An integrated approach to quantify the geological control of carbonate pore types on permeability
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2015 SEG. The compressional and shear velocities of carbonate rocks are affected by many factors such as mineral composition, fluid content, porosity and pore type, as well as temperature and pressure. Among these factors, carbonate pore structure plays a significant role in determining the permeability behavior when compared to its effect in clastic reservoir rocks. The goal of this study is two-fold: 1. to understand the control of different carbonate pore types on permeability using velocity information from core and log data and 2. to estimate the spatial distribution of permeability by angle stack seismic inversion. A predefined pore structure parameter ( ) affecting shear wave velocity from a rock physics model is used here for the first time to be related with different pore types in a deeply buried carbonate reservoir of interest. Results indicate that this parameter could be used to separate the intercrystalline pores of secondary dolomite from unaltered moldic pores of the ooid grainstones. Two distinctive permeability trends are observed due to pore type difference and are explained using the pore structure parameter and core data. When >4, the dominant pore type is intercrytalline, porosity and permeability vary between 0.01-0.16 and 0.08-900md respectively. When < 4, the dominant pore type is moldic; porosity and permeability vary between 0.16-0.3 and 0.02-8md respectively. Intercrystalline pores with larger pore throat size lead to much higher permeability compared to moldic pores at a constant porosity. Isolated moldic pores with high porosity, however, have relatively low permeability. Different empirical fits to the permeability trends were applied to estimate permeability from porosity. The feasibility of extracting those reservoir properties from inversion is first studied by examining the relationships among acoustic impedance at zero offset, elastic properties at far offset, and Vp/Vs ratio. Based on these, the spatial distribution of permeability can be obtained for field production by using the inversion results of porosity and pore structure parameter from rock physics-guided angle stack inversion.
