Corrosion Inhibitor Squeeze Technique - Field Evaluation of Engineered Squeezes

Abstract

Abstract Successful corrosion control in well tubing by the inhibitor squeeze technique depends on the adsorption of inhibitor on reservoir rock and then slow desorption into the produced fluids. Lack of fundamental data has, heretofore, handicapped the treating procedures. Methods are presented for the laboratory measurement of adsorption and desorption characteristics of reservoir core samples. The amount of corrosion inhibitor adsorbed by formation cores and the amount reversibly desorbed varied widely. Laboratory-determined adsorption and desorption characteristics of reservoir core samples were used in the design of field squeeze treatments. Important variables determined were the required quantity of inhibitor, concentration in the carrier fluid, volume of formation to contact, amount of overflush needed, and necessary shut-in time. Engineered field tests are compared and correlated to laboratory core data. Results of repeated squeezes on the same well illustrate the reversible physical adsorption and irreversible chemisorption of sand and clay. Introduction The squeeze technique for placing inhibitors is one method of corrosion control of oilfield tubing that is particularly applicable to wells containing packers or to tubingless completions. In the squeeze technique, first described by Poetker, an inhibitor is dissolved in a suitable carrier fluid and injected into the producing formation rock or sand. The inhibitor adsorbs on the formation rock, and subsequently desorbs into produced fluids which carry it to the well tubing. Long-term success of a squeeze treatment depends on continued, slow desorption of inhibitor from the reservoir rock. The squeeze technique has been used successfully in both oil and gas wells; however, details of the treating procedure of most field squeezes have been decided arbitrarily or established by trial and error. Both research and experience have shown that selected corrosion inhibitors ordinarily do not cause formation damage or affect well productivity significantly. Although comprehensive texts are available in the broad field of adsorption, and several authors have conducted detailed investigations of the adsorption of corrosion inhibitors on metals, little is known about the adsorption-desorption characteristics of inhibitor on reservoir formation rock. Raifsnider et al. described the return of inhibitor from two wells. A recent paper described the adsorption-desorption behavior of inhibitor on sands, clays and limestones and indicated that large differences in the adsorption characteristics of reservoir core samples could be expected."The purpose of the work described in this paper was to gain more precise knowledge of the adsorption-desorption characteristics of inhibitors on reservoir core samples and to demonstrate how this knowledge could be used as a foundation for the engineering design of squeeze treatments. Experiments were performed to answer these questions: How much inhibitor is required for a squeeze treatment? To what concentration should the inhibitor be diluted with a carrier fluid? What volume of formation should be contacted?Laboratory data were then used to design and execute field inhibitor squeeze treatments. The field treatments and subsequent production were controlled and monitored to determine the correlation between laboratory and field results and to investigate additional variables. Results of this work, given in subsequent sections of this paper, show that laboratory data can be used to predict feedback of inhibitor and thus provide a basis for the design of field inhibitor squeeze treatments. Laboratory Investigation of Adsorption-Desorption Characteristics of Inhibitors on Core Samples The considerable differences in inhibitor adsorption on sand and clay (as much as a thousand-fold) found by Kerver and Morgan were a spur to measure adsorption on actual core samples. A fluid flow apparatus was made by coating the cylindrical surface of a core with epoxy resin and fitting it with special flow heads attached with epoxy adhesive. JPT P. 29ˆ