SODIUM POLYPHOSPHATE-MODIFIED CLASS C/CLASS F FLY ASH BLEND CEMENTS FOR GEOTHERMAL WELLS.

SUGAMA, T. ; BROTHERS, L.E. ; KASPEREIT, D.

Brookhaven National Laboratory

关键词: Combustion;    Cements;    Sodium;    Mullite;    Zeolites Geothermal Legacy;   

DOI  :  10.2172/877284
RP-ID  :  BNL--75530-2006-IR
RP-ID  :  DE-AC02-98CH10886
RP-ID  :  877284

美国|英语

来源: UNT Digital Library

【 摘 要 】

The authors investigated the usefulness of the coal combustion by-products, Class C fly ash (C) and Class F fly ash (F), in developing cost-effective acid-resistant phosphate-based cements for geothermal wells. In the temperature range of 20-100 C, sodium polyphosphate (NaP) as the acidic cement-forming solution preferentially reacted with calcium sulfate and lime in the C as the base solid reactant through the exothermic acid-base reaction route, rather than with the tricalcium aluminate in C. This reaction led to the formation of hydroxyapatite (HOAp). In contrast, there was no acid-base reaction between the F as the acidic solid reactant and NaP. After autoclaving the cements at 250 C, a well-crystallized HOAp phase was formed in the NaP-modified C cement that was responsible for densifying the cement's structure, thereby conferring low water permeability and good compressive strength on the cement. however, the HOAp was susceptible to hot CO{sub 2}-laden H{sub 2}SO{sub 4} solution (pH 1.1), allowing some acid erosion of the cement. On the other hand, the mullite in F hydrothermally reacted with the Na from NaP to form the analcime phase. Although this phase played a pivotal role in abating acid erosion, its generation created an undesirable porous structure in the cement. They demonstrated that blending fly ash with a C/F ratio of 70/30 resulted in the most suitable properties for acid-resistant phosphate-based cement systems.