Final PhD Seminar

Improved Characterization of Thin Bed and Low-Resistivity/Low-Contrast Hydrocarbon Reservoirs

Mr Hijaz Hasnan
Applied Mathematics

Heterolithic deposits in thin bed low-resistivity/low-contrast reservoirs contain up to 30% of the global hydrocarbon reserves. However, due to millimetre-to-centimetre thin sandstone, forecasting hydrocarbon reserves and production are challenging. Producing hydrocarbon economically from heterolithic deposits in thin bed low-resistivity/low-contrast reservoirs requires the characterization of small-scale flow properties of thin beds for improved hydrocarbon reserves and production estimates. Sedimentology interpretation of the study area and reservoir in Malaysia shows that heterolithic deposits are part of tidal bars in a shallow marine environment with large areal extent and substantial volume which represent commercially viable amount of potential hydrocarbon reserves. Conventional Well Logs and Experimental Core Analysis are unable to resolve and represent the flow properties in millimetre-to-centimetre scale sandstone layers in heterolithic deposits which resulted in underestimated hydrocarbon reserves estimates. Characterization of flow properties in thin sandstone layers are a first step in a multiscale workflow in reservoir modelling that could improve hydrocarbon reserves estimates in heterolithic deposits.

This thesis applied X-Ray Micro-CT Imaging and Analysis, Digital Core Analysis, permeability gas probe analysis and 3D Visualization on five mini plugs from the sand dominated regions of two muddy heterolithic core plugs, two laminated rock core plugs and one sandy heterolithic core plug that represent sandstone units in the reservoir. The objective is to characterize the porosity, permeability and connectivity of the thin sandstone layers in the heterolithic samples and investigate multi-scale impact of small-scale heterogeneities such as average grain size and carbonate laminates on permeability.

Computed porosities of the five mini plugs are consistent with the experimental results that validated the computed porosity using digital core analysis. The computed permeability of a mini plug from one heterolithic core plug is similar to the results of the laminated sandstone mini plugs which are benchmark reservoir sandstones. 3D visualization of the heterolithic core plug reveal laterally continuous thin sandstone layers that are well connected and represent potential hidden sand pay and additional hydrocarbon reserves in heterolithic deposits. Permeability gas probe measurements of the surfaces of the core plugs validated the computed results of all samples and verified the presence of permeable thin sandstone layers in the heterolithic core plug. In addition, 3D visualization of the sandstone core plugs reveals substantial amount of carbonate minerals with different geometry that resulted in lower core plug permeability compared to their more homogeneous mini plugs, highlighting multi-scale effects of small-scale heterogeneities on permeability at larger scales. Grain size analysis of all samples indicated that permeability increases with smaller average grain sizes and is a main factor in permeability difference between similar rock types. The developed methodology characterized the permeability of millimetre-to-centimetre scale sandstone layers in heterolithic deposits and their correlation to the geometry of carbonate laminates in sandstone sandstones layers that affect permeabilities at different scale and the effects of average sediment size on permeability. The results from this thesis’ methodology contributes to the first stages of a multi-scale workflow for reservoir simulation of heterolithic deposits in thin bed LRLC reservoirs that incorporates the millimetre-to-centimetre scale sandstone layers and other small-scale heterogeneities in the reservoir model can improve the hydrocarbon reserves forecasts and production.

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