High-sulfur Gas Research Articles

Optimization of fracturing parameters for horizontal wells in high-sulfur gas reservoirs considering the effect of sulfur deposition

During the development of high-sulfur gas reservoirs, the precipitation and deposition of elemental sulfur can lead to a reduction in reservoir porosity and permeability. Previous studies focus on the well production with optimized operational parameters, but the effect of sulfur deposition is not included, which impacts fracturing parameters, well production, and economic evaluation. Therefore, this work proposes a reasonable approach for parameter optimization considering sulfur. The variation of porosity and permeability are first evaluated during sulfur deposition. After that, fracture half-length, fracture spacing, fracture conductivity, and fracture distribution are optimized with orthogonalization factor analysis, and the influence of sulfur deposition on different fracture parameters are detailed analyzed. The results shown that the fracture half-length and fracture conductivity are greatly affected by sulfur deposition. Finally, net profit value is applied to obtain the optimal fracture spacing interval. With economic evaluation, the optimal fracture spacing interval of 125 m∼ 150 m is determined considering the net profit and the payback period. This work provides a useful economic method for fracture parameter optimization high-sulfur gas reservoirs, which benefits for the development and production of gas reservoirs.

Interfacial properties of CO2 and liquid sulfur in high-sulfur gas fields: Molecular simulations on carbonate mineral surfaces

As the global energy landscape transforms, the development of high-sulfur natural gas has become increasingly critical. However, sulfur deposition during these gas field developments significantly affects operational efficiency. This study employed molecular dynamics simulation to explore the effectiveness of CO2 in alleviating sulfur deposition on carbonate rock reservoirs. Specifically, it examined the interfacial tension between liquid sulfur and CO2, the wettability of sulfur on carbonate rock mineral surfaces, and the kinetics of CO2 displacing liquid sulfur. Results show that as CO2 pressure increases from 10 MPa to 60 MPa, the interfacial tension between liquid sulfur and CO2 decreases by 84 %, from 35.54 mN/m to 5.53 mN/m. The contact angles of sulfur droplets on calcite and dolomite surfaces stabilize at 41.82° ± 2.10° and 44.33° ± 3.27°, respectively, indicating greater sulfur spread on calcite surfaces. With higher CO2 pressures, sulfur deposition on mineral surfaces and interfacial tension both decrease significantly, while the wetting angle of liquid sulfur increases, particularly on dolomite. At 60 MPa CO2 pressure, the adsorption energy of dolomite for liquid sulfur drops from 364.56 kcal/mol to 25.46 kcal/mol, a 93 % reduction, suggesting CO2′s dual role in displacing sulfur and promoting its desorption from mineral surfaces. Furthermore, the efficiency of sulfur deposition alleviation in carbonate rock slit structures improves and stabilizes at around 40 MPa CO2 pressure. This study presents a potential environmentally friendly approach for efficiently developing high-sulfur gas fields, and its findings provide practical insights for optimizing CO2 injection strategies to mitigate sulfur deposition.

Research advances on the mechanisms of reservoir formation and hydrocarbon accumulation and the oil and gas development methods of deep and ultra-deep marine carbonates

