A proactive approach for predicting and preventing wax deposition in production tubing strings – The Niger Delta experience

A. A. Sulaimon¹*, G. K. Falade¹ and W. DeLandro²

¹Department of Petroleum Engineering, University of Ibadan, Oyo State, Nigeria.

²Shell Petroleum Development Company, Nigeria.

*Corresponding author. E-mail: aa.sulaimon@mail.ui.edu.ng, alisulal1@yahoo.com. Tel: +234 803 667 5249.

Accepted 13 April, 2010

   Abstract

A proactive approach for managing wax deposition problems during production operation is presented. A predictive thermodynamic model is employed to determine the onset condition(s) for wax precipitation in hydrocarbon mixtures. The parameters of a continuous distribution function are used to establish the nature of hydrocarbon mixtures while a fluid temperature distribution model enables the determination of the potential wax precipitating point in the production tubing. A field case study was conducted on 17 reservoirs in a field located in (Niger Delta, Nigeria). Results show that the thermodynamic model predicted Wax Appearance Temperature (WAT) decreases with reservoir depth. The WAT ranged between 21 and 46°C from the deepest (8,000 ft) to the shallowest (5,000 ft) reservoir. Field observation shows that wax formation is effectively prevented when the Wax-Inhibiting-Tool (WIT) is installed 100 - 500 ft below the tubing depth corresponding to the predicted WAT. Proper placement of the WIT has substantially reduced wax precipitation and potential problems that might have occurred due to wax deposition.

Key words: Thermodynamic model; wax appearance temperature; fluid temperature distribution; wax inhibiting tool, gamma distribution parameters.