Pressure Propagation Characteristics Research Articles

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.

Experimental and simulation study of the pulsation characteristics of underwater semiclosed initial intermittent bubbles

Bubbles at the cylinder outlet are a typical feature of the underwater ejection process. The interaction between gas and water is turbulent and results in an unstable bubble interface. In this work, experimental and numerical methods were used to determine the evolution of underwater semiclosed initial intermittent bubbles and their pressure propagation characteristics. Direct measurements of the interfacial migration behaviour of the bubbles were made using a high-speed video camera, and the variation in the pressure law in the flow field was obtained using a pressure sensor. The bubble pulsation characteristics were also analysed in conjunction with numerical simulations. The results show that the bubble at the mouth of the cylinder underwent the process of expansion, contraction, necking, and fracture under the coupled effect of the inertial motion of the liquid phase and the pressure inside the bubble and exhibited obvious periodic evolution characteristics. The flow instability driven by the velocity and density gradient gradually destabilised the bubble boundary, resulting in the phenomenon of necking of the gas cluster. Simulations were carried out for different diaphragm opening states to investigate the effects of the diaphragm cracking state on bubble evolution and pressure fluctuations.

Experimental Study on Gas–Liquid Two-Phase Flow Upstream and Downstream of U-Bends

In this study, the influence of U-bends on the flow and pressure propagation characteristics of a gas–liquid two-phase flow in upstream and downstream straight pipes was investigated experimentally. The superficial velocities of the gas and liquid are 0.18–25.11 m/s and 0.20–1.98 m/s, respectively, covering plug flow, slug flow, and annular flow. The experiments were conducted in U-tubes with inner diameters of 9 mm and 12 mm and with a curvature ratio of 8.33. The U-tube was C-shaped. The pressure fluctuations at the axial measurement points of the straight tubes were measured. Flow images of the distal straight tubes and U-bends were obtained. The disturbance from U-bends in the two-phase flow in the vicinity of the bend is very obvious. The perturbation from U-bends in the fluid in the adjacent straight tubes is highly related to the incoming flow pattern. The slug flow has the most significant influence, whereas the effects of the plug and annular flows are small. Fundamentally, it mainly depends on the weight relationship between the gravity, centrifugal force, and inertial force of the gas–liquid two-phase fluid. The pressure fluctuation propagates in the form of a wave with the same dominant frequency in the straight pipes of the U-tube. The pressure pulsation energy in the straight tubes strengthens with decreasing distance from the 180° return bend. In addition, the pressure fluctuation energy downstream of the U-bend is greater than that upstream of the return bend.

Temperature and pressure propagation characteristics in multi-media interfaces of PVDF pressure sensor near underwater explosion source

In this paper, based on the self-made PVDF pressure sensor, the underwater explosion test of the emulsion explosive was performed to verify the measurement accuracy of the self-made PVDF pressure sensor and the feasibility of the pressure measurement near the explosive source. Then the single column emulsion explosive and gram-grade Al/PTFE underwater explosion experiment and numerical simulation were carried out, and the error between the experimental and numerical simulation results is small (The difference between the pressure peaks obtained from the emulsion explosive experiment and numerical simulation is about 25.07 MPa and the pressure decay trend is close; the peak difference in lane 1 obtained by Al/PTFE experiment and simulation is about 23 MPa, the second peak difference is about 0.8 MPa, the pressure decay trend after the second peak is close, and the shock wave arrival moment in experiment lags the numerical simulation by about 30μs), which verifies the reliability of the simulation model. Meanwhile, the numerical simulation of explosion at a depth of 10m below sea level was performed, the evolutionary law of the sensor and water pressure at 1–10 times the charge diameter is expounded, the variable rule of temperature during sensor response period is analyzed. The numerical simulation results show that the time-history curve of pressure includes two stages: bubble microjet and shock wave propagation, which the bubble microjet pressure can reach 10 GPa, and the sensor structure and shock wave pressure test will not be affected within the response period. The time history curves of shock wave pressure in experiments are basically the same by comparing with the simulation results of underwater pressure at the same position, and impact temperature rise will affect the measurement accuracy of PVDF film, but the lasting time of heat conduction in the PVDF sensor is longer than the response period of impact pressure, therefore the influence of heat conduction on the test accuracy can be ignored.

