Experimental Study of Oil-Water Flow Patterns in a Large Diameter Flow Loop—The Effect on Water Wetting and Corrosion

Carbon steel pipelines are commonly used in transporting hydrocarbon products. In offshore oilfields, the produced crude oil generally contains water flowing concurrently in the flowlines. The presence of water can lead to internal corrosion problems when free water is in contact with the pipe wall surface. Hence, it is pertinent to study how the distribution of water under different oil-water flow conditions could affect the surface wetting on the steel pipe, i.e., whether the wall surface is wetted by water or oil phase. In this experimental work, a large scale 0.1 m (4 in) internal diameter inclinable flow loop was used to study the two phase oil-water flow in horizontal and vertical positions. Paraffinic light model oil (40°API) and 1 wt% NaCl aqueous solutions were utilized as the test fluids. Two measurement techniques, flush mounted conductivity pins and high-speed camera, were used for surface wetting determination and flow patterns visualization, respectively. The wetting data were classified based on four types of wetting behaviors: stable water wet, unstable water wet, unstable oil wet, and stable oil wet. The wetting results from the conductivity pins were found to match with the visualization results from the high-speed camera. The horizontal oil-water flow results showed that water flows separately and wets the pipe bottom at low mixture liquid velocity. In addition, not all of the water was fully entrained in high flow rate, as traces of water could still be found to wet the surface intermittently, causing unstable oil wetting. Based on the iron counts measurement, the corrosion rate was highest when the oil-water flow was laden with high water cut coupled with high flow velocity, corresponding to water wetting behavior.