Properties Of Brine Research Articles

Investigating the hysteretic behavior of Mars-relevant chlorides

Liquid solution stability has been a highly studied topic in the Martian community since the detection of perchlorate (ClO4−) at the Phoenix landing site and the global detection of chloride (Cl−) by THEMIS (Thermal Emission Imagining System, onboard Mars Odyssey). Understanding how brines form and react to changing environmental conditions helps identify potentially habitable environments on Mars, both at present and in the past. Here we measure the extent of metastability of magnesium chloride (MgCl2) and sodium chloride (NaCl) brines when freezing. We find that the metastable eutectic temperature of MgCl2 depends on the maximum temperature (Tmax) reached before freezing. If Tmax < −15 °C, the metastable eutectic temperature (mTeu) is only 3 °C below the stable eutectic temperature, and if Tmax > −15 °C, mTeu is 15 °C below the stable eutectic temperature (Teu). We speculate that this metastable behavior follows the phase diagram for the transition into the 8 hydrate for MgCl2, thus, yielding a different freezing temperature, the peritectic for MgCl2·8H2O. However, mTeu for NaCl is independent of Tmax and was constantly at 3 °C below Teu with no peritectic (consistent with the phase diagram). We also found that MgCl2 brine can exist for at least 60 h at 5 °C below its Teu. Applying our findings, we determined the potential time evolution of brines at Palikir crater, using a time-series of modeled temperature profiles. Surficial layers melt more frequently, but layers at 2–3 cm depth are able to warm above Tmax > −15 °C and maintain brine for longer than surficial layers. The evaporation rate of brine buried by 2–3 cm of regolith is greatly reduced due to the generally cold temperatures, solute concentration, and by the regolith overburden. We also found that at Palikir crater, only the deep subsurface (~9.5 cm depth) has water activities (~0.75) high enough to support life. Overall, the metastable properties of brines can drastically affect their formation and longevity on Mars, and should be considered in future models.

Simulation study of surfactant injection in a fractured core

Surfactant flooding could be used to improve water flooding in fractured reservoirs due to the main mechanisms of wettability alteration and interfacial tension reduction. However, the surfactant flooding in fractured reservoir is not well studied. And there still exist some disputes like surfactant injection rate, surfactant application timing and surfactant injection size. The objective of this work is to study the effects of those parameters on surfactant oil recovery. A spontaneous imbibition model is established based on spontaneous imbibition experiments to verify the properties of rock, brine, oil and surfactant that would be used in the study of surfactant flooding. The spontaneous imbibition model is cut into two parts to create a vertical fracture in the middle. Then the fractured matrix is used as the model in the study of surfactant flooding. The simulation results show that considering the time cost and surfactant consumption, the surfactant injection rate of 0.027 cm3/h (i.e., 0.001 PV/h) is a proper injection rate for the base case, since the oil recovery rate is the same for the injection rate that is higher than 0.027 cm3/h, and the oil recovery is up to 90% ultimate oil recovery after injecting 2 PV surfactant solution. The analysis of surfactant diffusion and fracture porosity effects on surfactant oil recovery indicates that the surfactant diffusion is a key parameter to facilitate the movement of surfactant into the matrix. The injection rate has larger effect in the system with smaller fracture porosity. When the injection rate is higher than 0.53 cm3/h, the ultimate oil recovery is larger in the system with fracture porosity of 0.1% than the system with fracture porosity of 0.5%. In general, the earlier injection of surfactant results in a better result. For the base case, the surfactant flooding time and the required surfactant volume are smaller for the earlier application of surfactant. If the surfactant diffusion is negligible, the early injection of surfactant could increase the ultimate oil recovery. The maximum oil recovery is obtained after injecting 1.3 PV surfactant solution with the concentration of 0.01 g/cm3. But for the lower surfactant concentration, it needs more surfactant solution. Furthermore, the surfactant efficiency is reduced because less surfactant is imbibed into the matrix. So under the condition of injection safety, higher surfactant concentration should be applied. This work not only studied the injection rate effect on oil recovery, it also analysed the effect of surfactant diffusion and fracture properties on the choice of injection rate. In addition, this work explained why the surfactant should be applied before water flooding and whether surfactant application is feasible after completed water flooding. At the end, the surfactant slug size effect on oil recovery and how it is affected by the surfactant concentration are discussed.

