Pressure Propagation Research Articles

Mechanisms of separation of the elastic step and the thermal step

The elastic interaction causes a two‐step conversion from the low‐spin (LS) to the high‐spin state (HS) following a femtosecond laser pulse excitation. These steps occur on different timescales: a spin conversion (elastic step) in a short time due to pressure propagation and a late spin conversion (thermal step) resulting from heat diffusion. In this paper, we provide a brief review of models for spin crossover phenomena, emphasizing the role of the difference of degeneracy of the HS state and LS state and elastic interaction due to changes in local structures. We also review theoretical approaches to these effects. Additionally, to analyze the dynamical process of spin conversion after photo‐irradiation, it is necessary to consider mechanisms of heat transfer among spins. Recently, we proposed a two‐temperature model that incorporates both lattice and spin temperatures, which enables us to reproduce the two steps under an early uniformization of the lattice temperature, highlighting the importance of the timescales of these processes. Furthermore, we explore possible mechanisms to separate the two steps by examining the different timescales of processes of spin conversions by mechanical and entropic forces, and also by considering changes of local temperature due to spin conversion.

Effect of Isotropic and Anisotropic Permeability on Gas Production Behavior of Site NGHP-01-10D in Krishna-Godavari Basin

This study reports an investigation into both isotropic and anisotropic permeability effects on gas production behavior during depressurization-induced natural gas hydrate dissociation at site NGHP-01-10D in the Krishna-Godavari basin. Numerical simulations were performed on a reservoir-scale model incorporating a single vertical well, examining different scenarios of permeability ratios (rrz). The investigation assessed gas and water production rates, cumulative production volumes, the gas-to-water ratio, and the spatial distribution of reservoir parameters throughout a production duration of 3 years. The findings indicate that permeability anisotropy has a substantial impact on hydrate dissociation and gas recovery. For rrz > 1, horizontal pressure propagation was promoted and gas production increased. For example, at t = 1100 days, the total gas production improved from 7.88 × 105 ST m3 for rrz = 1 to 55.9 × 105 ST m3 for rrz = 10. For rrz < 1, vertical pressure propagation resulted in higher water production with concomitantly lower rates of gas production rates. Spatial distribution analysis revealed that higher rrz values led to more extensive radial propagation of pressure drop, temperature decrease, gas saturation increase, and hydrate dissociation. The study concludes that higher horizontal permeability enhances depressurization effects, resulting in higher gas production rates and more favorable gas-to-water ratios.

Research on Gas Explosion Pressure and Flame Propagation Characteristics in Turning Pipelines.

In order to investigate the overpressure and flame propagation characteristics of gas explosions in turning pipelines, this study designed a transparent organic glass pipeline test system with different turning angles (30°, 60°, 90°, 120°, and 150°) and conducted a series of experimental studies to analyze the explosion shock wave overpressure and flame propagation behavior. The experimental results show that with the increase of the turning angle of the pipeline, the overpressure of the explosion shock wave significantly increases. In terms of flame propagation characteristics, when the turning angle is small, the flame can adhere to the outer wall of the pipeline corner and gradually fill the entire pipeline section. When the turning angle increases, the flame forms a blank area near the outer wall of the corner, and the blank area expands with the increase in the corner. In addition, the increase in the turning angle promotes the increase in the velocity of the explosion flame front. The research results of this review are of great significance for a deeper understanding of the mechanism of gas explosions in turning pipelines and evaluating their potential hazards.

