Effect of Temperature on Phase Behavior, Pore Morphology, and Multiphase Flow Properties of Diatomite
Abstract/Contents
- Abstract
- Coreflood experiments were conducted on various diatomite field samples to measure oil recovery as a function of temperature and to quantify changes, if any, in the rock fabric resulting from the flow of high-temperature, alkaline brine through diatomite. Most samples analyzed here originate from South Belridge and a limited number of tests were conducted on core samples from Midway-Sunset, to provide a comparison. With respect to oil recovery, we perform spontaneous imbibition tests at temperature to gauge oil recovery potential at negligible pressure gradient. This is a conservative laboratory test that characterizes baseline thermal recovery. Spontaneous imbibition is followed by forced imbibition to measure residual oil saturation and characterize any changes in residual saturation as a function of temperature. In previous thermal tests using diatomite, we witnessed a favorable shift in wettability of the rock that aided oil recovery. This shift was accompanied by the production of fines liberated from pore wall surfaces. The specific objectives of this study are to - verify previous experimental results that South Belridge diatomite imbibes water more strongly at elevated temperature (roughly 400 °F) as the result of a shift toward water wetness, - examine fines detachment as a function of temperature in reservoir core samples that have never been subject to heating, - compare fines release from two different reservoirs to obtain a more general understanding of the process, - quantify changes, if any, of diatomite pore morphology and texture accompanying the flow of steam condensate, - link any changes found at the pore level to alteration in core permeability, porosity, and - probe the possibility and mechanisms of so-called fracture healing accompanying hot fluid injection Numerous imbibition tests and long-term corefloods were conducted at elevated temperature (350-440°F) using pH=7 brine and pH=9.8 synthetic steam condensate. Two different stress states were imposed on samples as well. The first is the typical radial confining stress associated with a Hassler-type core holder whereas the second is a uniform stress imposed on all surfaces of the core. In all cases the net effective stress is roughly 300 psi. Primary conclusions follow: - All core flow tests indicate that oil recovery from diatomite is accelerated and enhanced at elevated temperature. - A systematic shift toward greater water wetness at elevated temperature is noted in these samples. The main evidence is the ability of the rock to release greater volumes of oil at very small pressure gradients when the temperature is high. - Core permeabilities following significant volumes of high temperature fluid injection decreased by roughly 10% in most cases whereas porosity varied from 5 to 30%. These alterations in core properties had no apparent effect on oil recovery behavior. - The grain density of samples increases as samples are subjected to heating. This appears to result from preferential dissolution of less dense minerals. - Hot alkaline fluid injection combined with moderate confining stress lead to “fracture healing” in the laboratory. Visual inspection, X-ray CT scans, as well as tracer characterization of cores suggests that fractured cores behave in a more homogeneous, unfractured fashion following heating. The results reported here suggest that thermal recovery of oil from diatomite is an effective process that occurs with minimal damage to the rock matrix. For more complete understanding of diatomite properties, we developed an analytical model of core flooding with silica dissolution/precipitation and we quantified rock matrix damage through the amount of dissolved silica. The primary conclusions from this analysis are, first, that long water flooding dissolves a significant amount of amorphous silica and opal-CT, resulting in an increase of the rock density since heavier minerals stay in the matrix. Second, the amorphous silica to opal-CT transition is minimal and contributes a very small extent to rock density change. This work goes in the direction of developing an understanding of the pore-types, sizes, and shapes across a variety of diatomite reservoirs. Such information improves our ability to predict and understand the relative permeability for light and heavy-oil diatomite as well as the response of diatomite to steam.
Description
| Type of resource | text |
|---|---|
| Date created | June 2007 |
Creators/Contributors
| Author | Ikeda, Maki |
|---|---|
| Primary advisor | Kovscek, Anthony R. |
| Degree granting institution | Stanford University, Department of Petroleum Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
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Preferred citation
- Preferred Citation
- Ikeda, Maki. (2007). Effect of Temperature on Phase Behavior, Pore Morphology, and Multiphase Flow Properties of Diatomite. Stanford Digital Repository. Available at: https://purl.stanford.edu/sj587pn5903
Collection
Master's Theses, Doerr School of Sustainability
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