Geophysical Monitoring of Gaseous and Supercritical CO2 Fracture Flow Through a Brine-Saturated Shale Caprock

Pre-existing and induced fractures and faults can play a role as bypass conduits and fast leaking channels in CO2 storage sites. They should therefore be well characterized during site selection, and monitored thoroughly during operation to track the movement and fate of the CO2 plume. Despite to date extensive research on the geophysical properties of brine- and CO2-saturated porous reservoir rocks, changes in acoustic velocity and electrical resistivity during a sole fracture fluid displacement are, however, rather little investigated. Hence, we herein present a laboratory study of core-scale geophysical monitoring during drainage-imbibition cycles of the brine-CO2 system through a shale caprock core sample with a vertical fracture. The experiments were conducted using both gaseous and scCO2 with 4 and 9 MPa pore pressures, respectively, at 12 MPa confining pressure. The tests were performed at 40°C during the loading and unloading stages in order to look into the hysteresis effect. We used a fractured core sample from the Upper Jurassic organic-rich shales of the Draupne Formation, which is the primary caprock for the Smeaheia CO2 storage site – a full-scale CCS project in Norway. The primary objective of the experiment was to compare the geophysical measurements using gaseous and scCO2 drainage-imbibition cycles during the tests in a core-scale experiment. Moreover, we were interested to see how sensitive acoustic velocity and electrical resistance techniques are to the fracture fluid displacement using different CO2 phase states. The outcomes of our high-pressure high-temperature experiment of simultaneous measurements of fracture flow and geophysical properties indicate that potential leakage of injected CO2 through the fractured-shale caprock can be detected in the core-scale laboratory experiments. The performed drainage-imbibition cycles using gaseous and scCO2 resulted in different behaviors in P-wave velocity (Vp) and electrical resistance in axial and radial directions for these two phase states. The measured Vp during the displacement of fracture fluid, CO2-brine subsequent cycles, showed a limited sensitivity in terms of magnitude and relative change. The electrical resistance, on the other hand, shows higher sensitivity and larger variation during fluid displacement along the fracture. It was also observed that the crossplot of Vp versus electrical resistance could detect and even differentiate the different phases during the loading and unloading stages.

THM modeling of hydrothermal circulation at Rittershoffen geothermal site, France

BackgroundThe Rittershoffen deep geothermal project located 6 km east from Soultz-sous-Forts EGS site (France) includes a doublet GRT-1 and GRT-2 to exploit the geothermal resource at the sediments–granite transition where higher temperatures than those of Soultz-sous-Forêts have been measured. Detailed stratigraphic and geophysical data, temperature logs, and tracer surveys have been collected. However, no reservoir model, integrating large-scale geophysical measurements, exists for this site.MethodsWe developed a reservoir model in two dimensions (10 km × 5 km) based on a finite element method. It includes thermo–hydro–mechanical (THM) coupling and extended brine properties. A representative elementary volume of 100 m is assumed to homogenize the fault network complexity at small scales. A back analysis is performed to obtain large-scale rock properties using GRT-1 temperature log and regional stress-depth profiles.ResultsThe inverted large-scale properties are consistent with their counterparts measured at the laboratory scale. The bottom of the hydraulic cap rock is 1.2 km ± 0.1 km deep. It is shallower than the discontinuity of the thermal gradient. Hydrothermal convection cells are 2.7 km high which is larger than that previously proposed.ConclusionsA very good fit of the GRT-1 temperature log is obtained using our simplified two-dimensional THM model with four homogenized units at a 100 m scale. The comparison between Rittershoffen and Soultz-sous-Forêts models highlights many similarities in terms of rock properties, decoupling of hydraulic and thermal cap rocks and temperature spatial variability (about 50 °C). Predictions of the relationship between reservoir temperature and surface thermal gradients are proposed for future explorations.

