Capillary Pressure and Wettability Indications of Middle Bakken Core Plugs for Improved Oil Recovery

Abstract

Summary Understanding reservoir-rock characteristics and the forces that mobilize oil in unconventional reservoirs is critical in designing oil-recovery schemes. Thus, we conducted laboratory experiments for three preserved Middle Bakken cores using centrifuge and nuclear-magnetic-resonance (NMR) instruments to understand oil-recovery mechanisms in the Bakken. Specifically, we measured capillary pressure, pore-size distribution (PSD), and oil and brine saturations and distributions. A series of oil/brine-replacement experiments (drainage and imbibition) were conducted for the preserved cores using a high-speed centrifuge. T2 time distribution and 1D saturation-profile measurements were obtained using a 2-MHz NMR instrument before and after centrifuge experiments. Moreover, PSD was determined from mercury-intrusion capillary pressure (MICP) and nitrogen-gas-adsorption experiments. We conducted scanning-electron-microscope (SEM) imaging on polished cubical cores to determine pore shapes and mineralogy of pore walls using a field-emission SEM (FE-SEM). Our measurements show that these three preserved Middle Bakken cores show mixed-wet characteristics. Water resides in smaller pores and oil resides in larger pores in all experiments. Using a low-salinity synthetic brine of 50,000 ppm to surround Bakken cores of much-higher salinity, we produced up to 6.33% [of pore volume (PV)] oil from two higher-porosity (approximately 8%) cores, and 10.72% (of PV) oil from one lower-porosity (approximately 2%) core in a spontaneous-imbibition (SI) experiment. Up to 6.62% (of PV) oil from the two higher-porosity cores and 11.23% (of PV) oil from the lower-porosity core were produced in a forced-imbibition (FI) experiment as well. These experiments indicate that molecular diffusion/capillary osmosis overrides the wettability effects in low-permeability Middle Bakken cores. The new observations regarding molecular diffusion/capillary osmosis have altered our classical notion of capillary imbibition in low-permeability reservoirs.

A Literature Review of CO2, Natural Gas, and Water-Based Fluids for Enhanced Oil Recovery in Unconventional Reservoirs

“…Another investigation with Bakken cores indicated that while the amount of oil recoverable with LSW was not large, it was significantly greater than that obtained with high salinity brine . During a study of capillary pressure and wettability, the same team demonstrated that when LSW was used, oil production from Middle Bakken cores via spontaneous imbibition was comparable to that achieved with forced imbibition, which indicated that molecular diffusion and capillary osmosis were more dominant than wettability effects regarding oil recovery …”

“…271 During a study of capillary pressure and wettability, the same team demonstrated that when LSW was used, oil production from Middle Bakken cores via spontaneous imbibition was comparable to that achieved with forced imbibition, which indicated that molecular diffusion and capillary osmosis were more dominant than wettability effects regarding oil recovery. 272 5.2. Alkaline Solutions for EOR in ULRs.…”

Laboratory Characterization of Shale Oil Storage Behavior: A Comprehensive Review

“…Ternary plot of minerals for different basins (Ordos Basin, , Fort Worth Basin, ,− Maverick Basin, ,, Williston Basin, , Bohaiwan Basin, ,,,, Songliao Basin, − , Permian Basin, and Junggar Basin − ).…”

“…The pore shape is a descriptive parameter and can be well-measured using observational methods, such as scanning electron microscopy (SEM), or modeled from lowpressure N 2 adsorption/desorption isotherm hysteresis curves. 81 Shale pore shapes are mainly slit, ink-bottle, honeycomb, bubble, elliptical, cylindrical, elongated, and 38,50,55 Williston Basin, 38,43 Bohaiwan Basin, 5,49,66,67,104 Songliao Basin, [57][58][59]71 Permian Basin, 55 and Junggar Basin 71−73 ).…”

Optimization of Huff-n-Puff Field Gas Enhanced Oil Recovery through a Vertical Well with Multiple Fractures in a Low-Permeability Shale–Sand–Carbonate Reservoir

“…All of the arguments pointed out above should be taken into account in optimizing huff-n-puff field gas EOR implementation in unconventional reservoirs. The optimization is necessary in order to maximize the value of unconventional oil reserves through the increase in oil recovery. An approach that can be used in formulating the optimization strategy is through the determination of the most favorable conditions for oil production that can be achieved by the modification of the operational parameters, such as the amount of gas injected.…”