Wax formation in oil pipelines: A critical review

Superhydrophobic Coatings for Steel Pipeline Protection in Oil and Gas Industries: A Comprehensive Review

Computational and Rheological Study of Wax Deposition and Gelation in Subsea Pipelines.

One of the major issues in flow assurance includes pipeline plugging due to hydrate formation and deposition. A key uncertainty in gas pipelines is hydrate deposition on the pipe wall. This work demonstrates hydrate formation and deposition on a cold surface in water-saturated gas systems. Methane hydrate deposition can be achieved in a laboratory-scale apparatus by formation of hydrates from the gas phase on the outer surface of a cold surface. The deposit evolves from the initial formation to growth to hardening stages, observed to be initially a porous deposit that later anneals to a relatively nonporous deposit. The hydrate deposit thickness gradually reaches a limit as the hydrate surface approaches the hydrate equilibrium temperature. Performing the measurements at higher initial subcooling in the system results in a thicker hydrate deposit. The average calculated hydrate deposit porosity decreases during the experiment and reaches ∼5% during the annealing stage.

Gas Hydrate Deposition on a Cold Surface in Water-Saturated Gas Systems

Paraffin deposition in subsea pipelines is one of the flow assurance problems for oil and gas production. A reliable paraffin deposition prediction tool is needed to develop mitigation strategies. Most of the studies address single-phase paraffin deposition. However, in practice, multiphase flow is a common occurrence during oil and gas production. Paraffin deposition prediction under multiphase flowing conditions is largely ignored. The current practice is to use single-phase paraffin deposition models in conjunction with multiphase flow hydrodynamic and thermal models. Thermal models used mostly do not consider the flow pattern effects rigorously. The use of a single-phase paraffin deposition model for multiphase flow is not proper and may lead to significant uncertainty in predictions. Thus, there is a need to better understand paraffin deposition under multiphase flow conditions. A limited number of research studies has been conducted. This paper reviews the current state-of-the-art in multiphase para...

Review of Paraffin Deposition Research under Multiphase Flow Conditions

Metabolic engineering aims to improve the production of economically valuable molecules through the genetic manipulation of microbial metabolism. While the discipline is a little over 30 years old, advancements in metabolic engineering have given way to industrial-level molecule production benefitting multiple industries such as chemical, agriculture, food, pharmaceutical, and energy industries. This review describes the design, build, test, and learn steps necessary for leading a successful metabolic engineering campaign. Moreover, we highlight major applications of metabolic engineering, including synthesizing chemicals and fuels, broadening substrate utilization, and improving host robustness with a focus on specific case studies. Finally, we conclude with a discussion on perspectives and future challenges related to metabolic engineering.

Metabolic Engineering: Methodologies and Applications.

Results are presented from two-phase flow wax deposition tests using a state-of-the-art, high-pressure, multiphase flow test facility. Wax deposition was found to be flow pattern specific and dependent on the flow velocities of the two-phase fluids. Wax deposition occurs only along the pipe wall in contact with a waxy crude oil. An increase in mixture velocity results in harder deposits, but with a lower deposit thickness. The wax buildup trend at low mixture velocities is similar to that observed in laminar single-phase flow tests. The wax buildup trend at high mixture velocities is similar to that observed in turbulent single-phase flow tests. Thinner and harder deposits at the bottom than at the top of the pipe were observed in horizontal and near-horizontal intermittent flow tests. For annular flow tests, thicker and harder deposits were observed at low superficial liquid velocity than at high superficial liquid velocity. In stratified flow tests, no wax deposition was observed along the upper portion of the pipe.

Investigation of Paraffin Deposition During Multiphase Flow in Pipelines and Wellbores—Part 2: Modeling

An Investigation of Two-Phase Oil/Water Paraffin Deposition

Pigging is recognized as one of the most used techniques for removing wax deposits in pipelines. In an earlier paper, the mechanics of the wax removal was studied using an experimental setup under dry conditions, i.e., no oil presence. In this study, the pigging experiments are conducted for both regular disc and by-pass disc pigs under flowing conditions. A new test facility was designed and constructed. The test section is 6.1 m (20-ft) long Schedule 40 steel pipe with an inner diameter of 0.0762 m (3-in.). A mixture of a commercial wax and a mineral oil is cast inside the spool pieces for different wax thicknesses and wax oil contents. The wax breaking and plug transportation forces are investigated separately. The results indicated that the wax breaking force increases as wax thickness increases, and the wax plug transportation force gradient is independent of the wax plug length. In comparison to previous test results, presence of oil reduced the wax plug transportation force. Experimental results also showed that the wax transport behavior of the by-pass pig is significantly different than that of the regular pig. The by-pass pig allows the oil to flow through the by-pass holes and mobilizes the removed wax in front of the pig resulting in no discernible wax accumulation in front of the pig. Therefore, no measurable transportation force was observed for the by-pass pig tests.Copyright © 2007 by ASME

An Experimental Study on Wax Removal in Pipes With Oil Flow

Paraffin deposition under single-phase flow conditions was investigated to determine its dependence on shear stripping, deposit aging, flow regime, temperature gradient, and fluid properties. In this study, a new model for the prediction of single-phase wax deposition has been developed. Most of the models previously used assume that equilibrium exists at the deposit-fluid interface. A kinetic resistance of the fluid is considered in the new model. Therefore, the interfacial-wax concentration might be different from the equilibrium-wax concentration. The model also includes continuous diffusion of wax into the deposit. We believe that this enrichment of the deposit is responsible for the increasing hardness of the deposit with time—a process known as “aging.” The effect of shear stripping may also be incorporated in the prediction. The model predictions are compared with predictions from previous models, as well as with experimental data gathered at the Tulsa U. Paraffin Deposition Projects, with two different oils: a black oil and a condensate. Even though some tuning is required for each type of oil, the new model is based on physical phenomena, reducing the empiricism of previous models.

Improvements in Single-Phase Paraffin Deposition Modeling

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