A critical factor in improving the efficiency and longevity of geothermal systems is the careful selection of materials capable of withstanding extreme environmental conditions, including high temperatures, corrosive fluids, and mechanical stresses. This paper aims to provide insights into various grades of stainless steel that are particularly suitable for geothermal energy applications, with a focus on their corrosion resistance in brine.

For well construction it is paramount to assess the influence of design features, such as crevices, bends and welded joints, in the corrosion resistance of the materials, reason why we also included those assemblies in our study. The tested grades were S31603, N08904, S32205, S32750, S31254 and N08935.

This study combines historical and new data to obtain an overview of how various stainless steel grades behave in different brines. Recognizing that the risk of corrosion in brines is influenced by various factors, this research evaluates the performance of stainless steels against localized corrosion in chloride concentrations of 20000, 100000 and 200000 ppm, solutions at a temperature of 90°C, pH 4 and 8, with and without aeration.

The findings of this study outline the localized corrosion performance of stainless steel, offering valuable insights for material selection in geothermal applications. Furthermore, the discussion thoroughly explores the factors affecting the corrosion resistance of stainless steel, including chloride content, oxygen levels, and solution pH, thereby contributing to a deeper understanding of the materials best suited to withstand the challenges posed by geothermal environments.

Silica scaling is an operational issue in geothermal energy production. In this work, a static bottle test methodology was developed to assist in identification of silicate inhibitors, demonstrating 80-90% inhibition performance, for application in low-enthalpy geothermal systems. To identify effective products for the control of amorphous and magnesium silicate scaling, the inhibition mechanisms and inhibition efficiency (IE) of two sulphonated polymer-based scale inhibitors, denoted A5 and SI B, were studied. This was done for a brine containing [Mg] = 120ppm and [Si] = 1880 ppm at 95ºC and pH 8.5. The impact of adding 500ppm calcium was subsequently assessed.

In the absence of calcium, Minimum Inhibitor Concentrations (MIC) of ~50ppm for SI B and ~100ppm for A5 were required to control amorphous and magnesium silicate scale effectively at ~60-90% IE. In the system containing calcium, although two approaches were used to adjust the pH of the brine to 8.5 to reduce the tendency for Ca(OH)₂ precipitation, and thereby improve scale inhibitor effectiveness, neither SI B nor A5 prevented precipitation of silicate-based scale.

Consumption of A5 and SI B was tracked using two methods to assess the inhibition mechanism: (i) by measuring the concentration of sulphur (S) contained within the A5 and SI B structure, by Inductively Coupled Plasma-Optical Emissions Spectrometer (ICP-OES), and (ii) by using a matrix-matching Hyamine technique, to enable A5 and SI B to be assayed as a polymer product. The outcomes contribute to a better understanding of the silicate inhibition mechanism.

The primary objective of acidizing injector wells in sandstones is to remove scales impeding the pathway of water and hence increase the injectivity of the formation. HCl-based treatment fluids are commonly used while employing diverting agents to prevent acids from leaking into the most permeable sub-layer of the target zone is recommendable. These additives function by creating a temporary blocking effect which causes fluid diversion facilitating successful acidizing.

This paper presents a surfactant-based product with a tendency of forming rodlike micelles in acidic solutions, where a chaotic worm-like arrangement of dissolved molecules leads to an increase in fluid viscosity. In preparation of the first field trial in a Dutch geothermal well, we performed extensive lab experiments regarding solubility of bailer samples, corrosion of L-80 coupons, and rheology of acidic recipes.

Skin removal and improvement of injectivity were the main objectives. For dissolving carbonates, as well as silicates in the Slochteren sandstone formation, a combination of hydrochloric and hydrofluoric acid was bull-headed in a stepwise approach. The subsequent injection test with brine served to evaluate the treatment and to displace spent acid systems deep into the reservoir.

Due to the superior chemical properties of our innovative diverter agent combined with the great effectiveness of the tailor-made treatment fluids, we achieved a significant improvement in injectivity. While keeping the well head pressure at a constant level, we could increase the pumping rate by a factor of four. Thus, impressively proofing that we have reached the next level of acidizing sandstones.

Digital twins for geothermal wells can boost performance, predictive maintenance, and decision-making by diagnosing issues. The software models a geothermal system and currently covers the ESP (Electric Submersible Pump), injectivity/productivity and the Well Integrity Management System (WIMS). An important feature of the WIMS model is the corrosion modelling which uses real-time data and time-lapse data as calliper logs. The corrosion model can be used early warning system for well barrier issues.

The presentation will explain the Digital Twin and the opportunities it offers.

The current climate and energy crisis requires the development of alternatives to conventional energy sources to ensure national independence in the provision of electricity and heat. In this context, (deep) geothermal energy offers a readily available, environmentally friendly, and climate-neutral alternative to fossil fuels. It has the potential to play a central role in the implementation of the heat transition. However, for the long-term and stable use of deep geothermal energy, reliable pumping systems are essential to convey the thermal water from the reservoir to the surface.

Two main systems are currently in use: electrical submersible pumps (TKP/ESP) and line shaft pumps (LSP). However, both systems have deficiencies under the specific operating conditions of geothermal energy, which affect both their economic viability and security of supply. Significant improvements in the development and standards of these pumps are therefore crucial for the safety, reliability, and profitability of geothermal plants. The ANtLiA project, funded by the German Federal Ministry for Economic Affairs and Climate Protection (BMWK), aims to identify and optimize the currently limiting factors of the above-mentioned pumping systems. This is intended to extend operating times and reduce costs, sustainably improving the economic viability of geothermal projects and their security of supply. In addition, targeted further developments of both systems will be carried out, including new subsystems for ESPs and the redesign of the lubrication system for LSPs, which will be tested and evaluated for suitability in the newly designed test rig.