Velocity-Effective Stress Response of CO2-Saturated Sandstones

摘要: Three differing sandstones, two synthetic and one field sample, have been tested ultrasonically under a range of confining pressures pore representative in-situ reservoir pressures. These sandstones include: sandstone with calcite intergranular cement produced using the CSIRO Calcite In-situ Precipitation Process (CIPS); silica cement; core sample from Otway Basin Waarre Formation, Boggy Creek 1 well, target lithology for trial CO2 pilot project. Initial testing was carried on cores at ?room-dried? conditions, up to 65 MPa in steps 5 MPa. All were then flooded CO2, initially gas phase 6 MPa, 22°C, liquid-phase temperature 22°C 7 17 Confining varied 10 Ultrasonic waveforms both P- S-waves recorded each effective pressure increment. Velocity versus responses calculated experimental data S-waves. Attenuations (1/Qp) waveform spectral ratio methods. Theoretical calculations velocity as function made pressure-density bulk modulus-pressure diagrams Gassmann medium theory. Flooding gaseous negligible change velocity-effective stress relationships compared dry state (air saturated). various lowered velocities by approximately 8% average air-saturated state. increased flooding case. Experimental agreed high The ?critical? pressure, which agreement theory occurred, type. Discrepancies are thought be due micro-crack populations microstructure is significant gives some confidence predicting seismic behaviour conditions when injected.