Water Saturation Changes Research Articles

Seasonal shifts in the solute ion ratios of vadose zone rock moisture from the Eel River Critical Zone Observatory

One of the greatest challenges in critical zone studies is to document the moisture dynamics, water flux, and solute chemistry of the unsaturated, fractured and weathered bedrock that lies between the soil and groundwater table. The central impediment to quantifying this component of the subsurface is the difficulty associated with direct observations. Here, we report solute chemistry as a function of depth collected over a full year across the shale-derived vadose zone of the Eel River Critical Zone Observatory using a set of novel sub-horizontal wellbores, referred to as the vadose zone monitoring system. The results of this first geochemical glimpse into the deep vadose zone indicate a dynamic temporal and depth-resolved structure. Major cation concentrations reflect seasonal changes in precipitation and water saturation, and normalized ratios span the full range of values reported for the world’s largest rivers.

Geo-electrical Characterisation for CO2 Sequestration in Porous Media

Developing monitoring strategies for the detection and monitoring of possible CO2 leakage or migration from existing and anticipated storage media are important because they can provide an early warning of unplanned CO2 leakage from a storage site. While previous works have concentrated on silicate and carbonate porous media, this work explores geoelectrical techniques in basalt medium in a series of well-defined laboratory experiments. These were carried out to identify the key factors which affect geoelectrical monitoring technique of CO2 in porous media using low cost and efficient time domain reflectometry (TDR). The system has been set up for simultaneous measurement of the bulk electrical conductivity and bulk dielectric permittivity of CO2-water-porous media system in silica sand, basalt and limestone. Factors investigated include pH, pressure, temperature, salinity, salt type and the materials of the porous media. Results show that the bulk electrical conductivity and dielectric permittivity decrease as water saturation decreases. Noticeably, electrical conductivity and permittivity decrease due to the changes in water saturation and the relationship remains the highest in limestone except at the start of the experiment. Also, an increase in temperature, pressure and salinity tend to increase the bulk electrical conductivity (σb) and permittivity (eb) of the CO2-water-porous media system during the drainage experiment. On the other hand, pH and concentrations of different types of salt do not seem to have significant effect on the geoelectrical characteristics of the system. It was evident that Archie’s equation fit the experimental results well and the parameters obtained were in good agreement with those in the literatures. The regression shows a good reliability in the prediction of electrical properties during the monitoring process of CO2 sequestration.

Simulation of Petrophysical Parameters of Asmari Reservoir Using SGS Method in Mansuri Oil Field, Southwest of Iran

Porosity and water saturations are the most important petrophysical parameters of hydrocarbon reservoirs that accurate assessment of them in hydrocarbon reservoirs is an effective tool, important and efficient for industry experts, in the context of a comprehensive study of reservoirs and production and management process of reservoir. In this study, using data from five wells of Mansuri oil field, and using the sequential simulation Gaussian method and using Petrel software, the trend of Porosity and water saturation changes in the mentioned field for four zones was simulated. Also the average maps for each zone have been created that results of the simulation parameters in this map showed that highest average porosity is 0.1401 and 0.2756 at least saturation of water is related to zone 1. Finally result of the simulation indicates the Zone 1 is of the best reservoir Zones.

Transient Liquid Water Distributions in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Observed through In-Operando Synchrotron X-ray Radiography

In this work, in-operando synchrotron X-ray radiography was used to capture the changes in the liquid water saturation of gas diffusion layers (GDLs) during changes in operating current density. Through in-operando visualizations at high temporal and spatial resolutions, we observed that the liquid water saturation increased with increasing current density. Eventually, a threshold water content in the GDL was reached despite further increases in current density. A time lag between the change in current density and the onset of increasing GDL water content was also observed. Current density consistently reached a steady state value before the GDL water content reached steady state, and the trends in liquid water distributions in the MPL were distinct from, yet influential to the accumulation in the substrate. We present a logarithmic growth function that describes the dynamic changes in GDL water content. The formulation of the GDL liquid water content transient response to changes in operating conditions provides a new metric for designing next generation fuel cell powertrains with fast dynamic responses. Through plane water thickness profiles were also used to show that the water accumulation patterns continued to evolve for up to 15 minutes at the low current density.