Non-reactive and reactive experiments to determine the electrical conductivities of aqueous geothermal solutions up to supercritical conditions

Electrolytes, dissolved in aqueous solutions, have the tendency to associate at near-critical temperature, which causes a removal of free charge carriers from the solution. This behavior is intensified in the “low” pressure range of the supercritical field and has become noticeable in a reduction of fluid conductivity by an order of magnitude. Thus, deep resistivity surveys are regarded to provide a convenient means for detecting supercritical roots of geothermal high-enthalpy reservoirs. In previous decades, the temperature dependence of electrical properties of single-component brines has been extensively studied up to supercritical conditions. Very few data are available for two-component brines, but none for multicomponent mixtures, representing natural geothermal fluids. Thus, we have developed a flow-through set-up to measure both the intrinsic temperature dependence of electrical properties of hydrothermal solutions and the effect of fluid-solid interactions on fluid conductivities in a temperature range of 23–422 °C at 31 MPa. Experimental conditions were adapted to those of two geothermally exploited areas on Iceland – the Krafla and the Reykjanes field – which are characterized by meteoric and by seawater controlled fluid systems, respectively.Our study shows that the intrinsic temperature dependence of mixed brines exhibit a similar left-skewed curve characteristic like those of single component brines with conductivities decreasing precipitously to a minimum at critical temperature. At further isobaric temperature rise conductivities remain on this level. The opposite was observed for reactive experiments, where fluid – solid interaction was allowed. In this case, conductivities re-increased by up to factor 7 within seconds, indicating a significant and immediate increase in solubility of rock and composite materials, which are in contact with supercritical aqueous solutions and suggest high reaction kinetics of this process. However, at supercritical conditions conductivities did not remain steady and the electrical properties of supercritical fluid-rock systems are characterized by a wide range of conductivities. The competing processes of mineral dissolution and new mineral formations are also evident from complementary micro-structural investigations as well as chemical analyses of the percolated fluids.

Exergoeconomic analysis and optimization of a combined double flash – binary cycle for Ulubelu geothermal power plant in Indonesia

In this paper, the combination of double-flash and binary cycles for Ulubelu geothermal power plant is proposed and optimized by using the Matlab software. This proposed system uses real data and properties of brine exploited from the Ulubelu geothermal well in Indonesia and four working fluid candidates, namely n-Pentane, R141b, R123 and R245fa are used in binary cycles. Optimization using a multi-objective genetic algorithm with an exergoenomic approach is applied to find out the proposed system performance from both thermodynamic and economic point of view. In the optimization procedure, the exergy efficiency and total specific cost of output power become objective functions while the first flash pressure, second flash pressure and Organic Rankine Cycle (ORC) turbine inlet temperature are selected as constraints. The system performance proposed in this paper is compared with the performance of the existing system. The results show that n-pentane is the best working fluid where multi-objective optimization indicates that the system can generate 63.54 MW of power with thermal and exergy efficiencies of 17.59% and 65.26% and specific cost of 1.7049 USD / GJ at the selected optimal design point. Compared to the existing system, there is a significant improvement in performance both from thermodynamic performance and economic performance.

Effect of brine-CO2 fracture flow on velocity and electrical resistivity of naturally fractured tight sandstones

