Freshwater Injection Research Articles

Deriving iceberg ablation rates using an on-iceberg autonomous phase-sensitive radar (ApRES)

Abstract The increase in iceberg discharge into the polar oceans highlights the importance of understanding how quickly icebergs are deteriorating and where the resulting freshwater injection is occurring. Recent advances in quantifying iceberg deterioration through combinations of modeling, remote sensing and direct in situ measurements have successfully calculated overall ablation rates, and surface and sidewall ablation; however, in situ measurements of basal melt rates have been difficult to obtain. Radar has successfully measured iceberg thickness, but repeat measurements, which would capture a change in iceberg thickness with time, have not yet been collected. Here we test the applicability of using an on-iceberg autonomous phase-sensitive radar (ApRES) to quantify basal ablation rates of a large (~800 m long) non-tabular Arctic iceberg during an intensive 2019 summer field campaign in Sermilik Fjord, southeast Greenland. We find that ApRES can be used to measure basal ablation even over a short deployment period (10 d), and also provide a lower bound on sidewall melt. This study fills a critical gap in iceberg research and pushes the limits of field instrumentation.

Experimental and numerical investigation of the effect of air injection on seawater intrusion mitigation

Previous studies have proposed compressed air injection to mitigate seawater intrusion, as a substitute for a hydraulic barrier created using freshwater injection. However, the current understanding of this strategy is based almost entirely on numerical simulation, and therefore, there is a need to investigate the complex processes accompanying this method within a physical setting. This study used sand tank experiments to explore the influence of air injection on the behavior of saltwater within a coastal confined aquifer, extending previous experiments by accounting for freshwater-saltwater density differences. Numerical modeling of the experiments assisted in interpreting experimental observations and allowed for field-scale conditions to be assessed. Numerical models were well matched to experimental observations, which showed a 34 % reduction in saltwater volume and a retreat of the saltwater toe length from 59 cm to 40 cm following air injection. A hypothetical field-scale confined aquifer model indicated that the largest seaward shift in the seawater wedge toe is obtained when the air-injection well is above the initial seawater wedge toe. However, maximal reductions in the seawater volume within the aquifer were obtained from injecting air within the original wedge rather than landward of the toe. This study provides the first physical evidence (through laboratory experiments) that injecting compressed air can effectively mitigate seawater intrusion. We considered a period of one year for field-scale applications, which show that the extent of desaturation likely needs to be mitigated from prolonged application of the method. Initial guidance is developed for the selection of air-injection locations, at least under simplified conditions (e.g. homogeneous, uniform aquifer, etc.).

Study on the Typical Environmental Factors in the Middle Part of Zhoushan Fishery Based on HY-1C/D and Other Multi-Source Data

This study utilizes satellite data, including HY-1C/D, along with reanalysis data, to unveil the typical environmental characteristics of the sea surface in the middle of Zhoushan fishery. The article addresses three main issues. The first one is the development of an ocean primary productivity (OPP) inversion algorithm model. The second one is the study of chlorophyll-α (Chl-α) concentration and OPP distribution characteristics in Zhoushan fishery using China’s domestically produced ocean satellite HY-1C/D CZI data. The last one is the revelation of the characteristics of typical environmental factors on the sea surface at Zhoushan fishery by combining HY-1C/D with multi-source data. The results show the following: (1) The middle part of Zhoushan fishery exhibits significant seasonal and regional variations in Chl-α concentration and OPP. Chl-α concentration ranges mainly between 0.2 and 2.9 µg/L, with higher concentrations in spring and summer and lower Chl-α concentrations in autumn and winter. Spatially, Chl-α concentration gradually decreases from west to east. The OPP in the study area ranges from 100 mg·m−2d−1 to 1000 mg·m−2d−1, with high OPP values distributed on the western side, ranging from 400 mg·m−2d−1 to 1000 mg·m−2d−1, and gradually decreasing seaward. The highest OPP occurs in summer and the lowest in winter. (2) The correlation analysis between Chl-α concentration and OPP revealed a strong positive relationship. Consequently, this study developed an empirical model for estimating OPP based on Chl-α concentration and validated its feasibility. The model applies to areas with Chl-α concentrations ranging from 0.2 to 4 µg/L. (3) The convergence of freshwater injection, multiple ocean currents, and seasonal upwelling in the study area brings about a rich supply of nutrients. Additionally, the region is characterized by suitable conditions, including optimal Chl-α concentrations, OPP, SST, salinity, currents, and geological water depths. The synergistic effect of these factors together contributed to the formation of Zhoushan fishery.