Estimation of reservoir fluid saturation from 4D seismic data: effects of noise on seismic amplitude and impedance attributes

Time-lapse (4D) seismic data sets have proven to be extremely useful for reservoir monitoring. Seismic-derived impedance estimates are commonly used as a 4D attribute to constrain updates to reservoir fluid flow models. However, 4D seismic estimates of P-wave impedance can contain significant errors associated with the effects of seismic noise and the inherent instability of inverse methods. These errors may compromise the geological accuracy of the reservoir model leading to incorrect reservoir model property updates and incorrect reservoir fluid flow predictions. To evaluate such errors and uncertainties we study two time-lapse scenarios based on 1D and 3D reservoir model examples, thereby exploring a number of inverse theory concepts associated with the instability and error of coloured inversion operators and their dependence on seismic noise levels. In the 1D example, we show that inverted band-limited impedance changes have a smaller root-mean-square (RMS) error in comparison to their absolute broadband counterpart for signal-to-noise ratios 10 and 5 while for signal-to-noise ratio (S/N) = 3 both inversion methods present similarly high errors. In the 3D example we use an oilfield benchmark case based on the Namorado Field in Campos Basin, Brazil. We introduce a histogram similarity measure to quantify the impact of seismic noise on maps of 4D seismic amplitude and impedance changes as a function of S/N levels, which indicate that amplitudes are less sensitive to 4D seismic noise than impedances. The RMS errors in the estimates of water saturation changes derived from 4D seismic amplitudes are also smaller than for 4D seismic impedances, over a wide range of typical seismic noise levels. These results quantitatively demonstrate that seismic amplitudes can be more accurate and robust than seismic impedances for quantifying water saturation changes with 4D seismic data, and emphasize that seismic amplitudes may be more reliable to update fluid flow model properties in the presence of realistic 4D seismic noise.

The time-lapse AVO difference inversion for changes in reservoir parameters

The result of conventional time-lapse seismic processing is the difference between the amplitude and the post-stack seismic data. Although stack processing can improve the signal-to-noise ratio (SNR) of seismic data, it also causes a considerable loss of important information about the amplitude changes and only gives the qualitative interpretation. To predict the changes in reservoir fluid more precisely and accurately, we also need the quantitative information of the reservoir. To achieve this aim, we develop the method of time-lapse AVO (amplitude versus offset) difference inversion. For the inversion of reservoir changes in elastic parameters, we apply the Gardner equation as the constraint and convert the three-parameter inversion of elastic parameter changes into a two-parameter inversion to make the inversion more stable. For the inversion of variations in the reservoir parameters, we infer the relation between the difference of the reflection coefficient and variations in the reservoir parameters, and then invert reservoir parameter changes directly. The results of the theoretical modeling computation and practical application show that our method can estimate the relative variations in reservoir density, P-wave and S-wave velocity, calculate reservoir changes in water saturation and effective pressure accurately, and then provide reference for the rational exploitation of the reservoir.

Determining the Impact of Dynamic Load Conditions on Interfacial Liquid Water Accumulation in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Using Synchrotron X-Ray Radiography

