Understanding Penetration Behavior of Microemulsions in Nanoporous Shale Formation

I.Y. Akkutlu, K. Bui, J. Silas, A. Zelenev
Texas A&M University,
United States

Keywords: microemulsion, droplet, nanopore, confinement, molecular dynamics

Summary:

Resource shale formations are naturally occurring nanoporous materials holding the hydrocarbon fluids in nanopores, channels and fractures. At nanoscale the hydrocarbon fluids are strongly held by the pore walls and cannot be effectively transported. In addition, nano-scale confinement has effects on fluid transport htat are not well-understood. In order to enhance the production of hydrocarbons, it is important to alleviate the pore-wall effects and the nano-confinement effect. This can be achieved by the application of specialized chemical treatment. Field studies have indicated that microemulsions that produce nano-size droplets were effective in enhancing both hydrocarbon production and water flowback from unconventional reservoirs. While it is believed that microemulsion droplets help to mobilize the oil inside the shale matrix, the penetration mechanisms of these droplets into nanopores and their interaction with rock matrix having different wettability on the scale of confined space is still poorly understood. 2. Methods, Procedures, Process In this work, we employ molecular dynamics simulations to address those questions and provide the fundamental understandings on the penetration behavior of microemulsion droplets during hydraulic fracturing stage. The model microemulsion droplet is considered to be formed with the C12E7 nonionic surfactant and d-limonene as a solubilized solvent phase. The oil-wet kerogen surface is modeled as graphite surface while the water-wet surface is modeled as brucite. 3. Results, Observations, Conclusions Our results indicate that the penetration of C12E7/d-limonene microemulsion into sub-10nm pores is strongly influenced by the wettability of the rock matrix. In the case of an oil-wet surface, such as kerogen, the microemulsion droplet was found to adsorb on the solid surface and hence revealed limited penetration ability. Oppositely, in the case of a water-wet rock modelled with brucite, there was no adsorption taking place, and the microemulsion droplet effectively penetrated into the pore. Molecular dynamics experiments have also shown that the droplets were capable of squeezing through the pores smaller than droplet’s own diameter. 4. Novel/Additive Information One major benefit associated with the use of microemulsions is the ability of the droplets to transport and deliver solvent to different parts of the reservoir. Our work has shown that with microemulsions the solvent and surfactant can be delivered into the pore network that is much smaller than the size of microemulsion droplets, and hence influence the mobility of hydrocarbons in the nanopores. This research can be extended to include different types of surfactants and rock surface chemistries in order to expand the knowledge base and to develop the next generation of microemulsion products with superior performance in well stimulation and enhanced oil recovery.