Developing a Polymer Scale Inhibitor for a Combined Fracture and Inhibitor Squeeze Treatment for High-Temperature Reservoirs

Abstract

A strategy combining fracturing and downhole scale inhibitor squeeze treatments was employed in an extremely tight high-temperature gas reservoir (200°C) with calcite and sulfate scaling problems. Challenges included developing a scale inhibitor that is thermally stable at this high temperature, fully compatible with the fracture fluid used, extremely beneficial with a low minimum effective concentration, with good adsorption/desorption properties for a long squeeze treatment life. Literature survey verifies that few reports are published discussing application of a combined fracture and downhole scale inhibitor squeeze treatment under such high-temperature reservoir conditions. Multiple laboratory tests were performed to qualify the scale inhibitor, including inhibitor dynamic tube blocking, static beaker, and fracture fluid property testing. Standard inhibition tests were adapted to confirm tests were designed to confirm that the scale inhibitor was thermally stable under application conditions (i.e., the scale inhibitor was blended with the fracture fluid (including breaker) at given concentrations and aged together at 200°C for a certain period). The aged scale inhibitor sample was then tested for its performance against scale and results compared to the unaged inhibitor sample. Further tests were designed for fracture fluid rheology and breaking time with the blended scale inhibitor to help ensure the scale inhibitor was fully compatible with the fracturing fluid and would not interfere with its properties. Laboratory test results demonstrated that the scale inhibitor is fully compatible with the fracturing fluid and formation brine. An extremely low minimum effective concentration of the scale inhibitor was determined to be 5 ppm with the aged and unaged scale inhibitor samples. With the addition of the scale inhibitor, the breaking time and rheology property of the fracture gel met all application requirements. The chemistry of the amine-containing polymer inhibitor and advantages of using this chemistry as a downhole squeeze product are discussed. Successful field treatment with the combined scale inhibitor and fracture fluid was conducted. A new scale inhibitor chemistry was developed for a high-temperature reservoir for combined fracture and downhole inhibitor squeeze treatments.