Fracture networks inside geologic [Formula: see text] storage reservoirs can serve as the primary fluid flow conduit, particularly in low-permeability formations. Although some experiments focus on the geophysical properties of brine- and [Formula: see text]-saturated rocks during matrix flow, geophysical monitoring of fracture flow when [Formula: see text] displaces brine inside the fracture seems to be overlooked. We have conducted laboratory geophysical monitoring of fluid flow in a naturally fractured tight sandstone during brine and liquid [Formula: see text] injection. For the experiment, the low-porosity, low-permeability, naturally fractured core sample from the Triassic De Geerdalen Formation was acquired from the Longyearbyen [Formula: see text] storage pilot at Svalbard, Norway. Stress dependence, hysteresis, and the influence of fluid-rock interactions on fracture permeability were investigated. The results suggest that in addition to stress level and pore pressure, mobility and fluid type can affect fracture permeability during loading and unloading cycles. Moreover, the fluid-rock interaction may impact volumetric strain and consequently fracture permeability through swelling and dry out during water and [Formula: see text] injection, respectively. Acoustic velocity and electrical resistivity were measured continuously in the axial direction and three radial levels. Geophysical monitoring of fracture flow revealed that the axial P-wave velocity and axial electrical resistivity are more sensitive to saturation change than the axial S-wave, radial P-wave, and radial resistivity measurements when [Formula: see text] was displacing brine, and the matrix flow was negligible. The marginal decreases of acoustic velocity (maximum 1.6% for axial [Formula: see text]) compared with the 11% increase in axial electrical resistivity suggest that in the case of dominant fracture flow within the fractured tight reservoirs, the use of electrical resistivity methods have a clear advantage compared with seismic methods to monitor [Formula: see text] plume. The knowledge learned from such experiments can be useful for monitoring geologic [Formula: see text] storage in which the primary fluid flow conduit is the fracture network.

Results of the numerical modelling of intra-annual variability of characteristics of the hydrological regime of the Kuyalnik Liman lagoon

In order to solve the problems of diagnosis and forecast of spatial-temporal variability of hydrological characteristics of the Kuyalnik Liman (water level, salinity and temperature) which cause chemical and biological processes occurring therein, and, therefore, affect the properties of brine and therapeutic mud, a non-stationary 3D numerical hydrothermodynamic model Delft3D-FLOW was applied.&#x0D; The model can be applied for research of the features and forecasting of spatial-temporal variability of hydrological characteristics of the Kuyalnik Liman under the influence of natural and anthropogenic factors forming its hydrological regime. Such opportunity is also indicated by the results of adaptation of the model to the Kuyalnik Liman conditions and its validation that are specified in this work.&#x0D; The important role of accounting of small streams flowing into the liman and accurate setting of intensity of storm rainfall during modelling is also shown. It is found that at the time of storm winds with longitudinal directions in relation to the liman’s water surface, the difference of watermarks in its northern and southern parts may reach 0.35-0.4 m.

Experimental Data and Modeling of Solution Density and Heat Capacity in the Na–K–Ca–Mg–Cl–H2O System up to 353.15 K and 5 mol·kg–1 Ionic Strength

This work is on in the volumetric and thermal properties of brines in the quinary Na–K–Ca–Mg–Cl–H2O chemical system. Its objective is twofold. First, by acquiring original data for temperatures ranging from 278.15 to 353.15 K and ionic strengths ranging from 1.3 to 5.1 mol·kg–1 it aimed to add to the experimental data set, usually acquired only at high ionic strengths or at 298.15 K. Experimental solution density was measured using a vibrating-tube densitometer with relative uncertainty, Δρ/ρ, better than 6 × 10–6. This property, combined with volumetric heat capacity measurements, provided the isobaric heat capacity of solution determined with a mean relative deviation better than 0.3%. Second, we used PhreeSCALE software to compute the density and heat capacity of the chemical system of interest, simultaneously applying the Pitzer and the Helgeson–Kirkham–Flowers (HKF) equations. We propose a new set of specific interaction parameters so that published and newly measured experimental data can be describ...

Dynamic Simulation of an Organic Rankine Cycle—Detailed Model of a Kettle Boiler

Organic Rankine Cycles (ORCs) are nowadays a valuable technology to produce electricity from low and medium temperature heat sources, e.g., in geothermal, biomass and waste heat recovery applications. Dynamic simulations can help improve the flexibility and operation of such plants, and guarantee a better economic performance. In this work, a dynamic model for a multi-pass kettle evaporator of a geothermal ORC power plant has been developed and its dynamics have been validated against measured data. The model combines the finite volume approach on the tube side and a two-volume cavity on the shell side. To validate the dynamic model, a positive and a negative step function in heat source flow rate is applied. The simulation model performed well in both cases. The liquid level appeared the most challenging quantity to simulate. A better agreement in temperature was achieved by increasing the volume flow rate of the geothermal brine by 2% over the entire simulation. Measurement errors, discrepancies in working fluid and thermal brine properties and uncertainties in heat transfer correlations can account for this. In the future, the entire geothermal power plant will be simulated, and suggestions to improve its dynamics and control by means of simulations will be provided.

