Carbonate Reservoir Characterization: Part 02
1. How exactly, will we be able to up-scale the properties associated with microscopic heterogeneities (facies characteristics, diagenetic effects, pore types, pore throat sizes, grain shape, size & packing, and mineralogy), that would remain applicable to a larger (carbonate reservoir) field-scale scenario, measured from thin sections, scanning electron microscope (SEM), mercury injection capillary pressure (MICP), core CT scanning and wireline-logs?
2. Leaving aside, the megascopic heterogeneities, considering, the sensitivity of tectonic activities, structural features and depositional conditions, do we have proper empirical relations or correlations that would take into account macroscopic heterogeneities (stratification, compartmentalization, sequence stratigraphy, reservoir zonation and lateral property trends) also, while characterizing a carbonate reservoir?
3. To what extent, the assumption of two for saturation exponent (n), would remain to be valid towards estimating water saturation of a carbonate reservoir (Sw) using Archie’s equation as a function of resistivity of formation water (Rw), porosity, cementation exponent (m) and true resistivity of the sample (Rt)?
4. Since, there is no known sonic transit time value for samples with different types of porosities such as found in a carbonate reservoir, to what extent, the estimation of porosity using Wyllie’s time-averaged equation as a function of sonic transit time in true formation, sonic transit time in rock matrix and sonic transit time in formation fluid – would remain to be meaningful?
5. How exactly the potential storage volume for hydrocarbons in a carbonate reservoir fundamentally differ from that of a sandstone reservoir? What is the implication behind the wide variation of porosity (1-35%) in carbonate reservoirs? Then, why do we have a relative low average porosities (around 10%) in dolomite reservoirs and limestone reservoirs?
6. Carbonate rocks being compressible, and since, porosity decreases with increasing effective stress, whether, porosity measurements are required to be carried out @ in-situ stress conditions? How about the loss of porosity with increasing confining pressure?
7. Unlike the inter-grain porosity associated with sedimentary rocks, whether, the shape of the grains; the presence of intra-grain porosity; and sorting, will have a significant effect on porosity in carbonate sediments? Feasible to capture the details on the presence of pore space within shells and peloids that make up the grains of carbonate sediments?
8. Would it remain feasible to deduce a finite relationship between porosity, grain size and sorting in carbonate rocks?
Suresh Kumar Govindarajan
https://home.iitm.ac.in/gskumar/
https://iitm.irins.org/profile/61643
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