Gas Gathering Research Articles

Experimental investigation of maldistribution characteristics of gas‐liquid two-phase flow in a horizontal pipeline

In the flow distribution of oil and gas gathering and transportation system, the flow pattern, inertia force, gravity, and other factors will lead to uneven flow distribution of each outlet pipe, which will seriously affect the economy and safety of the gathering and transportation system. Therefore, it is of great significance to analyze the characteristics of gas–liquid two-phase flow in horizontal pipelines. For this reason, an experimental device for maldistribution control of gas–liquid two-phase flow is developed in this article. In order to solve the problem of flow maldistribution in gas–liquid two-phase flow pipe, the test experiments of maldistribution control under the conditions of three flow patterns (stratified flow, slug flow, and annular flow) are carried out. Through experiments, we revealed the control law of flow pattern to liquid maldistribution and gas maldistribution with or without flute pipes and formed the maldistribution control scheme of gas–liquid two-phase flow in the horizontal pipeline. It is found that it is more beneficial to the control of average liquid maldistribution degree under the condition of slug flow pattern in horizontal manifold without flute pipe, and it is more beneficial to the control of average gas maldistribution degree under the condition of annular flow pattern without flute pipe. Without the function of the flute pipe and in the annular flow pattern, it is beneficial to the control of average maldistribution degree of gas–liquid two-phase flow. The findings of this research can be used as a reference for the field maldistribution control of oil and gas gathering and transportation systems.

SIMULATION OF NATURAL GAS INFRASTRUCTURE FOR CNG AND LPG RECOVERY - A CASE STUDY

This research is a case study focused at presenting a framework upon which design methods can be followed to achieve an effective natural gas gathering, processing and fractionation process. It also reveals the incentive for flare reduction while encouraging domestic consumption of Liquefied Petroleum Gas (LPG) and the use of Compressed Natural Gas (CNG) for electricity generation. The simulation of the plant was done using ASPEN HYSYS version 11.0 with the Peng Robinson equation of state as the thermodynamic fluid package. The gas was gathered from two flow stations 0.8km and 6.4km respectively from the proposed processing field. Since the gases from the region under study is a sweet with negligible sulphur content there was no need for a sweetening process. The Tri-Ethylene Glycol (TEG) was used for the gas dehydration, then fractionators were simulated to produce LPG and CNG of high purity. Results from the HYSYS report shows good energy and mass balance as well as efficient gas flow throughout the processing cycle. The resulting volume of CNG and LPG is substantial to power several households and supply them with cooking gas respectively. Keywords: Natural Gas Simulation, Liquefied Petroleum Gas, Compressed Natural Gas, Computer aided Design.

Development and Application of Gas Production Measurement System of Coal-Rock under Temperature-Pressure Coupling.

In this study, a measurement system for gas generation of coal-rock under temperature–pressure coupling was developed by adding gas extraction, collection, and flow-monitoring devices to the original stainless-steel liquid seepage pipeline of an MTS-815 rock triaxial testing machine, which can be used to study the production mechanism of coalbed methane in a real geological environment. The system has the functions of axial loading, confining pressure loading, continuous heating, gas gathering, etc., and has the advantages of good air tightness, high accuracy and stability, long-term loading and heating, and controllable single variables. The preliminary test for the gas production of anthracite in the Shaanxi Formation of the Qinshui Basin under temperature–pressure coupling was carried out by the developed test system. The results show that the test system can provide accurate and effective measurement means for the study of gas production by coal-rock deformation and is expected to provide effective help for the control and exploitation of coalbed methane.