Comprehensive seismic evidence for the inducing mechanism of extremely shallow 2019 Changning Ms 6.0 earthquake by solution salt mining, Sichuan Basin, China

Abstract In the Changning region of the Sichuan Basin, China, which has experienced decades-long injection of freshwater for commercial salt mining, a Ms 6.0 earthquake occurred in June 2019, along with four Ms >5 aftershocks. Using data from local and regional seismic stations, we determine accurate locations for this earthquake sequence, velocity structures, and excess pore fluid pressures of the source region. Our results show that the Ms 6.0 earthquake is extremely shallow (~1.6 km below mean sea level) and is associated with low Vs and high Vp/Vs values and excess fluid pressures, indicating a fluid-induced earthquake. The mainshock was likely the shallowest M >6.0 induced earthquake, and it was triggered by the combined effect of pore pressure increase from the diffusion of injected fluids, differential formation subsidence from salt caverns, and highly fractured slip-prone rocks enriched in quartz and silica content. Following Coulomb stress transfer from the mainshock, the sequence ruptured in a cascading manner involving preexisting oblique faults of varying dips.

Modeled variations of tropical cyclone genesis potential during Marine Isotope Stage 3

To advance our understanding of the responses of tropical cyclones (TCs) to abrupt climate transitions, we investigate the variation of genesis potential and the underlying mechanisms during Marine Isotope Stage 3 (MIS 3) that is characterized by frequent millennial-scale oscillations, using a set of coupled model simulations. We illustrate that genesis potential mainly increases over the eastern North Pacific and South Pacific in the storm season during MIS 3 interstadial relative to preindustrial, whereas it decreases over the western North Pacific, North Atlantic, South Indian Ocean, and Australian coast. The relative importance of each genesis factor to genesis potential change varies across oceans. During the transition from warm interstadial to cold stadial induced by freshwater injection, TC genesis potential generally decreases in the Northern Hemisphere, while increases in the Southern Hemisphere. These changes are associated with asymmetric variations of genesis factors between Northern and Southern Hemisphere, which are further tied to the adjustment of large-scale environmental factors in response to the weakened Atlantic meridional overturning circulation. Additionally, TC genesis potential exhibits a regional “overshoot” phenomenon when the freshwater injection is terminated, manifested by an increase over the eastern North Pacific and North Atlantic and a decrease over the South Pacific, compared with the initial interstadial state. Our results may help improve our knowledge on past TC behaviors and shed lights on TC response to potential abrupt climate transitions in a warmer future.

Pore-Scale Analysis of the Permeability Damage and Recovery during Cyclic Freshwater and Brine Injection in Porous Media Containing Non-Swelling Clays

Permeability damage in subsurface porous media caused by clay mobilization is encountered in many engineering applications, such as geothermal energy, water disposal, oil recovery, and underground CO2 storage. During the freshwater injection into rocks containing brine, the sudden decrease in salinity causes native clay fines to detach and clog pore throats, leading to a significant decline in permeability. The clay fines detach due to weakened net-attractive forces binding them to each other and the grain. Past experiments link this permeability damage on the immediate history of the salinity and the direction of flow. To better understand this phenomenon, we conducted pore-scale simulations of cyclic injection of freshwater and brine into sandstone containing Kaolinite clay. Our simulations establish a link between the clay-fine trajectory and the permeability trend observed by Khilar and Fogler (1983). For a uniform clay size of 3 microns, we observe a permeability decline by two orders of magnitude during freshwater injection with respect to brine injection. Increasing salinity and simultaneously reversing flow direction restores the permeability. The permeability restoration upon reversing the brine flow direction is attributed to the unblocking of pore throats in the reverse direction by the movement of the clay particles along the grain surfaces by the hydrodynamic force and the strong net-attractive force under high salinity.

