The production of water goes hand-in-hand with the production of oil. Indeed, Royal Dutch/Shell produces 6 million b/d of oil and 6 million b/d of water.
The ratio is even greater for many companies, and in the North Sea several wells are nearing the end of their productive lives, producing only minuscule traces of oil in the water flowing from their reservoirs. They will be abandoned, leaving behind large volumes of hydrocarbons. In some cases, this will be because of cost, while in others, it will be environmental legislation that can bring production to an end.
'Water to Value'
It is an issue that is concentrating the minds of the 19 companies that make up the Petroleum Environment Research Forum and in particular its chair, Zara Khatib, a chemical engineer who heads Shell's Water to Value (W2V) project team in The Hague.
Her team of 20 is made up of professionals in reservoir and petroleum engineering, production chemistry, production technology, process engineering, and water treatment. They are responsible for water management schemes, and she has set for them three clear objectives. The first is to mobilize advanced technology to cut unwanted water production by half; the second, to improve oil production from existing reservoirs by 10%; and third, to cut produced water treatment costs by 25%.
The team uses existing technologies and new technologies being developed, not just by Shell but by other companies. Khatib explained this philosophy: "We have taken a lot of technologies-even technologies developed by competitors-and implemented them. We use whatever technologies are available. The important thing for us isn't who developed the technology but what ultimate benefits we can derive from it in terms of reduced water and higher output."
Minimizing water a priority
Their priority is to minimize water production at the source and before it enters the wellbore.
Mechanical and chemical methods are used, and one cost-effective approach is to employ intelligent-well techniques that enable downhole separation and the reinjection of the water in specific zones, where the need for reservoir pressurization is greatest.
Another developing technology allows for reversible shut-off of watered-out zones, so much of the team budget is being spent on improving shut-off techniques for fractured and matrix-type reservoirs.
Handling water
However, water is increasingly produced even when these techniques are used, and it has to be handled. Mature techniques such as reinjection are being joined by new reservoir modeling technologies and new software and reservoir simulators. This can optimize the spacing of wells and choice of injection systems, cutting equipment costs and ensuring safe fracture containment within the injected zone.
Ironically, fields in the deserts of Oman are among the biggest producers of water. A pilot plant is using salt-tolerant reed beds to biologically treat this water, and other developments are taking place using solar-powered distillation.
Khatib said: "Our aim is to minimize the production of water. Where that is impossible, we work to mitigate the impact on the environment. Ultimately, we develop technologies that enable us to convert produced water into revenue. We should regard it as a product-after all, it represents a potential annual business value of over $1 billion."
