Development of Multi-Stage Fracturing System and Wellbore Tractor to Enable Zonal Isolation During Stimulation and Enhanced Geothermal System Operations in Horizontal Wellbores - First Year Progress
Authors: Fleckenstein W. W. , Kazemi H. , Miskimins J. L. , Eustes A. W. , Abdimaulen D. , Mindygaliyeva B. , Uzun O. , Amini K. , Hill T. , Mailand J. , Henschel R. , King G. , Ortiz S. , Keyes C. 
Published: October 2023

This paper describes first year’s progress on the three-year DOE funded project for the development of tools for the construction of a subsurface heat exchanger for Enhanced Geothermal Systems (EGS) at the Utah-FORGE site using unique casing sleeves that are cemented in place in horizontal wells. The sleeves function both as a system for rapid and inexpensive multi-stage stimulations and then are used to perform conformance control functions at 225 °C. A tractor uses modular capabilities to allow various tools and sensor packages to be attached with standard connections for flow conformance control of the system.

The original hydraulic tractor concept using coiled tubing was replaced with an electric wireline design to improve operating costs by not requiring coiled tubing. A flask design for critical electronic components was identified as a solution to the 225 °C wellbore conditions, eliminating the need for circulation of water for cooling the electronics. This high temperature tractor was developed using an electric wireline design with a fluid survey capability to detect fluid injection and production and allow closing or opening of the sleeve for fluid movement. Modeling was performed for determining temperature impacts on the tools, the effectiveness of well stimulation (pressure transient analysis, tracer flowback and inter-well analysis, heat gathering and transport to the surface.

The 7-inch frac sleeves were tested using single-sized 5-¾-inch frac balls to simulate conditions of cemented sleeves run on 7-inch, 38 ppf casing to actuate for fracture stimulation at ambient and 225 °C geothermal conditions. The sleeve components were first tested in hydraulic test fixtures followed by surface flow loops and are being prepared for a test deployment in an extended reach geothermal test well at Utah FORGE. The high temperature. electric wireline wellbore tractor’s specific mission critical components were tested to 225 °C for a 12-hour duty cycle, using flask heat protection for critical electrical components. Test results indicate that a simple cemented valve can be used for both multi-stage hydraulic fracturing and conformance control. The use of this valve with the electric wireline tractor will allow an economic subsurface heat exchanger to be constructed.

Two critical EGS well stimulation and operation technology gaps are addressed by these tools. First, development of multi-stage stimulation technology tools which do not have temperature limitations of the conventional "Plug and Perf" stimulation equipment. These tools are designed to be cemented in place. Second, EGS conformance control methods are demonstrated using a wireline tractor operable to 225 °C to detect fluid flow and close the same multi-stage stimulation sleeve. These tools allow an EGS system to be constructed to provide geothermal electric power.