Enhanced Geothermal Systems Projects and its Potential for Carbon Storage

Techno-economic assessment of repurposing oil & gas wells for Enhanced Geothermal Systems: A New Mexico, USA feasibility study

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 204097, “Constructing Deep Closed-Loop Geothermal Wells for Globally Scalable Energy Production by Leveraging Oil and Gas Extended-Reach Drilling and High-Pressure/High-Temperature Well-Construction Expertise,” by Eric van Oort, SPE, Dongmei Chen, SPE, and Pradeepkumar Ashok, SPE, The University of Texas at Austin, et al. The paper has not been peer reviewed. _ In the complete paper, deep closed-loop geothermal systems (DCLGS) are introduced as an alternative to traditional enhanced geothermal systems (EGS) for green energy production that is globally scalable and dispatchable. The authors demonstrate that DCLGS wells can generate power on a scale comparable to that of EGS. They also highlight technology gaps and needs that still exist for economically drilling DCLGS wells, writing that it is possible to extend oil and gas technology, expertise, and experience in extended-reach drilling (ERD) and high-pressure/high-temperature (HP/HT) drilling to construct complex DCLGS wells. Introduction CLGS is considered a subset of EGS, but the authors write that it is a distinct entity. EGS mostly involves well designs that rely on fractures for heat extraction. Such systems are different from CLGS wells in that the latter use closed conduits for thermal fluid circulation and heating. CLGS relies on fluids pumped through a closed loop. The authors treat CLGS systems as being different from EGS systems, with the understanding that drilling technologies discussed in the paper as enablers for CLGS wells apply equally to EGS wells. In the geothermal (GT) domain, the majority of attention and funding currently is assigned to EGS projects. A case is made in the complete paper to continue to develop DCLGS technology because of its favorable risk profile compared with EGS. Part I of the complete paper introduces a hydraulic model coupled with a thermal model suitable for calculating the power generation of DCLGS wells. This synopsis concentrates instead on Part II of the complete paper, in which technology gaps and needs of DCLGS drilling and well construction are highlighted and opportunities identified where oil and gas experience and technology can be directly applied and leveraged. Similarities and Differences of Deep GT and Oil and Gas HP/HT Wells - GT wells generally use larger production hole sizes than typical land wells. - Casing-cement annuli typically are cemented back to surface. - GT wells can be drilled in more-forgiving pore-pressure fracture gradient (PPFG) environments with wider drilling margins than geopressured HP/HT wells in hydrocarbon systems. - Severe lost circulation appears to be a universal problem in deep GT wells. - Drilling costs can account for 50% or more of the total capital costs for a GT energy project. - Data sets on GT wells are much smaller than those for oil and gas wells.

ABSTRACT: Geothermal energy exploration and production has a long history of inducing seismicity, both beneficial and disastrous. Seismicity is common in naturally occurring geothermal systems as they often are co-located in areas with high strain rates, low permeability but fractured rocks, and a shallow brittle-ductile transition. These conditions generally limit the maximum magnitudes of earthquakes, whether tectonic or induced. Furthermore, seismicity often aids in the identification of prominent fluid and heat pathways within the geothermal resource. Engineered or Enhanced Geothermal systems (EGS) need not be located in geologic settings akin to conventional geothermal resources and, thus, may have unknown fault and fracture locations and extents owing to lower tectonic seismicity prior to exploration and thicker crust increasing the likelihood of larger magnitude seismicity. Several EGS projects have experienced earthquakes during the exploration portion of the projects that caused significant damage, e.g. Basel, Switzerland (2006) and Pohang, South Korea (2017). Other more recent EGS projects have experienced little seismicity of concern for the safe operation of reservoir development, e.g. Milford, Utah (2022) and Blue Mountain, Nevada (2022). Both sites benefited from experience gained in previous EGS projects, extensive site characterization, and adherence to Best Practices developed in response to earlier unsuccessful projects. In all cases, probabilistic seismic hazard analyses (PSHA) are crucial steps during planning and stimulation. These generally include a variety of models that can range from simple relationships between expected seismicity and injected volume to detailed geomechanical models of resulting seismicity. Aseismic deformation is seldomly accounted for, although recent research suggests it plays a significant role in the deformation in geothermal resources. Here I will discuss the inclusion of deterministic reservoir models in standard PSHA models and focus on the effects of aseismic deformation in geothermal and EGS settings. Continual improvement in PSHA and reservoir exploration and stimulation that are part of EGS development can ensure that the vast potential of EGS can be unlocked safely.

