The main objectives of this work are to prevent water blockage problem of wells drilled to tight gas reservoirs by minimizing fluid invasion and to reduce solid invasion with the optimized sodium silicate concentration in actual drill-in fluid and ultimately, improving well productivity by obtaining high return permeability after forming the very thin, impermeable and easily removable filter cake.
Static filtration tests were conducted on 0.25″ tight cores at 300°F under 300 psi ΔP with 250 psi back pressure and 500 psi inlet pressure to collect filtrate volumes. Rheology tests were performed up to 140°F under atmospheric and at 300°F under 300 psi pressure. Rheology experiments were performed for base fluid and with 0.05, 0.075, 0.1 wt%, while filtrations were also performed for 0.5, 1 and 1.5 wt% sodium silicate concentrations. Initial and return permeabilities were measured by injecting 3 wt% KCl through 2″ core sample under constant flow rates after damaging it. CT numbers were obtained before and after damaging 2″ core by doing CT Scan.
Filtrate volume and cake thickness reduced by 53% and 65% with 0.075 wt% (3.5 ml & 0.7 mm), respectively, compared than base fluid (7.4 ml & 2 mm). 0.075 wt% determined as an optimum concentration. Water blockage problem of tight gas wells prevented by minimizing the fluid invasion. Measured initial and return permeabilities of 2″ core remained same as 1.3 mD. This result proved that no solid invasion occurs with 0.075 wt% sodium silicate and in case of 100% filter cake removal, return permeability will be 100%. Forming filter cake with 0.7 mm thickness lets us to claim that it can be completely removed by washing with 15 wt% HCl. Obtained CT numbers confirmed return permeability measurement as well.
Barite flotation recovery and solubility concentration of silica with PH are the two approaches that should be considered together to explain the mechanism of 0.075 wt% sodium silicate. Polymerization effect shows itself for ≤0.075 wt%, while amorphous silica effect occurs for >0.075 wt%. Polymerization effect became the evidence of obtaining 100% return permeability.