Brine Interface Research Articles

Geomechanical Model Calibration Using Field Measurements for a Petroleum Reserve

A finite element numerical analysis model has been constructed that consists of a mesh that effectively captures the geometries of Bayou Choctaw (BC) Strategic Petroleum Reserve (SPR) site and multimechanism deformation (M-D) salt constitutive model using the daily data of actual wellhead pressure and oil–brine interface location. The salt creep rate is not uniform in the salt dome, and the creep test data for BC salt are limited. Therefore, the model calibration is necessary to simulate the geomechanical behavior of the salt dome. The cavern volumetric closures of SPR caverns calculated from CAVEMAN are used as the field baseline measurement. The structure factor, A2, and transient strain limit factor, K0, in the M-D constitutive model are used for the calibration. The value of A2, obtained experimentally from BC salt, and the value of K0, obtained from Waste Isolation Pilot Plant salt, are used for the baseline values. To adjust the magnitude of A2 and K0, multiplication factors A2F and K0F are defined, respectively. The A2F and K0F values of the salt dome and salt drawdown skins surrounding each SPR cavern have been determined through a number of back analyses. The cavern volumetric closures calculated from this model correspond to the predictions from CAVEMAN for six SPR caverns. Therefore, this model is able to predict behaviors of the salt dome, caverns, caprock, and interbed layers. The geotechnical concerns associated with the BC site from this analysis will be explained in a follow-up paper.

Debrining prediction of a salt cavern used for compressed air energy storage

Using salt caverns for compressed air energy storage (CAES) is a main development direction in China to provide a continuous power supply produced by renewable energy (e.g., solar, wind, tidal energy). A mathematical model used to predict the debrining parameters for a salt cavern used for CAES is built based on the pressure equilibrium principle. Combined with the sonar survey data of a salt cavern, the equations are deduced for calculating the debrining parameters. A mathematical model is proposed for the calculation of the critical safe distance between the air and brine interface (AB interface) and debrining tubing inlet. Based on above mathematical models, a program is developed using Visual Basic computer language. A salt cavern of Jintan salt district, Changzhou city, Jiangsu province, China, is simulated as an example. Results show the tubing size is the most important parameter for improving debrining efficiency. The tubing with diameter and wall thickness of 139.7 mm × 6.98 mm is proposed in the CAES cavern debrining to replace the one with size of 114.3 mm × 6.88 mm used in the traditional debrining for the salt cavern gas storage of Jintan. This can decrease the total debrining time by 43%, and only increases energy consumption by about 10%. This study can provide a theoretical foundation and a technological reference for the debrining of Jintan salt cavern used for CAES.

Pore-scale Mass Transfer Experiments in Porous Media by X-ray CT Scanning

Understanding the physical trapping mechanisms is important to design successful CO2 storage projects. Among major trapping mechanism, the dissolution trapping is mainly influenced by the mass transfer between CO2 and brine interface. A typical dimensionless number, the Sherwood number, is predicted as empirical formulas with the CO2 volume fraction and the Reynolds number. Experiments of brine imbibition into pores which are occupied by CO2 are performed with different Re and injection direction. The most active mass transfer region are consist of relative high Re and high CO2 volume fraction according to the fitting results, and the Sh decrease intensely when Re decrease, especially when Re is below 0.1. Also the descending CO2 volume fraction have relative slight impact on Sh, inducing a probably decline of values. Thus for brine in aquifers a higher migration velocity when imbibition process will accelerate the dissolution process and be benefit to the safety of reservoir.

Stability of liquid bridges with elastic interface

Experimental demonstration that the enhanced elastic response of the brine–crude oil interface under low-salinity conditions increase the stability of the oil–brine interface as shown by uniquely designed bridge experiments.

Nonmonotonic Elasticity of the Crude Oil-Brine Interface in Relation to Improved Oil Recovery.

