Supercritical Methane Storage and Transport in Single-Wall Carbon Nanotubes

Quantification of gas storage and transport in organic-rich shale is important in determining natural gas production rates and reserves. However, laboratory measurements are challenging, due to very tight nature of the rock, and have large uncertainties due to presence of multiple mechanisms of gas storage and transport at multiple scales. The emphasis of this thesis is on understanding of storage and transport mechanisms and their interplay inside organic nano-capillaries. An atomistic modeling and molecular simulation approach is presented in investigating supercritical methane behavior in model carbon nanotubes representing nano-capillary. Equilibrium Monte Carlo simulations show a non-uniform methane density profile across the diameter of the capillary. The results show excess methane at the central portion of the capillary indicating deviations from Langmuir adsorption model. Amount of excess methane is dependent on the competition in between the fluid-wall and fluid-fluid interactions. To study the transport behavior of methane in nano-capillary, we performed nonequilibrium Molecular Dynamics simulations based on a moving piston model. The piston model allows us to study steady-state transport across the diameter of nanotube in order to understand the effects of adsorbed methane on transport under reservoir conditions. The results show that the adsorbed phase is not only mobile but also contribute significantly to total mass flux. The contribution of the adsorbed-phase is profound in smaller capillaries. Simulations of transport with different sizes of capillaries show that the adsorbed-phase transport velocity is independent of capillary size, but strongly dependent on the pressure drop across the capillary. This allows us to quantify the adsorbed-phase velocity into an adsorbed phase mobility factor

SIMULATION OF PROPPANT TRANSPORT IN HYDRAULIC AND NATURAL FRACTURES USING A COUPLED CFD-DEM METHOD

Understanding proppant transport is critically important in designing effective stimulation systems for low-permeability reservoirs, as it leads to better estimates of the propped fracture dimensions and stimulated reservoir volume. Existing models mostly represent proppant as a continuous fluid phase. This assumption is valid for the conventional fracturing designs, where high viscosity fluid (e.g., cross-linking gels) are used as the carrier fluid. Current fracturing designs mostly use low viscosity fluids (e.g., slick water). As a result, proppants behave more like discrete particles and less like a continuous fluid phase. Existing proppant transport models assume a single planar fracture as the main representation of the geometry of fractures, but the geometry of the subsurface fracture networks is much more complex. In this study I couple computational fluid dynamics with the discrete element method (CFD-DEM) to simulate proppant transport in a complex fracture network. The coupled simulator enables the explicit modeling of the motion of individual particles and offers a more accurate representation of the complex interactions between proppant particles, fracturing fluids, and fracture walls. To calibrate the numerical model, I first conducted validation simulations that imitated a particle settling test, a particle collision test and a laboratory proppant transport experiment. Through scoping calculations, I determined the correct drag force model and matched the model predictions with existing analytical solutions and experimental data for a wide range of flow regimes, including three different sizes of proppants (20-30 mesh, 30-40mesh and 50-70 mesh) in two types of fluids (water and oil). In the main component of my study, I built multiple 3-dimentional fracture network models, which include one baseline vertical fracture model, three dipping fracture models, two hydraulic fracture-natural fracture (HF-NF) intersection models (T-shaped and Z-shaped) and, finally, a multi-cluster horizontal wellbore model. In the baseline vertical fracture model, the simulation results show that the flow regime of proppant (suspension or bedload transport) plays a critical role in determining the proppant advance and distribution in the fracture. Higher fluid velocities lead to a larger suspension transport region and a higher proppant placement efficiency in the hydraulic fractures. In the dipping fracture models, my results show that decreasing the dipping angle increases the proppant placement efficiency. In the T-shaped HF-NF intersection model, I observed significantly better proppant placement in the NF when proppants are in the suspension transport regime. In the Z-shaped HF-NF intersection model, my study identified two parameters that are critical for estimating the occurrence of proppant bridging: the proppant concentration (Cp) and the ratio between the secondary fracture aperture and the proppant diameter (Rfp). At a fixed value of Rfp, continuous transport of proppant is possible when Cp is lower than a threshold value. Based on this determination, I use Rfp and Cp to propose a blocking criterion correlation. Lastly, in my multi-cluster wellbore model, I experimented with various pumping strategies and computed the proppant and fluid distribution at each cluster. By comparing the influence of injection rate, I discussed potential strategies to achieve a better (more even) proppant distribution at the different clusters

Elucidating the complex interplay between natural and anthropogenic factors in the deformation of the Muyubao landslide through time-series InSAR analysis

In the Three Gorges Reservoir area, landslide disasters occur frequently, making scientific monitoring and risk prediction crucial for disaster prevention and mitigation. However, most previous studies have been constrained by analysis of singular influencing factors. In this study, we employed multi-temporal InSAR techniques coupled with multivariate geospatial statistical analysis to monitor and analyze the dynamic evolution of the Muyuba landslide in Zigui County, Hubei Province, China from 2016 to 2023. The findings indicate that the Muyuba landslide was predominantly characterized by continuous, gradual subsidence. Key factors inducing deformation included well-developed drainage networks, gentle slopes of 15–30°, and the orientation of rock strata. Deformation rates in residential areas and along roadways exceeded background levels, implicating anthropogenic activities in the heightened landslide risk. A significant correlation was observed between landslide deformation and reservoir water level fluctuations, as opposed to rainfall patterns, highlighting reservoir regulation disturbances as a critical landslide triggering factor

In-situ Water quality monitoring in Oil and Gas operations

From agriculture to mining, to energy, surface water quality monitoring is an essential task. As oil and gas operators work to reduce the consumption of freshwater, it is increasingly important to actively manage fresh and non-fresh water resources over the long term. For large-scale monitoring, manual sampling at many sites has become too time-consuming and unsustainable, given the sheer number of dispersed ponds, small lakes, playas, and wetlands over a large area. Therefore, satellite-based environmental monitoring presents great potential. Many existing satellite-based monitoring studies utilize index-based methods to monitor large water bodies such as rivers and oceans. However, these existing methods fail when monitoring small ponds-the reflectance signal received from small water bodies is too weak to detect. To address this challenge, we propose a new Water Quality Enhanced Index (WQEI) Model, which is designed to enable users to determine contamination levels in water bodies with weak reflectance patterns. Our results show that 1) WQEI is a good indicator of water turbidity validated with 1200 water samples measured in the laboratory, and 2) by applying our method to commonly available satellite data (e.g. LandSat8), one can achieve high accuracy water quality monitoring efficiently in large regions. This provides a tool for operators to optimize the quality of water stored within surface storage ponds and increasing the readiness and availability of non-fresh water.Comment: 15 pages, 8 figures, SPIE Defense + Commercial: Algorithms, Technologies, and Applications for Multispectral and Hyperspectral Imaging XXI