Geothermal Industry Research Articles

Geoscience spillover: Gunnar Böðvarsson and the adoption of petroleum technologies in Iceland’s geothermal industry, 1940s–1970s

ABSTRACT During the twentieth century, Iceland became a leader in geothermal energy use, with hot water and steam providing for the heating of 9 out of 10 houses and almost one-third of the electricity supply. A crucial factor in the expansion of geothermal energy between the 1940s and 1970s were indirect ‘spillovers’ from the oil industry via the applied geosciences. While fundamentally different in end use, geothermal and hydrocarbon industries employ similar geoscientific methods for exploring and extracting fluids and gases. This article traces the spillovers from oil to geothermal by examining Iceland’s Geothermal Division and its founding director, Gunnar Böðvarsson. He saw the oil industry as a model and embraced its geoscientific exploration methods, oilwell rotary drilling and petroleum reservoir engineering. Adapted to the requirements of geothermal energy, petroleum technologies greatly improved the knowledge of geothermal reservoirs and the efficiency of well drilling and hot water and steam extraction. The geoscience spillover between oil and geothermal reveals an understudied dimension of geothermal history and the crucial role of the geosciences at the intersection of academia and energy industries, which also resulted in reverse spillovers from geothermal to oil and complicates the common dichotomization of fossil fuels vs. renewable alternatives.

Comparison of the Energy Contributions of Different Types of Ground Heat Exchangers Related to Cost in a Working Ground Source Heat Pump System

Geothermal systems face adoption challenges due to their high initial investment cost. Accurate cost analyses and a more precise understanding of updated prices could assist geothermal industry projects in obtaining investment financing and better money management with the right equipment. As the cost of geothermal installations can vary widely depending on case and location, it seems essential to clarify the factors and parameters that determine the cost of the system. These include the type of loop system, the ground conditions, the type of heat pump, the system size, and the geographical location. The scope of this study is to compare the operation of various types of ground heat exchangers (GHEs) present in a Ground Source Heat Pump (GSHP) system installed in the coastal area of the Mediterranean climate zone of Cyprus. The highlight of this work is that it presents real installation cost data as well as recorded total energy contributed by the GHEs to the GSHP system of a HP cooling and heating capacities of 101 kW and 117 kW, respectively. The input contribution from the GHEs to the HP is 85,650 kWh (308,340 MJ) in summer and 25,880 kWh (93,168 MJ) in winter. It is shown that, among the three groups of GHEs investigated, the open-well GHE complex has the lowest cost per kWh ratio (0.32 EUR/kWh), followed by the vertical GHE complex (1.05 EUR/kWh), and lastly by the helical coil GHE (2.77 EUR/kWh). This clearly suggests that when underground water is available, the open-well GHE is much more favorable than other GHE types.

Technology Focus: Reservoir Surveillance (September 2024)

In today’s oil and gas operations, surveillance technologies have undergone a revolution, reshaping how facilities, wells, and reservoirs are monitored. These advancements not only have increased the scale at which these technologies are deployed but also have led to an unprecedented influx of data. The sheer volume of data, however, poses a significant challenge to traditional analytical methods, overwhelming their capacity to derive actionable insights effectively. To address this challenge, the industry is rapidly advancing toward automated solutions powered by artificial-intelligence (AI) -driven analytics. These systems automate data ingestion and use machine-learning algorithms to sift through massive data sets, identifying anomalies and prioritizing actionable insights. By automating routine surveillance tasks, engineers can focus on critical actions that deliver substantial operational benefits. For example, in paper IPTC 23912, operators successfully optimized production operations by harnessing real-time field data through smart systems, effectively managing operations with complex near-critical fluids. Similarly, in paper SPE 218470, researchers proposed a novel workflow integrating virtual flowmetering and permanent downhole gauge data for pattern recognition to enhance real-time monitoring and decision-making in petroleum and geothermal industries. Nevertheless, ensuring effective surveillance of operational assets requires a strategic approach. A valuable tool in crafting such strategies is the value of information (VOI) assessment. This method systematically evaluates how acquiring specific information can influence decision-making and operational outcomes. For instance, paper SPE 215318 highlights a field operator’s systematic approach to VOI assessment, aiming to optimize daily operations and guide future development activities. In essence, while surveillance technologies have inundated operators with unprecedented data flows, advancements in automation and AI-driven analytics offer the promise of unlocking this data’s true potential. By embracing these technologies, the oil and gas industry can navigate the complexities of the modern energy landscape with greater agility, precision, and cost-effectiveness. Recommended additional reading at OnePetro: www.onepetro.org. SPE 215119 Surveillance, Analysis, and Optimization During Active Drilling Campaign by Yanfen Zhang, Chevron, et al. OTC 35413 New Opportunities in Well and Reservoir Surveillance Using Multiple Downhole Pressure Gauges in Deepwater Injector Wells by Piyush Pankaj, ExxonMobil, et al. OTC 34863 Digital Twin for Oil-Rim Management Using Early Warning System and Exception-Based Surveillance, Offshore Malaysia by M. Mahamad Amir, Petronas, et al.

