Carbonate reservoir characterization based on rock physics and seismic inversion helps in better understanding the influence of deposition and diagenesis on rock property. In this dissertation, I first study a modern carbonate platform to understand the relationship between dolomitization and sea level change and oceanography; I then analyze the geological control of diagenesis carbonate pore types on elastic properties, such as velocity and impedance, and finally I study the geophysical signatures and inversion of highly fractured zones in deeply buried carbonates using logs and seismic data.
On the Southern Marion platform, dolostone with large pores generally has high permeability, high sonic velocity, and high acoustic impedance at given porosity compared to limestone. Acoustic impedance inversion picks out three dolomitization events, matching well with three high stands of sea level events, to illustrate that the high stand of sea level induces the formation of dolomitization zones with large pores. This study demonstrates the positive feedback loop of dolomitization and ocean current circulation, as well as the relationship between dolomitization and sea level change.
The pore types in carbonates complicate the porosity-velocity and porosity-permeability relationships, lowering the prediction accuracy of porosity from porosity-impedance relationships. The application of the Sun rock physics model in an ultra-deep carbonate reservoir showed that the product of porosity and pore structure parameter has a much better linear relationship with velocity/impedance than porosity with velocity/impedance. This finding reveals that porosity--together with pore structure parameter, dominates the elastic rock properties in carbonates, not porosity alone.
The major storage spaces are fractures and fracture related dissolution pores (cavities, molds, and vugs) in Hexiwu carbonate buried hill, in the Bohai Bay basin, China. Log analysis shows fractured zones, with open- and large-angle fractures, have porosity less than 5%, bulk modulus less than 55 GPa, and acoustic impedance less than 15,500 (g/cc)x(m/s). These typical fractured zones have a high pore structure parameter--higher than 6--using the Sun model. Seismic inversion for porosity and pore structure parameter shows that the fractured and high-porosity zones are subject to the structural setting in this area, which is controlled by the regional tectonics in the Bohai Bay basin. The proposed methodology is applicable to fractured reservoirs in similar geological settings.
- Sun, Yuefeng Mollie B. & Richard A. Williford Professor