Diagnosis of multi-stage fracture stimulation in horizontal wells by downhole temperature measurements
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Copyright 2014, Society of Petroleum Engineers. Downhole temperature data measured by production logging tools (PLT) or distributed fiber -optic temperature sensors (DTS) are used frequently today to diagnose multi-stage fracture treatments in horizontal or highly deviated wells. This temperature data measured at the wellbore during and post fracture brings important transient flow information that helps engineers to understand the process of fracturing, the performance of fractured wells and therefore to optimize fracture design. The interpretation models developed to translate temperature data to flow conditions can be fully numerical -based simulations or analytical/semi-analytical approaches. With reasonable assumptions analytical/semi-analytical models are more suitable for real-time field applications. This paper presents the applications of using a coupled semi-analytical fracture model and a wellbore model to predict temperature and pressure behavior in multiple-fractured horizontal wells during production. The thermal model calculated the heat transfer in the fracture/reservoir/wellbore system considering subtle temperature changes caused by the Joule-Thompson cooling effects. The results showed that transient temperature behavior is sensitive to estimate the fracture initiation points, number of created fractures and fracture geometry. We discuss the characteristics of transient temperature behaviors corresponding to fracture geometry and flow rate distribution along a fractured horizontal wellbore. The temperature signal is typically strong at the toe and weak towards heel if the fractures are more evenly created along the wellbore due to the fluid mixture inside wellbore. Two field cases are presen ted to illustrate the application of using the temperature model to understand the fracture/flow distribution. The estimation of flow rate distribution from the temperature model is compared to the interpretation of flow by production logging tools. Although this is a single phase gas model, we can identify the water entries at certain location by matching the observed temperature with the calculated temperature. Flow distribution from the temperature model presents consistent trend with PLT measurement. Fracture diagnosis is more sensitive to the fluid entries (fracture locations) and less sensitive to the influence of multiphase flow inside the wellbore when compared with PLT tools.
