Fractured reservoirs, especially in low permeable carbonate rocks, are important
target for hydrocarbon exploration and production because fractures can control
fluid flow inside the reservoir. Hence, quantitative knowledge of fracture attributes is
important for optimal hydrocarbon production. However, in some cases fractures can
cause leakage of injected CO2 during enhanced oil recovery (EOR) or CO2 sequestration.
Furthermore, CO2 can geochemically interact with reservoir fluids and host
rock. Hence, time-lapse monitoring of the progress of CO2 in fractured reservoirs is
also very important.
In order to address these challenges, I have developed an integrated approach for
studying fluid flow and seismic wave propagation in fractured media using Discrete
Fracture Network (DFN) models. My seismic simulation study suggests that CO2
saturated reservoir shows approximately ten times more attenuation than brine saturated
reservoir. Similarly, large P-wave velocity variation in CO2 saturated reservoir
and amplitude variation with offset (AVO) results for our example model predicts
that CO2 is easier to detect than brine in the fractured reservoirs.
The effects of geochemical processes on seismics are simulated by time-lapse modeling
for t = 1000 years. My modeling study suggests that intra-aqueous reactions are
more significant during injection of CO2 for t = 6 years, while slower mineral reactions
dominate after pressure equilibrium is achieved that is from t = 6 to 1000 years.
Overall both types of geochemical reactions cause change in reflection coefficient of 2
to 5%, which may be difficult to detect in some cases. However, the significant change
in the seismic properties at the boundary of the CO2 front can be used to detect the
flow path of CO2 inside the reservoirs. Finally, a method for generating stochastic
fracture models was extended and improved to more realistic field model for seismic
and fluid modeling. My detail analysis suggests that fractures generated by isotropic
stress field favor orthogonal sets of fractures in most subsurface rocks that can be converted to seismic model, similar to DFN study. The quality and validity of the
models is assessed by comparisons to DFN models, including calculations of fractal
dimension measures that can help to characterize fractured reservoirs.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2752 |
| Date | 15 May 2009 |
| Creators | Shekhar, Ravi |
| Contributors | Gibson, Richard L. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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