Future high-speed electrical motor technology will utilise wellstream hydrocarbon gas as cooling medium. Such integrated motor-compressors are currently under qualification for use on the sea floor in the North Sea. A vital part of the insulation system is the resin used to impregnate the motor windings and the resins ability to withstand chemical aging caused by the components inside the wellstream gas. The purpose of the resin in such a machine is to give mechanical support to the winding and to fill all gaps and voids inside the mainwall insulation, which consists of a mica paper tape. Various types of epoxy resins were exposed to an environment consisting of hydrocarbon gas, condensate and a mixture of water and monoethylene glycol (MEG). The specimens were built by casting the resin into a mould and curing it in an oven according to the procedure recommended by the resin manufacturers. According to the tests, the epoxy novolac and bisphenol A epoxy resin with BCl 3 accelerator were able to withstand their tensile strength and e-modulus during the exposure far better than the bisphenol F epoxy resin. The influence of an accelerator in an epoxy anhydride resin system was detected. Resins accelerated with zinc naphthenate provided the highest modulus before the tests, but were not able to retain it during the exposure. Resins accelerated with BCl 3 seemed to tolerate the environment better. The tensile strength of the resin was also dependent upon the amount of BCl 3 accelerator used.

Wet gas compression technology renders possible new opportunities for future gas/condensate fields by means of sub sea boosting and increased recovery for fields in tail-end production. In the paper arguments for the wet gas compression concept are given. At present no commercial wet gas compressor for the petroleum sector is available. StatoilHydro projects are currently investigating the wet gas compressors suitability to be used and integrated in gas field production. The centrifugal compressor is known as a robust concept and the use is dominant in the oil and gas industry. It has therefore been of specific interest to evaluate its capability of handling wet hydrocarbon fluids. Statoil initiated a wet gas test of a 2.8 MW single-stage compressor in 2003. A full load and pressure test was performed using a mixture of hydrocarbon gas and condensate or water. Results from these tests are presented. A reduction in compressor performance is evident as fluid liquid content is increased. The introduction of wet gas and the use of sub sea solutions make more stringent demands for the compressor corrosion and erosion tolerance. The mechanical stress of the impeller increases when handling wet gas fluids due to an increased mass flow rate. Testing of different impeller materials and coatings has been an important part of the Statoil wet gas compressor development program. Testing of full scale (6–8 MW) sub sea integrated motor-compressors (dry gas centrifugal machines) will begin in 2008. Program sponsor is the A˚sgard Licence in the North Sea and the testing takes place at K-lab, Norway. Shallow water testing of a full scale sub sea compressor station (12.5 MW) will begin in 2010 (2 years testing planned). Program sponsor is the Ormen Lange Licence.

Oil and gas production in the Norwegian Sea has been ongoing for decades. The Åsgard B platform produces gas and condensate from the Mikkel and Midgard reservoirs from subsea wellheads with 50 to 80 km long pipeline tie-backs. Because the production started to decline, several innovative technologies were investigated to extend the production and increase the total recovery from the field. Artificial lift, by applying compressors installed on the seabed close to the wellheads, was the most favorable solution. An all-electric hermetically sealed integrated motor-compressor was selected to fulfil this duty and an extensive technology qualification program over 10 years was initiated. Machine qualification activities included both component and full scale testing levels with the aim to arrive at a low risk subsea compressor solution with utmost robustness and reliability. The component testing level placed major focus on screening available materials to withstand exposure to the raw wellstream fluid from the Åsgard field. Full scale motor compressor testing was performed in a dedicated test facility with hydrocarbon fluids to investigate overall machine performance and enhancement via the introduction of new machine components from the material screening testing. Valuable operational experience from the qualification efforts were collected and used to establish the design and material selection boundary conditions for the final dedicated subsea compression solution. A particular negative operational experience was fouling induced machine thermodynamic and rotordynamic performance degradation and the need to introduce integrated online washing and machine wet gas compression compatibility to reduce operational risks. To preserve machine robustness and mitigate potential corrosion and erosion problems, a machine concept with unconventional low operating speed and enhanced materials was selected. The world’s first subsea compressor with the above concept attributes was successfully manufactured, tested, installed, and operated subsea at a depth of 260 meters. The qualified machine has been designed and tested for presence of free liquids such as water, hydrocarbon condensate, and glycol in the gas stream and demonstrated full capability to operate within the complete compressor performance map with liquid content exceeding levels found in normal gas-condensate fields. An available high performance wellstream compressor can reduce the complexity and cost of future subsea compression systems.

This paper evaluates the performance analysis of wet gas compression. It reports the performance of a single stage gas centrifugal compressor tested on wet gas. These tests were performed at design operating range with real hydrocarbon mixtures. The gas volume fraction was varied from 0.97 to 1.00, with alternation in suction pressure. The range is representative for many of the gas/condensate fields encountered in the North Sea. The machine flow rate was varied to cover the entire operating range. The compressor was also tested on a hydrocarbon gas and water mixture to evaluate the impact of liquid properties on performance. No performance and test standards currently exist for wet gas compressors. To ensure nominated flow under varying fluid flow conditions, a complete understanding of compressor performance is essential. This paper gives an evaluation of real hydrocarbon multiphase flow and performance parameters as well as a wet gas performance analysis. The results clearly demonstrate that liquid properties influence compressor performance to a high degree. A shift in compressor characteristics is observed under different liquid level conditions. The results in this paper confirm the need for improved fundamental understanding of liquid impact on wet gas compression. The evaluation demonstrates that dry gas performance parameters are not applicable for wet gas performance analysis. Wet gas performance parameters verified against results from the tested compressor is presented.

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