Decreasing Water Saturation Research Articles

Core‐flooding experiments of various concentrations of CO2/N2 mixture in different rocks: II. Effect of rock properties on residual water

AbstractDuring CO2 storage in deep saline aquifers, the presence of residual water has an important influence on the storage efficiency and safety. In this study, natural rock cores taken from deep reservoirs in the Ordos Basin and Fukang, Xinjiang are used as research objects. Nine groups of core‐flooding experiments are performed under different CO2/N2 gas mixture ratios to study the influence of rock properties (mineral composition, permeability, porosity and pore structure) on the residual water. Furthermore, the geophysical and chemical properties of rock cores are analyzed by X‐ray diffraction, electron microscopy, field emission scanning electron microscopy and piezoelectric mercury method. The results show that residual water saturation is a quantitative power function of drainage time. The residual water saturation is positively correlated with the total amount of quartz and feldspar and increases with increasing permeability. Moreover, both the average and median pore throat radius show a strong inverse correlation with irreducible residual water saturation; as these radius increase, the residual water saturation decreases. In contrast, the porosity and maximum pore throat radius display a weaker correlation with irreducible residual water saturation. This study is of great value for engineering practices such as the site selection of CO2 storage projects in saline aquifer and improvement of CO2 storage efficiency. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

The study on the coupled influence of water saturation on heat and mass transfer processes within porous media under CW laser irradiation

Continuous wave (CW) laser irradiation induces temperature changes in various phases within porous media, accompanied by phase change and gas transport. Water saturation is a crucial factor influencing this context's moisture and heat transfer process. This paper addresses this issue by establishing a theoretical model for CW laser irradiation on unsaturated porous media. Through experiments and simulations, it studies the effects of different water saturations on heat and mass transfer under laser irradiation. The results indicate that the critical depth reflects the influence of water saturation under laser irradiation on the distribution of solid-phase temperature in both time and space dimensions. Specifically, an increase in water saturation enhances the uniformity of solid-phase temperature distribution, while the gas temperature exhibits a similar distribution pattern. For mass transfer processes, it increases the evaporation rate and Darcy velocity of porous media within the effective range of laser irradiation. Lower water saturation facilitates phase change processes and accelerates gas transport rates. Importantly, this trend remains consistent even with the emergence of dry-saturation zones. Additionally, the decrease in water saturation has a coupled promoting effect on gas temperature and mass transfer processes. Lowering water saturation can increase gas temperature and consequently enhance mass transfer processes. Simultaneously, enhancing mass transfer processes benefits heat exchange between the two phases. In the four sets of experiments, the conformity of the surface temperature rise curves obtained from experiments and simulations is good, indicating that the model can accurately reflect the temperature rise patterns of sand particles. In summary, this work provides valuable research results on the effects of different water saturations on laser irradiation-induced temperature rise, phase change, and gas and moisture transport within porous media. It lays a specific theoretical foundation for laser soil remediation technology.

Hydromechanical modelling of the influence of water saturation on the penetration performance of concrete target

The objective of the present paper is to study numerically the hydro-mechanical behaviour of concrete targets subjected to a rigid projectile, with special attention to the influence of water saturation. An elastoplastic model, encompassing two primary plastic mechanisms (shear and pore collapse), is improved to capture the influence of water saturation. The adopted model is implemented in the finite element code Abaqus/Explicit and validated by simulating two dynamic compression tests at the material point level and two penetration tests at the structure level. Not only a strong influence of water saturation on both volumetric and deviatoric behaviours of concrete is observed at material point level, but also the time-evolutions of projectile velocity, projectile deceleration and penetration depth in concrete targets are also satisfactorily reproduced by the numerical simulations. After that, a series of parametric studies are performed to understand the influence of water saturation on the penetration performance of concrete. It is found that with the presence of pore water, penetration resistance of concrete increases with decreasing water saturation, indicating a higher projectile deceleration and lower penetration depth obtained in saturated targets. Numerical modelling and analysis will enhance our understanding of the vulnerability of concrete infrastructures subjected to near-field detonations or impacts.

