Sharif Digital Repository

The behavior of a cemented gravely sand is studied using triaxial tests. Undrained tests were performed on saturated specimens, and stress-strain characteristics of the soil, along with volumetric and pore pressure changes, were recognized. Artificially cemented samples are prepared using calcite crystallization as the cementing agent in different percentages. The tests were done in usual range of confining pressures, from 50 to 1200 kPa. The results shows that dilation occurs even at highest confining pressure and least cement content. Also the friction angle of soils increases slightly with cement content, but cohesion intercept increasing is more noticeable  

In this paper we report the results of classical molecular dynamics (MD) simulation of hexanoic acid adsorption on calcite (101-4) surface plane using Pavese and AMBER force fields for calcite and hexanoic acid, respectively. Pair correlation function, strictly suggests a well-structured adsorption. Density profile indicates the adsorption occurs through double-bonded O atom of the acid head group by direct interaction with Ca atom at calcite surface. Adsorption orientation of H and double-bonded O atoms was found to be as lock and key with respect to calcite surface Ca and O atoms, facilitating an effective adsorption. Adsorption time evolution indicates that O atom adsorption is... 

The efficiency of water flooding methods is known to improve by applying ion-tuned water injection. Although there is a consensus that such improvement happens through reversing reservoir wettability characteristics to more water-wet state, the true impact of ions is still ambiguous among contradictory debates. The well-known molecular dynamics (MD) simulation techniques would shed light on such ambiguities to gain deep atomic-scale understanding of the process. Results from MD simulations show that the presence of Na+ and Cl¯ ions leads to the formation of an electrical double layer in adjacency of calcite surface while Mg2+ ions dominantly make complexes with hydrocarbons throughout the... 

In this study, the dynamic adsorption of asphaltene on a calcite surface is investigated. This study investigates the effect of mixed-salt brines on asphaltene adsorption. The results of this work can facilitate the understanding of the complex wettability behaviour of carbonate reservoirs. All experiments were performed in porous media, which were sand-packs filled with calcite powder, to study the influence of the type and concentration of salt on adsorption. The experiments were conducted with asphaltene concentration of 500 mg/L for brines of NaCl, Na2SO4, and a mixture of the two at various ionic strengths. In addition, two tests were performed with an asphaltene concentration of 2000... 

A continuum hydrodynamic model with immersed solid/fluid interface is developed for simulating calcite dissolution by hydrochloric acid (HCl) at the pore scale, and is most accurate for a mass-transfer-controlled dissolution regime under laminar flow conditions. The model uses averaged Navier-Stokes equations to model momentum transfer in porous media and adopts a theoretically developed mass-transfer formulation with assumptions. The model includes no fitting parameter and is validated using experimental results. The findings of previous research and existing models are briefly discussed and their shortcomings and advantages are elucidated. The present model is used in some pore-scale... 

In this work, application of silica nanoparticles for wettability alteration of initially oil-wet calcite was investigated through analysis of surface forces and DLVO theory. Doing so, the wettability and zeta potential of calcite surfaces were measured through the sessile drop method and an in-house experimental setup, respectively. Primary evaluation indicated that incorporating DLVO terms in the Frumkin-Derjaguin model was not sufficient to describe the wettability in an oil-wet calcite/nanofluid system. Sensitivity analysis showed that calculating the double-layer interaction using constant potential-constant potential boundaries along with structural hydrophobic forces (non-DLVO... 

This research concerns fundamentals of spontaneous transport of saltwater (1 mol·dm-3 NaCl solution) in nanopores of calcium carbonates. A fully atomistic model was adopted to scrutinize the temperature dependence of flow regimes during solution transport under CaCO3 nanoconfinement. The early time of capillary filling is inertia-dominated, and the solution penetrates with a near-planar meniscus at constant velocity. Following a transition period, the meniscus angle falls to a stabilized value, characterizing the capillary-viscous advancement in the calcite channel. At this stage, brine displacement follows a parabolic relationship consistent with the classical Lucas-Washburn (LW) theory.... 

