Understanding the temperature–resistance performance of a borate cross-linked hydroxypropyl guar gum fracturing fluid based on a facile evaluation method

摘要

The evaluation of the temperature–resistance performance of fracturing fluid is essential for choosing suitable fracturing fluids during fracturing treatment. In this work, related parameters for characterizing the temperature–resistance performance of fracturing fluids have been analysed systematically. The maximum temperature, T_max(η₀, t₀), which satisfies both the minimum viscosity requirement (η ≥ η₀) of fracturing fluid and the time requirement of fracturing treatment (t ≥ t₀), was used to characterize the temperature–resistance performance of fracturing fluids. A facile procedure for evaluating T_max(η₀, t₀) has been proposed based on a step-by-step numerical-search method. The search for T_max(η₀, t₀) starts from the upper limit temperature T_max, which is the maximum temperature where the apparent viscosity meets the minimum viscosity requirement, i.e., η ≥ η₀. Using a borate cross-linked hydroxypropyl guar gum fracturing fluid as an example, the effects of pH, and the concentrations of thickening agent (hydroxypropyl guar, HPG) and crosslinking agent (Na₂B₄O₇) on the crosslink and temperature–resistance properties are also investigated. It has been found that the crosslinking time t_c decreases with the increase of HPG concentration or Na₂B₄O₇ concentration. However, t_c was found to increase when pH increases. The variation tendencies of T_max(η₀, t₀) are different from that of T_max, viz., T_max(η₀, t₀) gradually increases with Na₂B₄O₇ concentration, whereas T_max increases significantly at low Na₂B₄O₇ concentration and remains almost unchanged at high Na₂B₄O₇ concentration. The possible mechanisms are proposed for interpreting the above phenomena according to related crosslinking-reaction kinetics and thermodynamics. Our work demonstrates a facile method for evaluating the temperature–resistance performance of the fracturing fluid and provides useful insights into the understanding of the temperature tolerance performance of the borate cross-linked hydroxypropyl guar gum fracturing fluid.