Geothermal Wells Research Articles

Optimization of a district heating system coupled with a deep open-loop geothermal well and heat pumps

The technical and economic aspects of a district heating system coupled with a deep open-loop geothermal well (DOLGW) and heat pumps were studied in the paper. A typical configuration of such a geothermal district heating system was proposed, and the corresponding thermal analysis was carried out. Based on the data from the DOLGW heat extraction test conducted in Hebei, China, the optimal size selections of heat pumps, plate heat exchangers, and terminal heat radiators for such a system was analyzed theoretically. In addition, an optimal control scheme for such a system with the change of environmental temperature or heating load were given.

Analytical study of integrating downhole thermoelectric power generation with a coaxial borehole heat exchanger in geothermal wells

Geothermal power generation employing Organic Rankine Cycle (ORC) technology is a widely acknowledged and conventional approach for harnessing geothermal energy. In an innovative advancement, we propose a novel design integrating downhole thermoelectric power generation with a coaxial borehole heat exchanger. This design aims to enhance the efficiency and sustainability of geothermal energy utilization. In this innovative design, the geothermal well is divided into two distinct sections: a power generation section and a heat exchanging section, achieved through the implementation of a packer positioned from the uppermost part of the targeted zone. The process involves the injection of cold fluid downhole via an insulated pipe. Subsequently, a portion of the injected fluid is directed to flow in reverse within the casing-tubing annulus above the packer, while another portion circulates into the casing-tubing annulus below the packer before ascending through the tubing. This dual flow mechanism establishes distinct cold and hot sources for the thermoelectric generator, a key feature facilitated by this innovative design. Analytical models detailing of downhole temperature distribution for thermoelectric power have been meticulously developed. A comprehensive case study, focusing on a geothermal well with 3000 m length of power generation section and 500 m heat exchanging section, has been conducted. The results indicate that a significant generating capacity could be achieved with a higher wellhead temperature, and the payback period under different carbon tax scenarios is about 6–8 year. Furthermore, the effects of injection rate, fluid diversion ratio, and casing-tubing configuration on power performance and thermal-electricity efficiency are also discussed. This method not only enables the concurrent harvesting of geothermal energy and power generation but also operates consistently throughout the year. The results thus emphasize the viability and economic feasibility of the proposed approach.

The Sealing Performance of Cement Sheaths under Thermal Cycles for Low-Enthalpy Geothermal Wells

The repetitive process of shut-in and production in geothermal wells promotes thermal stress on the wellbore components, including annular cement. A cement sheath at a relatively shallow depth undergoes the most significant stress change due to the high differential temperature between the geothermal gradient and the production fluid’s temperature. Understanding the impact of cyclical thermal stresses on cement is critical for assessing the barrier integrity at a shallow depth that serves as aquifer protection. A novel large-scale setup simulating a 1.5 m-long casing-cement-casing well section was built to study the changes in cement’s sealing performance of low-enthalpy geothermal wells during production. Using this setup, a cement sheath can be cured similarly to the in situ conditions, and the annular temperature can be cycled under realistic operating conditions. The change in flow rate through the cement sheath before and after cycling is quantified through leak tests. UV dye is injected at the end of the experiment to identify the location and type of damage in the cement sheath. A hydromechanically coupled finite element model was used to estimate the stress evolution in cement during the tests. The model incorporated the impact of cement hydration and strength development during curing. The numerical results were used as a guide to ensure the test design closely mimicked in situ conditions. The results show the presence of a small microannulus immediately after curing due to hydration shrinkage. Thermal cycles reduced the permeability of the microannulus. The size of the micro-annulus was observed to be sensitive to the backpressure applied to the cement sheath, indicating the need for pressure to maintain an open microannulus. Thirty-nine thermal cycles between 80 and 20 °C did not change the permeability of the cement sheath significantly. Tensile cracks in the cement sheath were not continuous and may not be a significant pathway. The new setup allows for measuring cement’s effectiveness in withstanding in situ stress conditions when exposed to thermal cycles such as geothermal and CCS wells.

