Showing papers on "Secondary air injection published in 2022"

Crude Oil Oxidation in an Air Injection Based Enhanced Oil Recovery Process: Chemical Reaction Mechanism and Catalysis

Abstract: Air injection as a thermal method for heavy oil recovery has a long history of about a century. However, it has not been widely applied in oilfields to date because of many challenges caused by its technical complexity. In the last two decades, more and more attention has been paid to the air injection technique because of the increasing demand for the effective development of hard-to-recover resources, including heavy oil, bitumen, oil shale, water-flooded mature reservoirs, etc. in a more energy-saving, cost-effective, environmentally friendly way. Consequently, many considerable improvements in both theory and technology have been made recently. This work first reviews the recent advances in the reaction mechanism of crude oil oxidation with highlights on the difference and connection between the oxidation of different oil components as well as their interaction during cocombustion; then, it discusses the catalytic methods for intensifying crude oil combustion with different types of catalysts, including nanometal-based particles, water-soluble metallic salts, and oil-dispersed metal-based catalysts. On the basis of the detailed review and discussion, we shed light on the challenges facing the air injection process and put forward possible methods to solve them. Simultaneously, we point out the neglected aspects of the air injection process and open the way toward fresh thinking for its technical application. And finally, we propose promising perspectives for future work for improving the performance of air injection and its wide application.

Analysis of ground deformation development and settlement prediction by air-boosted vacuum preloading

Abstract: Vacuum preloading has been widely used to improve soft soils in coastal areas of China. An increasing amount of evidence from field operations has shown that conventional vacuum preloading is prone to clogging in prefabricated vertical drains (PVDs) and demands a large volume of sand fills. In recent years, air-boosted vacuum preloading has been developed to overcome these limitations; however, this method still requires more data to verify its performance. In this study, a field test for air-boosted vacuum preloading was conducted, and a large-strain two-dimensional (2D) finite element (FE) model was developed and validated against the field test data. Then, a series of FE parametric analyses was performed to assess key factors, i.e. the air injection pressure, the injection spacing, and the characteristics of cyclic injection, which affect the performance of the air-boosted vacuum preloading. The results showed that the ground settlement and lateral displacement of the soils increased due to an increase in the injection pressure, a decrease in the injection spacing, or increases in the number and duration of the injection cycles. Based on the parametric analyses, an empirical formula for ground settlement prediction was proposed and compared with a case history reported in the literature, showing good agreement.

Effect of split injection in DI diesel engine with varying injection proportion

Abstract: A new injection mechanism, split injection was introduced in this research in a DI diesel engine. Injection proportion was analyzed in four different manner at the condition of 40° BTDC for first injection and 12° BTDC for second injection, 350 bar injection pressure. Brake Thermal Efficiency was observed to be increased and emissions were reduced. In the single injection, heterogeneous mixture occurs due to injection of diesel at the end of compression stroke. Comparatively, homogeneous mixture was increased in split injection due to the air and fuel mixing in pilot injection. Thus, complete combustion was increased and brake thermal efficiency was improved by 16.5%. In comparison with single injection, split injection can be operated in low temperature itself. NOx emission, therefore, was observed to be lower in split injection mechanism (reduced upto 32.6%). Due to homogeneous mixture and complete combustion, HC emission was also decreased in split injection by 9 ppm.

Efficacy of air tamponade treatment of idiopathic macular holes of different diameters and of follow-up intravitreal air tamponade for persistent holes

