In field work evaluation of using phenyl acetate as a thermally degrading tracer, we discovered that its hydrolysis is catalyzed by a heterogeneous reaction in the presence of silica surfaces. The catalytic effect of crushed sandstone, the host reservoir mineral in our field tests, was measured in a well-controlled fluid system over a range of fluid and mineral conditions. Under homogeneous conditions without minerals present, phenyl acetate hydrolysis is first-order and base-catalyzed at a pH of roughly 6.3 for temperatures from 10 to 65 ℃. Arrhenius parameters under homogeneous conditions were consistent with previous investigations. In a mixture of 100 ml of reacting fluid with 0.2-2 g crushed sandstone having a nominal particle diameter of 100 μm, the reaction rate increased dramatically. However, the catalytic effect develops slowly. In fact, a very limited catalytic effect is observed if mineral surfaces are only in contact with aqueous solution for short periods prior to introducing phenyl acetate. For longer exposure times catalytic effect can be significant, e.g. at 70 days, reaction rates doubled. Multiple techniques including SEM were employed to characterize the surface of the crushed sandstone particles.

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