It seems like “mud folks” always talk about water. The quality of makeup water for drilling fluids is a reoccurring topic of mud schools and articles. You occasionally see eyes rolling when the topic of water comes up, so I am not going to discuss that kind of water. This article will relate to geothermal mixes and water’s role in the quality, pumpability and final thermal conductivity (TC) of mixed geothermal grout.
When we first started teaching geothermal grouting classes, we focused on sand quality. We recommended round grains of uniform size with moisture content of <0.1% (in a perfect world). For those of you using sand or sand/graphite combinations today, we still recommend this. However, more and more we see sand take a backseat to graphite products as the “new” additive, and as a thermal conductivity (TC) booster. This is perfectly understandable, as engineers and system designers seek higher (TC) values in their mixes — up to 1.9 Btu/hr/ft/F value — but still want pumpable, easy-to-install grouts.