Predicting Permeability in Un-Cored Intervals/Wells Using Hydraulic Flow Unit Approach

Abstract

Abstract Prediction of permeability in un-cored intervals/wells is necessary to developing an effective reservoir characterization program and providing information on various depositional and diagenetic controls on pore geometry. Permeability can be obtained from well tests, core analysis, and well logs. Usually using well log data to derive estimates of permeability is the cheapest source. In this paper, routine core analysis and well log data of an actually existing sandstone reservoir in the Gulf of Suez (Egypt) were used to develop permeability correlations using a Hydraulic Flow Unit Approach (HFU). The core data were statistically treated for identification of Hydraulic Flow Units. This involves the calculations of Reservoir Quality Index (RQI), Flow Zone Indicator (FZI), and Pore Level Heterogeneity Index (PLHI). Results showed that six HFUs were identified from core data and each unit has its own FZI. A correlation between FZI calculated from core data and that obtained from well log data was developed for estimating permeability in un-cored intervals/wells. Application of the Pore Level Heterogeneity Index concept to the data determined the existence of six rock types in the studied reservoir. Introduction Estimating permeability in un-cored intervals/wells is a generic problem common to all reservoir engineers. Most of the field-scale reservoir characterization studies require detailed knowledge of petrophysical properties at the drilled wells. Since most wells are not cored, an accurate calculation method of permeability in uncored wells from log data is needed for achieving a realistic reservoir description. Several investigators(1–4) have proposed traditional approaches for permeability estimation. The approaches were based on linear regression or empirical inferences that use correlations among various well log responses. The empirically inferred models are locally applied because there may be large differences in depositional characteristics at other locations. The regression models assume that a linear relationship between logarithmic permeability and porosity exists. Another linear relationship between core porosity and log porosity was also proposed by Canas et al.(5). Both methods ignore the scatter of the data around the fitted line and attribute any scatter to measurement errors. A more reasonable technique is to employ the concept of Hydraulic Flow Units (HFUs) in predicting permeability and reservoir Description(6–12). The term Hydraulic Flow Unit is defined as a representative element volume of the total reservoir rock within which geological and petrophysical properties that affect fluid flow are internally consistent and predictably different from properties of other rock HFUs. Generally, permeability calculations using HFUs offer improved estimations over traditional regression-based averaged relationships. The extent of improvement depends mainly on the geological characteristics of the formation, with larger enhancements achieved in more heterogeneous deposits. In the present study, 510 measurements of porosity and permeability of different sandstone rocks, obtained from an oil reservoir existing offshore of Egypt (Gulf of Suez) were used to develop correlations for in situ permeability estimations. Statistical examination of the developed correlations shows a good agreement between the measured and calculated data.