Comparison and Analysis of Multiple Scenarios for Enhanced Geothermal Systems Designing Hydraulic Fracturing



Key Words:

hydraulic fracturing, enhanced geothermal system, proppants


Stanford Geothermal Workshop




Enhanced Geothermal Systems



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The Enhanced Geothermal Systems (EGS) has been identified as one of the Energy Systems that can support the effort in moving towards net-zero if properly studied and applied. The EGS is applied to produce electricity from very low permeability rocks and hot dry rocks geothermal resources. Generally, those reservoirs are usually located at 9000 ft to 18000 ft; and at a temperature above 150 °C. Principally, the energy is extracted to generate electricity using exergy and enhanced exergy tools after considering the environmental, economic, and exegetic life cycle of the identified Wells. The geothermal energy between the two wells is extracted by the circulating fluid through fractures. Those fractures are created through hydraulic fracturing treatment. Hence, hydraulic fracturing is the key technology in the enhanced geothermal system that helps capture geothermal energy. The potential resource size is huge, and the technology produces baseload, emission-free electricity in line with the net-zero aspirations. Currently, EGS is typically performed in a nearly vertical well, in some cases, water as a heat transporting fluid. The EGS community is focused on shear stimulation, injecting water to induce slip-on self-propping natural fractures. As a result, proppant is viewed as being unnecessary or ineffective; also, the use of packers to enable multiple stages is considered technically infeasible because EGS wells are completed open-hole to maximize connectivity to natural fractures, and reliable open hole packers are not available at high temperatures. However, In the past several years, the oil and gas industry has achieved radical improvements in stimulation performance by using multiple stages, proppant, and horizontal (or deviated) wells. For the most part, these technologies have not been adopted by EGS. This study designs a hydraulic fracturing model considering the creation of new fracture sets rather than stimulating natural fractures. In this design, a horizontal injector well is modeled and completed with cemented casing. Cased hole packers or bridge plugs are used for zonal isolation, allowing multiple-stage fracture treatments to be pumped through perforations in the casing. The purpose of this research is to study the feasibility of producing energy, creating permeable cracks by hydraulic fracturing, and evaluating the type of proppant and fracture fluids in different scenarios to determine the performance of an EGS reservoir involving flow rate between different scenarios. Hence, this study shows that an EGS design with multiple stages and proppant should improve economic performance relative to current designs. For hydraulic fracturing optimization, we design in the model the number and length of perforation clusters in each stage, proppant and fluid frac compatibilities, and optimum spacing. In our study, we aim to investigate the effects of varying fracture-cluster lengths, proppant types and sizes, and frac fluid types on hydraulic fracturing treatments using 2D and 3D simulation models. Finally, different scenarios are evaluated to understand if the hydraulic model is economically feasible in producing energy with the current electricity price, drilling cost, and hydraulic fracturing treatment.

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