This report describes the work performed during the second year of the project, "Investigating of Efficiency Improvements during CO 2 Injection in Hydraulically and Naturally Fractured Reservoirs." The objective of this project is to perform unique laboratory experiments with artificial fractured cores (AFCs) and X-ray CT to examine the physical mechanisms of bypassing in HFR and NFR that eventually result in less efficient CO 2 flooding in heterogeneous or fracture-dominated reservoirs. To

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... eve this objective, in this period we concentrated our effort on modeling the fluid flow in fracture surface, examining the fluid transfer mechanisms and describing the fracture aperture distribution under different overburden pressure using X-ray CT scanner. Modeling Fluid Flow through a Single Fracture using Experimental, Stochastic, and Simulation Approaches In this report, sensitivity of fracture modeling, error involved in the experiments and saturation match of fracture imbibition experiments using X-ray CT Scanner are established. A fracture is usually assumed as a set of smooth parallel plates separated by a constant width. However, the flow characteristics of an actual fracture surface are quite different, affected by tortuosity and the impact of surface roughness. Though several researchers have discussed the effect of friction on flow reduction, their efforts lack corroboration from experimental data and have not converged to form a unified methodology for studying flow on a rough fracture surface. The goal of this research is to examine the effect of surface roughness for flow through fractures and to effectively incorporate them into simulations with the aid of geostatistics. In this study, we have shown an integrated methodology, involving experiments, stochastics and numerical simulations that incorporate the fracture roughness and the friction factor, to describe flow on a rough fracture surface. Laboratory experiments were performed to support the study in quantifying the flow contributions from the matrix and the fracture under varying confining pressures. The results were used to modify the cubic law through reservoir simulations. Observations suggest that the fracture apertures need to be distributed to accurately model the experimental results. The methodology successfully modeled fractured core experiments, which were earlier not possible through parallel plate approach. A gravity drainage experiment using an Xray CT scan of a fractured core has also validated the methodology. Simulation of Naturally Fractured Reservoirs using Empirical Derived Transfer Function This research utilizes the imbibition experiments and X-Ray Tomography results for modeling fluid flow in naturally fractured reservoirs. Conventional dual porosity simulation requires large number of runs to quantify transfer function parameters for history matching purposes. In this study empirical transfer functions (ETF) are derived from imbibition experiments and this allows reduction in the uncertainty in modeling of transfer of fluids from the matrix to the fracture. The application of ETF approach is applied in two phases. In the first phase, imbibition experiments are numerically solved using the diffusivity equation with different boundary iv conditions. Usually only the oil recovery in imbibition experiments is matched, however, with the advent of X-Ray CT the spatial variation of the saturation can also be computed. The matching of this variation can lead to accurate reservoir characterization. In the second phase, the imbibition derived empirical transfer functions are used in developing a dual porosity reservoir simulator. The results from this study are compared with published results. The study reveals the impact of uncertainty in the transfer function parameters on the flow performance and reduces the computations to obtain transfer function required for dual porosity simulation. Fracture Aperture Calibration This study addresses the use of an X-Ray CT scanner to image fracture aperture distribution. By applying variable overburden on fractured media, the change in fracture aperture has been observed. The general distribution of fracture apertures is quite heterogeneous. In the past, lognormal function has been used to describe fracture aperture distribution. This study shows how to generate the fracture aperture calibration that be used later on to describe and confirm aperture distribution under different overburden conditions. Fracture Aperture Distribution The fracture aperture and fracture permeability are usually considered to remain the same during the producing life of a naturally fractured reservoir, regardless of degree of depletion, but reservoirs experience different stress state conditions, therefore understanding the fracture behavior becomes more complex. This research analyzes the effect of fracture aperture and fracture permeability on the fluid flow under different overburden pressure. This paper investigates the fracture apertures under different stress-state conditions. The equations to quantify the flow through the matrix and the fracture at different overburden pressures are provided. The X-ray CT scanner was used to obtain fracture aperture distributions at various overburden pressures to verify the applicability of lognormal distribution, for fracture aperture. This has been commonly used for distributing fracture apertures in the past but never verified experimentally. In addition, reservoir simulations are performed to duplicate the experimental results and to provide a valid model for future stress-sensitive reservoirs. Our experimental results show that the fracture aperture and fracture permeability have significant pressure-dependent changes in response to applying variable injection rates and overburden pressures. The laboratory results show that the change in overburden pressure significantly affects the reservoir properties. The change in matrix permeability with different injection rates under variable overburden pressures is not significant in contrast with that effect on fracture aperture and fracture permeability. Calibration curve was obtained to determine fracture aperture from the X-ray CT scanner results. This experimental research will increase the understanding of fluid flow behavior in fractured reservoirs. site lists the publications of our group and allows downloads of several papers, reports, and presentations. This website also allows downloading of software, i.e. spontaneous imbibition simulator, Delaunay Triangulation, reservoir management software (in progress) and reservoir modeling simulator (in progress).