Structural and fracture analysis using EMI and FMI image Log in the carbonate Asmari reservoir (Oligo-Miocene), SW Iran

Abstract

Assessment of the reservoir structure and determination of theinsitu stress direction arenecessary in oil production optimization and<br />field development. Today, the application of reservoir software and Image logsplay a central role in resolving this problem. Electric<br />and ultrasonic imaging tools record vast amounts of high-resolution data within the borehole wall. This enables the geoscientists to<br />describe in detailthe structuralfracture networksvery essential for stratigraphic and structural analysis and improved reservoir<br />characterization. A Six Arm Electrical Borehole Imaging (EMI) tool has recently been developed. This tool represents further<br />advancement in the evolution of electric borehole imaging. The electrode arrays mounted on six independent arms provide excellent<br />pad contact and produce very high resolution images for stratigraphic and structural analysis. Furthermore,the results of this study<br />indicate that EMI is a powerful technique for identifying thedominant porosity and defining the relationship between fractures and<br />permeability. In this study, data from two wells(well No.3 with FMI and well No.6 EMI image log) were utilized. The results of the<br />Velocity Deviation Log and images indicate that the production in the Asmari reservoir of this field is a combination of fractures and<br />rock matrix. Besides, the fractures and porous zones have effectively impacted the reservoir rock properties so that two general patterns<br />of tectonic fractures associated with longitudinal and diagonal wrinklingcan be identified. Longitudinal patterns are the dominant ones<br />and often form the open fractures. They are mainly oriented in the N45-90W direction and are chiefly observed in the upper Asmari<br />zones.Induced fractures and breakouts have been observed in the two wells, indicating a maximum horizontal stress orientation of<br />65°N in well No.6 and 295°N in well No.3. The stress direction in the western section of this oil field is therefore different from the<br />eastern one and does not follow the general Zagros trend.