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Inflow Measurement in Geothermal Wells Based on Chloride Concentration (2021-2024)

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Investigators: Luthfan Hafizha Judawisastra, Sarah Sausan

This is a joint project with Sandia National Laboratory, and is part of the Utah FORGE project supported by the US Department of Energy.

The ability to measure inflow from fractures formed after a stimulation is important to assess the success of geothermal wells. This measurement is also useful in understanding the fracture inflow evolution throughout the well lifetime. In this study, a downhole measurement technique was proposed to infer inflows from individual fractures by measuring chloride ion concentration of geothermal fluid along the wellbore. Expanding from a previous study based on a chloride measurement tool developed by Sandia National Laboratory, an analytical calculation was designed to suit fractured well configurations and multiple feed zones. Early result of error stochastic modelling suggested that measurement error may adversely affect the accuracy of flow rate estimates at and below a feed zone, although less so above a feed zone. Laboratory experiments confirmed that chloride measurement errors may occur due to the uneven mixing of geothermal fluids along the production zones depths, and suboptimal placement of the chloride measurement tool. Two different locations of blind spots were observed during dye tracer tests, i.e., above the feed zone inlet and around a half-diameter behind the inflow path. Numerical flow simulations were able to replicate the flow behavior observed in the laboratory experiments, including mixing zone blind spots, downward volume distribution, and a periodic turbulence causing the fluid flow path to alternate between a curved path and straight. The proposed technique is being developed in preparation for a field test at the Utah Frontier Observatory for Research in Energy (FORGE) site.

Experimental measurements using the Sandia probe in the lab at Stanford (left), and numerical simulation results (right) looking for distribution of inflowing chloride ions. The blue dye is used to assist the lab personnel visualize the inflow.