The Effect of Temperature on Irreducible Water Saturation of Water-wet Cores

The conventional measurement of a relative permeability curve (RPC) is usually conducted at room temperature, which is much lower than the reservoir temperature. Previous research work on high temperature relative permeability mainly take oil-wetted cores as objective. In this paper, laboratory test and measurement are conducted using water-wet cores from the Lunnan Oilfield. Since irreducible water saturation (Swi) is a critical factor that affects and controls the relative permeability curve, special tests are conducted to measure Swi at different temperatures for water-wet cores in the course of the experiment of relative permeability. The experimental results indicate that for the water-wet cores Swi decreased with the increasing temperature from ambient to 105℃,and the relative permeability curve shifted in a low water saturation direction, i.e. moved toward the left, while it moved toward the right for oil wetness reservoirs. Seen from both macroscopic and microcosmic view, the reasons and mechanisms of relative permeability change with temperature are discussed, and factors including core wetness, viscosity force, capillary forces, contact angle, interfacial tension change are considered.

Effects of Temperature and Water Saturation on CO_2 Production and Nitrogen Mineralization in Alpine Wetland Soils

Relationships between carbon (C) production and nitrogen (N) mineralization were investigated in two alpine wetland soils of the Tibetan Plateau using laboratory incubation under different temperatures (5, 15, 25, and 35 ℃) and water saturation (noninundation and inundation). A significant positive relationship was found between CO2 production and N mineralization under increasing temperatures from 5 to 35 ℃ with the same water saturation condition in the marsh soil (r2 > 0.49, P < 0.0001) and the peat soil (r2 > 0.38, P < 0.002), and a negative relationship with water saturation increasing at the same temperature, especially 25 and 35 ℃, in the marsh soil (r2 > 0.70, P < 0.009) and the peat soil (r2 > 0.61, P < 0.013). In conclusion, temperatures and water saturation could regulate the relationship between CO2 production and net N mineralization in the Tibetan alpine marsh and peat soils.

A new model for predicting irreducible water saturation in tight gas reservoirs

The irreducible water saturation(Swir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation.However,the complex pore structures of the tight rocks and multiple factors of the formation conditions make the parameter difficult to be accurately predicted by the conventional methods in tight gas reservoirs.In this study,a new model was derived to calculate Swir based on the capillary model and the fractal theory.The model incorporated different types of immobile water and considered the stress effect.The dead or stationary water(DSW) was considered in this model,which described the phenomena of water trapped in the dead-end pores due to detour flow and complex pore structures.The water film,stress effect and formation temperature were also considered in the proposed model.The results calculated by the proposed model are in a good agreement with the experimental data.This proves that for tight sandstone gas reservoirs the Swir calculated from the new model is more accurate.The irreducible water saturation calculated from the new model reveals that Swir is controlled by the critical capillary radius,DSW coefficient,effective stress and formation temperature.

Effects of water saturation and loading rate on direct shear tests of andesite

For estimating the long-term stability of underground framework,it is vital to learn the mechanical and rheological characteristics of rock in multiple water saturation conditions.However,the majority of previous studies explored the rheological properties of rock in air-dried and water saturated conditions,as well as the water effects on compressive and tensile strengths.In this study,andesite was subjected to direct shear tests under five water saturation conditions,which were controlled by varying the wetting and drying time.The tests were conducted at alternating displacement rates under three vertical stresses.The results reveal that the shear strength decreases exponentially as water saturation increases,and that the increase in shear strength with a tenfold increase in displacement rate is nearly constant for each of the vertical stresses.Based on the findings of the shear tests in this study and the compression and tension tests in previous studies,the influences of both water saturation and loading rate on the Hoek-Brown failure criterion for the andesite was examined.These results indicate that the brittleness index of the andesite,which is defined as the ratio of uniaxial compressive strength to tensile strength,is independent of both water saturation and loading rate and that the influences of the water saturation dependence and the loading rate dependence of the failure criterion can be converted between each other.

Study on water saturation computation models in complex pore volcanic reservoir

Determination of water saturation is important for reservoir evaluation. When complex pore structures such as fracture and cavity are present in reservoir, Archie equation is no longer suitable. According to different models of pore structure division, the authors studied water saturation conlputation models. The results show that dual porosity system is divided into four models. The first model is based on dual laterolog, the second is Dual Porosity I , the third is Dual Porosity Ⅱ , and the last one is based on the conductive pore. Besides, the triple porosity system is triple porosity model. Compute water saturation was using all the above five models in volcanic reservoir in Songnan gas field. The triple porosity system is the most suitable model for water saturation computation in complex pore structure volcanic reservoir.

