Increase In Permeability Ratio Research Articles

Parameter optimization of hot dry rock heat extraction based on discrete element crack network model

Hot-dry-rock (HDR) has long been considered a potential exploitable energy source due to its high energy content, cleanliness, and abundant reserves. However, HDR typically resides in ultra-deep strata with high temperatures and pressures, which makes its extraction a highly complex thermal-hydrological-mechanical (THM) coupling. In this paper, the THM coupling relationship in the geothermal extraction is clarified. It establishes a dynamic porosity and permeability model and creates a pair-well geothermal extraction model. The investigation focuses on understanding the influence of the pressure difference between pair-wells, number of cracks, and injection temperature on the heat extraction temperature, permeability ratio, geothermal reservoir reduction rate, and heat extraction temperature. The research findings indicate the following: (1) Increasing the inter-well pressure difference from 2 to 10 MPa reduces the extraction temperature from 155 to 138 °C. However, the thermal reservoir permeability ratio increases from 1.07 to 1.35. Consequently, the extraction efficiency rises from 6.2 to 12.4 MW. (2) The number of cracks from 200 to 400 led to a decrease in extraction temperature from 160 to 115 °C. However, the thermal reservoir permeability ratio increases from 1.12 to 1.35. In the first 8 years of extraction, the thermal pumping power of 400 cracks exceeded 200 cracks, but later this trend reversed. (3) Elevating the injection temperature from 20 to 60 °C increases the extraction temperature from 142 to 158 °C while reducing the permeability ratio from 1.28 to 1.20. Consequently, the extraction power decreases from 8 to 6 MW. (4) The inter-well pressure difference has the greatest impact on the decrease in extraction temperature, whereas the number of cracks has the greatest impact on the increase in permeability ratio. Injection temperature has the most significant impact on extraction power. This study reveals that increasing the pressure difference between wells, increasing the number of cracks, and lowering the injection fluid temperature will enhance geothermal extraction power. These findings provide valuable insights for geothermal development.

Analytical solutions for brine invasion across caprock and leakage through an abandoned well in CO2 storage sites

Success in subsurface CO2 storage requires a trapping mechanism that inhibits the flow of storage layer fluid. Due to the wide prevalence of abandoned wells across geological formations, unwanted leakage events of brine and CO2 may occur if old wells near storage sites are not evaluated accurately. The abandoned wells, with time, may become conducive to flow if a sufficient pressure gradient is realized. Classical analytical models theorized abandoned well problems based on Theis’s solution and proposed strategies to find radial coordinates of the abandoned wells. However, in those formulations, brine invasion from storage to the surrounding formation is either disregarded or assumed as a vertical-only flow. In this study, we report a novel mathematical model that accounts for both brine invasion and abandoned well flow. The leakage rate across the abandoned well segment is evaluated from three contributing pressure terms: injection- and the associated brine invasion-induced pressure build-up, leakage-induced pressure drawdown in the storage layer, and leakage-induced pressure build-up in the overlying aquifer. We evaluate the average radial pressure from a two-dimensional coupled flow problem by applying Laplace and Hankel transforms. The obtained solutions in the Hankel-Laplace space were inverted back to the radial-time domain by employing the integration-summation-extrapolation and Stehfest method, respectively. We verified the developed solution against the classical solution analytically and graphically. We observe that Theis’s solution always overestimates the radial pressure as the pressure is diffusing in the lateral direction only. We identified that the abandoned well leakage rate decreases with the increase of permeability ratio, and the degree of reduction is higher in late times. We measured the degree of overestimation in leakage rates compared to classical solutions. A maximum leakage rate is observed for open flow conditions. The abandoned well leakage rate reaches its maximum early when the permeability ratios are higher. The proposed work can be employed as a base solution in old-well leakage modeling to determine the radial coordinate of the abandoned wells with a higher degree of certainty.

Study on the development options of tight sandstone oil reservoirs and their influencing factors

