In-Situ Combustion Dynamics Visualized With X-Ray Computed Tomography
- Berna Hascakir (Stanford University) | Louis Marie Castanier (Stanford University) | Anthony Robert Kovscek (Stanford University)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 19-22 September, Florence, Italy
- Publication Date
- Document Type
- Conference Paper
- 2010. Society of Petroleum Engineers
- 4.1.5 Processing Equipment, 5.8.5 Oil Sand, Oil Shale, Bitumen, 1.2.2 Geomechanics, 5.4.11 Cold Heavy Oil Production (CHOPS), 5.3.1 Flow in Porous Media, 5.4.9 Miscible Methods, 5.4 Enhanced Recovery, 4.6 Natural Gas, 4.1.9 Heavy Oil Upgrading, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.2 Reservoir Fluid Dynamics, 2.4.3 Sand/Solids Control, 5.4.2 Gas Injection Methods, 4.1.2 Separation and Treating, 5.5.2 Core Analysis, 4.3.4 Scale, 5.4.6 Thermal Methods, 5.2.1 Phase Behavior and PVT Measurements
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One method to access unconventional, heavy-oil resources is to apply in-situ combustion (ISC) to oxidize in place a small fraction of the hydrocarbon thereby providing heat and pressure that enhances recovery. ISC is also attractive because it provides the opportunity to upgrade oil in-situ by increasing the API gravity and decreasing, for instance, sulfur content. Despite a considerable literature on ISC dynamics, the propagation of a combustion front through porous media has never been visualized directly. We use X-ray computed tomography (CT) to monitor ISC movement, displacement-front shape, and thickness in a 1m long combustion tube. Temperature profile history, liquid production, and effluent gas data are also obtained. Tests employ a 8.65 °API (at 21.6 °C) heavy crude oil and representative sand. The general trend of saturation profiles are defined through spatially and temporally varying CT numbers. The role of initial oil and water saturations is examined by packing the combustion tube with either multiple samples with different saturations or filling it with a uniform sample. Our work quantifies that ISC fronts display instabilities on a very fine scale (cm). ISC reactions appear to add to front instability in comparison to inert gas advance. The pressure gradients during ISC appear to influence grain arrangement for loose packing. These grain arrangements cause combustion front fingering suggesting that the geomechanical state is relevant to combustion. This new data advances the knowledge base significantly by providing a data set for benchmarking of ISC simulations.
In-situ combustion (ISC) is a thermal recovery process in which a small amount of oil is combusted in place that aids the displacement of the remaining oil by releasing thermal energy and gases (e.g., Alexander et al., 1962; Brigham and Castanier, 2007; Ursenbach et al. 2010). In the field, the ignition is started with an electrical or down-hole gas burner, and in some cases auto ignition (T reservoir > 180 oF) can be achieved (Tadema and Weijdema, 1970). The combustion is sustained by injecting air or an oxygen rich gas into the formation. The oil is driven toward the producer by the vigorous combustion gas, steam, and water drive
(Sarathi, 1998). The water drive results from water of combustion and recondensed formation water. This process is also called fire flooding to describe the movement of a burning front inside the reservoir. Based on the respective directions of front propagation and air flow, the process can be forward, when the combustion front advances in the same direction as the air flow, or reverse, when the front moves against the air flow (e.g., Akin et al., 2000; Brigham and Castanier, 2007). In this study, we focus on dry forward combustion.
As the combustion front moves away from the injection well, several well characterized zones develop in the reservoir between the injector and producer. These zones are the result of heat and mass transport and the chemical reactions that occur during forward in-situ combustion process (Castanier and Brigham, 2003). Although small (10's cm) in spatial extent, the coking zone and the subsequent combustion zone are key to effective combustion. In a linear sense, the combustion zone moves the most slowly.
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