Based on the new data of drilling, seismic, logging, test and experiments, the key scientific problems in reservoir formation, hydrocarbon accumulation and efficient oil and gas development methods of deep and ultra-deep marine carbonate strata in the central and western superimposed basin in China have been continuously studied. (1) The fault-controlled carbonate reservoir and the ancient dolomite reservoir are two important types of reservoirs in the deep and ultra-deep marine carbonates. According to the formation origin, the large-scale fault-controlled reservoir can be further divided into three types: fracture-cavity reservoir formed by tectonic rupture, fault and fluid-controlled reservoir, and shoal and mound reservoir modified by fault and fluid. The Sinian microbial dolomites are developed in the aragonite-dolomite sea. The predominant mound-shoal facies, early dolomitization and dissolution, acidic fluid environment, anhydrite capping and overpressure are the key factors for the formation and preservation of high-quality dolomite reservoirs. (2) The organic-rich shale of the marine carbonate strata in the superimposed basins of central and western China are mainly developed in the sedimentary environments of deep-water shelf of passive continental margin and carbonate ramp. The tectonic-thermal system is the important factor controlling the hydrocarbon phase in deep and ultra-deep reservoirs, and the reformed dynamic field controls oil and gas accumulation and distribution in deep and ultra-deep marine carbonates. (3) During the development of high-sulfur gas fields such as Puguang, sulfur precipitation blocks the wellbore. The application of sulfur solvent combined with coiled tubing has a significant effect on removing sulfur blockage. The integrated technology of dual-medium modeling and numerical simulation based on sedimentary simulation can accurately characterize the spatial distribution and changes of the water invasion front. Afterward, water control strategies for the entire life cycle of gas wells are proposed, including flow rate management, water drainage and plugging. (4) In the development of ultra-deep fault-controlled fractured-cavity reservoirs, well production declines rapidly due to the permeability reduction, which is a consequence of reservoir stress-sensitivity. The rapid phase change in condensate gas reservoir and pressure decline significantly affect the recovery of condensate oil. Innovative development methods such as gravity drive through water and natural gas injection, and natural gas drive through top injection and bottom production for ultra-deep fault-controlled condensate gas reservoirs are proposed. By adopting the hierarchical geological modeling and the fluid-solid-thermal coupled numerical simulation, the accuracy of producing performance prediction in oil and gas reservoirs has been effectively improved.

Separation of sulphur particles and droplets in high-sulfur gas fields based on a rotary thread demister: Experimentation, numerical simulation and optimization

To address the clogging of demister by elemental sulfur of high-sulfur gas fields, a rotary thread demister was proposed as an alternate. The results show: The feasibility of the rotary thread demister is verified through force analysis and simulation experiments; The experimental results revealed the Realizable k-ε turbulence model has the smallest average error of 3 %; Increases in rotational speed, count, diameter, and layers of the rotary thread enhance separation efficiency and pressure drop; Higher inlet velocities reduce separation efficiency while increasing pressure drop; Based on the response surface methodology and NSGA-II algorithm, the optimal parameters are determined, achieving separation efficiency of 100 % and pressure drop of 45.67 Pa for 19 μm sulfur particles and 20 μm droplets; The same parameters can remove the 3 μm size droplets and sulphur particles with separation efficiencies of 90.2 % and 92.3 %, respectively, at a pressure drop of 43.8 Pa without considering particle collisions.

A Predictive Model for Wellbore Temperature in High-Sulfur Gas Wells Incorporating Sulfur Deposition

HSG (high-sulfur gas) reservoirs are prevalent globally, yet their exploitation is hindered by elevated levels of hydrogen sulfide. A decrease in temperature and pressure may result in the formation of sulfur deposits, thereby exerting a notable influence on gas production. Test instruments are susceptible to significant corrosion due to the presence of hydrogen sulfide, resulting in challenges in obtaining bottom hole temperature and pressure test data. Consequently, a WTD (wellbore temperature distribution) model incorporating sulfur precipitation was developed based on PPP (physical property parameter), heat transfer, and GSTP (gas–solid two-phase) flow models. The comparison of a 2.53% temperature error and a 4.80% pressure error with actual field test data indicates that the established model exhibits high accuracy. An analysis is conducted on the impact of various factors, such as production, sulfur layer thickness, reservoir temperature, and reservoir pressure, on the distribution of the wellbore temperature field and pressure field. Increased gas production leads to higher wellhead temperatures. The presence of sulfur deposits reduces the flow area and wellhead pressure. A 40% concentration of hydrogen sulfide results in a 2 MPa pressure drop compared to a 20% concentration. Decreased reservoir pressure and temperature facilitate the formation of sulfur deposits at the wellhead.

Solubility evolution of elemental sulfur in natural gas with a varying H2S content.

