployment and subsurface imaging in geothermal wells. The survey configuration involved deploying the VEMP tool at the bottom of the ~3km deep 78-32B monitoring well and making measurements while electrically energizing injection well (16A) with an electrode at approximately 1.3km feet depth and a return electrode located on the Earth’s surface about 1 km to the north of the 16A well head. Because the LBNL high temperature logging truck was not ready for deployment prior to the April 2024 stimulation, only post-stimulation data were collected. The tool was extensively tested on the surface at FORGE prior to the survey and initially performed well in the shallower sections of the well. However, as the tool was lowered deeper into the borehole into pressure and temperature regimes that is could not be tested in, it failed several times requiring acquisition system modifications to be made on the fly. More importantly, we found that the incoming data became noisier and noisier with greater depth and temperature, eventually requiring some 20 minutes to collect a single data point. The cause of the poor data quality was uncovered in post survey tool evaluation where a connector was discovered that used low temperature solder. This intermittent connection would not be apparent at lower temperatures but the solder joints would melt at temperature above 180C causing a number of data issues. In the end 10Hz amplitude and phase measurements of the vertical magnetic field were collected at 30m to 40m increments over a profile extending from approximately 2200 to 2600m depth. The paper will outline the positives and negatives of the survey, highlight the data quality that was achieved through a comparison with numerical modeling results, will discuss how we plan to use the data in a multi-physics interpretation workflow, and provide learnings for future high-temperature logging tool development. |