Experimental study on ignition and blowout characteristics of dual combined flame stabilizers in scramjet

The ignition and blowout characteristics have a significant impact on the performance and operating limit of the scramjet. In this study, direct-connected ground tests of a typical scramjet combustor have been conducted to simulate the high-altitude flight condition of Mach 6. The incoming air has a total temperature of 1689 K and a dynamic pressure of 30 kPa. The ignition and blowout characteristics of the dual strut/cavity combined flame stabilizers in the scramjet are obtained. The immediate response of pressure at key positions is used to analyze the forward propagation characteristics of pressure during the ignition process and the pressure variation during the flame blowout process. The flame distribution and temperature variation during the ignition and blowout processes are obtained by high-speed photography, OH⁎ spontaneous radiation photography, spectrometer and multispectral imaging equipment. Results indicate that the process from local ignition to global ignition successfully has durations lasting for hundreds of milliseconds, comprising four stages with two pressure lift stages. The flame diffusing forward and upstream cavity igniting successfully are the main processes, constituting 60% and 30% of the duration, respectively. During the ignition process, the pressure response time of the two-stage cavity differs by several milliseconds. And the flame is transmitted forward to the upstream cavity through combustor walls. As the ignition process progresses under high equivalent ratio (ER) conditions, flame stabilization mode shifts from stabilizing flame in the recirculation zone of the cavity to stabilizing flame in the shear layer of the strut. Upon completion of global ignition, the flame temperature at the shear layer of the cavity upstream exceeds 2700 K, but decreases to 2125 K as the core reaction zone is shifted from the top of the strut to the tail and bottom of the cavity when the ER decreases. Two pressure drops occur during the flame blowout process, and the critical ER of the global blowout is approximately 0.33. The primary shear layer flame is blown out during the first pressure drop, and the intensity of the cavity flame decreases. Finally, the second pressure drop occurs as the flame in the cavity moves downstream and extinguishes.

Effects of residual resistance factor in the mobility control of the polymer flooding

AbstractTo broaden the application of the polymer flooding in complex reservoirs, the residual resistance factor (RRF) is sought to make up for the limitations of high‐viscosity polymer flooding. First, the polymer solution rheology, adsorption and retention behaviors were mathematically characterized, and subsequently substituted into the equation of motion of the aqueous phase to build a mathematical model of the polymer flooding percolation. Second, based on the built numerical model, the formation process of seepage resistance and pressure propagation characteristics of polymers with a high RRF in the porous media were investigated. Lastly, the effects arising from viscosity and RRF on the flow control of the polymer flooding were explored by comparing the injection capacity, crude oil utilization and profile control capacity of different permeable formations at different development stages. As revealed by the results, the RRF was found to be more favorable than the “viscosity” parameter in improving the injection capacity at the polymer flooding stage. Moreover, it was found to slow down the water‐cut increase at the subsequent water flooding stage and reduce the difference between the oil recovery rate and injection pressure at different stages. Furthermore, the viscosity was primarily adopted to facilitate oil recovery of medium and high‐permeability formations by increasing the oil replacement efficiency, while the RRF was primarily dependent on the regulation of interlayer water absorption differences, thus mobilizing the remaining oil under the low‐permeability formations.

