Technical Breakthrough in PCPs' Scaling Issue of ASP Flooding in Daqing Oil Field

Abstract

The ASP flooding Pilot tests in Daqing Oilfield commenced in 1982. And since 2005, APS flooding has entered commercial application in several main oil companies. Although the recovery rate can be improved by 20% over that with water flooding, severe scaling in downhole equipment turned out to be the biggest issue for artificial lift systems in ASP producers. Sucker rod failure rate was extremely high for beam pumping wells. As for PCP system, its running life was relatively the longest one among all lifting methods, but it was still not economic. Severe scaling on the surface of pump and string was the major factor causing drastic oscillation of operating load. Study indicated that surface energy of the material has great effect on scaling degree. Scale was easier to be formed on the materials with higher surface energy than that with lower surface energy. Using higher surface energy coating material was the main reason resulting in the severe scaling on traditional PCP rotors in ASP area. In that case, a novel ceramic coating technique was developed to decrease the coating material's surface energy to a much lower degree, and to prolong PCP wells' running lives effectively. Experiments showed that, elastomer's visco-elastic effect enhanced the periodic oscillation of PCPs' operating load leading to high rod fatigue failure rate. In addition, interference fit design between rotor and stator also has certain influence on PCPs' operation load. Based on the above studies, stator's surface modification technique and optimum interference fit design technique were developed to improve PCP's operation status. As an auxiliary treatment, a special chemical scale remover was developed to decrease the scaling degree of tubing and rod string. These novel techniques have been applied in 58 PCP wells, the average running life increased from several months to more than one year. PCP systems' operating status was improved effectively, and rod fatigue failure rate was decreaseddrastically. Background From 1993, three ASP pilot tests were implemented in Daqing Oilfield: West Central Block, Xing V Block, and West Block. Another two ASP industrial tests were put into production in Bei I Block and Xing II Block. These ASP pilot tests commenced after water flooding. Application indicated that the recovery rate was improved by 20% on average with ASP flooding. Although ASP flooding has made great success in improving the recovery, another negative issue emerged at the same time: severe scaling was formed on the surface of production systems and resulted in producers' abnormal operation. See Figure 1. In beam pumping systems, when scaling particles dropped and accumulated in the space between pump barrel and piston, pump would be blocked in a short period. It was recorded that the minimum running life was less than one month. In ESP systems, the main problem was motor failures resulted from separators blocked by scaling. The shortest running life was half a month. Due to the special structure, PCPs' failure rate was much lower than the above two lifting methods. The averaged running life was around 3 months, but still limited. The main problems were pump abrasion (See Figure 2) and rod fatigue broken. The Mechanism of PCP Scaling Issue Abrasion Wear In the process of ASP flooding, alkali lye reacted with rock mineral and formation water, causing the increment of scaling ions concentration (Ca2+??CO32-??SiO2–3 etc.) in formation. When the production fluid was driven close or into the wells, due to the drastic change of temperature and pressure, the balance of scaling ions was broken, and scaling was formed near the wellbore, on the surface of downhole equipments and inner surface of transferring pipes.

Experimental Investigation of Polymer-Induced Fouling of Heater Tubes in the First-Ever Polymer Flood Pilot on Alaska North Slope

“…The development pace of this vast resource has been slow because of high development costs and low oil recovery using conventional waterflood. Even after three decades of development efforts by multiple operators, the total viscous oil production rate from all ANS fields just reached 56,000 B/D by May 2017 (Cheng et al 2018). Although thermal enhanced oil recovery (EOR) methods have been recognized as the most effective techniques to recover heavy oil, they are impractical on ANS because of the high cost of generating steam in the Arctic and the potential of thawing the permafrost, which would lead to severe environmental impacts.…”

“…Recently, studies have been conducted to investigate the fouling issues in production systems of chemical EOR projects. Cao et al (2007) reported their novel techniques to solve the severe scaling issues associated with the downhole pumps in producers of an alkaline-surfactant-polymer flooding project in Daqing Oilfield, China. Wylde et al (2011Wylde et al ( , 2013 and Zheng et al (2011) reported and summarized the chemicals, especially the polymer-induced issues in oil and water separation and processing systems in chemical EOR projects, and they all recognized that the problems were particularly challenging in heat exchangers, which were commonly used to promote oil and water separation by heating the produced fluids.…”