Salinity-Sensitive Polymeric Particles for EOR
Physical Sciences : Petroleum
Available for licensing
- Kishore Mohanty, Ph.D. , Petroleum and Geosystems Engineering
- Krishna Panthi, Ph.D. , University of Texas at Austin
The growth of the global economy continues to fuel demand for petroleum and its byproducts. Increasing exploration and production costs force oil companies to squeeze every drop of crude from existing fields. Mature oilfields that are at the tail end of their primary and even secondary (waterflood) recovery phases are being re-evaluated based on application of enhanced oil recovery (EOR) methods.
Chemical enhanced oil recovery (CEOR) increases the amount of oil that can be obtained from an oilfield through the injection of chemicals into a reservoir that aids flow and reduces surface tension of the oil. In fractured reservoirs, injected fluids often flow through the fractures but avoid flowing through the matrix. Due to the low sweep efficiency of current EOR injection fluids, the oil in the matrix remains trapped in the reservoir. A method must be devised to reach the unswept oil located in the matrix of a reservoir and improve well efficiency.
Researchers at The University of Texas at Austin have developed salinity-sensitive polymeric particles (SSPP) that improve oil mobility by successfully sweeping the oil trapped in the matrix of a reservoir. The microparticles swell in deionized water and shrink in more saline brine, allowing for size manipulation of the particles. The goal of this invention is to block fractures and thief zones of fractured reservoirs and to divert injected EOR fluids into the matrix or low permeability zones, ultimately resulting in improved oil recovery.
The SSPPs are first injected into the well in saline brine, allowing the particles to flow into fractures rather than the matrix of a reservoir due to the matrix pores being too small for the particles to enter. A lower salinity brine is then injected, which swells the SSPPs and decreases the fluid conductivity of the fractures. The blockage of the reservoir’s fractures allows for any following injections of an oil-displacing agent to flow into the matrix or other low-permeability zones.
This EOR method is superior to current methods because the utilized cross-linked polymers tend to also enter the matrix of a reservoir and block them to some extent. Other polymeric particles, such as those that are temperature- or time-sensitive, do not swell as effectively as the SSPPs.
- Improves sweep efficiency and oil recovery
- Diverts EOR fluids to reach thief zones
- Manipulative and reversible particle size
- Can be used with any chemical oil-displacing agent (brine, gas, surfactant)
- Microparticle size is insensitive to pH
- Decreases amount of EOR fluid needed to obtain adequate EOR
- Salinity-sensitive polymeric particles (SSPPs) synthesized by polymerization reaction
- Microparticles swell in low-salinity brine and shrink in high-salinity brine
- Injection of high salinity brine to SSPP-containing reservoir allows particles to plug fractures
- Decreases conductivity of fractures and increases conductivity of low-permeability zones
- Stable for at least a month for temperatures below 80°C
- Stable in a pH range from 2 to 12, as in CO2 and ASP floods
Azoth Analytics reports that the global EOR market in the oil industry is anticipated to grow at a compound annual growth rate (CAGR) of 8.11% during the period 2016-2021, while BCC Research reports that the global EOR market value will increase to $34.4 billion from 2013 to 2018. Decreases in crude oil prices pressure the oil and gas industry to utilize traditional well operations, ultimately increasing the demand for EOR practices in the future.
According to a study conducted by Martin A. Fernø at the University of Bergen, the amount of recovered oil is significantly lower in fractured wells as opposed to non-fractured wells. For example, the oil recovery of a weakly oil-wet block at fractured state is 15%, compared to 65% without the presence of fractures. At weakly water-wet conditions, oil recovery with fractures is 22%, compared to 63% without fractures. Based on this analysis, it is critical to divert EOR fluids from fractures in a reservoir in order to improve oil recovery.
- 1 PCT patent application filed