Enhanced Oil Recovery in Liquid-Rich Shale Reservoirs: Laboratory to Field

Abstract

Production of tight oil from shale reservoirs in North America reduces oil imports and has better economics than natural gas. Consequently, there is a strong interest in oil production from Bakken, Eagle Ford, and Niobrara. However, oil recovery factor for Bakken remains low, which is about four to six percent of the oil in place. Even with this low oil recovery factor, Bakken recoverable reserves are estimated to be 7.4 billion barrels; thus, a large volume of oil will remain unrecovered. This low level of oil recovery was the motivation to investigate the feasibility of enhanced oil recovery (EOR) in liquid-rich shale reservoirs such as Bakken. In this paper, we will present both laboratory and numerical modeling of EOR in Bakken cores using CO2, C1-C2 mixture, and N2. The laboratory experiments were conducted at the Energy and Environmental Research Center (EERC). The experiments recovered 90+ percent oil from several Middle Bakken cores and nearly 40 percent from Lower Bakken cores. To decipher the oil recovery mechanisms in the experiments, a numerical compositional model was constructed to match laboratory oil recovery results. We concluded that solvent injection mobilizes matrix oil by miscible mixing and solvent extraction in a narrow region near the fracture-matrix interface, thus promoting counter-current flow of oil from the matrix instead of oil displacement through the matrix. Specifically, compositional modeling results indicate that the main oil recovery mechanism is miscible oil extraction at the matrix-fracture interface region. However, the controlling factors include re-pressurization, oil swelling, viscosity and interfacial tension reduction, diffusion-advection mass transfer, and wettability alternation. We scaled up laboratory results to field applications via a compositional numerical model. For field applications, we resorted to the huff-and-puff protocol to assess the EOR potential for a North Dakota Middle Bakken well. We concluded that long soak times yields only a small additional oil compared to short soak times, and re-injecting wet gas, composed of C1,C2, C3, and C4+, produces nearly as much oil as CO2 injection.

Simulation Study of CO2-EOR in Tight Oil Reservoirs with Complex Fracture Geometries

“…The fracture diagnostic technologies like microseismic 14 15 16 and the recent developed fracture propagation models 17 18 19 indicate that the fracture geometry is complex and non-planar. Although many efforts in the literature are dedicated to modeling CO 2 -EOR in tight oil reservoirs 20 21 22 23 , they made an assumption of simple bi-wing planar fracture geometry without considering the more-realistic complex fracture geometry. Even though the complex fracture networks provide the primary conduits for oil production, they might be detrimental to CO 2 flooding effectiveness 24 .…”

A Systematic Approach for Upscaling of the EOR Results from Lab-Scale to Well-Scale in Liquid-Rich Shale Plays

“…Our model utilizes the diffusion-dominant mechanism, as will be seen in the equations below. The diffusion mechanism is well studied and understood as, Kovscek et al, 2008, Vega et al, 2010, Hoteit et al, 2011and Alharthy et al, 2015 discuss the diffusion-driven IOR mechanism in their work.…”

Dynamical coupling of ion adsorption with fluid flow in nanopores

“…By mixing seawater with fresh water in nanochannels accompanied with ion adsorption, several devices/processes are designed for harvesting blue energy 10,11 . Other relevant applications widely lie in shale gas/oil recovery, 12 membrane processes including separation and purification, 13 interfacial catalysis, 14 etc.…”