A HOLISTIC OVERVIEW: INDONESIA'S GEOTHERMAL ENERGY ENCOURAGES GEOTHERMAL POWER PLANT INVESTMENT IN SUPPORT OF NATIONAL DEFENSE

The Pacific Ring of Fire passes across Indonesia physically, and the country's intense volcanic and tectonic activity has produced a wealth of geothermal resources that could reach 23,46 GW, distributed over 357 sites. To promote the decarbonization of Indonesia's electricity supply and the advancement of geothermal energy, the Indonesian government issued Presidential Regulation No. 112/2022 on the Acceleration of Renewable Energy Development for Electricity Supply in 2022. To incentivize GPPs to invest, the lack of bids in PLN's most recent procurement from 2021 requires more than the maximum electricity tariff. Investing in geothermal projects has some regulatory obstacles in addition to cost concerns. This study aims to assess geothermal investment in Indonesia and reduce reliance on fossil fuels, which are susceptible to price and supply volatility. GPPs ensure a consistent energy supply for national needs to support national defense. The method used is descriptive qualitative, which relies on literature studies that discuss appropriate issues. The National Energy Management Blueprint 2006-2025 presents the survey results. The Government of Indonesia plans geothermal energy to contribute about 5% of the national energy mix or about 7,32 GW in 2025. However, the realization of installed geothermal power plant capacity in 2023 only reached 2,38 GW, or 32,52 percent of the planned capacity to be installed. Through the Ministry of Energy and Mineral Resources, the government needs to increase the purchase price of electricity from IPP GPPs to create a good investment climate and continue to grow the geothermal industry.

Legal Policy Impact on Indonesia's Geothermal Industry Development: FDI Cooperation and NDC

Geothermal significantly contributes to the state's energy industry development as a widely available low-carbon, sustainable, and strategic resource. As Indonesia is committed to achieving NZE 2060, renewable energy development is being conducted massively. Seeking Indonesia's geothermal energy potential, several regulations, policies, and schemes are implemented, including investment schemes, as financing plays a vital role in the industry's development. However, establishing a seamless procurement is highly dependent on national law regulations which govern the financing, procurement, and utilizations up to investors benefits. This article identifies international and national regulations on FDI, business schemes, and its alignment with INDC strategic programs, demonstrating Indonesia's commitment. It finds much room for improvement in national law regulation, especially the upcoming RE Draft Bill, as the implementation of established FDI schemes has not met the investor's favors. However, among AMS, Indonesia is the most committed country to achieving NZE. Therefore this article examines the Legal Policy Impact on Indonesia’s Geothermal Industry Development through FDI Cooperation and NDC. This article is conducted in Normative Legal Research and uses the Statutory Approach as its problem approach.

Application of machine learning and deep learning in geothermal resource development: Trends and perspectives

AbstractThis study delves into the latest advancements in machine learning and deep learning applications in geothermal resource development, extending the analysis up to 2024. It focuses on artificial intelligence's transformative role in the geothermal industry, analyzing recent literature from Scopus and Google Scholar to identify emerging trends, challenges, and future opportunities. The results reveal a marked increase in artificial intelligence (AI) applications, particularly in reservoir engineering, with significant advancements observed post‐2019. This study highlights AI's potential in enhancing drilling and exploration, emphasizing the integration of detailed case studies and practical applications. It also underscores the importance of ongoing research and tailored AI applications, in light of the rapid technological advancements and future trends in the field.

