Gas Production Efficiency Research Articles

Mechanism of solar photo-thermal transformation for baffled liquid on energy and mass transfer efficiency in direct absorption anaerobic reactor

Agricultural and animal husbandry waste causes serious environmental pollution. A new coupling model of flow heat transfer and anaerobic fermentation is established in this study to enhance the operation efficiency of anaerobic treatment equipment and guard total environment. The model has a vital ability to cut down the difference value between truthful data and predicted data. This model is used in a push-flow anaerobic reactor to study the effect of the baffle on the reactor temperature field and gas production efficiency. The results show that the increase of the baffle improves the temperature uniformity and gas production rate inside the reactor. The duration of the reactors with 15 baffles is approximately 1800 s less than that without baffle, and the relative time saving rate is as high as 56.5%. The gas production of the reactor with 15 baffles is 3.18% higher than that of the reactor without baffle. As time goes on, the concentrations of propionic acid, acetic acid and hydrogen all increase first and then decrease, but the larger BT has the lower concentration of each substance. This improved model can be used to make more accurate predictions in terms of energy and production.

Pasture-finishing of late-maturing bulls or steers in a suckler calf-to-beef system: Animal production, meat quality, economics, greenhouse gas emissions and human-edible food-feed efficiency

CONTEXTDemand for efficient sustainably-produced ‘grass-fed’ beef is increasing. Steers predominate in pasture-based systems. Bulls are inherently more efficient than steers but are usually produced indoors on concentrate-based rations rather than at pasture. OBJECTIVEEvaluate the animal productivity, meat quality, financial performance, greenhouse gas (GHG) production and human-edible protein (HEP) efficiency of suckler calf-to-beef systems, in which male progeny were finished as bulls or steers at pasture, with or without concentrate supplementation, at 19.5 months-of-age. METHODSWeaned suckler male cattle, produced as either bulls or steers, were offered grass silage and supplementary barley-soybean meal-based concentrates during a ‘backgrounding’ phase, and then assigned to one of two finishing strategies: grazed pasture-only for 192-days (G-O) or pasture-only for 95 days followed by pasture supplemented with 3.2 kg concentrate dry matter daily for 97 days (G-C). The experimental data generated were used to parameterise a whole-farm systems model and the productivity, profitability and GHG production of suckler calf-to-beef systems (encompassing cows, replacement heifers, female and male - bulls vs. steers - progeny) were evaluated. RESULTS AND CONCLUSIONSBulls had a heavier carcass (+44 kg), greater kill-out proportion (+14 g/kg) and carcass conformation score (+1.6 units, scale 1–15), a lower carcass fat score (−2.3, scale 1–15), darker muscle and less yellow subcutaneous fat than steers. Concentrate supplementation increased daily live-weight gain (+0.36 kg), carcass weight (+37 kg), kill-out proportion (+12 g/kg), carcass conformation score (+1.1 units) and fat score (+1.0). Meat tenderness, texture and acceptability were lower for bulls than steers. Profitability of suckler calf-to-beef systems was greater where male progeny were finished as bulls rather than steers, and for G-C than G-O. The GHG emissions (CO2 eq) per cow were lower for steer compared to bull systems, and for G-O than G-C; however, when expressed per kg live-, carcass- and meat- weight, the opposite was found. Half of the GHG emissions within the calf-to-beef systems were attributed to the cow. The HEP ratio for G-O exceeded 1.0, but for G-C declined to 0.9 for steers and 1.0 for bulls: replacing cereal and soya-bean meal with by-products resulted in all systems having HEP efficiencies >1.0. Bull systems had lower meat eating quality, greater profit, lower GHG emissions intensity, and superior HEP efficiency than steers. Concentrate supplementation did not affect meat quality, increased profitability, and reduced GHG emission intensity and HEP. SIGNIFICANCEConsideration of unavoidable trade-offs in sustainability-related metrics between suckler beef systems is necessary.