Abstract: To evaluate the efficacy of air tamponade in idiopathic macular hole (iMH) surgery and of an additional intravitreal air injection in the treatment of persistent holes.Retrospective, observational case series. Sixty eyes of 60 patients with an iMH underwent phacoemulsification of cataract (when appropriate), pars plana vitrectomy, and internal limiting membrane peeling, followed by air tamponade. Eyes with persistent holes underwent an additional intravitreal air injection within 1 week after surgery. The iMH closure rate and the best-corrected visual acuity were evaluated.In all 30 eyes with an iMH diameter <400 µm, the iMH closed after the primary surgery; however, only 17 of 30 eyes with an iMH diameter of ≥400 µm closed after the primary surgery. For the 13 eyes with persistent holes, an additional intravitreal air injection resulted in successful hole closure. There was no significant difference in the best-corrected visual acuity at the final follow-up between the closed subgroup and the initially unclosed subgroup after closure.Pars plana vitrectomy combined with air tamponade effectively cured small iMHs. For large iMHs not closed after the primary surgery, an additional intravitreal air injection resulted in hole closure and achieved a good prognosis.

Optimal Parameters of Gas Drainage and Carbon Dioxide Inerting Technology and Its Application in a High Gassy and Spontaneous Combustion Mine

Abstract: In the process of coupling disaster prevention and control of gas and coal spontaneous combustion in goaf, there is a great contradiction between the gas drainage and carbon dioxide inerting technology. The key performance indexes are put forward to solve the coupling disaster, such as the air quantity of the intake airway (A), the gas drainage rate (B), the carbon dioxide injection rate (C), and the injection depth (D). Using the numerical simulation method and the orthogonal test of four factors and three levels, we establish the coupling disaster model of the no. 7436 working face in the Kongzhuang coal mine. Using a combination of the relative membership degree method and range analysis, the optimal level of each factor is determined, which is AIIBIIICIIDII. Furthermore, the distribution law of the airflow field is obtained under the conditions of different gas drainage rates and carbon dioxide injection rates. The results show that the gas concentration decreases with an increase in gas drainage in the upper corner, but it has little impact on the width of the oxidation zone. The gas concentration can be reduced to 1%, while the gas drainage rate is higher than 35 m3/min. With an increase in gas injection rate, the carbon dioxide emission rate increases in the upper corner, but the width of the oxidation zone decreases. Also, the gas injection rate should be less than 800 m3/h. Moreover, with an increase in injection time in the upper corner during the injection process, the carbon dioxide and gas concentrations increase, and the maximum carbon dioxide concentration is 1.3%, and the maximum gas concentration is 0.42%, which is consistent with the results of numerical simulations.

New Insights into the Understanding of In-Situ Combustion: The Nature of the Fuel and the Role of Operating Pressure

Abstract: Historically, the air injection literature has stated that the fuel for the in-situ combustion (ISC) process is the carbon-rich, solid-like residue resulting from distillation, oxidation, and thermal cracking of the residual oil near the combustion front, commonly referred to as “coke.” At first glance, that assumption appears sound, because many combustion tube (CT) tests reveal a “coke bank” at the point of termination of the combustion front. However, when one examines both the laboratory results from tests conducted on various oils at reservoir conditions and historical field data from different sources, the conclusion may be different from what has been assumed. For instance, CT tests performed on light oils, at elevated pressures, rarely display any significant sign of coke deposition, which would make them poor candidates for air injection; nevertheless, they have been some of the most successful ISC projects. An analysis of different ramped temperature cracking (RTC) and ramped temperature oxidation (RTO) experiments performed on oil samples ranging from 6.5 to 38.8 °API, at reservoir pressures, indicates that thermal cracking and oxidation do not tend to generate enough coke to sustain the ISC process in light oil reservoirs. Similarly, peak temperatures observed during RTO and CT tests performed on lighter oils, at high pressures, were below the levels required to be associated with the combustion of coke. Instead, RTC and RTO experiments indicate that flammable vapors are also generated and can be consumed as fuel, in a behavior that is consistent across the entire oil density spectrum. Such vapor fuel appears to be the result of oxidative and thermal cracking of original and oxidized oil fractions. Therefore, while coke may form as a result of low-temperature oxidation of heavy oil fractions, and while thermal cracking of those fractions on the pathway to coke may produce vapor components that may themselves burn, the coke itself is not necessarily the main fuel for the process, particularly for lighter oils. This paper presents new insights regarding the nature of the fuel utilized by the ISC process and the role played by the different hydrocarbon phases present. It discusses the fundamental aspects associated with the proposed theory, and it summarizes the laboratory evidence and the field evidence which support the concept. This new theory does still share much common ground with the current understanding of the ISC process, but with a twist. The new insights result from the analysis of laboratory tests performed on lighter oils at reservoir pressures; data that were not available at the time the original ISC concepts were developed. This material suggests a change to one of the most important paradigms related to the ISC process, which is the nature of the fuel. This affects the way we understand the process but provides a unified theory, which is important for the modeling efforts and overall development of the technology.

