It has been suggested that the elastic modulii changes due to pore fluid saturation which can be sensed by seismic data in the form of AVO, and then used as an indicator of fluid type. In this laboratory scale research, we investigated the use of AVO methods to determine reflectivity at various offsets in the absence of a rock matrix, to observe if such experiments can be tested and proven in practice. If this were the case- since it is normal to have a rock frame containing the fluid- we would go on to test the method to observe if it could separate a number of different injected mixtures, such as water, water plus NaCl (brine), water mixed with CO2 in which the CO2 was dissolved, water and oil, and other variations on these.
This work was performed in a small pressure cell, at pressures of 2.07 MPa (300 psi), 1.03 MPa (150 psi) and room pressure, to also observe the response prior to dissolved gas nucleation (since a gas cap would not assist AVO analysis).
The results indicated that AVO does indeed provide a response in the absence of a rock matrix in which the interface is of an elastic (Plexiglas) and acoustic (fluid) form, and that a good separation between hydrocarbons (oil) from CO2 can be produced in the AVO intercept and gradient domain. The results also indicate that AVO cannot separate a brine containing 30,000 ppm NaCl from distilled water, thereby diminishing the hope that we could use seismic AVO to determine whether a liquid is brine or fresh water.