The Influence of Various Structure Surface Boundary Conditions on Pressure Characteristics of Underwater Explosion

The shock wave of the underwater explosion can cause severe damage to the ship structure. The propagation characteristics of shock waves near the structure surface are complex, involving lots of complex phenomena such as reflection, transmission, diffraction, and cavitation. However, different structure surface boundaries have a significant effect on the propagation characteristics of pressure. This paper focuses on investigating the behavior of shock wave propagation and cavitation from underwater explosions near various structure surfaces. A coupled Runge–Kutta discontinuous Galerkin (RKDG) and finite element method (FEM) is utilized to solve the problem of the complex waves of fluids and structure dynamic response, considering the fluid compressibility. The level set (LS) method and the ghost fluid (GF) method are combined to capture the moving interface and deal with the stability of the coupling between the shock wave and structure surface. Besides, a cut-off cavitation model is introduced to the RKDG method. The validation of the numerical calculation model is discussed by comparing it with the known solution to verify the numerical solutions. Then, crucial kinds of structure surface boundary conditions include shallow-water single layer elasticity plate, double-layer crevasse elasticity plate, single layer curved elasticity plate, and double-layer curved elasticity plates are analyzed and discussed. The results and analysis can provide references for underwater explosion pressure characteristics, the impacting response of different boundary structures, and designing structures.

EXPLOSION IMPACT SIMULATION METHODS FOR PARALLEL PIPELINE LAYING IN THE SAME DITCH AFTER GAS LEAKAGE

The explosion impact after gas pipeline leakage can be simulated by Arbitrary Lagrange-Euler Algorithm (ALE), Blasting Cavity Theory (BC) and Smooth Particle Hydrodynamics - Finite Element Method (SPH-FEM), each method has its own characteristic. Using the experimental data of Defense Research Establishment Suffield of Canada, it is found that both ALE and SPH can describe the propagation characteristics of detonation waves in a soil well, and SPH-FEM can accurately reflect the compression, cracking and deformation of soil after an explosion. For parallel buried gas pipeline laying in one trench, three pipe-soil explosion models were design based on the mentioned three approaches above, and the same response of pipeline were obtained under the same operating conditions. However, the soil bulging deformation in BC was greater than that in SPH-FEM, the result of the former was more conservative. Moreover, the BC is dominated by the blasting cavity radius, i.e. it cannot be modeled when the radius is larger than the depth of an equivalent explosion. According to the pressure time history curve of the soil unit under the action of detonation wave, the pressure propagation characteristics were analyzed. Finally, the stress and deformation of the attack surface, top surface, back surface and bottom surface of a pipe were analyzed. The research evaluated the advantages and disadvantages of the existing explosion simulation approaches, which can provide technical references for the reliability analysis and risk prevention and control of parallel gas pipelines under extreme disasters.

Experimental Investigation of Oil Recovery from Tight Sandstone Oil Reservoirs by Pressure Depletion

Oil production by natural energy of the reservoir is usually the first choice for oil reservoir development. Conversely, to effectively develop tight oil reservoir is challenging due to its ultra-low formation permeability. A novel platform for experimental investigation of oil recovery from tight sandstone oil reservoirs by pressure depletion has been proposed in this paper. A series of experiments were conducted to evaluate the effects of pressure depletion degree, pressure depletion rate, reservoir temperature, overburden pressure, formation pressure coefficient and crude oil properties on oil recovery by reservoir pressure depletion. In addition, the characteristics of pressure propagation during the reservoir depletion process were monitored and studied. The experimental results showed that oil recovery factor positively correlated with pressure depletion degree when reservoir pressure was above the bubble point pressure. Moreover, equal pressure depletion degree led to the same oil recovery factor regardless of different pressure depletion rate. However, it was noticed that faster pressure drop resulted in a higher oil recovery rate. For oil reservoir without dissolved gas (dead oil), oil recovery was 2–3% due to the limited reservoir natural energy. In contrast, depletion from live oil reservoir resulted in an increased recovery rate ranging from 11% to 18% due to the presence of dissolved gas. This is attributed to the fact that when reservoir pressure drops below the bubble point pressure, the dissolved gas expands and pushes the oil out of the rock pore spaces which significantly improves the oil recovery. From the pressure propagation curve, the reason for improved oil recovery is that when the reservoir pressure is lower than the bubble point pressure, the dissolved gas constantly separates and provides additional pressure gradient to displace oil. The present study will help engineers to have a better understanding of the drive mechanisms and influencing factors that affect development of tight oil reservoirs, especially for predicting oil recovery by reservoir pressure depletion.

