Browsing by Subject "laboratory"
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Item Near-Field Sediment Resuspension Measurement and Modeling for Cutter Suction Dredging Operations(2011-02-22) Henriksen, John ChristopherThe sediment resuspension and turbidity created during dredging operations is both an economical and environmental issue. The movement of sediment plumes created from dredging operations has been predicted with numerical modeling, however, these far-field models need a ?source term? or near-field model as input. Although data from field tests have been used to create near-field models that predict the amount of material suspended in the water column, these results are skewed due to limitations such as non-uniform sediment distributions, water currents, and water quality issues. Laboratory investigations have obtained data for turbidity during dredging operations, but these results do not take advantage of the most contemporary testing methods. The purpose of this dissertation is to provide an estimation of turbidity created during a cutter suction dredging operation. This estimation was facilited by the development of resuspension measurement and data acquisition techniques in a laboratory setting. Near-field turbidity measurements around the cutter head were measured in the Haynes Coastal Engineering Laboratory at Texas A&M University. The laboratory contains a dredge/tow tank that is ideal for conducting dredging research. A dredge carriage is located in the dredge/tow tank and is composed of a carriage, cradle, and ladder. Acoustic Doppler Velocimetry (ADV) and Optical Backscatter Sensor (OBS) measurements were taken at specific points around the cutter head. The variables of suction flow rate, cutter speed, and the thickness of cut were investigated to understand their specific effect on turbidity generation and turbulence production around the cutter head. A near-field advection diffusion model was created to predict resuspension of sediment from a cutter suction dredge. The model incorporates the laboratory data to determine the velocity field as well as the turbulent diffusion. The model is validated with laboratory testing as well as field data. Conclusions from this research demonstrate undercutting consistently produced larger point specific turbidity maximum than overcutting in the laboratory testing. An increase in suction flow rate was shown to increase production and decrease turbidity around the cutter head. In general, an increase in cutter speed led to an increase in turbidity. The thickness of cut produced less resuspension for a full cut versus a partial cut. Data for a ?shallow cut? also produced less turbidity generation than partial cuts. The numerical model was compared to all laboratory testing cases as well as the Calumet Harbor and New Bedford cutter resuspension data and produced suitable MRA values for all tests. The numerical model produced higher point specific regions of turbidity for undercutting but produced larger mean values of turbidity for overcutting.Item The Effect of Proppant Size and Concentration on Hydraulic Fracture Conductivity in Shale Reservoirs(2013-04-11) Kamenov, AntonHydraulic fracture conductivity in ultra-low permeability shale reservoirs is directly related to well productivity. The main goal of hydraulic fracturing in shale formations is to create a network of conductive pathways in the rock which increase the surface area of the formation that is connected to the wellbore. These highly conductive fractures significantly increase the production rates of petroleum fluids. During the process of hydraulic fracturing proppant is pumped and distributed in the fractures to keep them open after closure. Economic considerations have driven the industry to find ways to determine the optimal type, size and concentration of proppant that would enhance fracture conductivity and improve well performance. Therefore, direct laboratory conductivity measurements using real shale samples under realistic experimental conditions are needed for reliable hydraulic fracturing design optimization. A series of laboratory experiments was conducted to measure the conductivity of propped and unpropped fractures of Barnett shale using a modified API conductivity cell at room temperature for both natural fractures and induced fractures. The induced fractures were artificially created along the bedding plane to account for the effect of fracture face roughness on conductivity. The cementing material present on the surface of the natural fractures was preserved only for the initial unpropped conductivity tests. Natural proppants of difference sizes were manually placed and evenly distributed along the fracture face. The effect of proppant monolayer was also studied.