Anoop Kanjirakat

Conventional methods of mitigating fluid loss in drilling operations rely heavily on chemical additives and nanoparticles, which may alter mud properties and introduce environmental and cost challenges. While the technique of ultrasonication is widely used in the oil and gas industry, especially for mixing these additives and nanoparticles into mud samples, the direct impact of ultrasonication of the base drilling mud sample alone on fluid loss behavior has been largely overlooked. This study investigates the effectiveness of ultrasonication in modifying the filtrate loss characteristics of water-based mud without any fluid loss additives. Drilling mud samples were subjected to ultrasonic treatment and compared with unsonicated samples through a series of high-pressure high-temperature (HPHT) filtration tests using ceramic disks with average pore throat sizes of 5-35 μm. The results demonstrate that sonicated mud significantly reduces filtrate loss, particularly in disks with smaller pore sizes, compared with unsonicated mud. Reductions in filtrate loss of approximately 16-45% were achieved with the 5, 10, and 20 μm pore size disks when sonicated mud was tested. These improvements were associated with the thinner and less permeable (0.2-0.4 mm) filter cakes compared to those of unsonicated mud, contributing to improved fluid retention. However, at a pore throat size of 35 μm, a significant increase in fluid loss was observed, suggesting that the benefits of ultrasonication are limited when the pore sizes exceed the effective range of the modified particle size distribution in the mud. Particle size distribution and scanning electron microscopy (SEM) data confirmed that ultrasonication fragmented and dispersed larger particles/aggregations, leading to a more stable suspension in the mud and denser mud cakes. The findings from this study demonstrate that ultrasonication of the base drilling mud alone is sufficient to improve its filtrate loss properties in most cases without the need for loss additives while being environmentally friendly and cost-effective. However, the study also implies the importance of adapting mud systems to formation properties, highlighting the critical role of the interaction between the particle size and pore dimensions in influencing fluid loss behavior and mud cake properties.

Stereolithography (SLA)-based three-dimensional (3D) printing has become a popular tool for creating experimental models to study the two-phase flow behavior in complex flow structures. The main drawback while implementing such models is the wettability nature of the 3D printed surfaces. As non-geological materials are used while printing the porous designs, the flow mechanics do not follow similar patterns as in the reservoir. This work demonstrates the feasibility of using an SLA-based printing technique to replicate a porous structure. The porosity and pore size values of the 3D print are observed to be very close to that of the porous input image of the rock sample. A simple method to modify the surface characteristics of 3D printed surfaces using an ultrasonic-atomized fine spraying technique is developed. Here a thin layer of CaCO₃ is deposited on the 3D printed surface by subjecting it to fine alternate sprays of calcium chloride and sodium carbonate. Thirty cycles of coating is observed to have altered the surface's wettability from neutral to oil-wet, resembling a carbonate reservoir.

Near-wall fluid velocimetry in the impingement zone of a microdroplet stream on a flat surface is reported utilizing microparticle tracking velocimetry (μPTV). The results are then compared with the near-wall fluid velocimetry in the impingement region of a steady microjet stream. The presence of tracer particles in the fluid results in a small random movement of the droplets away from the orifice axis, causing a change in the location of the droplet impingement center. A new method to find the center of impingement is described, and an algorithm is developed to obtain the radial velocities in the impingement zone at three out-of-plane heights of 2, 7, and 10 ± 2 μm from the wall. Single-frame double-exposed images of low loading fluorescent tracer particles are used for the experiments. As the impingement frequency of the droplet stream is much higher than the image-capturing rate of the camera, each double-exposed image corresponds to a random instance within the impingement period of the droplets. The presented results show the occurrence of a higher normalized root-mean-square along with positive skewness of the measured radial velocity values for the droplet stream. These indicate higher velocity fluctuations or fluid mixing characteristics induced by the droplet-crown propagation for the droplet stream when compared to that of a jet stream. The near-wall velocity measurements support previously reported observations of the enhanced convection heat transfer characteristics for a droplet stream case.

In a reservoir drilling application, the drilling mud should minimize the amount of the filtrate fluid entering into the reservoir formation. To ease the drilling process, the filter cake formed should also be thin, stable, and of uniform distribution. The addition of nanoparticles into the drilling mud is expected to improve these functionalities. In the present work, the effect of addition of carbon nanotubes (CNT) into a water-based drilling mud sample in improving its filtrate characteristics is studied. The filtrate volume, dry and wet weights, and thickness of the filter cakes are measured to evaluate the filtrate characteristics. Ceramic disks of two pore-throat sizes are used in the experimentation. The addition of CNT particles is observed to beneficial in reducing the filtrate amount or fluid loss. An increase in nanoparticle loading is observed to have increased the filtrate cake thickness. The porosity of the filter cake formed is observed to be lower than that of the ceramic disk used.

