Abstract

Salinity of injection water plays a critical role in optimizing IOR/EOR methods, mainly in water flooding, low salinity water flooding and chemically enhanced oil recovery techniques, such as polymer floods. For such low salinity applications, preferred salinity is often between 1,000 and 5,000 mg/L TDS. On offshore platforms, this is achieved through blending permeate from low sulfate, high salinity (approximately 30,000 mg/l TDS) water train with desalinated water train (approximately 100 mg/l TDS). This practice typically requires two nanofiltration (NF) stages and one reverse osmosis (RO) stage which results in high footprint, heavy and complex blending manifolds. This study investigates the possibility of achieving the desired injection water composition employing a lower-footprint one pass assembly (i.e. without the need to blend permeates from parallel NF and RO trains) to produce the desired permeate salinity. The objective of the trial was to test a system providing a permeate TDS of 1,000 - 3,000 mg/L and sulfate levels lower than 10 mg/L. Such system should work with at least 20 L/m2h average fluxes and with a total recovery of at least 50 %. This paper discusses aninnovative way of arranging Nanofiltration and Reverse Osmosis membrane elements on offshore platforms in order to achieve the target salinity and sulfate concentrations for Low Salinity injection water Floods (LSF) and displays the results obtained during its testing in an industrial scale asset. The arrangement was operated during three months, showinga stable performance at an average flux of 20 L/m2h and with a recovery of 55%, using a configuration of seven membrane elements in series. Permeate water salinity obtained at this configuration was lower than 3,000 mg/L, maintaining low sulfate passage (<5 mg/L). Conclusions show the following benefits when using the innovative design:

  1. Elimination of the blending system, thus reducing complex manifold and valves which will result in reduction of CAPEX and complexity.

  2. Achieving greater water recovery compared to operating separate RO and NF membrane systems.

  3. It is estimated that depending on the injection water requirements, there can be a reduction of up to 40% in footprint and weight of reverse osmosis and nanofiltration systems.

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