Reactions of Attapulgite and Sepiolite in High-Temperature Drilling Fluids
The fibrous clay minerals attapulgite and sepiolite have been subjected to hydrothermal reactions between 149 C (300 F) and 427 C (800 F). A 4% suspension of each of these clays was autoclaved for 16 to 24 hours with and without the addition of salts of NaCl and KC1 at 1% concentration. These fibrous clay minerals start to convert at 204 C (400 F) to a smectite with a lamellar morphology. In fact, attapulgite converts more readily than sepiolite, and the attapulgite-to-smectite transformation is fully completed at 316 C (600 F), whereas 20% to 50% of the sepiolite remains intact at this temperature. The conversion of the fibrous double- and triple-chain silicates of attapulgite and sepiolite to a layered silicate, such as smectite, favorably affects the rheology of the drilling fluids based on these clays. The mechanism of the conversion is, however, different for these fibrous clays. Attapulgite dissolves first and then smectite precipitates whereas this mechanism takes place for sepiolite at 316 C (600 F). Both attapulgite and sepiolite, and their reaction products, have been examined with an analytical electron microscope (JEM-100CX) in TEM, STEM, SEM, and SAD modes. The intensities of the characteristic X-ray spectra for the elements Mg, Al, Si, Fe, Ca, and K are measured. These observations indicate that (1) significant chemical differences exist between the fibrous clays and the smectites formed from them and (2) morphological features of the smectites vary with the temperature and with the presence of the salts in the system.
- Research Organization:
- DOEEEGTP (USDOE Office of Energy Efficiency and Renewable Energy Geothermal Tech Pgm)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 886128
- Report Number(s):
- SAND-81-0036C; CONF-810105-26
- Country of Publication:
- United States
- Language:
- English
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