Experimental Study on True Triaxial Pressure Plugging of Igneous Reservoirs with Distributed Optical Fiber Monitoring

In response to the frequent lost-circulation problems encountered during the drilling of igneous rock formations in the periphery of the Junggar Basin, this study employed distributed optical fiber monitoring technology usingoptical frequency domain reflectometry(OFDR) alongside physical simulation tests of true triaxial pressure plugging to systematically evaluate the plugging effects of bridging plugging slurry and rapid filtration-loss plugging slurry with different particle sizes on three types of igneous rocks (tuff, breccia, and basalt). The test results show that tuff fractures (with openings greater than 2 mm) are optimally plugged by material with a particle size of 2 mm. The pressure-bearing capacity of the plugging layer in this case is 71.48% higher than that adopting the plugging material with a particle size of 1 mm. In contrast, breccia and basalt (with crack openings of 1–2 mm) are compatible with a plugging material with a particle size of 1 mm. The achieving pressure-bearing capacities that are 35.2% and 80.03% higher, respectively, than those achieved with 2 mm particles. The rapid filtration-loss plugging slurry demonstrates superior performance in tuff and breccia. Compared to the bridging plugging slurry, the pressure-bearing capacity of the resulting plugging layer increases by 148% and 275%, respectively, while the formed filter cake is uniform and dense. Fiber-optic strain mapping indicates that the reduction in tensile strain field intensity correlates positively with the integrity of the plugging layer. Notably, after plugging, the breccia's pressure-bearing capacity exceeds its rock fracture pressure by 220.5%. The proposed lithology–particle size–plugging slurry matching strategy provides an experimental basis for efficient plugging in igneous rock formations, while distributed optical fiber technology offers a new method for real-time evaluation of the plugging process.