One-Step Furfuryl Alcohol Process for Formation Plugging

Abstract

A one-step furfuryl alcohol resin process has been developed for selective plugging in injection and production wells. Of 36 economic small-volume applications, 28 were successful in achieving permanent plugging. The process is especially useful in steam injection wells. The "chemical clock" catalyst system ensures a controllable, predictable gel time over a wide range of formation temperatures. Introduction Furfuryl alcohol (FA) resins are proving to be most useful in oilfield operations. When acidified, these liquids undergo rapid polymerizations to form hard, black, chemically resistant, thermally stable, thermosetting polymers. These polymers are the basis of previously described two-step sand consolidation, and formation plugging processes where either the FA or acid catalyst is placed in the formation first, followed by the other chemical; the chemicals mix, and the polymerization takes place. Generally, two steps with an intermediate spacer have been necessary because the solution rapidly solidifies when the FA and acid mix, whether in the formation, tubing, or pump. This paper describes a one-step FA process that overcomes the usual problems encountered with a two-step process. This process uses an FA system where, before pumping, the FA and catalyst are mixed to form a solution with a predictable minimum gel time (gel time is the time from mixing until the viscosity has built to the point where the fluid is no longer readily pumpable). Once the gel time is exceeded, the polymerization proceeds rapidly to the fully cured FA (furan) polymer. Acidic Catalysts There are three major obstacles to achieving predictable, reproducible FA gel times by adding acidic catalysts directly to the resin:sensitivities to catalyst concentration,reaction temperature, andFA batch history. The first two problems are illustrated in Fig. 1. Gel times for most polymerizing systems generally decrease with increasing catalyst concentration. This effect is quite pronounced in FA systems. To achieve predictable gel times with acidic catalysts requires accurate measurement of chemical volumes and rapid mixing, difficult requirements under field conditions. Also, to have a reasonable working life, the acid concentration must be so low that a "catalyst-starved" FA system can exist. The resulting polymerization may be benign and occur over a prolonged time span (and quite possibly never reach a high degree of cure). It is more desirable that once the polymerization starts it goes rapidly, with a high exotherm, to the final fully cured state.The temperature effect illustrated in Fig. 1 shows that FA polymerizations, as most chemical reactions, go faster with increasing temperatures. A 2-hour gel time for a given catalyst concentration at room temperature may only be 20 minutes at 140 degrees F (60 degrees C).FA batch history is the third problem. Freshly distilled FA is neutral, but with time and oxygen some of the FA will oxidize to complex acids and lower the pH. JPT P. 1834＾