Numerical and analytical models of the mechanism of torque and axial load transmission in a shock absorber for drilling oil, gas and geothermal wells

The paper proposes an improved design of a shock absorber used in drilling deep oil and gas and geothermal wells with polycrystalline diamond compact (PDC) bits. The proposed innovations successfully combat the dangerous phenomenon of self-excited vibrations, which can lead to malfunctions such as stick-slip and whirling of the drilling tool. Most conventional drill shock absorbers are designed to only absorb longitudinal vibrations, which was sufficient when using roller cutter bits for the drilling process. However, the design features of PDC bits and the phenomenon of interaction of their cutters with interlayered rocks during deep drilling impose new requirements on the properties of the drill shock absorber. To protect the downhole tool from abnormal torque values and torque oscillations, it is proposed to equip the shock absorber with a special torque transmission unit in the form of a fourteen-thread self-releasing screw pair. This unit is capable of transforming increases in external torque into increases in the force that loads the elastic element of the shock absorber. The numerical and analytical models of the mechanism of transferring external axial load and torque to the elastic element of the drill shock absorber are constructed. The distribution of contact pressures on the interacting surfaces of the screw pair and the distribution of equivalent stresses in the screw pair parts are analysed. The strength of the proposed drill shock absorber assembly was evaluated using the Huber-von Mises energy criterion. The dependence of the load transmitted to the elastic element of the shock absorber on changes in the external torque and external axial force is investigated. In general, it is determined that the external load is distributed evenly between all turns of the screw pair, and the limit state of the parts of the proposed assembly is not reached even under high-torque operating load. The obtained analytical dependencies will allow to effectively determine the required strength and stiffness of the elastic element of the drill shock absorber at the design stage. The obtained analytical results were verified using a finite element model.

Modelling the solubility of gases in aqueous solutions with a focus on geothermal applications– assessment and benchmarking of two free software packages

The interactions between aqueous solutions, gases, and minerals dictate the extent of issues such as scaling, degassing, and corrosion, which have a major impact on the performance of a vast number of industrial applications (e.g., geothermal plants, oil and gas production facilities, natural gas storage in saline aquifers, flue gas scrubbing, carbon sequestration, etc.). Among the different software programs available for aqueous chemistry calculations, Phreeqc and Reaktoro were tested and validated against a wide dataset of gas solubility measurements. For the datasets considered, the two programs essentially led to the same outcome with only a few discrepancies observed. Yet, the agreement between the models and experimental data was greatly affected by the selected database. The models implemented in Phreeqc and Reaktoro were also compared with the experimental bubble point pressure of fluids sampled at several geothermal wells. The satisfactory performance of both Phreeqc and Reaktoro for describing different chemical systems at a wide range of pressures and temperatures showcases their versatility and practicality for assisting in the design and optimization of various processes relevant to the energy transition (e.g., geothermal exploitation, CO2/H2 transport and storage).

Geological Mapping Optimisation Using Satellite Gravity, Satellite Imagery, and Seismic Shear Velocity (Vs30) to Monitor Lithological Condition in Geothermal Area of Mount Salak, West Java

Conventional geological mapping has several challenges such as limitation of area coverage, tough terrain, unstable weather condition, high-cost survey, also limitation of expert geologist that capable to do geological mapping. Remote sensing is an alternative solution to geological mapping through the combination of satellite gravity, satellite imagery, and seismic shear wave velocity. This research aims to optimise geological mapping activity in the Mount Salak geothermal area from ineffective area coverage mapping and inefficient budgeting allocation. Integration of rock density from satellite gravity, lithological distribution from satellite imagery, and seismic shear wave velocity from Vs30 are giving more detailed lithological units interpretation with specific physical conditions. There are two main area of Mount Salak that should be preserved geothermal resource sustainable. Northeast area needs to preserve heat source and groundwater recharge area, that consist of dense vegetation as landcover, relatively high rock density value (2.30 - 2.50 gr/cm3), high seismic shear wave velocity (600 – 900 m/s), also dominantly covers by Andesitic-Basaltic Lava. Southwest area preserve reservoir and caprock of geothermal conceptual model, where covers by dense vegetation with several bare land as geothermal wells and powerplants, relatively low rock density value (2.00 – 2.20 gr/cm3), moderate seismic shear wave velocity value (450-750 m/s), also dominated by several pyroclastic product such as Lapilli and Tuff. This research shows good indication in geothermal resource preservation in the Mount Salak, that keep natural aspect of geothermal conceptual model still preserved well.

