Precipitation of sparingly soluble salts in packed sandbeds in the presence of miscible and immiscible organic substances

Abstract

Sparingly soluble salts precipitation, e.g. calcium carbonate or calcium sulfate, results in pore clogging in rock formations and in the concomitant reduction of the local permeability of oil wells during the oil extraction processes. On the other hand, in situ controlled salt precipitation is desirable in various applications e.g. waterproofing of concrete constructions suffering from leakages, etc. In the present study, calcium carbonate (CaCO 3 ) precipitation in sandbeds was investigated, in the presence of organic solvents simulating the conditions prevalent in oil-well zones. CaCO 3 precipitation was investigated from supersaturated solutions prepared by in-situ mixing of NaHCO 3 and CaCl 2 .2H 2 O solutions before the inlet of sandbeds. The solution resulting from the mixing of the two solutions was supersaturated with respect to all calcium carbonate polymorphs. Three types of experiments were performed depending on the supersaturated solutions: a) aqueous solutions b) aqueous supersaturated solutions in contact with sandbeds presaturated with n-dodecane c) aqueous solutions containing monoethylene glycol (MEG). Results showed that oil-water interfaces enhanced the heterogeneity of the supersaturated solutions and accelerated crystal growth of calcium carbonate at the inlet of the sandbed, resulting in early pore clogging and limitation of local permeability. Maximum sandbed consolidation was obtained with the solutions containing MEG.

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

“…Interestingly, the presence of n-dodecane which is water immiscible organic phase accelerated crystal growth of the salts investigated leading to pore clogging at the inlet of the sandbeds. 44 In oil field conditions, nucleation and crystal growth of calcium carbonate take place from fluid media, supersaturated with respect to calcium carbonate in contact with solid substrates of various petrological compositions. As a rule, the fluids contain hydrocarbons (water insoluble) and other organic compounds (e.g., alcohols) are freely miscible with the aqueous phase.…”

“…Recent work concerning the effect of the presence of monoethylene glycol (MEG) on the formation of sparingly soluble salts in sandbeds showed maximum consolidation due to the formation of the respective salts in the space in between the sand grains. Interestingly, the presence of n -dodecane which is water immiscible organic phase accelerated crystal growth of the salts investigated leading to pore clogging at the inlet of the sandbeds …”

Mineral Scaling in the Presence of Oil–Water Interfaces Combined with the Substrate’s Wettability Effect: From Batch to Microfluidic Experiments

“…Earlier investigations of CaCO 3 precipitation in the presence of oil/water interfaces in larger plexiglass channels and in sand-packed beds showed acceleration of the nucleation in comparison with aqueous supersaturated solutions. The higher precipitation rates were attributed to the dodecane/water interfaces and to the lower value of interfacial tension, which reduced the free Gibbs energy for crystal nucleation. ,, CaCO 3 precipitation in plexiglass channels under S or conditions, yielded shorter induction times and larger number of smaller mean size crystals in comparison with the induction times and the corresponding crystallite mean size obtained at the corresponding SR values, in the absence of oil–water interfaces . Moreover, in addition to calcite, aragonite and vaterite were also identified with Raman spectroscopy, which were probably stabilized because of the varying interfacial energy conditions prevailing along the channel at the oil–water interfaces .…”

“…25 In the case of calcium carbonate precipitation in beds packed with sand, completely saturated with dodecane, the pores were clogged at the bed entrance, while along the beds, the deposition was minimal to null. 24 Larger quantities of calcium carbonate formed on surfaces of various wettabilities in the presence of oil, in comparison with the respective quantities formed from aqueous solutions under the same conditions. 26 Oil adhering onto hydrophobic surfaces inhibited crystal nucleation.…”

“…Except for the kinetics of the crystallization process, the calcium carbonate polymorph stabilization is also affected by the surface wettability and the existing thermodynamic conditions . In the case of calcium carbonate precipitation in beds packed with sand, completely saturated with dodecane, the pores were clogged at the bed entrance, while along the beds, the deposition was minimal to null . Larger quantities of calcium carbonate formed on surfaces of various wettabilities in the presence of oil, in comparison with the respective quantities formed from aqueous solutions under the same conditions .…”