Occurrence and Flow Behavior for Oil Transport in Mixed Wetting Nanoscale Shale Bedding Fractures.

Shale reservoirs are characterized by an abundance of nanoscale porosities and microfractures. The states of fluid occurrence and flow behaviors within nanoconfined spaces necessitate novel research approaches, as traditional percolation mathematical models are inadequate for accurately depicting these phenomena. This study takes the Gulong shale reservoir in China as the subject of its research. Initially, the unique mixed wetting characteristics of the Gulong shale reservoir are examined and characterized using actual micropore images. Subsequently, the occurrence and flow behavior of oil within the nanoscale bedding fractures under various wettability scenarios are described through a combination of microscopic pore image and molecular dynamics simulations. Ultimately, a mathematical model is established that depicts the velocity distribution of oil and its apparent permeability. This study findings indicate that when the scale of the shale bedding fractures is less than 100 nm, the impact of the nanoconfinement effect is significant and cannot be overlooked. In this scenario, the state of oil occurrence and its flow behavior are influenced by the initial oil-wet surface area on the mixed wetting walls. The study quantifies the velocity and density distribution of oil in mixed wetting nanoscale shale bedding fractures through a mathematical model, providing a crucial theoretical basis for upscaling from the nanoscale to the macroscale.

Study on the Nanopore Deformation Mechanisms in Shale Oil Reservoir: Insights from the Molecular Simulation.

The stress and adsorption motivation deformation during shale oil production directly affect its development dynamics. First, a mathematical simulation of pore deformation in shale oil under stress motivation is established. We analyzed the impact of factors including the reservoir pressure, Biot coefficient, bulk modulus, and tortuosity on the deformation characteristics of nanopores. Second, a pore deformation model under multifactor synergistic effect is derived by combining the molecular dynamics, which takes into account the influence of adsorption deformation on the total adsorption of shale oil reservoir. Finally, a shale oil pore deformation model under multifactor synergistic effect is obtained. The results show that the current pore diameter shows a trend of decreasing with the decrease of current formation pressure and the difference with original reservoir pressure increases. The pore shows a trend of less deformation with a decrease in the effective stress coefficient. When the Biot coefficient is 0.8, the pore diameter under 5 MPa is 4.01 nm. When the Biot coefficient decreases to 0.3, the pore diameter under 5 MPa becomes 9.12 nm, an increase of 127.43% compared to 4.01 nm. The bulk modulus affects the magnitude of pore deformation under the same pressure, which means that the pore diameter shows a tendency to deform more easily as the bulk modulus increases. Meanwhile, the pore diameter decreases with increasing tortuosity. In addition, the pore deformation is subject to both stress and adsorption motivation deformation synergistically. The stress motivation deformation leads to a decrease of pore diameter with pressure decrease, while, in contrast, the adsorption motivation leads to an increase of pore diameter. The pore diameter under synergy is influenced by the coupling effect, and the deformation under synergy tends to decrease as the pore diameter decreases. When the rock mechanical parameters are changed so that the pores are not easily deformed by stress, the adsorption motivation deformation plays a dominant role in synergy. The amount of synergistic deformation decreases with increasing temperature, while the change in the component ratio of multicomponent fluid mainly affects the corresponding adsorption and the amount of synergistic deformation. Interestingly, when the proportion of CO2 is the largest, the corresponding maximum deformation is higher than the other proportions (43.77%). It not only enhances the recovery rate of shale oil reservoirs by utilizing CO2 but also provides the possibility of geological CO2 burial.

Quantitative Analysis of Natural Gas Diffusion Characteristics in Tight Oil Reservoirs Based on Experimental and Numerical Simulation Methods.

As an important mechanism in gas injection development, the diffusion characteristics of natural gas in tight reservoirs are important in the dynamic prediction of the development effect and optimization of injection-production parameters. In this paper, a high-pressure and high-temperature oil-gas diffusion experimental device was built, which was used to study the effects of the porous medium, pressure, permeability, and fracture on oil-gas diffusion under tight reservoir conditions. Two mathematical models were used to calculate the diffusion coefficients of natural gas in bulk oil and cores. Besides, the numerical simulation model was established to study the diffusion characteristics of natural gas in gas flooding and huff-n-puff, and five diffusion coefficients were selected based on experimental results for simulation study. The remaining oil saturation of grids, the recovery of single layers, and the distribution of CH4 mole fraction in oil were analyzed based on the simulation results. The experimental results show that the diffusion process can be divided into three stages: the initial stage of instability, the diffusion stage, and the stable stage. The absence of medium, high pressure, high permeability, and the existence of fracture are beneficial to natural gas diffusion, which can also reduce the equilibrium time and increase the gas pressure drop. Furthermore, the existence of fracture is beneficial to the early diffusion of gas. The simulation results show that the diffusion coefficient has a greater influence on the oil recovery of huff-n-puff. For gas flooding and huff-n-puff, the diffusion features both perform such that a high diffusion coefficient results in a close diffusion distance, small sweep range, and low oil recovery. However, a high diffusion coefficient can achieve high oil washing efficiency near the injecting well. The study is helpful to provide theoretical guidance for natural gas injection in tight oil reservoirs.

Wearable Neck Surface Accelerometers for Occupational Vocal Health Monitoring: Instrument and Analysis Validation Study.