The technical and economic successes of deep geothermal development rely on reducing drilling and completion risks. In the closely related oil and gas activities, the risk taken by the investors is balanced by the high reward that successful projects achieve by immensely offsetting the losses of the failed wellbores. Geothermal projects experience similar risks, however, the potential reward is limited by the competition with other energy sources, in a heavily regulated market. The economic acceptability of geothermal power generation requires low risk drilling and completion technologies that would work under many different geological conditions. When wells are drilled into a petro-thermal formation, sometimes referred to as hot dry rock (HDR), there is normally no clear circulation path between these wells and when this path exists, the transmissivity is so low that no economical project is possible. Enhanced geothermal systems (EGS), in these circumstances is closer to reservoir creation than to conventional reservoir stimulation. Therefore, developing technologies that achieve the designed EGS size and transmissivity is vital to deep geothermal development. The EGS becomes a viable proposition, when enough rock surface can be contacted by the geothermal fluid, and when the flow path runs smoothly through a sufficient rock volume to minimize the energy depletion and have the project running over a long period, compatible with a positive net present value (NPV). To that end, the well design and its completion system have to be engineered to maximize the chances of properly creating the EGS. In this paper, lessons learnt from past geothermal experience are reviewed and analysed to propose a multi-stage system as a mean of improving geothermal wells completion reliability. Current oil and gas (namely "unconventional") completion technologies related to multi-stage stimulation have been reviewed and different options are discussed in the scope of a deep geothermal hot dry rock project. While previous works conclude that technologies developed for oil and gas are readily available and applicable to deep geothermal projects and EGS (Gradl, 2018), this study shows that shortcomings exist and that further developments are necessary to reliably and economically complete EGS projects. The necessary tests before running different parts is also discussed. Other options for reservoir creation are debated with their potential benefits and associated risks. The developments that could make them work in an EGS project are discussed.

Review of potential sites for Enhanced Geothermal Systems (EGS) and development of reference scenarios for EGS demonstration projects are two sub-tasks included in the FY 1999 EGS Research and Development (R&D) Management Task (DOE Task Order Number DE-AT07-99ID60365, included in the Appendix of this report). These sub-tasks are consistent with the EGS Strategic Plan, which includes milestones relating to EGS site selection (Milestone 4, to be completed in 2004) and development of a cost-shared, pilot-scale demonstration project (Milestone 5, to be completed in 2008). The purpose of the present work is to provide some reference points for discussing what type of EGS projects might be undertaken, where they might be located, and what the associated benefits are likely to be. The review of potential EGS sites is presented in Chapter 2 of this report. It draws upon site-selection criteria (and potential project sites that were identified using those criteria) developed at a mini-workshop held at the April 1998 DOE Geothermal Program Review to discuss EGS R&D issues. The criteria and the sites were the focus of a paper presented at the 4th International Hot Dry Rock Forum in Strasbourg in September 1998 (Sass and Robertson-Tait, 1998). The selection criteria, project sites and possible EGS developments discussed in the workshop and paper are described in more detail herein. Input from geothermal operators is incorporated, and water availability and transmission-line access are emphasized. The reference scenarios for EGS demonstration projects are presented in Chapter 3. Three alternative scenarios are discussed: (1) a stand-alone demonstration plant in an area with no existing geothermal development; (2) a separate generating facility adjacent to an existing geothermal development; and (3) an EGS project that supplies an existing geothermal power plant with additional generating capacity. Furthermore, information potentially useful to DOE in framing solicitations and selecting projects for funding is discussed objectively. Although defined as separate sub-tasks, the EGS site review and reference scenarios are closely related. The incremental approach to EGS development that has recently been adopted could logically be expected to yield proposals for studies that lead up to and include production-enhancement experiments in producing geothermal fields in the very near future. However, the strategic plan clearly calls for the development of a more comprehensive demonstration project that can generate up to perhaps 10 MW (gross). It is anticipated that a series of small-scale experiments will define what realistically may be achieved in the near future, thus setting the stage for a successful pilot demonstration. This report continues the process of presenting information on EGS sites and experiments, and begins the process of defining what a demonstration project might be.

