Preformed Particle Gel for Conformance Control: Transport Mechanism Through Porous Media

Abstract

Abstract Preformed particle gel (PG) has been successfully synthesized and applied to control excess water production in some mature water-flooded oilfields in China. Investigations show that PG is strength- and size-controlled, environment-friendly, stable over long periods of time, and very likely capable of overcoming some drawbacks inherent in gel treatments based on in-situ gelling. Its thermostabilization is not sensitive to reservoirs minerals and formation water salinity. To support its future applications, this paper describes experiments that investigate the mechanisms for PG propagation through porous media. Visual observations in etched-glass micro-models demonstrate that PG propagation exhibits six patterns of behavior: direct pass, adsorption and retention, deform and pass, snap-off and pass, shrink and pass, and trap. Which pattern is dominant is related to the diameter ratio of swollen PG and pore throat, PG strength and the driving force. In macroscopic scale, PG propagation through porous media can be described by three patterns: pass, broken and pass, and plug. Which kind of pattern is dominant can be determined by pressure change with time at different tap, particle size of effluent and residual resistance factor at different segment of a core. Measurements from core-flooding and micro-model experiments show that a swollen PG particle can pass through a pore throat whose diameter is smaller than its diameter due to the elasticity and deformability of swollen PG. PG strength is a principle parameter to determine the diameter ratio of a PG particle and a pore throat that PG can pass through a porous medium. A PG particle can move through a porous medium only if a driving pressure gradient is higher than a threshold pressure gradient. The threshold pressure depends on PG strength, the diameter ratio of particle and average pore size. Further work will investigate the potential for PG to improve oil recovery and the optimization method to design PG treatments.