Exergoeconomic analysis and multi-objective optimization of a novel combined flash-binary cycle for Sabalan geothermal power plant in Iran

Employing high-efficiency thermodynamic cycles for power generation from available heat sources is an effective strategy for sustainable energy development. In this regard in the present work, a novel combined flash-binary cycle is proposed for power generation from Sabalan geothermal wells in Iran, considering the wellhead temperature and pressure differences of existing wells. Exergoeconomic approach is applied to investigate the proposed system performance from the viewpoints of both thermodynamics and economics. Using the real data and properties of brine exploited from Sabalan geothermal field, the cycle performance is assessed and a single-objective optimization is performed considering the specific cost of output power as the objective function for four candidate working fluids for binary unit. Then, a multi-objective optimization is conducted and the Pareto frontier as a set of optimal solutions is presented. The results showed that, when single-objective optimization is performed, the proposed cycle with R141b as the binary unit working fluid has the best performance for which the specific cost of output power is calculated to be 4.901$/GJ with an exergy efficiency of 52.56%. However, the multi-objective optimization leads to an exergy efficiency of 54.87% and a power cost of 5.068$/GJ at the selected optimal design point. Finally, a performance comparison is made between the proposed cycle in this work with the previously proposed systems for Sabalan geothermal reservoirs and it is concluded that the flash-binary system proposed here has significantly better performance than the previous systems.

A new model for the computation of the formation factor of core rocks

Among all the rock parameters measured by modern well logging tools, the formation factor is essential because it can be used to calculate the volume of oil- and/or gas in wellsite. A new mathematical model to calculate the formation factor is analytically derived from first principles. Given the electrical properties of both rock and brine (resistivities) and tortuosity (a key parameter of the model), it is possible to calculate the dependence of the formation factor with porosity with good accuracy. When the cementation exponent ceases to remain constant with porosity; the new model is capable of capturing both: the non-linear behavior (for small porosity values) and the typical linear one in log-log plots for the formation factor vs. porosity. Comparisons with experimental data from four different conventional core rock lithologies: sands, sandstone, limestone and volcanic are shown, for all of them a good agreement is observed. This new model is robust, simple and of easy implementation for practical applications. In some cases, it could substitute Archie's law replacing its empirical nature.

Coupled thermo–hydro–mechanical simulation of CO2 enhanced gas recovery with an extended equation of state module for TOUGH2MP-FLAC3D

As one of the most important ways to reduce the greenhouse gas emission, carbon dioxide (CO2) enhanced gas recovery (CO2-EGR) is attractive since the gas recovery can be enhanced simultaneously with CO2 sequestration. Based on the existing equation of state (EOS) module of TOUGH2MP, extEOS7C is developed to calculate the phase partition of H2O–CO2–CH4–NaCl mixtures accurately with consideration of dissolved NaCl and brine properties at high pressure and temperature conditions. Verifications show that it can be applied up to the pressure of 100 MPa and temperature of 150 °C. The module was implemented in the linked simulator TOUGH2MP-FLAC3D for the coupled hydro–mechanical simulations. A simplified three-dimensional (3D) 1/4 model (2.2 km × 1 km × 1 km) which consists of the whole reservoir, caprock and baserock was generated based on the geological conditions of a gas field in the North German Basin. The simulation results show that, under an injection rate of 200,000 t/yr and production rate of 200,000 sm3/d, CO2 breakthrough occurred in the case with the initial reservoir pressure of 5 MPa but did not occur in the case of 42 MPa. Under low pressure conditions, the pressure driven horizontal transport is the dominant process; while under high pressure conditions, the density driven vertical flow is dominant. Under the considered conditions, the CO2-EGR caused only small pressure changes. The largest pore pressure increase (2 MPa) and uplift (7 mm) occurred at the caprock bottom induced by only CO2 injection. The caprock had still the primary stress state and its integrity was not affected. The formation water salinity and temperature variations of ±20 °C had small influences on the CO2-EGR process. In order to slow down the breakthrough, it is suggested that CO2-EGR should be carried out before the reservoir pressure drops below the critical pressure of CO2.