Corrosion mechanism of X65 steel exposed to H2S/CO2 brine and H2S/CO2 vapor corrosion environments

Wet gas gathering and transportation in natural gas production has good economic benefits, but it also brings many risks. Due to the synergistic effect of corrosive gas and multi-phase flow in the wet gas pipeline, there are two corrosive environments, which leads to frequent accidents of pipeline corrosion failure. In this paper, the corrosion experiments of X65 steel in two environments (H2S/CO2 vapor; H2S/CO2-dissolved brine) were completed by a high-temperature and high-pressure reactor. Combined with SEM, EDS and XRD instruments, the morphology, elements and compounds of corrosion products were analyzed. The corrosion impact of temperature, flow rate, CO2 and H2S in both environments was determined. Finally, corrosion mechanism in two corrosion environments were established. When CO2 and H2S coexisted, both in two corrosive environments, the two gases were involved in the corrosion of X65 steel, and the corrosion products formed were FeCO3 and FeS in the liquid phase. The difference was that the corrosion product film in the gas phase was denser than that in the liquid phase and the corrosion rate in the gas phase was smaller than that in the liquid. There was a large amount of Cl− and high shear force brought by the flowing, the corrosion product film fell off and formed local corrosion. In the gas phase, due to the H2S and CO2 higher concentration, a dense corrosion product film rapidly formed in the droplets. In the two environments, the order of corrosion factors is PH2S ≫PCO2 Velocity > Temperature. But in the gas phase environment, H2S dominates in the gas phase more than in the liquid phase because it is more soluble in droplets.

Investigating the micro-turbulent corrosion mechanism of pipeline defects based on a combined experimental and simulation approach

The existence of pipeline defects in oil and gas gathering pipelines predisposed the pipeline to rupture under the synergistic effects of local micro–turbulence and electrochemical corrosion. Here, a combination of experimental and simulation methods was proposed to facilitate the investigation of CO2 corrosion and the mass transfer process in pipeline defects. The corrosion kinetic characteristics of the defect region were clarified by coupling wire beam microelectrode (WBE) and electrochemical impedance spectroscopy (EIS). Additionally, the effect of flow mass transfer on the corrosion of pipeline defects was investigated by using the existing mass transfer models and COMSOL Multiphysics simulations. The results showed that different locations of the pipeline defects exhibited different mass transfer behavior and corrosion variations. The mass transfer process at the bottom of the defect was lower than that in the upper and lower edge of the defect. Furthermore, the bottom of the defect behaved as an anode and corrodes more severely at low flow velocities. The enhanced mass transfer process led to more severe corrosion at the upper and lower edges of the defect at high flow velocities.

Characteristics of liquid loading with surfactant injection in hilly terrain pipeline

Surfactant injection technology has recently been proposed as an alternative to mechanical pigging for liquid unloading from the wellhead to the surface gas gathering system. This study aimed to verify the effectiveness of the technology by experimentally evaluating the liquid loading characteristics of gas–liquid flow with a surfactant at the undeveloped and developed flow positions of the uphill test section (10°) of a hilly terrain pipeline. The inner diameter and length of the uphill test section were 50.0 mm and 16.0 m, respectively. The liquid and gas working fluids were deionized water or 250 ppm sodium dodecyl sulfate (SDS) surfactant solution and air with the superficial velocities of 0.001 to 0.010 m/s and 2.0 to 14.0 m/s. The liquid volume fraction and liquid holdup were measured using the image-quick closing valve method and wire mesh sensor method, respectively, and the liquid holdup data were visualized using the MATLAB program and Tecplot software. Owing to the effect of the surfactant, the flow range of low liquid loading increased significantly with the flow regime transition from intermittent flow to segregated flow. Because of the complex interaction between the morphology of the slug body and the foam formation, the fluctuation range and peak of liquid holdup and the liquid volume fraction decreased significantly in the intermittent flow. The liquid holdup fluctuation range and liquid volume fraction decreased to nearly zero, and a foam layer was formed and climbed up along the pipe wall in the segregated flow. The results and analyses are beneficial for improving the surfactant injection scheme and establishing a prediction model.

