Speaker
Description
Our research team is devoted to developing rock property acquisition techniques for CO2 sequestration projects in shallow aquifers. Target reservoir depth of CCS (Carbon Capture and Storage) in aquifers can be shallower than the most of E&P project in terms of economic efficiency. It infers that CCS projects have more chance to deal with unconsolidated rocks. Evaluating unconsolidated rocks is sometimes difficult, because there is uncertainty in acquisition of rock cores through drilling, which may result in lack of direct measurement of rock properties. To overcome this obstacle, we employed Digital Rock Physics (DRP) technology, which is indirect evaluative methodology applied for target reservoir. We created a digital model of the porous media simulating the reservoir rocks by packing objects that mimic sand particles. This synthetic digital model allowed us to calculate the permeability, which is a parameter indicative of the ease of fluid flow and essential for determining CO2 storage capacity.
In this study, we examined effect of particle shape on permeability. As parameters representing particle shape, circularity and aspect ratio of sand taken from the outcrop were measured. The aspect ratio of 0.7 and circularity of 0.917 were used for the models. Three types of particles model were prepared: sphere, ellipsoid, and Nonspherical Irregularly Shaped Particles (NISP). Ellipsoid model reflects aspect ratio, and NISP model reflects both aspect ratio and circularity. All three models reflect the particle size distribution measured by the sieve method.
Higher permeability was calculated with the model filled with sphere particle compared with the other two models. The calculated permeability of the ellipsoid and NISP models were close. It is interpreted that there is no significant difference between the ellipsoid and NISP models, which infers that the aspect ratio is the main control parameter for permeability in this case.
A sensitivity study was conducted on the aspect ratio and circularity to investigate effect of particle size on relationship between permeability and porosity. 15 ellipsoid models were created by changing the aspect ratio from 0.3 to 1.0. It is found out that the increase in permeability relative to the increase in porosity is smaller when aspect ratio is close to 1.0. Next, 144 NISP models were created with 32 circularity ranging from 0.81 to 0.98. The increase in permeability against increasing porosity tended to slow down with decreasing circularity. However, the relationship was not as clear as at aspect ratio.
Finally, a revised ellipsoid model was created by using high resolution particle size distribution. The calculated permeability was compared to measured permeability and found out that these permeabilities were within the same error range with previous studies which targeted consolidated sandstone. As a result, the permeability of unconsolidated sandstone was successfully estimated using the synthetic digital model with high resolution particle size distribution.
| Country | Japan |
|---|---|
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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