Permeability Estimation Using Hydraulic Flow Units in Carbonate Reservoirs

Abstract

Abstract This study focuses on the evaluation of formation permeability for a carbonate reservoir from well logs and core data using the concept of flow units. Characterization of carbonate reservoirs by flow units is a practical way of reservoir zonation. The study represents a petrophysical-based method that uses well loggings and core plug data to delineate flow units within the most productive carbonate reservoir of Derdere Formation in Y field, Southeast Turkey. Derdere Formation is composed of limestones and dolomites. Logs from the 5 wells are the starting point for the reservoir characterization. The general geologic framework obtained from the logs point out for discriminations within the formation. 58 representative core plug data from 4 different wells are utilized to better understand the petrophysical framework of the formation. The plots correlating petrophysical parameters and the frequency histograms suggest the presence of distinctive reservoir trends. These discriminations are also represented in Winland porosity-permeability crossplots resulted in clusters for different port-sizes that are responsible for different flow characteristics. Although the correlation between core plug porosity and air permeability yields a good correlation coefficient, the formation has to be studied within units due to differences in pore-throat sizes and reservoir process speed. Linear regression and multiple regression analyses are used for the study of each unit. The results are performed using STATGRAPH Version Plus 5.1 statistical software. The permeability models are constructed and their reliabilities are compared by the regression coefficients for predictions in un-cored sections. As a result of this study, 4 different units are identified in the Derdere Formation by using well logging data, and core plug analyses with the help of geostatistical methods. The predicted permeabilities for each unit show good correlations with the calculated ones from core plugs. Introduction Carbonate reservoirs show challenges to geologists and engineers to characterize because of their tendency to be tight and generally heterogeneous due to depositional and diagenetic processes. The extreme petrophysical heterogeneity of carbonate reservoirs is especially demonstrated by the wide variability observed especially in porosity-permeability crossplots. Knowledge of permeability is significant for developing an effective reservoir description and quality. Formation permeability controls the requirements in involving well completions, stimulations and reservoir managements. Since not all the wells are cored, permeability can be obtained from well tests, cores and well logs. The well logs, where one can use porosities and other derived attributes, are generally utilized for predictions. Characterization of carbonate reservoirs into flow units is a practical way of reservoir zonation. The presence of distinct units with particular petrophysical characteristics such as porosity, permeability, water saturation, pore throat radius, storage and flow capacities help researches to establish strong reservoir characterization. The earlier in the life of a reservoir the flow unit determination is done, the greater the understanding of the future reservoir performance. A quality and the future performance of a reservoir are controlled by hydrocarbon storage and flow capacity. These help to define intervals of similar and predictable flow characteristics, which are the flow units.