Abstract
Summary The physico‐chemical and rheological properties of low acyl gellan (LAG) were investigated in aqueous solutions of various salts. 1H NMR spectroscopic study of LAG was conducted in salt‐free solutions at different temperatures. FTIR spectra revealed that the characteristic bands of both asymmetric and symmetric carboxylate groups are shifted to higher frequency regions as a result of effective surrounding of glucuronate residuesby mono‐ and divalent cations of salts. According to viscometricresults the effectiveness of salts to enhance gelation of gellan changes in the following order: BaCl2 > CaCl2 ≈ MgCl2 > KCl > NaCl. The behavior of LAG in model aqueous‐salt solutions and real oilfield saline water was evaluated by means of rheological measurements.The shear rate (and effective viscosity) of 0.5 wt.% gellan solution versus shear stress increases (and decreases) in the sequence of CaCl2 > MgCl2 > KCl > NaCl demonstrating the pseudo plastic character. The sol‐gel and liquid‐solid phase transitions of gellan solutionswere observed upon addition of oilfield water containing 73 g · L−1 of alkaline and alkaline earth metal ions. The effectiveness of salts to induce the separation of liquid and solid phases changes in the sequence: NaCl > KCl > MgCl2 ≈ CaCl2 ≈ BaCl2. The mechanical properties of gellan gels under compression were studied and the Young modules and breaking stresses were found. Sol‐gel transition of gellan solution inside of sand pack model was demonstrated. The hydrodynamic behavior of 0.5 wt.% gellan solution injected into the sand pack model with high (20 d) and low (2 d) permeability is useful to model the oil reservoirs in the process of enhanced oil recovery. The influence of clay minerals – bentonite on the rheological characteristics of gellan solution was evaluated for simulation of drilling mud ability to carry up the drilled rock particles from the bottomhole of the well to the surface.