The world is facing the energy challenge to over-reliance to fossil-fuels, the development of renewable energy is inevitable. From a clean and economic view, enhanced geothermal system (EGS) provides an effective mean to utilize geothermal energy to generate. Different form the conventionalhydro geothermal, the host rock of EGS is Hot Dry Rock (HDR), which buries deeper with high temperature (more than 180°C). The generationof EGS is promising. The development of EGS can be combined with the tech Power to geothermal energy. Exceed power is supposed to drive fluid working in HDR layer to obtain geothermal energy for generation. The whole article can be divided into three parts. In the first art, evaluation indexes of EGS as well as pilot EGs Projects (e.g. Fenton Hill and Basel) and exiting EGS project (e.g. Paralana and Newberry) are summarized, which points a general impression on EGS site. The dominate indexes are heat flow, geothermal gradient and thermal storage. The second part is focused on the simulation methods and working fluids selection of EGS. A detailed comparison of the main simulation software (e.g. TOUGH2 and FEHM) is carried out. With the respect of working fluid selection, the comparison between water and CO2 is researched and CO2 is a preferred option for EGS development for less fluid loss and less dissolution to HDR. The art of CO2-EGS is introduced clearly in this part. The third part is about the addition consideration of EGS plant operation, it excludes auxiliary plant support and HSE management.

ABSTRACT: We developed a workflow to generate sensitivity analysis and optimization of an Enhanced Geothermal System (EGS) with vertical and horizontal wells in different patterns. The recovery factor, heat extraction, and NPV (Net Present Value) of each pattern were determined as a part of the sensitivity analysis. This study models a conceptual reservoir geometry and tries to answer questions related to injection patterns, reservoir parameters, and type of reservoir, and contribute with additional knowledge about how to improve an EGS. Hence, an optimal thermal flow rate that makes the most of NPV was calculated. A sensitivity study on the controlling parameters such as porosity, horizontal permeability, vertical permeability, natural fracture spacing, thermal conductivity, and thermal capacity to determine how these parameters affect the heat extraction of the reservoir was developed. A complete economic analysis of the electricity generation value was assessed from several scenarios with current electricity prices and drilling costs. 1. INTRODUCTION We generated a sensitivity analysis and optimization to evaluate how different parameters and patterns impact an EGS project economically, modeling some patterns of horizontal wells and vertical wells. The assessment covers a conceptual and simple representation of the reservoir. The purpose is to evaluate relationships between initial energy in situ of the rock and water. This evaluation was compared with the energy produced, considering a full economic analysis such as NPV, discount rate, reservoir temperature, number of horizontal and vertical drilled wells, depth, and electricity sale price. EGS is a significant opportunity to reconsider geothermal energy as a part of the next transition energy. EGS is located significantly deeper than conventional geothermal wells, between 2.7 Km to 5.5 Km; this depth is required to stimulate the rock, creating an artificial circulation system and developing a hydraulic fracturing (HF) or hydro-shearing (Gischig and Preisig, 2015). The hydraulic fracturing technique generates artificial fractures to improve the flow rate of an EGS project.

