| Title | Lightweight Variable-Density Well Cement with Self-Healing Properties for Applications in Geothermal Wells |
|---|---|
| Authors | George TRABITS, Geoff TRABITS |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | lightweight variable density well cement, self-repair, acid resistance, ferrierite, zeolite, intergrinding |
| Abstract | Lightweight Variable-Density Well Cement with Self-Healing Properties for Applications in Geothermal Wells. FlexCem® Lightweight Variable Density well cement was developed by Trabits Group following completion of a research grant from the Department of Energy Geothermal Technologies Office (GTO). This cement performs well in harsh geothermal conditions with thermal stability at temperatures of up to 300â°C with resistance to carbonation. An innovative cost-effective technology of intergrinding was developed for its manufacturing which results in a bimodal particle size distribution between harder cement clinker and softer zeolite. The FlexCem® intergrind method has been tested at four U.S. cement plants. Each of these full scale, large tonnage intergrinds were compared for resulting cement chemical properties and cement performance. All four intergrinds were essentially identical in properties and performance proving the method provides a consistent and repeatable cement product. The zeolite used in FlexCem® is Ferrierite which is rare natural crystalline, hydrated aluminosilicate of alkali and alkaline earth cations having an infinite, open, three-dimensional structure. The FlexCem® Ferrierite is mined from the only known minable deposit in the world, located 12 miles north of Lovelock, Nevada. The specific formulation and choice of zeolite results in a variable density cement with a working range of 1.32 kg/L to 1.71 kg/L (11.0 to 14.3 ppg). The cement retains the original GTO target qualities of thermal stability, resistance to carbonation and additionally exhibits the unique ability to self-repair in a wide range of temperatures. In this work strong-acid high-temperature resistance (pH 0.2, 90oC, 28 days) of FlexCem® is compared against that of common high-temperature formulations of Ordinary Portland Cement. The paper also presents results of moderate- (100oC) and high-temperature (270oC) cement strength recovery after imposed compressive damage and a short 5-day recovery period under the initial curing conditions. Phase analyses using x-ray diffraction, Fourier transform infrared analyses and scanning electron microscopy coupled with energy dispersive x-ray spectroscopy show that zeolite decomposes under hydrothermal alkaline conditions of cement slurries with release of hydrolysates that along with the hydrating cement participate in the formation of new phases contributing to strength recovery. In collaboration with Dr. Tatiana Pyatina Brookhaven National Laboratory. |