Experimental investigation on the vented flame and pressure behaviour of hydrogen-air mixtures

To explore the changes in pressure and flame propagation inside and outside the vessel when the pipe diameter does not match the vent diameter, and to check the conservatism of standards NFPA 68 and EN 14491 for this case, an experimental apparatus was utilized to investigate the influences of static activation pressure (0.7–1.75 bar) and vent diameter (30–70 mm) on the deflagration behavior of hydrogen–air mixtures (Φ: 0.6–1.4). The vented pressure, flame propagation, and pressure–flame interaction characteristics of hydrogen–air mixtures were observed and analyzed. Additionally, the conservatism of the calculated venting area under the experimental conditions of NPFA 68 and EN 14491 was verified. The results indicated that under an equivalence ratio of 0.6, the pressure-time curve inside the container exhibited only one peak (Pmax11). In the stoichiometric and fuel-rich states, the pressure-time curve inside the container exhibited two peaks attributed to the decrease in venting efficiency due to the secondary explosion inside the pipe, increasing the turbulence intensity within the container. When the static activation pressure is 0.7bar, the pressures of the three vent diameters of 30, 50 and 70 dropped by 11.34%, 24.38% and 26.86% respectively. And the Pmax11 at Φ= 1.0 and Φ= 1.4 are similar, while this phenomenon is not observed for other vent diameters. When the vent diameter was inconsistent with the duct diameter. the calculations of both standards were conservative. However, under these testing conditions (vent diameter: 30–70 mm, static activation pressure: 0.7–1.75 bar), the NPFA 68 calculations yield a conservatism range of 3.3 to 11, whereas EN14491 ranges from 1.6 to 15.7. The NPFA 68 results were more stable and concentrated, making these conditions more suitable for industry safety design in hydrogen venting.

Experimental study on inhibiting methane-coal dust explosion by APP-diatomite composite explosion suppressant in the pipe network

To prevent and control the methane/coal dust compound explosion disaster, the APP-diatomite composite powder inhibition of methane/coal dust compound explosion experiments were carried out in the self-constructed pipe network. The composite powder was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The change rules of methane/coal dust composite explosion pressure and flame propagation velocity were analyzed using different compounding ratios of powders in several monitoring points. The results show that the composite powder exhibited irregular morphology and the APP powder is uniformly distributed on the diatomite porous mesh structure. When the APP loading on the surface of diatomite is 40 wt%, composite powder has the best effect on explosion suppression, with the peak maximum explosion overpressure and the peak maximum flame propagation velocity reduced by 71.5% and 92.2%, respectively. The explosion suppression mechanism is revealed through pyrolysis properties, explosion products, and chain reaction.

Study on the hydrogen-air premixed flame propagation characteristics in semi-open space with obstacle

In semi-open space, obstacles have the potential to accelerate flame propagation and increase hydrogen-air deflagration pressure. Therefore, this paper is dedicated to exploring the influence of obstacles on the premixed hydrogen deflagration, which is crucial for enhancing the safety of industrial production and energy utilization. By using Large Eddy Simulation (LES) model in OpenFOAM, this study investigates the deflagration characteristics of premixed hydrogen in the presence of three different shaped obstacles. The analysis results reveal that under obstacle conditions, the flame shape can be categorized into four phases: the hemispherical phase, finger-shaped phase, jet phase, and vortex phase. The velocity of the flame front is nearly same for elliptical and rectangular obstacle condition, but it is 36% higher compared to triangular obstacle condition. The impact of triangular and rectangular obstacles on explosion overpressure is less than that of triangular obstacles on explosion overpressure, but it is 16% higher than that of elliptical obstacle. Analyzing the vorticity generated by different obstacle reveals that the vorticity produced by rectangular obstacle is twice as much as that produced by elliptical obstacle, whereas the vorticity produced by triangular obstacle is 2.4 times greater than that produced by elliptical obstacle. The acceleration of hydrogen-air explosion process occurs due to the narrow space created by obstacle and pipeline walls, and the shape of obstacle significantly influences this acceleration.

