Modification of Temperature Prediction Model to Accommodate I-Well Complexities

Abstract

Abstract Inflow profiling has proved to be a major application of Distributed Temperature Sensor (DTS) systems. The real-time, downhole temperature data is analyzed by matching the measurements with values predicted by a well thermal model; reducing the uncertainty in the well's production parameters (e.g. permeability, water cut). The accuracy of the resulting inflow profile depends heavily on the accuracy of the temperature prediction model. Existing wellbore fluid temperature models were developed for conventional wells. This paper focuses on the modification of these temperature models for application to intelligent completions equipped with DTS & Inflow Control Valves. A published temperature prediction model was modified to analyze an intelligent well's geometry i.e. distributed inflow into an annulus, fluid mixing at multiple points etc. The new model was used to demonstrate the effect of water production in an oil and water production environment on the valve's mixing temperature and the tubing's temperature profile. Our results show that the temperature profile and the mixing valve temperature are over-estimated by current models that represent the inflow of each zone of a multizone I-Wells by a single inflow point. As expected, increasing the number of inflow points within each zone reduces this discrepancy. This over-estimation reduces the accuracy of inflow profile analysis calculated from the DTS data. Changes in valve temperature in single phase production in a multi-zone intelligent well can be used to indicate the fraction of the zone that is main contributor to zonal inflow e.g. a higher temperature indicates the lower portion on the pay zone is the main contributor and vice versa. A sensitivity study showed that the valve temperatures experience a unique profile depending on which zone is producing water. Introduction The geometrical complexities of an intelligent completion complicate the analysis of the temperature profile behavior across the completion interval. This paper investigates how the different flow paths should be modeled and discusses the resulting impact of the new model on the in the wellbore's predicted temperature profile. This new solution extends the enthalpy/energy balance temperature prediction model developed by Hasan & Kabir [1] for a conventional well to make it applicable to steady-state modeling of intelligent completions. The model extension is based on altering the initial and the boundary conditions that represent the intelligent well's completion. The annulus, and its static fluid, plays an important role in the transfer of heat from the tubing to the surrounding formation. The description of annular heat transfer is even more important when annular flow occurs, as is the case for an intelligent well. The natural, convection heat transfer process (caused by density variations in the annulus) changes to forced convection within the flowing fluid. Forced convection can either increase or decrease the heat transfer rate from the tubing to the formation; depending on the type of flow (turbulent or laminar) and the fluid's thermo-physical properties. Understanding the added complexities of the intelligent well has implications when DTS or any other temperature sensor data is being interpreted for the detection of fluid/flow anomalies or when the DTS data is being is matched with the modeled wellbore temperature for zonal flow allocation. Accounting for the various flow scenarios encountered in intelligent completions can help the engineer avoid misinterpretation of the available data. The cooler annulus fluid also directly influences the temperature profile by mixing with the warmer, produced tubing fluid at the ICV. The effect of the annulus has been studied before from the point of view of conventional wells. However, an intelligent completion offers a different scenario due to the varying inflow profile. Conventional well temperature modeling assumes that the inflow enters the well at a single point at the bottom of the completion. An intelligent completion is different, the inflow zone of the perforated interval or open-hole may have a length of many hundreds or even thousands feet.