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 andfield development. Today, the application of reservoir software and Image logsplay a central role in resolving this problem. Electricand ultrasonic imaging tools record vast amounts of high-resolution data within the borehole wall. This enables the geoscientists todescribe in detailthe structuralfracture networksvery essential for stratigraphic and structural analysis and improved reservoircharacterization. A Six Arm Electrical Borehole Imaging (EMI) tool has recently been developed. This tool represents furtheradvancement in the evolution of electric borehole imaging. The electrode arrays mounted on six independent arms provide excellentpad contact and produce very high resolution images for stratigraphic and structural analysis. Furthermore,the results of this studyindicate that EMI is a powerful technique for identifying thedominant porosity and defining the relationship between fractures andpermeability. In this study, data from two wells(well No.3 with FMI and well No.6 EMI image log) were utilized. The results of theVelocity Deviation Log and images indicate that the production in the Asmari reservoir of this field is a combination of fractures androck matrix. Besides, the fractures and porous zones have effectively impacted the reservoir rock properties so that two general patternsof tectonic fractures associated with longitudinal and diagonal wrinklingcan be identified. Longitudinal patterns are the dominant onesand often form the open fractures. They are mainly oriented in the N45-90W direction and are chiefly observed in the upper Asmarizones.Induced fractures and breakouts have been observed in the two wells, indicating a maximum horizontal stress orientation of65°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 theeastern one and does not follow the general Zagros trend.