In-Situ Steam Generation Using Mist Water-Air Injection as Enhanced Oil Recovery and Energy Efficiency Process: Kinetic Modeling and Numerical Simulation Approach

Abstract: In the current energy transition era, oil exploitation and especially the development of heavy oil reservoirs are facing big challenges to overcome the possible limitations in terms of economy (oil price), energy efficiency, and carbon footprint. Particularly, thermal enhanced oil recovery processes need to be re-evaluated in an attempt to harness the injected and produced energy. In that sense, Ecopetrol is evaluating new strategies to optimize the current steam injection process using different hybrid technologies from laboratory to field scale. One of the most attractive initiatives is evaluating the in-situ steam generation using mist water-air injection. This process involves simultaneous air and water injection into the formation through a set of nozzles. It looks to use part of the in-situ oil as a fuel, using the reservoir not only as a tank of energy but also as a steam generator. The main contribution of the technique concerning conventional steam generation is the use of the heat from the combustion of the residual oil to generate an in-situ steam front to transfer the uncontacted oil. This is reflected in reduced carbon dioxide (CO2) emissions, reduced fuel and water requirements, and increased oil production and net energy recovery. This article describes the methodology, results, history matching, and kinetic modeling of experimental evaluations and the upscaling of the experimental observations to a representative sector model from a Colombian heavy oil field. Results are described in terms of incremental oil recovery, energy efficiency, and carbon intensity compared with the baseline (a traditional steamflooding scenario). The technology of in-situ steam generation using mist waterair injection led to benefits in terms of better energy use and reducing the external fuel dependency for steam generation at the surface. Additionally, it was possible to identify improvements in incremental oil recovery (around 90%), energy efficiency (about 10 times less energy required to produce 1 m3 of oil), and reduction in carbon intensity (up to 91%) considering as baseline a conventional steamflooding scenario. These results will be key input parameters for designing and commissioning future applications in the Colombian fields.

Effects of casing air injection on film cooling and aerodynamic performances of an axial turbine cascade

Abstract: Rotor casing injection is one of the technical means for tip leakage flow control and casing thermal management. In the current investigation, a series of numerical simulations with the unsteady sliding mesh method are conducted to illustrate the effects of injection location, tip clearance, and shaped injection hole on the aerodynamic and cooling performance of casing air injection in an axial turbine cascade, under three injection mass flow ratios (0.15%, 0.30%, and 0.45%). The results indicate that the casing injection at X/Ca = 0.1 performs the best in reducing the tip leakage mass flow rate, but the highest isentropic efficiency appears when the injection holes are located at X/Ca = 0.3. The increase of the tip clearance is detrimental to the aerodynamic and film cooling performances of the casing injection scheme. Moreover, the application of shaped holes (converging slot hole and fan-shaped hole) plays a positive role in improving film cooling effectiveness and increasing isentropic efficiency. Especially under a large coolant to mainstream mass flow ratio of 0.45%, the results show that the fan-shaped hole improves the spatially-averaged casing film cooling effectiveness by approximately 16% relative to the cylindrical hole.

