Corrosion Mitigation- A Critical Facet of Well Completion Design
Authors: Bradburn Joe B. , Kalra Satish K. 
Published: December 2007

Successful completion and production of deep hot corrosive wells can be accomplished by the development of a corrosion mitigation program during the initial stages of the drilling and completion phases. The mitigation programs that have proved safe, reliable, and effective programs that have proved safe, reliable, and effective address three critical areas:tubing selection,corrosion treatment method, andcompletion design.

These three areas when properly studied and evaluated result in a successful corrosion mitigation program and a well with a low work over frequency.

Introduction

Corrosion has been a problem in the petroleum industry for more than 100 years. However, it was not until 1943 that the significance of corrosion was brought to the attention of the industry. Since that time, the literature has become replete with case histories, corrosion surveys, and basic and applied research data dealing with the corrosiveness of both gas and oil wells. This increased interest in corrosion and related problems has focused attention on the necessity of histories, corrosion control an integral pall of a successful completion design. While corrosion control in the past was many times an afterthought to completion. today it is considered during the initial development of drilling and completion programs. In 1951, a major oil company conducted a survey on corrosion in gas-condensate wells. Twenty-six oil companies were contacted and the results showed that 47% of the wells reported were corrosive. Three years later. another industry-wide survey showed that 45% of the gas wells in the U.S. were corrosive. The percentage of corrosive wells is likely to increase further with the development of fields with abnormally high temperatures and pressures. pressures. The cost of corrosion to the petroleum industry has been estimated at more than $800 million annually, with oil companies spending an additional $50 million/yr on chemical inhibitors to control corrosion. The cost of corrosion is also reflected in a recent survey showing that work over costs increased 250% when corrosion was the reason for the remedial work. This paper describes a safe, reliable, and effective design approach for the completion of wells in hostile environments. It addressestubing selection.corrosion treatment methods, andcompletion design.

Examples of the application of this approach are supported by case histories.

Tubing Selection

One of the first decisions in well completion design is the selection of the proper tubing. Normally such areas as tensile, burst, and collapse are considered. But corrosion mitigation considerations require the selection process to take into account tubing ID, metallurgy, and thread-type. The selection of the proper ID is important in highly corrosive wells because of the synergism effect of erosion and corrosion. This synergism can accelerate the overall corrosion rate a hundred-fold by the removal of protective scales, oxides, and/or corrosion inhibitor protective scales, oxides, and/or corrosion inhibitor films. Therefore, calculation of the erosional velocity and the proper sizing of the tubing ID is a critical facet in mitigating the aggressiveness of a corrosive environment. The calculation of the erosional velocity and the minimum ID for a well involves three steps (Table 1). While the procedure is simple, there exists some uncertainty as to the proper value of the constant in Step 2. Currently, the Natl. Assn. of Corrosion Engineers (NACE) and the American Petroleum Inst. (API) are forming committees to study the erosional velocity constant and the effect of solids on its value.

JPT

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