Piperazine pyrophosphate-functionalized Ni-MOF metal framework: Fabrication and synergistic explosion suppression mechanisms

Dust explosion suppression is crucial for ensuring safe industrial operations. To explore composite explosion suppression powders with higher performance, piperazine pyrophosphate (PAPP)-functionalized nickel-based metal–organic framework (PAPP@Ni-MOF) synergistic suppression materials were designed and synthesized. The effectiveness of this suppressant in inhibiting the explosion flame and intensity of polypropylene (PP) dust was investigated using explosion flame propagation and explosion pressure test apparatus. The results indicate that the combination of N/P elements and Ni-MOF exhibits excellent catalytic carbonization performance. Adding 50 wt% PAPP@Ni-MOF can completely inhibit the propagation of PP explosion flames and the rise in explosion pressure. The maximum propagation distance of the explosion flame was reduced by 78.07 %, the overall flame propagation speed decreased by 84.54 %, and the maximum explosion pressure was reduced by 76.87 %. Through characterization experiments, the products before and after the explosion were analyzed. Combined with molecular dynamics (MD) simulation results, the efficient synergistic explosion suppression mechanism of PAPP@Ni-MOF for PP dust was revealed from the perspectives of thermal conduction isolation, key radical recombination, and volatile gas adsorption.

Investigating the explosive characteristics of hydrogen/ n-butane blended fuel: Experimental and kinetic insights

Investigating the explosive characteristics of H2/n-C4H10 mixtures is crucial for the safe utilization of this blended fuel. Our study focused on varying equivalent ratios and hydrogen blending ratios within a closed 20-L spherical explosion vessel. Additionally, the microscopic kinetics of the reactions were analyzed through chemical reaction simulation. Our findings indicate that the most violent explosion occurred at an equivalent ratio of 1.2. Increasing hydrogen content intensified combustion reactions, reducing flame thickness and inducing cellular structures along the flame front. This escalation also increased explosion pressure, flame temperature, and flame propagation speed, elevating explosion risk. Moreover, the equilibrium molar fraction of O2 and CO2 decreased while that of H2O increased with higher hydrogen blending ratios. Correspondingly, the heat release rate and generation rates of H•, O•, and OH• radicals increased. Notably, the peak time of C2H4 and CH4 consumption rates preceded. Additionally, R5: O2 + H• = O• + OH• and R978: C4H10 + H• = SC4H9 + H2 represented crucial promoting and inhibiting steps, respectively. These insights deepen our understanding of the explosion mechanism of H2/n-C4H10 mixtures, providing a theoretical basis for designing safer protective measures and evaluating explosion risks in industrial production.

Study on Nonlinear Parameter Inversion and Numerical Simulation in Condensate Reservoirs

The B6 metamorphic buried hill condensate gas reservoir exhibits a highly compact matrix, leading to a rapid decline in bottom-hole pressure during initial production. The minimal difference between formation and saturation pressures results in severe retrograde condensation, with multiphase flow further increasing resistance. Conventional numerical simulations often overestimate reservoir energy supply due to their failure to account for this additional resistance, leading to inaccuracies in bottom-hole pressure predictions and gas–oil ratio during history matching. To address these challenges, this study conducted research on nonlinear numerical simulation for buried hill condensate gas reservoirs and established a method for calculating a multiphase pressure sweep range based on the well testing theory. By correcting and fitting the pressure propagation boundaries with numerical simulation, the nonlinear flow parameters applicable to the B6 gas field were inversed. This study revealed that conventional Darcy flow is inadequate for predicting pressure propagation boundaries and that it is possible to reasonably characterize the pressure sweep range through nonlinear flow. This approach resulted in an improvement in the accuracy of historical matching for bottom-hole pressure and gas–oil ratio, which improve the historical fitting accuracy to 85%, providing valuable insights for the development of similar reservoirs.

