Estimating fracture intensity in hydrocarbon reservoir: an approach using DSI data analysis

Fracture detection and evaluation in carbonate reservoirs plays an important role in reservoir development and cost optimization. The majority of Iranian hydrocarbon reservoirs are carbonates for which the detection and evaluation of fractures is crucial. Cores and image logs are usual tools of fracture studying; however, it is both technically and financially impossible to core or image the whole thickness of the reservoir and in the whole wells. Other tools of fracture detection exploit the information conveyed by well log data. One application for dipole sonic imager (DSI) is its capability to evaluate fractures by measuring Stoneley wave. In this study, the DSI was used as a tool to position fractures and evaluate its intensity in the fractured bearing Darian formation. For this, the Stoneley wave data were analyzed using a commercial software. The direct and reflected Stoneley waves were subtracted from the original data and reflection coefficients were calculated afterwards. From the calculated reflection coefficients, positions and intensities of fracture were determined. The results were validated by the formation micro imager (FMI) log data. The reason of doing this project using Stoneley wave analysis obtained by acoustic tool in objective field is that core data and FMI data—which are direct method in fractures evaluating—are not accessible because of economical and technical reasons. In this project, a DSI is used for propagating Stoneley wave in a fractured zone in the Dariyan Formation. The Stoneley wave data were analyzed using commercial software. Then, reflected and direct waves were subtracted from the original data. As a result, reflection coefficients were calculated. According to calculated RC, position and intensity of fractures were detected. Finally, the results were validated by FMI image log data.