Engineered Nanoparticles as Harsh-Condition Emulsion and Foam Stabilizers and as Novel Sensors
Authors: Zhang Tiantian , Espinosa David , Yoon Ki Youl , Rahmani Amir R. , Yu Haiyang , Caldelas Federico Manuel , Ryoo Seungyup , Roberts Matthew , Prodanovic Masa , Johnston Keith P. , Milner Thomas E. , Bryant Steven Lawrence , Huh Chun 
Published: May 2011

Abstract
Nanoparticles, when synthesized in a specific size range and with a special surface coating tailored to achieve certain desired functionalities, exhibit unique properties. This is because they are almost of molecular size but still retain many useful colloidal characteristics. Recent developments on novel potential upstream applications of nanoparticles are reviewed with focus on research at our laboratory. Oil-water emulsions and CO2 foams that have long-term stability under harsh downhole conditions could be employed as alternatives to surfactant-stabilized emulsions and foams for drilling and other applications. Nanoparticles that show minimal retention can be employed as sensing-capability carrier to detect fluid and rock properties of the producing zone. For example, paramagnetic nanoparticles delivered to the target formation could evaluate fluids saturations there, with application of magnetic field and measurement of response.
Emulsions stabilized with surface-coated silica nanoparticles remain stable for months at high temperatures. By designing the hydrophilic/hydrophobic nature of surface coating, either oil-in-water or water-in-oil emulsions can be generated, with droplet size approaching uniform ~5 micron diameter, and with strongly shear-thinning rheology. Stable foams of supercritical CO2-in-water have been generated by co-injecting CO2 and silica nanoparticle aqueous dispersion through a glass-bead pack. The domain of foam stability and the apparent foam viscosity (which were 10 to 100 times more viscous than CO2) reveals threshold values of critical shear rate, particle concentration and phase ratio. An extensive series of sand-pack column and core-plug flow experiments revealed the mechanisms controlling retention of silica and paramagnetic iron-oxide nanoparticles in porous media. A wide range of particle loadings (0.1~18 wt%) and different rock samples were employed. With proper coating, retention was below 10% of the injected amount even in low permeability rock and with large particle concentrations. Potential for various novel upstream applications of engineered nanoparticles is demonstrated.

Introduction
Novel nanoscale structured materials, in the form of solid composites, complex fluids, and functional nanoparticle-fluid combinations, are bringing major technological advances in many industries. A few examples are the extraordinary material strength, elasticity and thermal conductivity of nano-based metal and polymer composites; targeted and programmed delivery of drugs and enhanced imaging of human organs in medicine; and chemical/physical properties of nano sensors. These and many other novel advances are due to the orders-of-magnitude increase in interfacial area and associated excess stress and chemical potential for the nano-structured materials; and some chemical and physical properties that are unique to nanoscale. In the petroleum/geosystems engineering discipline, research and applications of nanotechnology have been very limited. This is because subsurface formations have heterogeneity of all length scale and any treatments have to be carried out through boreholes, so that process control is generally difficult with significant uncertainties. And any process application requires a large volume treatment so that the material/process cost has to be small. Despite the difficulties, the current advances in nanotechnology are such that a judicious choice of potential applications, and carrying out focused research to bring those potentials to practical maturity, will result in quantum benefits to the oil and gas industry. The recent surge of interest on nanotechnology applications in upstream oil industry, as evidenced by the search of the SPE literature, shows that the important potential of the nanotechnology is beginning to be recognized.