A Dual Gas Tracer Technique for Determining Trapped Gas Saturation During Steady Foam Flow in Porous Media
- C.J. Radke (U. of California) | J.V. Gillis (U. of California)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 23-26 September, New Orleans, Louisiana
- Publication Date
- Document Type
- Conference Paper
- 1990. Society of Petroleum Engineers
- 5.6.5 Tracers, 5.2.1 Phase Behavior and PVT Measurements, 2.5.2 Fracturing Materials (Fluids, Proppant), 4.1.2 Separation and Treating, 5.1 Reservoir Characterisation, 5.3.2 Multiphase Flow, 4.1.5 Processing Equipment, 5.3.1 Flow in Porous Media, 5.4.2 Gas Injection Methods, 4.1.4 Gas Processing, 5.4 Enhanced Recovery, 1.6.9 Coring, Fishing, 6.1.5 Human Resources, Competence and Training, 4.3.4 Scale
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Foam is a possible mobility control agent for effective oil displacement from reservoirs. Thus, it is important to understand the mechanisms by which foam flows in porous media. Micromodel studies and prior gas-phase tracer experiments show that a significant fraction of the gas in a foam exists as trapped bubbles which, therefore, have a major impact on the flow resistance. Unfortunately, in the tracer experiments performed to date, partitioning of the tracer into the performed to date, partitioning of the tracer into the trapped gas has not been accounted for. Currently, only qualitative information is available on the actual amounts of trapped gas.
To overcome these limitations and obtain quantitative measurements of trapped gas saturations, we have developed a unique experimental apparatus employing dual gas tracers. During steady foam flow in a porous medium, dilute sulfur hexafluoride (SF6) and methane (CH ) tracers in a nitrogen carrier are injected, and the effluent concentration is monitored by gas chromatography. The measured tracer histories are fit to a simple mass transfer model which describes any partitioning between the mobil and trapped foam phases. Tracer effluent concentrations-predicted by the phases. Tracer effluent concentrations-predicted by the model are strongly influenced by the solubility of each tracer in the liquid phase. This behavior is observed in the experimental histories as well. Hence, multiple gas tracers provide a discriminating assessment of trapped gas saturation during foam flow through porous media.
New trapped gas saturations are reported for an aqueous C a-olefin sulfonate foamer solution and nitrogen flowing through a 2.3-um2 fired Berea sandstone at Pa (1 atm) back pressure and at room temperature. Total superficial velocities range from 0.4 to 4 m/day while inlet gas fractional flows are varied from 0.8 to 1.0. We find large fractions of trapped gas between 80 and almost 100% depending on the particular flow conditions. The importance of trapped gas to understanding foam-flow behavior is again confirmed.
Foam has been shown to exhibit high apparent viscosities in porous media. This leads to a vast improvement in the mobility ratio of, for example. A steam or CO flood. Both gravity override and channeling through high permeability zones are reduced when these fluids flow in the form of a foam. In addition, foam is relatively easy to apply. Its major component is gas, and the surfactants which stabilize the foam can be used in amounts on the order of 1 weight % of the liquid phase.
There are numerous, important pore-level phenomena involved in foam flow in porous media. One of the most important of these, and the subject of this paper, is trapped gas saturation. When foam transports through a porous medium not all of the gas in the foam actually flows. Several investigators have reported visual observations of appreciable bubble trapping in transparent micromodels and beadpacks [4-10]. Figure l, sketched from the etched-glass micromodel observations of Chambers, shows two origins of foam bubble trapping. In this figure shaded foam bubbles are trapped in the upper and lower channels which exhibit small pore throats. Flowing foam, shown clear, transports as bubble trains around the trapped clusters and through the intervening constricted pore characterized by large pore throats. Dark arrows locate the particular throats causing blockage. Trapping in the particular throats causing blockage. Trapping in the upper pore channel is due to a lamella residing just at the exit of the right most small pore throat, which terminates sharply into a downstream pore body. Lamellae in such configurations require large pressure drops to be mobilized. The trapped bubble cluster in the bottom most pore of Fig. 1 abuts against a wetting liquid lens (or against continuous liquid).
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