Corrosion in Gas Wells and Gas Gathering Systems
Authors: Fincher D.R. 
Published: December 2007

Failures of equipment handling or producing natural gas occur only in the absence of an adequate corrosion-control program. A successful program is shown to includeanticipation of corrosion in design factors of all equipment,detection of corrosion within the system and measurement of its severity for future reference,use of mitigation measures andcontinual follow-up and adjustment of control techniques.

Design factors to be considered are tubing couplings, packers, tubing grade and size, and the number of tubing strings to be set. Future corrosion problems and mitigation work should be recognized at the time the well completion is made so that the best possible design factors can be realized. Corrosion can be detected by gas analysis, water analysis, coupon exposures and caliper surveys. Quantitative data are needed to determine the severity of the problem and to design a suitable program of alleviation of the corrosion. Use of inhibitors and plastic coatings are popular methods for mitigation of corrosion. Both methods have advantages and disadvantages that must be realized and evaluated. Control limits for a mitigation program should be established so that the operator can be certain that he is receiving the desired protection. Gas gathering and process equipment also often suffer from corrosion. Attention to this type of equipment is sometimes slow in coming.

Introduction

Many oil companies have placed emphasis on development of gas reserves in the last decade. Deeper, more expensive wells have become commonplace. Corrosion is more likely to occur in such wells. Damage as a result of corrosion is also more costly, even when neglecting the loss of revenue during periods of nonproduction while repairs are being made. The Natural Gasoline Association of America book, Condensate Well Corrosion, indicated the cost of condensate well corrosion to be $4.27/MMcf of gas in 1951. It was estimated that the cost to gas producers was $12 million/year at that time. Since that time, repair costs have risen and the gas industry has expanded. A general review of the technical advancements as well as the roles of various personnel in corrosion control seems fitting. Corrosion has been formally recognized by operators of gas-producing properties for about 20 years. Many societies and individuals have studied the problem in the light of understanding the phenomenon, as well as mitigating the damage and subsequent expense caused by equipment failures. Although the literature contains sufficient technical information and case histories pertaining to corrosion control, equipment failures are still commonplace. In all probability, this is true due to the absence of a working program of corrosion control in many companies. The education of operating personnel in matters of corrosion control generally has been neglected, although most companies have capable corrosion engineers in their employ. Since corrosion is an operating problem, it is logical that each segment of a company's operating personnel must be aware of its role in controlling economic loss from corrosion. Often, the direct corrosion-control effort is placed in the hands of a relatively inexperienced engineer. He is assigned corrosion work for only a short time, and then he is given a new assignment just as he actually is beginning to become proficient in the work. At this point another inexperienced engineer is assigned to the project, resulting in a lapse in the proficiency of the work. This process is repeated until inattention to the detail of corrosion control in operations results in failures. It is suggested that an adequate corrosion-control program must include efforts at various levels of company operations. All engineers and supervisors must participate actively in the corrosion-control effort. As a property is being developed, corrosion control should be considered when the equipment to be used is being selected. When development is complete, the operating people must determine the seriousness of their corrosion problems. They must realize that the corrosion attack may change with changes in production characteristics and that absence of corrosion today does not guarantee absence of corrosion tomorrow. When corrosion is detected within an operation, mitigation is in order.

JPT

P. 847^