High-sulfur Gas Research Articles

Measurements and predictions of harmful releases of the gathering station over the mountainous terrain

Having a risk analysis of harmful releases over mountainous terrains through wind tunnel experiment is a frontier problem in China. In this paper, a straight-flow wind tunnel is applied to simulate the atmospheric boundary layer and research the motion of high-sulfur gas released to atmosphere when accidental releases occur in a gathering station over the mountainous terrain. After an analysis of hourly concentration in the field accident for eight wind directions, experimental results reveal that nearby concentration fields are dominated by wind and far-field concentration distribution is dominated by topography, which leads to complete levels of consequence impact for the personnel risk inside and around the gathering station. Based on CFD techniques, a three-dimensional modelling was established in comparison with the wind tunnel experiment, which suggests that CFD prediction had underestimated the near-field gas concentration and the performance could not precisely match actual risks the gathering station causes to the mountainous terrain, which leads to a modified equation for numerical prediction. Instead of proposing a lower personnel risk evaluation obtained through the use of CFD techniques, the wind tunnel experiment offers a new choice for the consequence impact analysis for the petrochemical industry in China.

Development of wellbore compound blockage removal technology to reduce production loss in the ultra-deep and high-sulfur Yuanba gas field

Wellbore compound blockage occurs in several wells of Yuanba gas field during production, which seriously affects the stable production. The prior treatment with inorganic acid injection does not show a good effect. Therefore, it is urgent to establish an effective blockage removal technology. In this work, the composition analysis of compound blockage samples is firstly carried out. Then, two types of acid solution and barite dissolvent for different types of wellbore blockage are developed. Finally, the corresponding crafts of wellbore blockage removal for different degrees of wellbore blockage are set up. Analysis results show that the inorganic components of blockages are mainly FeS2, CaCO3, BaSO4, and SiO2. The organic components of blockages are mainly the decomposition products of macromolecular materials and the asphaltene. There are differences in the components of blockages between different wells in Yuanba gas field. Some wells are the type of organic-based blockage, while others are the type of inorganic-based blockage. The field application shows that the developed wellbore compound blockage removal technology has successfully guided the in situ removal operation of eight wells in Yuanba gas field, ensuring the smooth completion of production task of this gas field. This effective blockage removal technology can be extended to similar ultra-deep and high-sulfur gas field.

Optimum design of downhole chokes with high sulfur content and large pressure difference

Natural gas resources are abundant in southwest China, but the exploitation environment with high pressure and sulfur always affects the working performance of downhole chokes, which in turn restricts the output of natural gas. In this paper, a high sulfur resistance fixed downhole choke is designed for high temperature (120°C), high production rate and high pressure difference (105MPa) sand-producing Wells. Through the nozzle discharge model to simulate the flow of the fluid through the nozzle, with Bono Maleev method to predict the hydrate formation conditions of downhole choke for the design of the structure. According to the failure forms of different parts, the materials were optimized, and the high sulfur resistant 3YC51 alloy, hard alloy and wear and corrosion resistant sulfur resistant rubber were selected through the test to improve the service life of the choke in the high sulfur high-pressure gas well and ensure the reliability of the tool. The results of numerical analysis on the tool holder and the pressure test of the Laboratory seal show that the choke designed has a good sealing and pressurization performance in the high temperature and high pressure difference environment of 120°C and 105MPa, and it can realize the function of lowering the pressure at the bottom of the well under this working condition, meeting the feasibility requirements. Through this design, the design and improvement of high sulfur gas well tool and new choke has guiding significance.

