Corrosion in geothermal is a process of material degradation caused by the chemical or electrochemical reaction of the geothermal fluids with the exposed surface of the material of the equipment. Most of the geothermal equipment is made from carbon steel material owing to its superior mechanical properties and high strength. However, carbon steel materials are susceptible to corrosion in low pH acidic, and hyper-saline geothermal fluid environments.
A lot of geothermal wells are not being utilized in the world because they are producing aggressive fluids which are either acidic or hyper-saline. This makes them corrosive to carbon steel. For subsurface requirements such as production casing and production liner, we supply pure corrosion-resistant alloy (CRA) such as 25Cr or 17Cr materials to eliminate corrosion at the subsurface level,
At the surface level, from wellhead to geothermal gathering systems, we eliminate corrosion with the application of weld-overlay cladding of critical geothermal equipment such as casing head flange (CHF), Master Valve, Wing Valves, Production Cross, Production Tee, Through Conduit Valve (TCV), and the rest of piping spools, fittings, and downstream valves.
A variety of CRA material are available that can be used in weld-overlay cladding. Currently, the material of choice by geothermal clients is Inconel Alloy 625. Inconel Alloy 625 material performed well in anti-corrosion application in acidic geothermal fluids as low as pH 2.2. We have provided cladded Master Valve to EDC in the Philippines in one (1) of its acid geothermal well production. In Indonesia, we have collaboration with Sarulla Geothermal Operations to supply weld-overlay cladded materials for five (5) wells that include cladded CHF, cladded Master Valve, cladded wing valves, cladded Production Cross, cladded production tee, piping spool, cladded elbow spool, cladded injection spool, and cladded sampling spool.
Inconel alloy 625 has been the anti-corrosion material of choice in Oil and Gas, petrochemical, and chemical industries. Wilclad bring this knowledge in anti-corrosion control in geothermal applications so that those aggressive wells will be utilized to give geothermal clients additional geothermal production, increased power generation, and increase rate of return.
Erosion is a material degradation at the surface of exposed material and is caused by mechanical action such as friction and impact caused by solids carry over in the fluids. This is also caused by the implosion of bubbles during flashing causing cavitation, and liquid droplet impingement. The solids from the geothermal fluids can be material from a reservoir or wellbore that has been carried to the surface due to being lifted by the fluids. Solids can also be from precipitates in the chemical reaction in the fluids as the fluid rises to the wellbore and chemical reactions occur due to the separation of steam and brine in the geothermal fluids.
Erosion removes the exposed surface of the material gradually until the critical thickness is reached. To mitigate corrosion, the solution is to do weld-overlay cladding of the exposed surface with a wear-resistant material. However, the wear-resistant material is very hard when applied as cladding is prone to cracking. To solve this phenomena, the base material is cladded first with Inconel Alloy 625. Once the Inconel alloy 625 is set, the wear-resistant alloy layer is then added on top. Inconel alloy 625 exhibits high corrosion resistance and high ductility which makes it a material of choice for base surface modification.
The erosion in geothermal production can also be due to changing geothermal reservoir characteristics. Each wellhead component and branch line piping design is usually according to the initial discharge characteristic of the well. Geothermal reservoir drawdown will occur over time. The well will produce more steam which increases its steam velocity and lifts more solid material to the surface. This will increases the likelihood of erosion. Erosion can also be process-specific and can be due to inappropriate piping configuration. As the geothermal fluids flow downstream with changing pressure, thermodynamic plays in the propagation of implosion of bubbles during flashing and cavitation, and liquid droplet impingement.
Wilclad solution for erosion mitigation is problem-specific. Our first approach is design modification specific to client requirement and our sustaining solution is the application of weld-overlay cladding with wear-resistant material for long-term erosion mitigation.
Solid deposition (scaling) is one of the major problems found in the utilization of geothermal wells in liquid-dominated geothermal fields. Its major impact is that it limits the development of geothermal resources for electrical power generation. Calcite and Silica are the most common scaling minerals present in geothermal systems, and they have been found in production casings and slotted liners in production wells. The problems caused by these scales are associated with changes in the production condition of the wells due to the flow restrictions and subsequent reduction in well output. Calcite scaling tends to form in the production wells while silica scaling usually occurs in the reinjection lines and reinjection wells.
Calcite scaling is associated with the onset of boiling inside the well, as calcite supersaturation occurs after boiling at a certain depth in the production well, boiling and degassing takes place. Not all wells will have calcite scaling because this is also dependent on the chemical components of the geothermal fluids and the dissolved gases. The inhibition of scale deposit by using chemical products has gained importance both technically and economically and seems to be the most promising system. The choice of suitable calcite inhibitor chemicals and the system of injecting them into the well is critical in this case. Scale inhibitor chemicals are added to normally scaling water to reduce, delay or prevent scale formation. This method consists of running a coiled tubinge into the well and setting it at the desired depth for injection of inhibitor chemicals. In most cases, this depth will be below or at the flashing point zone.
Silica scaling is also associated with the temperature change of the geothermal water, this is usually observed in the reinjection line or reinjection wells. Silica is more common than calcite scaling. Silica is one of the most common chemical species in geothermal production. Silica is dissolved depending on the temperature of the reservoir.
The dissolution of silica in water is a very long process. In the cycle of geothermal production, the process is very quick from production to separation to reinjection. There is no time for the silica to equilibrate to a lower temperature so what happens is there is so much excess silica going to the reinjection wells. This oversaturation will deposit silica in the reinjection line and the wellbore of the reinjection line. Inhibition of silica can be done by injecting proprietary inhibition chemicals at the two-phase line before the separation of steam and brine occurs. Silica inhibition can also be done by pH modification with the treatment of acid. At pH of 4.5 to 5.0, the polymerization of silica is delayed. There is also an online dissolution method where the injection of chemicals will be done while the reinjection well is online. Since the chemical is acidic, dosing is controlled to minimize the effects of corrosion.
Wilclad solution for scaling inhibition focus on the delivery of proprietary chemicals for scaling inhibition using our fluids management system (FMS). The FMS is designed according to the requirement of the client.
The Fluid Management System (FMS)
The fluid management system (FMS) is a physical system configuration consisting of tanks, pumps, control systems, injection systems, chemicals delivery and others. The purpose of FMS is to deliver liquid chemicals to a targeted objective zone to modify fluids chemistry such as acid neutralization, inhibition of calcite, and inhibition of silica scale. The chemicals delivery of the FMS can be at subsurface (reservoir depth). This is usually done in acid neutralization to mitigate corrosion problems at the reservoir and with calcite inhibition to keep the fluid minerals from precipitating. The surface injection injection can also be done with calcite inhibition (geothermal pipeline), for acid neutralization at wellhead and silica scaling at the brine line. The FMS can be a simple or complicated system and be designed and developed according to the geothermal client’s requirements and objectives.
FMS for Acid Neutralization consists of chemical storage tanks, mixing tanks for chemical dilution and holding tanks of chemicals for injection. This set-up will have tanks for the transfer of chemical and a high-pressure pump to deliver the chemicals. Delivery of chemicals to a target reservoir depth will be through a capillary tubing, an injection system that is set up at the wellhead, and a set-up of weights that will roll down the capillary tubing to the target depth.
FMS for Calcite Inhibition is almost similar to FMS for acid neutralization. With the minor difference in the tank configurations.
FMS for Silica Scaling Inhibition is a simple set-up for chemical delivery at the surface geothermal pipeline. The set-up will have a simplified set-up of tank configuration and low-pressure injection pumps
Wilclad can design, manufacture, procure, and install an FMS package suitable for geothermal client requirements and purposes.