Właściwości złoża jurajskiej formacji Khatatba: Pole naftowe Tut, Pustynia Północno-Zachodnia, Egipt

The Tut oil field is in the North-western part of the Western Desert. This work aims to study the reservoir characteristics, to evaluate the hydrocarbon potentiality of the Upper and Lower Safa Members based on the available subsurface data obtained from open-hole well log records of four wells distributed in the study area. Numerous isopach and lithofacies maps have been constructed. The petrophysical evaluation, in terms of determining reservoir net-pay thickness, shale content (Vsh), effective porosity (∅eff), water saturation (Sw) and hydrocarbon saturation (Sh), were estimated. The vertical and the lateral distribution of the reservoir characteristics, in the form of litho-saturation cross-plots, iso-parametric maps and lithologic-matrix cross-plots were constructed. Three hydrocarbon charged zones in the Khatatba Formation were defined and represented by the Upper Safa-Top, Upper Safa-Bottom and Lower Safa-Top. The upper most part of Upper Safa Member (Upper Safa-Top) reservoir represents an oil producing zone where it consists of shallow marine to alluvial sediments. The Lower most part of Upper Safa Member (Upper Safa-Bottom) reservoir represents gas producing zone where it consists of a thick alluvial sand body. Finally, the upper most part of Lower Safa Member (Lower Safa-Top) reservoir represents an oil-gas producing zone consisting of shallow marine sediments with high terrestrial input. The iso-parametric maps show that Northern and central parts of the study area are the most favorable parts for hydrocarbon accumulation due to the increase in net-pay thickness and average effective porosity and decrease in water saturation toward these parts.

Formation mechanisms of residual water in CO2-water-rock systems: Effects of the CO2 phase

This study focused on the effects of the CO2 phase on the formation mechanisms of residual water. Based on nine groups of core-flooding experiments, the order of residual water saturation was gaseous CO2 > supercritical CO2 > liquid CO2, and a quantitative power function relationship between residual water saturation and displacement time for different CO2 phases was proposed. The experimental results show that when CO2 transitions from the gaseous phase to the supercritical phase and then to the liquid phase, the decrease in the interfacial tension and cosine value of the contact angle in two-phase flow can lead to a decrease in residual water saturation. Meanwhile, an increase in the viscosity ratio of two-phase flow weakens the viscous fingering phenomenon and can also lead to a decrease in residual water saturation. However, the logCa-logM stability phase diagram reveals that the viscous force is the primary factor influencing all core-flooding experiments.

Thermal stabilities of CH4 and CO2 hydrates in quartz sands and modeling

Forming an impermeable hydrate bearing layer is a novel path to prevent CO2 leakage during marine carbon storage. To make an accurate description of the formation of impermeable hydrate bearing layer, the equilibria of CH4 and CO2 hydrates in quartz sands were measured in a temperature range from 273 to 283 K using isochoric pressure search method and HP-μDSC. The influence of particle size from 0.025 to 0.3 mm and water saturation from 5 to 30 % on the hydrate equilibrium were analyzed. Based on the typical hydrate equilibrium model, van Genuchten model was employed to describe the capillary effect. Results showed that particle size had negligible effect on the equilibria of CH4 and CO2 hydrates, but a decrease in water saturation was found to lead an exponential growth in temperature depression. As the water saturation reduced down to 10 % and below, the temperature depression surged from about 0.1 up to 0.89 K in maximum. The dissociation enthalpies of CH4 and CO2 hydrates were determined as 56.01 ± 1.29 and 64.98 ± 1.90 kJ/mol respectively. The reduction of water saturation from 30 to 5 % was found to enhance the dissociation enthalpy for CH4 hydrate, but no similar effect was observed for CO2 hydrate.

