This paper presents innovative iteration algorithms for multi-interface heat transfer in pipe flow. To the best of our knowledge, this is the first approach derived from Drift-flux Model (DFM), which is more competent than mechanistic models for high slippage gas-liquid flow. Consequently, the temperature/pressure distribution profiles can be accurately captured under transient condition.
For waxy crude fields, it's critical to sustain the flowing temperature above the Wax Appearance Temperature (WAT). This is especially challenging for gas-lift assisted wells. The injected gas, commonly at relatively low temperature, leads this flow assurance problem sophisticated. An effective practice is to heat up the flowing fluid by installing an electrical cable in tubing. Such the heat exchange happens at three interfaces in the production system: between cable and flowing crude, flowing crude and injected gas, injected gas and formation. Therefore, it is challenging to model such a multiphase production system including an inner annulus inside tubing as the electrical able installed, and an outer annulus where the gas is injected. To optimize this production system, a rigorous transient multiphase and multi-interface heat transfer simulator has been demanded.
With explicitly integrating with the subsurface boundary condition, our new algorithms can optimize the cable length, heating period, supplied power, or gas injection rate for the aforementioned production system. This new method has been successfully applied for several gas-lift assisted wells in a waxy crude field located in north China. The power consumption has been noticeably decreased by 30% than the historical field performance. The delegated optimization scheme reduces the shut-in time in winters, which has promised a cost-saving development.
The presented model not only satisfies the exceptional modeling requirements for periodically-heating crude producers, but also it is appropriate for other heat transfer investigations under transient multi-interface and multiphase flow condition.