Improving the performance of arid-zone geothermal power plants using seasonal heat storage

This report is the third in a series of reports sponsored by the U.S. Department of Energy Geothermal Technologies Program in which a range of water-related issues surrounding geothermal power production are evaluated. The first report made an initial attempt at quantifying the life cycle fresh water requirements of geothermal power-generating systems and explored operational and environmental concerns related to the geochemical composition of geothermal fluids. The initial analysis of life cycle fresh water consumption of geothermal power-generating systems identified that operational water requirements consumed the vast majority of water across the life cycle. However, it relied upon limited operational water consumption data and did not account for belowground operational losses for enhanced geothermal systems (EGSs). A second report presented an initial assessment of fresh water demand for future growth in utility-scale geothermal power generation. The current analysis builds upon this work to improve life cycle fresh water consumption estimates and incorporates regional water availability into the resource assessment to improve the identification of areas where future growth in geothermal electricity generation may encounter water challenges.

Geothermal energy is increasingly recognized for its potential to reduce carbon emissions and U.S. dependence on foreign oil. Energy and environmental analyses are critical to developing a robust set of geothermal energy technologies. This report summarizes what is currently known about the life cycle water requirements of geothermal electric power-generating systems and the water quality of geothermal waters. It is part of a larger effort to compare the life cycle impacts of large-scale geothermal electricity generation with other power generation technologies. The results of the life cycle analysis are summarized in a companion report, Life Cycle Analysis Results of Geothermal Systems in Comparison to Other Power Systems. This report is divided into six chapters. Chapter 1 gives the background of the project and its purpose, which is to inform power plant design and operations. Chapter 2 summarizes the geothermal electricity generation technologies evaluated in this study, which include conventional hydrothermal flash and binary systems, as well as enhanced geothermal systems (EGS) that rely on engineering a productive reservoir where heat exists but water availability or permeability may be limited. Chapter 3 describes the methods and approach to this work and identifies the four power plant scenarios evaluated: a 20-MW EGS plant, a 50-MW EGS plant, a 10-MW binary plant, and a 50-MW flash plant. The two EGS scenarios include hydraulic stimulation activities within the construction stage of the life cycle and assume binary power generation during operations. The EGS and binary scenarios are assumed to be air-cooled power plants, whereas the flash plant is assumed to rely on evaporative cooling. The well field and power plant design for the scenario were based on simulations using DOE's Geothermal Economic Technology Evaluation Model (GETEM). Chapter 4 presents the water requirements for the power plant life cycle for the scenarios evaluated. Geology, reservoir characteristics, and local climate have various effects on elements such as drilling rate, the number of production wells, and production flow rates. Over the life cycle of a geothermal power plant, from construction through 30 years of operation, plant operations is where the vast majority of water consumption occurs. Water consumption refers to the water that is withdrawn from a resource such as a river, lake, or non-geothermal aquifer that is not returned to that resource. For the EGS scenarios, plant operations consume between 0.29 and 0.72 gal/kWh. The binary plant experiences similar operational consumption, at 0.27 gal/kWh. Far less water, just 0.01 gal/kWh, is consumed during operations of the flash plant because geofluid is used for cooling and is not replaced. While the makeup water requirements are far less for a hydrothermal flash plant, the long-term sustainability of the reservoir is less certain due to estimated evaporative losses of 14.5-33% of produced geofluid at operating flash plants. For the hydrothermal flash scenario, the average loss of geofluid due to evaporation, drift, and blowdown is 2.7 gal/kWh. The construction stage requires considerably less water: 0.001 gal/kWh for both the binary and flash plant scenarios and 0.01 gal/kWh for the EGS scenarios. The additional water requirements for the EGS scenarios are caused by a combination of factors, including lower flow rates per well, which increases the total number of wells needed per plant, the assumed well depths, and the hydraulic stimulation required to engineer the reservoir. Water quality results are presented in Chapter 5. The chemical composition of geofluid has important implications for plant operations and the potential environmental impacts of geothermal energy production. An extensive dataset containing more than 53,000 geothermal geochemical data points was compiled and analyzed for general trends and statistics for typical geofluids. Geofluid composition was found to vary significantly both among and within geothermal fields. Seven main chemical constituents were found to account for 95-99% of the dissolved solids in typical geofluids. In order of abundance, they were chloride, sodium, bicarbonate, sulfate, silica, calcium, and potassium. The potential for water and soil contamination from accidents and spills was analyzed by comparing geofluid composition with U.S. drinking water standards. Geofluids were found to present a potential risk to drinking water, if released, due to high concentrations of antimony, arsenic, lead, and mercury. That risk could be mitigated through proper design and engineering controls. The concentration and impact of noncondensible gases (NCG) dissolved in the geofluid was evaluated. The majority of NCG was either nitrogen or carbon dioxide, but a small number of geofluids contain potentially recoverable concentrations of hydrogen or methane.