The research area of tight sandstone oil reservoirs was selected, a numerical model of the oil reservoir was developed, and a study of the development options and influencing factors was carried out to analyze the influence of different development methods, physical and engineering parameters on the development dynamics. Study shows that the two main factors limiting the efficient development of tight sandstone reservoirs are reservoir properties and formation energy. Fractured horizontal well injection huff and puff development can effectively improve reservoir physical properties and timely replenish formation energy, which is suitable for the development of such oil reservoirs. In dense sandstone reservoirs, its impact on production capacity is also relatively small when the permeability ratio is small. Due to both gravity and reservoir physical properties, the permeability ratio increases, the cumulative oil production of positive rhythm reservoirs decreases and that of reverse rhythm reservoirs increases, and the location of high-quality reservoirs in the upper part of producing wells is conducive to increasing the final recovery rate. A lower oil to water viscosity ratio can significantly increase the swept volume and improve development effect. Hydrophilic reservoirs can reduce the injection pressure and increase the spread range, effectively improving the problem of inability to inject, and improving reservoir hydrophilicity through surface activators can increase reservoir recovery. The water injection rate determines the recovery rate of formation energy. Generally, the faster the rate, the higher the cumulative oil production. Therefore, the rate of water injection should be increased as much as possible, taking into account construction conditions and economic evaluation. Additionally, the effect of water injection on the development effect is different at different stages, so the appropriate timing of water injection is very important to the water injection huff and puff development effect, and the use of early water injection in this research area is not conducive. Soaking can promote pressure and fluid redistribution and improve water injection huff and puff development effect, but soaking for a long time can lead to reservoir contamination and reduce crude oil production, so the preferred time for a soaking is about 20 days.

Effect of Parameters of Pool Geometry on Flow Structure in Nature-like Fishway.

Many uncertainties such as variable irregular structure and complex flow conditions bring difficulties to the design of a nature-like fishway. This study defines the main factors and parameters affecting flow conditions such as permeability ratio, offset ratio, bottom slope and pool length to simplify and generalize the irregular geometry of the nature-like fishway. According to the engineering requirements of the Mopiling nature-like fishway, the effect of the above parameters of pool geometry on the flow structure is investigated through a 3D turbulent numerical simulation, and the parameter thresholds are summarized according to the optimization of the flow conditions. The results show that under the same conditions, the maximum velocity of the control section increases with the increase in permeability ratio, bottom slope and pool length, and the offset ratio has limited effect on the maximum velocity of the control section. It is recommended that when the bottom slope is 1/250 and the pool length is 10 m, the permeability ratio should not be greater than 0.30 and the offset ratio should be located between 0.15 and 0.60. When the bottom slope is adjusted to 1/200, it is recommended to control the permeability ratio below 0.20, the offset ratio between 0.30 and 0.60, and the pool length can be adjusted to 8 m. Within the above threshold range of the design parameters, the maximum velocity in the fishway can be basically controlled at about 1.0 m/s. The mainstream in the pool is clear and the flow pattern is good, which can basically satisfy the requirements of fish passing. The relevant design parameters and optimization strategies can provide reference for similar projects.

Co-production of Tight Gas and Coalbed Methane from Single Wellbore: a Simulation Study from Northeastern Ordos Basin, China

Focusing on vertical multi-layer superimposition of unconventional natural gas reservoirs in coal-bearing strata, research on the co-production of tight gas and coalbed methane from a single wellbore was conducted. This study intended to obtain maximum economic benefit of a single well from multi-layers. According to the vertical combination of tight sandstone and coal in the eastern Ordos Basin, the reservoir combinations were classified into direct contact, fracture connected, and non-contact types. Based on the economic benefit of co-production, the inter-layer interference coefficient and applicability coefficient were established. The productivity of tight gas and coalbed methane co-production from one wellbore was numerically simulated using the black oil model. The results indicated that with increase in reservoir permeability, thickness, and average pressure, as well as the decrease in reservoir differential pressure, the combined gas production increased. Gas production rate from different reservoir combination types can be ranked in the following order: direct contact type > fracture connected type > non-contact type. In addition, with increase in permeability ratio (sandstone permeability vs. coal permeability) and average pressure, as well as with decrease in differential thickness and differential pressure, the co-production applicability increased. In addition, for different reservoir combinations, non-contact type co-production can be the first choice, and the next choice is fracture connected type. The results can be beneficial for conducting co-production choice in different unconventional natural gases superimposed basins.

Numerical study on the hydrodynamics of agglomerates at intermediate Reynolds numbers

Abstract The flow pattern and hydrodynamics of a heterogeneous permeable agglomerate in a uniform upward flow at intermediate Reynolds numbers (1–40) are analyzed from three-dimensional (3D) computational fluid dynamics simulations. Different from the homogeneous or stepwise-varying permeability models used in previous papers, a continuously radially varying permeability model is used in the present study. The effects of two dimensionless parameters, the Reynolds number and the permeability ratio, on the flow field and the hydrodynamics were investigated in detail. The results reveal that unlike the solid sphere, a small recirculating wake initially forms inside the agglomerate. The critical Reynolds number for the formation of the recirculating wake is lower than that of the solid sphere and it decreases with the increase of permeability ratio. A correlation of drag coefficient as a function of the Reynolds number and permeability ratio is proposed. Comparisons of drag coefficients obtained by different permeability models show that at intermediate Reynolds numbers (1–40), the effect of radially varying permeability on the drag coefficient must be considered.