Injection of optimized chemistry water in enhanced oil recovery (EOR) has gained much interest in the past few years. Crude oil-water interfaces can have a viscoelastic character affected by the adsorption of amphiphilic molecules. The brine concentration as well as surfactants may strongly affect the fluid-fluid interfacial viscoelasticity. In this work we investigate interfacial viscoelasticity of two different oils in terms of brine concentration and a nonionic surfactant. We correlate these measurements with oil recovery in a glass-etched flow microchannel. Interfacial viscoelasticity develops relatively fast in both oils, stabilizing at about 48 h. The interfaces are found to be more elastic than viscous. The interfacial elastic (G') and viscous (G″) moduli increase as the salt concentration decreases until a maximum in viscoelasticity is observed around 0.01 wt % of salt. Monovalent (Na(+)) and divalent (Mg(2+)) cations are used to investigate the effect of ion type; no difference is observed at low salinity. The introduction of a small amount of a surfactant (100 ppm) increases the elasticity of the crude oil-water interface at high salt concentration. Aqueous solutions that give the maximum interface viscoelasticity and high salinity brines are used to displace oil in a glass-etched "porous media" micromodel. Pressure fluctuations after breakthrough are observed in systems with high salt concentration while at low salt concentration there are no appreciable pressure fluctuations. Oil recovery increases by 5-10% in low salinity brines. By using a small amount of a nonionic surfactant with high salinity brine, oil recovery is enhanced 10% with no pressure fluctuations. Interface elasticity reduces the snap-off of the oil phase, leading to reduced pressure fluctuations. This study sheds light on significance of interface viscoelasticity in oil recovery by change in salt concentration and by addition of a small amount of a nonionic surfactant.

Investigation on porosity and permeability change of Mount Simon sandstone (Knox County, IN, USA) under geological CO2 sequestration conditions: a numerical simulation approach

AbstractA numerical model was developed to simulate reactive transport with porosity and permeability change of Mount Simon sandstone (samples from Knox County, IN, USA) after 180 days of exposure to CO2‐saturated brine under CO2 sequestration conditions. The model predicted formation of a high‐porosity zone adjacent to the surface of the sample in contact with bulk brine, and a lower porosity zone just beyond that high‐porosity zone along the path from the sample/bulk brine interface to sample core. The formation of the high porosity zone was attributed to the dissolution of quartz and muscovite/illite, while the formation of the lower porosity zone adjacent to the high porosity zone was attributed to precipitation of kaolinite and feldspar. The model predicted a 40% permeability increase for the Knox sandstone sample after 180 days of exposure to CO2‐saturated brine, which was consistent with laboratory‐measured permeability results. Model‐predicted solution chemistry results were also found to be consistent with laboratory‐measured solution chemistry data. Initial porosity, initial feldspar content, and the exponent n value (determined by pore structure and tortuosity) used in permeability calculations were three important factors affecting permeability evolution of sandstone samples under CO2 sequestration conditions.

Interfacial Properties of Asphaltenes at the Heptol–Brine Interface

Water–oil emulsion is inevitable in the production of crude oil. Understanding the role of asphaltenes at the Heptol (mixture of n-heptane and toluene)–brine interface is of significant importance to deal with oil lost and the waste disposal. The effect of asphaltene concentration on the interfacial tension at the Heptol-brine interface at various times and temperatures (25.0–85.0 °C), as well as in the presence or absence of hydrophobic or hydrophilic silica particles, was tested using a Tracker tensiometer. A transparent quartz packed-bed microreactor with in-line analytics was designed to test the emulsion block in porous media. Experimental results show that the presence of asphaltenes and large hydrophobic inorganic particles in Heptol could stabilize the water in oil emulsions. The results could aid in the design of remediation to improve water displacement of crude oil in sandstone reservoirs and enhance the crude oil recovery.

An Evaluation of Sharp Interface Models for CO2 -Brine Displacement in Aquifers.

Understanding multiphase transport within saline aquifers is necessary for safe and efficient CO2 sequestration. To that end, numerous full-physics codes exist for rigorously modeling multiphase flow within porous and permeable rock formations. High-fidelity simulation with such codes is data- and computation-intensive, and may not be suitable for screening-level calculations. Alternatively, under conditions of vertical equilibrium, a class of sharp-interface models result in simplified relationships that can be solved with limited computing resources and geologic/fluidic data. In this study, the sharp-interface model of Nordbotten and Celia (2006a,2006b) is evaluated against results from a commercial full-physics simulator for a semi-confined system with vertical permeability heterogeneity. In general, significant differences were observed between the simulator and the sharp-interface model results. A variety of adjustments were made to the sharp-interface model including modifications to the fluid saturation and effective viscosity in the two-phase region behind the CO2 -brine interface. These adaptations significantly improved the predictive ability of the sharp interface model while maintaining overall tractability.