Changes in shale gas produced water DOM during its early storage period: Molecular composition correlated with microbial functions

The environmental problem posed by shale gas wastewater has received considerable research attention. Researchers mostly focus on the technical aspect of terminal centralized treatment with little concern on the topic of early collection and on-site pretreatment of PW near gas gathering stations. In this study, the short-term fluctuations of the DOM molecular composition and the concurrent transformation of the microbial community and functions were carefully examined when the PW was temporarily stored in a simulated reservoir near gas wells. Ultra-high resolution mass spectrometry was used to determine the molecular structure of the DOM samples. The data showed that during the short-term storage of PW, strongly polarized and nonvolatile organic compounds developed a complex molecular structure, resulting in molecules that were more unsaturated and lower bioavailability. Microbial activity was responsible for the changes in organic matter composition that occurred in the later stages of the storage process, during which the amount of nitrogenous organic molecules increased. Network analysis offered vital information on microbial functions related to organic matter composition and the patterns of interaction between them. Organic molecule consumption and accumulation were intimately connected to the interactions between various bacteria the same as the consumption and accumulation of DOM molecules.

Analysis and investigation of the leakage failure on the shale gas gathering and transmission pipeline

There is an accident that a shale gas gathering and transportation pipeline suffer corrosion and leakage within less than 10 months of its operation, which is rare for pipelines to have corrosion faults in such a short time. In this paper, through a series of experiments such as macroscopic observation, wall thickness measurement, physical and chemical inspection, optical microscope (OM), scanning electron microscope (SEM) as well as energy dispersive spectrometry techniques (EDS), the failed pipeline was analyzed, and subsequently the water quality analysis and bacterial counts were performed on the gas field produced water in the transmission medium. Consequently, according to the experimental results and field investigation, the root cause was identified that the failure mode of seamless steel pipe was corrosion leakage caused by local corrosion. The main reason for corrosion and leakage is that the metal on the inner wall of the pipeline is first corroded by sulfate-reducing bacteria (SRB) in the transmission medium, and a layer of black corrosion biofilm is deposited at the bottom of the steel pipe. If the corrosion biofilm has defects such as damage, the exposed metal and black corrosion biofilm will form the electrode corrosion with large cathode and the small anode, which will accelerate the corrosion rate and eventually lead to rapid corrosion failure of steel pipe. For the purpose of avoiding similar accidents, suggestions to prevent such failures were proposed in this paper.

Mixed Potential Electrochemical Sensors – Ceramic Substrate and Electrolyte Effects on Sensor Response to Methane and Simulated Natural Gas

The US Environmental Protection Agency estimates emissions from US natural gas drilling and processing amounted to 197 million metric tons of CO2 equivalent in 2019.1 Research by Marchese et al. suggests that CH4 emissions could be up to three times higher.2 Current natural gas emissions detection methods consist mainly of active optical monitoring, typically with long path IR sensors.3 These monitoring methods capable of ppb level accuracy are expensive, fragile, and require accurately calibrated mirrors. Mixed potential electrochemical sensors (MPES) are robust, low-cost, and selective sensors, making them appropriate option for methane emission monitoring.4 Previously we have reported on a four electrode MPES with 3 mol% YSZ electrolyte fabricated with direct write 3D printing5, here we investigate substrate and electrode material effects on the sensor response.The response of a four electrode La0.87Sr0.13CrO3, Indium Tin Oxide (In2O3 90 wt%, SnO2 10 wt%), Au, Pt mixed potential electrochemical sensor to methane and simulated natural gas at operating temperatures of 450 – 600 °C was studied. Sensors were fabricated on substrates of yttria stabilized zirconia, ceria stabilized zirconia, and magnesia stabilized zirconia manufactured by direct write extrusion 3D printing of aqueous pastes. These materials are selected to maximize the mixed potential difference by better isolation of the sensing electrodes. Data is presented with a solid electrolyte of 3 mol % yttria stabilized zirconia, and various other solid ceramic electrolytes will be studied. The effect of sensor response with respect to the ionic conductivity of substrate material is studied. The sensor limit of detection for CH4, natural gas, CH4/NH3, and CH4/H2 mixes will be reported. We will also train artificial neural networks to quantify the concentration of CH4 and other subcomponents given a subset of signals taken from the sensors operated at different temperatures.AcknowledgementsThis project was supported by US Department of Energy Office of Fossil Energy and Carbon Management through award DE-FE0031864.References(1) US EPA, O. Estimates of Methane Emissions by Segment in the United States https://www.epa.gov/natural-gas-star-program/estimates-methane-emissions-segment-united-states (accessed 2021 -12 -13).(2) Marchese, A. J.; Vaughn, T. L.; Zimmerle, D. J.; Martinez, D. M.; Williams, L. L.; Robinson, A. L.; Mitchell, A. L.; Subramanian, R.; Tkacik, D. S.; Roscioli, J. R.; Herndon, S. C. Methane Emissions from United States Natural Gas Gathering and Processing. Environ. Sci. Technol. 2015, 49 (17), 10718–10727. https://doi.org/10.1021/acs.est.5b02275.(3) Aldhafeeri, T.; Tran, M.-K.; Vrolyk, R.; Pope, M.; Fowler, M. A Review of Methane Gas Detection Sensors: Recent Developments and Future Perspectives. Inventions 2020, 5 (3), 28. https://doi.org/10.3390/inventions5030028.(4) Garzon, F. H.; Mukundan, R.; Brosha, E. L. Solid-State Mixed Potential Gas Sensors: Theory, Experiments and Challenges. Solid State Ion. 2000, 136, 633–638.(5) Halley, S.; Tsui, L.; Garzon, F. Combined Mixed Potential Electrochemical Sensors and Artificial Neural Networks for the Quantificationand Identification of Methane in Natural Gas Emissions Monitoring. J. Electrochem. Soc. 2021, 168 (9), 097506. https://doi.org/10.1149/1945-7111/ac2465. Figure 1. Four electrode MPES response at 600 °C to CH4 in simulated air, low ethane simulated natural gas in air, and high ethane simulated natural gas in air, from left to right, respectively. Top row – ceria stabilized zirconia substrate. Bottom row – magnesia stabilized zirconia substrate. Figure 1