Application value of high-frequency ultrasound combined with ultrasonography in the diagnosis of neonatal esophageal atresia.

To explore the application value of high-frequency ultrasound combined with ultrasonography in the diagnosis of neonatal esophageal atresia (EA). Seventy neonates with suspected EA who received healing in our hospital from August 2019 to April 2022 were retrospectively selected as the study subjects and their preoperative esophageal high-frequency ultrasound and ultrasound hydrography data were analysed. The diagnostic value of high-frequency ultrasound, ultrasound hydrography and combined detection in neonatal EA was analysed using intraoperative findings as the gold standard. (1) Among the 70 children with suspected EA, 62 were confirmed to be positive and 8 were negative; 59 were positive and 11 were negative by ultrasound hydrography alone; 61 were positive and 9 were negative by high-frequency ultrasound alone; 62 were positive and 8 were negative by combined detection.(2) The accuracy of combined detection was 97.14%, which was notably different from 92.86% by high-frequency ultrasound and 84.29% by ultrasound hydrography (P < 0.05).(3) The diagnostic AUC of ultrasound hydrography, high-frequency ultrasound, and combined detection for EA was 0.6125, 0.6500, and 0.6563, respectively (P < 0.05).(4) There was no significant variation in the distance between preoperative high-frequency ultrasound, ultrasound hydrography, and intraoperative measurements of distal and proximal blind ends of type IIIA and IIIB EA esophagus (P > 0.05). High frequency ultrasound and super fresh water injection angiography have good application value in the diagnosis of neonatal EA. There is no significant difference between the distance between the distal and proximal blind ends of the esophagus before and during the operation of type III EA and that during the operation of super fresh water injection angiography. However, in consideration of the risk of radiation and poisoning caused by esophagography, it is recommended that high-frequency ultrasound be selected first for diagnosis and if necessary, esophagography be supplemented for joint diagnosis.

Reactive Transport Modelling of carbon mineralization – a machine learning-based approach

