Quantifying Water Control Gelant Injectivity into Matrix: Gel Time vs. Working Time

Summary Gel treatments for water control are popular techniques used in the oilfield industry. One risk of injecting gelant is the premature setting of the gel, which can plug the tubing and require an unplanned workover operation. Gel times are measured in the laboratory by various methods depending on the author and type of gel. The meaning of gel time, as stated by the authors, varies from the point of initial crosslinking to the time available for gel placement and even to the time to achieve a mature gel. With more than 500 hits in a search of the OnePetro database using “gel time” as a search parameter, the lack of a formal definition is concerning. A frequently cited method for gel time measurement is to use a steady shear viscometer and capture the time when the viscosity increases rapidly. Studies have shown that the shear involved in the measurement extends the gel time compared with nuclear magnetic resonance (NMR) measurements on a quiescent sample. A working time method based on injectivity loss through a filter paper can provide a better estimate of available pumping time into a porous media and potentially prevent premature gelation. This method uses a slightly modified version of the common high-pressure, high-temperature fluid loss apparatus and does not suffer from shear effects, which can alter the gel time measurement. Because it uses porous media, it better mimics the actual injection into reservoir rock. Various effects on the working time in laboratory and field operation are discussed. The apparatus and data analysis are fully described in this paper.