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This paper summarizes results of a successful laboratory investigation to visualize and quantify pyrolysis-induced porosity evolution of Uinta Basin organic-rich source rock using X-ray computed tomography (CT). Combining CT imaging techniques with a radio-opaque gas as a pore contrast fluid allowed for the description of porosity changes within source rock rather than limiting quantification to a single bulk value, as obtained by conventional porosity measurement techniques. The porosity of the immature and thermally matured rock sample, a Green River oil shale, increased from 9 to 25% as a result of kerogen conversion and delamination. Porosity distributions of immature samples showed unimodal behavior, whereas matured samples displayed multimodal characteristics. These new measurements indicate that porosity evolution during maturation is not well-described by bulk measurements.

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Suplacu de Barcau, a heavy oil field in Romania with more than 2,700 wells and over 50 years of air injection history, is considered one of the world's largest in-situ combustion projects. This paper describes a 3D simulation study of a sector of the field. The sector chosen spans the entire history of the field, from a short period of cold production in the early 1960s to the current production method of cyclic steam stimulation followed by air injection. To date, about 200 wells have been drilled in this sector, which covers approximately 1.1 km2. We present the different stages of the numerical study and review some of the difficulties involved in modeling in-situ combustion in a large model. We describe how we managed the uncertainties in the reservoir and in the fluid description, and how we overcame limitations in the available data. Kinematic data from laboratory experiments were used as a starting point, and we present details of the simplified kinematic formulation that was needed to improve the numerical performance of the simulation model. The model is heterogeneous, so there is an uneven propagation of the combustion front. We compare historical production rates with the model predictions and estimate areas of oil that were bypassed due to this heterogeneity and to gravity override.

A conventional high-pressure/high-temperature experimental apparatus for combined geomechanical and flow-through testing of rocks is not X-ray compatible. Additionally, current X-ray transparent systems for computed tomography (CT) of cm-sized samples are limited to design temperatures below 180 °C. We describe a novel, high-temperature (>400 °C), high-pressure (>2000 psi/>13.8 MPa confining, >10 000 psi/>68.9 MPa vertical load) triaxial core holder suitable for X-ray CT scanning. The new triaxial system permits time-lapse imaging to capture the role of effective stress on fluid distribution and porous medium mechanics. System capabilities are demonstrated using ultimate compressive strength (UCS) tests of Castlegate sandstone. In this case, flooding the porous medium with a radio-opaque gas such as krypton before and after the UCS test improves the discrimination of rock features such as fractures. The results of high-temperature tests are also presented. A Uintah Basin sample of immature oil shale is heated from room temperature to 459 °C under uniaxial compression. The sample contains kerogen that pyrolyzes as temperature rises, releasing hydrocarbons. Imaging reveals the formation of stress bands as well as the evolution and connectivity of the fracture network within the sample as a function of time.

Summary Shale-matrix-associated transport phenomena exhibit multiple mechanisms including advective-,diffusive-, and adsorptive-driven transport modes, depending on the pore type. Diffusive processes are governed by the shale organic constituents known as kerogens. Kerogens, composed of fine-scale organic microstructures, vary with respect to their petrophysical properties, depending on their origin and maturity level. The extent to which kerogens contribute to the overall transport is governed by their ability to diffuse hydrocarbons contained within. The diffusion coefficient is a crucial parameter used to quantify diffusivity based on the interactions between the host material and the diffusing molecules. Kerogen as a hosting medium allows for diffusion of natural gas at various rates based on several factors. One of these factors, kerogen porosity, is conjectured to significantly influence diffusive transport phenomena. In this paper, taking advantage of the predictive power of molecular dynamics (MD) simulation, we investigate the impact of kerogen porosity on the diffusivity coefficient of natural gas. Starting from a single type II kerogen macromolecule, several kerogen structures for a realistic range of porosity values were created and, subsequently, used for diffusivity calculations of methane molecules. Simulation results suggest a direct link between diffusion and kerogen porosity, allowing for delineation of the diffusion tortuosity factor. Furthermore, the microscale tortuosity–diffusivity relationship in kerogens was investigated at the reservoir scale by means of a shale permeability model. The results substantiate the critical impact of the diffusion process on the shale permeability.