The Panola Mountain Research Watershed (PMRW) is a 41 ha forested watershed, located 25 km southeast of Atlanta, Georgia. Within that watershed is a 10 ha sub-catchment which contains the headwaters of the watersheds main stream, as well as two outcrops of Panola Granite (Burns et al. 2001). On the hill-slope below the northernmost outcrop, is a 20m long trench that has been excavated down to bedrock, a depth that ranges from 0.5-1.5m. In previous studies (Burns et al., 2001; Freer, et al., 2002), discharge through the overlying soils was measured along the trench in 2m sections across the full length of the trench. In those studies, it was assumed that the underlying bedrock was impermeable. However, Burns et al. (2003) showed that the riparian groundwater downslope from the trenched hillslope site was only 6 to 7 years old. The permeability of the Panola granite in question was proven by a recent Lithium- Bromide line tracer experiment -van Meerveld et al., in review. Due to the levels of bromide in the bedrock measured at the trench, it has become apparent that fluid is being lost to hidden hydraulic pathways, those probably being fractures. The objective of this thesis is to test the viability of using shallow seismic reflection to map out fracture zones at the trenched hillslope site, using GPR and shallow seismic refraction as supplemental techniques to verify the interpretation. Data from two seismic common shot point (CSP) surveys permitted an image of the soil/bedrock interface to be constructed, as well as enabling an acoustic velocity profile to be calculated for the area. This velocity profile is then used with data from five reflection surveys (one seismic and four radar) to create vertical profiles of the subsurface. Although the resulting SSR profile is less than optimum, higher amplitude arrivals related to structure were still able to be detected. From this profile, as well as those from the GPR survey, it can be concluded that the proposed hidden hydraulic pathways due indeed exist, and also that they can be accurately mapped out using the previously mentioned geophysical methods.

Fractured reservoirs, especially in low permeable carbonate rocks, are important target for hydrocarbon exploration and production because fractures can control fluid flow inside the reservoir. Hence, quantitative knowledge of fracture attributes is important for optimal hydrocarbon production. However, in some cases fractures can cause leakage of injected CO2 during enhanced oil recovery (EOR) or CO2 sequestration. Furthermore, CO2 can geochemically interact with reservoir fluids and host rock. Hence, time-lapse monitoring of the progress of CO2 in fractured reservoirs is also very important. In order to address these challenges, I have developed an integrated approach for studying fluid flow and seismic wave propagation in fractured media using Discrete Fracture Network (DFN) models. My seismic simulation study suggests that CO2 saturated reservoir shows approximately ten times more attenuation than brine saturated reservoir. Similarly, large P-wave velocity variation in CO2 saturated reservoir and amplitude variation with offset (AVO) results for our example model predicts that CO2 is easier to detect than brine in the fractured reservoirs. The effects of geochemical processes on seismics are simulated by time-lapse modeling for t = 1000 years. My modeling study suggests that intra-aqueous reactions are more significant during injection of CO2 for t = 6 years, while slower mineral reactions dominate after pressure equilibrium is achieved that is from t = 6 to 1000 years. Overall both types of geochemical reactions cause change in reflection coefficient of 2 to 5%, which may be difficult to detect in some cases. However, the significant change in the seismic properties at the boundary of the CO2 front can be used to detect the flow path of CO2 inside the reservoirs. Finally, a method for generating stochastic fracture models was extended and improved to more realistic field model for seismic and fluid modeling. My detail analysis suggests that fractures generated by isotropic stress field favor orthogonal sets of fractures in most subsurface rocks that can be converted to seismic model, similar to DFN study. The quality and validity of the models is assessed by comparisons to DFN models, including calculations of fractal dimension measures that can help to characterize fractured reservoirs.

Multiple transverse fracturing along a horizontal well is a relatively new technology that is designed to increase well productivity by increasing the contact between the reservoir and the wellbore. For multiple transverse fractures, the performance of the well system is determined by three aspects: the inflow from the reservoir to the fracture, the flow from the fracture to the wellbore, and the inflow from the reservoir to the horizontal wellbore. These three aspects influence each other and combined, influence the wellbore outflow. In this study, we develop a model to effectively formulate the inter-relationships of a multi-fracture system. This model includes a reservoir model and a wellbore model. The reservoir model is established to calculate both independent and inter-fracture productivity index to quantify the contribution from all fractures on pressure drop of each fracture, by using the source functions to solve the single-phase gas reservoir flow model. The wellbore model is used to calculate the pressure distribution along the wellbore and the relationship of pressure between neighboring fractures, based on the basic pressure drop model derived from the mechanical energy balance. A set of equations with exactly the same number of fractures will be formed to model the system by integrating the two models. Because the equations are nonlinear, iteration method is used to solve them. With our integrated reservoir and wellbore model, we conduct a field study to find the best strategy to develop the field by hydraulic fracturing. The influence of reservoir size, horizontal and vertical permeability, well placement, and fracture orientation, type (longitudinal and transverse), number and distribution are completely examined in this study. For any specific field, a rigorous step-by-step procedure is proposed to optimize the field.

