Fe ³⁺ ‐Coordinated Phosphate Ester Networks for Oil‐Based Fracturing Fluids: Rheology and Formation Damage

ABSTRACT

An Fe ³⁺ ‐coordinated oil‐based fracturing fluid was constructed using a previously prepared phosphate ester component (PE) as the coordination‐active precursor. Because the molecular‐level structure of PE was not fully resolved, this study focuses on coordination‐related spectroscopic changes and macroscopic performance. Metal‐ion type, counter‐anion, crosslinker formulation, oil phase, and crosslinker dosage were evaluated to identify conditions favorable for network formation. Among four metal‐salt systems, the Fe ₂ (SO ₄ ) ₃ ‐derived product (PEFS) exhibited the highest apparent viscosity under its optimized preparation conditions (230.8 mPa·s). Changes in the PO/PO region of the FTIR spectra and in the Fe 2p and P 2p XPS signals were consistent with FeOP coordination interactions. The optimized diesel‐based fluid exhibited shear thinning followed by rapid viscosity recovery, retained > 360 mPa·s after 60 min at 100°C and 170 s ⁻¹ , and showed G ′ >  G ″ above approximately 0.6 Hz at 90°C. With 0.8 wt% sodium acetate, the broken‐fluid viscosity decreased below 5 mPa·s at 4 h. Proppant settling rates were 0.10–0.15 cm·min ⁻¹ , and the average permeability damage rate of three tested sandstone cores was 19.03%. These results characterize the formulation‐dependent rheological and application performance and are consistent with a dynamic coordination‐network interpretation under the tested laboratory conditions.