Adaptability of riser topside choking method of controlling pigging slugs in submarine pipelines

When new oil and gas blocks are developed in the pattern of tying back to the built-up processing facilities via newly constructed submarine pipelines, there are many restrictions in using riser topside choking method of controlling the pigging slugs in the newly constructed submarine pipelines. Therefore, it is quite significant to analyze the adaptability of riser topside choking method to the existing facilities. In this paper, the pigging operation in submarine pipelines were dynamically simulated by the OLGA software, the effects of topside choking on pigging parameters were compared, and then the effects of throttle opening and pigging gas flowrate on the surge volume of pigging slug were analyzed. It is indicated that the smaller the throttle opening, the more serious the hold pressure of pipeline system, the higher the pressure difference before and behind the throttle and the pressure at outlet riser bottom, and the smaller the surge volume of pigging slug. The surge volume of pigging slug doesn't reduce linearly with the decreasing of throttle equivalent opening, and it is not until the throttle equivalent opening drops to a certain threshold and below it can better result be realized. The gas plug in submarine pipeline which appears at the startup of throttle can be alleviated by prolonging the opening time of the valve. The surge volume of pigging slug, the pressure difference before and behind the throttle and the pressure at outlet riser bottom decrease with the decreasing of the pigging gas flow rate. Research results provide the technical support for the safe transportation and smooth pigging operation of submarine oil and gas mixed transportation pipelines.