Water distribution in pore systems and its influences on gas-bearing property of deep shale: A case study of the Longmaxi Formation in the Luzhou area, southern Sichuan Basin

The deeply-buried (>3500 m) Longmaxi Formation (LMX) shale in the southern Sichuan Basin, China, has become an attractive target for shale gas exploration owing to its huge resource potential. Exploration shows that the deep shale has a wide range of gas-in-place (GIP) contents, with variable gas yields, but the reason remains unclear, especially the impact of pore water on gas-bearing property lacks systematic research. In the present study, a suite of deep LMX shale samples was collected from the well FB1 in the Luzhou area of the southern Sichuan Basin, and techniques such as the pore water content measurements, low-pressure gas (CO2 and N2) adsorption and high-pressure methane adsorption experiments of the moist and dry samples were employed to investigate the distribution of water in the nanopores and its effects on the gas-bearing property. The results show that the deep shale is characterized by a high water content, with a high water saturation (average up to 69.80%), and the water occurs in both the inorganic and organic pores. The water reduces the effective specific surface area and pore volume of the shale averagely by 79.01% and 22.56%. Consequently, the water results in the decrease of methane adsorption capacity averagely by 45.13%. The GIP content models of two typical shale samples indicate that their total gas content is < 3 m3/t under the actual conditions, without development potential, and it will increase significantly to >3 m3/t with decreasing water saturation to <40–50%, especially under overpressure conditions. The gas-bearing property of deep LMX shale reservoirs in the complex faulted zones or structural-complex zones would mainly depend on the pore water content except for the properties of shale itself (e.g., maturity, TOC content, mineral composition, porosity and pore structure).

Effect of coupled physical and chemical heterogeneity on the transport of pristine and aged pyrogenic carbon colloids in unsaturated porous media

Due to extensive application and recurrent wildfires, an increasing number of pyrogenic carbon (PyC) colloids are present in the environment, experiencing processes of environmental aging. Subsurface environments are typically heterogeneous in unsaturated conditions, which may affect the transport of PyC colloids. This study focused on the transport of both pristine and aged PyC colloids in physically (clean coarse and fine sand) and physicochemically (iron oxides-coated coarse and clean fine sand) heterogeneous porous media at three different water saturations (100 %, 70 %, and 40 %). In physically heterogeneous porous media, the decrease in water saturation from 100 % to 40 % led to a shift in the main water flow from the clean coarse sand to the clean fine sand domain, resulting in a continuous decrease in the transport of PyC colloids. In physicochemically heterogeneous porous media, the primary water flow shifted from the iron oxides-coated coarse sand to the clean fine sand domain, resulting in an initial increase and subsequent decrease in PyC colloid transport. Aging enhanced the transport of PyC colloids, attributed to the increasingly negative and hydrophilic surface. Retention profiles revealed substantial PyC colloid retention at the interface between coarse and fine sand domains. The release of retained PyC colloids exhibited two peaks at 100 % and 70 % water saturations, along with a single peak at 40 % water saturation. Additionally, the increased irreversible retention was observed at lower water saturation. This study underscores the significance of water content, environmental aging, and heterogeneity in PyC colloid transport. It provides essential insights into the environmental fate of PyC colloids in natural field conditions.

Development of technology for obtaining asphalt concrete mixture using oil sludge as an additive

Oil sludge is similar in composition to the composition of bitumen, which is one of the important components of asphalt concrete mixture. Therefore, oil waste can be used in the production of asphalt concrete, both as an organic binder to strengthen local soils and as a binder to produce organomineral mixtures. The use of oil sludge in road construction helps preserve natural resources, improve the environmental situation, and reduce the cost of building materials. In this work, physical and mechanical properties of asphalt concrete mixture of grade I type B were researched. To improve the performance characteristics of asphalt concrete oil sludge from oil company Zhaik Munay LLP (Uralsk) was used as an additive. Oil sludge was added to the asphalt concrete mixture in amounts of 5, 10 and 15%. When using 5% oil sludge, no significant changes in the properties of asphalt concrete are observed. An addition of 15% of oil went to the reduction of maximum efficiency during compression (0.03% by volume) and shear resistance by the efficiency of internal friction coefficient (0.01% by volume). The optimal amount is to use 10% oil sludge, at the same time, the compressive strength increases by 0.07% by volume, water resistance increases (0.02% by volume), water saturation decreases by 0.28% by volume, which has a positive effect on the quality of asphalt concrete. The properties of asphalt concrete before and after adding oil sludge were studied: compressive strength, water resistance, water saturation, shear resistance. It was concluded that it is advisable to use oil sludge as an additive. A technology for producing asphalt concrete mixture using oil sludge has been developed, which allows reducing its cost.

