Propagation of Measurement-While-Drilling Mud Pulse during High Temperature Deep Well Drilling Operations

Signal attenuates while Measurement-While-Drilling (MWD) mud pulse is transmited in drill string during high temperature deep well drilling. In this work, an analytical model for the propagation of mud pulse was presented. The model consists of continuity, momentum, and state equations with analytical solutions based on the linear perturbation analysis. The model can predict the wave speed and attenuation coefficient of mud pulse. The calculated results were compared with the experimental data showing a good agreement. Effects of the angular frequency, static velocity, mud viscosity, and mud density behavior on speed and attenuation coefficients were included in this paper. Simulated results indicate that the effects of angular frequency, static velocity, and mud viscosity are important, and lower frequency, viscosity, and static velocity benefit the transmission of mud pulse. Influenced by density behavior, the speed and attenuation coefficients in drill string are seen to have different values with respect to well depth. For different circulation times, the profiles of speed and attenuation coefficients behave distinctly different especially in lower section. In general, the effects of variables above on speed are seen to be small in comparison

Thermal Decomposition Mechanisms of Molecules Relevant to Chemical Vapor Deposition and Fuel Combustion by Flash Pyrolysis Photoionization Time-of-Flight Mass Spectrometry

Flash pyrolysis microreactor coupled with molecular beam extraction and photoionization time-of-flight mass spectrometry along with theoretical calculations are employed to study the pyrolysis of gas phase molecules with relevance to chemical vapor deposition (CVD) and fuel combustion. This dissertation presents a comprehensive exploration of the flash pyrolysis mechanisms of various organosilanes and hydrocarbons, including allyltrichlorosilane, allyltrimethylsilane, 1,1,2,2-tetraethylsilane, trimethylchlorosilane, tetraethylsilane, cyclohexane, and cycloheptane. Chapters 3 to 6 of this dissertation focus on investigating the decomposition pathways and identifying key reaction products of various CVD precursors through a combination of experimental observations and theoretical analyses. The study specifically examines allyltrichlorosilane, allyltrimethylsilane, 1,1,2,2-tetramethylsilane, trimethylchlorosilane, and tetraethylsilane. The findings reveal that allyltrichlorosilane decomposes primarily through Si-C bond homolysis, while the thermal decomposition of allyltrimethylsilane proceeds primarily via molecular eliminations. The pyrolysis of 1,1,2,2-tetramethylsilane involves molecular elimination reactions, Si-Si bond fission, H2 elimination, and decomposition to trimethylsilane and methylsilylene. Trimethylchlorosilane predominantly undergoes HCl molecular elimination, while tetraethylsilane follows Si-C bond homolysis. These studies have conducted a thorough examination of the pyrolysis mechanism of organosilane precursors, providing a comprehensive overview, and investigating their potential applications in SiC thin film production. Additionally, Chapters 7 and 8 explore the thermal decomposition mechanisms of cyclohexane and cycloheptane, elucidating the diradical mechanism in the primary initiation reactions. These comprehensive studies provide valuable insights into the intricate pyrolysis mechanisms of organosilanes and aviation fuel prototypes, facilitating the development of accurate models and efficient utilization strategies for these compounds

Steadiness of wave complex induced by oblique detonation wave reflection before an expansion corner

Oblique detonation wave (ODW) reflection before an expansion corner leads to a sophisticated wave complex, whose steadiness is critical to achieve a practical oblique detonation engine. Both steady and unsteady wave complexes have been observed before, but the features of unsteady wave dynamics with related unsteadiness rules are still unclear so far. In this study, the ODW reflections before an expansion corner have been simulated using the reactive Euler equations with a two-step induction-reaction kinetic model, and the wave complex structures and dynamics have been analyzed correspondingly. Three subsonic zones have been distinguished, and their interactions were found to determine the wave complex steadiness. The main subsonic zone derives from the ODW reflection, which locates behind the Mach stem, while two other subsonic zones form due to the shock reflection downstream. The two downstream subsonic zones might travel upstream and combine with the main subsonic zone, resulting in two different unsteadiness modes. These wave complex dynamics were analyzed with respect to the deflection location, deflection angle and inflow Mach number, leading to the boundaries of combustion modes and ascertaining the rule of mode regime. Some transient phenomena related with the flow instability have been also discussed, clarifying fine flow structures further. (C) 2021 Elsevier Masson SAS. All rights reserved

Numerical Investigation of the Oblique Detonation Waves and Stability in a Super-Detonative Ram Accelerator

This study numerically investigates the effects of diluent gas proportion, the overdrive factor, and throat width on the wave structure and thrust performance of a ram accelerator operating in super-detonative mode. For premixed gas of a high energy density, a typical unstart oblique detonation wave system is observed due to the ignition on the front wedge of the projectile, and the detonation waves move downstream to the shoulder as the energy density decreases. In the start range of the overdrive factor, the wave position also shows a tendency to move downstream as the projectile velocity increases, accompanied by oscillations of the wave surface and thrust. As the throat width increases, the wave standing position changes non-monotonously, with an interval of upstream movement and Mach reflection. The typical wave structure of a ram accelerator in super-detonative mode is identified, as well as the unstart stable wave features and the unstable process for choking, which can provide theoretical guidance for avoiding unstart issues in ram accelerators and optimizing their performance