Automakers around the world are investing in polymer electrolyte membrane (PEM) fuel cells for the next generation drivetrains for their low emission automobiles. For PEM fuel cell vehicles to become commercially competitive, fuel cell efficiency and durability must increase. However, in order to advance the performance of PEM fuel cells, the dynamic behaviour of liquid water transport must be taken into consideration, particularly because fuel cell cars will be driven with dynamic load (power draw) conditions1. The relationship between PEM fuel cell performance and dynamic load must be well understood so that next generation fuel cells can be tailored for optimal dynamic operation. Effective water management is key to obtaining the optimal performance of fuel cells2,3. It has also been shown that the transient response of two-phase flows of water is significantly longer compared to the electrochemical response1. Therefore, the changes in two-phase flows in the fuel cell can have a larger impact on the dynamic performance of fuel cells4,5. Liquid water evolves in the porous layers of the fuel cell until it reaches a steady state for the current density of operation6. However, there is a scarcity of experimental observations focused on GDL liquid water saturation as a function of time with changes in operational current density. In this work, the transient response of the cell potential and the dynamic change in water saturation of the gas diffusion layer (GDL) are investigated. The current density of the cell was increased from 0 A/cm2 to prescribed values at various rates of increasing current density (ramp rates), while the response of the cell potential was concurrently measured. Figure 1 shows the transient response of the cell potential due to a change in the current density from 0 to 1.2 A/cm2 at various rates of increase. With a step change in the current density, the voltage fluctuated for a few minutes before the potential of the cell dropped, leading to performance failure that was indicative of flooding. However, when a ramp was applied to gradually reach the same current density as the step change, the cell was able to maintain a steady potential. This shows that the ramp rate of increasing current density has a direct impact on the cell performance and its transient response. In addition, X-ray radiographic evidence of water in the porous layers of the PEM fuel cell during transient operation will be presented. The dynamic water evolution at the microporous layer (MPL)|catalyst layer interface and the MPL|GDL interface are highly influenced by the rate of increasing current density. The cell performance was correlated to the time-dependent water evolution patterns in order to identify the interfacial liquid water accumulation as a function of changing current density.

Pore geometry effects on elastic properties of Opalinus Clay

Regarding the storage of nuclear waste within clay rock formations requires fundamental understanding of elastic properties of this rock type with regard to the risk evaluation process. The influence of the pore geometry on elastic properties of Opalinus Clay is studied on the basis of realistic pore microstructure, which is reconstructed from image data acquired by focused ion beam nanotomography. These microstructures are used as input pore geometries for linear elastic finite-element modeling to determine Thomsen’s [Formula: see text], [Formula: see text], and [Formula: see text] anisotropy parameters and the effective elastic moduli related to the porous material. The presence of fully drained intergranular pores substantially increases the values of [Formula: see text] and [Formula: see text]. For the investigated sample with an expected porosity of approximately 10 vol.%, the anisotropic pore space contributes similarly to the anisotropy parameters when compared with the contribution related to the preferred orientation of minerals. On the other hand, if the pore space is undrained, the effect of pores is smaller and the anisotropy is largely controlled by the preferred orientation of minerals. It is revealed that the value of [Formula: see text] is most sensitive to changes in water saturation. In case water is drained from the pores, the vertical Young’s modulus [Formula: see text] reduces significantly more when compared with the horizontal modulus [Formula: see text]. Presuming that the drainable porosity corresponds to a volume fraction of 10 vol.%, [Formula: see text] reduces by approximately 15%–20%. The effect of drainage is even more pronounced for the Poisson’s ratios, whereas the shear moduli are not much affected by drainage.

Determining the Impact of Dynamic Load Conditions on Interfacial Liquid Water Accumulation in Polymer Electrolyte Membrane Fuel Cell Gas Diffusion Layers Using Synchrotron X-Ray Radiography

Automotive power demand is dynamic, so the transient multiphase transport behavior must be understood and considered in the design of next generation polymer electrolyte membrane (PEM) fuel cell materials. In-operando synchrotron X-ray radiography was used to measure the changes in liquid water saturation of the gas diffusion layer (GDL) during changes in operational current density. Through in-operando visualizations at high temporal and spatial resolutions, we observed that the liquid water saturation of the GDL increases with increasing current density, but a threshold saturation in the GDL is eventually reached, despite further increases in current density. A time lag between the change in current density and the onset of increasing GDL saturation was also observed.

