Abstract

This work uses a rotating disk instrument to measure dissolution rates of both calcite and dolomite rock samples. Results of more than 60 experiments are reported in this paper. The effect of common acidizing additives on the acid dissolution rate is measured for different acids containing quaternary amines, polymer, surfactant, mutual solvent, iron chelating additive, and dissolved iron. Measurements are made at 23 and 50 ºC for calcite marble and dolomite marble samples.

Marble samples from Turkey, Greece and Italy were analyzed to find suitable reference materials. Marble composed of 100% calcite (calcite marble) as well as 91% dolomite (dolomite marble) was used and compared very well with previously published results. Results of acid dissolution rates with common acidizing additives showed significant differences.

  • ·1.5 vol% cationic acrylamide polymer decreased the calcite and dolomite dissolution rates significantly. At 1000 rpm the calcite dissolution rate with 1.5 vol% polymer and 0.1N HCl had a value that was 11.4% of the value measured with 0.1N HCl alone.

  • ·Polymer changed the acid-rock reaction from mass transfer limited to surface reaction limited with both calcite and dolomite. This is a surface effect possibly due to polymer adsorption.

  • ·10 vol% mutual solvent increased the acid dissolution rate by 9% for calcite and by up to 29% for dolomite.

  • ·5,000 mg/L iron (III) resulted in surface deposition of iron (III) hydroxide. At low rotational speeds, this surface layer had an inhibiting effect on dissolution rate for both calcite and dolomite.

  • ·2 vol% corrosion inhibitor decreased the calcite dissolution rate by approximately 9%.

  • ·Citric acid at 12 g/L decreased the dissolution rate of calcite by an average of 9%, possibly due to the formation of calcium citrate at the surface.

  • ·0.2 vol% nonionic surfactant had no significant effect on acid dissolution rate of calcite.

Introduction

The rotating disk instrument has been widely used in the petroleum industry for kinetic studies of the reaction of acidic fluids and chelating agents with reactive rock. This system allows the determination of rock dissolution rate, reaction rate constants, reaction order, and diffusion coefficients.

Lund et al. studied the dissolution of both calcite and dolomite with the rotating disk instrument. Their work showed that at 25 ºC the dissolution of calcite is mass transfer limited even at high disk rotational speeds, while at –15.6 ºC both mass transfer and surface reaction rates limit the dissolution rate.In contrast, Lund et al. showed that the dissolution of dolomite was surface reaction rate limited at 25 ºC even at low disk rotational speeds. As the temperature was increased to 100 ºC, the dissolution process approached diffusion limitation even at relatively high rotational speeds.

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