According to the Energy Information Administration (EIA) of the U.S. Department of Energy (DOE), geothermal energy generation in the United States is projected to more than triple by 2040 (EIA 2013). This addition, which translates to more than 5 GW of generation capacity, is anticipated because of technological advances and an increase in available sources through the continued development of enhanced geothermal systems (EGSs) and low-temperature resources (EIA 2013). Studies have shown that air emissions, water consumption, and land use for geothermal electricity generation have less of an impact than traditional fossil fuel?based electricity generation; however, the long-term sustainability of geothermal power plants can be affected by insufficient replacement of aboveground or belowground operational fluid losses resulting from normal operations (Schroeder et al. 2014). Thus, access to water is therefore critical for increased deployment of EGS technologies and, therefore, growth of the geothermal sector. This paper examines water issues relating to EGS development from a variety of perspectives. It starts by exploring the relationship between EGS site geology, stimulation protocols, and below ground water loss, which is one of the largest drivers of water consumption for EGS projects. It then examines the relative costs of different potential traditional and alternativemore » water sources for EGS. Finally it summarizes specific state policies relevant to the use of alternative water sources for EGS, and finally explores the relationship between EGS site geology, stimulation protocols, and below ground water loss, which is one of the largest drivers of water consumption for EGS projects.« less

We investigated the techno-economic feasibility and power supply potential of enhanced geothermal systems (EGS) across the contiguous United States using a new subsurface temperature model and detailed simulations of EGS project life cycle. Under business-as-usual scenarios and across depths of 1–7 kilometers, we estimated 82,945 GW and 0.65 GW of EGS supply capacity with lower levelized cost of electricity than conventional hydrothermal and solar photovoltaic projects, respectively. Considering the scenario of flexible geothermal dispatch via wellhead throttling and power plant bypass, these estimates climbed up to 184,112 GW and 44.66 GW, respectively. The majority of EGS supply potential was found in the Western and Southwestern regions of the United States, where California, Oregon, Nevada, Montana, and Texas had the greatest EGS capacity potential. With advanced drilling rates based on state-of-the-art implementations of recent EGS projects, we estimated an average improvement of 25.1% in the levelized cost of electricity. These findings underscored the pivotal role of flexible operations in enhancing the competitiveness and scalability of EGS as a dispatchable renewable energy source.

An investigation of stimulation mechanisms in Enhanced Geothermal Systems

Diagnostic vacuum gauge measuring total and partial pressures

Geothermal energy is believed to be an important source among the renewable energy sources to provide the base load electricity. Although there has been a drastic increase in the use of geothermal heat pump in Korea, there is no geothermal power plant in operation in Korea. Fortunately, the first EGS (Enhanced Geothermal System) Project in Korea has started in Dec 2010. This five year project is divided into two stages; two years for exploration and drilling of 3 km depth to confirm the minimum target temperature of 100 degrees, and another three years composed drilling 5 km doublet, hydraulic stimulation of geothermal reservoir with expected temperature of 180 degrees (40 kg/s) and construction of MW geothermal power plant in the surface. This EGS project would be a landmark effort that invited a consortium of industry, research institutes and university with expertises in the fields of geology, hydrogeology, geophysics, geomechanics and plant engineering.