The Study on Non-Heating Transportation of Carbon Dioxide Flooding Pipeline

For most high water-cut pipelines, even if the transportation temperature drops below the gel point of crude oil, the pipeline can still operate safely. Especially when the crude oil has dissolved a certain amount of gas, its flow characteristics are significantly improved, and which can achieve non-heating transportation easily. However, the oil particles will adhere to the pipe wall (which called wall sticking), and become difficult to be swept down with the drop of temperature, which undoubtedly increases the risk of pipe blockage. In order to prevent the occurrence of pipe blockage, it is necessary to find the minimum temperature that allows non-heating transportation. In the study of non-heating transportation, minimum transportation temperature (MTT) and wall sticking congealed oil amount (WSOA) are the most important research objectives. When the temperature is between the gel point of crude oil and MTT, the crude oil gel only forms a thin oil layer on the pipe wall, which does not affect the safe operation of the pipeline. Once the temperature drops below MTT, a large amount of congealed oil will stick to the pipe wall, reducing the inner diameter of the pipe and increasing the risk of plugging. This paper has studied the effect of carbon dioxide on non-heating transportation and found that the presence of carbon dioxide can make WSOA significantly reduced and the congealed oil becomes softer, but MTT does not change. According to the measurement of the rheological characteristics of crude oil before and after dissolving carbon dioxide, it is believed that the above experimental results may be due to the decrease in viscosity and wax appearance temperature of crude oil after dissolving gas, which hinders the precipitation and aggregation of wax crystals and inhibits the formation of crude oil gel. In addition, it is speculated that the surface of the dissolved gas crude oil is covered with a large number of bubbles. These bubbles will reduce the contact area of the crude oil and the wall surface, resulting in a decrease of WSOA. In a word, the research methods mentioned in this paper are suitable for the study of non-heating transportation of carbon dioxide flooding pipeline.