Development of Downhole Measurement to Detect Inflow in Fractured Enhanced Geothermal Systems (EGS) Wells

Abstract

The ability to measure inflow from fractures formed after a stimulation is crucial to assess the success of Enhanced Geothermal Systems (EGS) wells. A downhole technique was proposed to detect and quantify inflows from individual fractures by measuring the chloride ion concentration along the wellbore. The technique is being developed in preparation for a field test at the Utah Frontier Observatory for Research in Energy (FORGE) site. Analytical calculations from a previous study were modified to suit the fractured EGS well configuration and expanded to consider the case of a well with multiple fracture zones. Measurement error stochastic modeling at a single feed zone (i.e., single fracture zone) shows 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 were conducted to reconfirm tool calibration from the previous study and obtain data for measurement error. Calibration results were qualitatively in agreement with the previous study, and the accuracy of the calculated chloride concentrations showed a promising result. Further calibration trials are planned to improve the accuracy of the voltage-chloride relationship. Finally, data collected from the Geothermal Data Repository (GDR) and previous studies were analyzed to plan for the field test. The analysis points to well 58-32 as the most suitable candidate to test the ruggedized wireline version of the chloride measurement tool. The ongoing work will further improve the analytical approach and laboratory experiments in preparation for the field test. In addition, the study will also perform numerical simulations using computational fluid dynamics to better understand the fluid mechanics of the fracture inflows within the wellbore.