Exploration and Production Technologies

Cooperative Agreement on Energy Technologies: Evaluation of Wax Deposition and its Control during Production of Alaska North Slope Oils

DE-FC26-01NT41248 (Task 3.05.1)

Goals
The project goals are to:

  • Conduct laboratory tests to characterize wax properties of Alaska North Slope oils.
  • Determine the effect of flow rate and well completion on wax deposition.
  • Develop a computer predictive model to predict wax deposition and how crystal modifiers affect it.
  • Evaluate methods to prevent wax deposition.

Performer
University of Alaska, Fairbanks, AK

Results 
The project researchers have:

  • Completed molecular weight measurement, density measurement as a function of temperature, wax appearance temperature (WAT) determination by viscometry, and cross polar microscopy of all oil samples.
  • Developed a computer program to predict bubble point to determine the two-phase envelope.
  • Completed a sample transfer of live oil and determined the gas-oil ratio as part of the process.
  • Completed composition analysis of 10 samples.
  • Developed an analytical solution for the wellbore heat transfer problem.

Benefits 
The production rate of an oil well decreases significantly if wax precipitation in a wellbore acts to reduce the cross-sectional area available to flow. Being able to predict the wax deposition properties of oil allows an operator to know when the conditions in the wellbore need to be modified to maintain the oil production rate.

Wax deposition in pipelines during transportation of oil causes increasingly severe pressure drops along the length of the pipeline, requiring increased energy consumption to move the oil. By utilizing the solutions obtained from this study, the wax deposition in pipelines can be avoided and power consumption can be drastically reduced.

Background 
Alaska’s North Slope is a unique petroleum province in the United States in that it is underlain by thick permafrost, which is a tremendous heat sink for produced fluids. Because of the severe conditions and remote location, Alaska’s North Slope is also a very high-cost petroleum province, effectively raising the economic limit well above that for other onshore fields. Solving the wax deposition problem in producing wells could significantly reduce the economic limit and spur development of smaller accumulations of oil resources on Alaska’s North Slope.

Summary 
The primary goal of the project is to come up with a solution for preventing wax deposition and the first step toward that end is to characterize the wax-forming properties of the oil being produced. The evaluation of possible solutions is supported by the development of a simulator that considers thermodynamics and kinetics of wax deposition, along with related heat transfer in the wellbore. In order to characterize wax properties, it is necessary to measure molecular weight, density, and viscosity, along with pressure-volume-temperature and composition analysis. A thermodynamic model will be developed that can predict wax deposition and the effect of various parameters on it. A dynamic model will be developed that will utilize this thermodynamic model and predict wax deposition in the wellbore and the effect of wellbore heat transfer on depsition. This simulator will then be used to evaluate various methods of wax prevention.

Current Status (April 2007) 
The project is in its second year, which began October 1, 2005. The project is scheduled to be completed by September 30, 2008.

Funding 
This project was selected in response to DOE’s Oil Exploration and Production solicitation DE-FC26-01NT41248.

Project Start: October 1, 2006 
Project End: September 30, 2008

Anticipated DOE Contribution: $ not available
Performer Contribution: $ not available

Contact Information
NETL - James Hemsath (james.hemsath@netl.doe.gov or 907-474-2559)
U. of Alaska Fairbanks - Tao Zhu (fftz@uaf.edu or 907-474-5141)

Publications 
No publications have been released. An abstract has been submitted to the 2007 Society of Petroleum Engineers’ international petroleum technology conference focusing on the determination and prediction of wax deposition.

Wax deposition in tubing at 90º F. for an ANS field.

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