Study of Intra-Chamber Processes in Solid Rocket Motors by Fiber Optic Sensors

In this study, an experimental study of the burning rate of solid fuel in a model solid propellant rocket motor (SRM) E-5-0 was conducted using a non-invasive control method with fiber-optic sensors (FOSs). Three sensors based on the Mach–Zehnder interferometer (MZI), fixed on the SRM E-5-0, recorded the vibration signal during the entire cycle of solid fuel burning. The results showed that, when using MZI sensors, the non-invasive control of solid fuel burnout is made possible both by recording the time of arrival of the combustion front to the sensor and by analyzing the peaks on the spectrogram of the recorded FOS signal. The main mode of acoustic vibrations of the chamber of the model SRM is longitudinal, and it changes with time, depending on the chamber length. Longitudinal modes of the combustion chamber were detected by MZI only after the combustion front passed its fixing point, and the microphone was unable to register them at all. The results showed that the combustion rate was practically constant after the first second, which was confirmed by the graph of the pressure versus time at the nozzle exit.

Use of two vertical injectors in place of a horizontal injector to improve the efficiency and stability of THAI in situ combustion process for producing heavy oils

The current commercial technologies used to produce heavy oils and bitumen are carbon-, energy-, and wastewater-intensive. These make them to be out of line with the global efforts of decarbonisation. Alternative processes such as the toe-to-heel air injection (THAI) that works as an in situ combustion process that uses horizontal producer well to recover partially upgraded oil from heavy oils and bitumen reservoirs are needed. However, THAI is yet to be technically and economically well proven despite pilot and semi-commercial operations. Some studies concluded using field data that THAI is a low-oil-production-rate process. However, no study has thoroughly investigated the simultaneous effects of start-up methods and wells configuration on both the short and long terms stability, sustainability, and profitability of the process. Using THAI validated model, three models having a horizontal producer well arranged in staggered line drive with the injector wells are simulated using CMG STARS. Model A has two vertical injectors via which steam was used for pre-ignition heating, and models B and C each has a horizontal injector via which electrical heater and steam were respectively used for pre-ignition heating. It is found that during start-up, ultimately, steam injection instead of electrical heating should be used for the pre-ignition heating. Clearly, it is shown that model A has higher oil production rates after the increase in air flux and also has a higher cumulative oil recovery of 2350 cm3 which is greater than those of models B and C by 9.6% and 4.3% respectively. Thus, it can be concluded that for long-term projects, model A settings and wells configuration should be used. Although it is now discovered that the peak temperature cannot in all settings tell how healthy a combustion front is, it has revealed that model A does indeed have far more stable, safer, and efficient combustion front burning quality and propagation due to the maintenance of very high peak temperatures of mostly greater than 600 °C and very low concentrations of produced oxygen of lower than 0.4 mol% compared to up to 2.75 mol% in model C and 1 mol% in model B. Conclusively, since drilling of, and achieving uniform air distribution in horizontal injector (HI) well in actual field reservoir are costly and impracticable at the moment, and that electrical heating will require unphysically long time before mobilised fluids reach the HP well as heat transfer is mainly by conduction, these findings have shown decisively that the easy-and-cheaper-to-drill two vertical injector wells configured in a staggered line drive pattern with the horizontal producer should be used, and steam is thus to be used for pre-ignition heating.

Understanding the mobilised oil drainage dynamics inside laboratory-scale and field-scale reservoirs for more accurate THAI process design and operation procedures