Investigating the factor influencing the flow behavior and performance of condensate gas reservoirs

Well productivity is an important issue in the development of most low and medium- permeability gas-condensate reservoirs. However, accurate forecasts of productivity can be difficult because of the need to understand and account for the complex processes that occur in the near-well region. When the well pressure falls below the dew-point, a region of high liquid saturation builds up around the well, impairing the flow of gas and reducing the well productivity. It is essential to take account of this condensate-blockage effect when calculating well productivity. Most of the pressure drop in a gas condensate well occurs close to the well walls. Because of the increase in pressure drop and the increase in flow rate, two additional phenomena get involved in gas flow control: The effect of positive coupling (due to increased capillary number) and the effect of inertia (due to non-Darcy flow). In many gas-condensate wells, the final result of these two parameters is improving well productivity, reducing the impairment caused by condensate blockage. Another phenomenon that can take place in high temperature gas reservoir is water vaporization. Pressure drop near well wall causes molar content of water in gas-phase to increase, therefore connate water starts to vaporize near the well walls. This change in connate water saturation near the well wall can influence well productivity by changing saturation of fluids near well walls. The effect of water vaporization on well productivity of gas and gas - condensate reservoirs are investigated by considering a single well one dimensional radial model simulation. The simulations show that water vaporization increases productivity of well by increasing gas saturation and relative permeability near the well walls and improving the mobility of gas; and this effect is stronger in rich gas condensate reservoir than the lean ones.

INVESTIGATING THE EFFECTS OF WATER VAPORIZATION ON THE PRODUCTION OF GAS CONDENSATE RESERVOIRS

Well productivity is an important issue in the development of most low and mediumpermeability gas-condensate reservoirs. However, accurate forecasts of productivity can be difficult because of the need to understand and account for the complex processes that occur in the near-well region. When the well pressure falls below the dew-point, a region of high liquid saturation builds up around the well, impairing the flow of gas and reducing the well productivity. It is essential to take account of this condensate-blockage effect when calculating well productivity. Most of the pressure drop in a gas condensate well occurs close to the well walls. Because of the increase in pressure drop and the increase in flow rate, two additional phenomena get involved in gas flow control: The effect of positive coupling (due to increased capillary number) and the effect of inertia (due to non-Darcy flow). In many gas-condensate wells, the final result of these two parameters is improving well productivity, reducing the impairment caused by condensate blockage. Another phenomenon that can take place in high temperature gas reservoir is water vaporization. Pressure drop near well wall causes molar content of water in gas-phase to increase, therefore connate water starts to vaporize near the well walls. This change in connate water saturation near the well wall can influence well productivity by changing saturation of fluids near well walls. The effect of water vaporization on well productivity of gas and gas - condensate reservoirs are investigated by considering a single well one dimensional radial model simulation. The simulations show that water vaporization increases productivity of well by increasing gas saturation and relative permeability near the well walls and improving the mobility of gas; and this effect is stronger in rich gas condensate reservoir than the lean ones. Keywords: Well, Gas, Pressure Drop, Vapor pressure of water

Investigating the effects of water vaporization on the production of gas condensate reservoirs

Well productivity is an important issue in the development of most low and mediumpermeability gas-condensate reservoirs. However, accurate forecasts of productivity can be difficult because of the need to understand and account for the complex processes that occur in the near-well region. When the well pressure falls below the dew-point, a region of high liquid saturation builds up around the well, impairing the flow of gas and reducing the well productivity. It is essential to take account of this condensate-blockage effect when calculating well productivity. Most of the pressure drop in a gas condensate well occurs close to the well walls. Because of the increase in pressure drop and the increase in flow rate, two additional phenomena get involved in gas flow control: The effect of positive coupling (due to increased capillary number) and the effect of inertia (due to non-Darcy flow). In many gas-condensate wells, the final result of these two parameters is improving well productivity, reducing the impairment caused by condensate blockage. Another phenomenon that can take place in high temperature gas reservoir is water vaporization.Pressure drop near well wall causes molar content of water in gas-phase to increase, therefore connate water starts to vaporize near the well walls. This change in connate water saturation near the well wall can influence well productivity by changing saturation of fluids near well walls. The effect of water vaporization on well productivity of gas and gas - condensate reservoirs are investigated by considering a single well one dimensional radial model simulation. The simulations show that water vaporization increases productivity of well by increasing gas saturation and relative permeability near the well walls and improving the mobility of gas; and this effect is stronger in rich gas condensate reservoir than the lean ones.Keywords: Well, Gas, Pressure Drop, Vapor pressure of water