Numerical study on reflection of an oblique detonation wave on an outward turning wall

Oblique detonation waves (ODWs) have been studied widely as the basis of detonation-based hypersonic engines, but there are few studies on ODWs in a confined space. This study simulates ODW reflection on a solid wall before an outward turning corner for a simplified combustor-nozzle flow based on a two-step kinetic model. Numerical results reveal three types of ODW structures: stable, critical, and unstable. When the reflection occurs at the turning point, the stable ODW structure remains almost the same as before reflection. When the wave reflects at the wall before the turning point, either the critical structure or the unstable structure arises, which has never been investigated before. Both structures have the same initial two-section detonation surface: but the critical one becomes stationary at a certain position, while the unstable one keeps traveling upstream. By adjusting the location of the expansion wave and degree of the turning angle, the difference of the two structures is attributed to the thermal choking appearing only in the unstable structure. The thermal choking is achieved by the merging of subsonic zones, whose dependence on the various parameters is discussed

Unsteady Oblique Detonation Waves in a Tunnel Induced by Inflow Mach Number Variation

Oblique detonation waves (ODWs) have been investigated widely aiming at facilitating their application in hypersonic engines. However, there is a lack of research on unsteady ODWs which are unavoidable in the hypersonic air-breathing scenario. In this study, unsteady ODWs triggered by the variation of the inflow Mach number (M0) have been studied and the geometric model is a tunnel with an outward-deflection upper wall to mimic an engine outlet. Numerical results demonstrate that when M0 deviates from the designed state, two typical wave structures arise, featuring a Mach stem of detonation or a post-corner recirculation zone. A sudden change in M0 leads to the transition of these two structures, generating unsteady ODWs temporally with a multi-segment-complex wave surface caused by triple points. The wave structures near the corner have been analyzed in detail, revealing how the Mach stem and the recirculation zone evolve into each other. Furthermore, the effects of unsteady ODWs on hypersonic propulsion applications have been discussed, providing possible ways to suppress the Mach stem of detonation

Pilot test of horizontal drilling and completion techniques in Nanpu Oilfield

The main reservoir of Nanpu Oilfield has considerable lateral variation and uncertain stratigraphic dip and faults making its geological tracking difficult. Because of the environmental constraints, few wells were drilled and the implementation of efficient development level is difficult. After analyzing the stability of the well bores, pore pressure, fracture pressure, collapse pressure, drill ability of basalt, reservoir characteristics and physical properties, reservoir structure, characteristics of oil and gas shows, reservoir damage, and reservoir sand, optimization research and pilot applications of extended-reach horizontal drilling, including optimal design of well profile and structure, well path control, individualized design of bit, optimization of drilling fluid system, reservoir protection, and screen completion, were carried out. All the three horizontal wells tested were successful in oil production. The early daily oil production in the three wells is 505, 736, and 1058 t, respectively. The production was normal and no sand was produced in the case of high production. The main drilling and completion techniques established in this study proved to be efficient. Key words: Nanpu Oilfield, pilot test, horizontal well, drilling and completion technique

Effects of Cowl-Induced Expansion on the Wave Complex Induced by Oblique Detonation Wave Reflection

Oblique detonation wave (ODW) reflection on the upper wall leads to a sophisticated wave complex, whose stability is critical to the application of oblique detonation engines. The unstable wave complex characterized with a continuous moving Mach stem has been observed, but the corresponding re-stability adjusting method is still unclear so far. In this study, the cowl-induced expansion wave based on the model with an upper-side expansion wall is introduced, and the ODW dynamics have been analyzed using the reactive Euler equations with a two-step induction-reaction kinetic model. With the addition of a cowl-induced expansion wave, the re-stabilized Mach stem has been distinguished. This re-stability is determined by the weakened secondary reflection wave of lower wall, while the final location of Mach stem is not sensitive to the position of the expansion corner. The re-stabilized ODW structure is also basically irrelevant to the expansion angle, while it may shift to unstable due to the merging of subsonic zones. Transient phenomena for the unstable state have been also discussed, clarifying fine wave structures further

Detonation wave structure and thrust variation of a ram accelerator with different projectile velocities

A study was conducted to investigate the effect of velocity on the detonation wave structure and thrust of a ram accelerator using a simulation of a premixed, reacting flow over a conical projectile. The simulation involved solving the compressible reactive Navier-Stokes equations with a detailed chemical model in a channel with a supersonic stoichiometric hydrogen-oxygen inflow. Results showed that at projectile velocities lower than the Chapman-Jouguet detonation velocity, a thermally choked unstart occurs. As the projectile velocity increases, the overdriven detonation mode, trans-detonative mode, and super-detonative mode successively form. The maximum thrust was achieved at the lower velocity limit under the overdriven normal detonation condition, but decreased continuously as an oblique detonation wave formed. The super-detonative mode was distinguished by the smoothness of the tail thrust derived from the recirculation zone and ignition before the conical ramp led to an unstart at the upper velocity limit