A new analytical method for characterization of fractured reservoirs

Abstract

Structural delineation is the main issue in the evaluation of carbonate reservoirs in structurally complex areas. Permeability is a critical reservoir parameter that influences well and/or reservoir performance and it is even more challenging when the reservoir is fractured. Oil Based Mud Micro Imager - resistivity of invading zone (OBMI-Rxo) is a high resolution curve that is sensitive to fluid mobility near the borehole wall and indicates invasion. However most operators are not using an accurate Rxo curve of OBMI for reservoir and petrophysical applications. After drilling it is important that the borehole stays in good shape, morevere, borehole instability will reduce the working life of the well. The main aim of this study is to design a workflow in order to establish an advanced formation evaluation in a carbonate fractured and clastic reservoirs. The entire workflow involved incorporating borehole images, petrophysical logs, Modular Formation Dynamics Tester tool (MDT), Xpress Pressure Tool (XPT) and cores in characterizing fractured and non-fractured reservoirs. Image log data are processed and interpreted in the computer using a Geoframe software. The bedding, deviation survey and image logs are imported into the Bortex software and the heterogeneity analysis of reservoirs from borehole images is computed based on the same resistivity contrast principle than the layer delineation. Respectively, the Formation Micro Imager (FMI) and OBMI images are used to examine permeability and index mobility in conjunction with open hole logs. As a result, the answers provided by the FMI tool helped in understanding the reservoir structure, identify and evaluate fractures, visualize the rock texture, and complement coring programs. Single-well permeability distribution was demonstrated by the use of advanced image analysis. OBMI-Rxo helped to identify zones of higher permeability when combined with conventional induction logs and porosity logs. In addition, working on advanced borehole shape analysis improved information about the well condition.