Permeation Characteristics of CH4 in PVDF with Crude Oil-Containing.

The liner of reinforced thermoplastic composite pipes (RTPs) used for oil and gas gathering and transportation experienced blister failure due to gas permeation. Few reports have appeared on the problem of gas permeation in thermoplastics with absorbed crude oil. Accordingly, the permeability of CH4 in polyvinylidene fluoride (PVDF) containing crude oil was studied at the normal service conditions by molecular simulations. The results showed that the solubility coefficients of CH4 in PVDF containing crude oil were much lower than those in pure PVDF. It can be concluded that the crude oil molecules absorbed into PVDF occupied certain adsorption sites, resulting in a decrease in the adsorption capacity of CH4 molecules in PVDF. The diffusion coefficients of CH4 in oil-containing PVDF were significantly greater than in PVDF. This is because the absorption of oil molecules leads to the volume swelling of PVDF and then increases the free volume for diffusion. The permeation process showed that CH4 molecules were selective-aggregate adsorbed in the region with low potential energy in oil-containing PVDF firstly, and then they vibrated within the holes of PVDF containing oil in most cases and jumped into the neighboring holes at high temperatures and pressures.

Research on Internal Parameter Filtering of Natural Gas Pipeline under Duty Cycle Transmission Mechanism

In recent years, with the continuous growth of China's long-distance oil and gas pipeline network, wireless communication network applications have become more and more extensive with the continuous promotion of intelligent oilfield construction, while the energy-saving problem in the process of information transmission has become increasingly prominent. In order to ensure the sustainable development of China's oil and gas industry, low-power wireless transmission has become a basic requirement for the current intelligent oil and gas pipeline communication construction. For the monitoring of pipeline operating conditions, pressure and flow rate values are important parameters. If the accuracy and comprehensiveness of pipeline operation data can be ensured simultaneously under an energy-efficient transmission mechanism, it will provide strong support for the green and safe operation of pipelines. Therefore, in this paper, a recursive filtering study is conducted for natural gas gathering pipeline flow system under duty cycle transmission mechanism to complete the reliable monitoring of pipeline fluid transportation status.