Effect of barite and gas oil drilling fluid additives on the reservoir rock characteristics

This research presents a study of the effect of drilling fluid on the reservoir rock properties. The interactions between the clay minerals existing in the formations and the drilling fluids have been studied. Two types of drilling fluids, which are water-based ferrochrome lignosulfonate base mud and lime mud, were prepared for the study. About 100 core plugs were prepared from seven oil wells of Zubair Formation from depths of over (3000) m. The core plugs were cut, cleaned, dried, and then subjected to petrophysical tests, which are permeability, saturation, X-ray diffraction, and the petrographical analyses. Clay minerals like kaolinite, illite, and montmorillonite were found in the core samples. The static immersion test shows that the clay minerals reacted with the drilling fluids and created swelling and spalling in the core samples and changed the original petrophysical rock properties. Different concentrations of gas oil and barite were added to improve the properties of the used drilling fluids and to decrease their negative impact on the petrophysical rock properties. A comparison is made between the permeability and water saturation before and after exposure to the drilling fluids. The percentage change in permeability and water saturation is calculated. The results showed that the additives to the drilling fluids reduced the formations damage. Finally, the study indicates that the major formation damage in southern Iraqi oil fields is induced by mechanical and chemical mechanizes.

Effects of aligned fractures on the response of velocity and attenuation ratios to water saturation variation: a laboratory study using synthetic sandstones

ABSTRACTP‐wave‐to‐S‐wave ratios are important seismic characterization attributes. Velocity ratios are sensitive to the petrophysical properties of rocks and to the presence of gas. Attenuation ratios have also been shown to be sensitive to the presence of partial liquid/gas saturation. The relationship between liquid/gas saturation and P‐wave and S‐wave ratios has been used to distinguish gas‐saturated rocks from liquid‐saturated rocks. Aligned fractures are common in the Earth's crust and cause seismic anisotropy and shear wave splitting. However, most existing relationships between partial gas/liquid saturation and P‐wave and S‐wave ratios are for non‐fractured rocks. We present experimental results comparing the effects of changing water saturation on Qs/Qp versus Vp/Vs ratios between a non‐fractured rock and one containing fractures aligned parallel to wave propagation direction. We also study the effects of aligned fractures on the response of Vp/Vs to changing water saturation using synthetic fractured sandstones with fractures aligned at 45o and parallel to the wave propagation direction. The results suggest that aligned fractures could have significant effects on the observed trends, some of which may not be obvious. Fractures aligned parallel to wave propagation could change the response of Qs/Qp versus Vp/Vs ratios to water saturation from previously reported trends. Shear wave splitting due to the presence of aligned fractures results in two velocity ratios (Vp/Vs1 and Vp/Vs2). The fluid independence of shear wave splitting for fractures aligned parallel to wave propagation direction means the difference between Vp/Vs1 and Vp/Vs2 is independent of water saturation. For fractures aligned at oblique angles, shear wave splitting can be sensitive to water saturation and consequently be frequency dependent, which can lead to fluid and frequency‐dependent differences between Vp/Vs1 and Vp/Vs2. The effect of aligned fractures on Vp/Vs ratios not only depends on the fracture effects on both P‐wave and S‐wave velocities but also on the effects of water saturation distribution on the rock and fracture stiffness, and hence on the P‐wave and S‐wave velocities. As such, these effects can be frequency dependent due to wave‐induced fluid flow. A simple modelling study combining a frequency‐dependent fractured rock model, and a frequency‐dependent partial saturation model was used to gain valuable interpretations of our experimental observations and possible implications, which would be useful for field seismic data interpretation.