The effect of mirabilite precipitation on the absolute and practical salinities of sea ice brines

The sea ice cover of high latitude oceans contains concentrated brines which are the site of in-situ chemical and biological reactions. The brines become supersaturated with respect to mirabilite (Na2SO4·10H2O) below −6.4°C, and the associated removal of Na+ and SO42− from the brine results in considerable non-conservative changes to its composition. The changes are reflected in the brine salinity, which is a fundamental physico-chemical parameter in the sea ice brine system. Here, measurements of electrical conductivity and brine composition in synthetic sea ice brines between −1.8 and −20.6°C, obtained during a comprehensive investigation of the brine-mirabilite equilibrium at below-zero temperatures reported elsewhere, are combined with modelled estimates to assess the behaviour of the absolute (SA) and practical (SP) salinities of sea ice brines. Results display substantial divergence of SP from SA below −6.4°C, reaching a 7.2% difference at −22.8°C. This is shown to create inaccuracies when SP is assumed to be equivalent to SA, firstly by misrepresenting the conditions inhabited by sea ice biota, whilst also creating errors in the calculation of physical sea ice parameters. Our measured and modelled data are used to refine the SA−T relationship for sea ice brines, implicit of mirabilite precipitation, which is crucial in estimating brine properties in absence of salinity data. Furthermore, because SP is the parameter measured in field studies, we provide an SP−T relationship for sea ice brines to −22.8°C, which aids in explaining the trends observed in available SP−T data from sea ice brines in the Southern Ocean, demonstrating the importance of the mirabilite-brine equilibrium in natural sea ice. Finally, we initiate the development of a conversion factor for the estimation of SA from SP measurement in sea ice brines, and produce an equation that can calculate SA from modelled brine density. This work ultimately highlights careful consideration of salinity concepts when applied to the sea ice system.

Development of calorimetric methods for the characterization of different aqueous deicers

Different aqueous deicers in the range of 20–50 mass% were investigated by calorimetric methods. A dynamic differential scanning calorimetry (DSC) procedure was developed to determine the thermal properties (freezing point, melting enthalpy) of aqueous brines. Phase change temperatures were characterized for the broad melting peak determining two specific temperatures: extremum peak temperature (Tpeak) and the temperature corresponding to the inflection point of heat flow curve, which represents the end of the phase change (Tend). Heating rates of 0.2, 0.5 and 1.0 °C min−1 were used to extrapolate the characteristic temperatures at zero heating rate. For each sample, at least three runs were performed to check the reproducibility. Thermal analyses were conducted with Setaram DSC and with Netzsch DSC. Additionally, the influence of different kinds of sample cells was compared. The results demonstrated that the developed calorimetric method is suitable for the characterization of aqueous deicers. Our studies confirmed that the enthalpy of fusion is appropriate to assess the performance of aqueous deicers. The extrapolated end temperatures at zero heating rate matched the literature values very well.

Low salinity injection into asphaltenic-carbonate oil reservoir, mechanistical study

The impacts of salinity adjustment of displacing fluid have recently gained special attention to enhanced oil recovery (EOR). Different mechanisms have been studied widely in the literature while some of them are still subjugated to more scrutiny. The effects of diluted sea water on the interfacial properties of brine and asphaltenic-acidic crude oil and the wettability alteration of carbonate reservoir rock are investigated in this experimental observational work. The measurements of interfacial tension (IFT) and contact angle (CA) as two main parameters are studied. Besides, the effects of asphaltene and resin in the crude oil on the IFT values between the crude oil and aqueous solution are investigated.The experimental results show that the lowest IFT values are obtained at high salinity conditions, while the surface rock wettability alterations are observed at low salinity conditions. Based on the obtained results, a combined mechanism is proposed to describe the wettability alteration towards more water wet at low salt conditions.

