Multiphase meets gas compression

Flowtronex and Weatherford are combining efforts to bring multiphase pumping and gas compression together to enhanced field production at a lower cost.

Aug 1st, 1999

Flowtronex and Weatherford are combining efforts to bring multiphase pumping and gas compression together to enhanced field production at a lower cost. Multiphase pumping systems are a key component to transporting crude, water, and gas through a single pipeline.

The Dual Booster Systemtrademark is a patent pending system that uses a conventional reciprocating or rotary gas compressor in parallel with a multiphase pump to boost multiphase flow of wells. Weatherford Global, the compression services division of Weatherford, is in the process of acquiring this technology from Flowtronex, which packages multiphase pumping systems. Weatherford Global has the field service team to provide product support and maintenance services for this new system once it is installed in the field.

While multiphase pumps are a good way to boost the pressure in a multiphase flow stream, they become less efficient as the inlet pressures drop. At lower inlet pressure, the gas fraction volume in the flow expands. This increases the amount of compression the must be achieved in order to increase the pressure of the flow mixture. It is more efficient to achieve this compression with a gas compressor, rather than using a large multiphase pump or multiple pumps.

In the Dual Booster system, the gas compressor takes most of the gas in the stream and compresses it, working more efficiently than the multiphase pump. The remaining flow, consisting of liquid slugs and some residual gas, is divided out by catchers installed upstream of the compressor and then directed into a small multiphase pump. This pump has the capacity to handle this flow mixture easily, continually pumping down the catcher volumes to the lowest level. The multiphase pump is connected to the compressor's scrubber system, so it is constantly draining and clearing condensates and collected liquids from the compressor.

Using the compressor in combination with the multiphase pump requires less horsepower in most cases than a multiphase pump alone, Weatherford said. The addition of gas compression to the multiphase system means fewer pumps would be required to do the same job, and there would be less reliance on the natural reservoir pressure to transport

the multiphase production. According to Weatherford, the system is more efficient in situations where the gas volume fractions are relatively high (>80-85%).

Running a multiphase pump in parallel with gas compression can reduce facilities costs up to 50% over conventional pumping methods, claims Robert Stiles, President and CEO of Weatherford Global. He said the system should also improve production volumes up to 15% at the same time. A system was installed for a subsidiary of Ocean Energy in an East Texas gas gathering facility.

Ziff/Halliburton floats deepwater survey

Ziff Energy group and Halliburton Energy Services have announced plans to conduct a new deepwater study evaluating subsea operations, "from design perspective to operational performance." The goal is to analyze deepwater subsea operations in terms of technology.

The survey will attempt to define the link between new technology and results in deep water strategies, according to Gordon Chapman, Vice-President with responsibility for Halliburton Subsea Systems. This deep water development analysis will be conducted by Ziff with Halliburton serving as technical/operations advisor for the best practices section of the study.

The survey will cover companies operating in the deepwaters of the Gulf of Mexico and is the second survey of its kind to be conducted by Ziff. The scope of study for this project was defined in June. Deepwater assets will be grouped into three types of development systems fixed/compliant, floating production systems, and subsea. Costs will be analyzed in 29 categories. A meeting in July will determine the parameters of the subsea best practices assessment. Delivery of the study is scheduled for the fourth quarter of this year.

ABB puts Subsis to the test

ABB Offshore Systems recently announced it had completed the shallow water tests of its subsea separation station called Subsis. The tests were concluded in June off Norway. Integration tests are scheduled for July. The $25 million, 350-ton unit, was designed by ABB Offshore Systems and fabricated at Nymo's yard near Arendal. It will be installed in 350 meters of water on Norsk Hydro's Troll C development by the Maxita this September. Subsis is controlled by a subsea umbilical from the platform and is capable of handling 63,000 b/d of liquids and 800,000 MMcm/d of gas. Inititially, the water injection pump and the system, which will return separated water to the reservoir via a yet-to-be-drilled well, will not be fitted into the unit. Plans are to install the injection system in the first quarter of next year. ABB now is planning a next-generation subsea process plant with the aim of producing directly to shore. Such a system could reduce field development time by 50% and operating costs by 30-60%.

Vertical slipform for a concrete riser?

Floating formwork technology has been around for years. The Norwegians use it to build their beautiful and breath-takingly heavy gravity base platforms, but at least one individual believes the technology, properly refined, could be used to install a concrete riser system for ultra deepwater. Prompted by recent interest in riser solutions for 15,000 ft and beyond, Industrial Engineer Martin Iorns said he developed a process that could overcome the limitations of conventional riser technology for a fraction of the price of steel.

Iorns developed a method to downward slipform a large diameter concrete seawater pipe to a depth of 4,000 ft from a floating platform. The goal was to take advantage of the technology known as ocean thermal energy conversion to tap into a cheap source of energy. With a subsequent drop in oil prices, this project was tabled, but the techniques developed are patented and could be used to build a riser, Iorns said. He describes a monolithic pipe of any diameter, with a wall thickness of as little as 3 mm or as thick as needed to overcome the huge pressures imposed by deepwater.

Other possibilities include double walls for added rigidity, hollow compartments to store compressed air (for buoyancy). By releasing or adding air to the chambers a telescoping portion of the riser could be raised or lowered for hook up or disconnect. Iorns said there would even be a method for repairing or patching the riser in place. He said the floating vertical slipform system can be free floating or installed in a large moonpool. For more information, contact Iorns atmiorns@att.net.

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