During downhole oil extraction, water is injected to apply pressure and aid in the forcing of oil out of tight formations in reservoirs. A disadvantageous effect of adding water is the production of oil-water emulsions, from which the oil portion is challenging to extract. Water-oil emulsions can also be formed at other stages and locations including during drilling, producing, transporting and processing, in hydrocarbon reservoirs, well bores, surface facilities, transportation systems and refineries. During field production, as the percentage of the water in the emulsions, known as the “water cut” can reach to up to 90% of the total.
An emulsion is generally defined as a heterogeneous liquid system consisting of two immiscible liquids where one the liquids is totally dispersed as droplets in the second liquid. The emulsions can be classified into three broad groups: water in oil (W/O), oil in water (O/W) and multiple or complex emulsions. The formation and the stability of water-oil emulsions have been widely investigated. The stability and enhancement of emulsions formation can be affected by several parameters such as water/oil ratio, emulsifier/surfactant ratio, the presence of solids, surface tension, presence of a high boiling point fraction (e.g. asphaltenes, resins, organic acids), temperature, salinity and pH.
Techniques are currently in development to enhance the water injection performance and reduce the water cut during the production life of oil reservoir. These techniques seeks to minimize the added water using inflow control devices, treat and dispose water at the surface, and separate water from oil downhole in reservoirs. Specific techniques and mechanism include hydrocyclone, gravity separators, and centrifugal separator for separation of oil from water coupled with supplemental technologies such as mechanical blocking devices (e.g. packer and plugs) and water additives (e.g., polymer gel, nanoparticles).
In the past decade, studies showed that nanoparticle additives including metal oxides and carbon nanotubes can be used to enhance the oil recovery. Due to their characteristics including wettability, interfacial tension reduction and viscosity modification capability, and their stability in injected fluid, nanoparticles are potential candidates to be used to increase oil recover from water-oil emulsions.
However, the techniques disclosed to date employ combinations of particles with chemical additives, and utilize particle size ranges (<50 nanometers) that are suited for combinations with the chemical additives.
What is therefore needed is a cost-effective, easy-to-implement and effective technique for separating or preventing water-oil emulsions at various stages of the oil production process.