A semi-supervised leakage detection method driven by multivariate time series for natural gas gathering pipeline

Real-time and accurate leakage detection of natural gas gathering pipelines is critical to the safe and reliable operation of the gas and oil industry. Modern data-driven fault detection and diagnosis techniques have recently gained increasing attention because model-based techniques are practically prohibitive. However, most existing data-driven leakage detection approaches are obtained through supervised learning, which requires a substantial set of labelled data. Especially in real-world scenarios, leakage samples are rare. To reduce the dependence of the leakage detection method on leakage data and make full use of numerous normal datasets generated under normal working conditions, we propose a semi-supervised leakage detection method which consists of two components: an improved long short term memory autoencoder (LSTM-AE) network and one-class support vector machine (OCSVM). The LSTM-AE is first trained to learn the intrinsic features of a normal dataset of pipeline parameters which are multivariate time series. The OCSVM is then applied to calculate the score which is used to infer leak existence. The performance of the proposed method is evaluated on the real natural gas gathering pipelines, and the results confirm that the proposed method achieved 98% accuracy and 99% AUC (Area Under Curve) in a real-life dataset.

Concurrent 18. Presentation for: Simplicity and digitalisation – using GIS to reduce design and operation costs in gas gathering systems

Presented on Wednesday 18 May: Session 18 With the drive to continually reduce the cost of connecting new Coal Seam Gas (CSG) wells, Worley developed new methodologies using commercial off-the-shelf software, and custom development, to automate engineering and improve operational efficiency for pipelines and gathering systems. One of the recent developments is an automated and data-driven approach to produce Gathering Network Diagrams (GNDs), an alternative to conventional Piping & Instrumentation Diagrams (P&IDs). On a recent project, Worley implemented a GND workflow capable of showing ~40 wells per A3 deliverable in conformance with intelligent drafting standards. This reduced ~2000 as-built P&IDs to ~200 GNDs (and associated standard details) with a significant improvement in quality and usability. Prior to generation, a site walkdown was conducted to address mismatches between as-built P&IDs, Geographic Information System (GIS) and what was actually installed at site. Our client now has a suite of GNDs that match the installed asset and are produced from the corporate GIS database, essentially their Digital Twin. Worley then focused on integrating flow assurance software with GIS allowing data-driven execution of future design packages to be incorporated into the master GNDs. We successfully integrated with PipeSIM and GAP, allowing for seamless transfer of hydraulic inputs from GIS to the modelling software. Engineers can now synchronise the confirmed process design back to GIS without producing red-lined and/or CAD-drafted deliverables which greatly improves efficiency and reduces human error. This paper demonstrates how digital automation can be applied to the CSG industry to significantly reduce cost and schedule whilst enabling data-driven operational efficiencies. To access the presentation click the link on the right. To read the full paper click here

Erosion hot spots of drain valve under higher particle flow rates

Drain valves mounted onto the blow-off pipelines of natural gas gathering plants are often used to discharge deposited particles in separators. Particle flows (greater than 0.01 kg/s) always lead to inner and even outer leakage owing to erosion hot spots in the valve body and valve core. In this study, various approaches, including online particle monitoring experiments, ultrasonic wall thickness measurements, and flow control methods were used to investigate valve erosion hot spots in field experiments. Numerical simulations with a large-scale moving grid method were conducted to demonstrate the dynamic erosion in a compressible gas flow. The results reveal that the erosion hot spots continuously shifted to nearby areas during the surface evolution. The local erosion rate of the original erosion hot spots always exhibited a decreasing trend, while the erosion rates of the nearby hot zones exhibited an increasing–decreasing trend. The erosion rate of the erosion-deformed zones that suffered delayed particle impacts always exhibited an increasing trend. When the pressure increased from 0.5 MPa to 3.5 MPa, the erosion hot spots shifted to Point_B 3. The velocity contour considering the gas compressibility was also determined for this process, and the gas velocity spraying to the facing wall was successfully created. The Oka erosion model was combined with the moving grid method and validated as the most appropriate method for predicting erosion hot spots. As time evolved, the operational flow rate of a 10% valve opening at 46,080 s was equal to the flow rate of a 40% opening at 0 s. On the basis of this relationship, the entire failure process of the valve was accurately obtained using a semi-empirical method. Finally, two novel valve structures are proposed to create a strong erosion–absorbing effect and thereby weaken the erosion hot spot of the valve.

