Scale Control in Geothermal Wells – What are the Options for Effective and Economic Scale Management?

Abstract

Abstract The drive towards net zero by 2050 has instigated the development of alternative energy sources to fossil fuels which has resulted in a big focus on geothermal energy projects. Geothermal brines typically contain dissolved minerals and gases that can cause scale deposition in wells and topside plant equipment. The presence of scale within a geothermal system can cause various issues leading to decreased efficiency of thermal energy production due to inefficiency of heat exchangers and turbines and the potential for reduced flow capacity in injection wells. In geothermal systems, the conditions and brine chemistry of each geothermal plant can vary greatly, and the selection of a suitable scale management process will be crucial for the sustainable production of geothermal energy. As with all scaling issues in the energy industry, prevention via chemical inhibition and/or chemical removal is the preferable method of dealing with scale compared to costly mechanical removal although non-chemical methods now offer an attractive alternative especially for reducing CO2 footprint. Chemical treatment can be by continuous topside chemical injection, scale squeeze or batch treatment in the injection and/or production wells. The high temperatures of geothermal wells coupled with high water throughput can create quite a challenge for chemical scale control and removal. Any selected scale inhibitor/dissolver will need to be thermally stable to up to 250°C, preferably biodegradable (although this is not essential) and display good efficiency against calcium carbonate and silica/silicate scales. Geothermal brines contain dissolved CO2 and H2S and this can make fluids corrosive so the interaction between scale and corrosion inhibitors will also need to be considered as part of any scale or corrosion management strategy. This may also require modified laboratory test methods, especially for geothermal plants with water re-injection. This paper will review geothermal scale and its mechanisms of formation and will highlight the options available for scale management including both chemical and non-chemical treatments. In addition, the impact of well completion, high water production, corrosion, CO2 footprint and the challenges for chemical treatments in terms of thermal stability and laboratory testing will be discussed.