RSC Advances View Article Online PAPER View Journal | View Issue Understanding the temperature–resistance performance of a borate cross-linked Cite this: RSC Adv.,2017,7,53290 hydroxypropyl guar gum fracturing fluid based on a facile evaluation method† Haiming Fan, *ab Zheng Gong,a Zhiyi Wei,a Haolin Chen,a Haijian Fan,a Jie Geng,a Wanli Kang a and Caili Daia 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, Tmax(h0, t0), which satisfies both the minimum viscosity requirement (h $ h0)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 Tmax(h0, t0) Creative Commons Attribution 3.0 Unported Licence. has been proposed based on a step-by-step numerical-search method. The search for Tmax(h0, t0) starts from the upper limit temperature Tmax, which is the maximum temperature where the apparent viscosity meets the minimum viscosity requirement, i.e., h $ h0. 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 tc decreases with the increase of HPG concentration or Na2B4O7 concentration. However, tc was found to increase when pH increases. The variation tendencies of Tmax(h0, t0) are different from that of Tmax, viz., Tmax(h0, t0) This article is licensed under a gradually increases with Na2B4O7 concentration, whereas Tmax increases significantly at low Na2B4O7 concentration and remains almost unchanged at high Na2B4O7 concentration. The possible mechanisms Received 23rd October 2017 are proposed for interpreting the above phenomena according to related crosslinking-reaction kinetics Accepted 14th November 2017 and thermodynamics. Our work demonstrates a facile method for evaluating the temperature–resistance Open Access Article. Published on 20 November 2017. Downloaded 9/24/2021 6:14:20 PM. DOI: 10.1039/c7ra11687j performance of the fracturing fluid and provides useful insights into the understanding of the rsc.li/rsc-advances temperature tolerance performance of the borate cross-linked hydroxypropyl guar gum fracturing fluid. 1. Introduction reservoir depletion. It is also used in unconventional reservoirs where the intrinsic permeability is too low to yield economical – Hydraulic fracturing is a commonly used technique to stimulate production.3 5 Fracturing uid is of great signicance for hydrocarbon production by creating a network of highly hydraulic fracturing treatment. The main functions of frac- conductive fractures in the area surrounding a wellbore.1 The turing uid include opening the fracture, and suspending and network of fractures can not only improve the hydraulic transporting proppants.1 So, a fracturing uid is supposed to conductivity of the reservoir rock, but also increase the surface provide sufficient viscosity to ensure proper proppant transport area contributing to enhanced hydrocarbon production.1,2 and the even distribution of proppants along the fractures. Over Thus, hydraulic fracturing is used in conventional hydrocarbon the past few decades, linear or cross-linked polymer solu- – – reservoirs to increase permeability in damaged formations or in tions,6 9 energized uids,10 12 and viscoelastic surfactants – formations that exhibit signicantly lower production owing to (VES)13 18 have been developed as water-based fracturing uids. Biopolymers such as guar gum and cellulose derivatives, synthetic polymers such as polyacrylamide, are introduced in a Shandong Provincial Key Laboratory of Oil eld Chemistry, School of Petroleum Engineering, China University of Petroleum (East China), Qingdao 266580, the water-based fracturing uids for improving the rheological 2 Shandong Province, P. R. China. E-mail: [email protected] performance. Crosslinking improves the rheological properties bState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest of the polymers for fracturing purposes, e.g. borate, Ti(IV), Zr(IV), Petroleum University, Chengdu 610500, Sichuan Province, P. R. China and Al(III) ions are oen used to crosslink water soluble poly- † Electronic supplementary information (ESI) available. See DOI: mers.19–21 Guar gum and its derivatives, such as hydroxypropyl 10.1039/c7ra11687j 53290 | RSC Adv.,2017,7, 53290–53300 This journal is © The Royal Society of Chemistry 2017 View Article Online Paper RSC Advances guar (HPG), carboxymethyl guar (CMG) and carboxymethyl agent, crosslinking agent and other chemical additive agents. hydroxypropyl guar (CMHPG), are the most-common polymers Furthermore, so far as we know, there is no evaluation method used