Modeling Permeability Alteration in Diatomite Reservoirs During Steam Drive
Abstract/Contents
- Abstract
- There is an estimated 10 billion barrels of original oil in place (OOIP) in diatomaceous reservoirs in Kern County, California. These reservoirs have low permeability ranging from 0.1 to 10 mD. Injection pressure controlled steam drive has been found to be an efficient way to recover oil from these reservoirs. However, steam drive in these reservoirs has its own complications.The rock matrix is primarily silica (SiO2). It is a known fact that silica is soluble in hot water and its solubility varies with temperature and pH. Due to this fact, the rock matrix in diatomite may dissolve into the aqueous phase as the temperature at a location increases or it may precipitate from the aqueous phase onto the rock grains as the temperature decreases. Thus, during steam drive silica redistribution will occur in the reservoir along with oil recovery. This silica redistribution causes the permeability and porosity of the reservoir to change. Understanding and quantifying these silica redistribution effects on the reservoir permeability might prove to be a key aspect of designing a steam drive project in these formations.In this study the first aspect that we examine is the relative importance of the factors that govern the transfer of silica between the rock matrix and the aqueous phase. On the basis of analytical solutions for simple one-dimensional systems and the conditions that typically exist in diatomite reservoirs, we conclude that the silica concentration in the aqueous phase is the equilibrium silica solubility corresponding to the temperature of that location. This is likely true for the whole length of the reservoir, except near injectors and producers. We call this attainment of 'local chemical equilibrium'. This implies for a given location, that when we know the temperature variation, we can predict the amount of silica transfer between rock grains and the aqueous phase surrounding it.From a qualitative argument we know that the extent of permeability alteration will depend on the pore-level characteristics of this rock apart from the extent of silica redistribution. We tried to infer the pore-level shapes and distributions of pore-sizes of this rock by a variety of experimental methods including mercury intrusion / retraction porosimetery, scanning electron microscopy, core-level permeability measurements and X-ray computed tomography (CT scanning). On basis of these investigations we inferred the shape of pore-body and pore-throat size distributions for an outcrop sample of diatomite. These were unimodel distributions with a high positive skew. The average pore-throat size was around 6 mm and the average pore-body size was around 40 mm. In the final phase of this study, we found mathematical relations that are useful to predict the permeability alteration with amount of silica transfer between the rock matrix and the aqueous phase given the pore-level information of diatomite. This was done using pore-network models. To start, we correlated the pore dimensions with properties like permeability and porosity. Next, we modeled the deposition / dissolution processes in terms of changing pore dimensions and then used these altered pore dimensions to find the altered permeability and porosity. This way, we were able to quantify the effect of silica redistribution on permeability of the reservoir.
Description
| Type of resource | text |
|---|---|
| Date created | July 1998 |
Creators/Contributors
| Author | Bhat, Suniti Kumar |
|---|---|
| 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
- Bhat, Suniti Kumar. (1998). Modeling Permeability Alteration in Diatomite Reservoirs During Steam Drive. Stanford Digital Repository. Available at: https://purl.stanford.edu/qw183sx2533
Collection
Master's Theses, Doerr School of Sustainability
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