Evaluating the maximum drilling length of horizontal geothermal wells utilizing temperature constraints

The geothermal industry faces a significant challenge in exploring and developing resources due to elevated temperatures in downhole environments. Successful drilling in high-temperature geothermal wells requires precise thermal management. This research assesses constraints on horizontal section length and temperature during geothermal horizontal well drilling, aiming to formulate effective wellbore temperature management guidelines.The study utilizes thermal resistance analysis to establish a tailored transient heat transfer model for high-temperature horizontal geothermal well drilling. Parameters such as circulation time, horizontal section length, flow rate, drilling fluid properties, formation thermal conductivity, and drill string thermal conductivity are thoroughly investigated. Treating input parameters as triangular distributions, Monte Carlo simulation techniques conduct sensitivity analysis. Tornado diagrams quantitatively determine key parameter impacts on bottom-hole temperature. The research introduces a procedural framework for geothermal well drilling, aiding engineers in swiftly identifying operational parameter combinations for effective wellbore temperature management. This workflow provides practical guidance for geothermal resource development, ensuring drilling safety in diverse conditions.

Numerical investigation of closed-loop heat extraction in different-layout geothermal wells with particular reference to thermal interference analyses

Harnessing geothermal energy through closed-loop heat extraction in deep geothermal wells for building heating in dense urban residential areas is a challenge, especially when the spare surface area is very limited for arranging the wellheads. In this study, 3-D models of closed-loop heat extraction in vertical, L- and deviated wells are established. It is found that, when the wellhead spacing is 5 m, there is almost no thermal interference among the symmetrically-arranged deviated wells, indicating that the deviated well clusters have obvious advantages over the vertical well clusters. At the end of the first heating season, the heat extraction rate of the four deviated well cluster (FDS) is 246 kW higher than that of the four vertical well cluster (FVS). The heat extraction rate of FDS exceeds that of the five vertical well cluster. After 10-year operation, the heat extraction rate of the FDS is 350 kW higher than that of FVS. When the wellhead spacing of FVS exceeds 80 m, the thermal interference factor (TIF) is less than 0.19 %, equivalent to the degree of the thermal interference among the wells of FDS with a wellhead spacing of 5 m. The results obtained in this study are of engineering-guiding significance for geothermal industries.

Applying Deep Electrical-Resistivity Tomography Techniques for the Exploration of Medium- and Low-Geothermal Energy Resources

The growth of the geothermal industry demands the constant search of techniques with the aim of reducing exploration efforts whilst minimizing subsurface uncertainty. The exploration of geothermal resources is fundamental from the exploitation point of view, especially in those regions where this energy is not as widespread as the rest of renewable sources. This research shows how geoelectrical methods can contribute to the investigation and characterization of medium–low enthalpy geothermal resources until about 800 m of depth. A 2000 m long electrical-resistivity tomography profile was performed in a region of Southern Spain with previous evidence of moderate geothermal potential. Results of this geophysical campaign (together with a preliminary geological characterization) allowed for the obtainment of a 2D profile and a pseudo-3D model with extensive information about the subsoil in terms of geological composition and formations. The interpretation of geophysical results denotes the existence of a potential formation constituted by carbonate materials with thickness greater than 300 m, crossing different fractures. Once the ideal location for the geothermal exploitation is defined, the research evaluates the contribution of the possible energy source, deducing that the energy extraction in the potential fracturing area would be double that of the one in the vicinity of the site.

Thermodynamic Analysis of an Increasing-Pressure Endothermic Power Cycle Integrated with Closed-Loop Geothermal Energy Extraction

The thermodynamic analysis of an increasing-pressure endothermic power cycle (IPEPC) integrated with closed-loop geothermal energy extraction (CLGEE) in a geothermal well at a depth from 2 km to 5 km has been carried out in this study. Using CLGEE can avoid some typical problems associated with traditional EGS technology, such as water contamination and seismic-induced risk. Simultaneous optimization has been conducted for the structural parameters of the downhole heat exchanger (DHE), the CO2 mixture working fluid type, and the IPEPC operating parameters. The CO2-R32 mixture has been selected as the optimal working fluid for the IPEPC based on the highest net power output obtained. It has been found that, when the DHE length is 4 km, the thermosiphon effect is capable of compensating for 53.8% of the pump power consumption. As long as the DHE inlet pressure is higher than the critical pressure, a lower DHE inlet pressure results in more power production. The power generation performance of the IPEPC has been compared with that of the organic Rankine cycle (ORC), trans-critical carbon dioxide cycle (t-CO2), and single-flash (SF) systems. The comparison shows that the IPEPC has more net power output than other systems in the case that the DHE length is less than 3 km, along with a DHE outer diameter of 0.155 m. When the DHE outer diameter is increased to 0.22 m, the IPEPC has the highest net power output for the DHE length ranging from 2 km to 5 km. The application scopes obtained in this study for different power generation systems are of engineering-guiding significance for geothermal industries.