Seismic Velocity Prediction in Shallow (<30 m) Partially Saturated, Unconsolidated Sediments Using Effective Medium Theory

Seismic velocity models of the near-surface (<30 m) better explain seismic velocities when all elements of total effective stress are considered, especially in materials with large cohesive and soil suction stress such as clays. Traditional constitutive elastic models that predict velocities in granular materials simplify the effect of total effective stress by equating it to net overburden stress, while excluding interparticle stresses and soil suction stress. A new proposed methodology calculates elastic moduli of granular matrices in near-surface environments by incorporating an updated definition of total effective stress into Hertz-Mindlin theory and calculates the elastic moduli of granular materials by extending Biot-Gassmann theory to include pressure effects induced by water saturation changes and cohesion. At shallow depths, when water saturation increases, theoretically calculated seismic velocities decrease in clay and increase in sand because interparticle stresses suppress the Biot-Gassmann effect. For standard sand and clay properties, net overburden stress becomes more influential than interparticle stresses at depths greater than 10 cm in sand and 100 m in clay. Pore pressure in the new model also incorporates the effect of layer thickness and pore size variation. Traditional calculation of pore pressure assumes a constant pore size medium, but may lead to an under- or overestimation of velocity by up to 20%. In clays, the variation of seismic velocity with water saturation is almost double the range predicted when only net overburden stress is considered to influence stress at the grain contacts. The proposed model predicts seismic velocities that compare well with measured field velocities from the literature.

Saturation effects on the joint elastic–dielectric properties of carbonates

We used a common microstructural model to investigate the cross-property relations between elastic wave velocities and dielectric permittivity in carbonate rocks. A unified model based on validated self-consistent effective medium theory was used to quantify the effects of porosity and water saturation on both elastic properties (compressional and shear wave velocities) and electromagnetic properties (dielectric permittivity). The results of the forward models are presented as a series of cross-plots covering a wide range of porosities and water saturations and for microstructures that correspond to different predominant aspect ratios. It was found that dielectric permittivity correlated approximately linearly with elastic wave velocity at each saturation stage, with slopes varying gradually from positive at low saturation conditions to negative at higher saturations. The differing sensitivities of the elastic and dielectric rock properties to changes in porosity, pore morphology and water saturation can be used to reduce uncertainty in subsurface fluid saturation estimation when co-located sonic and dielectric surveys are available. The joint approach is useful for cross-validation of rock physics models for analysing pore structure and saturation effects on elastic and dielectric responses.

Transient Earth system responses to cumulative carbon dioxide emissions: linearities, uncertainties, and probabilities in an observation-constrained model ensemble

Abstract. Information on the relationship between cumulative fossil CO2 emissions and multiple climate targets is essential to design emission mitigation and climate adaptation strategies. In this study, the transient response of a climate or environmental variable per trillion tonnes of CO2 emissions, termed TRE, is quantified for a set of impact-relevant climate variables and from a large set of multi-forcing scenarios extended to year 2300 towards stabilization. An ∼ 1000-member ensemble of the Bern3D-LPJ carbon–climate model is applied and model outcomes are constrained by 26 physical and biogeochemical observational data sets in a Bayesian, Monte Carlo-type framework. Uncertainties in TRE estimates include both scenario uncertainty and model response uncertainty. Cumulative fossil emissions of 1000 Gt C result in a global mean surface air temperature change of 1.9 °C (68 % confidence interval (c.i.): 1.3 to 2.7 °C), a decrease in surface ocean pH of 0.19 (0.18 to 0.22), and a steric sea level rise of 20 cm (13 to 27 cm until 2300). Linearity between cumulative emissions and transient response is high for pH and reasonably high for surface air and sea surface temperatures, but less pronounced for changes in Atlantic meridional overturning, Southern Ocean and tropical surface water saturation with respect to biogenic structures of calcium carbonate, and carbon stocks in soils. The constrained model ensemble is also applied to determine the response to a pulse-like emission and in idealized CO2-only simulations. The transient climate response is constrained, primarily by long-term ocean heat observations, to 1.7 °C (68 % c.i.: 1.3 to 2.2 °C) and the equilibrium climate sensitivity to 2.9 °C (2.0 to 4.2 °C). This is consistent with results by CMIP5 models but inconsistent with recent studies that relied on short-term air temperature data affected by natural climate variability.