Molecular Dynamics Characterizations of the Supercritical CO2–Mediated Hexane–Brine Interface

In the carbon dioxide (CO2) enhanced oil recovery (EOR) process and subsequent geological CO2 sequestration, a ternary system consisting of CO2, crude oil, and brine exists in the reservoir due to the common practice of injecting CO2 together with brine. In this paper, we carried out molecular dynamics simulations to study the interfacial properties of the ternary CO2, hexane, and 1.52 mol/L sodium chloride (NaCl) solution system under 330 K and 20 MPa with different CO2 compositions at the supercritical state, which are very important for the efficiency of the EOR and CO2 sequestration processes. We observed that CO2 mixes well with hexane and a clear interface separates the CO2–hexane mixture with the NaCl solution. The interfacial roughness increases with the CO2 composition, indicating deeper molecular penetrations and shorter capillary wavelengths, which leads to the reduced interfacial tension. Interestingly, the surface excess of CO2 reaches maximum at a CO2 molar fraction of 62.5% (or a weight fraction of 46%), which implies the amphiphilic feature of CO2, acting like surfactants, toward the hexane–brine interface. The orientational preferences of CO2, hexane, and water molecules at the interface are more random at higher CO2 compositions, as a result of the increased absolute amount of CO2 and the absence of hexane at the interface.

Microbial community of the deep-sea brine Lake Kryos seawater-brine interface is active below the chaotropicity limit of life as revealed by recovery of mRNA.

Within the complex of deep, hypersaline anoxic lakes (DHALs) of the Mediterranean Ridge, we identified a new, unexplored DHAL and named it 'Lake Kryos' after a nearby depression. This lake is filled with magnesium chloride (MgCl2 )-rich, athalassohaline brine (salinity > 470 practical salinity units), presumably formed by the dissolution of Messinian bischofite. Compared with the DHAL Discovery, it contains elevated concentrations of kosmotropic sodium and sulfate ions, which are capable of reducing the net chaotropicily of MgCl2 -rich solutions. The brine of Lake Kryos may therefore be biologically permissive at MgCl2 concentrations previously considered incompatible with life. We characterized the microbiology of the seawater-Kryos brine interface and managed to recover mRNA from the 2.27-3.03 M MgCl2 layer (equivalent to 0.747-0.631 water activity), thereby expanding the established chaotropicity window-for-life. The primary bacterial taxa present there were Kebrit Deep Bacteria 1 candidate division and DHAL-specific group of organisms, distantly related to Desulfohalobium. Two euryarchaeal candidate divisions, Mediterranean Sea Brine Lakes group 1 and halophilic cluster 1, accounted for > 85% of the rRNA-containing archaeal clones derived from the 2.27-3.03 M MgCl2 layer, but were minority community-members in the overlying interface-layers. These findings shed light on the plausibility of life in highly chaotropic environments, geochemical windows for microbial extremophiles, and have implications for habitability elsewhere in the Solar System.

