The Impact of Oil Chemistry on Heavy-Oil Solution Gas Drive and Fracture Reconsolidation of Diatomite During Thermal Operations
Abstract/Contents
- Abstract
- Two different unconventional resources and two different recovery processes are studied in this work. The first is heavy oil recovered by solution gas drive. The second is steam injection into low permeability diatomite reservoir for conventional and heavy-oil recovery. The role of oil chemistry on heavy-oil solution gas drive is studied. Measurements of the concentration of organic acid and base groups as well as asphaltene content of crude oil are combined with data from laboratory-scale heavy-oil solution gas drive experiments. We find that significant asphaltene content as well as substantial acid and base numbers are indicators of whether oil is foamy. The acid number is the amount of potassium hydroxide in mg needed to neutralize the acid groups in 1 g of crude oil, whereas the base number is the amount of potassium hydroxide in mg that is required to neutralize the titrant used in an acid titration of 1g of crude oil. The partitioning of acid and base groups between the asphaltene fraction and de- asphalted oil is also studied. Organic acid and base groups are clearly present in the asphaltene fraction. We investigate the lifetime of single foam films of crude-oil and asphaltene solutions. Transparent micromodels etched with a sandstone pore network and containing gas dispersed within the oil are also used to investigate the correlation of acid number, base number, and asphaltene content with gas-bubble coalescence. The results show that a high concentration of asphaltene that exhibits acid and base functional groups tends to increase foamability and film life time of gas-crude-oil dispersions. The deasphalted fraction is not foamy despite possessing significant acid and base number. We conclude that acid and base in asphaltene are the source of interfacial properties. Asphaltene content and acid/base number of asphaltene are important factors accounting for the stabilization of dispersed gas bubbles in foamy oil. Additionally, factors related to the silica dissolution process and the mechanism of fracture reconsolidation are studied. Short-time fluid injection was conducted to study the influence of pH, temperature, salinity, and metal ions on silica dissolution. The experimental results suggest that temperature and pH are the two most important factors, in agreement with the literature. Salinity can also affect the dissolution process, while the influence of metal ions can be neglected. The influence of steam was also studied, indicating that the presence of steam hinders silica dissolution of diatomite. Based on the results of the silica dissolution study, an optimal condition for dissolution was obtained and used in hot-fluid injection experiments with relatively long periods of time. With longer experiment time, more aspects of silica dissolution were studied. At elevated temperature, strong silica dissolution happens even under very acidic conditions. Wormholes form during the injection of hot alkaline fluid if the basic pH is maintained within rock. As a result, permeability is enhanced and porosity of the inlet area also increases. Several fractured cores were prepared to study the mechanism of fracture reconsolidation. Fractures were oriented lateral to and normal to flow. Fractured cores were subject to different brine formulations at different temperatures and confining pressures. Fracture healing and rock reconsolidation were observed when hot fluid was injected at elevated temperature. The results of other tests suggest that both silica dissolution and confining stress are necessary for fracture reconsolidation. The proposed mechanism for this process has three steps. The first step is aqueous silicate production by silica dissolution. In the next step, silicate gelation happens within the pore space and fracture. Confining stress is important in the last step. It enhances the transformation of silica gel to solid silica. Given enough experiment time, fracture reconsolidation happens.
Description
| Type of resource | text |
|---|---|
| Date created | August 2009 |
Creators/Contributors
| Author | Peng, Jing |
|---|---|
| Primary advisor | Kovscek, Anthony R. |
| Advisor | Castanier, Louis |
| Degree granting institution | Stanford University, Department of Energy Resources Engineering |
Subjects
| Subject | School of Earth Energy & Environmental Sciences |
|---|---|
| Genre | Thesis |
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Preferred citation
- Preferred Citation
- Peng, Jing. (2009). The Impact of Oil Chemistry on Heavy-Oil Solution Gas Drive and Fracture Reconsolidation of Diatomite During Thermal Operations. Stanford Digital Repository. Available at: https://purl.stanford.edu/dn535hv1906
Collection
Master's Theses, Doerr School of Sustainability
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