Application of a Developed Numerical Model for Surfactant Flushing Combined with Intermittent Air Injection at Field Scale

Abstract: Surfactant flushing with intermittent air injection, referred to as enhanced flushing, has been proposed at a site in Korea contaminated by military activity to overcome the difficulty of treatment caused by a layered geological structure. In this study, we developed a simple numerical model for exploring the effects of various physical and chemical processes associated with enhanced flushing on pollutant removal efficiency and applied it in a field-scale test. This simple numerical model considers only enhanced hydraulic conductivity rather than all of the interacting parameters associated with the complex chemical and physical processes related to air and surfactant behavior during enhanced flushing treatment. In the numerical experiment, the removal efficiency of residual non-aqueous phase liquid (NAPL) was approximately 12% greater with enhanced, rather than conventional, flushing because the hydraulic conductivity of the low-permeability layer was enhanced 5-fold, thus accelerating surfactant transport in the low-permeability layer and facilitating enhanced dissolution of residual NAPL. To test whether the enhanced flushing method is superior to conventional flushing, as observed in the field-scale test, successive soil flushing operations were simulated using the newly developed model, and the results were compared to field data. Overall, the simulation results aligned well with the field data.

Exhaust Gas Temperature Pulsations of a Gasoline Engine and Its Stabilization Using Thermal Energy Storage System to Reduce Emissions

Abstract: Modern automotive gasoline engines have highly efficient after-treatment systems that reduce exhaust gas emissions. However, this efficiency greatly depends on the conditions of the exhaust gas, mainly the temperature and air–fuel ratio. The temperature instability during transient conditions may cause a reduction in the efficiency of the three-way catalyst (TWC). By using a thermal energy storage system before TWC, this negative effect can be suppressed. In this paper, the effects of the temperature stabilization on the efficiency of the three-way catalyst were investigated on a 1-D turbocharged gasoline engine model, with a focus on fuel consumption and emissions. The thermal energy storage system (TESS) was based on PCM materials and was built in the exhaust between the turbine and TWC to use the energy of the exhaust gas. Three different materials were picked up as possible mediums in the storage system. Based on the results, the usage of a TESS in a gasoline after-treatment system has shown great potential in improving TWC efficiency. This approach can assist the catalyst to operate under optimal conditions during the drive. In this study, it was found that facilitating the heat transfer between the PCM and the catalyst can significantly improve the emissions’ reduction performance by avoiding the catalyst to light out after the cold start. The TESS with PCM H430 proved to reduce the cumulative CO and HC emissions by 8.2% and 10.6%, respectively, during the drive. Although a TES system increases the after-treatment cost, it can result in emission reductions and fuel consumption over the vehicle’s operating life.

Experimental Evaluation of Shale Oil Development Effectiveness by Air Injection

Abstract: In recent years, as an important part of unconventional resources, the effective development of shale oil has been a key area of research in petroleum engineering. Given the widespread availability and low cost of air, the evaluation of air injection in shale reservoirs is a topic worth exploring. This paper analyzes the production performance of different methods of air injection development in the shale reservoir, including air flooding and air huff and puff (HnP), based on full-diameter core air injection experiments. Meanwhile, the characteristics of the residual oil and produced oil are revealed by forming a systematic evaluation method that includes nuclear magnetic resonance (NMR), laser scanning confocal microscopy (LSCM), and gas chromatographic (GC) analysis. The results show that air flooding development is characterized by early gas breakthrough, long oil production period, and “L” shape oil production decline; while air HnP is characterized by first producing gas and then producing oil, rapid oil production, and high oil recovery efficiency in the first round. Compared with air flooding, the replacement efficiency of the first round of air HnP is significantly higher, demonstrating higher feasibility of air HnP in the early stages of development, although the cumulative recovery of three rounds air HnP (17.17%) is lower than that of air flooding (23.36%). The large pores (T2 > 10 ms) are the main source of air injection recovery, while the residual oil is mainly concentrated in the medium pores (1–10 ms). Air injection development has a higher recovery factor for light components (C15−), resulting in a higher level of heavy components in the residual oil. This paper discusses the feasibility and development effectiveness of air injection in shale oil reservoirs, and its development characteristics are further clarified.