Temperature Geothermal Wells Research Articles

Innovative drilling fluid containing sand grafted with a cationic surfactant capable of drilling high pressure and high temperature geothermal and petroleum wells

Maintaining the rheology and filtration properties of a drilling fluid plays a vital role during a drilling operation. With the current challenges of high pressure and high temperature environments, there is an urgent need to design thermally stable water-based mud systems (WBM) which are environmentally clean and economically cheap.High pressure and high temperature (HPHT) environments affect drilling fluid systems leading to degradation of additives hence reducing the efficiency of the drilling fluid. Nanotechnology has been widely used to answer questions about additive degradation, and many studies are currently being conducted on how to use nanotechnology to design smart drilling fluids. However, nanotechnology comes at a high cost, resulting in an increase in the overall drilling operation costs and the project as a all. Therefore, the effectiveness of sand particles as a replacement of commercial nanoparticles is investigated in this study as an additive for designing effective-performance water-based drilling fluids. Effective-performance drilling fluids are environmentally friendly, stable at high temperatures, and help to avoid well damage during drilling operations.The research compared sand particles, which are widely available and inexpensive to silica nanoparticles at 0.5 wt% concentration. The samples were tested at different aging temperatures. Rheological properties were measured at room temperature up to 232 °C. The performance of sand and silica nanoparticles was studied by comparing each of the nanoparticle muds with the reference mud sample, taking filtration and rheological properties as the benchmark parameters. Experimental data showed that sand particles enhanced almost all the rheological and filtration properties of the WBM compared to the reference mud. When compared to silica nanoparticles, the results showed neither statistically significant variance in plastic viscosity and yield point among the samples, with muds containing sand particles performing similarly or better. Formulation S2 (35–70 μm) demonstrated the ability to improve the rheology of WBM. At 204 °C and 232 °C, Formulation S2 (35–70 μm) filtrate loss decreased by 16.35% and 29.52%, respectively, compared to 5.66% and 11.32% by mud containing nano silica. The same mud sample decreased the mud cake thickness at the same temperatures conditions by 54.74% and 45.45%, respectively, as opposed to 36.84% and 11.81%. The new innovative mud system can be used to drill in HPHT conditions.

Feasibility Analysis of Drilling with Liquid Nitrogen in High Temperature Geothermal Wells

The main costs of developing geothermal processes are concentrated in the project of drilling, accounting for more than 70% of the total budget. Inspired by thermal stimulation technology，a new concept of drilling with liquid nitrogen was presented in this paper. The main objective of this paper is to investigate the effect of rapid cooling on bit-rock interaction and the feasibility of drilling with liquid nitrogen. Through the hardness test experiment results, it showed that the thermal stress caused by rapid cooling can reduce the resistance of indenter invades the rock. Then the micro-bit drilling experiment results indicated that liquid nitrogen can eliminate the thermal damage and enhance the wear resistance, which is the main factor affected the life and footage per bit in geothermal drilling. The negative effect is that liquid nitrogen increase the rock failure resistance slightly and need about 8% more mechanical specific energy compared with drilling with air, but the increase about 8% in mechanical specific energy is affordable to drilling engineers. All these results showed that drilling with liquid nitrogen is beneficial to improve the life and footage per bit, reduce non-production time and reduce drilling costs, it is a promising technology in geothermal engineering.

Modeling of two-phase flow of high temperature geothermal production wells in the Yangbajing geothermal field, Tibet

Two-phase flow (flow of water in both liquid and gas phase, containing a non-condensable gas such as CO2) in the wellbore is one of the most important processes in the production performance and wellbore scaling evaluations of high temperature geothermal wells. This paper first describes the discharge tests in the Yangbajing geothermal field, Tibet. Next, a simple model for governing the two-phase flow in the presence of CO2 in the wellbore is constructed and a robust calculation method is presented. The model is applied to three production wells in the Yangbajing geothermal field. The results show that the velocity difference between the gas and liquid phase should be included in the model. Ignoring this difference (i.e., homogeneous model) would result in a significant deviation between measurements and calculations. A drift flux model (DFM) describes the velocity difference, where the specifics of the particular model can have significant effects on the results for the pressure and temperature profiles in the wellbore. Three commonly used DFMs are compared to estimate their performance. The calculated wellhead pressure and temperature are in the range of 2,3 bar and 125°C–135°C for all three wells at a production rate of about 20 kg/s. The estimated wellhead gas mass fraction is between 3% and 8%. Considering CO2 content, three different scenarios were evaluated, although the effect on the pressure and temperature profiles were limited. However, CO2 content has a much more significant effect on the flash depth, which is an important parameter for the estimation of calcite scaling.

Using Fumed Silica to Develop Thermal Insulation Cement for Medium-Low Temperature Geothermal Wells.