Development and Evaluation of Nanoemulsion gel for transdermal delivery of Valdecoxib

To enhance the solubility and permeability of poorly water soluble Valdecoxib, Nanoemulsion gel was formulated for the treatment of rheumatoid arthritis. Among the oils, surfactants and co-surfactants elainic acid, tween80 and ethanol were selected as they showed maximum solubility to Valdecoxib. The pseudo ternary phase-diagrams was constructed to find optimal concentration that provided the highest drug loading. The prepared Nanoemulsions were subjected trough thermodynamic stability testing. The droplet size, scanning electron microscopy (SEM) and zeta-potential were investigated. The optimized formulation of Nanoemusion NE2 which was showing 87.63% drug release was incorporated into polymeric gel of Carbopol940 for convenient application and evaluated for viscosity, PH, in-vitro permeations studies, skin irritation test and anti-inflammatory activity. The in-vitro skin permeations profile of optimized formulation was compared with normal Valdecoxib gel and Nanoemulsiongel NG2. The significant increase in permeability ratio (Kp), flux (Jss) and enhancement ratio (Er) was observed. The anti-inflammatory effect of formulation NG2 showed significant increase 72% inhibition effect in 24hrs when compared to Valdecoxib gel on Carrgeenan induced paw edema in rats. The results suggested that Nanoemulsion gels are potential vehicles for improved transdermal delivery of Valdecoxib.

Experimental study on a new plugging agent during CO2 flooding for heterogeneous oil reservoirs: A case study of Block G89-1 of Shengli oilfield

In oilfield operations, CO2 has been applied to enhance oil recovery (EOR). However, CO2 injection in heterogeneous oil reservoirs lacks acceptable sweep efficiency due to the high mobility of CO2. A suitable composite organic granule plugging agent was developed to control CO2 mobility and hence, improve sweep efficiency and oil recovery. The reaction mechanism involved hydroquinone, formaldehyde, furfural and heptyl alcohol catalyzed by p-toluene sulfonic acid at supercritical CO2 to initiate carbonyl addition and condensation reaction via sol-gel polymerization to form granulated polymer. This system is suitable for low permeability and low water-cut oil reservoirs. The core experiments show that the system is easy for injection, and the plugging ratio is more than 98% after injecting 1PV. The parallel sand pack model experiments show that the system can enter the high permeability reservoirs first and as the increase of permeability ratio, the profile modification becomes better. The core flooding experiment shows that the system had good performance of sealing for CO2 and the EOR can be further improved 11.9% at the same time.

CO2 mobility control and sweep efficiency improvement using starch gel or ethylenediamine in ultra-low permeability oil layers with different types of heterogeneity

Abstract Reservoir heterogeneity and natural fractures greatly affect CO 2 flooding efficiency in ultra-low permeability oil reservoirs. CO 2 water alternating gas (WAG) flooding and the combinations of continuous CO 2 flooding and gas channeling treatments are recognized as effective approaches to improve CO 2 sweep efficiency. It is of major interest to propose the novel gas channeling treatments and conduct a feasibility study of different CO 2 -EOR technologies. Heterogeneous cores with different permeability ratios and fracture model were utilized in the laboratory experiments to simulate different types of heterogeneity in the oil reservoirs. Continuous CO 2 flooding, CO 2 WAG flooding, continuous CO 2 flooding+one-stage gas channeling control, and continuous CO 2 flooding+two-stage gas channeling control were conducted after water flooding in homogeneous and heterogeneous cores and fracture model. Ethylenediamine and modified starch gel were proposed as blocking agents to mitigate gas channeling. During the experiments, the CO 2 flooding efficiency was evaluated through the oil recovery increment, fluid mobility control and the changes of producing pressure drop. Experimental results show that producing pressure drop during continuous CO 2 flooding decreases rapidly with an increase in permeability ratio. Continuous CO 2 flooding cannot displace much of remaining oil in low permeability layers due to high mobility of CO 2 and serious heterogeneity. WAG flooding can effectively control the fluid mobility and improve CO 2 flooding efficiency when the permeability ratio is less or equal to 30. Plenty of remaining oil can be displaced by combining continuous CO 2 flooding and gas channeling treatments. When the permeability ratio is less or equal to 100, ammonium carbamate, the reaction product of injected ethylenediamine and CO 2 can block off high permeability layer and impel the injecting gas into low permeability layer. The two-stage injection of modified starch gel and etheylenediamine can significantly mitigate the gas channeling within high-capacity gas channel model and fracture model during continuous CO 2 flooding, and the incremental oil recovery could be more than 20%. Pilot test of CO 2 flooding was operated in Northwest China and concentrations of CO 2 are monitored in six production wells. Two kinds of construction plans for gas channeling treatments have been preliminary designed to control the gas channeling in the pilot.