A novel method for formation evaluation of undersaturated coalbed methane reservoirs using dewatering data

Accurate acquisition of reservoir properties can provide an important basis for the evaluation of coalbed methane (CBM) reservoirs. To date, there are many methods that can be utilized to estimate reservoir properties. Analyzing production data by productivity equation has attracted attention of many researchers due to its simple and convenient characteristics. However, most of the productivity analysis methods are established for non-fractured wells in conventional sandstone gas reservoirs, and have restrictive requirements on boundary conditions, that is, the dominant flow-regime is boundary-dominated flow. Some CBM reservoirs have extremely low porosity and permeability, which need hydraulic fracturing to achieve greater yields. Furthermore, the reservoir fluid flow gradually changes from single-phase water flow to gas-water two-phase flow during the production process, which can increase seepage resistance and change the form of pressure propagation. Hence, there are some limitations for conventional method of productivity analysis when applying to CBM reservoirs, and the prediction results tend to have greater deviation.In this paper, a new method for evaluating formation properties of under-saturated CBM reservoirs is proposed. The method takes into account the characteristics of pressure propagation and only requires production data in single-phase water flow stage. In addition, some CBM wells are not appropriately controlled during dewatering process resulting in stress sensitive and permeability change. For this kind of wells, this paper also puts forward the relevant method to estimate the permeability change coefficient of reservoirs. The evaluation method is applicable to reservoirs which have long single-phase water flow period without well interference during the process and the pressure does not propagate to the flow boundary in dewatering stage. Hence, the greatest advantage of the proposed method is that the reservoir properties can be easily obtained only by using the water production and well bottom hole flowing pressure data at the early production stage of CBM wells.The proposed method is verified by numerical simulation data and production data calculated by analytical method, which show that this novel method is more appropriate to apply to CBM reservoirs. It is convenient and reliable in providing basic parameters for reservoir evaluation and production prediction.

The gas-water two phase flow behavior in low-permeability CBM reservoirs with multiple mechanisms coupling

Although considerable advances have been achieved in recent years, it is still challenging to describe gas-water two phase flow behavior in low-permeability CBM (Coalbed methane) reservoirs. The pressure propagation characteristics at different production stages are generally overlooked, which play a crucial role to affect overall productivity and are required to be incorporated. In this work, a completely new production prediction model is established. Firstly, to consider pressure and saturation gradients, the pressure-saturation relationship is developed after rigorous derivation process in terms of partial differential equations for gas-water two phase flow. Subsequently, the gas/water phase productivity equations are modified on the basis of the key relationship. Secondly, according to the relationship between formation pressure and critical desorption pressure, the whole coal seam is divided into desorption area and without-desorption area. Moreover, pressure distribution features in desorption area and that in without-desorption area are characterized. Finally, an efficient iterative algorithm is present to predict the production performance and quantify the expansion regularities of drainage and desorption area at different production stages. The proposed model is utilized to shed light on the optimization of production strategy as well. Some meaningful conclusions and practical insights are drawn.

A semi-analytical model for drainage and desorption area expansion during coal-bed methane production