Hydraulic fracturing of a naturally-fractured reservoir is a challenge for industry, as fractures can have complex growth patterns when propagating in systems of natural fractures in the reservoir. Fracture propagation near a natural fracture (NF) considering interaction between a hydraulic fracture (HF) and a pre-existing NF, has been investigated comprehensively using a two dimensional Displacement Discontinuity Method (DDM) Model in this thesis. The rock is first considered as an elastic impermeable medium (with no leakoff), and then the effects of pore pressure change as a result of leakoff of fracturing fluid are considered. A uniform pressure fluid model and a Newtonian fluid flow model are used to calculate the fluid flow, fluid pressure and width distribution along the fracture. Joint elements are implemented to describe different NF contact modes (stick, slip, and open mode). The structural criterion is used for predicting the direction and mode of fracture propagation. The numerical model was used to first examine the mechanical response of the NF to predict potential reactivation of the NF and the resultant probable location for fracture re-initiation. Results demonstrate that: 1) Before the HF reaches a NF, the possibility of fracture re-initiation across the NF and with an offset is enhanced when the NF has weaker interfaces; 2) During the stage of fluid infiltration along the NF, a maximum tensile stress peak can be generated at the end of the opening zone along the NF ahead of the fluid front; 3) Poroelastic effects, arising from fluid diffusion into the rock deformation can induce closure and compressive stress at the center of the NF ahead of the HF tip before HF arrival. Upon coalescence when fluid flows along the NF, the poroelastic effects tend to reduce the value of the HF aperture and this decreases the tension peak and the possibility of fracture re-initiation with time. Next, HF trajectories near a NF were examined prior to coalesce with the NF using different joint, rock and fluid properties. Our analysis shows that: 1) Hydraulic fracture trajectories near a NF may bend and deviate from the direction of the maximum horizontal stress when using a joint model that includes initial joint deformation; 2) Hydraulic fractures propagating with higher injection rate or fracturing fluid of higher viscosity propagate longer distance when turning to the direction of maximum horizontal stress; 3) Fracture trajectories are less dependent on injection rate or fluid viscosity when using a joint model that includes initial joint deformation; whereas, they are more dominated by injection rate and fluid viscosity when using a joint model that excludes initial joint deformation.

This thesis presents procedures to properly simulate naturally fractured reservoirs using dual-porosity models. The main objectives of this work are to: (1) determine if the spontaneous imbibition can be simulated using a two phase CMG simulator and validate it with laboratory experiments in the literature; (2) study the effect of countercurrent imbibition in field scale applications; and (3) develop procedures for using the dual-porosity to simulate fluid displacement in a naturally fractured reservoir. Reservoir simulation techniques, analytical solutions and numerical simulation for a two phase single and dual-porosity are used to achieve our objectives. Analysis of a single matrix block with an injector and a producer well connected by a single fracture is analyzed and compared with both two phase single and dual-porosity models. Procedures for obtaining reliable results when modeling a naturally fractured reservoir with a two phase dual-porosity model are presented and analyzed.

Triaxial extension experiments on Carrara Marble demonstrate that there is a continuous transition from extension to shear fracture on the basis of mechanical behavior, macroscopic fracture orientation and fracture morphology where hybrid fractures with extension and shear fracture characteristics are formed at the intermediate stress conditions. Extension fracture surfaces display discrete, highly reflective cleavage planes and shear fracture surfaces are covered with calcite gouge and display grooves and striations that are aligned parallel to slip. This study uses the fractured samples that were formed under triaxial extension experiments to characterize 1) microscopic surface features using scanning electron microscopy, 2) fracture surface morphology using laser profilometry, and 3) off-fracture damage using optical microscopy. These data are used to test the step-crack model of fracture development for the formation of hybrid fractures. Spectral analysis of the profiles demonstrates that microscopic roughness decreases gradually across the extension-to-shear fracture transition in both the orientations parallel and perpendicular to slip. However, macroscopic roughness gradually increases then decreases across the transition in the direction parallel to slip. The greatest macroscopic roughness occurs at the transition from extension fractures to tensile-hybrid fractures and is attributed to the presence of macroscopic steps in hybrid fractures surfaces. The treads of the steps in the hybrid fracture surfaces have characteristics of extension fracture surfaces and the risers have characteristics of shear fracture surfaces. The treads have a right-stepping left lateral geometry that is consistent with the step-crack model. Thin sections of hybrid fractures display systematically spaced, pinnate, microfractures that emanate from both sides of the macroscopic fracture surface. The pinnate fractures on both sides correlate across the macroscopic fracture, suggesting that they are precursory to the formation of the macroscopic fracture surface. The spacing to length ratio of the pinnate fractures and the macroscopic orientation of the fracture surface are also consistent the relationship dictated by the step-crack model of fault formation.