During geothermal energy development, the bottom high-temperature fluid continuously exchanges heat with the upper low-temperature wellbore and the stratum during its rising process. Thermal insulation cement (TIC) can increase the outlet temperature, thus effectively reducing the heat loss of the geothermal fluid and improving energy efficiency. In this study, vitrified microbubbles (VMB) were screened out by conducting an orthogonal test of compressive strength (CS) and thermal conductivity (TC) on three inorganic thermal insulation materials (VMB, expanded perlite (EP), and fly-ash cenosphere (FAC)). Fumed silica (FS) was introduced into the cement with VMBs, as its significant decreasing effect on the TC. Moreover, a cement reinforcing agent (RA) and calcium hydroxide [CH] were added to further improve the CS of TIC at 90 °C. The fresh properties, CS, TC, hydration products, pore-size distribution, and the microstructure of the cement were investigated. As a result, a TIC with a TC of 0.1905 W/(m·K) and CS of 5.85 MPa was developed. The main conclusions are as follows: (1) Increasing the mass fraction of the thermal insulation material (TIM) is an effective method to reduce TC. (2) The CH content was reduced, but the C–S–H gel increased as FS content increased due to the pozzolanic reaction of the FS. (3) As the C–S–H gel is the main product of both the hydration and pozzolanic reactions, the matrix of the cement containing 60% FS and VMBs was mainly composed of gel. (4) The 10% RA improved the cement fluidity and increased the CS of TIC from 3.5 MPa to 5.85 MPa by promoting hydration.

Light-weight temporary-sealing cement for medium temperature geothermal wells by using polyvinyl alcohol fibers and fly ash cenospheres

A new lightweight temporary-sealing cement (LTC) is developed in this study to prevent lost circulation and simultaneously protect target formation during drilling. Water-soluble polyvinyl alcohol (PVA) fibers and fly ash cenospheres (FACs), were added to class G cement to develop the LTC for 90–150 °C geothermal wells, on the basis of the temperature change process related to cement plugging. Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), scanning electron microscopy/energy dispersive spectroscopy (SEM-EDS) and total organic carbon (TOC) tests were conducted to investigate the chemical composition, crystalline phases, pore diameter distribution, permeability, microstructure of the specimens and the dissolution rate of PVA fibers in hardened cement. The following conclusions can be drawn. 1) The addition of 10% FACs and 3% PVA fibers optimized the cement slurry density to 1.54 g/cm3 2) The addition of PVA fibers enhanced the cement flexural strength. And all the compressive strengths of the samples were greater than 6.5 MPa 3) The fibers in hardened cement could maintain integrity in 60 °C water, and remain soluble under 120 °C dry condition, demonstrating that they could work with cement and FACs to seal the fracture for drilling at lower temperature, and dissolve out from hardened cement in ≥90 °C water. 4) Most of the PVA fibers dissolved and leached out of the cement within 4 h in 90 °C water immersion. The elongated holes formed by fiber dissolution, interconnected with other pores in cement matrix, contributing to the less tortuosity and substantially increased permeability of LTC. In general, the enough strength and high permeability of degraded LTC prove that the 90 °C water-soluble PVA fibers and FACs could be used to prepare the partially degradable LTC for 90–150 °C geothermal wells.

Thermo-mechanical tensile testing of geothermal casing materials

Ultra-high temperature geothermal wells (>450 °C) have a large potential for increased energy yield as compared to conventional high-temperature geothermal wells (200-300 °C), but several research challenges must be resolved before robust operation in this temperature range can be achieved. In this study, yield- and tensile strength data for several relevant carbon steels and corrosion resistant alloys are generated as a step on the way to enable design of collapse- and tensile capacity for geothermal casings exposed to temperatures up to 500-550 °C. The experiments extend the data set listed in NZS 2403:2015 by providing data for higher temperatures and different material classes. It is found that the carbon steels follow the same near linear decay in strength as the NZS 2403:2015 curves up to 350 °C, and then display a significant drop in tensile strength at higher temperatures, particularly for the lower strength steels. The alloys with high nickel content work harden significantly more than the carbon steels at high temperatures and they tend to retain their strength at temperatures above 350 °C. The tested titanium alloy shows high yield strength and low work-hardening at 500 °C and in contrast to the tested nickel alloys, do not display dynamic strain ageing.