In coal-bed methane (CBM) field development plan, more attention is paid to production forecasting, well spacing optimization, pressure transient analysis and adsorption/desorption mechanism within coal matrix. Few studies were carried out to investigate the expansion of drainage and desorption area based on the characteristics of pressure propagation in CBM reservoir. Moreover, the production rate and bottom-hole pressure (BHP) are usually variable, while the production system in current analytical models are either at constant production rate or constant BHP. When optimizing the production system of CBM well, the knowledge of expansion principle of drainage and desorption area can help obtain the critical time of interference and its intensity, which are both key factors for efficient development of CBM reservoirs.In this paper, a comprehensive method for drainage and desorption area expansion during coal-bed methane production is proposed, in which the variable rate and BHP in different production stages and saturation distribution are considered. The coal seam is divided into two areas, namely desorption and without-desorption area, and the production life is divided into five stages. The pressure profiles at different production stages are detailed investigated utilizing diffusivity equation which is solved by the continuous succession of steady states. By assuming the desorption area with low water-gas ratio and without-desorption area with high water-gas ratio, the pressure-squared approach is applied in desorption area and pressure approach is employed in without-desorption area. Finally, a model for predicting drainage and desorption area is developed by generating pressure profile and material balance equation.The proposed semi-analytical model is verified by numerical simulation with excellent agreement with the simulation data. Results show that the drainage area expands much faster at early production stage than that at late stage when desorption area starts expanding in the coal-bed reservoir. In addition, the production system of CBM well is found to play a significant role in the expansion characteristics of desorption area. Considering these characteristics of CBM, we shed light on the production system optimization in different production stages and apply the developed production system to a CBM well in Qinshui field, China. In summary, this method only requires BHP, gas and water production, and turns out to be simple, reliable and powerful in application.

Dewatering rate optimization for coal-bed methane well based on the characteristics of pressure propagation

In coal-bed methane (CBM) reservoirs, gas is mainly stored in matrix as adsorbed gas and the cleats are commonly saturated with water. To produce the adsorbed gas, the cleat pressure should be reduced to critical desorption pressure by dewatering first. But how to dewater more efficiently is a difficult issue. Apparently low dewatering rate is uneconomical due to excessive development times required. But from the field experiences, high dewatering rate will bring more problems such as coal break, stress sensitivity and two-phase flow in earliest stage, which will reduce the productivity, or sometimes make the well abandoned. Literatures have studied much about the effect of coal break and stress sensitivity. However, there is no discussion about the relationship between two-phase flow and dewatering rate. High dewatering rate is companied with high pressure drawdown which will cause gas desorption near wellbore area and simultaneously cause two-phase flow. Two-phase flow has significant negative effect on pressure propagation, which controls investigation distance or drainage area in the early stage, and therefore affects the overall productivity. Since the purpose of dewatering is to maximize the drainage area and maximize the depressurization for whole reservoir, the dewatering rate should be controlled to ensure well-bottom hole flowing pressure (BHFP) is larger than critical desorption pressure in order to avoid the occurrence of two-phase flow in the dewatering stage. Based on this principle, a procedure for optimal dewatering rate is presented and a mathematic model is established. It is shown that initial pressure, critical desorption pressure, permeability, porosity, and fracture half-length play significant roles in dewatering rate determination. This method is easy, and has applied in CBM development region of Han-Cheng, China.

Pressure Propagation Characteristics of Solid Waste Backfilling Material During Compaction and Its Applications In Situ

Solid waste backfilling techniques are widely employed in the coal mining industry and the pressure propagation characteristics of solid waste backfilling materials are important considerations in evaluating a techniques overall effectiveness. This paper presents an experiment that evaluates the pressure propagation characteristics of backfilling materials of different particle sizes. The results show that backfilling materials with larger particle sizes have higher pressure propagation properties, while backfilling materials with smaller particle sizes are less capable of transferring pressure. Analysis indicates that there is an exponential relationship between influence factor (I) and vertical distance (Z/D), where Z/D is the depth below the center of the loading platen divided by the loading platen diameter. There is also a GaussAmp relationship between I and horizontal displacement (L/R), where L/R is the abscissa divided by the loading platen radius. The results indicate that more than 70 % of loading pressure is dissipated in the Z/D range of 0–2.75 and virtually all pressure is dissipated within the L/R range of 0–5. The results were applied in the Wugou coal mine to evaluate the effectiveness of backfilling compaction methods and the evaluate results show the backfilling compaction mechanism can work effectively.