A numerical investigation into the propagation of acid-etched wormholes in geothermal wells

Carbonate geothermal reservoirs are widespread in the Beijing-Tianjin-Hebei region, and acidification stands out as the most effective method to enhance the heat recovery potential of these reservoirs. To understand the propagation patterns of acidized wormholes in geothermal reservoirs, a pore-Darcy scale mathematical model of acidizing reactions in geothermal reservoirs has been established. A normal random distribution function is introduced to depict the reservoir's heterogeneity. Using the finite element method, the study simulated the impact of injection rate, acid concentration, diffusion coefficient, and acid-rock reaction rate on wormhole morphology. The findings indicate that the reaction is uniform in the early stage of acidification, becoming non-uniform in the late stage, ultimately forming distinctive wormhole structures. The acidification radius is more extensive along a particular direction post-acidification. Increasing the acid injection rate, acid concentration, and initial specific surface area proves beneficial in enhancing the acidizing effect. The outcomes of this study hold theoretical and technical significance for optimizing the thermal recovery efficiency of geothermal reservoirs.

The Exergy and Energy Analysis of Change Phase Steam in Patuha Geothermal Well Production

A Geothermal Power Plant Company in West Java Indonesia have capacity around 55MW. It company have increased the well production quality to keep up the Indonesia's energy demands. The power plant has been operated around ten years, it has ten geothermal production wells and two injection wells. The either of it wells has an abnormality. It wells has water dominated condition so, the separator equipment is required to separate the steam from water and vapor. Previous study indicated that subsurface water entering the broken reservoir pipe. That leaks in reservoir pipe was repaired in 2020. The impact after the pipe have been repaired it made the fluid characteristic of reservoir be vapor dominated. After that a separator as a steam separator is no longer required. The study compares the value energy and exergy power of the power plant. The calculations are performed from the well reservoir and all power plant equipment. According to the results of the energy study, the plant's energy efficiency after the transformation increased by 0.03%, from 19.48% to 19.52%. The exergy value of the brine in either wells (separated steam cycle) is also known to be 2.512,52 kW, beyond which the value will become zero.

Reuse of Oil Wells in Geothermal District Heating Networks: A Sustainable Opportunity for Cities of the Future

Climate change and the energy crisis forced industrialized countries to contain CO2 emissions and use indigenous renewable energy sources. Geothermal energy undoubtedly has great potential, particularly thermal energy, given that 48% of the final energy consumption in the EU20 countries in 2021 was related to heating and cooling systems. The present study verifies and compares the feasibility of realizing district heating systems in two different contexts: (i) depleted hydrocarbon fields with the repurposing of existing hydrocarbon wells into geothermal wells and (ii) areas with documented geothermal resources. The two selected case studies are located, respectively, near Romentino (Northern Italy, province of Novara) and Tuscania (Central Italy, province of Viterbo). Following an assessment of the geothermal resources in the two selected case studies, specific methodological tools have been developed to evaluate the energy demand in the municipalities and determine the projects’ economics. Both case studies show positive economic indices assuming heat tariffs aligned with the values recorded in the 2020–2021 period. However, our results show how reusing hydrocarbon wells in geothermal wells constitutes an excellent opportunity to access geothermal resources, significantly reducing the necessary investment and the mining risk and strongly improving the economics of the projects.

Evaluation of in-situ stress orientations within the Central Kenyan rift, through analysis of borehole images of wells drilled in Menengai Geothermal field, Kenya

The Menengai Caldera is in a complex structural zone within the Kenyan Central Rift and hosts the Menengai Geothermal Field. In assessing the subsurface characteristics of many geological resources, knowledge of in-situ stress orientations and magnitudes at depth is essential. Acoustic televiewer logging campaigns carried out in Menengai Geothermal Field between 2018 and 2019 in the production zones of three geothermal wells, have provided an on-site assessment of horizontal in-situ stress orientation in an area lacking such data. Data generated from drilling-induced features in the Menengai Geothermal Field revealed that the average SHmax orientation for MW-34 is NW-SE, whereas the average SHmax orientation for MW-20B is NE-SW, and the average SHmax orientation for MW-15A is NNE-SSW. Subsurface variations of in-situ stress orientations are related to large-scale features such as fractures, fissures, and fault architecture in the geothermal field. The NW-SE SHmax in-situ stress orientation around MW-34 agrees with the Molo (TVA) structural orientation, the Menengai pre-caldera shield orientation, and the Aswa shear zone. The NNE-SSW strike direction of the southern Kenyan Rift Valley, which changes orientation at the triple junction, is compatible with the NE-SW and NNE-SSW SHmax orientations of MW-20B and MW-15A. MW-34 is aligned to the Solai TVA/Graben because of its NE-SW Shmin orientation. In addition, the MW-15A's almost E-W Shmin orientations coincide with the Kenyan Rift's extension direction, which corresponds to the orientation of the E-W striking horsetail fracture inside the Menengai caldera. Localized stress perturbations manifest as rotations of BOs or DITFs orientations along the well as a function of depth.