Coupled Modeling of the Surface Pipeline Network in a Low-Enthalpy Geothermal Field

This paper addresses the often overlooked, yet critical, aspect of designing and optimizing the surface pipeline network for the transportation of geothermal fluids from the wellheads to the delivery point, such as greenhouses, food drying plants, or fish farming units. While research on the geothermal industry predominately focuses on the reservoir and well engineering aspects of exploitation, insufficient attention has been given to the design of the pipeline network, leading to improper design and significant, yet avoidable, energy losses. Thus, this paper presents a comprehensive methodology for modeling and simulating geothermal fluid flow within the pipeline network by fully considering all hydraulic (friction, viscous flow, and gravity effects) and thermal (open air and underground pipeline heat loss) phenomena. These two aspects are handled simultaneously by setting up and solving the coupled set of the governing (differential) equations. We also demonstrate the difficulties that arise when attempting the solution of the mathematical problem, such as potential instability or lack of convergence. Finally, a fully detailed study of the real-world geothermal production system is presented utilizing the developed methodology to optimize the design and operation conditions of the system. By integrating debottlenecking strategies into the analysis, this approach not only maximizes power output, but also identifies and mitigates constraints within the system, ensuring efficient operation and performance increase.

Comparison of SWCNT + MWCNT and SWCNT + MWCNT + Fe3O4 nanofluid across a spinning disk with suspended joule heating and non-linear thermal radiation: Multi-linear optimization

Background Fluid flow over an infinite impermeable rotating disk has profound applications in computer storage, lubrication, aerospace, chemical engineering, the geothermal industry, the food industry, the cooling of rotating machinery, gas turbines, thermal energy systems, etc. This motivated me to mathematically model the radiative magnetohydrodynamic Over an endlessly impermeable rotating disk, nanofluid flows. Appropriate similarity frameworks are utilized to solve the nonlinear PDEs. Methodology Further, ODE45 (MATLAB) is used to analyze the transport of heat, mass, and flow. The distinction of this model is the mixture of nanoparticles in the fluid’s base. The flow is analyzed considering two cases. Case 1: SWCNT + MWCNT + PEG + H 2 O and Case 2: SWCNT + MWCNT + F e 3 O 4 + PEG + H 2 O . Conclusion A straightforward solution for the radial F ( ζ ) , axial G ( ζ ) , and azimuthal velocity H ( ζ ) , heat and substance concentration ϕ ( ζ ) is discovered, and its impact on fluid movement is studied with relation to several dimensionless characteristics. A good agreement is obtained in the present model with certain added features to the existing work. The primary finding of this research is the inclusion of SWCNT, and MWCNT has exhibited more comparing skin friction, the Nusselt number, and the Sherwood number SWCNT, MWCNT, and in the same carrier fluid. SWCNT and MWCNT In industrial procedures, nanoparticles are more effective for cooling purposes. Compared with SWCNT, MWCNT, and F e 3 O 4 .

TRIBOLOGY OF DRILL BITS IN THE GEOTHERMAL INDUSTRY: A LITERATURE REVIEW

Energy from the earth’s heat is critical to the energy supply of countries with this resource. This literature review highlights the tribology applied to drill bits in the geothermal industry. Facing a diverse geological environment, drill bits are critical to energy efficiency, with significant friction, wear and lubrication challenges. This paper addresses the complexity of drill bit interaction with diverse geothermal formations, highlighting the importance of understanding tribological phenomena. Advances in materials and coatings, such as composites, heat-resistant alloys and ceramic coatings, are explored, along with innovative geometric design strategies. Attention on lubrication, cooling and continuous monitoring systems highlights the quest for efficiency and extended drill bit life. This review provides a comprehensive overview of advances in bit tribological research in the geothermal industry, identifying emerging trends and critical challenges for the sustainable development of this form of renewable energy.

