Calcite–Brine Interface and Its Implications in Oilfield Applications: Insights from Zeta Potential Experiments and Molecular Dynamics Simulations

Abstract

Carbonate reservoirs are made up of predominantly calcite and dolomite minerals and hold significant hydrocarbon reserves globally. However, the production from carbonate reservoirs is limited due to their wettability, which controls the production and fluid distribution. To develop efficient strategies for producing from these formations, it is necessary to understand the underlining mechanisms of carbonate rock wettability. We believe that understanding the native state of the rock mineral in the reservoir environment and how oilfield operations affect the wetting state of minerals is critical to demystifying the change in carbonate rock wettability. Thus, this study extends the understanding of the surface charge development of calcite minerals and provides useful insight into the mineral's surface charge development. Zeta potential measurements and molecular dynamics (MD) simulations of calcite in different fluids of varying composition and salinity were investigated. We have considered both the mixed brine (seawater and reservoir water) and individual salt brine (i.e., NaCl, MgCl 2 , and CaCl 2 ). The results show that the calcite mineral surface charge is controlled by the composition and salinity of the surrounding fluids. Indeed, we found that monovalent ions have dominant contributions to the total calcite surface charge. The adsorptions of Na + and Cl − shape the stern layer structure in the first two calcite hydration monolayers. We found that the interplay between the calcite surface affinity to the brine ions and the hydration-free energies are the two critical parameters shaping the final mineral surface charge. We believe that our study provides essential atomic insights into the calcite−brine interfaces and how ions interact with the surface to control the surface charge, which are vital to the quest for wettability control.

Wettability of Caprock–H2–Water: Insights from Molecular Dynamic Simulations and Sessile-Drop Experiment

“…The extended simple point charge (SPC/E) is model applied for water molecules. We have applied SPC/E model based on previous work on the calcite-brine interface and other benchmarks reported in the literature. ,, In these benchmarks, SPC/E displays the most accurate bulk water properties compared to the experimental data (diffusion coefficient, radial distribution function, density, and dipole moment). Further, it produces a very accurate static dielectric constant at different conditions of temperatures and pressures .…”

Electrokinetic Property and Colloidal Stability Study of Igneous Rocks: Implication on Carbon Mineralization and Underground CO2 Storage

“…A charged body experiences the EDL effect when it is surrounded by opposite charges and a layer of mixed charges (positive and negative), i.e., a parallel layer of charges. 32 More specifically, as ions and surfaces interact or approach one another, the corresponding EDLs initially begin to overlap, causing the interfacial boundary to be compressed before finally collapsing under confinement. This is controlled by the pH and the ionic strength of the system.…”

“…This is so because as we move in the acidic pH direction, one would expect the magnitude of the negative surface charge to decrease due to increased H + density in the system, but the reverse is observed, which is only possible if the EDL compression is at play. A charged body experiences the EDL effect when it is surrounded by opposite charges and a layer of mixed charges (positive and negative), i.e., a parallel layer of charges . More specifically, as ions and surfaces interact or approach one another, the corresponding EDLs initially begin to overlap, causing the interfacial boundary to be compressed before finally collapsing under confinement.…”

“…The samples’ makeup was determined using an X-ray diffraction (XRD) system by Malvern Panalytical, with the composition shown in Table . Salts used in this study to prepare the brine solution (Table ) are of ACS reagent grade and included salts such as NaCl, NaHCO 3 , Na 2 SO 4 , MgCl 2 , and CaCl 2 as reported in an earlier study . pH modification carried out throughout this study utilized 0.1 M solutions of NaOH and nitric acid.…”

Shale Electrokinetic Property and Colloidal Stability: Potential for Subsurface CO2 Storage

“…The electrokinetic properties of suspended colloids such as mineral particles, e.g., calcite and clays, have been reported to be controlled by mineral dissolution, especially in DI water or freshwater environments. 20 However, an in-depth analysis to support or refute this notion has not been presented. To provide evidence to ascertain the presence of mineral dissolution or transformation, in the case of shale samples, ion analysis of the fluid in which the shale samples were aged should be conducted.…”