Effects of Guanidinoacetic Acid on Ruminal Fermentation and Greenhouse Gas Production Using Fresh Forage and Silage from Different Maize (Zea mays L.) Genotypes

Guanidinoacetic acid (GAA) is a feed additive that promotes growth in animals, while maize (Zea mays L.) is used for the mitigation of ruminal greenhouse gases. However, it is unknown if GAA affects the efficiency of maize in mitigating gases or if there is synergy between them. Therefore, the objective of this study was to evaluate the in vitro production of total gas, methane (CH4), carbon monoxide (CO), and hydrogen sulfide (H2S), ruminal fermentation characteristics, and the CH4 conversion efficiency of fresh forage and silage of different genotypes (Amarillo, Montesa, Olotillo, Tampiqueño, and Tuxpeño) of maize, with and without the addition of GAA. The silage of the Amarillo genotype without AAG had the highest (p = 0.01) total gas production rate and the lowest (p = 0.044) delay time before gas production. In addition, at 48 h, the Amarillo silage with GAA increased the production of total gas (p = 0.0001) and CH4, as well as the proportion of CH4 (mL CH4 100 mL−1 total gas). The Amarillo and Tuxpeño genotype produced more (p = 0.033) CO in the first 24 h of incubation, while silage and the addition of GAA only increased (p = 0.001) CO at 6 h. The highest (p = 0.02) H2S production was observed with the ensiled Amarillo genotype with GAA. Regarding fermentation characteristics, the silage of the Amarillo and Montesa genotypes presented the highest degradation of dry matter (DMD), short-chain fatty acids (SCFA), and metabolizable energy (ME), and although there was no effect on CH4 efficiency, the Amarillo and Olotillo genotypes produced more SCFA, ME, and OM per unit of CH4. It can be concluded that rumen gas production, fermentation characteristics, and CH4 conversion efficiency are more influenced by the maize genotype and forage condition than by the addition of guanidinoacetic acid, and of the genotypes evaluated, the forage silage from Amarillo showed the best characteristics and efficiency of CH4.

IMPROVING THE PERFORMANCE OF THE GAS LIFT VALVE SEAL

Currently, gas lift valves are widely used in the gas industry to maintain pressure in wells. However, there are often problems with sealing valves, which leads to a loss of efficiency and increased energy consumption. Improving the operability of the sealing element of the gas lift valve will reduce the likelihood of gas leaks and increase the reliability and efficiency of the entire gas lift device. In addition, this will reduce the cost of repairing and replacing faulty sealing elements and improve the economic efficiency of gas production. The sealing element of the gas lift valve plays a key role in ensuring reliable and efficient operation of this device. A malfunction of the sealing element can lead to a gas leak, which will entail significant financial losses and risks to the safety of personnel and the environment. Therefore, the urgency of improving the operability of the sealing element of the gas lift valve is to ensure the safe and reliable operation of oil and gas equipment, improve the economic efficiency of production and reduce financial losses of companies engaged in gas production and transportation. The purpose of the work is to study the provision of a gas lift valve and a check valve with a flexible, sealing element and means to protect the element from deflection or destruction. Keywords: gas lift valve, Bellows type, Valve sealing, Composite materials, Fluoroplast-4, Carbon fiber, Socket for the sealing.

Multi-scale spatiotemporal feature lithology identification method based on split-frequency weighted reconstruction

The accurate identification of lithology in thin and deep layers is a crucial task in logging. However, traditional logging lithology identification methods are often inefficient for thin and deep layers and sometimes require human intervention, which greatly reduces the efficiency of oil and gas production. Therefore, this study proposes a multi-scale spatiotemporal feature lithology identification method under split-frequency weighted reconstruction. First, split-frequency weighted reconstruction of the logging curves is performed by Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (CEEMDAN) to improve their thin layer resolution. Subsequently, a feature fusion model of multi-scale convolutional neural networks and bidirectional gated recurrent neural networks (MCNN-BIGRU) is constructed to learn the spatiotemporal features of the logging curves. Finally, during feature propagation, the attention mechanism assigns weights to historical features to mitigate the accumulation of error information, thereby improving the lithology recognition effect. To verify the model's performance, we constructed a lithology dataset with five wells and conducted an experiment to show that the reconstructed logging curves have significantly higher vertical resolution than the original curves. Furthermore, the MCNN-BIGRU-AT model developed in this study exhibited a better lithology identification effect than the single-structure model, with a highest accuracy of 96.69%. In summary, the proposed method is a novel and efficient method for lithology identification.