Experimental study and application of tannin foam for profile modification in cyclic steam stimulated well

Abstract Background Tannin foam is a good blocking agent with permeability selection and high temperature tolerance. Tannin foam can improve strength and stability of aqueous foam. Methods The aim of the study was to investigate whether tannin foam has good performance for profile modification in cyclic steam stimulated well. Through sandpack displacement experiments with single and parallel sandpacks under high-temperature, the effects of foam quality, permeability, injection mode, temperature, permeability ratio, and oil saturation on blocking and profile modification capabilities of tannin foam were studied. The performances of tannin foam and conventional high-temperature foam were compared. Results Experimental results indicate that blocking capability for tannin foam first increases and then reduces with the foam quality, and the best foam quality is 50% in the experiments. The resistance factor increases with permeability, and decreases with temperature. Co-injection of tannin solution and gas is better than SAG injection. Gelled tannin may enhance the bubble film strength, and increase the foam stability and blocking capability compared to the conventional high-temperature foam. When the permeability ratio of two sandpacks is less than 4.18, the profile modification is good. As the permeability ratio increases, tannin foam is easy to flow out of the high permeability sandpack, and profile modification decreases. Although irreducible oil in the sandpack reduces foam strength, tannin foam still has obvious profile modification capability in sandpacks with water-flood irreducible oil. Tannin foam was applied for profile modification in two cyclic steam stimulated wells. The wellhead pressure for steam injection with tannin foam increased at least 2 MPa, indicating that tannin foam blocked steam channels in formation. Oil production improvement and water cut decrease are obvious. Conclusion Tannin foam is effective for modifying steam profile, increasing oil production, and decreasing water cut in cyclic steam stimulated wells with high water cut.

Numerical simulation of preformed particle gel flooding for enhancing oil recovery

Abstract As a new type of oil recovery enhancing technology, preformed particle gel (PPG) flooding has been gradually used for high water-cut reservoir development. However, the current commercial software cannot simulate the processes of PPG flooding. In this paper, a novel mathematical model considering the behaviors of pore-throat plugging and particles restarting, the matching relations of particle size, throat size and pressure gradient is established based on the mass conservation equation and solved by IMPES and typical four-order Runge–Kutta methods. Also, the codes are written by Visual Basic, and the verification is proved by experimental data. Then, the influences of injection rate, suspension concentration, mean particle diameter, critical threshold pressure gradient and permeability ratio in ultimate oil recovery factor and water-cut are studied. The results show that, with the injection rate, mean particle diameter and critical restarting pressure gradient coefficient increasing, the ultimate oil recovery factor will increase first, and then decrease. As the concentration of injection suspension increases, the ultimate oil recovery factor will increase first, but at the later stage it tends to be smooth. As the permeability ratio increases, the enhanced recovery factor will also increase first, and then tend to be smooth.

Research and Application of Floaters Produced from Water Treatment in Oilfield SZ36-1 as Profile Control Agent

Composition and structural characteristics of floaters were detected and forming reasons were analysed through modern reservoir engineering theory, equipment analysis and physical simulation.Experiments on flowing characteristics, fluid diversion effect and driving effect were carried out. The results show that floaters are formed by huge amounts of tiny bubble absorbing crude oil and suspended solids in floating progress which make their density lower than water. Disposed floaters have better adaptability and can block off high-permeability. Furthermore, profile control effect turns better as particle concentration and permeability ratio increases. However,floater particles have selectivity to permeability ratio. When permeability ratio is not less than 8, profile control agent may damage low-permeability layers and cause succeeding water passing through high-permeability layers. Therefore, only when floaters adapt well to permeability ratio can we get better profile control effect.

Experimental study and application on profile control using high-temperature foam

Through single-core and dual-core experiments, blocking and profile control capability of high-temperature foam were investigated. Experiment results indicate that with the increase of foam quality, the resistance factor reduces, and the best foam quality is 0.50. The resistance factor increases with permeability, and decreases with temperature. Co-injection of surfactant solution and gas is better than SAG injection. During the hot water reverse injection period, resistance factor decreased to 75, and then basically remained stable. Irreducible oil in sandpack can reduce blocking capability to some extent. When the permeability ratio is less than 6, the profile control effect is good. As the increase of permeability ratio, profile control effect decreases. High-temperature foam still has some profile control capability in sandpacks with irreducible oil. Foam in porous media can withstand reverse flow of water under high-temperature conditions. In site application for steam profile control using high-temperature nitrogen foam, oil production improvement and water cut decrease are obvious. This technology is useful for improving oil production in cyclic steam stimulated wells.

