Impact of Maturity on Kerogen Pore Wettability: A Modeling Study

Abstract

Kerogen wettability is essential to evaluate hydrocarbon storage and quantify reserves estimates, to develop models for multiphase and multicomponent transport especially in oil shales and to predict recoveries of fracture water as well as predict the placement of fracture water during re-fracture treatments. The widely held view for kerogen pores is generally hydrocarbon-wetting; however, some recent experimental work indicates the existence of water content in kerogen. The kerogen maturation process is associated with the loss of H/C and O/C ratios which may influence the wettability depending on the affinity of these functionalized molecules with water. In this paper, we provide a microscopic study of the role of kerogen maturity on wettability of organic pore systems.Varying maturation degree of kerogen surfaces are built by grafting functionalized groups onto the traditional graphene model. We study a mixture of water and alkanes in organic pores with effective width of 5 nm. We find that water aggregates to form clusters, and the shape and the location of the water molecules are strongly linked to the density of the functionalized groups. By determining the contact angles, we are able to quantify the relationship of kerogen wettability with the maturity level.We demonstrate that the wettability in kerogen is very likely to be heterogeneous. Depending on the maturity level, kerogen may be hydrocarbon wetting at high maturity, neutral wetting at intermediate maturities or even hydrophilic for organic surfaces of very low maturities. In addition, we also demonstrate the influence of surface heterogeneity and the distribution of polar molecules on kerogen wettability. Our results indicate that in kerogen there may be a critical local density of surface functionalized sites that may create optimal conditions for hydrophilic kerogen surfaces.

Two-Phase Transport Characteristic of Shale Gas and Water through Hydrophilic and Hydrophobic Nanopores

“…It is well accepted that shale is a heterogeneous rock consisting of an organic matter (OM) and inorganic matter (IOM). ,, Ordinarily, organic nanopores are considered to be hydrophobic, while inorganic nanopores are hydrophilic. − This means that both inorganic (hydrophilic) and organic (hydrophobic) nanopores should be considered together to reveal the gas and water two-phase transport in nanopores. However, a number of recent simulation studies pointed out that organic shale nanopores with various components and maturities show different wettability. − Extensive experimental measurements also indicate that the water contact angle of shale rock ranges from 10° to 130° depending on the sources of shale samples. ,− For the sake of focusing on the influences of wettability and water content of nanopores to the two phase transport mechanisms, we eliminate the differences on surface activity, anisotropy, and geometry for both hydrophilic and hydrophobic nanopores.…”

“…The non-bonding energy is described by the 12-6 LJ-Coulomb mixed model: where the subscripts i and j represent two separated particle sites i and j ; ε and σ are the LJ potential well depth and zero-potential distance, respectively; r denotes the distance between two particles; q is the electric quantity of particle; and ε 0 is the permittivity of the vacuum. The non-bonding parameter of water is adapted from the classical SPC/E model, − and the methane molecule is simplified as a single electrical neutrality particle. ,,, The force field of solid walls is chosen by carbon atoms, which is the major element in shale. − Expect that the parameter between water molecules and walls is tuned for hydrophilic (0.45 kcal/mol) and hydrophobic (0.06 kcal/mol) nanochannels (as shown in Figure S1 in Supporting Information), the values of all other parameters mentioned above are listed in Table . , The long-range Coulombic interaction is calculated by the particle-particle-particle-mesh (PPPM) algorithm with an accuracy of 10 –4 . The cutoff distance for LJ potential energy is set to be 10 Å.…”

“…64−66 Expect that the parameter between water molecules and walls is tuned for hydrophilic (0.45 kcal/mol) and hydrophobic (0.06 kcal/mol) nanochannels (as shown in Figure S1 in Supporting Information), the values of all other parameters mentioned above are listed in Table 2. 11,46 The long-range Coulombic interaction is calculated by the particle-particle-particle-mesh (PPPM) algorithm 67 with an accuracy of 10 −4 . The cutoff distance for LJ potential energy is set to be 10 Å.…”

Mixture Composition Effect on Hydrocarbon–Water Transport in Shale Organic Nanochannels

“…However, mixture flow in nanopores is more general in nature, such as the red blood cell flow, the alcoholism phenomenon, and drug delivery. − Especially in the shale oil development process, oil is extracted from the organic nanochannels of shale formations associated with connate water , and hydraulic fracturing water. , Thus, developing an effective theory to describe mixture flow in nanochannels means a lot to biochemistry, geophysics, petroleum engineering, etc.…”

Adsorption and Phase Behavior of Pure/Mixed Alkanes in Nanoslit Graphite Pores: An iSAFT Application

“…The suppressed critical point was shown to cause a large compositional change in gas production. In a series of molecular dynamics studies by Hu et al, − an activated kerogen model, namely, graphene fragments with oxidized functional groups, was proposed in comparison with the simple graphite model. They have studied the behavior of water and hydrocarbons in model shale nanopores.…”