Analysis on a five-spot well for enhancing energy recovery from silty natural gas hydrate deposits in the South China Sea

The five-spot well is a promising technique for enhancing the inherent low gas production rate from silty natural gas hydrate (NGH) reservoirs with low permeability in the South China Sea (SCS). However, the production characteristics and the responses to key geological and engineering factors are still unclear and warrants investigation. Herein, we first establish a three-dimensional reservoir model based on the SH2 NGH deposits at SCS with the implementation of a five-spot well. We systematically examine the gas production enhancement effect and the unexpected well-to-well interaction induced by long-term depressurization. A sensitivity analysis on the effects of bottomhole pressure (Pbtm), permeability (k) and hydrate saturation (SH) is conducted to elucidate the key factors controlling the gas production enhancement. Our results reveal that the five-spot well significantly improves the gas productivity with cumulative gas production increased to 4.12 times that of a single well over 10 years. The well interference on gas production is not significant in the early stage but becomes more significant as depressurization sustains. Due to the relatively slow pressure propagation at the inner well, contribution to gas production from the inner well decreases over time while the outer wells increase. Based on the sensitivity analysis, gas production increases with decreasing Pbtm, increasing k, and decreasing SH with Pbtm and k as the key controlling factors. The findings provide valuable design basis for the adoption of a multi-well system in enhancing gas production for targeted NGH reservoirs in the next field production trial at SCS.

Experimental Study on Explosion Characteristics and Consequences for Homogeneous and Inhomogeneous Methane-Air Mixtures within a Kitchen

ABSTRACT Owing to the effect of a non-uniform concentration distribution, natural gas leakage explosion accidents usually cause different degrees of damage inside residential kitchens. According to the similarity principle, a reduced-scale experiment setup of a kitchen was established. Uniform and non-uniform explosion experiments for methane-air mixtures with concentrations of 7.7%, 9.5%, and 11.2% were performed. The flame propagation behavior and pressure evolution characteristics were analyzed for homogeneous and inhomogeneous methane-air mixtures. In addition, two dimensionless coefficients, namely macroscopic and directional non-uniformity coefficients, were introduced to quantify the uneven distribution of gas concentration within the kitchen. Furthermore, the flame development process and pressure evolvement characteristics were compared between homogeneous and inhomogeneous methane-air mixtures in a fuel-lean, chemical equivalence concentration and fuel-rich state. The results show that the macroscopic non-uniformity coefficients are 0.0998, 0.0653, and 0.0571 on the fuel-lean, chemical equivalence concentration and fuel-rich conditions, respectively. It indicates that the greatest non-uniformity of methane concentration distribution within the kitchen is represented on the fuel-lean condition. The concentration gradient could obviously reduce the explosion overpressure in the fuel-lean condition, whereas it would not significantly decrease the explosion overpressure in the chemical equivalence concentration or fuel-rich condition. It means that the greater the non-uniformity coefficient is, the more significant the effect on the overpressure peak is.

Research on pressure propagation in long-distance water pipelines for fault conditions by VMD and wavelet transform

Long-distance water pipelines in complex geographical environments face potential risks such as leaks. This study uses variational mode decomposition (VMD) and continuous wavelet transform (WT) to analyze pressure fluctuation signals in pipelines for detecting and locating leaks and other anomalies. CFD simulations are conducted to obtain pressure fluctuation data under various fault conditions. The pressure signals are then decomposed into multiple Intrinsic Mode Functions (IMFs) using VMD, and WT is applied to analyze their time–frequency characteristics. The results show significant differences in amplitude and frequency of IMF components between fault and normal conditions, with reduced amplitude and altered frequency under fault conditions, providing a basis for fault detection. Additionally, the IMF characteristics differ at different fault locations, aiding in fault localization. This research offers an effective method for leak detection and localization in long-distance pipelines, crucial for enhancing safety and stability.

