Fracture Identification and Productivity Predictions in a Carbonate Reef Complex

Abstract

ABSTRACT In order to optimise well completions and production in naturally fractured reservoirs and to predict the effectiveness of enhanced oil recovery schemes, it is important to locate and describe the in-situ fractures. A combination of log measurements and core data were employed to locate and orient the fractures and assess their overall contribution to reservoir performance in a Devonian reef complex. These techniques include the imaging of the wellbore with the Formation MicroScanner Log (FMS)* and the Borehole Televiewer (BHTV). The image data were compared to detailed core analysis, where available, and were used to determine the length, orientation and probability of fractures as a function of porosity. The Array-Sonic* tool was also run to help identify fractured zones using full waveform data and to quantify producibility from Stoneley wave data in comparison to flowmeter production logs. From the comparison of the images with core, the utility of the FMS and BHTV Logs were established in identifying fractures and fracture sets as well as detenriining the orientation and vertical extent of the fractures. In addition, the response of FMS images to different porosity types was confirmed by core data. Comparison of the Array-Sonic data and the flowmeter production log data established the usefulness of the Stoneley wave attenuation as a means of identifying permeable zones. The study results permit better definition of tool response to porosity types and fractures, and reveals the influence of fractures on the overall production of the reef complex. These results have implications on the initial and secondary production techniques of this and other carbonate reservoirs.