Carbon mineralisation is currently one of the most promising Carbon Capture and Storage (CSS) options for permanent gas sequestration since it ensures a rapid conversion of carbon from the gas phase to a carbonate mineral. Mafic and ultramafic rocks are the best geological options for mineral carbonation due to the relatively fast dissolution rates of the mineral components that can release carbonatable divalent cations such as Mg2+, Sr2+, Ba2+, Mn2+, Ca2+ and Fe2+. Once in solution, these cations react with dissolved carbonate ions to form, under convenient pH and temperature conditions, carbonate minerals like calcite, magnesite, siderite, rhodochrosite, or dolomite.&#x0D; The viability of carbon mineralization with injection of freshwater has been proven in the CarbFix project [1]. The main feature of the CarbFix method is that CO2 (and other minor gases) is not injected under its gaseous form but already dissolved in an aqueous fluid, which greatly enhances the mineralisation rates. The methodology, however, requires vast amounts of water that can be a limited resource in many regions. Seawater may be the most viable water source for underground carbonation in many areas, but its use raises questions on the efficiency of the carbonation process. The high ionic strength of seawater makes the geochemical interactions between CO2-rock and seawater more complex and, so far, more unpredictable. Reactive transport modelling (RTM) based on experimental thermodynamic and kinetic data of seawater-basalt interaction [2, 3] can shed some light on the expected mineralisation progress in sites with different mineralogy and variable temperature conditions. Figure 1 shows the results obtained with a reactive transport model that simulates the injection of CO2-charged seawater in basaltic rock.&#x0D; geochemical reaction calculations in particular might be considerably slow and are sometimes redundant as they might be based on a very similar set of input values. These challenges are usually faced by introducing a number of simplifications in the models to meet the objectives of the simulation studies. Thus, alternative ways to solving the full system are a priori a potential way to reduce the computational burden of numerical models.&#x0D; One of such alternatives is Machine Learning (ML) and, more specifically, Artificial Neural Networks (ANN), which are inspired on biological neural networks as the ones found in the human brain. They contain several computational “neurons” arranged in different layers. Each of these neurons can be activated based on the response of the other connected neurons. The training process consists of feeding data into the ANN and fitting the connection weights between the neurons to reproduce and learn the hidden relationships of the data. Recently, the authors have coupled ANNs of a geochemical system into a reactive transport simulator [5]. In this approach, Supervised Machine Learning with ANNs is used to accurately predict the geochemical evolution in a reactive transport framework without the need of actually performing the (expensive) chemical equilibrium calculations in the reactive transport model.&#x0D; The goal of this work is to apply and further develop the technology based on Supervised Machine Learning algorithms to drastically boost the efficiency of reactive transport models of carbon mineralization in the Carbfix system [6]. Firstly, a set of geochemical models of CCS are developed in batch systems (0D) as well as reactive transport models in 1D axisymmetric, 2D, and 3D RTM modelling with different degrees of complexity. Modelling focuses on the injection of CO2-charged seawater into basaltic rocks. In this system, CO2 is consumed via a two-step reaction: (1) Dissolution of Basaltic Glass and release of cations (Ca and Mg), and (2) precipitation of Ca-Mg carbonates and other secondary minerals. The RTM models consider a 1 km domain and a characteristic mineralization of 3-4 years. As a first step, these models are solved with the convential (non ML-based) reactive transport simulator iCP [7]. Then, ANNs are trained and validated with the latest developments in setting up neural networks and used to solve these RTM systems with a Comsol-ML library. The resulting ANNs present good accuracies with coefficients of determination (R2) above 0.95 for all outputs, and a batch calculation speedup of 30 as compared to traditional chemical equilibration with PhreeqC. Preliminary results of RTM using ML to predict the chemical step indicate a speedup of on order of magnitude and reasonable accuracy as compared to conventional RTM. Our results demonstrate that it is conceivable to replace a geochemical solver in a RTM environment with significantly faster surrogate-based models powered by a machine learning algorithm

Thermal effects of freshwater injection on flow and salinity distributions in tidally-affected coastal unconfined aquifers

Freshwater injection is a practical and efficient solution to mitigate seawater intrusion in coastal aquifers, but its thermal impacts on groundwater flow and salt transport are still poorly understood. This study investigates the dynamic characteristics of salinity distributions and seawater recirculation in coastal unconfined aquifers subjected to freshwater injection and tides. The results show that the seaward development of thermal plume modifies the transience of upper saline plume and saltwater wedge, significantly prolonging the aquifer response to injected freshwater. Three temporal variations of upper saline plume due to freshwater injection are driven by pressure waves of injected freshwater, thermal plume-induced changes of hydraulic gradients and saltwater wedge, and the hydraulic conductivity within the upper saline plume. Moreover, a delayed reduction in seawater recirculation in response to the thermal impacts of cold-water injection induces a significant and long-lasting overshoot of total water efflux. An increased tidal amplitude facilitates thermal effects on flow and salinity distributions. A deeper injection well extends the flow path of injected freshwater and thermally regulates discharge rates along the beach surface, thereby enhancing overshoot magnitude of total water efflux. These results improve the understanding of underlying processes related to freshwater injection in coastal aquifers and provide guidance for better managing coastal groundwater resources.

