When Near-Wellbore Conditions Blur PLT Response: Integrated Interpretation and Diagnosis in a Naturally Fractured Reservoir

Abstract

Water production is a major challenge in naturally fractured carbonate reservoirs, particularly in wells with long open-hole completions where multiple reservoir intervals may contribute to wellbore flow. Identifying the intervals responsible for water production is important for effective reservoir management and intervention planning. In this study, an integrated reservoir characterization approach was applied to evaluate the flow behavior of a vertical well with an approximately 300 m open-hole completion spanning multiple reservoir units. Static and dynamic data, including conventional and image logs, fracture interpretations, time-lapse resistivity data evaluating changes in resistivity along the wellbore during the initial and subsequent recompletion periods, production logging tool (PLT) measurements, and production history, were analyzed together with sector reservoir simulation. The radius of investigation from the only drill-stem test (DST) performed in the studied well was used as a reference for defining the sector model boundaries, and the information obtained from the test was also considered when interpreting selected model responses. The aim was to improve the understanding of the flow behavior around the well and to provide a basis for selecting an appropriate intervention strategy. The results showed that flow behavior was strongly influenced by the natural fracture system, whereas fracture density alone was insufficient to explain the observed flow distribution. The comparison of PLT measurements and simulation results also showed that flow contributions identified from different datasets may not always align at the interval scale. This highlighted the importance of considering the static reservoir structure, wellbore conditions, and dynamic behavior together when interpreting PLT results. The integrated evaluation was used to identify intervals relevant to water production and to support the selection of the recompletion strategy. Following the intervention, water production was eliminated while the production rate remained close to the pre-intervention level. The results demonstrate that combining static and dynamic data with reservoir simulation can provide a more consistent interpretation of complex well and reservoir flow behavior and support reservoir management and intervention decisions in naturally fractured carbonate reservoirs.