Hydraulic flow units and permeability prediction in a carbonate reservoir, Southern Iraq from well log data using non-parametric correlation

The determination of permeability in heterogeneous and anisotropic reservoirs is a complex problem, because core samples and well test data are usually only available for limited number of wells. This paper presents hydraulic flow units and flow zone indicator for predicting permeability of rock mass from core and well log-data. The concept is applied to some uncored wells/intervals to predict their permeability. Flow zone indicator depends on geological characteristics of the material and various pore geometry of rock mass; hence it is a good parameter for determining hydraulic flow units (HFU). Flow zone indicator is a function of reservoir quality index and void ratio. We are determined flow zone indicator from well log and core data and divided the reservoir into various hydraulic flow units using K-means. Then will be develop a correlation (The Alternating Conditional Expectation (ACE) technique will be used and tested in this study) between hydraulic flow units from the core and the well log data which can be used to estimate permeability in un-cored wells, these correlations enable to estimate reservoir permeability at the "flow unit" scale. Finally, having effective porosity and flow zone indicator, permeability was calculated in each hydraulic flow unit. Results of permeability prediction based on HFU were examined for a number of wells and were compared with the measured permeability value of cores. Then will be evaluate a good correlation between the predicted and measured permeability. Introduction A hydraulic flow unit is a section of reservoir which is different from other parts by means of hydraulic characteristics or characters controlling fluid flow in reservoir. 1 Thus, if we divide the reservoir into various flow units, permeability can be estimated with sufficient accuracy. Hydraulic flow units, HFU which is a function of flow zone indicator, FZI. FZI is also dependent upon Reservoir Quality Index, RQI and void ratio, φz. 2 A knowledge of these two properties is essential before questions concerning types of fluids, amount of fluids, rates of fluid flow, and fluid recovery estimates can be answered. Methods for measuring porosity and permeability have comprised much of the technical literature of the oil industry. Permeability is one of the essential parameters in reservoir calculation, modeling, and production estimation. It is determined in different methods such as well test data, log data, and core analysis. In some intervals/wells core is not available to be tested, thus estimation of permeability should be carry out based on other types of data. Several authors have tried to estimate permeability of rock mass from well logs. 3 Predicting permeability with low cost and sufficient accuracy is an important issue. Flow zone indicator can be calculated using ACE to represent mathematical model between input and output data is used in this study to determine flow zone indicator in uncored wells. Theory of Flow Units The Hydraulic Unit concept (Amaefule et al., 1993) 1 was selected for subdividing the reservoir into distinct petrophysical types. Each distinct reservoir type has a unique Flow Zone Indicator (FZI) value. According to Tiab (2000) 4 , a hydraulic flow unit is a continuous body over a specific reservoir volume that practically possesses consistent petrophysical and fluid properties, which uniquely characterize its static and dynamic communication with the wellbore. This technique is based on a modified Kozeny-Carman (1927) 5 (cited in Jude O. Amaefule 1993) 1 and the concept of mean hydraulic radius: k = 1 2τSgv 2 φe 3 1−φe 2 .................(1) Sgv: may also be define as the surface area of grains exposed to fluid per unit volume of soild material. Flow zone indicator depends on geological characteristics of the material and various pore geometry of a rock mass; hence, it is a good parameter for determining hydraulic flow units (HFU). Flow zone indicator is a function of reservoir quality index and void ratio. 18 International Journal of Enhanced Research in Science Technology & Engineering, ISSN: 2319-7463 Vol. 3 Issue 1, January-2014, pp: (480-486), Impact Factor: 1.252, Available online at: www.erpublications.com Page | 481 Amaefule et al. (1993) 1 addressed the variability of Kozeny’s constant by dividing Eq. (1) by the effective porosity, φe and taking the logarithm: Defining the flow zone indictor FZI (μm) as: 2 FZI = 1 Sgv τ Fs .....................(2) Reservoir quality index RQI (μm) as: 2 RQI=0.0314 k φe ................(3) Normalized porosity φz (fraction) as: 2 φz = φe 1−φe .....................(4) Eq. (1) becomes: RQI= FZI × φz.................. (5) Taking the logarithm of both sides of Eq. (5) yields: Log RQI= Log FZI + Log φz......(6) On a log-log plot of RQ1 versus φz, all samples with similar FZl values will lie on a straight line with unit slope, Figure (1). Samples with different FZ1 values will lie on other parallel lines, Figure (2). The value of the FZ1constant can be determined from the intercept of the unit slope straight line at φz =1. Samples that lie on the same straight line have similar pore throat attributes and, thereby, constitute hydraulic unit. The permeability of a sample point is then calculated from a pertinent HFU using the mean FZI value and the corresponding sample porosity using the following equation: 1 k =1014 FZI φe 1−φe 2 ................(7) Results and Discussion Determining the number of Hydraulic Flow Units from core data We determined the number of hydraulic flow units in three different ways by using Statistica v.5 program and compared the results obtained: