Engineering water-shut-off operations: Application of rheological time-temperature superposition approach for organically-crosslinked polymer gel systems

Abstract

Polymer-based gels have been extensively utilized in reservoirs to prevent excessive water production and improve oil recovery. In this study, a sulfonated-hydrolyzed polyacrylamide polymer (HPAM-S) and low-toxic organic crosslinkers (hydroquinone and hexamethylenetetramine) were mixed in brine at specified concentrations to formulate the polymer-crosslinker fluid system. The quantitative rheological analysis, along with the TTS (Time-Temperature Superposition) approach, was examined for the first time to achieve the water shut-off operations in high-temperature reservoirs (90 °C–150 °C). The TTS approach was defined as modelling of the viscosity vs. time data obtained at various temperatures using an appropriate empirical shift factor (at) such that a single master curve is established for the viscosity evolution of the given fluid system. This approach facilitates the prediction of the gelation behavior of polymer-crosslinker fluid systems as a function of time at varied reservoir temperatures especially over time scales that are not experimentally accessible. The time-dependent rheological evolution of the fluid system was experimentally investigated using batch-wise bottle testing methods as well as viscosity and viscoelastic measurements by employing an advanced rheometer. The TTS approach was applied to the obtained rheological data at varied temperatures. The model was validated for an unknown set of temperature vs. viscosity data. Based on the TTS approach, the term ‘gelation time’ was defined as the time required to reach a pre-specified viscosity to signify a transition from the liquid-like state to the solid-like state. The gelation time decreases with increasing temperatures. After the gelation time, at each temperature, a swift increase in the fluid viscosity was observed, indicating the initiation of the rapid crosslinking in the fluid systems. It was found that beyond the gelation time, the batch-wise bottle testing showed (G-I) gel strength (qualitative). Analogously, the visco-elasticity test demonstrated a rapid rise in elastic modulus (G′) beyond the gelation time. An underlying mechanism based on polymer hydrolysis was utilized to explain the evolution of distinct viscous and viscoelastic properties as a function of temperature. Moreover, the modeling predictions for the fluid systems were examined for in-situ rock plugging with the help of core-flood equipment. The core-flooding tests confirmed a 99% reduction in the rock permeability beyond the gelation time. The gelation time values obtained from both the batch-wise bottle testing method and rheological tests for the polymer-crosslinker fluid systems were found in agreement with each other, with a tolerance of (±5%).