Integrated finite element analysis and machine learning approach for propagation pressure prediction in hybrid Steel-CFRP subsea pipelines

Accurate prediction of the propagation pressure (PP) in hybrid steel-CFRP pipe systems presents a substantial challenge due to intricate interactions and complex collapse failure modes. An efficient FE-based algorithm is programmed using ANSYS to numerically estimate the PP of hybrid steel-CFRP pipe, subjected to external pressure. This study employs a machine learning (ML) framework, addressing the inherent complexity with a three-phase approach: Parameter Design, Buckle Propagation Analysis, and ML Model Development. The dataset, encompassing about two thousand observations with four key features, undergoes k-fold cross-validation and min-max normalization for robust ML performance. Five ML models—Random Forest (RF), K-Nearest Neighbors (KNN), Genetic Programming (GP), Multi-layer Perceptron (MLP), and Support Vector Machine (SVM)—are developed and evaluated. The results revealed a significant influence of Ds/ts, a three-phase relationship with ts/tc, and a substantial decrease in PPh/PPs with increasing σys/σuc, predominantly exhibiting U-shaped or dog-bone failure modes in different scenarios. Proven that GP, KNN, and RF are the superior performers, ranking ahead of SVM with Gaussian Kernel (SVM-GK), MLP, and SVM with Linear Kernel (SVM-LK). Statistical metrics, Taylor Diagram analysis, and comparisons with FE results emphasize the effectiveness of GP, KNN, and RF. Additionally, normality tests and feature importance analysis provide nuanced insights.

Investigation on the flame and pressure behaviors of vented hydrogen-air deflagration from a duct-connected vessel: Effects of venting diameter and static activation pressure

To investigate the effect of venting diameter and static activation pressure on the explosion venting behavior of hydrogen-air mixtures, tests were performed utilizing the explosion venting test platform. The pressure and flame propagation characteristics under different venting diameters (30–70 mm) and pressures (0.1–0.4 MPa) were experimentally examined, and numerical calculation was employed to analyze the explosion venting characteristics of hydrogen at a stoichiometric ratio. Compared to fuel-lean and fuel-rich hydrogen conditions, the first peak pressure within the container is maximal under the hydrogen-air mixtures at a stoichiometric ratio. Under stoichiometric and fuel-rich hydrogen-air mixtures, pressure peak structures inside the container are both bimodal. When D = 30 mm, as Pstat is increased from 0.1 to 0.2 MPa, Pmax11 increases. However, when Pstat exceeds 0.2 MPa, with the increase of Pstat, Pmax11 remains at the level of 0.69 MPa, reaching the “venting bottleneck”. The discovery of this phenomenon is crucial for the research and development of the venting device for hydrogen storage equipment. Numerical simulations indicate the formation of the second peak pressure inside the container is primarily attributed to the intense obstruction of venting by secondary explosions within the duct.

Genomic diversity and nutritional analysis of multi-drug resistant extended spectrum β-lactamase Producing-Klebsiella pneumoniae genes isolated from mastitic cattle milk in district peshawar, Pakistan

The increasing incidence of resistance extended spectrum-beta lactamase (ESBL) producing Klebsiella pneumonia become worldwide issue. The current study aimed to determine the genomic diversity of ESBL-producing K. pneumoniae in milk samples collected from cows with mastitis as well as their antibiotic sensitivity profiles and genetic identification in Peshawar, Pakistan. The california mastitis test (CMT) was initially used to verify the presence for mastitis in 700 collected milk samples. The molecular identification of the 16SrRNA gene confirmed 120/700 (17.14 %) propagation of K. pneumonia. Out of these isolates MDR ESBL-producing isolates were 60/120 (50 %). The lactose were found (M = 3.96 ± 0.28, SD = 2.19), followed by fats (M = 3.12 ± 0.11, SD = 0.90), protein (M = 5.97 ± 0.24, SD = 1.84), sodium (M = 55.74 ± 2.07, SD = 15.81), potassium (M = 138.5 ± 1.53, SD = 11.71), chloride (M = 0.74 ± 0.03, SD = 0.24), calcium (M = 10.27 ± 0.31, SD = 2.42), and chlorine (M = 2.80 ± 0.22, SD = 1.70), respectively. Amikacin (80 %), ceftazidime (71 %), and tetracycline (71 %) were shown to be the most effective antimicrobials against all of the isolates. The occurrence of the blaSHV gene was observed at 56.00 % whereas the blaTEM gene and blaCTX-M gene were 36.00 %, and 30.00 %. The distribution of blaCTX-M subgroup genes was followed by blaCTX-M-1 (38.00 %), blaCTX-M-9 (22.20 %), and blaCTX-M-15 (61.10 %). Co-occurrence of blaCTX-M+ blaSHV was (15.00 %), blaCTX-M+ blaTEM were (6.60 %), and blaSHV + blaTEM were (10.00 %), respectively. The inappropriate, prolonged and common use of antibiotics may apply selective pressure for propagation and the occurrence of resistant isolates.

