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Technology Building Blocks
Five years ago the building blocks of this technology were not in place for this concept to have a credible engineering background. Emerging and established technologies have recently come together to resolve pumping issues, power distribution, filtration, materials availability and reservoir concerns which have kept rawwater injection out of mainstream technology thinking. Subsea rawwater injection is now an inevitable reality.
In 1992 a project was launched to explore the impact of aerobic seawater injection upon injection string materials and reservoir microbiology. The Rawwater Programme brought together reservoir engineers, corrosion engineers and oilfield microbiologists to focus on chlorinated aerobic water. This project attracted eleven participating companies: Amerada Hess, BP Exploration, Norsk Hydro, Phillips Petroleum, Statoil, Saga, The Norwegian Petroleum Directorate, The Nickel Development Institute, Cabval - Haynes International, Amoco Norge and Shell UK.
In early 1994 both Mentor Engineering Consultants, part of McDermott Marine Engineering and UMIST had conceptual schemes for seabed rawwater injection. Neither was aware of the other's activities until BP Exploration suggested a collaboration. The partnership worked with Mentor handling the seabed engineering design and project management and UMIST the materials selection, water processing and reservoir effects. The result of this first project was the subsea rawwater injection facility concept.
Economically Attractive
Industry wide discussion and feedback indicated that CAPEX savings of 40% would be needed to make the subsea rawwater injection system economically attractive. The Rawwater Engineering Study, a Joint Industry Project funded by BP Exploration, Shell (UK), Amerada Hess and Texaco (Britain) was completed in May 1996. This project identified available CAPEX savings of approximately 47%.
Rawwater Injection System Design
The subsea rawwater injection system is designed to supply medium filtered, minimally treated, aerobic sea water to the injection well. Water leaving the rawwater system is supplied directly to a conventional water injection tree. The rawwater system comprises three main elements:-
Filtration
This comprises a sand settler unit to remove approx. 98% of hard particulates greater than 22 microns. Neutrally buoyant matter, mostly living organisms, of greater than 150 microns is also removed in the system. |
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Pump
In the subsea configuration insert retrievable booster pump draws water through the sand settler from the area around the installation site and pumps it directly into the tree flowline connection. |
Biocide
A subsea version of an electro-chlorinator can be used to provide chlorine as a biocide agent for the injection water. Conventional chemical injection can still be used.
The subsea concept for a 30,000 bpd system is configured onto a flowbase approximately the size of that used for subsea trees, aprox 3.5m square and typically 5m high depending on the pump used. |
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