The solubility variations of elemental sulfur are of great importance in the prevention of sulfur deposition during the development of high-sulfur gas formations. It has been observed that the solubility varies with H2S content, which is the main solvent of elemental sulfur in natural gas. Moreover, the addition of small amounts of CH4 and/or CO2 in H2S leads to a dramatic solubility reduction of which the mechanism remains unclear. Using a modified direct coexistence method, molecular dynamics simulations are conducted to uncover the molecular mechanism of the solubility reduction. The observed solubility variations with H2S content are reproduced, and the solubility reduction is interpreted by the antisolvent effect of CH4 and CO2. While the H2S content varies in a wide range in the known high-sulfur gas formation, our simulations provide useful information for controlling the sulfur deposition in gas development. Molecular dynamics simulations are carried out using the LAMMPS package. The initial models are constructed with the Packmol software. The Ballone and Jones' potential is used for S8, the Galliero's potential for H2S and CO2, and the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field for CH4. The time step is set to 1fs, and the molecular trajectories of additional 2ns after equilibrium are collected for analysis.

Adsorption mechanism study of sour natural gas and sulfur in high-sulfur carbonate rock gas reservoirs

As the world pivots towards green and renewable energy sources, natural gas stands out as a clean and efficient alternative. In particular, there has been an upsurge in the exploration and development of gas fields rich in hydrogen sulfide (H2S). However, an escalating issue of sulfur deposition is notably pronounced in carbonate rock reservoirs predominantly comprised of dolomite, as exemplified in China's Yuan Ba gas field. This study examines sulfur adsorption in high-sulfur gas reservoirs and its effects on carbonate rock formations. Molecular simulation analysis reveals that the sour natural gas density in 20 Å dolomite nanopore structure experiences an average increase of 30% at the nanoscale. Notably, CO2 and H2S manifested strong adsorption tendencies in smaller pore sizes, with CO2's strong adsorption state layer thickness measuring approximately 2.93 Å, and H2S's at about 1.871 Å. Additionally, it was found that the adsorption energy of sour natural gas decreases with rising temperature and pore size, and falling pressure, yet the temperature's effect on excess adsorption density is minor above 40 MPa. As the pore size reaches 160 Å, the strong adsorption states of CO2 and H2S dissipate. Beyond 160 Å, the influence of nanoscale dimensions is negligible, with only a 2.23% increase in adsorbed phase density compared to the bulk phase. The introduction of S8 molecules amplified the adsorption proclivities of CO2 and H2S, urging them closer to the pore wall. The study reveals that CO2 or H2S reinjection into formations could effectively mitigate sulfur deposition in pores smaller than 160 Å, offering valuable insights for the development of high-sulfur gas fields.

Residual strength of a casing with corrosion semi-ellipsoid defect in high-sulfur gas wells

There are few studies on the residual strength of semi-ellipsoid defect casing considering the bending moment load in high sulfur gas well. In this paper, a numerical model of a casing with corrosion defects exposed to bending moment is proposed. The effect of the defect positions along the circumference on the residual strength of the casing with bending moment is investigated. Parametric studies highlight that defect size have significant effect on the residual strength of the casing, and the circumferential defect and the axial defect can change the critical internal pressure and the critical axial load. This finding has a significant guidance for residual intensity evaluation of a casing with defect.

Application Study on the Activated Coke for Mercury Adsorption in the Nonferrous Smelting Industry

The massive release of mercury undermines environmental sustainability, and with the official entry into force of the Minamata Convention, it is urgent to strengthen the control of mercury pollution. The effectiveness of activated coke (AC) in removing elemental mercury (Hg0) from high temperatures and sulfur nonferrous smelting flue gas before acid production was studied. Experimental results indicated that the optimal temperature for Hg0 adsorption by AC was 150 °C. And the adsorption of Hg0 by AC was predominantly attributed to physical adsorption. Flue gas components (SO2 and O2) impact studies indicated that O2 did not significantly affect Hg0 adsorption compared to pure N2. Conversely, SO2 suppressed the adsorption capacity, while the simultaneous presence of SO2 and O2 exhibited a synergistic effect in facilitating the removal of Hg0. The characterization results of X-ray photoelectron spectroscopy (XPS) indicated that the SO2 molecule favored to anchor at the Oα site, leading to the formation of SO3. This subsequently oxidized the mercury to HgSO4 instead of HgO. The study demonstrates that cheap and easily accessible AC applications in the adsorption of mercury technology may help improve the sustainability of the circular economy and positively impact various environmental aspects.

Molecular mechanism of elemental sulfur dissolution in H2S under stratal conditions.

