Scaling Inhibition

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.