Research and Application of Thermally Activated Gel for Control of Lost Circulations

Summary Thermally activated gel (TAG) for control of lost circulations was evaluated, which is based on acrylamide (AM) and N-vinylpyrrolidone (NVP) copolymers crosslinked by polyethyleneimine (PEI). Viscoelasticity, pumpable time, breakthrough pressures, thermal tolerance, and fluid compatibility were tested in this paper, and then field applications in Missan Oilfield, Iraq, were introduced. Laboratory results showed that the strain limit in the linear viscoelastic region was 169% and storage modulus was 870 Pa. Pumpable time of TAG varies with pH values, so pumpable time can be controlled above 60 minutes by adjusting pH values in the temperature ranges of 100°C to 140°C. Breakthrough pressures were tested in 5-mm (inner diameter) and 10-mm (inner diameter) simulating pipes.The breakthrough pressure gradients were 1.172 psi/cm and 1.200 psi/cm at 0.5 mL/min and 1.0 mL/min, respectively, for 10-mm simulating pipes, 1.872 psi/cm and 2.200 psi/cm for 5-mm simulating pipes. TAG maintained morphologies completely and dehydrated slightly after 30 days of aging at 140°C, transformed into a degraded and low-viscosity fluid after 45 days of aging. Tests proved that invasions of inorganic electrolytes, drilling fluid additives, and drilling fluids can lengthen the pumpable time of TAG, so flash settings due to invasions could not occur. Applications in Missan Oilfield verified the performances of TAG mentioned above.