Knowing the exact flow allocation for each controlled zone is important for well optimization and the management of an intelligent well system (IWS). For two-zone IWS producers, a broadly accepted downhole gauge configuration uses the triple-gauge system, where two gauges give the upstream side pressure/temperature (P/T) of the two downhole control valves, and one gauge gives the P/T inside tubing of the commingled fluid. Theoretically, this configuration gives the P/T boundary conditions between the two valves and the gauge carrier, where flow allocations can be solved numerically, based on the gauge readings and control valve settings. However, from what we have seen in the past 10 years of IWS applications, only a few have successfully published application cases regarding this topic. Is this an indication that a large number of two-zone triple-gauge IWS wells are operating in the low-confidence region of the two zone's production flow allocations?
In this work, a comprehensive hydraulic model has been developed to address this topic. This paper will discuss a recent application of such a model to estimate the flow allocations of an existing two-zone deep-water IWS oil producer. The well began production in 2007. A total of 1,362 daily triple gauge data points are available for this study, where the monitored P/T data indicates that the well was flowed in multiphase conditions at downhole for a large percent of its production life. Verification was completed by comparing the predicted flow allocation results with this well's measured total rates and daily allocation rates. Further comparisons of the zonal allocations, between the model calculated results versus the zonal reservoir deliverability study predicted results, were also provided. These comparisons showed an excellent match between the predicted results, measured data, and the available reservoir study results. Descriptions of key factors to address the accuracy of the method have been provided, including compensated differential pressure, multiphase choke model, choke discharged coefficient, and fluid pressure-volume-temperature (PVT) behavior impact. A modified multiphase choke model was proposed in this study. The authors believe it will be more suitable for downhole valve operating and multiphase flow conditions.
This case study has proven a very promising independent solution for continuous well rates estimation, with the solution based purely on choke pressure drops and intelligent well valve positions. The downhole monitoring P/T is normally based on seconds, which means that intelligent well flow allocations can be calculated in real-time without installing downhole venturi flow meters that may jeopardize well profitability and integrity. This solution brings measurable benefits for those IWS wells with no downhole flow meters, when taking into account the time and effort spent on periodic production tests, reservoir/well deliverability studies for production allocations, and potential production loss during the production tests.