Towards Online Analysis of Sub-sea Process Streams Using Low-Field NMR

Sub-sea separation (the remote splitting of oilfield product fluid phases (oil, water, condensate, gas) in sub-sea production systems) has the potential to unlock significant hydrocarbon resources offshore, but this potential is limited by the available remote metrology systems for measuring both the multiphase flow entering the separation process and the quality of the separated phases, specifically the discharge water. Here we explore the use of low-field bench-top NMR to measure such quantities. In terms of multi-phase flow metering, we present preliminary results featuring remote detection of a turbulent flow stream using the Earth's magnetic field and a mobile upstream permanent magnet, as depicted in fig. 1. The consequential data (NMR signal intensity as a function of separation distance) is well described by an appropriate model as a range of flow-rates featuring no free parameters [1]. These measurements and model developments form the foundations for further developments of a low-cost, small sized NMR based multiphase flow meter technology.

Fig. 1: Schematic of the flow loop used in this study, which consists of a centrifugal pump, a flow control valve to allow partial recycling, polarising magnet, EF NMR NMR console, a flow meter and a water tank.