Vibration Characteristics of Liquid-Filled Pipes Under Different Levels of Submergence

Based on the acousto-solid coupling theory, the vibroacoustic radiation characteristics of the liquid-filled pipeline are studied under different submergence depths, and the changes of sound pressure level of pipeline are analyzed under different submergence depths of the flow transfer pipeline. The vibration characteristics of liquid-filled pipes with different submergence degrees were numerically analyzed from the pressure-acoustic domain and the solid mechanics domain, and the two-way coupled data exchange was realized by using acoustic-structural boundary multi-physical field function. The sound pressure level variation curves of the liquid-filled pipes were calculated for different submergence depths under the simultaneous action of internal and external flow fields, respectively. The results show that when the pipe is submerged in the lower and middle positions of the center of the circle, the sound pressure fluctuations of the pipe radiating outward are more consistent, and when submerged in the upper half, the sound pressure concentration phenomenon occurs in the lower and middle regions outside the pipe. When the free boundary outside the pipe is subjected to the boundary load, the pipe submerged in the lower position of the center of the circle is most obviously affected by the load. The tube submerged in the upper and lower positions of the center of the tube will produce two-way, increasing the form of sound pressure propagation in the tube towards the upper and lower sides, these findings can provide a certain reference for the study of pipe vibroacoustics. Therefore, research on the acoustic radiation properties of liquid-filled pipelines under various submergence depths is of great theoretical significance and engineering application value. This information can be applied widely in the fields of anti-fatigue design, fatigue damage analysis, and safety assessment of oil and gas pipeline structures, providing strong scientific support to ensure their safe and reliable service.

Buckle propagation failure of subsea pipelines; experimental, analytical, and numerical simulations

This research program investigates buckle propagation in subsea pipeline systems, The study aims to understand and predict propagation pressure (PP ), essential for ensuring the structural integrity and safe operation of these pipelines, hypothesizing that incorporating strain hardening effects into the strain energy approach can significantly enhance the prediction of propagation pressure (PP ) and that geometric parameters, particularly the diameter-to-thickness (D/t) ratio, play a major role in PP prediction. Accurate PP prediction is essential for ensuring the structural integrity and safe operation of these pipelines. The investigation is conducted through analytical, experimental, numerical, and machine learning approaches. A new analytical solution for PP is proposed, incorporating strain hardening effects using a strain energy approach. Experimental tests conducted using a hyperbaric chamber cover a wide range of pipeline configurations and materials, including steel, aluminum, and stainless steel. Complementing experimental data, numerical simulations using finite element methods facilitate parametric dependence analysis and the visualization of results through 3D charts. More than 600 FE models were simulated to investigate the influence of geometric and material parameters on PP . The findings from both experimental and numerical analyses indicated that the geometric and material properties have a significant impact on PP , specifically, the diameter-to-thickness (D/t) ratio, yield stress (σy ), and tangent modulus (E′). Furthermore, Machine Learning (ML) techniques have been used to predict the PP value and have concluded that the Random Forest (RF) technique outperformed the K-Nearest Neighbors (KNN), and Multi-layer Perceptron (MLP) neural network techniques. Overall, this study concludes that analytical, numerical, and machine learning approaches offer valuable insights into buckle propagation in subsea pipelines, contributing to improved safety and reliability in offshore oil and gas operations.