Change in blood-brain barrier permeability during pediatric diabetic ketoacidosis treatment.

Cerebral edema is a devastating complication of pediatric diabetic ketoacidosis. We aimed to examine blood-brain barrier permeability during treatment of diabetic ketoacidosis in children. Prospective observational study. Seattle Children's Hospital, Seattle, WA. Children admitted with diabetic ketoacidosis (pH <7.3, HCO3 <15 mEq/L, glucose >300 mg/dL, and ketosis). None. Subjects underwent two serial paired contrast-enhanced perfusion (gadolinium) and diffusion magnetic resonance imaging scans. Change in whole brain and regional blood-brain barrier permeability (permeability ratio*100 and % permeability ratio change) between illness and recovery were determined. Time 0 reflects start of insulin treatment. Thirteen children (median age 10.0 +/- 1.1 yrs; seven female) with diabetic ketoacidosis were enrolled. Permeability ratio increased from time 1 (first magnetic resonance image after time 0) to time 2 (second magnetic resonance image after time 0) in the frontal cortex (ten of 13 subjects), occipital cortex (ten of 13 subjects), and basal ganglia (nine of 13). Whole brain permeability ratio increased from time 1 to time 2 (160%) and regional increase in permeability ratio was greatest in the frontal cortex (148%) compared with the occipital cortex (128%) and basal ganglia (112%). Overall, whole brain and regional blood-brain barrier permeability increased in most subjects during diabetic ketoacidosis treatment. The frontal region had more blood-brain barrier permeability than other brain regions examined.

Inertia Effects in High-Rate Flow Through Heterogeneous Porous Media

The paper deals with the effects of large scale permeability–heterogeneity on flows at high velocities through porous media. The media is made of a large number of homogeneous blocks where the flow is assumed to be governed by the Forchheimer equation with a constant inertial coefficient. By assuming the validity of the Forchheimer equation at the large scale, an effective inertial coefficient is deduced from numerical simulations. Different media are investigated: serial-layers, parallel-layers and correlated media. The numerical results show that: (i) for the serial-layers, the effective inertial coefficient is independent of the Reynolds number and decreases when the variance and the mean permeability ratio increases; (ii) for the parallel-layers and the correlated media, the effective inertial coefficient is function of the Reynolds number and increases when the variance and the mean permeability ratio increases. Theoretical relationships are proposed for the inertial coefficient as function of the Reynolds number and the characteristics of the media.

Influence of viscosity variations on the forced convection flow through two types of heterogeneous porous media with isoflux boundary condition

A theoretical analysis of fully developed forced convection flow through a heterogeneous porous medium with isoflux boundary condition is carried out by invoking a varying viscosity model to determine its effect on the resulting heat and fluid flow characteristics. Two different types of permeability and thermal conductivity variations, in the transverse direction of the channel, are accounted for in the analysis, viz., continuous weak and step-wise variations. Analytical solutions are obtained and graphical illustrations are presented to reveal the influence of thermal conductivity, permeability and viscosity variations. The results indicate that the viscosity variations have significant effect on the resulting heat transfer characteristics interpreted in terms of the Nusselt number. Moreover, the results reveal that the heat transfer rate decreases with the increase of permeability ratio for strong viscosity variations, which cannot be captured if a constant viscosity model is assumed.

Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.

Microvascular permeability after cardiopulmonary bypass: An experimental study

Microvascular permeability is presumed to increase during cardiopulmonary bypass, but this has not been directly demonstrated. Therefore, a controlled experimental study was performed in dogs in which the permeability ratio of the small intestinal microvasculature was determined. Shortly after 120 minutes of cardiopulmonary bypass (experimental group, n = 7) or a sham procedure (control group, n = 7), the superior mesenteric venous pressure was raised in a stepwise fashion until the intestinal lymph/plasma protein concentration stabilized at a minimum value. Minimal lymph/plasma concentration ratio (permeability ratio) of the total proteins and each of six protein fractions was greater in dogs that had been on bypass than in control dogs (p = 0.01 for total proteins and less than 0.05 for five of the fractions). The variability in this regard was large in both groups, and in some animals subjected to bypass the permeability ratio was more than twice the maximum value for the control group. The increase in permeability ratio was greater for large molecules. Inferences: Cardiopulmonary bypass results in a variable increase in microvascular permeability. This results primarily from an increase in the size of large pores in the microvascular barrier.