Simplicity and digitalisation – using GIS to reduce design and operation costs in gas gathering systems

With the drive to continually reduce the cost of connecting new Coal Seam Gas (CSG) wells, Worley developed new methodologies using commercial off-the-shelf software, and custom development, to automate engineering and improve operational efficiency for pipelines and gathering systems. One of the recent developments is an automated and data-driven approach to produce Gathering Network Diagrams (GNDs), an alternative to conventional Piping & Instrumentation Diagrams (P&IDs). On a recent project, Worley implemented a GND workflow capable of showing ~40 wells per A3 deliverable in conformance with intelligent drafting standards. This reduced ~2000 as-built P&IDs to ~200 GNDs (and associated standard details) with a significant improvement in quality and usability. Prior to generation, a site walkdown was conducted to address mismatches between as-built P&IDs, Geographic Information System (GIS) and what was actually installed at site. Our client now has a suite of GNDs that match the installed asset and are produced from the corporate GIS database, essentially their Digital Twin. Worley then focused on integrating flow assurance software with GIS allowing data-driven execution of future design packages to be incorporated into the master GNDs. We successfully integrated with PipeSIM and GAP, allowing for seamless transfer of hydraulic inputs from GIS to the modelling software. Engineers can now synchronise the confirmed process design back to GIS without producing red-lined and/or CAD-drafted deliverables which greatly improves efficiency and reduces human error. This paper demonstrates how digital automation can be applied to the CSG industry to significantly reduce cost and schedule whilst enabling data-driven operational efficiencies.

Risk Classification of Shale Gas Gathering and Transportation Pipelines Running through High Consequence Areas

Shale gas gathering and transportation pipeline poses significant risk due to special geographical conditions and different climatic conditions in high consequence areas such as Sichuan and Chongqing. The risks become critical as gas pipelines run through high consequence areas such as hospital, market, and scenic areas. This study presents a risk classification method for the pipelines running through high consequence areas. The proposed method considers different failure scenarios including third-party damage, corrosion, design and construction defects, mis-operation, and natural disasters. The method uses subjective and objective data from different sources. To minimize the subjectivity and data uncertainty, an improved fuzzy analytic hierarchy process was used to process data. The estimated risk is used to classify different risk zones. After the failure of shale gas pipelines in HCAs, in order to reduce the adverse impact of emergencies, personnel should immediately organize an evacuation to a safe area, focusing on the diagnosis and analysis of risk factors that are more likely to lead to pipeline leakage. The developed classes are verified using field data. The study observes that risk levels classified using the proposed method provide realistic assessments of hazard zoning. Risk zoning will help develop effective risk management strategies.

Experimental Study on Hydrate Safe Flow in Pipelines under a Swirl Flow System.

With the development of oil and gas resources gradually extending to the deep sea, the blockage of gas hydrate is attracting more and more attention. How to inhibit hydrate blockage efficiently and economically in oil and gas gathering transportation pipelines and ensure the safe operation has become a hot and difficult point in the field of oil and gas gathering and transportation research. At present, the research on the safe flow of gas hydrate is still in the exploratory stage, and applying swirl flow to hydrate risk control technology has a great engineering application value. A systematic experimental study on the safe flow of gas hydrate in a swirl flow system is carried out herein. The experimental results show the following: (1) The laws of gas hydrate flow, transport, deposition, and pipe plugging under various experimental conditions of the swirl flow system are obtained, the safe flow region of hydrate under the swirl flow system in the pipeline is obtained, and the safe flow boundary of hydrate is expanded. (2) Beginning with the theoretical analysis of the safe flow of gas hydrate in a pipeline, the flow characteristics of gas hydrate in the flow system are described; the special flow form of swirl flow has a great influence on the safe flow law of hydrate. (3) The growth and coalescence mechanisms of spiral hydrate in two mainstream systems of separated flow and dispersed flow are explored and researched. The critical tangential velocity of flow is taken as the standard of criterion.