Gas lifting design and application in geothermal wells: A case study from West Anatolia, Turkiye

The gas content of the producing fluid has crucial effects on the production performance of geothermal wells. The decline of non-condensable gases (NCG) could result in significant performance reduction of the wells. Artificial production techniques such as pumps (i.e., Line Shaft Pump and Electrical Submersible Pump) and gas lifting are the widely known methods for enhancing the production performance of wells. Due to the high-temperature working environment and the well's inclination, pumps might be inconvenient for geothermal wells. Continuous injection of gases such as nitrogen (N2) and carbon dioxide (CO2) serving as gas lifting might be the appropriate method to enhance production from geothermal wells suffering from low gas content and reservoir pressure. This study investigates production enhancement with gas lifting in a geothermal field in Turkiye. The study aims to fill the gap of gas lifting in the geothermal industry as an alternative to downhole pumps such as ESP and LSP. The sensitivity analyses were performed on the design parameters such as injection depth, rates, tubing size, number of valves, and injectate gas type influencing the production performance of gas lifting. The study found that gas lifting is an optimization problem that needs to be solved by considering gas sources, infrastructure sizes, wellbore geometry, and operating parameters.

Evidence of caged to normal diffusion transition in benzene along supercritical isobars: Insights from molecular dynamics simulations

Understanding the behavior of supercritical fluids holds both fundamental and practical significance. From a practical standpoint, these fluids find numerous technological applications across environmental, mechanical, chemical, biological, and geothermal industries. However, from a fundamental scientific perspective, unraveling the intricate structure, thermodynamics, and dynamics of supercritical fluids remains an ongoing challenge. In this work, we address this task by employing NPT molecular dynamics simulations on a rigid benzene model under high pressures. Our observations reveal a striking dynamical transition, with a caged regime at low temperatures and a normal diffusion regime at high temperatures. Notably, the subdiffusive region aligns with the compressible region from the experimental phase diagram, while the normal diffusion occurs in the supercritical region. Furthermore, we present compelling evidence linking the subdiffusion to a caged trajectory and illustrate how uncaging and clustering play a key role in the dynamical transition. The identification of the subdiffusive and normal diffusion regimes provides valuable information for optimizing processes involving supercritical fluids in various industries. Moreover, the link between caged trajectories and dynamical transitions adds a new dimension to our understanding of molecular behavior in supercritical systems.

Cultural sustainability thresholds to measure the mauri of Indigenous Māori values impacted by geothermal engineering projects

Aotearoa New Zealand's current geothermal laws require that any engineering utilisation of geothermal resources includes an assessment of how Māori values are impacted, being the values held by the country's Indigenous Peoples. A series of wānanga (Māori-based workshops) were conducted with Māori participants to develop a list of Māori values pertinent to geothermal development, followed by a companion list of corresponding sustainability indicators that defined measurable parameters as quantitative representations of these Māori values. For each indicator, sustainability thresholds were developed, which described three possible impacted indicator states that constituted denigrated, neutral, and enhanced levels of mauri respectively, where mauri was a proposed measure of wellbeing. The information contained in the thresholds provided a means to numerically assess the extent to which an engineering project in Aotearoa would sustain the wellbeing of the listed indicators, and in turn the listed Māori values. The insights within the thresholds may be used by other researchers to develop thresholds specific to other indigenous cultures around the world and empower such cultures in their countries' own geothermal industries.

Evaluating healthy workplace in geothermal industry

The geothermal industry is located in mountainous areas and far from urban centers that are at risk of danger. Hazard management is one aspect of occupational safety health management, including occupational environmental health. Therefore, this study aims to evaluate the healthy workplace in geothermal industry. Observation and measurement technique are used to determine the light intensity, noise, humidity and temperature in all room in the industry. The results state that there are three rooms that did not meet the standard, the noisy still eligible both for offices (65dBA) and PLTP (85 dBA), the humidity is quite high (60%) and the average temperature is 15-20oC. Most of the indicators are still below the limit value based on the company and local regulations. Pengukuran aspek fisik monitoring kesehatan lingkungan kerja sudah memperoleh hasil yang baik. Namun, masih ada beberapa lokasi lingkungan kerja yang perli dilakukan perbaikan lagi dari segi pencahayaan dengan penggantian jenis lampu LED, dan pengaturan suhu dan kelembapan ruang. The assessment of healthy workplace is needed to improve the well-being of the workers in geothermal industry.