Resulting from the solubility reduction of elemental sulfur during the development of high sulfur gas formations, sulfur deposition often occurs to reduce the gas production and threaten the safety of gas wells. Understanding the dissolution mechanism of elemental sulfur in natural gas is essential to reduce the risk caused by sulfur deposition. Because of the harsh conditions in the high-sulfur formations, it remains challenging to in situ characterize the dissolution-precipitation processes, making deficient the knowledge of sulfur dissolution mechanism. The dissolution of sulfur allotropes (SN, N = 2, 4, 6 and 8) in H2S, the main solvent of sulfur in natural gas, is studied in this work by means of first-principles calculations and molecular dynamics simulations. While S6 and S8 undergo physical interaction with H2S under the conditions corresponding to those at 1-6 km stratigraphic depths, S2 and S4 react with H2S and form stable polysulfides. Unravelling the mechanism would be helpful for understanding and controlling the sulfur deposition in high-sulfur gas development.

Numerical simulation of welding residual stress in Incoloy 825/L360QS bimetal clad tube

With severe corrosion issues afflicting nearly half of all high sulfur gas fields, bimetal composite tubes have emerged as an optimal solution due to their superior corrosion resistance, mechanical properties, and cost-effectiveness. These tubes have gained widespread adoption in gas gathering applications. However, the evaluation of the corrosion performance of Incoloy 825 bimetal composite tubes within high sulfur gas field environments is yet to be adequately addressed. An investigation into the welding performance of both the base metal and weld is instrumental in ascertaining the safety and reliability of bimetal composite pipes. To this end, this paper presents a thermodynamically coupled finite element model of bimetal composite pipes, developed using SYSWELD software, and corroborates the model using the borehole method for empirical verification. The study further delineates the distribution of residual stress encountered during multi-layer and multi-pass welding of bimetal composite pipes.

Molecular mechanism in the solubility reduction of elemental sulfur in H2S/CH4 mixtures: A molecular modeling study

The solubility evolution of elemental sulfur in sour gas is key to study the occurrence and inhibition of sulfur deposition in the exploitation of high-sulfur gas reservoirs. Elemental sulfur mainly dissolves in H2S, and its solubility decreases dramatically in the presence of methane. As both methane and H2S are the main components in high-sulfur gas, it is essential to understand the molecular mechanism of the solubility reduction in H2S/CH4 mixtures. Molecular dynamics simulations are carried out for the S8, H2S and CH4 mixtures to reproduce the solubility reduction upon methane addition, and then used to reveal the reduction mechanism at the level of intermolecular interaction. The simulations reveal that both the strong competitiveness and high collision probability of H2S–CH4 pairs reduce the average densities of H2S–S(S8) and H2S–H2S pairs, which reduce the sulfur solubility in a direct/indirect but cooperative way. The role of methane in the solubility reduction is then discussed and the molecular mechanism of sulfur dissolution and precipitation in the sour gasses is addressed.

Optimization of CuO@SiO2 core-shell catalysts for catalytic AsH3 oxidation

Eliminating arsine (AsH3) from arc-furnace off-gas is becoming increasingly urgent owing to its hypertoxicity and overburdened environment. Herein, a series of CuO@SiO2 core-shell catalysts were synthesized for catalytic AsH3 oxidation in simulated arc furnaces off-gas. The effects of the hydrothermal temperature, CuO amount, and ammonia concentration on the AsH3 removal performance of the CuO@SiO2 catalysts were investigated. After optimization, many physical and chemical properties of the CuO@SiO2 catalysts, including the active components, were improved, resulting in considerable performance in AsH3 oxidation. The CuO@SiO2 catalysts also exhibited robust AsH3 removal performance in the presence of high concentration CO or organic sulfur gas (COS and CS2). In contrast, the coexisting gases H2S and PH3 could occupy the active sites, leading to the degradation of the AsH3 removal performance over the CuO@SiO2 catalysts. This study provides a new route for deep purification of AsH3 from arc furnaces off-gas.