Numerical Simulation of Sulfur Deposit with Particle Release

Sulfur deposition commonly occurs during the development of a high-sulfur gas reservoirs. Due to the high gas flow velocity near the wellbore, some of the deposited sulfur particles re-enter the pores and continue to migrate driven by the high-speed gas flow. The current mathematical model for sulfur deposition ignores the viscosity between particles, rising flow caused by turbulence, and the corresponding research on the release ratio of particles. In order to solve the above problems, firstly, the viscous force and rising force caused by turbulence disturbance are introduced, and the critical release velocity of sulfur particles is derived. Then, a release model of sulfur particles that consider the critical release velocity and release ratio is proposed by combining the probability theory with the hydrodynamics theory. Notably, based on the experimental data, the deposition ratio of sulfur particles and the damage coefficient in the sulfur damage model are determined. Finally, a comprehensive particle migration model considering the deposition and release of sulfur particles is established. The model is then applied to the actual gas wells with visible sulfur deposition that target the Da-wan gas reservoir, and the results show that the model correctly reflects flow transport during the process of sulfur deposition in porous media. In addition, through the numerical simulation experiments, it was found that considering the release of sulfur particles reduces the saturation of sulfur particles within a specific range around the well and improve the reservoir permeability in this range. From the perspective of gas production rate, the release of sulfur particles has a limited effect on the gas production rate, which is mainly due to the sulfur particle release being limited, having only a 5 m range near the wellbore area, and thus the amount of gas flow from the unaffected area is basically unchanged.

元坝高含硫气藏水平井产能预测

元坝高含硫气藏水平井产能预测

A numerical study of harmful gas dispersion based on CALPUFF model

Severe gas leakage accidents occasionally happened during the exploitation of high-sulfur gas, the consequent harmful gas dispersion could seriously impact the air quality, cause large-scale casualties and economic losses. Therefore, people’s comprehensive understanding of harmful gas dispersion in both spatial and temporal dimensions should be improved. This paper takes gas well blowout accident in Kai County, China, as the case study, simulates and analyzes the dispersion characteristics of the leaked gas, mainly focuses on H2S. The CALPUFF model is applied to execute the experiment, the detailed meteorological data, complex terrain data, wet deposition and chemical transformations are all under consideration. The result shows that due to different impact factors, such as complex terrain and gas density variations, H2S exposure risk was higher in the valley area than that on the mountain, which also explains why Xiaoyang and Gaowang villages have a great number of casualties. Besides, the analysis result is basically consistent with the historical local news and reported data, which demonstrated that our case study of H2S gas dispersion simulation is reasonable and reliable.

The impact of sulfur precipitation in developing a sour gas reservoir with pressure-sensitive effects

During the development of high sulfur gas fifields, gaseous sulfur is likely to precipitate and deposit in the reservoirs due to the changes of temperature, pressure, and gas compositions. Therefore, how to establish an accurate prediction model of elemental sulfur solubility in gas mixtures is a key issue. At present, most scholars use Roberts elemental sulfur solubility model (SPE Reserv. Eng. 1997, 12(2): 118-123) to describe the damage caused by sulfur deposition in high-sulfur gas reservoirs. However, some scholars believe that the Roberts model needs to be improved and relevant works have been done. In this study, a one-dimensional radial production model is established using the HU model (J. Nat. Gas. Sci. Eng. 2014, 18: 31-38) and the Roberts elemental sulfur solubility model. These models can be used to describe the permeability and pressure changes caused by sulfur deposition more accurately. The results show that the permeability and pressure changes in the Roberts model are larger than that of which in the HU model and the pressure-sensitive effects may increase the reservoir damage. The comparison of the calculated results with the true values shows that the HU model is more accurate. This paper may change a number of views about sulfur deposition in high-sulfur gas reservoirs. Cited as : Ru, Z., An, K., Hu, J. The impact of sulfur precipitation in developing a sour gas reservoir with pressure-sensitive effects. Advances in Geo-Energy Research, 2019, 3(3): 268-276, doi: 10.26804/ager.2019.03.05

Development dynamic monitoring technologies used in the Puguang high-sulfur gas field