Mitigation of oxygen decline in fjords by freshwater injection

The exchange of water masses between deep fjords and the open ocean is commonly constrained by a topographical barrier called the sill. While fjord water above the sill depth communicates relatively freely with the open ocean, water below the sill depth is caught inside the fjord basin. This basin water may remain stagnant in deep fjords for many successive years. During these periods, the biological consumption of dissolved oxygen is larger than the supply of new oxygen, and the fjord basin might experience hypoxia and even anoxia. Such deoxygenation is natural but can be amplified by warming and human activities involving supplies of organic matter and other nutrients. Here, we use a general circulation model to explore how deoxygenation can be mitigated by injecting fresh water into the fjord basin. The freshwater injection causes density reduction of the basin water with subsequent water exchange and oxygenation. Our results suggest that the basin water of Masfjorden, a 480 m deep fjord with a basin volume of 4 × 109 m3, can avoid deoxygenation with a continuous freshwater injection of 0.05 m3 s−1. We conclude that freshwater injection might be an efficient tool to mitigate the deoxygenation of fjord basins.

Influence of tides on the effectiveness of artificial freshwater injection in mitigating seawater intrusion in an unconfined coastal aquifer

Managed aquifer recharge (MAR) using artificial freshwater recharge from infiltration basins or injection wells is an effective method to control seawater intrusion. The effect of oceanic tides, however, are usually not considered when dimensioning and operating freshwater injection installations. This study employed lab-scale physical experiments and groundwater numerical models to investigate salt transport and salinity distributions as driven by artificial freshwater injection under the influence of tides in an unconfined coastal aquifer. Results revealed that the effectiveness of artificial freshwater injection is significantly reduced under tidal conditions as compared to conditions without tides. The response of the upper saline plume (the tidal recirculation cell) to artificial freshwater injection in tidal conditions is nearly twice more rapid than that of the lower seawater wedge. The seaward displacement of the seawater wedge toe is higher for low seawater concentration isohalines (5%) than for higher concentration isohalines (50% to 95%). It was further found that an overshoot phenomenon (whereby the seawater toe first moves seaward before moving landward again) occurs and mainly affects the higher concentration isohalines. This further decreases the effectiveness of freshwater injection in controlling seawater intrusion, and the phenomenon is more pronounced with increased injection rates, increased distance between injection well and coastal line, increased tidal amplitude and decreased tidal periods. This study provides insights with direct implications for design of artificial freshwater injection wells to control seawater intrusion in tidally-influenced unconfined coastal aquifers.

Modeling and verification of non-linear mineral dissolution processes with buoyancy effects

A new methodology for the simulation of salt cavity development by dissolution is presented, verified and qualitatively validated by experiments. Starting from an initial cavity, the simulator models the injection of fresh water, natural and forced convection of the brine, and the evolution of the cavity walls due to dissolution. The nonlinear model couples brine mass and momentum conservation (governed by incompressible Navier–Stokes equations) with the buoyancy effect due to the brine density variations. Vortex generation and density-driven brine plume rise demonstrate the impact of complex brine flow patterns on the dissolution front evolution. A new explicit interface tracking strategy is employed to investigate the dissolution front movement and an improved smoothing algorithm to enhance the model robustness, contributing to low computational cost and stable simulation for the long-term dissolution process simulation. The proposed model is verified by conducting spatial and temporal convergence studies and qualitatively validated using lab-scale experiments. The agreement between experiments and simulations of horizontal and vertical dissolution cases demonstrates the utility of the model. The simulation results indicate that the rising plume of brine results in a “morning glory” shape cavity under a vertical dissolution scenario and a significant difference between upper and lower fronts dissolution rates for the horizontal dissolution case. The coupling effect of eddy development and cavity shape evolution is also discussed. This work furthers the understanding of the interaction between brine transport in an initially-formed cavity and dissolution patterns of the cavity boundaries, driven by gravity and convective flows.

