Application and Status of New Building Blocks for Subsea Boosting and Processing Systems
Authors: Skiftesvik Per K. , Svaeren Jon Arve 
Published: October 2008

The clear trend for future oil and gas activities is that the production will come from mature fields, new smaller and marginal fields including tieback fields to existing infrastructure and also larger fields in deep and ultra-deep waters. The industry will be faced with several challenges both technical and economical as these fields may be complex in nature, tieback distances can be significant and so can the water depths. The relative low and often unstable oil prices that the industry has experienced the last years has also had a great impact on how these fields must be developed and operated. More cost-effective solutions must be developed to meet the challenges related to future exploration and production from existing and new fields. All these new requirements have been the basis and background for the development of subsea pressure boosting and processing systems, which include several different technologies to enhance the production from new and mature fields. Most of these different technology building blocks are successfully being used by operators. This paper presents an overview of these new technologies, the main economical benefits and technical status. The system elements as described are mainly Framo technology or technology jointly being developed by Framo Engineering AS and ABB Offshore Systems AS (subsea separation and subsea power distribution).

Introduction

When evaluating applications for pressure boosting and processing subsea which are located in deep and ultra-deep waters, several drive parameters should be addressed, the most important being:Flow assurance in well, flowlines and risersRequirements for artificial lift due to large water depths and possible long tie-backsRelatively low GOR resulting in need for artificial liftShallow reservoirs with low pressuresHigh permeability reservoirs with high productivity index which may have great benefits of pressure boosting to strengthen the economy by increased production and even improved field recoveryPressure balancing of manifolded wellsRequirements for pressure boosting at increased water cut in combination with long distances and great water depthsRequirements to separate water from the well stream as close to the wells as possible to prevent hydrate formation and potentially increase production

Subsea Pressure Boosting - Applications and Benefits

The basic principle of using pressure boosting is shown in figure 1.

The pressure from the well is used to drive the oil to the 1st stage separator. The resistance is made up of a static pressure and a dynamic flow resistance that together make up the system resistance curve. The well production is found from the intersection of the two curves.

If a booster pump is installed, increasing the pressure in the well fluid, the effect is increased production rates as the flowing wellhead pressure is decreased. The flow from the wells will increase until a new balance between the fluid pressure and the system resistance is achieved and the effect is a net increase in oil production with benefits such as:Accelerated production with reduced production timeProvide lift to wells with low natural production (low GOR, high water cut, very deep water)