Abstract
Combining both geological and petrophysical properties, a reliable rock typing scheme can be achieved. Two steps are included in rock typing. Step 1: rocks are classified into lithofacies based on core observations and thin sections; Step 2: lithofacies are further subdivided into rock types according to petrophysical properties such as MICP (Mercury Injection Capillary Pressure) and K-Phi relationships. By correlating rock types to electrofacies (clusters of log data), we can group the target formation into 12 rock types. Then it is possible to predict the distributions of rock types laterally and vertically using wireline logs. To avoid the defect of the classical J-function saturation model that includes permeability which is quite uncertain especially in carbonate rocks, a modified J-function was created and used in the paper. In this function, water saturation is simply expressed as a function of height above free water level for a specific rock type. Different water saturation models are established for different rock types. Finally, the water saturation model has been successfully constructed and verified to be appropriate.
Highlights
Water saturation is the key reservoir parameter in reservoir evaluation, modeling and reserve calculation
Two steps are included in rock typing
Step 1: rocks are classified into lithofacies based on core observations and thin sections; Step 2: lithofacies are further subdivided into rock types according to petrophysical properties such as Mercury Injection Capillary Pressure (MICP) and K-Phi relationships
Summary
Water saturation is the key reservoir parameter in reservoir evaluation, modeling and reserve calculation. Water saturation distribution calculated from the workflows above is quite far away from accuracy especially in giant carbonates characterized by complex petrophysical. That is because water saturation is controlled by the porosity, lithofacies, and other parameters in Archie formula, and by pore structure, shale content and wettability that are often not consistent in carbonate reservoir [1, 2]. Geological properties include lithofacies, rock texture, pore types, etc., whereas petrophysical properties include porosity, permeability, wettability, capillary pressure, pore throat size distribution. Rock typing absorbs the geological and petrophysical connotation which is a process of classifying reservoir into distinct units and each rock type is characterized by same depositional and diagenetic processes and unique physical properties, capillary pressure curves (or J-function) and relative permeability curves [14–28]. We firstly group KB into different kinds of rock types and construct different water saturation models for different rock types using the modified J-function
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