Modelling of column lithium adsorption from pH-buffered brine using surface Li+/H+ ion exchange reaction

A model consisting of surface Li+/H+ exchange followed by Li+ transport with linear driving force (LDF) approximation was proposed for the analysis of column Li+ adsorption from pH-buffered brine on granulated H1.33Mn1.67O4. The advection equations for Li+ and OH− and the equations for Li+ and H+ transports in the solid phase were numerically solved using the finite difference technique, taking into account the acid–base properties of brine. The breakthrough curve and the pH change of the eluate could be calculated using the ion exchange capacity (Q0), ion exchange selectivity (Kc), and Li+ diffusivity in the solid phase (Ds). The calculated breakthrough curves had good approximations to the experimental ones with the values of Q0=3.0mol/kg, Kc=0.75, and Ds=5×10−9m2/h; these values agreed comparatively well with those determined individually by the column and batch adsorptions with H1.33Mn1.67O4 type adsorbent (Q0=3.4mol/kg, Kc=0.1, and Ds=4.2×10−9m2/h, respectively). The rate of Li+ recovery from the brine and the Li+ saturation degree of adsorbent, which are important for designing the column Li+ recovery process, could be evaluated from the breakthrough curves calculated at different flow rates.

Prediction of reservoir brine properties using radial basis function (RBF) neural network

Abstract Aquifers, which play a prominent role as an effective tool to recover hydrocarbon from reservoirs, assist the production of hydrocarbon in various ways. In so-called water flooding methods, the pressure of the reservoir is intensified by the injection of water into the formation, increasing the capacity of the reservoir to allow for more hydrocarbon extraction. Some studies have indicated that oil recovery can be increased by modifying the salinity of the injected brine in water flooding methods. Furthermore, various characteristics of brines are required for different calculations used within the petroleum industry. Consequently, it is of great significance to acquire the exact information about PVT properties of brine extracted from reservoirs. The properties of brine that are of great importance are density, enthalpy, and vapor pressure. In this study, radial basis function neural networks assisted with genetic algorithm were utilized to predict the mentioned properties. The root mean squared error of 0.270810, 0.455726, and 1.264687 were obtained for reservoir brine density, enthalpy, and vapor pressure, respectively. The predicted values obtained by the proposed models were in great agreement with experimental values. In addition, a comparison between the proposed model in this study and a previously proposed model revealed the superiority of the proposed GA-RBF model.

Temperature Dependence of Electrical Resistivity - Part I: Experimental Investigations of Hydrothermal Fluids

The temperature dependence of electrical properties of single-component brines was extensively studied up to supercritical condi- tions. However, only very few data are available for multicomponent brines, representing natural geothermal fluid compositions. We present a new measuring cell, designed to investigate electrical resistivities of mixed salt solutions at conditions simulating su-percritical hydrothermal reservoirs. The cell was tested at 23MPa and 23 – 380 °C on a diluted aqueous solution of NaCl, CaCl2, and K2SO4, simulating the Icelandic Krafla hydrothermal system. The measured data are used to calibrate resistivity measurementson fluid saturated rock samples, which are presented in an associated paper.

Prediction of the properties of brines using least squares support vector machine (LS-SVM) computational strategy

Natural brines occur underground or in salt lakes are commercially main sources of common salt and other salts, such as sulfates and chlorides of potassium and magnesium. This paper reports the implementation of a novel least square support vector machine (LS-SVM) algorithm for the development of improved models capable of predicting the properties of reservoir brine properties i.e., liquid saturation vapor pressure, density and enthalpy. The validity of the presented models was evaluated by using several statistical parameters. The predictions of the developed models for determining the liquid saturation vapor pressure, density and enthalpy were in excellent agreement with the reported data with an average absolute relative deviation (AARD) of %0.069, %0.033, %0.072, respectively and coefficient of determination values (R2) 0.999. According to the results of comparative studies, the developed models are more robust, reliable and efficient for calculating properties of oil field formation water during crude oil production than other techniques.