ROCK-PROPERTY ESTIMATION FROM SEISMIC AND CSEM ATTRIBUTES USING A ROCK-PHYSICS FRAMEWORK
Rock-property estimation (fluid saturation, porosity, and lithology) is the final goal of geologists, geophysicists, and reservoir engineers. We all try to combine well and surface measurements to generate a model of rock properties that can be used to generate an exploration, appraisal, or exploitation plan and quantify the hydrocarbon resources available. Since hydrocarbon exploration began in the 19th century, technology and innovation have driven the process of subsurface rock-property prediction, from exploration, solely based on surface geology, to the progressive inclusion of 2D seismic (early 1920s), gravity, magnetic, 3D seismic (late 1960s), AVO analysis (Ostrander, 1984) and, most recently, control source electromagnetic (CSEM) data (Ellingsrud et al., 2002).
Nowadays, the integration of pre-stack seismic inversion attributes with CSEM attributes using a rockphysics framework constitutes one of the most modern and robust methodologies to carry out seismic reservoir characterization. Each method provides independent physical measurements of the subsurface that complement each other and can be validated by well-log measurements and forward-modeled at different reservoir conditions through the application of rock-physics principles. Seismic provides the structural framework and, from AVO information, the possibility to derive P- and S-wave impedance volumes, which are two valuable, independent measurements, that can be linked to porosity, lithology, geomechanical properties, and, under certain conditions, to fluid saturation prediction. On the other hand, CSEM data provide a lower resolution measure of resistivity, which, when constrained with the structural framework and seismically derived volumes of porosity and lithology, can be linked to fluid saturation and hydrocarbon reserves estimation, and overcome seismic ambiguity related to similar AVO responses in both low- and high-saturated hydrocarbon reservoirs.
The lecture will cover different methodologies to estimate rock-property volumes from different types of seismic attributes, including AVO and inversion attributes using empirical and theoretical rock-physics principles calibrated with well-log data. Next, we will show how the results of quantitative seismic interpretation can be used to feed an integrated seismic-CSEM interpretation allowing us to create a geologic model of rock properties that honors both data sets and how it can be used to de-risk a prospect and spatially characterize the petrophysical properties of the reservoir.