Abstract
[Truncated abstract] Knowledge of the pressure dependence of rock properties is important for a diverse range of earth science problems, including seismic characterisation and monitoring of subsurface fluid flow processes, common in hydrocarbon, groundwater, and CO2 sequestration reservoirs. This thesis focuses on developing a better understanding of the pressure-dependent elastic properties of unconsolidated and partially consolidated sandstones. The key contribution of this thesis is to improve the prediction and interpretation of pressure-dependent rock properties and their effects in seismic data.
A long-standing research problem is that theoretical models of velocity-pressure response often do not match laboratory measurements, and alternately, empirical regressions fit to lab data do not extrapolate accurately to wider pressure ranges since they have little or no underlying physical basis. In this thesis we develop a new model to describe the pressure sensitivity of the bulk and shear moduli for weakely cemented sedimentary rocks. The model incorporates effects of sedimentary compaction and the concept of critical porosity, including a relationship to account for porosity and density change with pressure. We demonstrate a method to estimate the critical porosity constraint at zero effective pressure using grain-size distribution data. The strong physical basis of this model, along with a unique two-stage model parameter fitting process, enables us to predict the elastic properties of unconsolidated sediments at a wide range of pressures, including low effective pressure when only data at higher pressures is available. The model is tested on laboratory measurements for various rock samples and fits well over a wide range of pressures. The new model should have implications for the improved prediction and interpretation of 3D and 4D seismic data, including for pressure prediction, quantitative AVO analysis, seismic reservoir characterisation, and time-lapse fluid-flow monitoring.
A long-standing research problem is that theoretical models of velocity-pressure response often do not match laboratory measurements, and alternately, empirical regressions fit to lab data do not extrapolate accurately to wider pressure ranges since they have little or no underlying physical basis. In this thesis we develop a new model to describe the pressure sensitivity of the bulk and shear moduli for weakely cemented sedimentary rocks. The model incorporates effects of sedimentary compaction and the concept of critical porosity, including a relationship to account for porosity and density change with pressure. We demonstrate a method to estimate the critical porosity constraint at zero effective pressure using grain-size distribution data. The strong physical basis of this model, along with a unique two-stage model parameter fitting process, enables us to predict the elastic properties of unconsolidated sediments at a wide range of pressures, including low effective pressure when only data at higher pressures is available. The model is tested on laboratory measurements for various rock samples and fits well over a wide range of pressures. The new model should have implications for the improved prediction and interpretation of 3D and 4D seismic data, including for pressure prediction, quantitative AVO analysis, seismic reservoir characterisation, and time-lapse fluid-flow monitoring.
| Original language | English |
|---|---|
| Qualification | Doctor of Philosophy |
| Publication status | Unpublished - 2014 |