Understanding Enhanced Geothermal Systems
GTO Technology’s Principal System
The foundational technologies that will be commercialized by GTO Technologies is the patented system & equipment that is designed to create, then control the flow distribution of a massive subsurface heat exchanger created by EGS wells (US Patent 1,1959,666).
This subsurface architecture can also be used for subsurface solution mining, with the ability to control the injection of solvent in areas of the resource with the greatest opportunity for high grade solute recovery.
In addition to the process patent, GTO Technologies has sole rights to the two issued patents that cover the “FracOPTIMAL” sleeves and gives GTO Technologies a competitive advantage including: 1) the sliding frac sleeve (FracOptimal Sleeve) itself that enables multistage stimulation and conformance control, and 2) the use of sliding sleeves to fracture stimulate the resource rock and then using the same sleeve to manage the injection rates into individual induced fractures. This minimizes thermal decline by either positioning the sleeve to a fully open position, flow regulator position or a shut off position. Additionally, GTO Technologies also has helped develop a high temperature tractor for the production/injection logging of horizontal wells at geothermal temperatures to understand the injection pattern then provide the ability to manipulation sleeves to the desired position.
These technologies and patents allow for the only system on the market that allows for both the creation of the EGS system’s fracture network and the regulator system for conformance control to be installed without reduction of the original casing diameter. This system reduces parasitic losses by over 2 times!
These technologies were developed and rigorously tested as part of a $5.3 million DOE grant to the Colorado School of Mines, of which Dr. Fleckenstein was the Principal Investigator.
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Selecting the Correct Sleeve and Actuating It for the Stimulation
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Using the Tractor to Position the Sleeve (Open/Closed/Regulated)
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Alternatives to Create and Control the EGS
In order to first create and then control the subsurface heat exchanger, two or more wells must be drilled in close proximity, to sufficient depth to achieve the desired heat (>400 F), and at a near horizontal angle. The wells must then be interconnected through a fracture stimulation. Once interconnected the flow through the fractures must be regulated to ensure the flow rate down each fracture is as consistent as possible. This is referred to as conformance control.
Currently the only two systems on the market allow for numerous, sequential fracture stimulations to connect the horizontal wells are GTO Technologies’ process using frac sleeves and “Perf & Plug”.
The “Perf & Plug” system is the preferred system for shale and tight development. It consists of perforating the pipe in 1-3 clusters of perforations and fracture stimulating the clusters in one pumping stage. Once the stage is completed, a bridge plug is set above the clusters and the process is repeated for the desired number of stages. The problem with “Perf & Plug” is once the holes are cut through the pipe using shape charges, the only proven alternative to achieve conformance control is to run an expensive inner-string with a set of packers for each stage and outflow control devices set between the packers. This is problematic for two reasons. First the cost and reliability risk of the extreme temperature packers set between each stage will be significant. Second, the reduction in diameter from casing to injection tubing will result in large frictional pressure increases, requiring significant increases in electrical usage to run the injection system pumps, decreasing the electricity available to be sold at a premium as carbon free energy. The electricity used to circulate water through the system is referred to as parasitic losses.
A standard producer-injector pair, which is designed to have a 1-mile lateral length, 7″ casing through the reservoir, and generate 5MW of electricity will typically require 50,000 BWPD to be circulated through the system. To move this amount of fluid will require 1.1 MW of electricity, thus generating 3.9 MW of salable electricity. This difference is the parasitic losses.
Once an inner string is run inside of the original casing to provide conformance control for a “Perf & Plug” system, the frictional loads begin to overwhelm the system. To circulate the same fluid using a 4″ conformance string across the reservoir will result in parasitic loads increasing to 2.4 MW leaving only 2.6 MW of salable electricity!