The objective of this study was to visualize and simulate the thermal physical process during double droplet train impingement for three different horizontal impact spacings (S = 0.65 mm, 1.2 mm and 2 mm). Two identical HFE-7100 droplet trains were produced using a piezoelectric droplet generator at a frequency of 6000 Hz with a corresponding droplet Weber number of 312. A translucent sapphire substrate with a thin film ITO coating was used as heater in the experiments. The heat transfer and hydrodynamics of double droplet train impingement have been visualized using IR thermal imaging and high speed optical imaging techniques, respectively. The double droplet train impingement process was also simulated numerically using the Coupled Level Set-Volume of Fluid (CLS-VOF) approach with dynamic mesh adaption (DMA). Humps were observed both numerically and experimentally between two adjacent impact craters due to the interactions caused by the impinging droplet trains. It was found that the hump height decreased when impact spacing increased. IR images show that higher impact spacing leads to better heat transfer performance, which could be due to the lower hump height at greater impact spacing conditions. It was also observed that higher impact spacing leads to better thermo-hydrodynamics within and outside the impingement zone. In summary, results show that horizontal impact spacing plays a significant role in double droplet train impingement cooling. This work was supported by the National Priority Research Program of the Qatar National Research Fund, Grant No.: NPRP 6-1304-2-525.

The objective of this study was to visualize the droplet-induced crown splashing dynamics at high spatial and temporal resolutions. In this work, the effects of droplet train impingement on crown splashing dynamics were investigated experimentally and numerically. Experimentally, a HFE-7100 droplet train was produced using a piezo-electric droplet generator at a frequency ( f ) of 7500 Hz resulting in a droplet Weber number (We) of 489. Droplet-induced crown splashing dynamics was captured using a high-speed imaging system. It was observed that the free rim of the droplet-induced crown was smooth and axisymmetric during the early crown propagation phases (t*< 5, where t* = 2πft). However, development of cusps was observed on the free rim during the intermediate phases (5< t* 8.5), fingering, detachment and secondary droplets (i.e. splashing) were observed on the free rim. Results show that the number of cusps (finally becoming fingers and spikes) based on experiments (ncups,exp) agrees well with the prediction (ncups,th) given by the Plateau-Rayleigh instability theory. Numerical simulations were carried out using a 3D transient coupled level set-volume of fluid (CLSVOF) solver with Courant number less than 1. A grid independence study was performed to ensure the results were independent of grid size. Reasonable agreement was reached between the numerical and experimental data in terms of crown morphology at different phases. This study should lead to a better understanding of the evolution of droplet-induced crown morphology at splashing conditions.

The influence of nanoparticles' dispersion on the physical properties of aviation fuel and its spray performance has been investigated in this work. To this end, the conventional Jet A-1 aviation fuel and its mixtures with alumina nanoparticles (nanofuel) at different weight concentrations are investigated. The key fuel physical properties such as density, viscosity, and surface tension that are of importance to the fuel atomization process are measured for the base fuel and nanofuels. The macroscopic spray features like spray cone angle and sheet breakup length are determined using the shadowgraph technique. The microscopic spray characteristics such as droplet diameter, droplet velocity, and their distributions are also measured by employing phase Doppler anemometry (PDA) technique. The spray performance is measured at two nozzle injection pressures of 0.3 and 0.9 MPa. The results show that with the increase in nanoparticle concentrations in the base fuel, the fuel viscosity and density increase, whereas the surface tension decreases. On the spray performance, the liquid sheet breakup length decreases with increasing nanoparticle concentrations. Furthermore, the mean droplet diameters of nanofuel are found to be lower than those of the base fuel.

The effects of droplet train impingement on spreading-splashing transition and surface heat transfer were investigated experimentally and numerically. Experimentally, a single stream of HFE-7100 droplet train was generated using a piezo-electric droplet generator with the ability to adjust parameters such as droplet impingement frequency, droplet diameter and droplet impingement velocity. A thin layer of Indium Tin Oxide (ITO) was coated on a translucent sapphire substrate, which was used as heating element. High-speed and infrared imaging techniques were employed to characterize the hydrodynamics and heat transfer of droplet train impingement. Numerically, the high frequency droplet train impingement process was simulated using ANSYS-Fluent with the Volume of Fluid (VOF) method [1]. The heat transfer process was simulated by applying constant heat flux conditions on the droplet receiving surface. Droplet-induced spreading-splashing transition behavior was investigated by increasing the droplet Weber number while holding flow rate constant. High speed crown propagation images showed that at low-Weber number (We < 400), droplet impingements resulted in smooth spreading of the droplet-induced crown. However, within the transitional droplet Weber number range (We = 400–500), fingering and splashing (i.e. emergence of secondary droplets) could be observed at the crown’s rim. At high droplet Weber number (We > 800), breakup of the crown was observed during the crown propagation process in which the liquid film behaved chaotically. Droplet-induced spreading-splashing transition phenomena were also investigated numerically. Reasonable agreement was reached between the experimental and numerical results in terms of crown morphology at different droplet Weber number values. The effects of spreading-splashing transition on surface heat transfer were also investigated at fixed flow rate conditions. Time-averaged Infrared (IR) temperature measurements indicate that heat flux-surface temperature curves are linear at low surface temperatures and before the onset of dry-out, which indicate that single phase forced convection is the primary heat transfer mechanism under those conditions. Numerical heat transfer simulations were performed within the single phase forced convection regime only. Instantaneous numerical results reveal that droplet-induced crown propagation effectively convect heat radially outward within the droplet impingement zone. Under high heat flux conditions, a sharp increase in surface temperature was observed experimentally when dry-out appeared on the heater surface. It was also found that strong splashing (We > 800) is unfavorable for heat transfer at high surface temperature due to the onset of instabilities seen in the liquid film, which leads to dry-out conditions. In summary, the results indicate that droplet Weber number is a significant factor in the spreading-splashing transition and surface heat transfer.