There is lack of performance monitoring technologies and related standards and specifications in the Puguang gas field, which is ultra-deep with high sulfur content. In this paper, five key technologies of dynamic monitoring were developed and the related standards and specifications were formulated by investigating high-sulfur gas fields at home and abroad, combined with equipment development, laboratory experiments, theoretical research and field tests. The five key technologies include gas production profile logging, downhole sampling and fluid phase analysis, dynamic water invasion prediction and water producing horizon identification, gas well productivity testing and evaluation, and development monitoring and safety control of high-sulfur ultra-deep wells. Then, these key technologies were applied for verification in the Puguang gas field. And the following research results were obtained. First, the sulfur-resistant gas production profile logging tool has a temperature resistance of 175 °C and pressure resistance of 105 MPa. Forty-three well times gas production profile logging is carried out with a success ratio of 100%. Second, the high-sulfur downhole pressure sampler has a temperature resistance of 150 °C and pressure resistance of 70 MPa. Seven well times downhole pressure sampling is carried out with a success ratio of 100%. Third, elemental sulfur is precipitated in the formation when the formation pressure drops to 29.5 MPa. And no sulfur is deposited in the wellbore when the production rate of gas well is higher than 20 × 104 m3/d. Fourth, water producing horizons can be identified accurately and water breakthrough time of gas wells can be predicted by using water producing horizon identification technology and dynamic water invasion prediction model. Water influx rates can be controlled and water-free gas production period of gas wells can be extended by optimizing and adjusting the working systems of gas wells. And fifth, full coverage of gas well productivity testing is realized by using the testing technology of "downhole implanted gauge & cable delivery & wellhead flow-variable rate", pressure calculation model and well testing interpretation model, and the productivity evaluation results of gas wells are accurate. Sixth, the dynamic gas tight pressure of the cable multi-stage leakage control system of super-high pressure and gas tightness is 50 MPa, and the processing technology for waste gas of blowout hookup is applied to 143 well times testing operation with zero leakage and zero pollution. In conclusion, these performance monitoring technologies have been playing an important role in scientifically formulating the production and reserves increase measures and ensuring long-term stable production of the Puguang gas field.

元坝超深高含硫气井油套环空窜气综合治理技术

元坝超深高含硫气井油套环空窜气综合治理技术

Drainage gas recovery technology for high-sulfur gas wells by a canned ESP system

In order to apply the electric submersible pump (ESP) based drainage gas recovery technology commonly used in conventional gas wells to high-sulfur gas wells, and meet the requirements of casing protection in high-sulfur gas wells, we conducted a series of technical researches on casing protection, gas interference and vibration of deep-well ESP set in terms of a completion string design and support tools based on the completion modes of high-sulfur gas wells and the technical characteristics of ESP drainage gas recovery technologies. Simultaneously, drainage gas recovery technology was designed for Well L2. The research and application results show: firstly, the completion string system of high-sulfur gas wells composed of a canned ESP system and an anchor intubation packer can realize the normal operation of ESP and meet the requirements of casing protection; secondly, multiphase pump and bleeder line can be used to solve the problem of gas interference, the automatic reverse valve can be used to reduce the effect of ESP complex flow path on the flowing of the gas well, and the anchor intubation packer can be used to reduce the string vibration; thirdly, the canned ESP system designed in this paper is applicable to Ø244.5 mm and Ø177.8 mm casings, specifically, the ESP corresponding to Ø244.5 mm casing has the maximum flow rate of 900 m3/d and the maximum lift height of 4500 m, and that corresponding to Ø177.8 mm casing has the maximum flow rate of 300 m3/d and the maximum lift height of 3000 m. It is concluded that this research result provides a technical support for the implementation of ESP based drainage gas recovery technology in high-sulfur gas wells.

Preference-driven yield-and-quality optimization for high-sulfur gas sweetening process by extreme learning machine model

Yield and quality, as the two most important output variables of high-sulfur gas (HSG) sweetening process, are affected by the operating parameters. The HSG sweetening process involves more than ten operating parameters, so the relationship between the parameters and output variables is complex, non-linear and strong coupling. This paper tries to use data mining methods to explore this relationship and apply it to optimize the yield and quality. First, a ten (inputs)-to-three (outputs) model is established by extreme learning machine (ELM). Then, a preference-driven multi-objective optimization algorithm is used to maximize the yield while ensuring that the concentration of carbon dioxide (CO2) and the concentration of hydrogen sulfide (H2S) in the treated gas are close to but not exceeding 3% and 4 ppm respectively. The proposed method is validated in a HSG purification plant in southwest China. A set of 3044 production data is collected and randomly divided into 80 and 20% for training and testing. The results show that the established ELM model is in good agreement with the actual operation data. The maximum deviation of mean square error (MSE), mean absolute error (MAE) and average absolute deviation percent (AAD %) of the predictions in three scenarios are 0.2047, 0.3177 and 7.91% respectively. Moreover, the optimization based on the obtained ELM model is also validated. In particular, the H2S concentration and CO2 concentration in the treated gas are significantly higher than those before optimization, but have not exceeding the limits. Thus, the consumptions of energy and amine solvents decreased, while the yield increased.