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

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

Effects of nanobubbles on methane hydrate dissociation: A molecular simulation study

Hydrate dissociation is often accompanied by the formation of nanobubbles. Knowledge of the effects of nanobubbles on hydrate dissociation is essential for understanding the dynamic behavior of the hydrate phase change and improving the gas production efficiency. Here, molecular dynamics simulations were performed to study the methane hydrate dissociation kinetics with and without a pre-existing methane nanobubble. The results show that the hydrate cluster in the liquid phase dissociates layer-by-layer. This process is shown to be independent of the temperature and nanobubble presence at the simulation conditions. Hydrate dissociation does not always lead to nanobubble formation because the supersaturated methane solution can be stable for a long time. A steep methane concentration gradient was observed between the hydrate cluster surface and the methane nanobubble, which can enhance the directional migration of methane and effectively minimize the methane concentration in the liquid phase, thereby increasing the driving force for the hydrate dissociation. Our findings indicate that the presence of a nanobubble near the hydrate surface does not decrease the activation energy of hydrate dissociation, but it can increase the intrinsic decomposition rate. The average hydrate dissociation rate is linearly correlated with the mass flow rate towards the nanobubble. The mass flow rate is determined by the nanobubble size and hydrate-nanobubble distance. Our findings contribute to the fundamental understanding of the dissociation mechanism of gas hydrates in the liquid phase, which is crucial for the design and optimization of efficient gas hydrate production techniques.

Effect of laser spot diameter on oxygen bubble behavior in photoelectrochemical water splitting

The detrimental effect caused by the long-term adhesion of bubbles on the gas production efficiency has been the main bottleneck limiting the efficiency improvement of photoelectrochemical water splitting. The evolution of oxygen bubbles on the fixed photoelectrode surface of TiO2 films was observed in-situ using a combination of a synchronized high-speed microscopic camera and an electrochemical workstation. The effect of oxygen bubble evolution on the current during the photoelectrochemical reaction was investigated under different laser spot diameters. When the spot diameter increased 1.68 times from 700 μm to 1176 μm with a laser power of 5 mW, the bubble detachment diameter and growth period increased 2.7 times and 20.2 times, respectively, yet the gas production efficiency decreased by 34.7%. Meanwhile, the peak current caused by the bubble detachment gradually increased. However, the valley current at the nucleation waiting stage of the bubble did not have obvious changes. The model for the gas evolving based on supersaturation was adopted. It illustrated that the concentration gradient of dissolved gas perpendicular to the photoelectrode surface increased with the increase of spot diameter, leading to an increase in the bubble surface tension gradient, and causing the Marangoni force to inhibit the detachment of bubbles. A force balance model was developed to evaluate the Marangoni forces and the buoyancy forces. The growth rate of the Marangoni force was found to be proportional to the spot diameter. Therefore, reducing the laser spot diameter is a means to effectively remove the bubbles from the photoelectrode surface.

Characteristics of In Situ Stress and Reservoir Pressure in Deep Coal Seams and Their Influences on Reservoir Depletion: A Field Case Study

The production of coalbed methane resources is greatly dependent on the reservoir depletion process. To improve the depressurization efficiency of deep coalbed methane (DCBM) reservoirs, the fluid production characteristics and implications of in situ stress and reservoir pressure for reservoir depletion in the eastern margin of the Ordos Basin are analyzed. The results indicate that the duration of the single-phase water production stage is overall long, with the gas declining stage occurring too early. The daily gas production volume of DCBM wells is only a few hundred m3. For DCBM reservoirs, it is considered that in situ stress, initial reservoir pressure, and critical desorption pressure significantly affect the fluid production and depressurization process. A high in situ stress in deep coal seams is likely to damage the flow conductivity of fracture systems due to the increase in effective stress during reservoir depletion. Based on the in situ stress characteristics of deep coal seams and their implications for reservoir depletion, we propose that the depressurization of DCBM reservoirs during gas production can be promoted via a new method of stress release. Slots or cavities created in coal seams by high-pressure hydraulic jet can provide space for stress release. This novel depressurization method could help improve the gas production efficiency of DCBM reservoirs.

Modeling and Simulation of Autonomous Inflow Control Devices for Gas Exploitation.

Horizontal well technology is an efficient method of oil and gas exploitation. The goal of increasing oil production and improving productivity can be achieved by increasing the contact area between the reservoir and the wellbore. The presence of bottom water cresting reduces the efficiency of oil and gas production significantly. Autonomous inflow control devices (AICDs) are widely used to delay the influx of water into the wellbore. Two kinds of AICDs are proposed to restrain the bottom water breakthrough during natural gas production. The fluid flows in the AICDs are simulated numerically. The pressure difference between the inlet and outlet is calculated to evaluate the ability of blocking the flow. A dual-inlet design can increase the flow rate of AICDs, thus enhancing the water blocking effect. Numerical simulations show that the devices can block water flowing into the wellbore effectively.