Two-phase convective mixing under a buoyant plume of CO2 in deep saline aquifers

The storage of carbon dioxide (CO2) in deep saline aquifers has been suggested as a promising method for stabilizing the atmospheric concentration of CO2. An accurate evaluation of the CO2 trapping mechanisms, such as convective mixing, is crucial for estimates of storage capacity and security. We recently investigated the gravitational stability of the diffusive boundary layer underneath a capillary transition zone by performing a linear stability analysis, which provides a quantitative description of the onset of convection for the two-phase, buoyancy-driven flow in the presence of the capillary transition zone (Emami-Meybodi and Hassanzadeh, 2013). In this paper, we further examine the effect of the capillary transition zone on the onset of convection and subsequent convective mixing using direct numerical simulations. We describe key features of the two-phase convective mixing for systems with low Rayleigh numbers (Ra≤1000) and the measurement of several global quantities, such as the total CO2 dissolution, Sherwood number, swelling factor, and interface velocity. We show that the commonly used assumption of a sharp CO2–brine interface with constant CO2 concentration at the top of an aquifer (i.e. single-phase system) may lead to erroneous estimates of not only the onset of convection, but also of the rate and magnitude of CO2 dissolution. The significant effect of the capillary transition zone on the dissolution of CO2 under a buoyant plume in saline aquifers is explained; and, the link between the capillary transition zone and the volume change, due to CO2 dissolution and the interface velocity over the mixing process, is demonstrated. Compared to the single-phase system, a crossflow through the interface of the diffusive boundary layer with the capillary transition zone, as well as the upward advance of the interface motion, may enhance the convective mixing early in the period of natural convection. The decrease in the onset time and stronger mass flux may be more profound in the two-phase system than in the previously reported single-phase models. Furthermore, we report several scaling relationships that characterize the mixing process in the presence of the capillary transition zone. Our findings provide further insight into the understanding of the two-phase mixing features and the long-term fate of the injected CO2 in deep saline aquifers.

Pore-scale contact angle measurements at reservoir conditions using X-ray microtomography

Contact angle is a principal control of the flow of multiple fluid phases through porous media; however its measurement on other than flat surfaces remains a challenge. A new method is presented for the measurement of the contact angle between immiscible fluids at the pore scale at reservoir conditions (10MPa and 50°C) inside a quarry limestone through the use of X-ray microtomography. It is applied to a super-critical CO2–brine–carbonate system by resampling the micro-CT data onto planes orthogonal to the contact lines, allowing for vectors to be traced along the grain surface and the CO2–brine interface. A distribution of contact angles ranging from 35° to 55° is observed, indicating that the CO2–brine–carbonate system is weakly water-wet. This range of contact angles can be understood as the result of contact angle hysteresis and surface heterogeneity on a range of length scales. Surface heterogeneity is examined by comparison of micro-CT results with optical thin sections and SEM images.

Sediment geochemistry of the Thetis hypersaline anoxic basin (eastern Mediterranean Sea)

The Thetis basin is a deep hypersaline anoxic basin in the western part of the Mediterranean Ridge (eastern Mediterranean Sea). It is characterised by highly sulphidic NaCl-saturated brine with one of the highest values of salinity reported from similar basins (S ~348‰). The strong pycnocline at the seawater–brine interface induces permanent anoxic bottom conditions driving depositional processes and distribution patterns of redox-sensitive metals in the sediments. This work presents a high-resolution dataset of sedimentological, mineralogical and geochemical features and planktonic foraminifera distribution, derived from the exploration of a 52cm long box-core sampled in the Thetis sediments. Basing on direct comparisons with available data from other hypersaline records and ancient anoxic organic-rich deep-sea records (sapropels and black shales), we aim to explore the potential of these anoxic basins as natural laboratories to better understand the mechanisms driving geochemical patterns in recent/ancient anoxic sediments.

Dynamics of convective dissolution from a migrating current of carbon dioxide

During geologic storage of carbon dioxide (CO2), trapping of the buoyant CO2 after injection is essential in order to minimize the risk of leakage into shallower formations through a fracture or abandoned well. Models for the subsurface behavior of the CO2 are useful for the design, implementation, and long-term monitoring of injection sites, but traditional reservoir-simulation tools are currently unable to resolve the impact of small-scale trapping processes on fluid flow at the scale of a geologic basin. Here, we study the impact of solubility trapping from convective dissolution on the up-dip migration of a buoyant gravity current in a sloping aquifer. To do so, we conduct high-resolution numerical simulations of the gravity current that forms from a pair of miscible analogue fluids. Our simulations fully resolve the dense, sinking fingers that drive the convective dissolution process. We analyze the dynamics of the dissolution flux along the moving CO2–brine interface, including its decay as dissolved buoyant fluid accumulates beneath the buoyant current. We show that the dynamics of the dissolution flux and the macroscopic features of the migrating current can be captured with an upscaled sharp-interface model.

