An improved solution to flow assurance in natural gas pipeline enabled by a novel self-regulated bypass pig prototype: An experimental and numerical study

Abstract

Bypass pigging is an emerging strategy in effectively overcoming inherent issues of high pig speed and overflow of pigging-induced slug volume concomitantly caused by traditional pigging for natural gas pipelines, which is attracting wide attention for flow assurance in oil and gas industry. In view of most bypass pigs with simple bypass structures, the risk of pig stalling or pipeline blockage accidents can be encountered when suffering from increased resistance forces. Accordingly, a novel bypass pig prototype with a self-regulated module is proposed in this study as an improved solution to strengthening pigging safety, efficiency and flow assurance. A self-regulated, easily assembled bypass pig prototype was fabricated for experimental studies in a horizontal transparent gas pipeline system. The pressure mitigation and pig velocity characteristics were fully evaluated under varying bypass fractions. Specifically, when the bypass fraction increases from 0% to 3%, the average pig velocity can be reduced by 64.3–81.5% and pressure fluctuations are more stable. Besides, as an important structural parameter in affecting pig velocity and accuracy of dynamic pigging simulation, the pressure drop coefficient of gas through the bypass pig structure with an internal regulating valve was numerically studied. Compared to the common bypass pig with only a simple bypass port, the addition of the bypass regulating valve will notably increase the pressure drop coefficient. In particular, when the bypass fraction is increased to 7%, pressure drop coefficients for the bypass pig without or with an internal valve are 1.03 and 1.97, respectively, with the deviation of 90.9%. Finally, an optimal design scheme for bypass pigging operations was newly proposed to optimize bypass fractions in accordance with practical scenarios. This study can provide an effective pathway towards the implementation of self-regulated bypass pigging technology in substantially improving flow assurance of natural gas pipeline systems.