Mechanisms of imbibition during hydraulic fracturing in shale formations

Abstract Hydraulic fracturing technology has been proven to significantly increase production from shale gas and oil formations. However, during a hydraulic fracturing treatment a large percentage of the fracturing fluid usually remains unrecovered. Therefore, the reasons for this low fracturing fluid recovery have become the focus of many studies. Imbibition of fracturing fluid in the shale is believed to be one of the explanations for the low amount of the fracture fluid recovery. The fluid is imbibed by the shale matrix and trapped inside the rock. Capillarity has generally been the primary mechanism considered during imbibition in conventional formations, such as sandstone and carbonate formations. In shale formations osmosis diffusion also exists and cannot be ignored because the clay in the shale rock functions similarly to that of a membrane. It is believed that both capillarity and osmosis diffusion work together to result in imbibition during hydraulic fracturing in shale formations. This paper investigates the effects of both capillarity and osmosis diffusion as the key mechanisms in fluid imbibition through simultaneous imbibition experiments. The results of these tests illustrate that the imbibition process is dominated by both capillarity and osmosis diffusion. This domination is based on the change of water saturation in shale rocks. In addition, the capillary and osmotic pressures, which influence the imbibed rate, can be qualitatively determined by the contact angle and salinity, respectively. Higher capillary and osmotic pressures correlate to faster rates of imbibition. This study, which examines the mechanisms of imbibition and their influences, can improve the understanding of fluid behavior when imbibition occurs during hydraulic fracturing in shale formations. The understanding of this behavior is useful for further simulation research.

Resistivity and induced polarization monitoring of biogas combined with microbial ecology at a brownfield site

The accumulation of biogenic greenhouse gases (methane, carbon dioxide) in organic sediments is an important factor in the redevelopment and risk management of many brownfield sites. Good practice with brownfield site characterization requires the identification of free-gas phases and pathways that allow its migration and release at the ground surface. Gas pockets trapped in the subsurface have contrasting properties with the surrounding porous media that favor their detection using geophysical methods. We have developed a case study in which pockets of gas were intercepted with multilevel monitoring wells, and their lateral continuity was monitored over time using resistivity. We have developed a novel interpretation procedure based on Archie’s law to evaluate changes in water and gas content with respect to a mean background medium. We have used induced polarization data to account for errors in applying Archie’s law due to the contribution of surface conductivity effects. Mosaics defined by changes in water saturation allowed the recognition of gas migration and groundwater infiltration routes and the association of gas and groundwater fluxes. The inference on flux patterns was analyzed by taking into account pressure measurements in trapped gas reservoirs and by metagenomic analysis of the microbiological content, which was retrieved from suspended sediments in groundwater sampled in multilevel monitoring wells. A conceptual model combining physical and microbiological subsurface processes suggested that biogas trapped at depth may have the ability to quickly travel to the surface.

The influence of pore media distribution on the elastic parameters of rocks in Miocene sediments (Carpathian Foredeep, Poland, B deposit)

This paper presents the results of modelling compressional and shear wave velocities and elastic moduli, and Poisson’s coefficient changes in the sandstone-shale rocks, based on the distribution of media reservoir (water, gas) in the pore space. Modelling was performed using Estymacja-TP computer program and theoretical Kuster-Toksoz and Biot-Gassmann relationships. The phase distribution of saturating pores (inclusions) in several ways was assumed. Calculations were made of elastic parameters in the deposits of the autochthonous Miocene Sarmatian in the borehole B-4. Using a method similar to the so-called “ Fluid substitution” modelling velocity changes of compressional and shear waves, elastic modulus, Poisson's ratio and the bulk density under various conditions of water and gas saturation were performed. The assumed of change in water saturation ranged from SW = 0% to 100 %.