BACKGROUND: Neck surface accelerometer (NSA) wearable devices have been developed for voice and upper airway health monitoring. As opposed to acoustic sounds, NSA senses mechanical vibrations propagated from the vocal tract to neck skin, which are indicative of a person's voice and airway conditions. NSA signals do not carry identifiable speech information and a speaker's privacy is thus protected, which is important and necessary for continuous wearable monitoring. Our device was already tested for its durable endurance and signal processing algorithms in controlled laboratory conditions. OBJECTIVE: This study aims to further evaluate both instrument and analysis validity in a group of occupational vocal users, namely, voice actors, who use their voices extensively at work in an ecologically valid setting. METHODS: A total of 16 professional voice actors (age range 21-50 years; 11 females and 5 males) participated in this study. All participants were mounted with an NSA on their sternal notches during the voice acting and voice assessment sessions. The voice acting session was 4-hour long, directed by a voice director in a professional sound studio. Voice assessment sessions were conducted before, during, and 48 hours after the acting session. The assessment included phonation tasks of passage reading, sustained vowels, maximum vowel phonation, and pitch glides. Clinical acoustic metrics (eg, fundamental frequency, cepstral measures) and a vocal dose measure (ie, accumulated distance dose from acting) were computed from NSA signals. A commonly used online questionnaire (Self-Administered Voice Rating questionnaire) was also implemented to track participants' perception of vocal fatigue. RESULTS: The NSA wearables stayed in place for all participants despite active body movements during the acting. The ensued body noise did not interfere with the NSA signal quality. All planned acoustic metrics were successfully derived from NSA signals and their numerical values were comparable with literature data. For a 4-hour long voice acting, the averaged distance dose was about 8354 m with no gender differences. Participants perceived vocal fatigue as early as 2 hours after the start of voice acting, with recovery 24-48 hours after the acting session. Among all acoustic metrics across phonation tasks, cepstral peak prominence and spectral tilt from the passage reading most closely mirrored trends in perceived fatigue. CONCLUSIONS: The ecological validity of an in-house NSA wearable was vetted in a workplace setting. One key application of this wearable is to prompt occupational voice users when their vocal safety limits are reached for duly protection. Signal processing algorithms can thus be further developed for near real-time estimation of clinically relevant metrics, such as accumulated distance dose, cepstral peak prominence, and spectral tilt. This functionality will enable continuous self-awareness of vocal behavior and protection of vocal safety in occupational voice users.

Dynamic wetting of solid-liquid-liquid system by molecular kinetic theory.

HYPOTHESIS: The mechanisms of dynamic wetting of solid-liquid-liquid (SLL) system, especially the viscosity effects of two liquids, can be investigated by the molecular kinetic theory (MKT). METHODS: The molecular kinetic theory combined with published data was used to study the roles of a fluid viscosity and a solid surface in dynamic wetting. FINDINGS: First, the MKT on dynamic wetting was introduced and its limitation was analyzed. Second, a viscosity effect and a solid surface effect were considered. The viscosity effect was divided into three parts for the first time, including two pure liquid zones and a mixing zone. Third, a coefficient activation free energy model was proposed, considering the effects of mixing liquids and a solid surface. Finally, the key parameters in the MKT and the application and validation of the coefficient activation free energy model were discussed in detail. This model can explain the energy dissipation in a vicinity of a three-phase contact-line successfully in a SLL wetting system. This work sheds light on the physical mechanisms of fluid and solid surface properties on the dynamic wetting in a SLL system.

Investigation of Vocal Fatigue Using a Dose-Based Vocal Loading Task.

Vocal loading tasks are often used to investigate the relationship between voice use and vocal fatigue in laboratory settings. The present study investigated the concept of a novel quantitative dose-based vocal loading task for vocal fatigue evaluation. Ten female subjects participated in the study. Voice use was monitored and quantified using an online vocal distance dose calculator during six consecutive 30-min long sessions. Voice quality was evaluated subjectively using the CAPE-V and SAVRa before, between, and after each vocal loading task session. Fatigue-indicative symptoms, such as cough, swallowing, and voice clearance, were recorded. Statistical analysis of the results showed that the overall severity, the roughness, and the strain ratings obtained from CAPE-V obeyed similar trends as the three ratings from the SAVRa. These metrics increased over the first two thirds of the sessions to reach a maximum, and then decreased slightly near the session end. Quantitative metrics obtained from surface neck accelerometer signals were found to obey similar trends. The results consistently showed that an initial adjustment of voice quality was followed by vocal saturation, supporting the effectiveness of the proposed loading task.

Discrimination between Modal, Breathy and Pressed Voice for Single Vowels Using Neck-Surface Vibration Signals.

The purpose of this study was to investigate the feasibility of using neck-surface acceleration signals to discriminate between modal, breathy and pressed voice. Voice data for five English single vowels were collected from 31 female native Canadian English speakers using a portable Neck Surface Accelerometer (NSA) and a condenser microphone. Firstly, auditory-perceptual ratings were conducted by five clinically-certificated Speech Language Pathologists (SLPs) to categorize voice type using the audio recordings. Intra- and inter-rater analyses were used to determine the SLPs' reliability for the perceptual categorization task. Mixed-type samples were screened out, and congruent samples were kept for the subsequent classification task. Secondly, features such as spectral harmonics, jitter, shimmer and spectral entropy were extracted from the NSA data. Supervised learning algorithms were used to map feature vectors to voice type categories. A feature wrapper strategy was used to evaluate the contribution of each feature or feature combinations to the classification between different voice types. The results showed that the highest classification accuracy on a full set was 82.5%. The breathy voice classification accuracy was notably greater (approximately 12%) than those of the other two voice types. Shimmer and spectral entropy were the best correlated metrics for the classification accuracy.