Coupled Effects of Density and Dual‐Domain Mass Transfer on Aquifer Storage and Recovery

AbstractAquifer storage and recovery (ASR) involves the injection of freshwater into an aquifer for temporary water storage and later use. Previous studies have shown that density‐driven convection may render part of the injectant unrecoverable when ASR is implemented in a saline aquifer. Where heterogeneity creates a significant proportion of immobile groundwater, dual‐domain (immobile and mobile porosities) effects also lead to reductions in the efficiency of ASR schemes. Presuming constant total porosity (sum of the mobile and immobile porosities), the combined effects of dual‐domain properties and water density on ASR are investigated for the first time in the present study, using numerical modeling of otherwise similar conceptual models to previous ASR analyses. Results show that the interactions between the density effect and dual‐domain mass transfer lead to complex controlling patterns of the density contrast, the ratio of immobile‐mobile porosities, the parameterization of immobile‐mobile solute exchange, and the number of cycles. The influence of these factors on mixing processes and the recovery efficiency (proportion of freshwater injectant recovered by extraction) during ASR are shown. Dual‐domain effects, where they occur in aquifers, must be included explicitly in models to reproduce recovery efficiencies, especially during early cycles, unless the immobile porosity is very small or the conductance between mobile and immobile regions is at extremes. Otherwise, a single‐domain model can be utilized. The findings of this research illustrate the influence of both density effects and dual‐domain processes on ASR and the need to account for both in assessing ASR feasibility in complex hydrogeological settings.

Freshwater routing in eddy-permitting simulations of the last deglacial: the impact of realistic freshwater discharge

Abstract. Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial- to millennial-scale climate variability, such as the Younger Dryas and Dansgaard–Oeschger events, but this relationship is not straightforward. Large-scale glacial runoff events, such as Meltwater Pulse 1a (MWP1a), are not always temporally proximal to subsequent large-scale cooling. Moreover, the typical design of hosing experiments that support this relationship tends to artificially amplify the climate response. This study explores the impact that limitations in the representation of runoff in conventional “hosing” simulations has on our understanding of this relationship by examining where coastally released freshwater is transported when it reaches the ocean. We particularly focus on the impact of (1) the injection of freshwater directly over sites of deep-water formation (DWF) rather than at runoff locations (i.e. hosing), (2) excessive freshwater injection volumes (often by a factor of 5), and (3) the use of present-day (rather than palaeo) ocean gateways. We track the routing of glaciologically constrained freshwater volumes from four different inferred injection locations in a suite of eddy-permitting glacial ocean simulations using the Massachusetts Institute of Technology General Circulation Model (MITgcm) under both open and closed Bering Strait conditions. Restricting freshwater forcing values to realistic ranges results in less spreading of freshwater across the North Atlantic and indicates that the freshwater anomalies over DWF sites depend strongly on the geographical location of meltwater input. In particular, freshwater released into the Gulf of Mexico generates a very weak freshwater signal over DWF regions as a result of entrainment by the turbulent Gulf Stream. In contrast, freshwater released into the Arctic with an open Bering Strait or from the Eurasian ice sheet is found to generate the largest salinity anomalies over DWF regions in the North Atlantic and GIN (Greenland–Iceland–Norwegian) seas region respectively. Experiments show that when the Bering Strait is open, the Mackenzie River source exhibits more than twice as much freshening of the North Atlantic deep-water formation regions as when the Bering Strait is closed. Our results illustrate that applying freshwater hosing directly into the North Atlantic with even “realistic” freshwater amounts still overestimates the amount of terrestrial runoff reaching DWF regions. Given the simulated salinity anomaly distributions and the lack of reconstructed impact on deep-water formation during the Bølling–Allerød, our results support that the majority of the North American contribution to MWP1a was not routed through the Mackenzie River.