Study on residual strength of defective production string under complex loads in high-sulfur gas wells

The existing studies on residual strength for the defective production string in high-sulfur gas wells mainly focus on defect shape and size under complex loads without bending moment. In this paper, a numerical model of a production string with corrosion defects under the complicated load with bending moment is established. The accuracy of the model is validated by comparing with standards. The effect of the defect positions on the residual strength of the production string under the action of bending moment is investigated. The influences of different defect shape and defect size on the equivalent stress distribution and residual strength of production string under different compound loads is also analyzed. It is found that the bending moment have great effect on the residual strength of the production string. Meanwhile, it is shows that both the defect geometry configuration and size have a significant effect on the equivalent stress distribution and residual strength of the tube. In addition, the circumferential defect and the axial defect can change the internal pressure load and the axial load. It is also revealed that the rectangular defect has the greatest influence on the residual strength of the production string than the circular and elliptical defects, and the depth factor in the defect size is dominant. The obtained results provide useful information for the use of the production string, rectangular defect with a large depth should be avoided.

Research on safety early warning of abnormal A-annular pressure of “three-high” gas wells based on data mining

A major safety accident will be triggered when the A-annular pressure value of high pressure, high productivity and high sulfur gas well exceeded the maximum allowable value. The A-annular pressure value of high pressure high productivity and high sulfur gas well once exceeded the allowable value will trigger a major safety accident. Therefore, this paper proposed a data mining based the gas well early warning strategy by analyzing the annular pressure mechanism and the change in the pattern of instantaneous gas volume, well temperature, and annular pressure in various conditions. To summarize, the law of gas well abnormal A-annular pressure is aimed at constructing a gas well safety warning rule for gas well stable production stage and shutdown period where the initial parameters setting in the early warning rule and adjustment optimization mechanism is also determined. Lastly, with the use of historical abnormal samples, the gas well early warning strategy bought up in this paper was verified. The example shown that compared with the traditional DCS system warning strategy, the gas well safety early warning strategy can identify the abnormal A-annular pressure phenomenon 82 h in advance thus achieving production safety management.

Numerical Simulation of Sulfur Deposition in Wellbore of Sour-Gas Reservoir

Sulfur deposition has an important effect on the productivity of sour-gas wells. Accurately predicting the occurrence of sulfur deposition and the location and amount of sulfur deposition in wellbore can effectively guide the production of gas wells. In this paper, the wellbore sulfur deposition model, pressure model, and transient temperature model are established for various well types. Then, numerical simulations of sulfur deposition in the sour-gas well were conducted by coupling these models. Examples show that the proposed methodology has high accuracy, and the average relative error of the calculated results is 3.61%. Based on the model, a sensitivity analysis was performed on the factors affecting sulfur deposition. The results show that with the increase of wellbore inclination angle, the critical sulfur carrying velocity first increased and then decreased, and the maximum critical velocity is about 30% larger than that of the vertical section. The amount of wellbore sulfur deposition increases with increased production time and decreased wellbore pressure, and the amount of wellbore sulfur deposition decreases with increased gas production rate, H2S content, and inclination angle. The results suggest that the sour-gas reservoir should be developed with the horizontal or deviated well, timely adjust the production system, and keep the gas-well production higher than the critical flow rate as much as possible. At the same time, wellbore heating and insulation, pre-cleaning technology, and the closely implemented sulfur deposition prevention technology in the middle and late stage of development can be adopted to reduce the occurrence of sulfur deposition to ensure the safe and efficient development of high-sulfur gas wells.

Application and Development of Selective Catalytic Reduction Technology for Marine Low-Speed Diesel Engine: Trade-Off among High Sulfur Fuel, High Thermal Efficiency, and Low Pollution Emission