Геоэкологические проблемы излива термальных вод скважины 9-Т Каргалинская

Based on stock materials on the Kargalinskoye thermal water deposit and field studies in the area of the geothermal well 9-T Kargalinskaya (Chechen Republic), mapping of the area of impact of the outflowing waters of this well was carried out and a comprehensive geoecological assessment of their impact on the landscape and land use was given. At the mesolevel, an assessment was made of the integration of the well into the regional landscape structure (a profile was built on which the main geological and geographical boundaries and units of physical and geographical differentiation are indicated: types and groups of landscapes). At a large-scale level, a comprehensive mapping of landscapes and land use was carried out on a scale of 1:10 000. In the field, characteristics were given to natural complexes of the rank of tracts and facies (with a description of vegetation, soils and actual use), water temperatures were measured, and water samples were taken for chemical analysis from a well and a groundwater basin used for drip irrigation of agricultural land. Geobotanical studies of the flora were carried out with the identification of the main phytocenoses, at some points of which transects (1 m2) were laid, dominant associations, the number of dominants, and the total projective cover were determined.

Impact of well placement and flow rate on production efficiency and stress field in the fractured geothermal reservoirs

AbstractGeothermal energy has gained wide attention as a renewable alternative for mitigating greenhouse gas emissions. The advancements in enhanced geothermal system technology have enabled the exploitation of previously inaccessible geothermal resources. However, the extraction of geothermal energy from deep reservoirs poses many challenges due to high‐temperature and high‐geostress conditions. These factors can significantly impact the surrounding rock and its fracture formation. A comprehensive understanding of the thermal–hydraulic–mechanical (THM) coupling effect is crucial to the safe and efficient exploitation of geothermal resources. This study presented a THM coupling numerical model for the geothermal reservoir of the Yangbajing geothermal system. This proposed model investigated the geothermal exploitation performance and the stress distribution within the reservoir under various combinations of geothermal wells and mass flow rates. The geothermal system performance was evaluated by the criteria of outlet temperature and geothermal productivity. The results indicate that the longer distance between wells can increase the outlet temperature of production wells and improve extraction efficiency in the short term. In contrast, the shorter distance between wells can reduce the heat exchange area and thus mitigate the impact on the reservoir stress. A larger mass flow rate is conducive to the production capacity enhancement of the geothermal system and, in turn causes a wider range of stress disturbance. These findings provide valuable insights into the optimization of geothermal energy extraction while considering reservoir safety and long‐term sustainability. This study deepens the understanding of the THM coupling effects in geothermal systems and provides an efficient and environmentally friendly strategy for a geothermal energy system.

Economic Analysis of Gas Turbine Using to Increase Efficiency of the Organic Rankine Cycle

In this research, a modified organic Rankine cycle (ORC) system has been presented and examined. This system incorporates a gas turbine as an additional subsystem to boost the enthalpy of geothermal brine. The primary objective of this study is to perform an economic evaluation of the modified ORC system, wherein a gas turbine is utilized to enhance the quality of geothermal steam. The suggested modified ORC system is particularly well-suited for areas abundant in geothermal resources with low to medium temperatures. It offers a more effective utilization of such resources, resulting in improved efficiency. The study considered 10 different working fluids and 8 types of gas turbines used to heat the geothermal water brine witch, the temperature vary of which varies between 80–130 °C. Various flue gas temperatures behind the heat exchanger, as well as temperatures of the return of the geothermal water to the injection hole, were examined. Based on that, 990 variations of configuration have been analyzed. The research showed that the lowest simple payback time (SPBT) values were achieved for the SGT-800 gas turbine and the working fluid R1336mzz(Z), for example, for an electricity price equal 200 USD/MWh and a natural gas price equal to 0.4 USD/hg, resulting in a SPBT value of 1.45 years. Additionally, for this variant, the dependence of SPBT on the price of electricity and the depth of the geothermal well was calculated; assuming the depth of the geothermal well is 2000 m, SPBT changes depending on the adopted gas prices and so for 150 USD/MWh it is 2.2 years, while at the price of 100 USD/MWh it is 5.5 years. It can be concluded that a decrease in SPBT is observed with an increase in the price of electricity and a decrease in the depth of the geothermal well. The findings of this study can help us to better understand the need to utilize low and medium temperature geothermal heat by using combined cycles (including gas turbines), also from an economic point of view.

