Precipitation of Calcium Carbonate in Porous Media in the Presence of n-Dodecane

The precipitation and crystal growth of sparingly soluble salts are associated with scaling problems in oil and gas extraction processes. The presence of oleic phases and/or organic solvents added as inhibitors of the gas hydrates often complicates scale formation problems. The pore structure of the oil reservoir walls is of particular interest in the process of scale formation. In the present work the effect of the presence of n-dodecane in the crystallization of CaCO3 was investigated. The study was done in simulated one-dimensional porous media made of Plexiglas, in which supersaturated solutions of various supersaturation ratios (SRinitial) with respect to calcite were introduced. The growth of the precipitated crystals was continuously monitored by optical microscopy and calcium concentration monitoring. At high SRinitial values, larger numbers of small size crystals were grown, mainly near the oil-water interface. The presence of n-dodecane resulted in the reduction of the induction time preceding the appearance of CaCO3 crystals. The measured precipitation rates of CaCO3 were higher with increasing SRinitial values. The presence of n-dodecane in the supersaturated solutions, in the respective two-phase system, favored the stabilization of the thermodynamically less stable polymorphs of CaCO3 (aragonite, vaterite). Mapping analysis of the deposits polymorphs using Raman spectroscopy showed that the precipitation was not homogeneous along the flow channel at the experimental conditions of the present work.