This paper presents the implementation and value of Virtual Flow Metering (VFM) concepts for Kashagan Field wells. The VFM models are used for real time well performance estimation. The models are expected to be used to detect fluid properties changes, restrictions in the well tubing and instrumentation malfunctioning.
The paper also describes how the virtual meters are built, tuned and maintained.
One of the VFM techniques is use of Vertical Lift Performance (VLP) equation. The equation describes the relationship between the velocity of the reservoir fluid in the well tubing and pressure drop across the tubing, fluid and tubing parameters. The method consists of testing each well at wide range of flow rates and tuning the VFM model, based on VLP equation.
The method was tested on wells equipped with individual MPFM. After tuning stage, the model was compared against real time MPFM measurements. The models are also tested by estimation of bottom-hole pressure (BHP) using physically measured flow rate as an input and comparing against measured BHP. The fluid properties and phase fractions are calculated using Peng-Robinson EOS programming routines. Wells used for testing have different deviations from vertical.
The results of tuning the VFM models and testing against real time measurements show that the method can be used for accurate well performance estimation in real time. The models are capable of estimating flow rates with an average error of ±5% of span. It is observed that better match is acquired for high flow rates and for wells with less deviation from vertical. Good results were achieved in estimation of BHP using same tuned models.
The inferred friction coefficients were also compared against friction coefficients calculated by use of Colebrook-White equation. The observation is that there is very good match between the two for certain flow range.
The implementation of VFM models was instrumental on improving the overall reconciliation factor for hydrocarbon allocation process.
As a future work, it is important to better understand the following:
Impact of slippage between phases to friction loss in the well production tubing;
Impact of flow pattern to friction loss;
Impact of well curvature (deviation) to friction loss.
The method presented in the paper makes it possible for an engineer, involved in well performance measurements, to implement using readily available tools with no additional cost for dedicated software. This is a practical implementation of simple VLP equation based VFM model which were tested on producing wells with real time measurements.