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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.

In-situ Combustion (ISC) is widely accepted as an enhanced oil recovery method that is applicable to various oilreservoir types. Prediction of the likelihood of a successful ISC project from first principles, however, is still unclear. Conventionally, combustion tube tests of a crude-oil and rock are used to infer whether one expects that ISC works at reservoir scale and the oxygen requirements. Combustion tube test results may lead to field-scale simulation on a coarse grid with Arrhenius reaction kinetics. If ISC is unsuccessful at field scale whereas tube tests are positive, the reservoir geological heterogeneity or operational problems are generally blamed. As an alternative, this paper suggests a comprehensive workflow to predict the likelihood of a successful combustion at the reservoir scale, based on both 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 obtain an estimate of kinetic parameters versus temperature and combustion characteristics of the sample. Results from the isoconversional interpretation also provide a first screen of the likelihood that a combustion front can be propagated successfully. Then, a full-physics simulation model of the kinetics cell experiment is used to simulate the flue gas production. The model combines a detailed PVT of the multiphase system and a multistep reaction model. A genetic algorithm is used to estimate reaction parameters and thereby match oxygen consumption and gas production. 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 high-resolution simulation model of the combustion tube test is developed and validated. This simulation uses the reaction model we have obtained from the genetic algorithm and/or isoconversional analysis. Finally, the high-resolution model is used as a basis for upscaling the reaction model to field dimensions employing nonArrhenius kinetics.