Shengyan Gao

Micro/Nano-pore Network Analysis of Gas Flow in Shale Matrix.

The gas flow in shale matrix is of great research interests for optimized shale gas extraction. The gas flow in the nano-scale pore may fall in flow regimes such as viscous flow, slip flow and Knudsen diffusion. A 3-dimensional nano-scale pore network model was developed to simulate dynamic gas flow, and to describe the transient properties of flow regimes. The proposed pore network model accounts for the various size distributions and low connectivity of shale pores. The pore size, pore throat size and coordination number obey normal distribution, and the average values can be obtained from shale reservoir data. The gas flow regimes were simulated using an extracted pore network backbone. The numerical results show that apparent permeability is strongly dependent on pore pressure in the reservoir and pore throat size, which is overestimated by low-pressure laboratory tests. With the decrease of reservoir pressure, viscous flow is weakening, then slip flow and Knudsen diffusion are gradually becoming dominant flow regimes. The fingering phenomenon can be predicted by micro/nano-pore network for gas flow, which provides an effective way to capture heterogeneity of shale gas reservoir.

Physical modeling of air flow during air sparging remediation.

Air sparging (AS) is one of the most efficient techniques for remediating saturated soils and groundwater contaminated with volatile organic compounds. A series of physical modeling tests for different sizes of porous media under varied injection pressure were conducted to investigate the effect of particle size and air injection pressure on size and shape of the zone of influence (ZOI). The test results show that ZOI can be expressed by two components: the horizontal expansion due to pneumatic fracture or preferential intrusion around the injection point and the angle of ZOI which is the angle between the vertical line and the boundary of ZOI. There exists a limited angle of ZOI for each type of porous media. The measured minimum and maximum air injection pressures in 1g tests are compared with corresponding theoretical values, and it is found that the measured minimum injection pressure is slightly lower than the theoretical value, while the measured maximum injection pressure is much higher than the theoretical maximum injection pressure. Centrifugal test results confirmed nonapplicability of theoretical maximum injection pressure to air sparging design. All of the above provide valuable information for design and theoretical modeling of air sparging for groundwater remediation.

Simulation of Dynamic Two-Phase Flow During Multistep Air Sparging

Air sparging is an in situ soil/groundwater remediation technology, which involves the injection of pressurized air through air sparging well below the zone of contamination. To investigate the rate-dependent flow properties during multistep air sparging, a rule-based dynamic two-phase flow model was developed and applied to a 3D pore network which is employed to characterize the void structure of porous media. The simulated dynamic two-phase flow at the pore scale or microscale was translated into functional relationships at the continuum-scale of capillary pressure–saturation (Pc–S) and relative permeability—saturation (Kr–S) relationships. A significant contribution from the air injection pressure step and duration time of each air injection pressure on both of the above relationships was observed during the multistep air sparging tests. It is observed from the simulation that at a given matric potential, larger amount of water is retained during transient flow than that during steady flow. Shorter the duration of each air injection pressure step, there is higher fraction of retained water. The relative air/water permeability values are also greatly affected by the pressure step. With large air injection pressure step, the air/water relative permeability is much higher than that with a smaller air injection pressure step at the same water saturation level. However, the impact of pressure step on relative permeability is not consistent for flows with different capillary numbers (Nca). When compared with relative air permeability, relative water permeability has a higher scatter. It was further observed that the dynamic effects on the relative permeability curve are more apparent for networks with larger pore sizes than that with smaller pore sizes. In addition, the effect of pore size on relative water permeability is higher than that on relative air permeability.

Roughness Progression Model for Asphalt Pavements Using Long-Term Pavement Performance Data

AbstractA reliable pavement performance prediction model is needed for road infrastructure asset management systems or pavement management systems. In this study, the data on roughness progression of asphalt pavements in the long-term pavement performance (LTPP) database was analyzed in order to develop such a model. The international roughness index (IRI) is a reasonable measure of the ride comfort perceived by occupants of passenger cars and hence used as the basis for the pavement performance prediction model developed in this research. A quantitative relationship between roughness progression and accumulative traffic load, structural number, annual precipitation, and freezing index was developed and validated. Five pavement performance levels were developed to express the extent of asphalt pavement deterioration. This is coupled with a reliability analysis based on the Weibull model to estimate the remaining service life of asphalt pavements. Effective treatments of pavements at the project level for ...