Determination of Water Saturation （SW%） by Using P-wave Velocities for Saturated Sandstone

The seismic velocities are strongly influenced by porosity and degree of water saturation, as well as other petrophysical properties, such as density and elastic properties of the rocks. In this paper, the saturation of water percentage for sandstones （SW%） has been calculated by mathematical equation, which is based on the relation between the seismic velocity of water to the seismic velocity obtained in the field （for p-wave velocity only）. The results of this equation which ranged between （30% to 100%） are connected with the results of seismic velocity-porosity relation for saturated sandstone through model, this model can be used for determining the porosity （Φ） and water saturation percentage （SW%） of the sandstones in the same time.

Estimation of water saturation by using radial based function artificial neural network in carbonate reservoir:A case study in Sarvak formation

Water saturation determination in core laboratory is known as a cost and time consuming labor.Hitherto,many scientists attempted to estimate accurately water saturation from well-logging data which has a continuous record without losing information.Therefore,various model were introduced to relate reservoir properties and water saturation.Since carbonate reservoir is very heterogeneous in shape and size of pore throat,the relation between water saturation and other carbonates reservoir properties is very complex,and causes considerable overall errors in water saturation calculation.By increasing the usage and improvement of soft computing methods in engineering problems,petroleum engineers have been attended them to measure the petrophysical properties of the reservoir.In this study,a radial basis function neural network(RBFNN)improved by genetic algorithm has been employed to estimate formation water saturation by using conventional well-logging data.The used logging and core data have been gathered from a carbonated formation from one of oilfield located in south-west Iran,and finally their results of the proposed model were compared with the core analysis results.By checking the testing data from another well,it showed this method had a 0.027 for mean square errors and its correlation coefficient is equal to 0.870.These results implied on high accuracy of this model for oil saturation degree estimation.While the common methods like Archie,had a 0.041 mean square error and 0.720 of the correlation coefficient,which indicate a high ability of RBF model than the other usual empirical methods.

Parameters of new three-water model based on nuclear magnetic experiment and optimization algorithm

Clastic rock reservoir is the main reservoir type in the oil and gas field.Archie formula or various conductive models developed on the basis of Archie’s formula are usually used to interpret this kind of reservoir,and the three-water model is widely used as well.However,there are many parameters in the threewater model,and some of them are difficult to determine.Most of the determination methods are based on the statistics of large amount of experimental data.In this study,the authors determine the value of the parameters of the new three-water model based on the nuclear magnetic data and the genetic optimization algorithm.The relative error between the resistivity calculated based on these parameters and the resistivity measured experimentally at 100%water content is 0.9024.The method studied in this paper can be easily applied without much experimental data.It can provide reference for other regions to determine the parameters of the new three-water model.

Failure process and characteristics of three-dimensional high-stress circular tunnel under saturated water content

True-triaxial compression tests were carried out on cubic granite samples with a circular through hole using a true-triaxial testing system to investigate the influence of saturated water content(SWC) on the failure process and characteristics of a circular tunnel of surrounding rocks. The spalling failure under SWC can be divided into four periods: calm period, buckling deformation period, period of rock fragment gradual buckling and exfoliation, and period of formation of symmetrical V-shaped notches. When the horizontal axial and vertical stresses were constant, the spalling failure severity was reduced with the increase in lateral stress. Under natural water content, a strong rockburst with dynamic failure characteristics occurred on the circular hole sidewall. Under SWC, the failure severity was reduced and the circular hole sidewall experienced spalling failure, exhibiting progressive static failure characteristics.Therefore, water can reduce the failure severity of surrounding rocks in deep underground engineering, which has a certain guiding significance for the prevention and control of rockbursts.

Effect of Pisha sandstone on water infiltration of different soils on the Chinese Loess Plateau

The infiltration of water into soil is one of the most important soil physical properties that affect soil erosion and the eco-environment, especially in the Pisha sandstone area on the Chinese Loess Plateau. We studied the one-dimensional vertical infiltration of water in three experimental soils, created by mixing Pisha sandstone with sandy soil, irrigation-silted soil, and loessial soil, at mass ratios of 1：1, 1：2, 1：3, 1：4, and 1：5. Our objective was to compare water infiltration in the experimental soils and to evaluate the effect of Pisha sandstone on water infiltration. We assessed the effect by measuring soil bulk density（BD）, porosity, cumulative infiltration, infiltration rate and saturated hydraulic conductivity（Ks）. The results showed that Pisha sandstone decreased the infiltration rate and saturated hydraulic conductivity in the three experimental soils. Cumulative infiltration over time was well described by the Philip equation. Sandy soil mixed with the Pisha sandstone at a ratio of 1：3 had the best water-holding capacity. The results provided experimental evidence for the movement of soil water and a technical support for the reconstruction and reclamation of mining soils in the Pisha sandstone area.

