Development and application of a comprehensive multi-indicator method for evaluating gel breaking in fracturing fluids

Conventional methods for assessing gel breaker efficiency in viscoelastic fracturing fluids mainly rely on monitoring a single parameter, the viscosity of the broken fluid supernatant. This approach, though simple, has significant limitations and fails to capture the full physical state of broken gel, especially when residual undissolved fragments (“fish-eyes”) remain, impairing fracture conductivity and causing formation damage. This incomplete assessment may lead to suboptimal selection and dosage of the breaker, ultimately impacting well productivity. Therefore, there is a pressing need for more holistic and reliable methods for a comprehensive evaluation of the gel-breaking process. This study aimed to develop and validate a new multi-index, comprehensive evaluation system to provide an improved scientific tool for optimizing fracturing fluid formulations and breaker strategies, particularly in complex reservoirs.

A dual approach was used, consisting of method development and systematic experimental validation. Two representative gelled fracturing fluids were formulated: a widely used borate-crosslinked hydroxypropyl guar (HPG) gel and a zirconium-crosslinked synthetic polymer gel. Fourteen breakers from different mechanistic categories were selected, including oxidative agents (Ammonium Persulfate, Potassium Persulfate), acidic agents (oxalic acid, citric acid, ammonium hydrogen sulfate), and various chelating agents (e.g., EDTA-2Na, sodium citrate, sodium tartrate). A key feature of this study is the development of a new multi-parameter evaluation framework. This framework moves beyond single-point viscosity measurement by introducing a comprehensive “integrity index” (ψ), which is derived from simultaneous measurements of (1) the dynamic viscosity of the clear broken gel filtrate and (2) the mass of remaining solid-like gel fragments after a standardized breaking process. A specially designed calculation model, involving segmented functions, converts these two physical measurements into a single, continuous ψ value ranging from 1.0 (intact gel) to near 0.0 (complete breakdown), providing a nuanced and quantitative scale for assessing breaking extent. The accuracy and reliability of this new ψ-based system were thoroughly verified by comparing it with established analytical techniques. Macroscopic validation involved detailed rheological analysis of the evolution of viscoelastic moduli (G', G") and steady-shear viscosity throughout the breaking process. Microscopic validation was achieved by directly analyzing changes in the molecular weight distribution and polydispersity index of a polymer via gel permeation chromatography (GPC), confirming chemical degradation of the polymer chains.

This new multi-index approach produced clear and distinct results. The integrity index ψ effectively served as a sensitive metric for continuously ranking the performance of all tested breakers across both gel types. Oxidative breakers like APS and KPS, along with the acidic breaker ammonium hydrogen sulfate, showed exceptional efficiency in breaking the borate-crosslinked HPG gel. At a moderate concentration of 0.25%, these breakers reduced ψ below 0.1, indicating near-complete gel disintegration. In contrast, most chelating agents had minimal effect on this gel system, with high ψ values remaining. Similar trends were observed for the zirconium-crosslinked polymer gel, confirming the robustness of the method across different chemistries. Oxidative and acidic breakers again proved most effective. Among chelators, EDTA-2Na showed the highest activity in this metal-crosslinked system, although overall performance based on ψ remained inferior to the top oxidative/acidic breakers. Validation data strongly supported the ψ index results. The viscoelastic network of samples with low ψ values collapsed entirely in rheological tests, transitioning from a solid-like gel to a Newtonian fluid. Conversely, samples with higher ψ values retained measurable elasticity. Crucially, GPC analysis provided molecular-level evidence: effective breakers with low ψ values caused a significant reduction in the weight-average molecular weight and increased molecular weight distribution broadening, confirming extensive polymer chain scission. This close correlation between the macroscopic ψ index, rheology, and microscopic polymer analysis conclusively validated the proposed comprehensive evaluation method.

A novel multi-index method for assessing the extent of gel-breaking in fracturing fluids was successfully developed and validated. The introduced integrity index ψ, which combines information from fluid viscosity and residual gel mass, offers a major improvement over traditional single-parameter methods by delivering a more complete, quantitative, and reliable characterization. The method effectively differentiates breaker performance and correlates well with independent rheological and polymer degradation analyses. This robust framework can be a valuable practical tool for optimizing breaker selection and dosing, helping to minimize fracture-conductivity damage and enhance well productivity. As a technical innovation with direct field application, it has great potential to improve stimulation treatment efficiency, especially in challenging reservoir environments, and adds valuable insights to the broader field of production chemistry.