Relationship between consistency and compaction of clay soils (Saint-Petersburg)

Clay soils are often found under building foundations, construction properties of which depend on many factors. One of them is the natural soil compaction, which is relevant in the construction classification of soils. This paper analyzes the relationship between the consistency and compaction of clay soils of different genesis and consistency using the Priklonskii soil compaction index. Water saturation of clay soil affects the relative discrepancy between the consistency coefficient and compaction index for soils of different genesis and consistency. It is noted that for soils with the water saturation coefficient lower than one, the consistency coefficient differs from the compaction index. This difference increases with decreasing water saturation coefficient. It is essential that significant differences can also appear when the water saturation coefficient is equal to 0.95 or more, approaching to unity. It is shown that the assessment of the natural compaction of clay soils should be based on their formation conditions. A study of various genetic types of clay soils affecting natural densification and consistency provides a reasonable approach to use of soil densification in the construction classification of soils.

An experimental study on the measurement of gas diffusivities in un-saturated clay based materials

Gas migration in porous media in the context of nuclear waste disposal is dominated by diffusion. The availability of abundant data on diffusion coefficients of different gases in many clay based materials such as Boom Clay, Opalinus Clay and Callovo-Oxfordian Clays provides a good overview of the rates of gas transport through these different clay rocks [1]. Such formations are being considered as potential host rocks for the disposal of high and intermediate level radioactive wastes across Europe. Diffusion coefficients have been studied with particular interest due to the unavoidable gas generation phase in the nuclear waste repository [2]. However, all the diffusion measurements performed so far have been under fully saturated conditions, with little experimental data on gas diffusivities in partially saturated conditions, which have been hypothesized to exist during the early part of the life cycle of the repository [3]. The objective of the current study is to provide an overview of the effect of desaturation on the rate of diffusive transport of gases in partially saturated clay based materials.&#x0D; The experimental methodology is based on the double through diffusion setup used in previous studies to measure gas diffusivities in saturated clays [1]. However, the setup is modified so as to keep a fixed level of unsaturation in the clay sample. This is done by employing the vapour equilibrium technique, using oversaturated salt solutions in both upstream and downstream reservoirs to maintain a constant relative humidity in the entire setup [4].&#x0D; Preliminary pore network modelling has already shown that the gas diffusivity increases with a decrease in water saturation of the clay material. However, the predicted trend also suggests that this increase is only marginal and should not normally exceed an order of magnitude. This is shown in the figure below.&#x0D; All the diffusion measurements are carried out on synthetic clay samples of dimensions 3.8 cm (diameter) and 2 cm (height). In Table 1, the Sw stands for water saturation. The compositions of the synthetic clay samples (60% clay, 20% sand, 20% silt) have been adjusted so as to most closely mimic the mineralogical compostion of Boom Clay. Synthetic samples are used instead of natural samples like Boom Clay because of their better physical response to drying than Boom Clay.&#x0D; The selected control variable to lower the saturation of the material is suction, which is imposed by changing the relative humidity of the environment using oversaturated salt solutions [4]. Suction can be kept constant given constant ambient temperature and pressure. Thus, the clay sample is conditioned at a certain suction, which in turn leads to desaturation in the range of 70-100% of total saturation depending on the level of suction. For this study, the saturation range has been fixed in between 70-100% of total saturation. This range has been chosen because of what is expected in a real life nuclear waste repository. The first measured diffusion coefficients in two partially saturated samples are shown in Table 1. The initial measurements of gas diffusion coefficients in unsaturated synthetic clays show that the increase in diffusivity of helium is higher than that of argon. Helium is the second lightest known element and has an extremely small molecular size and hence the impact of desaturation on helium diffusivity could be more pronounced than the same for heavier gases.