Study of Pressure Propagation Characteristics to Determine Stress Sensitivity of Low-Permeability Gas Reservoir

The permeability sensitivity of formation is one of the primary causes of damage to low-permeability reservoir. Experiments were conducted on change in pressure propagation characteristics with reference to matrix rock (core) samples taken from a low-permeability reservoir in Changqing oilfield, China. Based on the experimental results, pressure propagation values were obtained using CMG numerical simulation software that takes account of permeability sensitivity of the formation. The experimental and simulation results indicate that gas well productivity in lowpermeability gas reservoir cannot be increased significantly by increasing pressure difference in low-permeability gas reservoir. With increase of permeability sensitivity of formation stressed state the pressure propagation coefficient decreases, pressure propagation delay increases, and steady gas production time becomes shorter with higher gas flow rate.

Relative Time scale analysis for pressure propagation during ignition process of a scramjet

The supersonic combustion ramjet (scramjet) engine is expected to become the most efficient air breathing propulsion system in the hypersonic flight regime. The behavior of wall pressures propagation was examined using a direct-connect model scramjet experiment along with high-frequency pressure measurements. High-frequency pressure transducers are employed to record the history of pressure response during ignition process. A first order plus dead time (FOPDT) model is employed to model the S-shape step response curve. The time scale distributions of pressure propagation are reported in this paper. The characteristics of pressure propagation are closely related to the combustion mode of the scramjet.

Mechanism of pressure propagation and weakly compressible homogeneous and heterogeneous thixotropic gel breakage to study flow restart

Pressure propagation in the soft gels is commonly considered either in terms of acoustic waves or gel degradation. However, in a complete description, acoustic, viscous and gel degradation effects should all be considered simultaneously. Here a creep model is discussed with a suitable time scale. The model predicts a specific mechanism of pressure propagation, indicating that gel behaves like a creeping fluid rather than a fluid shearing only above a critical yield stress. The characteristics of pressure propagation can be used to distinguish between creeping and yield stress fluid. The presented results provide a new physical interpretation of recent experimental data. It is also shown that heterogeneity in the gel can cause center-core cohesive failure, as opposed to the near-wall failure which occurs in homogeneous gels.

Accuracy of the wave equation in predicting arterial pulse propagation

This paper investigates the effect of the various terms in the one-dimensional acoustic wave equation on the pulse characteristics within the aorta. To mimic the physiological nature of the systemic arteries, the aorta is modelled as an elastic conical tube. The frequency spectrum is used to study the effect of different terms in this equation on the pressure ratio between the aortic root at the heart exit and the iliac bifurcation. For validation, the effective reflection distance calculated using this model is within 7% error of clinical observations, suggesting that the model is able to mimic physiological pressure propagation with a high degree of accuracy and can therefore be used to generate and test hypotheses. This work demonstrates that: (i) tapering in the aorta lumen radius causes supplementary amplification of the pressure pulses in the system and increases the propagation velocity; however, tapering in the aorta wall thickness generates opposite effects, (ii) increasing the wall stiffness causes a change in the natural frequency of the system and increases the propagation velocity, and (iii) inclusion of either the advective momentum correction term or the viscosity term insignificantly affects the pressure ratio. The last observation suggests that the flow pattern does not influence the pressure propagation characteristics.

PREDICTION OF PROPERTIES OF MARINE SAND BY IN-SITU MEASUREMENT OF WAVE INDUCE PORE PRESSURE

The purpose of this paper is to predict the physical and mechanical properties of deposits near the surface of the seabed by in-situ measurements of the wave-induced pore pressure. First, the wave-induced pressure both at the surface of the seabed and inside the seabed are examined by frequency analysis, to clarify the propagation characteristics of pressure in the seabed. Secondly, a theoretical equation which gives the relationship between pore pressure fluctuation and wave pressure fluctuation is proposed. Thirdly, the porosity of the seabed is predicted by the propagating characteristics of the pore pressure within the seabed based on the results of both the model tests by wave tank and the field measurements of the wave-induced pore pressure. Finally, by fitting the theoretical equation to the spectral ratio of the in-situ measured pore pressure fluctuation to wave pressure fluctuation, the bulk modulus of the seabed and the degree of saturation are predicted.

高油圧パイプケーブルの油圧伝搬特性

高油圧パイプケーブルの油圧伝搬特性