Pressure Depletion Experiments in Highly Viscous Oil Systems
Abstract/Contents
- Abstract
- Greater recovery than predicted during primary production has been observed in several heavy-oil reservoirs. The reasons for higher than anticipated efficiency of the solution gas drive process in viscous oil systems are unclear. Depletion experiments were conducted using a sandpack to investigate this anomalous behavior further and to gain a better understanding of the liquid-gas interactions. The effects of viscosity and depletion rate perhaps play significant roles in determining accuracy of predictions and as such, the experiments conducted consisted of varying both viscosity (among three oils of different viscosity) as well as the constant pressure depletion rate. Pressure profiles, in-situ gas saturation, and effluent composition were monitored during depletion of a sandpack.Live oils were created by saturating viscous mineral oils with carbon dioxide and an attempt was made to keep the gas-oil ratio for all live oils the same. A multiplexer and pressure transducer were used in conjunction to facilitate accurate pressure measurements. An X-ray computerized tomography (CT) scanner was used to measure gas-phase saturation inside the sandpack during the experiments. A video camera was setup at the outlet to monitor the fractional flow of gas during production.Physical phenomena examined include apparent supersaturation, critical gas saturation, and gas nucleation properties. The experiments show that gas nucleates and grows preferentially towards the outlet when depletion rates are large. Gas saturation is highest at the non-producing end for any depletion rate, provided the production period is long enough. It is inferred from the CT images that the gas-phase within the core is continuous over dimensions much greater than that of single pores.Fractional flow of gas at the outlet is affected by viscosity and lower viscosity oils tend to produce at higher initial fractional flow of gas. Solution gas drive of a lower viscosity oil also leads to a more intermittent flow of oil and gas. Both the differential pressure and gas-oil ratio of produced fluid fluctuates significantly, which is consistent with the observation of intermittent flow.Critical gas saturation was found to increase with decreasing oil viscosity. But solely looking at critical gas saturation to comment on recovery does not consider the important aspect of production after critical gas saturation has been reached. Post-critical gas saturation production may be sizable depending on viscosity of the oil. Smooth gas fractional flow trends are seen as oil viscosity increases while abrupt changes in fractional flow of gas and intermittent flow of gas and oil occur for low viscosity oils. From a phenomenological standpoint, the greatest oil production occurs when the gas and oil flow are intermittent.
Description
| Type of resource | text |
|---|---|
| Date created | June 2002 |
Creators/Contributors
| Author | Leung, Yi Tak |
|---|---|
| Primary advisor | Kovscek, Anthony R. |
| Degree granting institution | Stanford University, Department of Petroleum Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
Bibliographic information
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Preferred citation
- Preferred Citation
- Leung, Yi Tak. (2002). Pressure Depletion Experiments in Highly Viscous Oil Systems. Stanford Digital Repository. Available at: https://purl.stanford.edu/kc689rv7123
Collection
Master's Theses, Doerr School of Sustainability
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