in fracturing uid, accounting for up to 90% of all gelled for accurately determining the maximum tolerance temperature fracturing uids.1,22 Meanwhile, to satisfy the criterion to frac- of the fracturing uid, which leads to the fact that the effec- ture deeper and hotter wells, synthetic terpolymer of 2- tiveness of temperature stabilizer and chelating agent can only acrylamido-2-methylpropanesulfonic acid (AMPS), acrylamide be indirectly reected by measuring the apparent viscosity and acrylate cross-linked by Zr has been developed and used as changes of the fracturing uid at a certain temperature.36,37 a fracturing uid.23,24 Thus, it is still necessary to explore a standard method on The evaluation on the temperature–resistance performance evaluating the temperature–resistance performance of frac- of fracturing uid is essential for choosing the suitable frac- turing uid, which will remarkably benet researchers and turing uid with excellent performance. Generally, two main users for the screening and developing of fracturing uids. methods were used to evaluate the temperature–resistance The key point of the evaluation on the temperature–resis- performance of fracturing uid.25–35 One is to monitor the tance performance of fracturing uid is to establish a method changes of the apparent viscosity at a constant shear rate with for measuring the maximum tolerance temperature which increasing temperature by continuously heating the fracturing meets the criteria for the apparent viscosity and the time uid.25–27 The apparent viscosity decreases with increasing requirement of the fracturing treatment. Our previous work temperature and when it drops to a certain value, the indicated demonstrated a way of evaluating the effectiveness of temper- temperature is used as the thermal stability temperature of ature stabilizer by measuring the difference of the maximum fracturing uid. For example, Baruah et al. found that the VES tolerance temperature in satisfying the criteria of fracturing fracturing uid developed from Tween 80/NaOA/2-ethyl treatment before and aer adding the temperature stabilizer.38 hexanol/clove oil/water system presented an apparent viscosity However, no systematic study on the inuence of main À at shear rate 100 s 1 greater than 90 mPa s when the tempera- components in fracturing uid on the temperature resistance Creative Commons Attribution 3.0 Unported Licence. ture is below 116.3 C. The insertion of 500 ppm ZnO nano- performance has been published yet. Herein, in this work, particle further improved the thermal stability temperature to related parameters for characterizing the temperature–resis- 119.5 C.25 The other method is to measure the changes of the tance performance of fracturing uid have been analysed. And apparent viscosity with time under constant temperature. the maximum tolerance temperature is determined by a step-by- Generally, the temperature–resistance performance of the step numerical search method starting from the upper limit fracturing uid is obtained by either analysing the apparent temperature. By using this method, inuence factors such as viscosity aer heating or measuring the stability time when the pH, the concentration of thickening agent (e.g., HPG) and apparent viscosity of the uid is above criterion value at crosslinking agent (e.g.,Na2B4O7) on the crosslink and different temperatures.28–35 For example, Holtsclaw et al. temperature–resistance properties of borate cross-linked This article is licensed under a measured the apparent viscosity of zirconium cross-linked hydroxypropyl guar gum fracturing uid are investigated and terpolymer gel as a function of time at 177, 191, 204 and the inuence mechanisms are also discussed. À 218 C. It is found that the apparent viscosity at shear rate 40 s 1 of the gel was greater than 2000 mPa s aer shearing for 4 hours Open Access Article. Published on 20 November 2017. Downloaded 9/24/2021 6:14:20 PM. at 177 C, almost 500 mPa s aer shearing for 4 hours at 204 C, 2. Materials and methods and approximately 300 mPa s aer shearing for 2 hours at 2.1. Materials 29 218 C. So they concluded the synthetic zirconium cross- Hydroxypropyl guar gum with an average molecular weight of linked terpolymer gel with good stability at temperature larger 3.2 Â 106 Da is commercially available and supplied by Shan- than 177 C. Wang et al. found that the apparent viscosity of dong Dongying Xinde Chemical Co., Ltd. Borax