Monitoring and Controlling Paraffin Deposition by a Direct Assessment Technique

Abstract

This paper presents the results of the evaluation of paraffin control treatments applied in rod pumped wells in La Concepcion oilfield, located at the western of Venezuela and operated by Petrowayuu, which is a mature field with paraffin deposition problems. Before the study, the only treatment applied on the wells to control paraffin deposition was hot watering. Because the average production rate of the wells was 30 BFPD, the application of high volume treatments, as hot watering, implied production deferral due to their low productivity index (around 0.09 BFPD/psi). Paraffin dispersant cold batch was used as an alternative treatment. To assess the effectiveness of the paraffin control treatments and their optimal application frequencies, it was necessary to use scale coupons observation, flowline pressure monitoring, and dynamometer cards analysis. It was found that paraffin dispersant cold batch treatment resulted to be the most cost-effective way to control the problem in all of the wells evaluated and the optimal batch treatment frequency was determined for each well. Moreover, most of the wells had been treated in a very low frequency. Besides this, it was demonstrated that circulation of high volume of hot water generated production deferral. This enabled Petrowayuu to increase its earnings in approximately 500,000 U.S. $/yr, compared with hot watering costs, mainly because of production deferral reduction. Introduction Over the years, paraffin deposition has been a constant problem in the rod pumped wells of La Concepcion field. This deposition has been observed during pulling jobs (Fig. 1) in which approximately 1.000 ft of tubing are plenty of solid paraffin. An analysis of the subsurface rod pump failure statistics, which included data from 2003 to 2005, revealed that paraffin deposition resulted to be the main cause of the failures (Fig. 2). To control the problem, Petrowayuu had tried several methods such as, steam injection, magnetic devices, bacteria injection, hot oiling, and lately hot watering. All of the methods applied had resulted to be unefficient or non cost-effective. As a result of this and based on the experience that A. Haudet had in Medanito, it was developed a methodology to determine the optimal paraffin control method and frequency for each well. This methodology combined the use of scale coupons observation, flowline pressure monitoring, and dynamometer cards analysis. Once the most cost-effective treatment was applied, production deferral due to hot water jobs was reduced to a minimum. Methods of Paraffin Control There are many literatures reporting methods of paraffin control[1,2], they can be divided into four categories: Mechanical, thermal, chemical, and combinations of those. Mechanical methods basically include scrapers. On the other hand, thermal methods include steam injection, bottomhole heaters, and circulation of hot oil or hot water. In hot watering, heated water is pumped down the tubing or casing when there is no packer. Chemical methods include solvents, wax crystal modifiers, and paraffin dispersants. Paraffin dispersants are surface-active agents that dissolve the paraffin deposited on the tubing wall. In cold batches, water provides the dispersing medium for the paraffin compounds while is carried out of the well. In some cases, one method is not enough to control the problem itself, so it is necessary to combine them. Methods of Paraffin Deposition Assessment The methods of paraffin deposition assessment used in this study were dynamometer cards analysis, scale coupons observation, and flowline pressure monitoring. Analysis of dynamometer card is the main diagnostic tool for rod pumped wells. Paraffin can cause an increase of the load on the polished rod, so a treatment that removes this deposition will cause a decrease on load. Scale coupons are metal pieces with small holes that promote scale deposition; they are commonly used in water systems, and are inserted in the flow stream to simulate what happens in the inner walls of the lines. By observing an exposed coupon, valuable information can be provided regarding the effectiveness of an applied treatment (Fig. 3).

Experimental Results of a High-Power Laser for Underwater Paraffin Removal

“…These problems make underwater operations difficult, often requiring their elimination using expensive and time-consuming methods that can damage equipment [2]. While there are solutions to reduce [3][4] [5] paraffin deposits, it is impossible to completely prevent them [6].…”

“…Over time, the deposition of paraffin causes a decrease in production capacity and ability. These deposits vary in thickness and composition, from soft to hard [3][5] [11].…”