Growing Offshore Water Production Pushes Search for Subsea Solutions

Abstract

There are strong arguments for moving water processing from deepwater platforms to the seafloor in many fields. There need to be, given the daunting challenges to doing so. One of the prime targets is older offshore fields producing more water than oil. When the water treatment facility on the topside reaches its capacity, it puts a cap on oil output. The rising water cut increases the force needed to lift a production stream holding ever less oil, as the pressure in the reservoir declines. Ultimately the natural force isn’t enough to lift the water and oil from deepwater fields, which will mean the end of production if nothing is done. “When you can’t get it to the surface, you are left with nothing, unless you have got a way to pump it,” said Tim Daigle, senior project engineer at Fluor Offshore Solutions. There are two ways to do that: Increase the lift with pumps, or reduce the load by removing the water on the seafloor and disposing of it there. After nearly two decades of development and testing, the latter option is beginning to emerge as an alternative. Oil companies are turning to subsea processing for projects that are challenged by the economics, looking for ways to make them profitable, or to improve their results, said Mike Robinson, a sales and marketing manager at FMC Technologies, which is a leader in this area. Statoil’s Tordis field offshore Norway shows the upside and downside of subsea water separation. The company predicted the combination of subsea water processing and improvements in the pumping system on its Gullfaks C platform would increase ultimate production by 35 million BOE, pushing the field’s recovery rate from 49% to 55%. The design is based on what Statoil learned from its earlier pilot test installed on its Troll C platform in 2001, which is still processing 50,000 bbl a day and reinjecting the water into an aquifer. Rune Ramberg, chief engineer of sub-sea technology at Statoil, said there are many reasons for the Norwegian company’s push to develop subsea water treatment systems. It has long relied on subsea completions. Developing Arctic resources will require alternatives to offshore platforms, which are vulnerable to ice. And most importantly: “We are not making money transporting water,” Ramberg said.