Hydrophobic Lightweight Cement with Thermal Shock Resistance and Thermal Insulating Properties for Energy-Storage Geothermal Well Systems

Abstract

This study assessed the possibility of using polymethylhydrosiloxane (PMHS)-treated fly ash cenospheres (FCS) for formulating a thermally insulating and thermal shock (TS)-resistant cementitious blend with calcium aluminate cement. To prevent FCS degradation in an alkaline cement environment at high temperatures, the cenospheres were pre-treated with sodium metasilicate to form silanol and aluminol groups on their surface. These groups participated in a dehydrogenation reaction with the functional ≡Si–H groups within PMHS with the formation of siloxane oxygen-linked M-FCS (M: Al or Si). At high hydrothermal temperatures of 175 and 250 °C, some Si–O–Si and SiCH3 bonds ruptured, causing depolymerization of the polymer at the FCS surface and hydroxylation of the raptured sites with the formation of silanol groups. Repolymerization through self-condensation between the silanol groups followed, resulting in the transformation of siloxane to low crosslinked silicon-like polymer as a repolymerization-induced product (RIP) without carbon. The RIP provided adequate protection of FCS from pozzolanic reactions (PR), which was confirmed by the decline in zeolites as the products of PR of FCS. Cements with PMHS-treated FCS withstood both hydrothermal and thermal temperature of 250 °C in TS tests, and they also showed improved compressive strength, toughness, and water repellency as well as decreased thermal conductivity. The lubricating properties of PMHS increased the fluidity of lightweight slurries.

Hydrophobic, Thermal Shock-and-Corrosion-Resistant XSBR Latex-Modified Lightweight Class G Cement Composites in Geothermal Well Energy Storage Systems

“…Additionally, this hydrophobic continuous film may cover the surfaces of FCSs, protecting them from pozzolanic reactions in alkali cement. Hence, unlike in the case of the two technologies reported previously, where hydrophobic insulating composites were achieved by the inclusion of superhydrophobic PMHS-and HMDA-treated insulating aggregates [1,2], in this case the whole composite matrix including the insulating aggregates would be hy-drophobic. Since the ingress of water into cement is undesirable for thermal insulation, the hydrophobic cement matrix may have better water-proofing performance than composites with hydrophobic aggregates.…”

“…CenoStar Corp. (Newburyport, MA, USA) provided the fly ash cenospheres (FCSs) under the trade name "CenoStar ES500". The FCSs' bulk density is 0.32-0.45 g/cm 3 and TC is 0.1-0.2 W/mK [1]. The major crystalline phases of FCSs were mullite (ICDD# 04-016-1586, Al 2 .…”

“…In such systems cement sheaths can encounter significant thermal stresses when hot fluid is pumped into the relatively cold reservoir or when hot fluid is recovered from it passing through the cool upper parts of the well. In the earlier two works we reported the formulation and testing of a highly hydrophobic lightweight cement composite with a TC of 0.28-0.5 W/mK under watersaturated conditions [1,2]. The first of the developed technologies involved the use of hollow fly ash cenospheres (FCSs) treated with polymethylhydrosiloxane (PMHS), that chemically tailors the microsphere surfaces making them hydrophobic and providing their stability under alkaline cement environments, in combination with calcium aluminate cement (CAC).…”

“…The first of the developed technologies involved the use of hollow fly ash cenospheres (FCSs) treated with polymethylhydrosiloxane (PMHS), that chemically tailors the microsphere surfaces making them hydrophobic and providing their stability under alkaline cement environments, in combination with calcium aluminate cement (CAC). This technology allowed decreasing the TC of the composite to 0.4 W/mK and was designed to be used in high-temperature RTES where the composite would set at 250 • C and experience a thermal gradient of 225 • C [1].…”

Using Fumed Silica to Develop Thermal Insulation Cement for Medium–Low Temperature Geothermal Wells

“…The theory that decreasing the thermal conductivity of cement can significantly reduce heat loss was first proposed by Ichim et al [ 12 ] in 2016; they later estimated the thermal properties of cement using a three-phase model for application in geothermal wells in 2018 [ 5 ]. Sugama and Tatiana assessed the possibility of using polymethyl hydrosiloxane-treated fly-ash cenospheres (FACs) to formulate a thermally insulated and thermal shock-resistant cementitious blend with calcium aluminate cement [ 13 ]. Zhang and Li developed a TIC for geothermal wells by introducing floating beads and expanded perlite (EP) into Class G oil-well cement [ 4 ].…”