Hydrocarbon storage mechanisms in organic rich mudstones are complex systems which are affected by intricate depositional and diagenetic processes. The in-situ pore system is a result of the combined processes of inorganic porosity evolution via compaction and diagenesis, and organic porosity generation and preservation due to organic matter conversion to hydrocarbons. Estimating hydrocarbon storage in organic rich mudrocks has proven challenging for many reasons, including but not limited to the uncertainties in porosity estimation, mudrock electrical properties, connate water salinity, and the lack of reliable saturation calibration data.
The pore scale characterization of organic rich mudstones is additionally challenged by issues of measuring properties of nanometer sized pores. The small pores and consequently low permeability impact the representativeness of the rock samples measured, primarily due to the introduction of artifacts during core acquisition. These coring induced artifacts also impair the ability to restore the rock to in-situ conditions for representative measurements.
This work focuses on reducing uncertainty in hydrocarbon storage estimation by integrating core measurements (crushed rock porosity, Dean-Stark saturations, pyrolysis and nuclear magnetic resonance), source rock kinetics, and pore scale imaging. The result is a consistent view of hydrocarbon saturation that honors all core measurements and modelled constraints. Specific focus is paid to correcting routine observational data, utilizing traditional data for non-standard applications, kinetic modelling for additional volumetric constraint, and validation of final interpreted volumes via representative and quantitative pore scale imaging and digital rock modelling.
A framework for integration of measured data, modelling, and observations is outlined. Two case studies are presented highlighting measurement uncertainty, model calibration, and integration for improved understanding of reservoir storage mechanisms and ultimately reduced uncertainty in hydrocarbon storage estimation.
Saturation of conventional hydrocarbon reservoirs is most commonly estimated utilizing log based resistivity models that are calibrated to core. Accurate water salinity, core porosity, core water saturation, and core electrical properties (FFI, Co/Cw, RI) are required for accurate saturation calculations. Organic rich mudrocks present unique challenges. Uncontaminated water samples are difficult to acquire and salinity can be highly variable. The low permeability of organic rich mudrocks can lead to core damage during retrieval. Additionally, the variable clay content and low permeability nature of organic rich mudrocks are unsuitable for conventional cleaning, drying, and core electrical property experiments which require complete fluid displacement.