Effects of foam on slug generation mechanism in a hilly terrain pipeline

Liquid accumulation is one of the most common challenges associated with natural gas gathering processes, particularly in pipelines where mechanical pigging is infeasible and there is a risk of terrain slugging. Aqueous foam drainage technology is a potential method to remove liquid accumulation owing to its low risk and cost, and lack of constraints. An experimental study of gas–liquid two-phase flow with foam was conducted to clarify the effects of foam on the slug generation mechanisms at the elbow of upward-inclined pipelines. The experiments were conducted in horizontal-upward pipelines at different inclination angles (5°, 10°, and 20°). The flow pattern was captured by a high-speed camera and the real-time differential pressures along the pipeline were recorded. The results indicate that the slug generation mechanisms at the elbow mainly consist of an interfacial wave growth mechanism at low gas velocities and an interfacial wave aggregation mechanism at high gas velocities. In the presence of aqueous foam, the interfacial wave growth mechanism still exists. In contrast, the interfacial wave aggregation mechanism disappears, and the flow pattern transforms into wavy foam flow under the same conditions. In addition, the increase in the inclination angles intensified the liquid backflow in the upward-inclined section and contributed to the liquid accumulation at the elbow. Furthermore, owing to the Bernoulli effect, the increase also enhanced the liquid-carrying capacity of the gas in the divergent section of the elbow, resulting in increased interfacial fluctuations and promoting the generation of liquid slugs. Meanwhile, the eigenvalues extracted from the fast Fourier transform (FFT) of the differential pressures correlate well with the flow characteristics at the elbow, and the average values at separated flow conditions are all below 0.05, which proves that the method enables an accurate prediction of whether the liquid slug is generated at the elbow of the upward-inclined pipe.

A MINLP model for combination pressurization optimization of shale gas gathering system

The combination pressurization of the shale gas gathering system is one of the most common pressurization methods in the current engineering site, but it is mostly set by manual experience or simulation analysis, and thus the optimal pressurization scheme cannot be obtained. In order to optimize the pressurization mode of the shale gas gathering and transportation system, a mixed integer nonlinear programming model (MINLP) is established based on the existing pressurization mode of the shale gas field. The model takes the minimum total cost of the compressor unit as the objective function. Various constraints are also taken into account, such as pipe pressure, flowrate, compressor related, well and platform throttling, uniqueness for well and platform pressurization. Solving this optimization model can figure out the appropriate pressurization position, operating power, and compressor unit cost. An actual case for a shale gas block is applied to determine the combined pressurization scheme suitable for this production condition. The results show that the combination of more pressurization methods can meet the pressurization requirements under different production conditions. When both well and platform pressurization are considered, the optimized pressurization position is more concentrated, the number of compressors is reduced by two sets, and the total compressor cost is reduced by 99.28 × 104 Yuan, which reflects the advantages of combined pressurization in the pressurization of shale gas gathering and transportation systems.

Correlation analysis of pipeline corrosion and liquid accumulation in gas gathering station based on computational fluid dynamics

In the natural gas station, the produced natural gas often contains water, and there will be obvious liquid phase accumulation in the elbow and straight pipe section. Currently, the selection of pipeline detection points in stations is too empirical to detect all parts of pipelines, which poses a serious threat to safety in production. For a natural gas mainline of a station, based on actual engineering conditions, the CFD method is used to analyze the formation of the liquid film in the pipeline and the distribution of liquid phase in the pipeline to determine the location where the liquid phase is likely to accumulate. The size and distribution of liquid volume fraction reflect the liquid phase aggregation, which is closely related to the pipe structure. The Pearson correlation is used to verify the correlation between the measured data of field wall thickness and the liquid volume fraction of the simulated pipe section. It is found that the correlation degree of the elbow is over 83%, that of the straight pipe section is up to 67%, and that the correlation degree is relatively high. This provides guidance for a reasonable selection of pipeline inspection points on site, reduces on-site inspection workload and cost, and improves the level of integrity management in the station.