Qiyu Huang

Effect of Water Fraction on Rheological Properties of Waxy Crude Oil Emulsions

This article discusses the effect of water fraction on the rheological properties of waxy crude oil emulsions including gel point, yield stress, viscosity, and thixotropy. The experimental results reveal that the rheological behaviors of the w/o emulsion samples all intensify with the increase of water volume fraction within 60%. Of more significance is that a correlation for w/o emulsions between yield stress and water volume fraction is put forward with an average relative error of 6.75%. In addition, some mainstream viscosity prediction models of w/o emulsions are evaluated, and Elgibaly model is the best-fit for the emulsions in this study.

Effect of operating conditions on wax deposition in a laboratory flow loop characterized with DSC technique

In this paper, an experimental study about the influence of operating conditions in a laboratory flow loop on wax deposition phenomena by using DSC technique is presented. The operating conditions studied were oil temperature, wall temperature, temperature difference (between the bulk and the ambient), and flow velocity. Results were obtained and explained in terms of deposition rate and wax deposit composition (DSC curve shape). So that higher deposition rate was obtained for the following cases: oil temperature increasing, wall temperature decreasing, and at lower flow velocities. On the other hand, a wax deposit with heavier hydrocarbons was obtained when all the operating conditions evaluated were increased. These results will facilitate a better understanding of the physic of the wax deposition. Also, it will help in developing “hardness” model of the wax deposit, and thus provide a solid bearing on the pigging operation in petroleum industry.

Determination of the optimizing operating procedure for DSC test of wax-solvent samples with narrow and sharp wax peak and error analysis of data reliability

Differential scanning calorimetry (DSC), as a convenient and reliable thermal analysis technique, is widely used to analyze wax precipitation characteristics. This paper studies the optimizing operation conditions in DSC test for wax-solvent mixtures characterized by a narrow and sharp wax peak to promote the test reliability. The influences of cooling rate and isothermal time on the wax precipitation characteristics of wax-solvent samples are investigated through DSC experiments. The shape of heat flow curve, wax precipitation temperature and measured wax content are all affected. According to the stability and repeatability of test results, the optimizing procedure is determined for this kind of oil samples. What is more, this paper analyzes the applicability of the optimizing procedure on a crude oil sample with broad and mild wax peak. Experiment errors in the parallel experiments conducted under the determined procedure are checked, and all of them are in acceptable error ranges. This study may provide a meaningful reference for DSC application and a rethink of the test standard in practical operation for particular waxy mixtures.

The wax deposition rate of water-in-crude oil emulsions based on the laboratory flow loop experiment

ABSTRACT This paper aims to develop a mathematical model to predict the wax deposition rate of waxy crude emulsions, combining heat and mass transfer mechanisms. According to the flow loop experimental results, the wax deposition rate increases with the decreasing average temperature of oil/wall in a manner of linear regularity, and shows a downtrend with the increase of water cut due to diffusion resistance. An applicable model is developed regarding emulsion properties, radial temperature gradient, shear stress, and wax diffusion coefficient. In model validation, the prediction results are in good agreement with experimental data with the relative errors within 28.87%. GRAPHICAL ABSTRACT

EXPERIMENTAL INVESTIGATION OF WAX DEPOSITION AT DIFFERENT DEPOSIT LOCATIONS THROUGH A DETACHABLE FLOW LOOP APPARATUS

ABSTRACT Wax deposition has always been a focus in the research field of flow assurance. Operating conditions are among the predominant factors that control the deposition rate and the nature of the formed deposits. However, the disadvantages of the available wax thickness measurement techniques applied to laboratory flow loops Appearance Temperature (WAT) during limit deeper studies on this issue. In this work, the effects of operating conditions, including temperature interval and flow rate, on wax deposition at different deposit locations are experimentally studied using a detachable flow loop apparatus. With the detachable test section, it is achievable to obtain the thickness and the wax content profiles of the deposit as functions of axial location and time. The temperature fields in the test section under both temperature intervals are simulated with CFD software FLUENT to provide more information for the analysis of deposition process. As the results manifest, the low temperature interval tends to intensify deposition, relating to the inner temperature field and wax precipitated property of the oil. The larger flow rate leads to a growth in the deposit thickness under the laminar flow regime such as temperature field, flow rate as weland brings about a distinct rise in the wax content of deposit at inlet. In addition, the increase in deposit thickness and wax content indicates the phenomenon of deposit aging, and the wax deposit layer is thinner but with higher wax content at the inlet, due to the strong flow scour.

Identifying Optimal Pigging Frequency for Oil Pipelines Subject to Non-Uniform Wax Deposition Distribution

Wax deposition in oil pipelines causes reduced throughput and other associated problems. Periodical pigging program can effectively minimize the cost of wax deposition. This paper shows a typical pigging case study for a field pipeline subject to non-uniform wax deposition distribution by using a developed wax deposition model. The model prediction results prove that the wax is distributed in a short, localized accumulation along the first half pipeline. The resultant pressure drop along the pipeline was examined to reveal the effects of non-uniform wax deposition distribution on the pipeline production. In extreme case, the pressure drop of severe localized section increases by 50%, while this value between pump stations is merely 3%. A maximum wax thickness of 2–4 mm is used as a criterion to determine an optimal pigging frequency. The case study pipeline is recommended to be pigged at a frequency of 10 to 15 days, using by-pass pigs.Copyright

Evaluation of Measurement Methods of Waxy Crude Oil Thixotropy

The thixotropy of three waxy crude oils was measured to evaluate different measurement methods using RheolabQC. The results showed that the average relative deviation using the hysteresis loop method was 24.4%, the lowest among the methods evaluated. The method of stepwise-increase in shear rate was able to obtain several rheological characteristics from a single experiment, and such a thixotropic experiment can be performed with any rheometer. This makes the stepwise-increase in shear rate the method of choice when considering convenience. However, the method of hysteresis loop is preferable when it comes to the reliability of measuring thixotropic parameters.

Investigation of wax deposition and effective diffusion coefficient in water-in-oil emulsion system

As pipeline transportation is widely used in the petroleum industry, the problem of wax deposition is a severe threat to the safety of oil and gas transportation. In addition, the mechanism of wax deposition is very complicated due to the presence of water phase. This paper tries to clarify the effects of water fraction, temperature difference and experimental period on the wax deposition process in water-in-oil emulsion system by a series of static cold finger experiments. The experimental results reveal that the average diffusion rates decrease with increased water fraction, longer experimental period and reduced temperature difference. Furthermore, on the basis of wax deposition experiments in cold finger apparatus and radial temperature distribution simulations via Fluent, the influence of water phase on heat transfer occurring in the wax molecular diffusion process is revealed, and relationship between mass transfer and heat transfer is investigated. Additionally, the effective diffusion coefficient of wax molecules is calculated on the basis of experimental and simulation results. The calculated effective diffusion coefficients using this approach are significantly lower than the calculated results from conventional methods. This explains the remarkable disparity with previous works due to underestimating the influence of dispersed water.

Transportation technology with pour point depressant and wax deposition in a crude oil pipeline

ABSTRACT The authors systematically studied transportation technology with pour point depressant and wax deposition in an industrial crude oil pipeline. Experiment results manifest that beneficiated oil acquires obvious modification effect and the reheating temperature of intermediate heat stations should be above 55°C to avoid effect deterioration. Heating schemes are made with lower heating temperature and wider output range. Moreover, an applicable wax deposition model is established to predict wax deposition distribution along the pipeline under various operating conditions. Wax deposition rate varies severely along the pipeline and it is necessary to consider its non-uniformity in production.