Dispersion hydrophobic electrolyte enables lithium-oxygen battery enduring saturated water vapor

Li-O_(2) batteries gain widespread attention as a can didate for next-generati on energy storage devices due to their extraordinary theoretic specific energy.The semi-open structure of Li-O_(2) batteries causes many parasitic reactions,especially related to water.Water is a double-edged sword,which destroys Li anode and simultaneously triggers a solution-based pathway of the discharge product.In this work,hexamethyldisilazane(HMDS)is introduced into the electrolyte of an aprotic Li-O_(2) battery.HMDS has a strong ability to combine with a trace of water to gen erate a hydrophobic hexamethyldisiloxa ne(MM),which eliminates water from the electrolyte decomposition and then prevents the Li anode from producing the insulating LiOH with water.In this case,the hydrophobic MM disperses in the ether-based electrolyte,forming a dispersion hydrophobic electrolyte.This electrolyte can anchor water from the environment on the cathode side,which triggers a solution-based pathway and regulates the growth morphology of the discharge product and consequently increases the discharge capacity.Compared with the Li-O_(2) battery without the HMDS,the HMDS-containing Li-O_(2) battery contributes an about 13-fold increase of cyclability(400 cycles,1800 h)in the extreme environment of saturated water vapor.This work opens a new approach for directly operating aprotic Li-O_(2) batteries in ambient air.

Fractal Analysis on Methane Hydrate Formation in Porous Media

The study of the hydrate formation process in porous media is of great significance for hydrate application.In this work,the formation process of methane hydrate in porous media was monitored in situ by a low-field magnetic resonance imaging(MRI)system.The formation characteristics of methane hydrate in porous media and the change of fractal dimension of pore space were studied through the change of residual water saturation and T2 relaxation time distribution.The experimental results show that the hydrate formation process is divided into two stages:fast and slow.During the formation process,the water in the pores is continuously consumed and transformed into hydrate,and the overall T2 distribution gradually shifts to the left.In the formation process of hydrate,the pore space becomes more complex,the change of fractal dimension from top to bottom of the reactor gradually increases,and the hydrate formation rate also gradually increases.

BISQ model based on a Kelvin-Voigt viscoelastic frame in a partially saturated porous medium

Taking into account three important porous media mechanisms during wave propagation （the Biot-flow, squirt-flow, and solid-skeleton viscoelastic mechanisms）, we introduce water saturation into the dynamic governing equations of wave propagation by analyzing the effective medium theory and then providing a viscoelastic Biot/squirt （BISQ） model which can analyze the wave propagation problems in a partially viscous pore fluid saturated porous media. In this model, the effects of pore fluid distribution patterns on the effective bulk modulus at different frequencies are considered. Then we derive the wave dynamic equations in the time-space domain. The phase velocity and the attenuation coefficient equations of the viscoelatic BISQ model in the frequency-wavenumber domain are deduced through a set of plane harmonic solution assumptions. Finally, by means of numerical simulations, we investigate the effects of water saturation, permeability, and frequency on compressional wave velocity and attenuation. Based on tight sandstone and carbonate experimental observed data, the compressional wave velocities of partially saturated reservoir rocks are calculated. The compressional wave velocity in carbonate reservoirs is more sensitive to gas saturation than in sandstone reservoirs.

Spontaneous imbibition characteristics of shale oil reservoir under the influence of osmosis

The spontaneous imbibition(SI)process in shale oil reservoirs is not only infuenced by capillary force,but also by the osmotic pressure between the fracturing fuid and formation water in the nanopores media.In this study,experimental methods are used to investigate the mechanisms of osmosis in the SI,taking into account the presence of initial formation water in shale oil reservoirs.To investigate the efect of osmosis,SI experiments were performed on the fne-grained felsic shale of the Qikou sag of Dagang oilfeld.Low-feld NMR testers and high-precision electronic balances are utilized for the measuring of oil–water migration.The results show that,when Sw≠0,high-salinity fuid SI can be divided into four stages:initial imbibition stage,drainage stage,secondary imbibition stage and stationary stage;when Sw=0,there is no drainage stage of high-salinity fuid SI;when Sw≠0 or Sw=0,low-salinity fuid SI can be called the“osmosis-enhanced SI”;and we have found that“newly formed pores or microfractures”as well as reducing salinity can promote SI.This article presents a systematic study of SI of shale oil reservoirs under the infuence of osmosis,which provide useful information for reservoir numerical simulation and development program design.

