Characterization and Rheological Performance of Novel Viscoelastic Surfactants for Hydraulic Fracturing in Unconventional Reservoirs

This study aims to synthesize and characterize a novel viscoelastic surfactant formulation for hydraulic fracturing, evaluating its rheological properties, temperature profile, salinity resilience, and the effectiveness of breaking mechanisms in unconventional reservoirs. The goal is to enhance fluid flow, proppant transport, and operational sustainability, contributing to more efficient and environmentally friendly fracturing practices. Two locally produced pyridinium-based Gemini surfactants, featuring mono-phenyl and di-phenyl spacers, were synthesized and tested with carboxylate-terminated low molecular weight polyethylene amine (C-PEI). These formulations were combined with varying concentrations of CaCl₂(up to 20%) to assess their viscous and elastic properties. Rheological behavior was analyzed using a high-temperature cone-plate rheometer across shear rates ranging from 0.1 to 100 s^-1. The effectiveness of breakers, including Tetrasodium Glutamate Diacetate (GLDA) and a dead Saudi Arabian crude oil (API 30), was evaluated based on viscosity reduction The formulation containing di-phenyl spacer (G-18Dia) demonstrated superior gelation, forming an immoveable gel, whereas the mono-phenyl Gemini surfactant (G-18Mono) and Diethylenetriamine Penta acetic Acid (DTAB) formulations remained flowable, indicating the critical role of the di-phenyl spacer in enhancing gel strength. Optimal gel strength was achieved at 5% CaCl₂ and at preparation temperature of 50°C. Higher CaCl₂ concentrations (>10%) led to gel weakening at elevated temperatures, while lower concentrations (<2.5%) resulted in excessive rigidity or failed gelation. The gels exhibited shear-thinning behavior, with the highest viscosity observed at 25°C, suggesting this temperature as optimal for robust gel formation. At elevated temperatures, viscosity decreased, facilitating deeper reservoir propagation. Under a constant shear rate of 1 s^-1, the G-18Dia formulation (5% CaCl₂) showed a gradual viscosity increase from ~1000 cP to ~4250 cP, stabilizing as an immoveable gel at 25°C, confirming a time-dependent gelation mechanism attributed to C-PEI crosslinking and calcium ion interactions. Both GLDA and crude oil effectively reduced viscosity, achieving final values of ~12 cP and ~13 cP at 100 s^-1, respectively. GLDA exhibited a more gradual viscosity decline, indicating chemical degradation, while crude oil relied on mechanical shear for gel breakdown The introduction of a unique viscoelastic surfactant formulation represents a significant enhancement in fracturing fluid technology, specifically designed for unconventional reservoirs. This research introduces innovative solutions to overcome existing challenges in fracturing fluid design.