Pavement texture from high-speed laser for pavement management system

The locked-wheel skid trailer (ASTM E274) is commonly used to estimate the skid resistance of pavements in the United States. However, this method is very expensive and disturbs the traffic flows during the test. Hence, a correlation was developed between skid resistance or skid number (SN40R) values obtained using skid tester and the texture data or mean profile depth (MPD), collected using a vehicle-mounted laser operating at highway speeds from nine highway test sections. This paper describes two field tests performed to validate the above-mentioned Skid Resistance versus MPD correlation and to also develop a rapid screening methodology for skid resistance of a network of pavements. In addition to the locked-wheel skid trailer and vehicle-mounted laser, several other tests such as the Dynamic Friction Test (DFT), circular texture meter (CTM) and sand patch tests were also performed. The MPD values obtained from the vehicle-mounted laser operating at highway speeds and cumulative daily traffic volumes for each pavement were used to estimate the equivalent SN40R values. The measured and estimated SN40R values compared well with a maximum variance of less than 5. The proposed screening methodology to estimate skid numbers from measured texture data was embedded into computer code and was incorporated into the Pavement Management System for rapid screening of skid resistance.

Study of Flow Transitions during Air Sparging Using the Geotechnical Centrifuge

AbstractAir sparging (AS) is an in-situ groundwater remediation technique for volatile organic compounds (VOCs) in contaminated sites. Knowledge of effect of the injected air on air flow patterns and extent of the zone known as zone of influence (ZOI) is crucial for design of in situ air sparging. The two main objectives of this research are to study transition of air flow patterns and characteristics of ZOI under different air injection pressures during centrifugal tests and to find the scaling factors for centrifugal tests under different gravitational levels (N times gravitational force). In this research, the modeling of models test was first performed to validate centrifugal technique for simulating air sparging. Then, a set of two-dimensional (2D) centrifugal modeling tests were performed under various gravitational levels to study the transition of air flow patterns and characteristics of ZOI during air sparging. The centrifugal model tests showed that the observed 2D ZOI was truncated-cone under v...

Microscopic Modeling of Air Migration during Air Sparging

Air sparging is an emerging soil remediation method to decontaminate saturated granular soils and groundwater with volatile organic compounds (VOCs). The efficiency of an in situ sparging system is controlled by the extent of the contact between injected air and contaminated soil and pore fluid. Characterizing the mechanisms governing the movement of air through saturated porous media is therefore critical to the design of an effective cleanup treatment system. In this paper, an overview of the existing conceptual models and related microscopic research on air sparging is provided. Then, main issues associated with microscopic modeling of air sparging, including simulation of microstructure of porous medium, migration of fine particles along the air flow path, air flow pattern transition criteria, and critical size of air bubbles or clusters are discussed. Finally, three-dimensional (3D) networks of pore bodies connected by pore throats representing the main skeleton of the pore structure of porous media ...

Fleet size estimation for spreading operation considering road geometry, weather and traffic

Abstract: Extreme weather conditions(i.e. snow storm) in winter time have caused significant travel disruptions and increased delay and traffic accidents. Snow plowing and salt spreading are the most common counter-measures for making our roads safer for motorists. To assist highway maintenance authorities with better planning and allocation of winter maintenance resources, this study introduces an analytical model to estimate the required number of trucks for spreading operation subjective to pre-specified service time constraints considering road geometry, weather and traffic. The complexity of the research problem lies in dealing with heterogeneous road geometry of road sections, truck capacities, spreading patterns, and traffic speeds under different weather conditions and time periods of an event. The proposed model is applied to two maintenance yards with seven road sections in New Jersey (USA), which demonstrates itself fairly practical to be implemented, considering diverse operational conditions.

Fleet Size Estimation for Snowplowing Operation Considering Road Geometry, Weather, and Traffic Speed

Estimating truck fleet size for winter road maintenance, such as snowplowing, is a challenging task for highway maintenance agencies. To estimate the fleet size for a snowplowing operation, a mathematic model is developed considering road geometry, weather, and traffic speed, subject to service time limit. The complexity of the problem lies in the varying pavement width of road sections, different plowing patterns on the mainline and ramps, weather- and time-dependent traffic speed, and the use of mixed types of plows. With real-world data, the developed model is applied in a case study, and the model demonstrates itself to be considerably flexible in adapting to various circumstances in estimating fleet size for snowplowing operations.

Gasoline Contaminated Sites: Pollutant Transport and Remediation

Gasoline type contaminants are a serious threat to soil and groundwater quality as well as health and welfare of general public. Most constituents of gasoline are volatile organic compounds. Soil vapor extraction and air sparging (SVE/AS) are the most efficient techniques to remediate soils and groundwater contaminated with volatile organic compounds. Hence in this state-of-the-art review paper the transport of gasoline-type contaminants in subsurface system and subsequent remediation process are introduced, discussed and summarized. First the mechanism of contaminant transport in subsurface system is briefly introduced, and the mass transport equations, fluid flow equations, and the constitutive model of relative permeability — saturation — capillary pressure are discussed. Then the numerical method is introduced to simulate the process of multiphase flow and contaminate transport in porous media, and the tempo-spatial distribution of contaminants. Then the geotechnical centrifuge modeling, a convenient and efficient physical modeling technique is introduced.