Simulation of the Internal Transport Phenomena for PEM Fuel Cells with Different Modes of Flow

A numerical model for proton exchange membrane (PEM) fuel cell is developed, which can simulate such basic transport phenomena as gas-liquid two-phase flow in a working fuel cell. Boundary conditions for both the conventional and the interdigitated modes of flow are presented on a three-dimensional basis. Numerical techniques for this model are discussed in detail. Validation shows good agreement between simulating results and experimental data. Furthermore, internal transport phenomena are discussed and compared for PEM fuel cells with conventional and interdigitated flows. It is found that the dead-ended structure of an interdigitated flow does increase the oxygen mass fraction and decrease the liquid water saturation in the gas diffusion layer as compared to the conventional mode of flow. However, the cathode humidification is important for an interdigitated flow to acquire better performance than a conventional flow fuel cell.

Impacts of anisotropy coefficient and porosity on the thermal conductivity and P-wave velocity of calcarenites used as building materials of historical monuments in Morocco

It is essential to study the porosity,thermal conductivity,and P-wave velocity of calcarenites,as well as the anisotropy coefficients of the thermal conductivity and P-wave velocity,for civil engineering,and conservation and restoration of historical monuments.This study focuses on measuring the thermal conductivity using the thermal conductivity scanning(TCS)technique and measuring the P-wave ve-locity using portable equipment.This was applied for some dry and saturated calcarenite samples in the horizontal and vertical directions(parallel and perpendicular to the bedding plane,respectively).The calcarenites were selected from some historical monuments in Morocco.These physical properties were measured in the laboratory to find a reliable relationship between all of these properties.As a result of the statistical analysis of the obtained data,excellent linear relationships were observed between the porosity and both the thermal conductivity and porosity.These relationships are characterized by relatively high coefficients of determination for the horizontal and vertical samples.Based on the thermal conductivity and P-wave velocity values in these two directions,the anisotropy coefficients of these two properties were calculated.The internal structure and the pore fabric of the calcarenite samples were delineated using scanning electron microscopy(SEM),while their chemical and mineral compositions were studied using the energy dispersive X-ray analysis(EDXA)and X-ray diffraction(XRD)techniques.

Impact of pertinent parameters on foam behavior in the entrance region of porous media:mathematical modeling

Foam injection is a promising solution for control of mobility in oil and gas field exploration and development,including enhanced oil recovery,matrix-acidization treatments,contaminated-aquifer remediation and gas leakage prevention.This study presents a numerical investigation of foam behavior in a porous medium.Fractional flow method is applied to describe steady-state foam displacement in the entrance region.In this model,foam flow for the cases of excluding and including capillary pressure and for two types of gas,nitrogen(N2)and carbon dioxide(CO2)are investigated.Effects of pertinent parameters are also verified.Results indicate that the foam texture strongly governs foam flow in porous media.Required entrance region may be quite different for foam texture to accede local equilibrium,depending on the case and physical properties that are used.According to the fact that the aim of foaming of injected gas is to reduce gas mobility,results show that CO2 is a more proper injecting gas than N2.There are also some ideas presented here on improvement in foam displacement process.This study will provide an insight into future laboratory research and development of full-field foam flow in a porous medium.

Influences of pore fluid on gas production from hydrate-bearing reservoir by depressurization

In addition to the temperature and pressure conditions,the pore fluid composition and migration behavior are also crucial to control hydrate decomposition in the exploitation process.In this work,to investigate the effects of these factors,a series of depressurization experiments were carried out in a visible one-dimensional reactor,using hydrate reservoir samples with water saturations ranging from 20%to 65%.The results showed a linear relationship between gas production rates and gas saturations of the reservoir,suggesting that a larger gas-phase space was conducive to hydrate decomposition and gas outflow.Therefore,the rapid water production in the early stage of hydrate exploitation could release more gas-phase space in the water-rich reservoir,which in turn improved the gas production efficiency.Meanwhile,the spatiotemporal evolution of pore fluids could lead to partial accelerated decomposition or secondary formation of hydrates.In the unsealed reservoir,the peripheral water infiltration kept reservoir at a high water saturation,which hindered the overall production process and caused higher water production.Importantly,depressurization assisted with the N2 sweep could displace the pore water rapidly.According to the results,it is recommended that using the short-term N2 sweep as an auxiliary means in the early stage of depressurization to expand the gas-phase space in order to achieve the highest production efficiency.

Effects of vugs on resistivity of vuggy carbonate reservoirs

The pore structure characteristic parameters of vuggy carbonate reservoirs were extracted,and matrix resistivity of vuggy reservoir was calculated by the percolation network simulation.A segmented cross-scale resistivity calculation method was established,in which the finite element method was used to simulate the resistivity of vuggy reservoirs.The mathematical models of vug porosity and water saturation with rock resistivity in vuggy carbonate reservoir were established,and the relationships between them were obtained.Experimental results verified the reliability of the simulation results.The method presented provides new technical means and research method for the resistivity log interpretation of vuggy carbonate reservoirs.The matrix porosity,vug porosity and matrix pore water saturation are the key factors determining the resistivity of reservoir rocks.