In recent years, the International Maritime Organization (IMO), Europe, and the United States and other countries have set up different emission control areas (ECA) for ship exhaust pollutants to enforce more stringent pollutant emission regulations. In order to meet the current IMO Tier III emission regulations, an after-treatment device must be installed in the exhaust system of the ship power plant to reduce the ship NOx emissions. At present, selective catalytic reduction technology (SCR) is one of the main technical routes to resolve excess NOx emissions of marine diesel engines, and is the only NOx emission reduction technology recognized by the IMO that can be used for various ship engines. Compared with the conventional low-pressure SCR system, the high-pressure SCR system can be applied to low-speed marine diesel engines that burn inferior fuels, but its working conditions are relatively harsh, and it can be susceptible to operational problems such as sulfuric acid corrosion, salt blockage, and switching delay during the actual ship tests and ship applications. Therefore, it is necessary to improve the design method and matching strategy of the high-pressure SCR system to achieve a more efficient and reliable operation. This article summarizes the technical characteristics and application problems of marine diesel engine SCR systems in detail, tracks the development trend of the catalytic reaction mechanism, engine tuning, and control strategy under high sulfur exhaust gas conditions. Results showed that low temperature is an important reason for the formation of ammonium nitrate, ammonium sulfate, and other deposits. Additionally, the formed deposits will directly affect the working performance of the SCR systems. The development of SCR technology for marine low-speed engines should be the compromise solution under the requirements of high sulfur fuel, high thermal efficiency, and low pollution emissions. Under the dual restrictions of high sulfur fuel and low exhaust temperature, the low-speed diesel engine SCR systems will inevitably sacrifice part of the engine economy to obtain higher denitrification efficiency and operational reliability.

Analysis of sulfur deposition for high-sulfur gas reservoirs

Wellbore sulfur deposition is one of the most common problems during the development of high-sulfur gas reservoirs, which also affects the accuracy of bottomhole pressure(BHP) calculations. However, the existing BHP calculation methods have poor applicability to high-sulfur and water-producing gas wells. In this study, a model for calculating bottomhole pressure suitable for high-sulfur and water-producing gas wells was established. The model was solved by finite difference and iterative methods, and its accuracy was verified by a typical high-sulfur gas well in China. The results show: The pressure prediction errors are mainly distributed within −1%∼5%; As the well depth decreases, the precipitation trend of sulfur gradually increases due to the decrease in solubility; Affected by temperature and pressure distribution, liquid sulfur is often deposited in the lower part of wellbore, while solid sulfur is deposited in the middle-upper section, which will increase the pressure loss and the occurrence of production accidents. Controlling production pressure difference, adopting production system, and injecting sulfur dissolving agents can help prevent sulfur deposits and ensure the safe-efficient production. The findings of this study can help to more clearly reveal the wellbore sulfur deposits characteristics and more accurately calculate the bottom hole pressure of high-sulfur gas wells.

Development Status of Drainage Gas Recovery Technology in High Sulfur Gas Wells

Due to the particularity of its stratigraphic structure, Sichuan Basin is rich in natural gas resources. With the production of gas wells, effusion is bound to occur in the wellbore. Once water invasion occurs, it will lead to the decline of natural gas production and even shutdown of the wells. Therefore, timely drainage of water in the wellbore is the key to restoring gas well production. Because of the high sulfur content of natural gas in Sichuan Basin, the conventional gas well drainage measures are difficult to apply, and some special drainage measures need to be taken. This paper mainly reviews the development and present situation of drainage technology for gas wells with high sulfur content, and introduces four main types of high sulfur gas well drainage gas recovery technologies: plunger gas lift, tubing perforation, electrical submersible pump drainage gas recovery technology, and foam drainage gas recovery, and compares their applicability, advantages and disadvantages.

Effect of grain boundary engineering on corrosion behavior of nickel-based alloy 825 in sulfur environment

Grain boundary engineering (GBE) by appropriate deformation and heat treatment processes was applied to nickel-based alloy 825 due to its excellent corrosion resistance. The microstructure of nickel-based alloy was analyzed by electron backscatter diffraction (EBSD) and the effect of GBE on the corrosion resistance in high sulfur-containing environments was studied by electrochemical method. The results show that the ratio of low Σvalue coincidence site lattice (CSL) grain boundary is obviously improved from 47.1% to 65.5%. The special angle grain boundaries Σ3, Σ9, Σ27 and so on are randomly distributed on the network of the large angle grain boundaries, which destroy the connectivity of the original grain boundary network, and effectively block the corrosion cracking of the material along them. The corrosion resistance of nickel-based alloy 825 in high sulfur environments is enhanced verified by polarization curve and scanning electrochemical microscope, providing references for corrosion protection during the exploitation of high sulfur gas reservoirs.