Ž . Chemical Geology 157 1999 13–26 An experimental study of dolomite dissolution rates as a function of pH from y0.5 to 5 and temperature from 25 to 808C Maud Gautelier ) , Eric H. Oelkers, Jacques Schott Laboratoire de Geochimie, CNRS r UMR 5563-OMP-UniÕersite Paul-Sabatier, 38 rue des Trente-Six Ponts, 31400 Toulouse, France ´ ´ Received 27 January 1998; revised 13 November 1998; accepted 13 November 1998 Abstract Steady-state dissolution rates of Haute Vallee de l’Aude dolomite were measured in mixed-flow reactors using rotating ´ disk techniques. Experiments were performed in aqueous HCl solutions over the bulk solution pH range y0.39 to 4.44, and at temperatures of 25, 50 and 808C. Dissolution rates were found to depend on disk rotation speed at all temperatures and w pH. Interpretation of these rates using equations reported by Gregory and Riddiford Gregory, D.P., Riddiford, A.C., 1956. x Transport to the surface of a rotating disk. J. Chem. Soc., 33, 37–56 yields steady-state dissolution rates as a function of the Ž . solution pH adjacent to dolomite surface pH . Rates at all temperatures and 1 -pH -5 are found to be consistent surf surf with r ska n 1 q , where r refers to surface area normalized steady-state dissolution rates, k stands for a rate constant, 1 H ,surf 1 and a q designates hydrogen ion activity in the solution adjacent to the dolomite surface, and n denotes a constant H ,surf 1 equal to 0.63, 0.73 and 0.80 "0.05 at 25, 50 and 808C, respectively. Rates tend towards pH independence at more acidic conditions suggesting the saturation of dolomite surfaces with rate controlling protonated species. Additional experiments performed to assess the effect of the presence of aqueous Ca 2q and Mg 2q demonstrate that these species have little to no effect on dolomite dissolution rates at pH s2 and 508C. q 1999 Elsevier Science B.V. All rights reserved. Keywords: Dolomite; Dissolution kinetics; Chemical weathering; Water–rock interaction 1. Introduction The goal of this work is the improved understand- ing of dolomite dissolution kinetics at low tempera- ture acidic conditions. This knowledge is essential for optimizing acid induced fracturing of carbonate rocks leading to the improved recovery of oil and Ž gas from sedimentary basins Van Poolen and Aragon, 1968; Nierode and William, 1972; Lund et al., 1973; Daccord et al., 1989; Gdanski and Lee, ) Corresponding author. Fax: q33-561-520544; e-mail: gautelie@lucid.ups-tlse.fr 1989; Hung et al., 1989; Hoefner and Fogler, 1989; Anderson, 1991; Van Domelen, 1992; Wang et al., . 1993; Yan et al., 1993; Hill et al., 1994 . Of the two dominant carbonates present in oil field reservoirs, calcite and dolomite, calcite dissolution has received Ž considerable attention see Alkattan et al., 1998 for . an extensive list of published studies while there have been far fewer studies devoted to dolomite Ž Lund et al., 1973; Busenberg and Plummer, 1982; Herman and White, 1984; Chou et al., 1989; Wol- . last, 1990; Anderson, 1991; Orton and Unwin, 1993 . These studies demonstrated that calcite and dolomite dissolution rates at acid conditions are functions of 0009-2541r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0009-2541 98 00193-4