The technical and economic validities of the toe-to-heel air injection (THAI) process for heavy oils upgrading and production are yet to be fully realised even though it has been operated at laboratory, pilot, and semi-commercial levels. The findings from Canadian Kerrobert THAI project suggested that there is no proportionality between oil production and air injection rates. However, this conclusion was reached without having to dig deeper into the dynamics of the transport processes inside the reservoir especially that efficient combustion was clearly taking place as the mol% oxygen in the produced gas was negligible. As a result, this study is conducted with aims of identifying the similarities and differences of the dynamics of the transport processes in lab-scale and field-scale reservoirs. For the first time, this study has found oil drainage dynamics inside the reservoir to be both scale-dependent and operation-dependent. For the laboratory-scale numerical model E, what is clearest is that all of the head of the oil flux vectors are either totally vertically directed or slightly inclined and pointing upward towards the heel. None of them is pointing backward towards the toe of the HP well. Thus, it is apparent that oil drainage pattern in this laboratory-scale model E is efficient as all the mobilised upgraded oil, including from the base of the combustion cell, is produced as the combustion front advances in the toe-to-heel manner. However, the combustion front has a backward-leaning shape which is an indicator that it is propagating even inside the HP well. This implies that the process is operating in an unstable, inefficient, and unsafe mode. These two opposing patterns at laboratory-scale must be resolved to ensure healthy combustion front propagation with efficient oil drainage and production rates are achieved. At the field scale (i.e. model F), this study has shown for the first time that there are actually two mobile oil zones: the one ahead of the combustion front with lower oil flux magnitude (i.e. MOZ) and the one containing large pool of mobilised partially upgraded oil at the base of the reservoir just behind the toe of the HP well. The above findings in model F show that there is conflicting dynamics about the goal of achieving large oil production rates downstream of the combustion front with the propagation of forward-tilting stable, safe, and efficient combustion front. If the combustion is to be optimally sustained, then most of the mobilised upgraded oil might be lost going in the wrong direction towards the region behind the toe of the HP well. In actual reservoir in the field, shale with very low permeability and porosity must be present behind the toe in order for the large pool of mobilised upgraded oil that is continuously draining from the vertical adjacent planes to be forced into the toe of the HP well. As a result, to balance these two conflicting dynamics of upward-tilted combustion front going longitudinally towards the heel of the HP well and the mobilised oil draining down at an angle towards the region behind the toe of the HP well, future studies are essentially required. These are proposed and also listed under the conclusion section in order to ensure thorough design and operation procedures for the THAI process are established.

An Experimental Investigation of In Situ Combustion in High Permeability Contrast Systems

A significant portion of world oil reserves reside in naturally fractured reservoirs and a considerable amount of these resources includes heavy oil and bitumen. Thermal enhanced oil recovery methods (EOR) are mostly applied in heavy oil reservoirs to improve oil recovery. In situ combustion (/SC) is one of the thermal EOR methods that could be applicable in a variety of reservoirs. Unlike steam, heat is generated in situ due to the injection of air or oxygen enriched air into a reservoir. Energy is provided by multi-step reactions between oxygen and the fuel at particular temperatures underground. This method upgrades the oil in situ while the heaviest fraction of the oil is burned during the process. The application of /SC in fractured reservoirs is challenging since the injected air would flow through the fracture and a small portion of oil in the/near fracture would react with the injected air. Only a few researchers have studied /SC in fractured or high permeability contrast systems experimentally. For in situ combustion to be applied in fractured systems in an efficient way, the underlying mechanism needs to be understood. In this study, the major focus is permeability variation that is the most prominent feature of fractured systems. The effect of orientation and width of the region with higher permeability on the sustainability of front propagation are studied. The contrast in permeability was experimentally simulated with sand of different particle size. These higher permeability regions are analogous to fractures within a naturally fractured rock. Several /SC tests with sand-pack were carried out to obtain a better understanding of the effect of horizontal vertical, and combined (both vertical and horizontal) orientation of the high permeability region with respect to airflow to investigate the conditions that are required for a self-sustained front propagation and to understand the fundamental behavior. Within the experimental conditions of the study, the test results showed that combustion front propagated faster in the higher permeability region. In addition, horizontal orientation almost had no effect on the sustainability of the front; however, it affected oxygen consumption, temperature, and velocity of the front. On the contrary, the vertical orientation of the higher permeability region had a profound effect on the sustainability of the combustion front. The combustion behavior was poorer for the tests with vertical orientation, yet the produced oil AP/ gravity was higher. Based on the experimental results a mechanism has been proposed to explain the behavior of combustion front in systems with high permeability contrast.

Formation of multiple combustion fronts in an imbert downdraft gasification reactor

The experimental study of downdraft gasification was performed in this paper. The operation which led to the formation of the second combustion front was pointed out. In this situation, both combustion fronts will lose their intensity and finally be extinguished. The operation was unintentionally stopped. It was revealed that the combustion front propagated upward in the reactor after starting the test. While it was about to reach the air inlet nozzle, the second combustion front was detected by an abrupt temperature rise of the thermocouple above the air supply nozzle. After the formation of the second combustion front, both fronts started to lose their intensity which indicated by the decrease in temperature corresponding with their locations. It was possible that the second combustion front would dilute the oxygen concentration supplied to the first combustion front. The decreasing temperature of the first combustion front reduced the heat transfer rate to the second combustion front. Finally, both combustion fronts were extinguished. The operation was unintentionally stopped.