Experimental Study of Paraffin Deposition Under Two-Phase Gas/Oil Slug Flow in Horizontal Pipes

Abstract

Summary Paraffin or wax deposition under two-phase gas/oil slug flow in horizontal pipes is studied experimentally. The experiments are conducted by use of a 2.067-in., large-scale multiphase flow loop under an operating pressure of 350 psig. Testing fluids are Garden Banks condensate and natural gas. Two-phase-flow hydrodynamics and single-phase paraffin-deposition experiments are conducted and used as base cases for a comprehensive data analysis. Deposition experiments are conducted with parametric variation of oil and gas superficial velocities and testing durations of 4, 12, and 24 hours. The bulk fluid and initial pipe-wall temperatures at a removable spool piece are kept below wax-appearance temperature (WAT) and relatively constant to ensure consistent initial dissolved-wax-concentration differences and to avoid thermal restriction in the growth of the deposit. Unprecedented detailed measurement and analysis of the circumferential local samples are conducted by use of a newly designed pigging tool with high-temperature-gas-chromatography (HTGC) and differential-scanning-calorimetry (DSC) deposit-characterization techniques. The results reveal that deposit thickness decreases with the increase in the superficial liquid velocity (vSL) for all two-phase-flow cases. The crossover trends of the thickness vs. time are suggested by the single-phase deposition data to occur at times less than 6 hours. Circumferential analysis shows that, for the slug-flow wax deposit, the deposit at the top wall is thicker (by a factor of approximately 1.9), softer, and contains more oil than the bottom deposit. The final overall deposit wax contents are found to increase with the superficial gas velocity (vSG) for the case of vSL = 1 ft/sec, but nonmonotonic change occurs for the case of vSL = 3 ft/sec. Wax deposits under slug flow have longer chain n-alkane compared with single-phase flow having the same wax-fraction cases. Wax mass at the top wall is greater (by a factor of approximately 1.7) than the bottom mass. This new set of complete experimental data serves as the fundamental understanding of single-phase and two-phase gas/oil slug-flow paraffin deposition.

A Mini Pilot-Scale Flow Loop Experimental Study of Turbulent Flow Wax Deposition by Using a Natural Gas Condensate

“…They showed that the turbulent flow wax deposit surface is visually smooth away from the inlet but there was a no-deposition zone and a patchwork zone near the test section inlet. Furthermore, Rittirong et al , recently confirmed that the single-phase turbulent and two-phase gas-oil slug flow had the visually smooth deposit surface for the region away from the test section inlet. In this case, they used a much longer test section and Garden Banks condensate (same fluid as in this study), instead of South Pelto crude oil …”

“…The condensate density at ∼12 psig (discharge pressure) was measured continuously, using a Coriolis flow meter (Micro Motion F100S), and was found to be ∼835 ± 1.5 kg/m 3 at 77 ± 0.2 °F. The WAT and n-C30+ fraction of oil (oil wax content, the wax fraction that participates in the wax deposition process for the set point used in this study) are 96 °F and 0.4% (w/w), respectively (complete composition data are given in Appendix A). The condensate viscosity was determined based on the pressure drop method and found to be consistent with the data reported in the works of Mirazizi and Rittirong, within the uncertainty of the measurement.…”

“…In fact, Singh et al showed that the pigging operation in the field was conducted before the steady state ( T i = WAT) was reached. We note that the flow loop results where the thermal steady state is reached within 30 min cannot be directly compared to the transient deposition cases, ,,,− ,,− including the field data (where the thermal steady state was not reached and the deposit thickness continued to increase with time). Nevertheless, the heat-transfer approach used by Mehrotra and co-workers ,, serves as the prediction of the maximum possible deposit thickness, by assuming that the thermal steady state is reached.…”

Development of Dimensionless Parameters and Groups of Heat and Mass Transfer to Predict Wax Deposition in Crude Oil Pipelines

“…Accurate prediction of the wax deposition process in a crude oil pipeline can help for timely planning of the pigging operation or hot oil circulation process to minimize production loss and ultimately economic losses. The predictions of the amount of wax deposition in the pipelines from available models 14 − 18 do not match with the field observations. Sometimes, even these predictions fail to match the data generated in the laboratory using flow loops, as shown in Table 1 .…”

“…However, crude oil is a multicomponent system, and a specie diffusion coefficient based on different n -alkanes and their amount should be utilized for better prediction purposes. Thus, there is a need to investigate and understand the wax deposition process in crude oil pipelines (experimental flow loops and field pipelines) along with the verification of available predictive models 14 − 18 for field pipelines. 5 A simple predictive tool, along with upscaling parameters, is required for accurate prediction of the wax deposition process in a crude oil pipeline.…”