Quantitative assessment of calcite scaling of a high temperature geothermal well in the Kangding geothermal field of Eastern Himalayan Syntax

High temperature geothermal systems in China are mainly located along the Himalayan belt and one of the main problems during production is calcite scaling. This paper presents a quantitative assessment of calcite scaling and possible removal and prevention methods for the Kangding geothermal field in the Western Sichuan Plateau, as an example. Reservoir fluid composition is reconstructed based on geochemical processes that may take place from reservoir to surface. Results show that the fluid is HCO3⋅Cl-Na or Cl⋅HCO3-Na type with a temperature of 259−283 °C. It’s over-saturated with respect to calcite in both surface and reservoir conditions but under-saturated to quartz and amorphous silica, indicating that the calcite scaling will be a problem. For well BH6, the fluid pH is 5.63 at reservoir conditions and the steam fraction at the wellhead is about 6.0 %. Adiabatic boiling calculation indicates that from reservoir to surface conditions, CO32− and CaCO3 concentrations in the fluid keep increasing and the fluid evolves to become over-saturated with respect to calcite and the saturation index is higher than 0.5 and calcite precipitates in the pipeline. The boiling depth is estimated to be about 150 m from the wellhead which can provide a guide for scaling depth determination. The calcite scale quantity is calculated to be 151−300 kg or a thickness of 0–2.94 cm according to the pumping test, consistent with what has been observed. Calcite scale can be removed mechanically or prevented by injecting chemical inhibitor as well as thermodynamic methods (including injecting acid, CO2, cold water and putting the feeding pump below the boiling depth). Counter-measures should be chosen based on the mode of utilization and its cost. For well BH6 that is planned to be used for power generation, chemical inhibition may be the choice.

Aerated drilling cutting transport analysis in geothermal well

Aeratad drilling widely used for geothermal drilling especially when drilled into predicted production zone. Aerated drilling give better performance on preventing lost circulation problem, improving rate of penetration, and avoiding drilling fluid invasion to productive zone. While well is drilled, cutting is produced and should be carried to surface by drilling fluid. Hole problem, especially pipe sticking will occur while the cutting is not lifted properly to surface. The problem will effect on drilling schedule; non-productive time finally result more cost to be spent. Geothermal formation has different characteristic comparing oil and gas formation. Geothermal mainly has igneous rock while oil and gas mostly sedimentary rock. In same depth, formation pressure in geothermal well commonly lower than oil and gas well while formation temperature geothermal well is higher. While aerated drilling is applied in geothermal well, Igneous rock density has higher density than sedimentary rock and aerated drilling fluid is lighter than water based mud hence minimum velocity requirement to transport cutting is larger than in oil/gas well drilling. Temperature and pressure also has impact on drilling fluid (aerated) density. High temperature in geothermal well decrease drilling fluid density hence the effect of pressure and temperature also considered. In this paper, Aerated drilling cutting transport performance on geothermal well will be analysed due to different rock and drilling fluid density. Additionally, temperature and pressure effect on drilling fluid density also presented to merge.

Structural modeling of the casings in the IDDP-1 well: Load history analysis

Flow testing of IDDP-1, the first Icelandic Deep Drilling Project (IDDP) well drilled in the Krafla geothermal field in Iceland, demonstrated promising results by producing superheated steam. During an unavoidable quenching of the well the innermost casing failed presumably due to tensile stresses caused by thermal contraction. Since the structural integrity of casings is essential for utilization of high temperature geothermal wells, the well has not been discharged again. In this paper, the casings of the well are analyzed structurally with a nonlinear finite-element model. The load history of the casings is followed from installation and through several thermal cycles, but the well was discharged at least six times before it was quenched with cold water. The results show that changes in stiffness due to the presence of casing shoes and changes in casing thickness have an effect on the stress and strain formations in neighboring casings. The results illustrate that during each thermal cycle, the wellbore thermal load is more severe for the production casing than for the external casings that are somewhat protected, provided that cementing in between is adequate.

Structural modeling of the casings in high temperature geothermal wells

High temperature geothermal wells are constructed of several concentric steel casings that are fully cemented up to the surface. The structural integrity of such casings is essential for the utilization of wells. The casing is subjected to multiple thermo-mechanical loads that can cause casing failures. Thermal expansion generates thermal stresses in the casings and causes the wellhead to rise slightly during discharge. In this paper, a nonlinear structural finite-element model of the cased section of a geothermal well is presented and validated. The numerical results show good agreement with wellhead displacement measurements of 5 different wells in Iceland.

Processing and analysis of high temperature geothermal acoustic borehole image logs in the Taupo Volcanic Zone, New Zealand

Acoustic borehole televiewer (BHTV) logs provide direct observations of lithology, structure and in situ stress in reservoirs, essential for successful well targeting and field management. Analyses of BHTV logs acquired in twenty-three high temperature (≤288°C) geothermal wells in the Taupo Volcanic Zone, New Zealand, resulted in the modification of BHTV processing techniques and the creation of a descriptive feature classification for hydrothermally altered, volcano-sedimentary-basement type reservoirs lacking other complementary information common in hydrocarbons or lower temperature geothermal systems. Lithological characteristics observed on these BHTV logs are presented, alongside an assessment of the reliability of the structural measurements and image interpretation.