Study of fatigue damage of pumping rods based on finite element simulation

This study performed in-depth analysis of onsite fatigue damage and stress distribution in pumping rods. Two aspects of fatigue damage were analyzed: macroscopic morphology and chemical properties. In terms of chemical properties, the crystalline phase composition and hardness of the product at fatigue damage were analyzed; the stress distribution was analyzed in term so of the rod-body stress and the connection-section stress. The cross-sectional characteristics of the fatigue crack expansion were summarized, and the types of fatigue fracture and the influencing factors of the pumping rod were obtained from these cross-sectional characteristics. Finally, modeling and stress analysis of the pumping rod were performed using SolidWorks and ABAQUS software. By comparing the stress cloud diagrams of different thread root shapes, the factors that cause fracture in the pumping rod and the locations of stress concentrations and dangerous cross-sections of the rod were determined. The highest principal stresses were obtained at the rod body near the upsetting flange of the pumping rod, and fatigue damage was the most likely to occur at this location. The shoulder of the unloading groove and the upsetting flange area were relatively safe because of their large cross-sectional area and less likelihood to produce stress concentrations. The results of this study can provide scientific guidance and reference for the development of pumping rods for efficient oil production and the improvement of oil and gas production efficiency.

Experimental study on the in-situ foam performance stabilized by microbial polysaccharide and its diverting characteristics at high temperature

Foam fluid shows good performance as diverting agent for reservoir stimulation, but complex generation procedure and high flow friction restrict its further application especially in offshore fields. To overcome these limitations, the objective of this study is to create stable in-situ foam system and investigate its potential in diverting fluid in heterogeneous reservoirs at high temperature. To prepare in-situ foam system, self-generated gas system was analyzed in terms of gas production volume and production efficiency. Foaming agents and foam stabilizers were optimized at the temperatures ranging from 70 ℃ to 90 ℃. Then in-situ foaming performance of the system combining self-generated gas reactants (sodium nitrite and ammonium chloride), the foaming agent (alpha olefin sulfonate), and the foam stabilizer (diutan gum) without blender was investigated based on foaming volume and bulk stability. Single core and parallel core flooding experiments were applied to investigate the plugging ability and diverting characteristics of in-situ foam. The results showed that the large pore volume was blocked by in-situ foam even at 150 ℃ as shown by the increase of residual resistance factor during subsequent water flooding. Parallel core flooding experiments also proved the diverting ability of in-situ foams as the diversion ratio of low-permeability core was higher than that of high-permeability core during subsequent water flooding. Moreover, the diversion performance of in-situ foam strongly depended on the permeability contrast, environment temperature, permeability of low-permeability core, and injection rate. Although diversion failed when permeability contrast was more than 10, in-situ foam also had good thermal stability and diverting ability at 150 ℃ in the permeability contrast range of 3 to 8. Such stable in-situ foam shows promising potential as diverting agent in heterogeneous formation for reservoir stimulation at high temperature.

Integrative project and asset management strategies to maximize gas production: A review of best practices

The growing demand for natural gas as a cleaner energy source has driven the need for optimized production strategies in the oil and gas sector. This paper reviews integrative project and asset management strategies designed to maximize gas production, drawing from best practices in the industry. The review highlights the critical role of strategic alignment between project management and asset optimization in achieving sustainable and efficient gas production. Key areas explored include the integration of predictive maintenance, digital twin technologies, and data analytics to improve decision-making and operational performance. Emphasizing a life-cycle approach to asset management, the paper discusses how proactive asset monitoring, risk management, and performance tracking contribute to long-term production efficiency. The importance of stakeholder collaboration and interdisciplinary coordination across technical, operational, and financial teams is also underscored, as it facilitates the seamless execution of projects from exploration to production. This review further examines case studies where digital tools and advanced project management methodologies have been successfully implemented to reduce downtime, optimize resource allocation, and enhance production capacity. Techniques such as Lean project management and Six Sigma are highlighted as effective in streamlining operations and reducing inefficiencies. The study concludes by discussing the future trends in gas production management, including the adoption of artificial intelligence (AI) and machine learning (ML) for predictive asset optimization and the integration of real-time monitoring systems for enhanced production forecasting. In summary, integrating advanced project and asset management strategies, with a focus on technology and collaboration, can significantly enhance gas production efficiency. By adopting these best practices, gas producers can meet rising global energy demands while maintaining operational sustainability and cost-effectiveness.