Integrated electrochemical-aerating oxidation in recovery system of seawater flue gas desulfurization

In recovery system of seawater flue gas desulfurization (SWFGD) process, a novel integrated electrochemical-aerating oxidation method is developed. The influences of process factors such as anode-cathode brush assembly, applied current and dilution ratio on S(IV) oxidation performance are investigated, in connection with S(IV) oxidation rate, the anodic potential range of S(IV) oxidation, energy consumption and total amount of seawater. Compared with the conventional aerating process, the integrated oxidation is confirmed as an energy-efficient and seawater-saving improvement for existing SWFGD recovery system. Based on these experiment results, the reaction mechanism is also proposed. The electrochemical reactions on modified polyacrylonitrile-based carbon fiber (MPAN-CF) brush anode and polyacrylonitrile-based carbon fiber (PAN-CF) brush cathode, together with aerating process, synergistically accelerate the S(IV) oxidation. Therefore, integrated electrochemical-aerating oxidation method using MPAN-CF&PAN-CF anode–cathode brushes is promising for industrial application and is expected for the treatment of high sulfur flue gas in future.

Gas-well water breakthrough time prediction model for high-sulfur gas reservoirs considering sulfur deposition

The sulfur-solubility decreases as a result of the decrease in gas reservoir pressure, leading to the solid-phase sulfur deposition. As a consequence, both the reservoir porosity and permeability decrease, subsequently influencing gas well water breakthrough time (GWWBT) in high sulfur gas reservoirs (HSGRs) with edge/bottom water. To acquire the value of GWWBT, a GWWBT prediction model for HSGRs should be established while taking into account sulfur deposition. Accordingly, based on gas Non-Darcy seepage law and sulfur deposition theory in porous media, a novel GWWBT in high sulfur gas reservoir with bottom water was developed in this study. The effect of dynamic factors (e.g., sulfur deposition, gas Non-Darcy flow, irreducible water saturation, and residual gas saturation) on GWWBT was involved in this model. The GWWBT was calculated via the proposed method and three classical models in five field basic parameters, and was compared with five filed values, respectively. This result indicates that the calculation of proposed method is in closer agreement with the field production data, and illustrates that the new proposed model is more reliable. In addition, the influence of dynamic factors was further discussed in detail by this proposed model.

A prediction model for water breakthrough time in high-sulfur gas reservoir with edge water

The water coning phenomenon leads to decrease the wellhead pressure with moving of water into gas production zone, which is regarded as one of most serious problems during gas production. It has been shown that water breakthrough time plays an important role in analyzing the water coning phenomenon and production of water. However, the existing prediction models of water breakthrough time are very scarce and need to be discussed. In this work, a novel model for water breakthrough time in high-sulfur gas reservoir with edge water is developed based on flow law and sulfur precipitation model in porous media. The effect of irreducible water saturation, residual gas saturation, and the distance between gas well and edge water, sulfur saturation and gas non-Darcy flow on water breakthrough time was involved in this model. The validity of the proposed model is verified by comparing the existing models available. A good trend is found between them. In addition, the influence of the distance between gas well and edge water, sulfur saturation and gas non-Darcy flow on water breakthrough time was detail discussed further.