A Semianalytical Model for Advanced Description of Pressure Drop Funnel during Coalbed Methane Production.

Advanced description of pressure drop funnel is crucial in coalbed methane (CBM) production because of dewatering and depressurization methods. Improving the precision of the pressure drop funnel description facilitates obtaining the actual production status and productivity potential, both pivotal for responsible development plans. The study presents a semianalytical model that integrates pressure profiles and material balance equations, incorporating inner and outer boundary conditions, and dynamic reservoir characteristics. The pressure propagation characteristics in undersaturated coal reservoirs are described during the production life of CBM wells, and the model is validated using two wells with different production characteristics. The results indicate that the effect of water saturation on the expansion of the drainage radius surpasses that of the desorption radius, demonstrating a more precise prediction of the production boundary when dynamic water saturation is considered. Additionally, a rapid drop rate of bottomhole flowing pressure triggers simultaneous propagation of the drainage and desorption radii, resulting in a smaller production boundary and fewer well-controlled resources. Conversely, an appropriate production strategy results in a larger drainage radius and lower boundary pressure before massive gas desorption, thereby facilitating efficient propagation of the pressure drop funnel. Moreover, the pressure drop funnel characterized by the model can compute the dynamic CBM resources and recovery efficiency of a single well, providing a valuable basis for assessing productivity potential. In summary, this model offers a time-saving and practical tool for describing the dynamic pressure drop funnel in various CBM production stages and promoting efficient development for undersaturated CBM reservoirs.

Numerical study on the stimulation effect of boundary sealing and hot water injection in marine challenging gas hydrate extraction

This study proposed a novel development mode combining boundary sealing and hot water injection to address the challenges of gas leakage, limited reservoir sensible heat, boundary water intrusion, and low productivity faced by challenging hydrate extraction, and the stimulation effect was numerically investigated with Shenhu hydrates as the geological background. The results showed that lower boundary permeability facilitated pressure propagation and achieved volumetric dissociation of hydrates, whereas insufficient formation energy resulted in substantial gas retention. Hot water injection was effective for stimulation, but open boundaries could not maintain the high injection pressure, leading to massive hot water losses and gas escapes. However, their combination achieved a synergistic stimulation like “1 + 1 > 2” because a piston water drive similar to secondary recovery in oil and gas development was formed. Relative to three-spot well patterns, the five-spot shortened the extraction cycle by 680 days and enhanced the gas-to-water ratio by 17%. Increasing injection pressure enhanced water yield more significantly while the improvement of gas yield was more significant by increasing hot water temperature. Overall, high-pressure and high-temperature injection was suggested for gas enhancement and water control. These findings provide important guidance for advancing the commercial development of challenging hydrates.

From Pre‐Darcy Flow to Darcy Flow in Porous Media: A Simple Unified Model

AbstractExtensive experiments have demonstrated that fluid flow in low‐permeability media deviates from Darcy's law at low pressure gradients, which is called pre‐Darcy flow. Although numerous pre‐Darcy flow models have been proposed, these models generally contain one or more empirical parameters with no clear physical meaning. In this paper, we present a simple unified model to describe pre‐Darcy flow in porous media by introducing the concept of loss permeability. The physical meaning of the loss permeability parameter and its relationship to permeability are analyzed. Based on the statistics of the loss permeability parameter results of 24 core samples, we found that there is a good positive correlation between the loss permeability parameter and the absolute permeability. A smaller loss permeability indicates a stronger fluid‐solid interaction and a stronger nonlinearity between the flow velocity and the pressure gradient. Taking a one‐dimensional linear unsteady flow of a slightly compressible fluid in a homogeneous porous medium as an example, we solve the pressure diffusion equation based on the proposed model using a finite difference method. Our results demonstrate that the rate of pressure propagation for pre‐Darcy flow is slower than that for Darcy flow for the entire observation period, which corrects previous conclusions. This study is highly important for improving the understanding of fluid flow in low‐permeability media.