Study of the Influence of the Composition of Hydrophobic Preventive “Protect-01” on the Physical and Mechanical Properties of Asphalt Concrete Pavement Materials

During operation, the asphalt concrete pavement is subjected to various destructive influences associated with external natural, climatic and operational factors, which can cause its premature failure. Over the past 10 years, there has been a significant increase in the fleet of vehicles in the Republic of Belarus, and, consequently, the intensity of traffic on the roads with a proportional increase in wear and destruction of their coatings. This situation is exacerbated by extended turnaround times for a number of transport facilities. The need to protect asphalt concrete pavements from the effects of external aggressive environments determines the search for new technological solutions in the creation of necessary materials, the range of which is quite wide. Existing protective compositions differ both in purpose and in the content of components. Modern research in the field of protective treatments for asphalt concrete pavements of highways, as well as technological processes used in road organizations, can effectively extend their service life. At the same time, the current research work, proven technological processes, as well as the well-known works of scientists in this field offer an insufficient number of sound technical and design solutions that allow for direct preventive protection of pavements and use for this purpose available, including secondary, materials. For more effective protection of pavements from the complex effects of water and traffic loads in the autumn-winter and spring-winter period, it is necessary to develop and implement alternative technologies, one of which is the treatment of road surfaces with the Protect-01 hydrophobic prophylactic composition. The paper presents the results of studies of the effect of treatment with the Protect-01 hydrophobic preventive composition on water saturation (decrease by 30–40 %,) frost resistance (increase by 10–12 %) and residual porosity (decrease by 12–25 %) of cores from asphalt concrete mixtures, as well as its optimal formulations.

A new method for the characterization of microcracks based on seepage characteristics

Microcracks are the main seepage channels and reservoir space for oil and gas in dense sandstone reservoirs, and the degree of development dominates the reservoir’s high and stable production capacity. A new method has been devised to address the lack of quantitative identification and characterization methods for microcrack networks. The method is based on core stress sensitivity, permeability anisotropy, and two-phase seepage rule testing. By improving upon the traditional black oil model, this method can accurately calculate the impact that microcracks of varying degrees of development have on the capacity of tight oil reservoirs. The study shows that 1) the higher the degree of microcrack development, the stronger the reservoir stress sensitivity and the greater the permeability anisotropy. As the degree of microcrack development increases, the irreducible water saturation decreases, the residual oil saturation gradually increases, and the oil–water two-phase co-infiltration zone becomes more extensive and smaller. The degree of microcrack development in tight reservoirs can be characterized based on the seepage characteristic parameters; 2) a microcrack characterization method and classification criteria have been established. It is based on stress sensitivity coefficients, permeability anisotropy parameters, and phase seepage characteristics in cores with different microcrack development degrees. For the first time, the method enables a macroscopic-level description of microcrack seepage; 3) numerical calculations show that the degree of microcrack development significantly affects the reservoir’s oil production and water production. The higher the degree of microcrack development, the higher the reservoir’s initial oil production and cumulative oil production. However, when the degree of microcrack development is too high, the microcracks are connected, thus exhibiting the nature of large fractures. This strengthens the bypassing communication effect and causes the microscopic inhomogeneity to strengthen, the oil production decreases rapidly, and water production increases quickly at the later stage. This research result enriches the reservoir microcrack characterization and evaluation system, which has essential theoretical guidance and practical significance for the rational and effective development of tight oil and tight sandstone gas.

