Experimental and Mechanism Investigation on Flowability and Wax Deposition of Waxy Crude Oil with Dissolved Ch4 by Pressurized Laboratory Apparatus

Abstract

In offshore oilfields, crude oils often contain dissolved gas, and are inevitable to transport under pressure. However, the flowability and wax deposition of crude oils with dissolved gas are rarely studied. In this paper, Methane (CH4) was used as a similar substitute for dissolved gas in crude oils, and a series of pressurized laboratory apparatus were developed to study the influencing mechanism of dissolved CH4 on the flowability and wax deposition of Changqing waxy crude oil. It was found that with the increase of the dissolved CH4 pressure, the crude oil flowability was improved, and the wax deposition rate was inhibited. However, the wax appearance temperature (WAT), the average wax content of wax deposit and the mass of wax diffused into wax deposits all increased accordingly. This was mainly attributed to the influence of dissolved CH4, which can effectively increase the intermolecular distance between wax molecules, decrease the intermolecular forces, and weaken the strength of wax crystals to overlap each other. The improvement of rheological properties, on the one hand, promotes the diffusion of wax molecules, which leads to the increase in the mass of wax diffused into wax deposits; on the other hand, it increases the wax content required for the formation of wax deposits according to the dynamic gelation mechanism, thus resulting in the decrease of wax deposition rate. Also, the wax stripping effect caused by the overflow of dissolved CH4 in the wax deposit during depressurization process cannot be ignored. The research results have guiding significance for the optimal design of the gathering and transportation pipeline network and the calculation of wax deposition.

Keywords: Flowability, Wax Deposition, Pressure, mechanism, Laboratory Apparatus