The University of Tulsa planned to use its state-of-the-art test facilities to gather single- and multi-phase flow data to enhance the capabilities of their paraffin deposition model (TUWAX). The work focused on three projects: 1) conducting single-phase flow tests to more accurately model single-phase deposition, 2) conducting two-phase flow tests to model two-phase deposition, and 3) focused experiments to determine deposition physics and the effects of water.

Program
This project was selected in response to DOE's Oil Exploration and Production solicitation DE-PS26-01NT41048 (focus area: Reservoir Efficiency Processes).

University of Tulsa
Tulsa, OK

The frontier for oil and gas exploration and production is deepwater; however, as oil and gas production moves to deeper and colder water, subsea multiphase production systems become critical for economic feasibility. It will also become increasingly imperative to adequately identify the conditions for paraffin precipitation and predict paraffin deposition rates to optimize the design and operation of these multiphase production systems. Accurate information about the potential for and extent of wax deposition is very critical, not only for the operation and design of these systems, but also for assuring their economic feasibility. Although several oil companies have paraffin deposition predictive capabilities for single-phase oil flow, these predictive capabilities are not suitable for the multi-phase flow conditions encountered in most flowlines and wellbores. DeepStar was formed to identify and develop the required technology. A $4.5 million joint industry partnership to investigate paraffin deposition at the University of Tulsa was formed in May 1995 and is a spin-off from DeepStar.

Project Results
Generating single- and two-phase paraffin deposition data that were used to update and validate the TUWAX program.

Benefits
Improved technology in the area of paraffin deposition modeling will play a significant role in reducing operating costs for oil and gas production. The single-phase and multi-phase deposition models generated in this project are being used by industry as a basis for designing prevention and remediation techniques as well as in the design of facilities to bring in new reserves. Remediation costs are on the order of $1 million at water depths of 400 meters, but the cost is proportionately greater as development depths increase. Being able to predict deposition has helped companies optimize the design of prevention programs, thereby minimizing or eliminating remediation costs for these projects and resulting in cost savings for the operators.

The improvements to the prediction model have provided engineers a degree of confidence when scaling up to larger-diameter pipes, a predictive model that is less dependent on a single oil and a model that can predict paraffin deposition in oil-water systems.

Project Summary
Three major studies were conducted. The key findings from these studies are:

• Deposition Physics Studies. A new facility was constructed to investigate long-term paraffin deposition behavior. Ten single-phase, long-term deposition tests were completed in the three test sections, with diameters of 0.5, 1.0, and 1.5 inches and with testing durations of 3 - 27 days. A 27-day test was conducted to investigate aging phenomena. Three oil-water two-phase tests were conducted in the 1.5-inch test section with water cuts of 25%, 40% and 75%. Two different crude oils were extensively studied under single-phase and two-phase oil-water conditions to assess their deposition tendencies using the cold finger device.
• Single-Phase Studies. A total of 19 single-phase tests were conducted successfully using a condensate fluid in two different flow loops and 12 tests with a heavier oil. Tests with the more-viscous crude oils produced deposits with relatively high oil content.
• Multi-phase Studies. Experimental heat transfer data were acquired on flow pattern transitions for horizontal, upward 1° and upward vertical crude oil-natural gas two-phase flow at high-pressure conditions. A total of 23 multiphase (gas-oil) tests in horizontal and vertical pipes were conducted to generate wax deposition data. Wax deposition was found to be a flow-pattern-dependent phenomenon.

The TUWAX model was enhanced to incorporate Venkatesan's (2004) model and the Singh et al. (2000) model. TUWAX was validated with a well-defined database. A test facility was constructed to study the shear prevention/removal and aging effect during the wax deposition process for turbulent-flow conditions. Follow-on funding was provided via DOE membership in the TUPDP joint industry project from May 2004 to May 2005.

Publications
Matzain, A., Creek, J.L., Apte, M.S., Zhang, H.Q., Volk, M., Redus, C.L., and Brill, J.P., Multiphase Flow Wax Deposition Modeling, ETCE2001-17114, proceedings from the ASME Energy Technology Conference and Exhibition, Houston, TX, February 5-7, 2001.

Hernandez, O.C., Sarica, C., Brill, J.P., Volk M., Delle-Case, E., and Creek, J., Effect of Flow Regime, Temperature Gradient and Shear Stripping in Single-Phase Paraffin Deposition, Presented at 11th International Conference Multiphase 03, San Remo, Italy, June 11-13, 2003.

Manabe, R., Wang, Q., Zhang, H.Q., Sarica, C., and Brill, J.P., A Mechanistic Heat Transfer Model for Vertical Two-Phase Flow, SPE 84226, Presented at the 2003 SPE Annual Technical Conference and Exhibition, Denver, CO, October 5 - 8, 2003.

DOE Final Technical Report, April 2001-March 2004, "Paraffin Deposition and Model Development"" [PDF-1.93KB], June 2004
Manabe, R., Wang, Q., Zhang, H.Q., Sarica, C., and Brill, J.P., A mechanistic heat transfer model for horizontal two-phase flow, Proceedings from the 4th North American Conference on Multiphase Technology, June 3-4, 2004, Banff, Canada.

Hernandez, O.C., Sarica, C., Volk, M., Brill, J.P., Delle-Case, E. and Hensley, H., Improvements in Single-Phase Paraffin Deposition Modeling, SPE 84502, SPE Production & Facilities Journal, November 2004.

$1,200,000 

$1,236,980 (51% of total)

Other Government Organizations Involved: Minerals Management Services

NETL - Sue Mehlhoff (sue.mehlhoff@netl.doe.gov or 918-699-2044)
U. of Tulsa - Cem Sarica (cem-sarica@utulsa.edu or 918-631-5154)