Experimental investigation of two-phase gas-oil stratified flow wax deposition in pipeline

Abstract

Wax deposition in the onshore and offshore pipelines is a common occurrence and typically disturbs the transportation of oil and gas. Accurate prediction of wax deposition in multiphase flow is of great importance to develop economical prevention and remediation strategies. However, reliable experimental data is lacking to understand the deposition process and validate the existing prediction models. In this work, two-phase gas-oil stratified flow wax deposition data at various liquid and gas flow rates have been obtained using Garden Banks condensate and natural gas in a 52.5-mm I.D. multiphase flow loop under the pressure of 2.41 MPa. It is evident that both deposit mass and wax content increase as superficial gas and liquid velocities increase. In addition, the deposit mass per unit area and wax content have a strong correlation with the actual liquid velocity deduced from superficial velocities. The local deposits are observed to be thinner but harder at the sides compared to the bottom of the pipe. The local deposit composition is also analyzed using high temperature gas chromatography (HTGC), revealing that the effect of vSG and vSL on the side deposits is more predominant than the bottom. It can be seen that the fraction of the high carbon number components increases as the superficial velocities increases. However, the increase due to the increase of vSG is more distinct compared to the vSL effect. Moreover, it has been observed that the local wax mass flux increases along the circumferential direction, namely, from the bottom towards the gas-liquid interface. Local deposit analysis in the circumferential direction provided insights to enhance our understanding on the deposition behavior and aid to improve or develop appropriate models.