Mechanically-Robust Nanocellulose Engineered Preformed-Particle-Gel for Conformance Control in Fractured Tight Reservoirs: Transport Through Proppant-Packed Porous Media

Abstract

Abstract Preformed-particle-gel (PPG) holds promising potential for conformance control in fractured tight reservoirs because it enables mitigation of fracture channeling with insignificant leakoff. However, conventional PPG with weak and brittle network is severely vulnerable to shrinkage, breakage, fatigue and even degradation during extruding through narrow fractures that were much smaller than themselves, and finally results in the failure of gel treatment. Therefore, in this work, a new kind of nanocellulose-regulated robust particle-gel (N-PPG) was designed and prepared using high-modulus and green nanocellulose (NCF). The mechanical properties of N-PPG including hardness, springiness, resilience, chewiness and cohesiveness were assessed using a texture analyzer at the grain-scale. The results demonstrated that the presence of NCF (0.1 wt%) noticeably improved the mechanical properties of PPG, 49.5% increment of hardness, 29.3% of resilience, 86.3% of chewiness and 25% of cohesiveness. The swelling test showed that the salinity had slight effect on the swelling kinetics and equilibrium swelling ratio (SR) of N-PPG. N-PPG exhibited excellent tolerance to the acidic solution. After aging for 44 days, SR fluctuated slightly and maintained at 9 cm3/g. The gel skeleton was not collapsed, and the microstructure was similar to the control group (aged in the neutral solution). Upon transporting through the fractures, the porous media was packed using millimetric-sized glass beads to replicate proppant-filled fractures after hydraulic fracturing. N-PPG exhibited significantly higher resistance factor (Fr) and residual resistance factor (Frr), indicative of better performance in conformance control. The influence of particle size, velocity, and PPG elasticity on the transport and placement of PPG in fractures were investigated. Due to the preeminent mechanical properties, N-PPG was hardly broken even after being extruded out from pore-throat geometries with up to a particle-throat diameter ratio (Dg/Dp) of 15, whereas the control PPG was notably crushed, implying the low efficiency in deep applications of conformance control. The Fr of PPG in fractures analogously depended on Dg/Dp even if the superficial velocity (u) was varied from 0.72 m/d to 4.32 m/d. To fully consider the interaction between deformable particle and fluid in the complex pore-throat geometries, an Immersed Boundary-Lattice Boltzmann modeling (IB-LBM) was developed to numerically simulate PPG passing through a throat (50 μm). A spring-network model was used to capture the deformation of PPG. The grain-scale modeling yielded the pressure profile of PPG, from which a clog-deform-pass procession mode was defined.