Carbon isotopic evidence for microbial control of carbon supply to Orca Basin at the seawater–brine interface

Abstract. Orca Basin, an intraslope basin on the Texas-Louisiana continental slope, hosts a hypersaline, anoxic brine in its lowermost 200 m in which limited microbial activity has been reported. This brine contains a large reservoir of reduced and aged carbon, and appears to be stable at decadal time scales: concentrations and isotopic composition of dissolved inorganic (DIC) and organic carbon (DOC) are similar to measurements made in the 1970s. Both DIC and DOC are more "aged" within the brine pool than in overlying water, and the isotopic contrast between brine carbon and seawater carbon is much greater for DIC than DOC. While the stable carbon isotopic composition of brine DIC points towards a combination of methane and organic carbon remineralization as its source, radiocarbon and box model results point to the brine interface as the major source region for DIC, allowing for only limited oxidation of methane diffusing upwards from sediments. This conclusion is consistent with previous studies that identify the seawater–brine interface as the focus of microbial activity associated with Orca Basin brine. Isotopic similarities between DIC and DOC suggest a different relationship between these two carbon reservoirs than is typically observed in deep ocean basins. Radiocarbon values implicate the seawater–brine interface region as the likely source region for DOC to the brine as well as DIC.

Distinctive Microbial Community Structure in Highly Stratified Deep-Sea Brine Water Columns

Atlantis II and Discovery are two hydrothermal and hypersaline deep-sea pools in the Red Sea rift that are characterized by strong thermohalo-stratification and temperatures steadily peaking near the bottom. We conducted comprehensive vertical profiling of the microbial populations in both pools and highlighted the influential environmental factors. Pyrosequencing of the 16S rRNA genes revealed shifts in community structures vis-à-vis depth. High diversity and low abundance were features of the deepest convective layers despite the low cell density. Surprisingly, the brine interfaces had significantly higher cell counts than the overlying deep-sea water, yet they were lowest in diversity. Vertical stratification of the bacterial populations was apparent as we moved from the Alphaproteobacteria-dominated deep sea to the Planctomycetaceae- or Deferribacteres-dominated interfaces to the Gammaproteobacteria-dominated brine layers. Archaeal marine group I was dominant in the deep-sea water and interfaces, while several euryarchaeotic groups increased in the brine. Across sites, microbial phylotypes and abundances varied substantially in the brine interface of Discovery compared with Atlantis II, despite the near-identical populations in the overlying deep-sea waters. The lowest convective layers harbored interestingly similar microbial communities, even though temperature and heavy metal concentrations were very different. Multivariate analysis indicated that temperature and salinity were the major influences shaping the communities. The harsh conditions and the low-abundance phylotypes could explain the observed correlation in the brine pools.

Aquifer-on-a-Chip: understanding pore-scale salt precipitation dynamics during CO2 sequestration

In this study, we develop a lab-on-a-chip approach to study pore-scale salt precipitation dynamics during CO2 sequestration in saline aquifers-a challenge with this carbon management strategy. Three distinct phases-CO2 (gas), brine (liquid), and salt (solid)-are tracked through microfluidic networks matched to the native geological formations. The resulting salt formation dynamics indicate porosity decreases of ~20% in keeping with large scale core studies. At the network scale, the salt precipitation front moves at a constant velocity, ~2% that of the superficial CO2 velocity in this case. At the pore-scale, we observe two dominant types of salt formation: (1) large bulk crystals, on the order of the pore size (20-50 μm), forming early within trapped brine phases; and (2) polycrystalline aggregated structures, ranging over broad length scales, forming late in the evaporation process and collecting/projecting from the CO2-brine interface. Together, these two salt formation mechanisms show particular propensity for pore blockage and reduced carbon storage capacity.