A golden era for natural gas development in the Sichuan Basin

Owing to the technical innovation as well as a better understanding of gas exploration, nine giant gas fields have been successively discovered in the Sichuan Basin with cumulative proven gas reserves of 3.69 trillion cubic meters, where the annual natural gas productivity ranks the second in China. The CNPC latest oil & gas resources evaluation results demonstrate that natural gas resources in the Sichuan Basin takes the first place among those petroliferous basins all over China, but its proved gas reserves is only 10%, so the exploration prospect is bright. Over the past decades, PetroChina Southwest Oil & Gas Field Company has made great efforts to complete its technical systems, improve gas pipeline networks, and streamline gas markets, laying a robust foundation for the natural gas development in the Sichuan Basin. To further enhance the natural gas reserves and productivity in this basin and to achieve the biggest gas province in China, this company presents the following major projects: progressive multi-strata exploration and development in the central Sichuan area, Safe and efficient development of high-sulfur gas fields in the northeastern Sichuan area, Demonstrative exploration and development of deep marine carbonate gas reservoirs in the northwestern Sichuan area, Exploitation and development of large Cambrian pre-salt structural gas reservoirs in the eastern Sichuan area, and Extensive and beneficial development of shale gas in southern Sichuan. As the key to the Southwest growth pole, the above projects cover all the important, hard and hot fields of the whole basin and multiple gas-bearing strata and layers. With all the projects fulfilled, natural gas productivity will be 25–29 billion cubic meters (bcm) in 2020, accounting for most parts of this company's whole planning production (30 bcm in total), and will reach up to 50–70 bcm in 2030. It is predicted that natural gas development in the Sichuan Basin will be in a golden era in the long term.

Characteristics of the Changxing Fm biohermal gas reservoir in the Yuanba Gasfield, Sichuan Basin and development countermeasures

Located in the Sichuan Basin, the Yuanba Gasfield is the deepest high-sulfur carbonate gas field among those discovered in the world. Its biohermal gas reservoir of the Upper Permian Changxing Fm is characterized by ultra depth, multi-stage small and scattered reef, thin reservoir, poor physical properties, strong heterogeneity, complex fluid distribution, and low production of vertical wells. The development of the biohermal gas reservoir is subject to many difficulties. For example, it is necessary to deepen the studies on time–space distribution laws of reef dolomite reservoirs; it is difficult to characterize small reefs precisely and predict thin reservoirs quantitatively; the deployment and optimization design of horizontal wells are influenced by multiple factors; and the difficulty for horizontal wells with long horizontal sections to run through high-quality thin reservoirs is high. In order to develop the Yuanba Gasfield efficiently, therefore, it is necessary to carry out a series of technical researches on the distribution laws and development models of biohermal reservoirs, precise characterization of small reefs, quantitative prediction of thin reservoirs, optimization design of horizontal wells in banded small reef gas reservoirs, and real-time trajectory optimization and adjustment of horizontal wells in ultra-deep thin reservoirs. These research results provide a powerful support for the development and construction of the Yuanba Gasfield. Based on these technologies, China's first ultra-deep high-sulfur large biohermal gas field was built with a mixed gas annual production capacity of 40 × 108 m3. The successful commissioning of the Yuanba Gasfield lays a basis for the leading position of China in the field of high-sulfur gas field development. In addition, it is of great significance to the long-term stable gas supply in 70 cities of six provinces and two municipalities along the “Sichuan-to-East China Gas Transmission Pipeline”, as well as to the industrial structure adjustment in central–western China and the economic development along the Yangtze River.

An isotope study of the accumulation mechanisms of high-sulfur gas from the Sichuan Basin, southwestern China

The mechanism of hydrogen sulfide (H2S) generation plays a key role in the exploration and development of marine high-sulfur natural gas, of which the major targets are the composition and isotope characteristics of sulfur-containing compounds. Hydrocarbon source rocks, reservoir rocks, natural gases and water-soluble gases from Sichuan Basin have been analyzed with an online method for the content of H2S and isotopic composition of different sulfur-containing compounds. The results of comparative analysis show that the sulfur-containing compounds in the source rocks are mainly formed by bacterial sulfate reduction (BSR), and the sulfur compounds in natural gas, water and reservoir are mainly formed by thermal sulfate reduction (TSR). Moreover, it has been shown that the isotopically reversion for methane and ethane in high sulfur content gas is caused by TSR. The sulfur isotopic composition of H2S in natural gas is inherited from the gypsum or brine of the same or adjacent layer, indicating that the generation and accumulation of H2S have the characteristics of either a self-generated source or a near-source.