Characteristics and prospect of geothermal industry in China under the “dual carbon” target

Geothermal energy utilization in China had been promoted actively during the 13th Five-Year Plan period (2016–2020), with resultant achievements showing unique Chinese characteristics. Buildings (measured by areas) heated/cooled by intermediate-to-deep geothermal energy increased more rapidly than those by shallow geothermal energy. Geothermal power generation was restricted by the distribution of the resource and the sufficiency of local power supply. With the proposition of “dual carbon goal” by the central government of China and the coming era of great development of renewable energy, geothermal energy will be provided more development opportunities in room heating/cooling and power generation in the country ever than before. However, tackling technology bottlenecks and introduction of appropriate policy support are still urgently needed for nurturing a healthy environment for geothermal industry. Analysis suggests that a near-to medium-term development of geothermal energy shall be focused on a comprehensive and efficient utilization both through heating/cooling and power generation. Room heating/cooling by intermediate-to-deep and shallow geothermal energy shall be promoted nationwide according to local resource endowment and economic conditions. Geothermal power generation in Yunnan and Tibet shall be pushed forward in an orderly way. For medium- and long-term development, focus shall be put on power generation by using low to medium temperature geothermal energy and hot dry rocks. The "hot spring +" model shall be adapted in steps on a regular basis. To achieve these, measures including attaching importance to tackling key technologies, promoting standards for geothermal energy development and utilization, strengthening geothermal energy exploration and evaluation, and seeking for necessary policy support shall be taken.

Predicting the Potential of China’s Geothermal Energy in Industrial Development and Carbon Emission Reduction

The goal of carbon peaking and carbon neutrality requires major systemic changes in the energy supply sector. As one of the major non-carbon-based energy sources, geothermal energy is characterized by large reserves, stability, and reliability. This paper summarizes the current situation of geothermal resource endowment and industrial development in China. Based on this, a system dynamics model of geothermal industrialization is established, and the potential of geothermal industrialization and carbon emission reduction in China is predicted. The prediction results show that the growth rate of geothermal heating and cooling areas in the next 40 years will follow a trend of acceleration followed by deceleration. China’s geothermal energy heating and cooling area will reach 11.32–14.68 billion m2 by 2060, an increase of about 9–12 times compared to 2020. The proportion of geothermal heating and cooling area to the total building area in China will reach 13.77–17.85%. The installed capacity of geothermal power generation will reach 14,452.80–20,963.20 MW by 2060 under the scenario with electricity subsidies. The proportion of geothermal energy in China’s primary energy consumption structure will reach 3.67–5.64%. The annual carbon emission reduction potential of the geothermal industry will reach 436–632 million tons, equivalent to 4.41–6.39% of China’s carbon emissions in 2020. The results of this study can provide a reference for the healthy and high-quality development of China’s geothermal industry and help to achieve carbon peaking and carbon neutrality goals.

Carbon dioxide-Induced Corrosion of AISI 4140 Steel in Acidified Artificial Geothermal Brine

Carbon dioxide (CO2)-induced corrosion often occurs in the structural materials of geothermal industry. The presence of CO2 influences the formation of various corrosion products. This research investigates the effect of dissolved CO2 in acidic brines on the corrosion behavior of AISI 4140 steel at atmospheric pressure. The brines were the standard brine, Ca-free brine, and high-salinity brine. The corrosion behavior was studied using electrochemical and immersion tests. A cyclic polarization test showed that the corrosion rate was higher in dissolved CO2 brine than in non-CO2 brine, and an immersion test demonstrated a similar result. In the absence of CO2, the presence of Ca ions in the brine reduced the corrosion rate of the alloy from 26.8 to 24.6 mmpy and further to 20.7 mmpy in the high-salinity brine. A similar trend was demonstrated during immersion in the CO2-containing brine, with higher rates of 37.1, 30.9, and 24.9 mmpy for the Ca-free, standard, and high-salinity brines, respectively. However, the Ca ions and high-salinity brines induced a more localized corrosion as pit and filiform. A surface analysis using an optical microscope revealed that immersion in CO2 brines generated 4–10-fold higher surface roughness than the non-CO2 brines. In all specimens, a protective layer was not established during the tests. No new phase was detected using X-Ray diffractometer after the immersion test. Moreover, no tendency of passivation was observed in the reverse scan of the cyclic polarization test.