A Study of Microscale Gas Trapping Using Etched Silicon Micromodels

Immobilization and trapping of carbon dioxide (CO2) enhances the security of geological storage. Trapping mechanisms have been characterized in four groups: structural, residual, dissolution, and mineralization. While structural trapping acts immediately when injection starts and is well investigated, the contribution of residual and dissolution trapping increases over storage time and these contributions need to be better understood for better predictions. This paper focuses on an experimental pore-scale investigation of residual and capillary trapping. CO2–water imbibition experiments were conducted in micromodels whose homogenous pore space is geometrically and topologically similar to Berea sandstone. Microvisual data, photographs and video footage, describes the trapping mechanism and, especially, the disconnection and shrinkage of the CO2 phase. Results show that depending on the flow rate of the imbibing water different trapping mechanisms are observed. Lower flow rates, comparable to the trailing edge of a CO2 plume, lead to more snap-off events and greater trapped residual saturation, whereas rates comparable to the near wellbore area during enhanced sequestration showed displacement of gas bubbles and greater dissolution that ultimately leads to very low or zero gas saturations. Furthermore, complete dissolution events showed that homogenous as well as heterogeneous dissolution occurs. Whereas the latter is subdivided into microbubble formation and dissolution on crevices or pore roughness, the former occurs without the influence of pore walls. Based on the observations we suggest that the type of rock and its roughness as well as the fines present at the CO2 brine interface are important factors determining the dissolution mechanism.

Ganglion Dynamics and Its Implications to Geologic Carbon Dioxide Storage

Capillary trapping of a nonwetting fluid phase in the subsurface has been considered as an important mechanism for geologic storage of carbon dioxide (CO(2)). This mechanism can potentially relax stringent requirements for the integrity of cap rocks for CO(2) storage and therefore can significantly enhance storage capacity and security. We here apply ganglion dynamics to understand the capillary trapping of supercritical CO(2) (scCO(2)) under relevant reservoir conditions. We show that, by breaking the injected scCO(2) into small disconnected ganglia, the efficiency of capillary trapping can be greatly enhanced, because the mobility of a ganglion is inversely dependent on its size. Supercritical CO(2) ganglia can be engineered by promoting CO(2)-water interface instability during immiscible displacement, and their size distribution can be controlled by injection mode (e.g., water-alternating-gas) and rate. We also show that a large mobile ganglion can potentially break into smaller ganglia due to CO(2)-brine interface instability during buoyant rise, thus becoming less mobile. The mobility of scCO(2) in the subsurface is therefore self-limited. Vertical structural heterogeneity within a reservoir can inhibit the buoyant rise of scCO(2) ganglia. The dynamics of scCO(2) ganglia described here provides a new perspective for the security and monitoring of subsurface CO(2) storage.

Effect of the Red Sea brine-filled deeps (Shaban and Kebrit) on the composition and abundance of benthic and planktonic foraminifera

Composition and abundance of benthic and planktonic foraminifera in surface sediments of the brine-filled Shaban and Kebrit Deeps and some bathyal-slope environments in the northern Red Sea were examined for correlation with environmental conditions (e.g., bathymetry, sediment grain-size, organic matter, and carbonates) of the brine-filled deeps and normal Red Sea water. About 67 benthic foraminiferal species were recorded in these sediments. The lowest faunal density and diversity were recorded in the Shaban and Kebrit Deeps, whereas the highest density and diversity were recorded in the bathyal-slope sediments. Cluster analysis divided the benthic foraminiferal species into three major faunal assemblages. Buccella granulata–Gyroidinoides soldanii–Bolivina persiensis assemblage dominated the 650–1,300 m depth due to predominance of oligotrophic, highly oxygenated bottom waters. The Melonis novozealandicum–Spirophthalmidium acutimargo assemblage was recorded in the deep and bathyal-slope sediments indicating its tolerance for wider ranges of environmental conditions. The deeps were only dominated by the Brizalina spathulata assemblage indicating existence of un-totally anoxic conditions. The deeps yielded also very low planktonic foraminiferal density that may be attributed to occurrence of the seawater–brine interface which not only minimized the deposition of high buoyancy, large-test species (Globigerinoides sacculifer, Globigerinella siphonifera, and Orbulina universa), but also overestimated the small-test species (Globigerinoides ruber, Globoturborotalita rubescens, and Globigerinita glutinata) in the sediments. These findings should be taken into consideration when reconstructing paleoceanographic conditions of the Red Sea using core sediments from the brine-filled deeps.