Paleo fluid system change from deep burial to exhumation of the Precambrian petroleum reservoirs in the Sichuan Basin, China: Evidence from P-T-X records

Economically viable accumulations of hydrocarbons hosted in the Precambrian rocks are globally rare, as a protracted history available for them to escape or be destroyed due to various processes including thermal and bacterial degradations and tectonic disruption. A recent gas discovery in the late Ediacaran dolomites of the Sichuan Basin (SW China) provides an opportunity to understand the formation and preservation of ancient petroleum systems. Paleo fluid pressure-temperature-composition (P-T-X) conditions from deep burial to exhumation are evaluated from microthermometry and Raman data obtained from fluid inclusions.We identified three texturally distinct generations of gas-bearing fluid inclusion assemblages (FIAs), which delineate an operating petroleum system where gas remigrated during exhumation that followed oil cracking during deep burial. The older FIAs (types 1 and 2) show a petrographic association with bitumen and are interpreted to be the result of thermal cracking. Type 1 FIAs formed through in-situ cracking of pre-existing oil inclusions and have recorded the paleo oil charge during the middle Triassic to early Jurassic. Type 2 FIAs were trapped during the prolonged intra-reservoir oil cracking that occurred between the late Jurassic and late Cretaceous. Our pore pressure calculations indicate overpressured conditions, a result of active gas generation during thermal cracking. Lithostatic overpressures accumulated and were sustained under weak tectonic compression prior to peak burial.Type 3 FIAs have been interpreted as reflective of the gas-bearing system reactivation during exhumation. These FIAs indicate the relative reduction in the proportion of aqueous to gas inclusions, which may be due to a decrease in water saturation following gas emplacement. Uplift processes during early exhumation likely facilitated breaching of the system and remobilization of fluids, resulting in gas escape and overpressure release. The drastic increase in formation water salinity, which was documented in the fluid inclusion dataset, points to the arrival of hypersaline brine during the Eocene to Oligocene. This brine could have originated either from the lower Cambrian evaporated CaCl2 seawater or from the dissolution of the lower-middle Triassic halite. From the late Miocene to present, progressively exhumed reservoirs may have received an influx of relatively fresh water from shallow aquifers, as shown by the correspondence between P-T-X records and present-day reservoir conditions.

Simulation of nuclear magnetic resonance response based on 3D CT images of sandstone core

In recent years, nuclear magnetic resonance (NMR) logging has become increasingly prevalent in the characterization of rock properties such as porosity, permeability, saturation, and pore size distribution. However, interpreting such properties accurately from NMR logging data is challenging for some reservoirs. In particular, the impact of salinity, viscosity, and saturation on NMR measurements is not always clear, which can lead to inaccuracies in the resulting data interpretation. Properly accounting for these factors is essential in order to obtain accurate and reliable measurements for effective characterization of subsurface formations. This study utilized a random walk technique to simulate the NMR response of homogeneous sandstones using 3D CT images and conducted a sensitivity analysis under various salinity, crude oil viscosity, and water saturation conditions. The results indicate that the T2 relaxation time slightly shifts toward the short relaxation direction as the salinity of the formation water increases. In addition, longer echo intervals result in a more significant forward shift in the T2 value than shorter intervals. Whereas, for crude oil, the T2 relaxation time becomes shorter as its viscosity increases. Furthermore, the effect of echo interval on the forward T2 shift is less pronounced for crude oil than it is for formation water. Under water wet conditions, the T2 spectrum of crude oil exhibits a peak at the volume relaxation position. As the water saturation decreases, the left two peaks in the T2 spectrum shift toward shorter relaxation times. Under oil wet conditions, the T2 spectrum exhibits a complex three-peak structure. The method provides a physical basis for interpreting NMR macroscopic responses, and the simulated NMR responses can help identify fluids in reservoirs.

