Experimental study on an oil-based polymer gel for lost circulation control in high-temperature fractured formation

Aiming at the lack of plugging agent for oil-based drilling fluid leakage in fractured formation, an oil-based gel-plugging agent with high structural strength and strong thermal stability was synthesized based on monomer polymerization and crosslinking. According to the preparation experiment, when the total concentration of methyl methacrylate (MMA) and butyl acrylate (BA) is 30% and the ratio is 6:4, the oil-based gel solution can be completely gelatinized from 80 to 200 degrees C, which has high gel strength and controllable gelation time. The effects of total concentration of BA and MMA, the ratio of BA and MMA, synthesis temperature, oil-based drilling fluid invasion, shear effect, and fiber concentration on gelling performance were systematically studied. Fourier transform infrared molecular structure analysis showed that the oil-based gel contained benzene ring group and ester characteristic group. From the rheological properties of oil-based gel with 30% gelling agent at 160 degrees C, it could be seen that the elastic modulus G ' of 10 Hz is 232 kPa, which is much larger than the storage modulus G '' is 99 kPa, which reflects the solid properties and has good elasticity and high strength. The displacement experiment of sand filling pipe and dynamic and static plugging experiment of high temperature and high pressure shows that the oil-based gel has high bearing capacity in fractures and sand filling pipe. The bearing pressure is 3.01 MPa in 6 mm fractures, and the bearing pressure gradient is 0.602 MPa/cm.