In the study presented herein, a simple method for laboratory calcite cementation of a reconstituted gravelly sand was presented. This method was used to prepare cemented gravelly sand specimens, which have similar natural characteristics to alluvial deposit of the city of Tehran. The formation and distribution of calcite bonds, as well as the effectiveness of the presented calcite cementation method in increasing interparticle cohesion, as observed in weakly to moderately cemented soil in Tehran, were evaluated by means of chemical analysis, X-ray diffraction technique, and unconfined compressive strength tests. The cementation technique was used to prepare triaxial specimens with calcite... 

One of the key open questions in the area of low or controlled salinity water flooding (LSWF or CSWF) is how the observed oil recovery at macro-scale (e.g. Darcy or core-scale) can the explained and what underlying microscopic mechanisms drive it. Thus far, the micromodel investigation of LSWF has been limited to sandstones, remaining challenging to apply to carbonates. In this paper we aim to i) extend the capability to fabricate a novel calcite micromodel using Iceland spar calcite crystal, ii) investigate the pore-scale mechanisms leading to oil recovery from carbonates. A target crude oil-brine-rock (COBR) system was first selected. To screen potential brines which can produce... 

Application of nanoparticles for wettability alteration offers a practical approach to resolve some surface-related problems encountered in the nowadays technological process. Examples are underground/subsurface engineering implications, including the enhanced oil recovery from the oil-wet carbonate reservoirs. However, the common wettability evaluating techniques such as contact angle and flotation cannot be representative of the dynamic phenomena occurring at the pore scale and hence are unable to give accurate information about the process. Therefore, in the present work, the electrokinetic evaluations are utilized to explore the wettability alteration of initially oil-wet carbonate rock... 

Molecular dynamics simulation was applied in this study to scrutinize the interfacial properties of water nano-film confined between calcite mineral and hydrocarbon layer, as two intrinsically different media. Such system resembles the environment experienced by water molecules in the pore spaces of underground carbonate reservoirs. The interplay between water film and confining phases, oil and mineral, strongly influences hydrocarbon production process; however, there is a lack of detailed understanding of the involved interactions. MD simulations indicate development of several layers with different water densities in the confined brine. Water molecules form well-ordered structure in three... 

The thin brine film that wets rock surfaces governs the wettability of underground reservoirs. The ionic composition and salinity of this nanosized brine film influence the wetting preference of the rock pore space occupied by hydrocarbons. Despite numerous investigations over the last decades, a unanimous fundamental understanding that concerns the contribution of ions in the original wetting state of the reservoir is lacking and hence the mechanisms responsible for the wettability reversal of the mineral are still unclear. This wettability reversal is the main consequence of ion-Tuned waterflooding. Although the method is widely accepted in practice, there is no universal consensus on the... 

This study aims to elucidate the impact of salinity on the interactions governing the adsorption of polar aromatic oil compounds onto calcite. To this end, molecular dynamics simulations were employed to assess adsorption of a model polar organic molecule (deprotonated benzoic acid, benzoate) on the calcite surface in NaCl brines of different concentration levels, namely, deionized water (DW), low-salinity water (LS, 5000 ppm), and sea water (SW; 45,000 ppm). Calcite was found to be completely covered by several well-ordered water layers. The top hydration layer is very compact and prevents direct adsorption of benzoates onto the substrate. Instead, Na+ ions form a distinct positively... 

Foam flooding has been applied as a promising method in enhanced oil recovery to obviate the challenges of gas flooding such as fingering, channeling and overriding. However, long-term foam stability is crucial for mobility control. In this work, the effective mechanisms on foam stability in the presence of CaCO3 nanoparticles were assessed both theoretically and experimentally. The static and dynamic behaviors of cationic surfactant (HTAB) foam in the presence of CaCO3 nanoparticles with different hydrophobicity were evaluated. The CaCO3 nanoparticles were treated with a series of long-chain fatty acids to generate a range of wettability. Afterward, the underlying mechanisms were revealed...