SPRINGS®, the first subsea unit for the treatment and injection of sea water, will help to reduce the development costs of remote deep offshore fields. As a confirmation of Total’s leading position in subsea processing, this technology endorses the Group’s ability to help establish new industrial standards.
More Cost-Effective Access to Remote Deep Offshore Fields
Reducing development costs for fields located far from existing production locations requires the intensification of subsea processing. We have partnered with Saipem and Veolia to meet this challenge and have developed a subsea unit for the treatment and injection of sea water: SPRINGS® (Subsea PRocessing and INjection Gear for Seawater). Designed to operate up to 3,000 m of sea depth, and treat and inject up to 60,000 barrels/day of seawater filtered to one thousandth of a micron (0.001 micrometer), SPRINGS® uses organic nano-filtration membranes. This is a first in the deep offshore industry.
The main benefit of treating seawater locally, closer to the injection well, is the elimination of the high-pressure water injection line between the topsides and the deposit. Compared to a conventional development solution (additional water treatment capacities on existing topsides + a new line and water injection riser), SPRINGS® proves more competitive for tie-back distances over 25 km.
We have found that increases in distance, depth and injection rate also add to its appeal. This is what our economic studies have shown for different distances (25, 50 and 75 km), water depths (500, 1,500 and 2,500 m) and water injection rates (20, 40 and 60 kb/d).
Springs® SRUS, A Simplified Treatment Process
The marinization of the SPRINGS® treatment unit had to meet two fundamental requirements: it had to be extremely durable, allowing it to operate without maintenance for six months to a year, as well as perfectly reliable. This second prerequisite stems from the crucial role water injection plays in improving oil field production and desulfation to prevent the formation of deposits in cases where barium or calcium are present in the deposits, or even the production of H2S due to the sulfate-reducing bacteria activity.
By choosing a simplified treatment design, we have succeeded in achieving this dual objective. Three modules, usually present in a “traditional” water treatment chain with an SRU (Sulfate Removal Unit, surface equipment that removes sulfates from seawater), have therefore been removed or simplified:
- the pre-filtration module upstream of the nano-filtration membrane desulfation module has been simplified. That was made possible by the improved quality of the deep seawater: beyond a depth of 500 m, it is actually cleaner than the water taken at shallower depths for surface treatment
- the water deoxygenation module (too complex an operation nowadays in deep water) has been eliminated: without it, resistant alloys must be used for the injection lines, because deep water still contains significant amounts of oxygen;
- the membrane cleaning module (CIP: Clean in Place) has also been eliminated: the clogged membranes are replaced by clean membranes every six months to a year and cleaned on shore.
In summary, this simplified process, conceived and adapted to deep water conditions, allows for the marinization of this water treatment. It yields a more competitive unit compared to the conventional model or a non-simplified station (considered in the early stages of the project but abandoned for reasons of cost and complexity).
A Commercially Viable Springs® in 2018
We have carried out an extensive test program to test the implementation of organic nano-filtration membranes in subsea conditions. From 2010 to 2013, a series of laboratory tests proved their ability to operate in deep sea conditions (300 bars and 4°C). Then, in 2014, the SPRINGS® treatment module passed the offshore test during an initial pilot phase carried out in the Republic of Congo.
Submerged for three months at a depth of 500 m, the nano-filtration membranes performed extremely well. In fact, they delivered water with a residual sulfate content much lower than the 40-ppm threshold required for injection into the reservoir. As with any pilot, this test has also helped to improve the SPRINGS® design.
SPRINGS® will be ready and available for field applications from 2018 on. Following in the footsteps of the Pazflor subsea gas/liquids gravity separator and the high boost multiphase pump system, we will once again have contributed to the emergence of a new industrial standard for deep offshore.
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