Pore-scale CFD simulations of clay mobilization in natural porous media due to fresh water injection

The present work investigates mechanisms of permeability impairment as a result of low-salinity fluid injection into brine-saturated porous media containing dispersible clays. We present a computational fluid dynamics model at the pore-scale to simulate detachment, migration and straining of fine particles in porous media. The model uses an immersed boundary method to simulate the motion of clay fines in a fluid. In addition to the hydrodynamic forces, we model the Derjaguin-Landau-Verwey-Overbeek forces (DLVO) between clay fines and grains. Our simulations show the impact of the injected fluid’s salinity and velocity on the concentration of clay fines retained on the grain surface. We see clay particles dislodging from the grain surface in clusters of up to 12 particles. Our simulation results also demonstrate clogging of narrow pore spaces by the detached particles from the grain surfaces.

Measurements of Iceberg Melt Rates Using High‐Resolution GPS and Iceberg Surface Scans

AbstractIncreasing freshwater input to the subpolar North Atlantic through iceberg melting can influence fjord‐scale to basin‐scale ocean circulation. However, the magnitude, timing, and distribution of this freshwater have been challenging to quantify due to minimal direct observations of subsurface iceberg geometry and melt rates. Here we present novel in situ methods capturing iceberg change at high‐temporal and ‐spatial resolution using four high‐precision GPS units deployed on two large icebergs (&gt;500 m length). In combination with measurements of surface and subsurface geometry, we calculate iceberg melt rates between 0.10 and 0.27 m/d over the 9‐day survey. These melt rates are lower than those proposed in previous studies, likely due to using individual subsurface iceberg geometries in calculations. In combining these new measurements of iceberg geometry and melt rate with the broad spatial coverage of remote sensing, we can better predict the impact of increasing freshwater injection from the Greenland Ice Sheet.

Using resistivity data to study the waterflooding process: A case study in tight sandstone reservoirs of the Ordos Basin, China

Water injection is one of the most common methods used to enhance the oil recovery of reservoirs with low permeability and strong heterogeneity. However, with the injection of water in the production process, the formation water salinity, oil saturation, and the distribution of the residual oil in the reservoir are altered, causing difficulties in the evaluation of the flooded layers. Consequently, it is crucial to understand the changes in reservoir resistivity when evaluating waterflooded layers with different wettabilities. Resistivity experiments for high-resistivity (HR) and normal-resistivity (NR) tight sandstone samples are carried out to simulate different types of waterflooding processes. Specifically, fresh water and the original formation water with higher salinity are separately used to displace oil in rock samples, including the HR and NR samples. Our results indicate that the salinity of injected water and the reservoir wettability can affect the reservoir resistivity after waterflooding. When fresh water is injected, the resistivity of NR and HR samples initially decreases, and then increases due to reduced oil saturation and increased salinity of the injected fresh water. In contrast, the resistivity of NR and HR samples decreases monotonically when the original formation water is injected. Our study also indicates that the formation water injection facilitates resistivity logging evaluation of high-resistance waterflooding layers better than fresh-water injection. To our knowledge, this is the first report of such a rich set of resistivity experiments in tight sandstone waterflooded reservoirs with complex wettability. Finally, combining waterflooding resistivity experiments with relative permeability, we have developed a fast, new, convenient method for evaluating the extent of waterflooding of a tight sandstone reservoir, which has been successfully applied to field-data examples for water-cut evaluation.