Shale Formation Damage during Fracturing Fluid Imbibition and Flowback Process Considering Adsorbed Methane

Hydraulic fracturing of shale gas reservoirs is characterized by large fracturing fluid consumption, long working cycle and low flowback efficiency. Huge amounts of fracturing fluid retained in shale reservoirs for a long time would definitely cause formation damage and reduce the gas production efficiency. In this work, a pressure decay method was conducted in order to measure the amount of fracturing fluid imbibition and sample permeability under the conditions of formation temperature, pressure and adsorbed methane in real time. Experimental results show that (1) the mass of imbibed fracturing fluid per unit mass of shale sample is 0.00021–0.00439 g/g considering the in-situ pressure, temperature and adsorbed methane. (2) The imbibition and flowback behavior of fracturing fluid are affected by the imbibition or flowback pressure difference, pore structure, pore surface properties, mechanical properties of shale and mineral contents. (3) 0.01 mD and 0.001 mD are the critical initial permeability of shales, which could be used to determine the relationship between the formation damage degree and the flowback pressure difference. This work is beneficial for a real experimental evaluation of shale formation damage induced by fracturing fluid.

Resource Conservation as the Main Factor in Increasing the Resource Efficiency of Russian Gas Companies

The complex modern trends in the growth of the consumption of raw hydrocarbon materials around the world, and as a consequence their accelerated depletion, have forced oil and gas industry enterprises to identify progressive resource-saving methods and technologies. Such methods could enable the environmental and technological effects of production processes to be achieved under conditions of sustainable economic development and with a policy of balanced consumption and resource provision. This research is devoted to the improvement of the scientific and methodological foundations and the development of predictive and analytical tools for assessing the efficiency of resource use in gas industry enterprises. With the application of the proposed instruments, we carry out simulation modeling of the efficiency of natural gas production, processing and pipeline transportation companies. In the course of a comparative analysis of the efficiency indicators for Russian gas companies, a resource-efficient variant of their development is selected and the most promising business projects are identified. Three branch companies of the Russian gas industry are accepted as the objects of the research in this study. As a result of the conducted approbation process, it is revealed that the existing practice of assessing consumption and resource provision in companies in the industry, as well as the use of methods and approaches to resource conservation, does not have a single and complex character. The methodology proposed by the authors makes it possible to approach industry companies with the same set of indicators, systematize and calculate them, identify existing unused reserves for resource conservation and identify promising resource-efficient projects.

A novel apparatus for modeling the geological responses of reservoir and fluid-solid production behaviors during hydrate production.

Gas hydrate is a promising alternative energy resource that undergoes complex phase changes and coupled geological responses during hydrate production. Insufficient knowledge of those coupled behaviors still challenge safe and efficient gas production from hydrate. Here, a novel experimental apparatus was developed to simulate the gas-water-sand production and to evaluate the related multifield and multiphase processes. The experimental apparatus is equipped with displacement, ultrasonic, and electrical resistivity sensors and gas/water flowmeters, and this apparatus can work up to a maximum loading stress of 25 MPa and a maximum pore pressure of 20 MPa over a temperature range from -20 to 50 °C. The hydrate production and sand production case were performed on a synthetic specimen with hydrate saturation of 12.8% by using multi-step depressurization. The pressure-temperature conditions, settlement, ultrasonic propagation, electrical resistivity, and permeability of hydrate reservoirs during production were simultaneously monitored to evaluate the geological characteristics and heat and mass transfer characteristics of the hydrate reservoir. The results indicated that the gas/water production mainly occurred during the first third of each depressurization period, and their production rates were low at the beginning. Flowing water mobilized the sand particles, and the addition of gas exacerbated the sand-particle migration. Interpretation of the coupled behaviors supported that the reservoir could maintain a temporary stable structure even when losing a certain amount of sand particles with no sand control methods; however, necessary sand-prevention approaches are wise to support long-term reservoir production operations. These laboratory insights would contribute to optimizing the field strategies for economical gas production from hydrate.