Micro seismic data and coring studies suggest that hydraulic fractures interact heavily with natural fractures creating complex fracture networks in naturally fractured reservoirs such as the Barnett shale, the Eagle Ford shale, and the Marcellus shale. However, since direct observations of subsurface hydraulic fracture geometries are incomplete or nonexistent, we look to properly scaled experimental research and computer modeling based on realistic assumptions to help us understand fracture intersection geometries. Most experimental analysis of this problem has focused on natural fractures with frictional interfaces. However, core observations from the Barnett and other shale plays suggest that natural fractures are largely cemented. To examine hydraulic fracture interactions with cemented natural fractures, we performed 9 hydraulic fracturing experiments in gypsum cement blocks that contained embedded planar glass, sandstone, and plaster discontinuities which acted as proxies for cemented natural fractures. There were three main fracture intersection geometries observed in our experimental program. 1) A hydraulic fracture is diverted into a different propagation path(s) along a natural fracture. 2) A taller hydraulic fracture bypasses a shorter natural fracture by propagating around it via height growth while also separating the weakly bonded interface between the natural fracture and the host rock. 3) A hydraulic fracture bypasses a natural fracture and also diverts down it to form separate fractures. The three main factors that seemed to have the strongest influence on fracture intersection geometry were the angle of intersection, the ratio of hydraulic fracture height to natural fracture height, and the differential stress. Our results show that bypass, separation of weakly bonded interfaces, diversion, and mixed mode propagation are likely in hydraulic fracture intersections with cemented natural fractures. The impact of this finding is that we need fully 3D computer models capable of accounting for bypass and mixed mode I-III fracture propagation in order to realistically simulate subsurface hydraulic fracture geometries. / text

published_or_final_version / Nursing Studies / Master / Master of Nursing

Osteoporotic fractures are still the major health concerns in many developed societies especially when the incidence of that tremendously increased with the aging population. However, the outcomes of osteoporotic fracture treatment have not been entirely satisfactory due to the poor quality of bone substance. Inspiringly, bone morphogenetic protein 2 (BMP2) with the ability to accelerate bone formation showed advantages over the conventional treatment. The only problem needed to overcome is its short half-life which resulted in the requirement of readministration and extremely high cost. As a solution to that, gene therapy provides a promising way to sustainably release this protein at the regeneration site. Since viral vectors have been hampered by genetic toxicity and immunogenicity, nanoscaled non-viral vectors offer an attractive means for gene delivery. Chitosan as non-viral vector has been widely investigated for its excellent biocompatibility. Most efforts have been given to improve its low transfection efficiency. In this study, chitosan was first modified with octaarginine, one of cell membrane penetrating peptides, and showed enhanced transfection activity, but which was not significant as expected. Following that, low molecular weight polyethyleminine (PEI) was introduced to modify chitosan through bioreducible disulfide linkage, denoted as Chitosan-ss-PEI. PEI is an efficient non-viral vector but hampered by molecular-weight dependent toxicity. The developed Chitosan-ss-PEI showed good biocompatibility in MTT assay in three different cell lines, during which cells were maintained 80% of viability when the concentration of this vector was up to 100 μg/mL. The optimal transfection efficiency of Chitosan-ss-PEI was higher than that of PEI 25k and comparable to Lipofectamine in delivering luciferase reporter gene. GFP expression mediated by Chitosan-ss-PEI also showed similar results. Chitosan-ss-PEI was then applied to deliver BMP2 gene to skeletal system cells and exhibited the osteogenic ability. For C2C12 myoblast cells, this system inhibited their myoblast differentiation and induced the osteogenic differentiation. It also showed stronger effect in promoting the differentiation of immature osteblast-like MG63 cells and in inducing C3H10T1/2 mesenchymal stem cells osteogenic differentiation in term of ALP activity and mineralization ability compared with other commercial available non-viral vectors. Primary MSCs such as bone marrow stromal cells (BMSC) and human umbilical cord blood mesenchymal stem cells (hUCB-MSC), are usually more difficult to transfect, but they showed stronger osteogenic differentiation ability induced by this system comparing with the cell lines. BMP2 usually requires extremely high concentration to realize its function. Through the investigation of BMP2 signaling regulation in this study, it was found that parathyroid hormone (PTH) could increase the access of BMP2 ligands to their receptors by negatively influencing BMPs antagonist network, resulted in enhanced BMP2 activity in bone remodeling and in promoting the commitment of MSC to osteoblast lineage both in vitro and in vivo. This course involved the endocytosis of PTHR with a complex of LRP6, which organized antagonist network on the cell surface to shield the BMPs receptors. Novel approaches are expected to be developed based on this mechanism with the purpose of intensifying the therapeutic effect of BMPs. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

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