An unusual case of low concentration mineral brines in the geothermal waters from Beiuș Basin (Northwestern Romania)

The aim of the BrineRIS project is to explore brines in RIS countries potential for critical metal extraction In the frame of this project the concentration of mineral brines in three geothermal wells located in the Beiuș Basin (northwestern Romania) was determined by analyzing the water from the wells. Until recently no reliable trace element data were available from Beiuș basin. Following the new analyses, the geothermal water extracted by TRANSGEX SA company from wells F-3001H, F-3003H, and F-3005H revealed exceptionally low concentrations of associated chemical compounds. The Li-concentration is only ~ 22 – 32 µg/l. Zn, I, Rb and As present in similar concentrations, while other trace elements (e.g. Co, V, Ti) are below detection limit. The Sr (~ 540 – 680 µg/l), Ba (~ 170 – 200 µg/l) and B (~ 70 – 100 µg/l) concentrations are slightly elevated, but still low. Therefore, the water in this "geothermal reservoir" can be classified as relatively potable, but it is not appropriate for critical metal extraction. In this paper, some documented concentrations from previous years have been compared to recent concentrations. In addition, the relationship between geology and water chemistry is emphasized in order to determine the reason for the absence of solutes that were expected to be found in this water.

Comparison and integration of pore pressure measurements and indicators from drilling data in a deep geothermal energy play in SE Germany

The North Alpine Foreland Basin in SE Germany is a post-mature petroleum basin and today Germany's most prolific deep geothermal energy play. Drilling of deep wells is often challenged by the complex pore pressure distribution, which has been studied in the past, but quality and reliability of individual pore pressure measurements and indicators have so far been barely addressed. This is particularly critical, since most datasets originate from old hydrocarbon wells and often display limited availability and poor quality. This paper analyses pore pressure measurements and indicators from 315 deep hydrocarbon and geothermal wells. The dataset covers pressure measurements, drilling mud weights, caliper logs, drilling events and gas readings. A large number of pressure measurements are exposed to uncertainties, resulting predominantly from incomplete pressure build-ups. In addition, investigation of drilling mud weights combined with wellbore instabilities, gas readings and pore pressure-related drilling problems suggest that many wells were subject to underbalanced drilling and mud weight alone is not a reliable pore pressure indicator. The study provides a recommendation for pre-drill pore pressure prediction based on the investigated datasets, which also presents a reference case for other post-mature petroleum basins transitioning to new industries, such as deep geothermal. Thematic collection: This article is part of the Earth as a thermal battery: future directions in subsurface thermal energy storage systems collection available at: https://www.lyellcollection.org/topic/collections/thermal-energy

Numerical analysis on the failure characteristics of hot dry rock subjected to axial-torsional coupled percussion with single cutter

High-hardness and poor-drillability of hot dry rock (HDR) impose great challenges on drilling-rate improvement, limiting the economic exploitation of HDR geothermal. Axial-torsional coupled percussive drilling (ATCPD), as a potential drilling-rate improvement method, might provide solutions for achieving efficient breaking of HDR. To determine the rock breaking performance of ATCPD in HDR, we investigate the failure behaviors of high temperature rocks under percussion loads. Three loading modes, i.e., static loading, axial percussion loading, and torsional percussion loading, are compared with axial-torsional coupled percussion loading (A-TCPL) mode, with respect to rock breaking capacity and failure behaviors. The effect of some important engineering parameters, e.g., rock temperature, impact amplitude and frequency, is put particular emphasis to obtain the great rock breaking performance. Results show that ATCPD is characterized by the higher amplitude force, lower torque and larger cracking volume as compared to other loading modes, thereby resulting in a growth drilling efficiency. A-TCPD shows greater performance to high temperature rocks in stress response and material damage. The maximum principal stress, tensile and compressive damage factors are positively correlated with rock temperatures under A-TCPL mode. Increasing the impact amplitude and frequency are beneficial for inducing damage on rocks with temperatures ranging from 200 to 600 °C. By using the rock breaking total displacement as the evaluation index, the optimal ratio of axial to torsional impact frequencies for greater rock breaking capacity is obtained. For rocks at 200 °C, 400 °C, and 600 °C, the optimal ratio of axial to torsional impact frequencies is 1:2, 1:3, and 2:3, respectively. The results are expected to provide new insights to enhance drilling rate for geothermal well and HDR excavation.

