This study used X ray computed tomography (CT) to investigate the variability in the aperture field of natural fractures in two granitic cores; one core, 57 mm in diameter and 146 mm in length, was studied with a medical CT scanner, whereas the other core, 87 mm in diameter and 245 mm long, was characterized by means of an industrial CT scanner. A quantitative methodology for measuring the fracture‐aperture thickness from CT images was developed and applied to images of cores to reconstruct the distribution of fracture aperture in the cores, with a spatial resolution of 1.4 mm by 1.4 mm by 5 mm. The CT images of the natural fractures revealed that the aperture thickness (1) is not constant within the fracture plane, (2) varies over several orders of magnitude, and (3) approximately followed a lognormal distribution for one of the cores. The CT method, when applied to monitor the movement of contrast agents injected into the cores, demonstrated fingering of the flow. Higher contrast agent concentrations and earlier contrast agent arrivals correlated with larger aperture regions of the core. The results of this study demonstrate that CT can be used to characterize fractures nondestructively and to detect the movement of contrast agents in granitic cores.

In this study, the kinetics of heavy crude-oil combustion in porous media are reported. Ramped temperature oxidation (RTO) tests with effluent gas analysis are conducted to probe in situ combustion (ISC) reaction kinetics along with isothermal coke formation experiments. The role of oxygen on coke formation reactions (i.e., fuel formation for ISC) is investigated using X-ray photoelectron spectroscopy (XPS) of intermediate reaction products. The XPS data is analyzed along with companion RTO experiments to obtain a simplified multistep reaction scheme. Synthetic cases illustrate the connection between a proposed reaction scheme for oil/matrix pairs and one-dimensional combustion front propagation. Analysis of experimental results illustrate that the reaction scheme is capable of reproducing experimental results including the basic trends in oxygen consumption and carbon oxides production for RTO experiments as a function of heating rate for both good and poor ISC candidates. The combination of XPS and RTO studies indicates that the quality (or reactivity) of coke formed during the process is a function of oxygen presence/absence. Coke formed in the presence of oxygen is significantly more reactive due to additional oxygen functional groups on the coke surface in comparison to coke formed under an inert atmosphere. Additionally, this work extends relatively easy to perform RTO tests as a screening tool for ISC performance.

Summary Of the various enhanced-oil-recovery (EOR) polymer formulations, newly developed associative polymers show special promise. We investigate pore and pore-network scales because polymer solutions ultimately flow through the pore space of rock to displace oil. We conduct and monitor optically water/oil and polymer-solution/oil displacements in a 2D etched-silicon micromodel. The micromodel has the geometrical and topological characteristics of sandstone. Conventional hydrolyzed-polyacrylamide solutions and newly developed associative-polymer solutions with concentrations ranging from 500 to 2,500 ppm were tested. The crude oil had a viscosity of 450 cp at test conditions. Our results provide new insight regarding the ability of polymer to stabilize multiphase flow. At zero and low polymer concentrations, relatively long and wide fingers of injectant developed, leading to early water break-through and low recoveries. At increased polymer concentration, a much greater number of relatively fine fingers formed. The width-to-length ratio of these fingers was quite small, and the absolute length of fingers decreased. At a larger scale of observation, the displacement front appears to be stabilized; hence, recovery efficiency improved remarkably. Above a concentration of 1,500 ppm, plugging of the micromodel by polymer and lower oil recovery was observed for both polymer types. For tertiary polymer injection that begins at breakthrough of water, the severe fingers resulting from water injection are modified significantly. Fingers become wider and grow in the direction normal to flow as polymer solution replaces water. Apparently, improved sweep efficiency of viscous oils is possible (at this scale of investigation) even after waterflooding. The associative- and conventional-polymer solutions improved oil recovery by approximately the same amount. The associative polymers, however, showed more-stable displacement fronts in comparison to conventional-polymer solutions.

No abstract

In-situ combustion (ISC) possesses advantages over surface-generated steam injection for deep reservoirs in terms of wellbore heat losses and generation of heat above the critical point of water. Additionally, ISC has drastically lower requirements for water and natural gas, and potentially a smaller surface footprint in comparison to steam. In spite of its apparent advantages, prediction of the likelihood of successful ISC is unclear. Conventionally, combustion tube tests of a crude-oil and rock are used to infer that ISC works at reservoir scale and estimate the oxygen requirements. Combustion tube test results may lead to field-scale simulation on a coarse grid with upscaled Arrhenius reaction kinetics. As an alternative, we suggest a comprehensive workflow to predict successful combustion at the reservoir scale. The method is based on experimental laboratory data and simulation models at all scales. In our workflow, a sample of crushed reservoir rock or an equivalent synthetic sample is mixed with water/brine and the crude-oil sample. The mixture is placed in a kinetics cell reactor and oxidized at different heating rates. An isoconversional method is used to estimate kinetic parameters versus temperature and combustion characteristics of the sample. Results from the isoconversional interpretation provide a first screen of the likelihood that a combustion front is propagated successfully. Then, a full-physics simulation of the kinetics cell experiment is used to predict the flue gas composition. The model combines a detailed PVT analysis of the multiphase system and a multistep reaction model. A mixture identical to that tested in the kinetics cell is also burned in a combustion tube experiment. Temperature profiles along the tube and also the flue gas compositions are measured during the experiment. A highresolution simulation model of the combustion tube test is developed and validated. Finally, the high-resolution model is used as a basis for upscaling the reaction model to field dimensions. Fieldscale simulations do not employ Arrhenius kinetics. As a result, significant stiffness is removed from the finite difference simulation of the governing equations. Preliminary field-scale simulation shows little sensitivity to grid-block size and the computational work per time step is much reduced.