Influence of matrix physical properties on flow characteristics in dual network model

The tight oil formation develops with microfractures and matrix pores, it is important to study the influence of matrix physical properties on flow characteristics. At first, the representative fracture and matrix samples are selected respectively in the dual media, the fracture and matrix digital rocks are constructed with micro-CT scanning at different resolutions, and the corresponding fracture and matrix pore networks are extracted, respectively. Then, the modified integration method is proposed to build the dual network model containing both fracture and matrix pore-throat elements, while the geometric-topological structure equivalent matrix pores are generated to fill in the skeleton domain of fracture network, the constructed dual network could describe the geometric-topological structure characteristics of fracture and matrix pore-throat simultaneously. At last, by adjusting the matrix pore density and the matrix filling domain factor, a series of dual network models are obtained to analyze the influence of matrix physical properties on flow characteristics in dual-media. It can be seen that the matrix system contributes more to the porosity of the dual media and less to the permeability. With the decrease in matrix pore density, the porosity/permeability contributions of matrix system to dual media keep decreasing, but the decrease is not significant, the oil–water co-flow zone decreases and the irreducible water saturation increases, and the saturation interval dominated by the fluid flow in the fracture keeps increasing. With the decrease in matrix filling domain factor, the porosity/permeability contributions of matrix system to dual media decreases, the oil–water co-flow zone increases and the irreducible water saturation decreases, and the saturation interval dominated by the fluid flow in the fracture keeps increasing. The results can be used to explain the dual-media flow pattern under different matrix types and different fracture control volumes during tight oil production.

Pore-Scale Modeling of Liquid Water Transport in Compressed Gas Diffusion Layer of Proton Exchange Membrane Fuel Cells Considering Fiber Anisotropy.

Water management of the gas diffusion layer (GDL) is crucial to the performance of proton exchange membrane fuel cells (PEMFCs). Appropriate water management ensures efficient transport of reactive gases and maintains wetting of the proton exchange membrane to enhance proton conduction. In this paper, a two-dimensional pseudo-potential multiphase lattice Boltzmann model is developed to study liquid water transport within the GDL. Liquid water transport from the GDL to the gas channel is the focus, and the effect of fiber anisotropy and compression on water management is evaluated. The results show that the fiber distribution approximately perpendicular to the rib reduces liquid water saturation within the GDL. Compression significantly changes the microstructure of the GDL under the ribs, which facilitates the formation of liquid water transport pathways under the gas channel, and the increase in the compression ratio leads to a decrease in liquid water saturation. The performed microstructure analysis and the pore-scale two-phase behavior simulation study comprise a promising technique for optimizing liquid water transport within the GDL.

Microscopic occurrence and movability mechanism of pore water in deep shale gas reservoirs: A typical case study of the Wufeng-Longmaxi Formation, Luzhou block, Sichuan Basin

Water in pore system (i.e., pore water) is of great significance for shale gas exploration and exploitation. However, the microscopic occurrence and movability mechanism of pore water is still unclear. In this study, the pore water of deep shale gas reservoirs of the Wufeng-Longmaxi Formation in the Luzhou block was quantitatively evaluated by a new theoretical approach. The microscopic distribution and movability of pore water were investigated by combining NMR technology and theoretical models, and then the influencing factors were discussed. The results show that the signal amplitude of dry shale originates from clay minerals and organic matter. For clay minerals, illite has the greatest influence on the signal amplitude, followed by illite-smectite mixed layer and chlorite. Pore water mainly exists in an adsorbed phase, with an average adsorbed ratio of 69.26%, and an average adsorption thickness (H) of 0.5392 nm. Adsorbed and free water coexist in pores of 3–100 nm, and have equivalent content and saturation in pores of 10 nm and 6–7 nm, respectively. The specific surface area and pore volume control the occurrence of adsorbed and free water respectively. With the increase in average pore size, the water-holding capacity of pore system weakens. Adsorbed water mainly occurs in pores related to organic matter and quartz, while free water tends to occur in clay minerals pores. The adsorption affinity of spherical pores is the strongest, followed by cylindrical and slit pores. The effective pore size threshold available for fluid flow in spherical, cylindrical, and slit pores is 6H, 4H, and 2H respectively. With increasing centrifugal pressure difference, the water saturation decreases, the adsorbed ratio and mobility increase. Shale with higher pore volume has stronger mobile potential and mobility. Clay minerals are essential for pore water movability, while organic matter and brittle minerals inhibit pore water movability. This study offers a novel approach for quantitatively characterize the occurrence and transport of pore water and potentially has wide application prospects.