A new model for predicting hydraulic fracture penetration or termination at an orthogonal interface between dissimilar formations

Vertical height growth of hydraulic fractures (HFs) can unexpectedly penetrate a stratigraphic interface and propagate into neighboring layers, thereby resulting in low gas-production efficiency and high risk of groundwater contamination or fault reactivation. Understanding of hydraulic fracture behavior at the interface is of pivotal importance for the successful development of layered reservoirs. In this paper, a two-dimensional analytical model was developed to examine HF penetration and termination behavior at an orthogonal interface between two dissimilar materials. This model involves changes in the stress singularity ahead of the HF tip, which may alter at the formation interface due to material heterogeneity. Three critical stress conditions were considered to assess possible fracture behavior (i.e., crossing, slippage, and opening) at the interface. Then, this model was verified by comparing its theoretical predictions to numerical simulations and three independent experiments. Good agreement with the simulation results and experimental data was observed, which shows the validity and reliability of this model. Finally, a parametric study was conducted to investigate the effects of key formation parameters (elastic modulus, Poisson's ratio, and fracture toughness) between adjacent layers. These results indicate that the variation in the introduced parameters can limit or promote vertical HF growth by redistributing the induced normal and shear stresses at the interface. Among the three studied parameters, Poisson's ratio has the least influence on the formation interface. When the fracture toughness and elastic modulus of the bounding layer are larger than those of the pay zone layer, the influence of fracture toughness will dominate the HF behavior at the interface; otherwise, the HF behavior will more likely be influenced by elastic modulus.

Reservoir stimulation of marine natural gas hydrate-a review

Low production rate, limited recovery range, and short period of stabilized production of natural gas hydrate (NGH) field trials indicate a large gap to commercial production. To improve the efficiency of gas recovery from NGH reservoir, a large number of studies on reservoir stimulation have been reported. In this review, various aspects of reservoir fracability, including brittleness, fracture toughness, and fracability index model are comprehensively analyzed to provide an overall view on the generation of fractures in marine NGH reservoir. The main reservoir stimulation methods are summarized into four aspects: hydraulic fracturing, jet breaking, overlying layer modification and split grouting, of which the working principle, advantages, and limitations are highlighted. It indicates split grouting is the most promising method for achieving two goals of both reservoir skeleton reinforcement and permeability enhancement. Besides, the production enhancement by reservoir stimulation of non-diagenetic hydrate reservoir should be further evaluated considering the evolution of artificial seepage channels during hydrate decomposition. Finally, further developments are suggested to obtain reliable results of the fracability of NGH reservoir, bridge the gap of reservoir stimulation between concept design and practical application, and highlight the combination between reservoir stimulation and NGH reservoir stability for safe and efficient gas production.

Application of the enlarged wellbore diameter to gas production enhancement from natural gas hydrates by complex structure well in the shenhu sea area

The current casing diameters of the production section are about 244 mm in marine natural gas hydrate (NGH) tried tests, which are a small order of magnitude and have the great potential to be enlarged. Expanding the contact areas between the wellbore and the NGH reservoir using complex structure wells has been popularly studied recently. In this study, the enlarged wellbore diameters (casing diameters) of complex structure wells were first proposed to enhance the gas recovery from the NGH reservoir in the Shenhu area of the South China Sea. The gas production characteristics, temperature, and pressure in the NGH reservoir and near the wellbore induced by the depressurization method were analyzed under various wellbore diameters of complex structure wells. Results indicate that using the enlarged wellbore diameter can further expand the contact areas between the wellbore and the NGH reservoir, promoting gas production efficiency, especially in short-term production. The evolutionary trends of temperature and pressure meet the conditions for stable short- and long-term production. Moreover, it was suggested that a relatively significant gas production increase of the enlarged wellbore diameter could be obtained by a slight increase in the wellbore diameter.

Enhanced gas production efficiency of class 1,2,3 hydrate reservoirs using hydraulic fracturing technique

Current gas hydrate production test indicates that it is difficult to reach the commercial level for low permeability hydrate-bearing formation by depressurization method. Hydraulic fracturing in hydrate-bearing sediments (HBS) is a promising method to enhance gas production efficiency. In this study, the use of hydraulic fracturing and depressurization method to improve the recovery rate for class 1,2,3 hydrate reservoirs is studied. The three-dimensional large-scale HBS simulation model is firstly established with the single bi-wing vertical fracture. The gas production behavior for cases with different fracture parameters is investigated including the fracture conductivity, position, scale, and length. The simulation results show that fracture parameters have significant influence on Class 2 and Class 3 hydrate reservoirs. By enlarging the fracture conductivity, fracture length, and fracture scale, the flow resistance around the well can remarkably decrease which is beneficial to the pressure spread and hydrate dissociation. The peak rate of gas production increases and the peak time arrives early. The production feature is analyzed based on the test data in Shenhu Area of the South China Sea (SCS) by numerical simulation method. The cumulative gas production substantially increases by using hydraulic fracturing technique compared to that without fracturing.