Corrosion Inhibition/Foamer Combination Treatment to Enhance Gas Production

Abstract

Abstract Liquid holdup may decrease the productivity of gas producing wells. The use of foaming agents is a popular method of reducing fluid levels and increasing well production. However, corrosion rates may still be excessive in these cases requiring a mitigation strategy. The use of chemicals that act as foaming agents and corrosion inhibitors have great utility in gas wells with excessive water holdup. The underlying physical principles and measurable parameters include dynamic interfacial tension, foaming ability, and corrosion inhibition. A mechanistic description to predict the performance of chemical foamers is developed based upon measurable parameters demonstrating that the dominant factor is foam density. In addition, the effectiveness of a chemical program to unload a well and inhibit corrosion is demonstrated. Introduction With the recent interest in optimizing gas production, the operation of marginal and older gas wells has become more important. Two major factors contributing to the continued viability of a well are the mitigation of corrosion and continued production as the reservoir is depleted and bottom hole pressure declines. The two factors are closely related; as production decreases due to lower pressures, a gas well may load with water and produce in intermittent slug flow1–2. The result is a dramatic decrease in well productivity. A significant increase in the corrosion rate may also be observed. Numerous methods have been used to address the build-up of liquid within a producing gas well including maintaining a sufficient natural flow through the use of controllers or assisting lift with mechanical or chemical means3. Frequently, a combination of methods is used to prevent liquid loading. This paper will focus on the use of a foamer additive which chemically assists the lift and inhibits corrosion. The chemical class that will be examined are surfactants that reduce surface tension and fluid density within the wellbore. A brief review of well loading literature and models used to predict gas well performance will be given. In addition, the theory of surfactants and foam formation as the underlying physical mechanism of well unloading will be discussed with an emphasis on the dynamic nature of the surface tension. While many papers1–5 address unloading gas wells, the properties of surfactants are mentioned only briefly. Recently, more attention has been given to the role of the chemistry in the prediction of unloading a gas well though the studies remain qualitative6–7. Some models have been developed to predict the removal of foams used in well completions and in enhanced oil recovery using a foamed gas lift8–9. Laboratory data on the physical properties of the surfactant and corrosion performance of the chemical additive will be presented. Finally, case studies demonstrating the efficacy of a chemical additive in enhancing production and mitigating corrosion will be presented. Theory The theory underlying the performance of surfactants that form a foam (foamers) is split into the description of foam formation and stability and the fluid mechanics models describing the production of a gas well. The following sections will attempt to emphasize and collect the critical parameters for using a chemical to foam and inhibit corrosion in a gas producing well.