Summary
This paper presents comprehensive rock/fluid experiments, by use of reservoir rock and fluids, to investigate wetting affinity of the Montney (MT) tight oil play in the Western Canadian Sedimentary Basin. Wettability characterization is essential for selecting optimum fracturing and treatment fluids by completion engineers and for selecting appropriate relative permeability and capillary pressure curves by reservoir engineers. Application of the conventional techniques for wettability evaluation of tight rocks is challenging primarily because of their extremely low permeability and complex pore structure. The objective of this paper is to develop an alternative laboratory protocol for evaluating the wettability of tight oil rocks reliably.
First, we conducted systematic spontaneous-imbibition tests on fresh core samples from two different wells drilled in the MT formation. We measured the air/brine, air/oil, and brine/oil contact angles for all samples. We used the end pieces of the samples to conduct scanning electron microscopy (SEM) and analysis of the elemental mapping, or energy-dispersive X-ray spectroscopy (EDS). Finally, we investigated the spontaneous imbibition of brine (or oil) into the samples partly saturated with oil (or brine). Both oil and brine spontaneously imbibe into the fresh samples, composed of quartz, carbonates (dolomite/calcite), clay minerals, feldspars, and organic matter. The results indicate that the effective pore network exhibits a mixed-wet behavior. Moreover, brine spontaneously imbibes into and forces the oil out of the oil-saturated samples, whereas oil cannot imbibe into the brine-saturated samples. This indicates that in the presence of both oil and brine, the rock affinity to brine is higher than that to oil.
We
conduct spontaneous imbibition experiments using different fluids
(deionized, DI, water and brines) and different media (unwashed and washed shale
powder) to study the wetting behavior of the shale samples from the
Horn River Basin (HRB), a massive unconventional gas play in the Western
Canadian Sedimentary Basin. As expected, unwashed shale powder imbibes
DI water faster than brine. Surprisingly, washing the powders results
in faster imbibition of DI water. The imbibition of DI water into
washed shale powders, which have a reduced soluble/leachable ion content,
cannot be fully explained by osmotic effects. We explain the observed
imbibition profiles using the electrostatic interaction theory. We
measure the ion concentration of the brines by ICP-MS analysis and
determine the ionic strength, I, of the in situ formed
brine. We also calculate the characteristic thickness of electrostatic
double layer, κ–1, formed around the surface
of charged shale powders. The results indicate that the imbibition
rate depends on the κ–1value of the in situ
formed brine. Electrostatic interaction is part of the disjoining
pressure which is not considered in the Young–Laplace equation.
A higher κ–1 value enlarges the electrostatic
interaction range, which results in formation of a thicker hydration
shell around the surface of the shale powder and increases the imbibition
rate.
Asphaltene is a complex macromolecule whose abundance strongly affects the physical and interfacial properties of crude oil. Asphaltene molecules may precipitate during crude oil production/transportation, which may lead to plugging/ clogging of wellbores, pipelines, and equipment. In this study, the solubility of asphaltene in toluene has been investigated by calculation of noncovalent interaction energies between asphaltenes in toluene medium. The results of this study revealed that the main interactions in the asphaltene−toluene system are Lifshitz−van der Waals and Lewis acid−base interactions, whereas the electrostatic double layer is of lower comparative order of significance specifically at lower separation distances and lower ζ potentials. However, the repulsive electrostatic double-layer interactions may assist in stabilizing the asphaltene−toluene system based on the comparative values of Lifshitz−van der Waals, Lewis acid−base, and electrostatic double-layer interactions. This is the case especially at higher separation distances and/or higher temperatures where asphaltene particles have greater values of ζ-potential. Furthermore, it is illustrated that when asphaltene has a lower electron-donor parameter, i.e., a lower basicity than toluene, then Lewis acid−base interactions between asphaltenes in toluene are repulsive. This repulsive Lewis acid−base interaction may compensate for the attractive van der Waals interactions between asphaltene particles at low asphaltene basicity. Finally, the electron donor/ acceptor component of the surface energy strongly determines the fate of asphaltene in crude oil colloidal system.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.