Multi-index-weighted geothermometer estimation of geothermal reservoir temperature: Applications and future directions

Geothermal reservoir temperature (GRT) is an important factor for estimation of geothermal resources and exploitative potential. Errors in the estimated temperature of a geothermal reservoir can likely result from the use of a single geothermometer or the average. Therefore, there is an urgent need for novel and more accurate methods for estimating GRT. Taking Yitong Basin, China as the study area, this study collected water samples and measured the geothermal water temperature of 26 geothermal wells. After application of the improved entropy method (IEM) to the collected data, a multi-index weighted geothermometer (MIWG) was proposed. The MIWG provided the most accurate estimation of temperature, with average errors in temperature estimation for quartz, chalcedony, Na–K, K–Mg, and MIWG of 57.58 %, 15.86 %, 29.92 %, 42.03 %, and 11.94 %, respectively. This novel approach to estimating GRT has clear advantages, including wide applicability, and can provide a new pathway for future related research.

A Fresh Look at the South Australian Onshore Otway Basin (Insights from Dem's Petroleum Systems Model Project)

The Otway Basin is one of the best known Mesozoic rift basins that span the southern coastline of Australia and has both on and offshore gas production and oil discoveries. 104 petroleum and 6 geothermal wells have drilled since the 1890s. In 1987 Katnook 1 discovered economic gas in the Penola Trough (the most significant hydrocarbon province in the SA part of the basin to date), further drilling led to more discoveries and construction of a processing plant.

Transition from oil & gas drilling fluids to geothermal drilling fluids

The harsh downhole conditions encountered in geothermal wells, specifically the high temperatures (HT) together with the toughness of the rock found in many geothermal formations, makes the drilling operation challenging. Drilling in such environments requires specialised drilling fluid formulations that have high thermal stability, good rheological properties, excellent lubricity and low formation damage. Given the wealth of experience in drilling wells in the oil industry, it is tempting to assume that the design of geothermal drilling fluids would be straightforward. However, is this the case? In this literature review, we have attempted to answer the question: “to what degree can developments in oil and gas drilling fluids be transferred to drilling fluids for geothermal wells?” To keep the scope of the review manageable, we have focused on two key aspects of drilling fluid design: rate of penetration (ROP) and HT fluid stability (and maintenance of the desired rheological properties of the fluid at high temperatures). The review has allowed the identification of gaps in both fundamental understanding and in existing technology. Rate of penetration is improved using low viscosity and low-density fluids, and we recommend that foams and aphron systems should be investigated to achieve this (depending on the application pressure). It should be noted, however, that such systems to date have only been studied at relatively low temperatures and the challenge of increasing the thermal stability of the formulation components needs to be addressed. Highly thermally stable polymer systems exist but these are both expensive and not widely available. A systematic study of the impact of copolymer molecular architecture on hydrolytic thermal stability is recommended. A promising solution to both maintaining good rheological properties at high temperature and providing fluid loss control is the use of particulates, especially those in the nano-size range. Additionally, nanocomposite systems show promise in this area and should be investigated. Particle stabilized foams and aphrons are a particularly interesting solution and we recommend that these are studied. It is also recommended to investigate the effect of drilling fluid on long term geothermal well performance.

Best Practices to Achieve Optimal Geothermal Drilling Performance in A Cost-Effective Manner: Case Study of the Fastest Geothermal Well Drilling in Java and Sumatra

Indonesia, recognized for possessing substantial geothermal energy potential, is working towards harnessing the resource to achieve numerous objectives. Among the primary challenges encountered is the considerable expense of geothermal drilling. One of the most significant obstacles to achieving this objective is the high drilling cost, which constitutes 35-40% of the total cost of geothermal energy development. The drilling cost is mainly affected by the time needed to drill one well because the faster the time, the lower the cost. Therefore, this research analyzed drilling activities, identified the fastest and most effective methods for optimal geothermal drilling performance, and reduced costs. The research also determined the factors that contributed to the sustained status of Well X as the fastest well drilled in the past decade. The methodology comprised literature review, data collection through adequate background on well and geothermal field, and data analysis. The result showed that the fastest drilling operation of a geothermal well in Indonesia in 2012 occured in West Java (Well X) for only 9.9 days with 1736.5 meters (mMD). Meanwhile, in 2021, Well Y in Sumatra spent 21.74 days to reach a depth of 2200 mMD. The use of a single-run and clean-out Bottom Hole Assembly (BHA) throughout the entire section affected the drilling duration and significantly reduced the inner side cleaning time, respectively. The cost of Well Y drilling, achieved using the best performance of two wells, reduced drilling costs by 19.2%.