MODELLING REFLECTION SIGNATURES OF PORE FLUIDS AND DUAL POROSITY IN CARBONATE RESERVOIRS

摘要

The motivation for this synthetic Amplitude Versus Angle (AVA) study of an isotropic carbonate reservoir consisting of a dual porosity on two scales is to identify possible seismic signatures of carbonate rocks containing various fluids and pore connection models. The reservoir is modelled for four scenarios on the basis of a general theory for visco-elastic waves, where the inclusion-based model operates with spheroidal cavities on two scales. While the total porosity of the reservoir is considered constant, the pores and cracks at the different scales are designed to be either connected or isolated. The pore systems are saturated with either gas, oil or water. Reflection coefficients are computed for a 2-layer model consisting of a cap rock of shale above the reservoir in order to analyze the effects of various pore to pore connection and pore fluid models in the double porosity systems.rnThe modelling shows how the AVA parameters change both due to varying pore to pore connection and various pore fluid saturation scenarios. If we assume estimated AVA parameters with some uncertainties, the study indicates that it should be possible to obtain measurable changes in the reflectivity due to changes of the pore connectivity also when the introduced fluid has almost equal acoustic properties as the displaced one. Such modelling studies should be of particular relevance for studying diagenetic effects on seismic signatures, as for instance, water and oil may have similar acoustic properties, but different impact on the pore system over time.