Emulsified Silica Gel for Deep Reservoir Water Conformance Control

Large volumes of water are produced with the production of oil, posing challenges of corrosion, scaling, and an increased water-oil ratio. Silica-based gels have previously been used as water sealants; however, reservoirs with high temperature and/or salinity cause early gelation, thereby preventing deep penetration into the reservoir. This work discusses factors affecting gel formation from colloidal silica and mixing methods for the preparation of a thermally stable Pickering emulsion and the effect of various parameters on its rheology. Sensitivities include salinities ranging from 5 to 20 wt % for seven different salts, silica gel concentrations from 20 to 28 wt %, pH values from 4 to 9, and temperatures from 80 to 150 °C. The effect of each parameter on the gelation time and gel strength was studied at a constant shear rate and pressure of 100 s^-1 and 1100 psi, respectively. A commercial phyllosilicate (organoclay) has been used with diesel to form an invert emulsion of 28% silica gel, with diesel as a continuous phase and colloidal silica as a dispersed phase. Dynamic gel tests were performed to study the effect of the emulsion mixing method, temperature, and organoclay concentrations on the emulsion stability, strength, and viscosity. A lower concentration of salt has a longer gelation time with a lower gel strength. Increasing pH increases the gel strength but reduces the gelation time. The Pickering emulsion formed is stable to high shear, high temperatures, and high salinities. The bulk mixing method produces a direct emulsion, whereas drop-by-drop mixing results in an invert emulsion. A comparison of the gelation time and viscosity has also been provided with non-emulsified silica gel to highlight the benefit of encapsulation in terms of increased gelation time. This work will help academia and industry in designing a cost-effective system for water conformance control in harsh reservoir conditions.