Geothermal well cementing, materials and placement techniques

Abstract

Geothermal wells are cemented using many of the same techniques as in the oil and gas industry. However, high temperatures, corrosive brines and carbon dioxide severely challenge the long-term durability of well cements. Well cementing is a critical part of well construction and requires a dedicated design and engineering process. Portland cement manufactured to API specifications, classes A and G, is most commonly utilised in geothermal wells cementing. The cements and cement additives selected and the cementing practices utilised are an integral part of sound well design, construction and well integrity. Selected cements, additives and mixing fluids should be laboratory tested in advance to ensure they meet the requirements of the well design. Silica flour is included in the design of cement slurry to prevent strength retrogression that occurs as a result of elevated temperatures encountered in geothermal wells. Proper well conditioning before cementing ensures a sound cement sheath. There are four common techniques utilised in the primary cementing of geothermal wells. There are other techniques used to execute remedial cementing jobs when the need arises. During cementing operations, various parameters are recorded as part of the monitoring of the cementing execution job and for post-job analyses. In the post-job evaluation, it is important to carry out acoustic logs.