Ethayaraja Mani

Stability of oil-in-water emulsions under high pressure and high temperature (HPHT) conditions has a significant interest in upstream oil and gas industrial applications. Such emulsions are generally stabilized with surfactants, which are thermodynamically unstable under HPHT conditions. Alternate to surfactants, the addition of nanoparticles has emerged as a method for emulsion stabilization, known as Pickering emulsion. In this work, a comparative study of the stability of silica nanoparticle (Ludox CL) stabilized Pickering emulsion against surfactant SDS (sodium dodecyl sulfate) stabilized emulsion under HPHT conditions has been explored. The stability of the emulsions was measured in terms of change in emulsion droplet diameter. Subsequently, emulsion samples are aged under different pressure and temperature conditions in an aging cell for 24 hours. The emulsion mean droplet diameter increases with an increase in temperature. The magnitude of change in the mean droplet diameter of aged SDS stabilized emulsion is higher as compared to Ludox CL stabilized emulsion under varying pressure (0.1–10 MPa) and temperature (303–363 K). It can be concluded that Ludox CL stabilized emulsion shows better stability as compared to SDS stabilized emulsion under HPHT conditions. Hence, emulsion stabilized by Ludox CL nanoparticle may withstand harsh reservoir conditions and can be used for enhanced oil recovery applications.

Emulsions have a wide range of applications, and with the advancement in the use of nanoparticles to form stable Pickering emulsions, it is important to understand their rheological properties to infer their stability under high-pressure and high-temperature (HPHT) compared to the emulsion formed using conventional surfactants. In oil and gas production strategies, oil often forms an emulsion with brine either within reservoirs or at surface facilities in the presence of natural or artificial surfactants. Nanoparticles are also being explored to increase oil recovery from matured reservoirs. In various instances, stable emulsions are either formed in-situ (within the reservoir) or at surface facilities or injected into the reservoir to mobilize the trapped oil. It is also essential to understand their rheology for efficient oilfield application. This study investigates the impact of surface-modified silica nanoparticles (Ludox CL), NaCl salt, and surfactant on the stability of oil-in-water Pickering and surfactant-stabilized emulsions under high-pressure (0.1–10) MPa and high-temperature (303–363) K conditions. The viscosity of emulsion samples was measured at varying shear rates (0.1–1000) s−1. The viscoelastic behavior (G′, G″, η*, and δ) of the Pickering emulsion and surfactant-stabilized emulsion were also measured. The stability of the emulsions was measured in terms of changes in emulsion viscosity and droplet diameter. Both emulsions showed non-Newtonian shear thinning behavior and an increase in droplet diameter under HPHT conditions. However, the surfactant-stabilized emulsion exhibits a greater degree of change in emulsion viscosity and droplet diameter than the Pickering emulsion. It indicates that the Pickering emulsion showed better stability than the surfactant-stabilized emulsion under HPHT conditions. Hence, Pickering emulsions are an incredibly promising tool that might be employed in HPHT applications, especially for enhanced oil recovery applications, due to their better rheological stability.