The Genesis and Prospecting Significance of High-sulfur Gas Condensates in the Deep Dolomite Reservoirs Beneath Gypsum Rocks: A Case Study of the Cambrian Reservoir in Tarim Basin

Comprehensive two-dimensional gas chromatography (GC×GC-TOFMS) was used to detect recently discovered condensates in the Cambrian dolomite reservoir beneath gypsum rocks of Tarim Basin. It was found that the thioadamantane and dibenzothiophene compounds are rich in the dolomite reservoirs, which indicates that the gas condensates have undergone hydrocarbon charging with TSR genesis. Based on the contents of SO42− and Mg2+ in the formation water of the Well ZS-1 reservoirs, the dolomite reservoirs and gypsum caps of intraplatform tidal flat facies sediments have been proven to be an effective geological combination to provide sulfate contact-ion pairs for TSR initiation. Compared with typical high-sulfur gas reservoirs with TSR throughout the world, the TSR extent in the Lower Cambrian dolomite reservoirs of ZS-1 is lower, and the liquid hydrocarbons in the Lower Cambrian of Well ZS-1 at the buried depth close to 7,000 m have not intensively cracked. Therefore, it is speculated that abundant cracking gas may occur in deeper slopes and basins (about 9,000 m) with high content of H2S and CO2. It is also revealed that deep dolomite reservoirs beneath gypsum rocks are the actual geological conditions for the accumulation and preservation of secondary H2S-bearing gas condensates.

New progresses in safe, clean and efficient development technologies for high-sulfur gas reservoirs

In China, there are a lot of high-sulfur gas reservoirs with total proved reserves of over 1 trillion m3, most of which were discovered in the Sichuan Basin. Most high-sulfur gas reservoirs in China, distributed in marine carbonate zones, are characterized by great buried depths, complex geologic conditions, high temperatures, high pressures, high H2S and CO2 content, presenting various challenges in gas field development engineering and production safety. Since the development of Sinian high-sulfur gas reservoirs in the Weiyuan area of the Sichuan Basin started in the 1960s, Wolonghe, Zhongba and other medium to small-scale gas reservoirs with medium to low sulfur content have been developed. Ever since 2009, successful production of Longgang and Puguang in the Sichuan Basin, together with some other high-sulfur gas reservoirs highlighted the breakthroughs in development technologies for high-sulfur gas reservoirs in China. This paper reviews the progress made in gas reservoir engineering, drilling and completion engineering, gas production, pipeline transportation, corrosion control, natural gas purification, HSE and other aspects with consideration of specific requirements related to safe, clean and high-efficient development of high-sulfur gas reservoirs since the “12th Five-Year Plan” period. Finally, considering the challenges in the development of high-sulfur gas reservoirs in China, we summarized the trend in future technological development with the following goals of reducing risks, minimizing environmental damages, and enhancing the efficiency of high-sulfur gas reservoir development.

A REAL-TIME GIS PLATFORM FOR HIGH SOUR GAS LEAKAGE SIMULATION, EVALUATION AND VISUALIZATION

Abstract. The development of high-sulfur gas fields, also known as sour gas field, is faced with a series of safety control and emergency management problems. The GIS-based emergency response system is placed high expectations under the consideration of high pressure, high content, complex terrain and highly density population in Sichuan Basin, southwest China. The most researches on high hydrogen sulphide gas dispersion simulation and evaluation are used for environmental impact assessment (EIA) or emergency preparedness planning. This paper introduces a real-time GIS platform for high-sulfur gas emergency response. Combining with real-time data from the leak detection systems and the meteorological monitoring stations, GIS platform provides the functions of simulating, evaluating and displaying of the different spatial-temporal toxic gas distribution patterns and evaluation results. This paper firstly proposes the architecture of Emergency Response/Management System, secondly explains EPA’s Gaussian dispersion model CALPUFF simulation workflow under high complex terrain and real-time data, thirdly explains the emergency workflow and spatial analysis functions of computing the accident influencing areas, population and the optimal evacuation routes. Finally, a well blow scenarios is used for verify the system. The study shows that GIS platform which integrates the real-time data and CALPUFF models will be one of the essential operational platforms for high-sulfur gas fields emergency management.