Workover Strategies in CHOPS Wells
Authors: Dusseault Maurice , Hayes Kirby , Kremer Michael , Wallin Chris 
Published: March 2010

Abstract
The most fruitful area for continued OPEX (Operating Expense) reductions in CHOPS (Cold Heavy Oil Production with Sand) operations now appears to be well workovers to solve mechanical and reservoir problems, and to improve production rates. Workovers (exclusive of water-blocking methods) were the subject of a one-day workshop organized by the Lloydminster and District Heavy Oil Section of the Petroleum Society in Lloydminster, March 15, 2000. Approximately 35 attendees participated in a wide-ranging discussion of various workover methods. Participants discussed well problems requiring workovers, and evaluated technologies for re-establishing production under various conditions. Attendees represented companies and agencies such as Petrovera, Husky, ExxonMobil, Anadarko, Nexen, the Alberta Research Council, and the Universities of Waterloo (Ontario) and Alberta (Edmonton).
The full information package that was developed for the workshop may be accessed at the website http://www.lloydminsterheavyoil.com/completionscience.htm. Development and assessment of workover techniques is a "work-in-progress"; these charts and slides are designed only as a guide to technical advances and to workover assessment. We feel strongly that the time has come for a joint industry project on the economic assessment of various workover approaches to optimize workover planning.

Introduction
CHOPS (Cold Heavy Oil Production with Sand) has been successfully implemented in many Canadian heavy oil fields (Figure 1), ranging in viscosity from 300 to 55,000 cP. CHOPS involves massive continuous sand influx, from &lt;0.5﹪/vol to as high as 10﹪/vol during the steady-state phase of oil production. This sand influx, and the necessity to maintain it to sustain economical oil production, generates an unusual set of operational demands and operators are gradually developing better production methods, waste disposal methods, and workover methods. A typical CHOPS well produces 5 - 25 m3/d (30 - 150 bbl/day) of oil, and, for a good well in viscous oil, perhaps as much as 500 - 800 tonnes of sand in a year. Most CHOPS wells now use progressing cavity pumps with surface drives, as these give good oil rates while handing large sand volumes and eliminating rod fall problems. Workovers are required during the life of a well to change r repair equipment, and to maintain or re-initiate sand and fluid influx.
The basic operational goal in the petroleum industry is to produce maximum oil with minimum OPEX over an optimal time to maximize netback. In the period between 1990 - 1998, the heavy oil industry in the Lloydminster area reduced OPEX in CHOPS wells from about $75/m3 to $44/m3 ($12.00/bbl to $7.00/bbl). This was achieved in large part through conversion to progressing cavity pumps, but also because of many micro-engineering advances in handling and disposing of sand, in developing better workover equipment and methods, and in refining details of well design.
FIGURE 1: Canadian heavy oil deposits. Available in Full Paper.
Currently, over 100,000 m3/d (600,000 bbl/d) of heavy oil are produced in Canada using CHOPS technology, comprising over 20﹪ of total Canadian oil production. This production level could easily be doubled in 24 months if the upgrading capacity in North America were expanded accordingly.