Experimental Study on Mechanisms of Wax Removal During Pipeline Pigging

Abstract

Pigging is widely used in pipelines for wax removal. However, pigging operation relies heavily on "rule-of-thumb." Because of its complexity and lack of methods, the wax removal mechanism is still poorly understood. This work aims to reveal the nature of the wax breaking process and thus promote understanding of wax removal physics. A unique experimental setup is designed and constructed to perform a series of wax removal experiments. The test section consisting of a 50-mm-ID, 600-mm-long, horizontal pipe has an accurate temperature control for wax casting and removal process. Different types of polyurethane pigs without oversize against the test section were used for the experiments to eliminate the influence of friction force between the pig and the pipe wall. Mixtures of crude oil and field wax deposit were cast inside the test section to carry out the experiments. In particular, a novel yield stress measurement was introduced into this study to characterize the wax hardness.The effects of wax thickness, mixing ratio of wax deposit to oil, pipe wall temperature, shape and aggressiveness of polyurethane pig on wax breaking force were investigated comprehensively. In particular, the dependences of wax breaking force on the pig aggressiveness and pipe wall temperature are clarified for the first time. In addition, it is found that the relationship between wax failure stress and yield stress can be well fitted as a linear relation. Furthermore, the dependences of wax breaking force on the wax hardness and pig design being used are revealed quantitatively. Subsequently, it is concluded that there is an overwhelming effect between wax failure stress and yield stress, where the wax failure stress exceeds the yield stress of the same wax deposit during the wax removal process. The findings of this paper are beneficial in determining the optimal de-waxing frequency and evaluating the pigging risks.

A non-inertial two-phase model of wax transport in a pipeline during pigging operations

“…The pipe diameter is 3in long and the pig is 1 diameter long. These dimensions are not typical of oil pipelines but can be found in test facilities (Barros Jr et al, 2005;Team, 2011;Wang et al, 2015;Huang et al, 2016). The ratio between the pipe and the bypass section is 156.25, which, for continuity reasons, is also the ratio between the bypass and the pipe axial velocity.…”

Efficiency Evaluation of the Heat Deparafinization of Producing Well Equipped by Sub Pump With Hollow Rods

“…There are thermal, chemical, and mechanical ways among different methods of ARPD removing from well (Huang, 2016;Wang, 2015). The simple-to-apply method is mechanical, but there is a risk of jamming rods and equipment failure when the process of paraffin deposition is quite intensive.…”

Establishment and application of heat flow coupling model

“…The commonly used techniques of paraffin removal include technology using strong magnetic force, microorganisms, chemicals, mechanical methods, and thermal paraffin removal techniques [3][4][5][6]. The paraffin deposition problem can also be solved by heating cable application, which can melt the paraffin by heating a steel pipe with a cable [7].…”