Effect of wettability on oil and water distribution and production performance in a tight sandstone reservoir

Wettability is an important factor that dominates the micro-distribution of initial oil and water, residual oil, and subsequent oil recovery in a tight oil reservoir. In this paper, integrated experimental techniques have been developed to examine the effect of wettability on oil and water micro-distribution together with production performance in a tight reservoir. Wettability alteration indicated by contact angles during the aging process was firstly monitored and measured continuously. Then, nuclear magnetic resonance (NMR) measurements were integrated with rate-controlled mercury injection (RMI) tests to determine pore and throat size distribution. Subsequently, NMR measurements were performed to not only characterize the oil and water distribution in the process of wettability change, but also evaluate the production performance and recovery potential. Furthermore, displacement experiments were carried out to visually observe the microscopic distribution of residual oil under different wettability conditions. For a strong water-wetting rock, oil is separated from the surface of a pore/throat on which a thin water film is adsorbed, and then fills the center of the pore in the form of oil droplets. The displacement experiments show that water saturation of a two-phase flow zone on relative permeability curves ranges from 22.5% to 55.1% and that water saturation at the isotonic point is 43.6% with its waterflooding oil recovery of 42.1%. For a weak oil-wetting rock, oil is mainly distributed in porous media in the form of an oil film. The water saturation of a two-phase flow zone ranges from 22.3% to 48.1%, while that of the isotonic point is 38.1% with waterflooding oil recovery of 33.2%. With wettability altering from strong water-wetting to weak oil-wetting, oil either is adsorbed on the pore and throat surface or migrates from the center of a larger pore to a smaller pore and/or throat. It is more unfavorable to the seepage of oil due to the fact that the two-phase flow zone is narrowed and a decrease in water saturation at the isotonic point, leading to a lower waterflooding oil recovery. After waterflooding, oil droplets caused by the Jamin effect, oil clusters resulted from heterogeneity, and small oil droplets dispersed at the corner of a pore are visually observed in cores with strong water-wetting. Within weak oil-wetting cores, residual oil is mainly distributed in a membrane-like form due to adsorption and oil clusters resulted from heterogeneity.

Abundance and variation of gaseous NH3 in relation with inorganic fertilizers and soil moisture during Kharif and Rabi season.

In an agricultural country like India, inorganic fertilizers are the major contributors of atmospheric NH3 in rural areas affecting soil, vegetation and water bodies. In this study, day-night and seasonal variation of ammonia emissions were measured from July 2017 to June 2018 during Kharif and Rabi crop seasons at a rural agricultural site in Jhajjar district of Haryana. Also, NH3 emission inventory is prepared for the amount of fertilizers applied during its basal and top dressing. NH3 concentrations were noticed significantly lower after basal dressing of DAP fertilizers as compared to the concentrations after top dressing of urea. NH3 concentration in air increased with decrease in water saturation of the soil. NH3 emission was recorded as 1.4 to 45.2, 63.1 to 190.9, and 98.9 to 187.5μgm-3 during sowing, fertilizer addition, and grain filling stages, respectively, in Kharif season. Apart from these crop stages, NH3 was measured as 56.8 to 249.5μgm-3 during crop residue burning period. On the other hand, NH3 emissions ranged from 22.9 to 68.4, 59.4 to 104.71, 26.3 to 56.0, 48.2 to 147.2, and 21.5 to 80.4μgm-3 during sowing, crown root initiation (CRI), panicle initiation, grain filling, and maturity crop, respectively, in Rabi season. The average NH3 concentrations during Kharif season (125.3μgm-3) were significantly greater than the concentrations during Rabi season (51.8μgm-3). However, a reduction in the NH3 values was observed in the period between Kharif and Rabi seasons, which could be attributed to the wet deposition during monsoon and gas to particle conversion due to less temperature conditions during the periods.