Kaolinite fines colloidal-suspension transport in high temperature porous subsurface aqueous environment: Implications to the geothermal sandstone and hot sedimentary aquifer reservoirs permeability

Phyllosilicates, specifically, the kaolinite clay mineral (Al2Si2O5(OH)4), which is a layered silicate mineral with one silica tetrahedral sheet connected with oxygen atoms to one alumina octahedral octahedral sheet is ubiquitous and abundant in sedimentary basins, especially sandstone formations. This particular type of clay mineral fine particles can easily and rapidly cause reservoir formation damage in high temperature aquifers, geothermal, and petroleum reservoirs by detaching from the porous rock surface and migrate, and plug the pore-throats of the rock matrix. Several factors such as, reservoir temperature, pressure, geochemical alteration, permeating fluid, reactive flow, and multi-phase flow are attributed to the permeability decline of the porous rocks and subsequent fluid flow reduction, and consequently, leading to well productivity loss. Therefore, this paper presents laboratory modeling of fines transport in the hot porous sedimentary aquifer. This type of aquifer is located in sedimentary basins with the elevated heat flow and having a characteristic of a shallow depth and a high volume, which indicates a high natural porosity and permeability. In this work, we have conducted three sets of coreflood experiments in the temperature ranges of 125 °C 150 °C, and 175 °C. Kaolinite suspension water has been injected into the porous sandstone core at these temperatures to investigate the feasibility of a permeability and injectivity decline. The major experimental results revealed that there is an increase in water saturation and heat transfer rates. The concentration of fines surges with increasing PVI and permeability declines with increased time. Pressure soars with increasing Pore Volume Injection (PVI), but it stabilized after some time. Actually, PVI is a ratio of cumulative water injection to each pore chamber volume of the rock core. Importantly, the water discharge rate decreases with increasing suspension injection and on the other side, with fresh water injection, the rate of water discharge rises steadily. Furthermore, the experimental and mathematical models were tested against statistical model, multiple linear regression for validation. The modelling results showed good agreement and, therefore, this paper has explicated the significance of fines transport in aquifers under hot sedimentary basins.

Effects of the capillary-entrapped phase on fines migration in porous media

A residual gas or oil present during fines migration in porous media can highly affect particle detachment, migration, and straining and thereby decrease rock permeability. Those effects are due to capillary forces and partial accessibility of the attached fines to the injected water under the presence of capillary-entrapped gaseous or oleic phase. We performed systematic study of fines migration in engineered sand-packs that contain different percentage of kaolinite and residual oil. Each coreflood consists of seven injections, the first with seawater ionic strength and the last with fresh water, and with piecewise-constant salinity decrease from step to step. Higher decline of permeability is found to occur during fresh water injection and to be accompanied by intensive fines production. Compared with fines migration under single-phase flow, having a residual phase significantly decreases the formation damage and the amount of produced kaolinite. For the first time, we determined dependencies of end-point saturations and end-point relative permeabilities versus kaolinite content. We established the phase permeability decrease with decrease in salinity for different kaolinite contents. The coreflood data are found to be in close agreement with the analytical model of 1D linear flow under the presence of residual phase. The laboratory-tuned model coefficients are used for well behaviour prediction using numerical 1D axisymmetric injection model.

Lab scale salt caverns – first results on construction and investigation techniques

Abstract. Salt caverns from solution mining in bedded or domal saline structures are of increasing importance as temporary subsurface storage space to buffer fluctuating renewables and secure a stable energy supply. To assure the integrity of caverns during operation and long term abandonment, knowledge of geochemical rock–water interactions in the transition zone between cavity and salt rock is necessary. Due to the inaccessibility of cavern walls, a set of lab-based experiments were performed in hand-sized specimens by creating cm-sized cavities using fresh water injection and brine removal. The experimental simulations proved challenging and vacuum pressure tests revealed frequent leakage subsequent to borehole preparation. The samples were cut to expose the formed cavity and its margin. Micro X-ray Fluorescence mapping was employed to obtain information on element distributions and showed a clear separation between Na, Mg and K salt layers. XRF mapping represents a suitable technique to track spatial mineralogical changes related to rock-fluid interaction in salt rocks. Fluorescent liquids were used to visualize potential fluid pathways. First results show that these methods are promising in detecting geochemical changes and their extent and are, thus, useful tools in unravelling geochemical processes related to marginal areas of cavernous structures in salt deposits based on lab-scale simulations.