关键词: 深部煤层气, 胍胶, 压裂返排液, 回用, 优化

Abstract: Water-based fracturing fluids, represented by guanidine gum, are widely used in the development of deep coalbed methane, a large amount of fracturing flowback fluid is generated while achieving high yields. It is of great significance to optimize the treatment technology for guanidine gum fracturing flowback fluid and continuously improve the recycling rate of flowback fluids. This study aims to address technical challenges in the recycling treatment of guanidine gum fracturing flowback fluid, such as incomplete breaking of the polymer and the difficulty in removing harmful ions. It has proved the effect of additives on polymer breaking through polymer-breaking parameter optimization experiments; using spectroscopic analysis and response surface methodology (RSM), it explores the mechanism of polymer breaking and the optimal process conditions for guanidine gum fracturing fluids under high-temperature environments during flowback in deep coalbed methane wells. This provides a theoretical basis for achieving the complete breaking of guanidine-based polymer in reservoirs. Through the experiments on the interaction of harmful ions in combination with redundancy analysis (RDA), the paper analyzes the interaction of residual ions in flowback fluids, as well as their effects on the formulation and performance of fracturing fluid, thus determining the influence patterns and optimal control indicators of different ions for fluid recycling. On this basis, the study proposes a design for the recycling treatment process of guanidine gum fracturing flowback fluid which is validated in practical applications. The results indicate that the relationship between the viscosity and residue content of breaking agent and the concentration of breaking agent, breaking temperature, and breaking time is in conformity with quadratic regression models. The lowest viscosity and residue content can be achieved at the breaking agent concentration of 0.03%, and 91℃ for 2.9 h. This has great significance for guiding fracturing production and reducing the viscosity of flowback fluids. The study also establishes the sequence of the major ions (B, Al³⁺, Fe³⁺, Na⁺, K⁺, Ca²⁺ and Fe²⁺) in flowback fluids that affect the properties of fracturing base fluids and crosslinked fracturing fluids. By adjusting the concentrations of different ions, the base fluid and fracturing fluid with optimal performance can be obtained, which can guide the control of ion concentrations during the recycling of flowback fluids during guanidine gum fracturing. After optimizing the treatment process of "polymer breaking and viscosity reduction+coagulation+air flotation+selective removal+filtration+boron removal, " the flowback fluids can meet the quality requirements for water preparation, and the properties of the prepared fracturing fluids meet the technical requirements for water-based fracturing fluids. The recycling rate has increased from 40.00% to over 92.01%, and the direct treatment cost has decreased from 120 yuan/m³ to 40 yuan/m³. This not only reduces water resource consumption and transportation frequency, but also saves development costs, lowers safety and environmental risks.

Key words: deep coalbed methane, guanidine gum, fracturing flowback fluid, recycling, optimization