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ABSTRACT: Long distance multiphase flow lines are now the predominant trend in the deep water production of oil and gas. Economics still demand the use of carbon steel as the material of construction even though carbon steel is prone to corrosion from the flowing mixture of oil/water/ gas. The prediction of the onset of corrosion with increasing water cut is very important in the design and operation of the flow lines. In addition, the proper selection of corrosion inhibitor is essential. This paper presents the results obtained from a large diameter multiphase flow loop test involving the baseline corrosion and three commercial corrosion inhibitors in environments to simulate the expected conditions in closed to wellhead (flow line). Light condensate oil was used and water cut was 20%. The experiments were undertaken at pressures of 6 bar and temperatures of 58 oC with carbon dioxide as the gas. Electrical resistance (ER) probes for inhibitor screening tests and carbon steel weight-loss coupons for inhibitor validation tests were used for the measurement of corrosion rates. The results showed that the baseline corrosion rates (without inhibitors) at the bottom and top of the pipes were around 0.8 mm/yr and 0.25 mm/yr, respectively in both 0o and 3o inclinations. The tests discriminated between different inhibitors. Only one corrosion inhibitor achieved the target corrosion rate of less than 0.1 mm/yr under 100 ppm concentration. INTRODUCTION One of the frequent and major problems encountered in the oil and gas production is the internal corrosion of carbon steel pipelines. In production systems, the multiphase mixtures (e.g. oil/water/gas) are transported over long distances using carbon steel pipes which have poor resistance to corrosion. Change in inclinations can cause change in the flow regime and other characteristics affecting the pressure drop and corrosion.
ABSTRACT: Dense phase conditions are expected in several gas export pipelines in deep water fields where high pressure and low temperature can give hydrocarbon gas as a dense phase. Problems with dewatering may introduce a free water phase in the pipeline, so corrosion inhibitors must be used to mitigate CO2 corrosion. Since dense hydrocarbon fluids are good solvents, partitioning of corrosion inhibitors to the dense phase could be a potential problem. A corrosion loop where a dense hydrocarbon phase at 180 bar pressure can be used together with a water phase was used to study the partitioning process. The experiments showed that partitioning to the dense hydrocarbon phase may reduce the inhibitor efficiency somewhat, but no dramatic effects were seen compared to the more familiar situation with oil or condensate. INTRODUCTION Dense phase conditions are expected in several gas export pipelines in some of Petrobras’ deep water fields where high pressure and low temperature can give hydrocarbon gas in the supercritical conditions, or as a dense phase. The operational conditions are up to 200 bar total pressure and temperatures from 5 to 40 °C. Water precipitation is anticipated and it is desirable to inhibit corrosion rather than improving dehydration. The gas composition varies. Typical CO2 contents range from 0.2 to 2 mole%. A dense phase loop has been built in the authors'' laboratories in Norway as part of the project. In this loop it is possible to perform corrosion experiments in a water phase which is in contact with a dense hydrocarbon phase at pressures up to 180 bar. It has been speculated that the organic corrosion inhibitors might partition differently between this dense phase and the water phase compared to the more well-known behavior in condensate - water or oil - water systems.
- South America > Brazil (0.68)
- North America > United States > Texas (0.19)
- Energy > Oil & Gas > Upstream (1.00)
- Materials > Chemicals > Commodity Chemicals > Petrochemicals (0.35)
- Reservoir Description and Dynamics > Fluid Characterization > Phase behavior and PVT measurements (1.00)
- Production and Well Operations > Production Chemistry, Metallurgy and Biology > Corrosion inhibition and management (including H2S and CO2) (1.00)
- Facilities Design, Construction and Operation > Pipelines, Flowlines and Risers (1.00)