Drilling and Completion Techniques for High-Temperature Geothermal Wells

The high temperature formation, strong abrasiveness, numerous fractures and caves are the main problems of high temperature geothermal well drilling, cementing. Cone bit teeth repeated impact tests show that bit life mainly affected by tooth shape, materials, solid tooth technology. Setting special materials around the teeth and adjusting the fitting wring will improve the life of cone bit teeth. Study of quartz sand amount and fineness ratio effect on cement high temperature compressive strength, permeability show that optimization of high temperature cement slurry can improve the high temperature leakage zone cementing sealing and long-term effectiveness.

Study on Well Control Technology of High Temperature Geothermal Drilling

With the rapid development and research of geothermal resources, the number, drilling depth and formation temperature of high temperature geothermal wells increases year by year. But, so far the well control technology of high temperature geothermal drilling has not been paid attention to by relative person, the serious shortage of related technology and equipments retards the development of geothermal resources. This article describes the calculating methods of formation pressure, collapse pressure, circulating temperature, saturation vapor pressure and mud circulating temperature in high temperature geothermal wells, it can offer reference data for the design of drilling fluid, bottom hole assembly (BHA), well control equipment. High temperature geothermal drilling depends on the formation pressure and collapse pressure, the safe mud window is very narrow, suitable for pressure balance or underbalanced drilling, we design a simple structure, high speed, good heat resistance rotary blowout preventer (RBOP), which can increase the operability of geothermal wells balanced drilling.

The Theistareykir Geothermal Field, NE Iceland: Fluid Chemistry and Production Properties

Chemical analyses on samples from six high temperature geothermal wells in the Theistareykir geothermal field in NE Iceland are reported. The aquifer temperature is estimated to be in the range 270-290°C, although bedrock temperature exceeds 300°C. The wells have enthalpy ranging from liquid enthalpy at the aquifer temperature up to dry vapour enthalpy, in which case excess enthalpy is primarily due to phase segregation. The liquid is relatively dilute and under-saturated with respect to amorphous silica, down to about 10 bar-a.

２０世紀からの贈り物 掘削トラブルからの教訓 地熱井での掘削トラブル統計と掘削トラブル事例

Drilling problems that occurred during the last 15 years within JMC-Geothermal group while drilling geothermal wells, are reviewed. BHA parting, stuck BHA, and down-time caused by poorly maintained equipment, are three major problems to be avoided. Three processes that occurred during drilling a high temperature geothermal well in Kakkonda, are also discussed. They are mud deterioration caused by high temperature borehole conditions, unsuccessful sidetracking operations, and casing wear.

Potential use of geothermal steam in industrial processes. Results of icetec studies

During the last decade various steam consuming industrial processes have been studied at IceTec. The prerequisite for the studies was the potential and available cheap steam from high temperature geothermal wells. Steam prices in the early eighties were estimated in the range of 1.5 - 3.0 USD/t steam, based on transport distance and well productivity, giving geothermal steam an advantage of 10 - 12 USD/t steam, compared to steam fired boilers. Additionally at that time, changes were seen in the industry such as feedstock shortages, higher energy cost and more stringent pollution requirements. Different processes have been studied, having steam consumption from 4 - 110 ton steam per ton product. Most of these processes are based on hydrothermal technology, either leaching and/or precipitation. The steam consuming process steps are digestion, evaporation, hydrolysis, drying, distillation etc. Based on prices at the time of study, the savings were estimated to be up to one fifth of the production cost. Geothermal steam is very localised energy source, which consequently restricts the siting of new industrial plants. Despite apparent cost benefits, the direct use of geothermal steam in industry, is growing very slowly.

地熱井掘削時の坑井内温度の推定

It is important to know the temperature distribution in the wellbore during drilling to develop and evaluate the bit and/or mud for high temperature geothermal wells. But, normally only the inlet and outlet temperatures of drilling fluid can be measured during drilling in the field.Authours proposed a method which estimates temperature distribution in the wellbore from measured inlet and outlet temperatures of drilling fluid by computer simulation even when formation temperature distribution is not known exactly. In this paper, we described the method and estimated bottom-hole temperatures during drilling for four geothermal wells. Conclusions are as follows:(1) When the fluid is circulated in the well at a certain flow rate and the inlet and outlet fluid temperatures coincide with the given inlet and outlet temperatures respectively, the temperature distributions in the wellbore are almost the same for different formation temperature distributions.(2) The temperature distribution in the wellbore during drilling can be estimated from the measured inlet and outlet temperatures of drilling fluid even when undisturbed temperature distribution and thermal disturbance in the formation are not given exactly.(3) The estimated bottom-hole temperatures of mud during drilling were about 140 to 200°C lower than the undisturbedf ormation temperatures.Differences between the bottom-hole temperature and the outlet temperature of mud were only 1 to 18°C.