Geochemical signatures of rapid calcium carbonate crystallization in well scales
Carbonate well scales from California oil fields show oxygen isotopic disequilibrium and highly variable magnesium content, apparently due to rapid CO2 degassing and crystallization. The δ18O of calcite scales is consistently 1 to 10‰ more positive than expected for equilibrium with pore water. CO2 degassing preferentially strips the lighter isotopes from the water and leaves precipitated calcite enriched in 13C. Most of the scales have positive δ13C values (+6.83 to +28.7 ‰). Assuming a constant input fluid composition, a positive δ13C/δ18O slope is evidence of rapid crystallization. Scale samples all show positive δ13C/δ18O slopes (typically +0.9 to +5.5), which are intermediate of the proposed range (+0.6 to +8.3) indicative of rapid CO2 degassing (Hendy, 1971). Calcite scales, from waters with constant temperature and fluid composition, show 4 to 16 mole percent Mg content. The relatively constant well bore conditions suggest that precipitation rate is controlling the Mg content of the scales.
G.F.Giles J.R.Boles
Department of Earth Science, University of California, Santa Barbara, California, USA
国际会议
第十二届水-岩相互作用国际研讨会(P0roceedings of the 12th International Symposium on Water-Rock Interaction)
昆明
英文
315-319
2007-07-31（万方平台首次上网日期，不代表论文的发表时间）