Development Of Supramolecular-gel Fracturing Fluid And Action Mechanism Research

Current fracturing fluids,such as the Viscoelastic Surfactant（VES）suffer from poor stability in high temperatures and high cost,in addition to large reservoir damage of guar fracturing fluid.In order to solve these problems,a supramolecular gel fracturing fluid（SMGF）was developed based on the mechanism of supramolecular chemistry.The main components of the SMGF are polymer thickener（SMPT）and physical crosslinking agent（PHCA）.The viscosity of SMGF keeps at 73.9m Pa?s after being tested for Temperature-tolerant and Shear-resistant ability under the condition of160℃,170s^-1 for 2 hours.Compared with HPAM（Mv=17000k Da）,the SMPT（Mv=2000k Da）)prepared by myself has better Dynamic light scattering particle size,yield value of stress and smaller proppant settling rate.When the SMPT is with the hydrolysis degree of 27.5%and the concentration of 0.2wt%,its best drag reducing efficiency is 56.7%,which could maintain stability under the condition of a high Reynolds number.SEM pictures of the SMPT solution（0.6wt%）show a polymer ribbon network structure.TEM pictures review that the 0.02wt%SMPT can form a"dendritic"network structure.SMPT and PHCA can form a“honeycomb structure”with through the interaction effect of Non-covalent bond（hydrogen bond,coordination bond,etc）.The research proved this“honeycomb structure”can make excellent viscoelasticity and structural stability through analyzing viscoelastic modulus,yield value of stress,support agent sedimentation rate and gel structure transition point of SMGF.According to the data analysis on the Elastic Modulus（G′）and Viscosity modulus（G″）,Elastic factor（G′/G″）and Elastic factor retention rate((G_after′/G_after″)/(G_before′/G_before″))of the samples before and after the Temperature-tolerance and Shear-resistance test under the condition of150℃,170s^-1 for 2 hours.SMGF with the main components of SMPT and PHCA can keep the Elastic factor retention rate((G_after′/G_after″)/(G_before′/G_before″))at 73.7%.This shows that the“honeycomb structure”formed through interaction effect of PHCA and SMPT,is the main reason for Temperature-tolerance and shear-resistance.Rheology and hydrogen spectrum test show that the interaction between SMPT and PHCA,through long hydrophobic side chain,which lowers the activation energy and constraining the degradation of SMPT.The gel forming mechanism of the supramolecular gel developed in this study is:the hydrophobic association and electrostatic interaction of Nasal and EHSB help PHCA micelles to form gel.The hydrophobic chain of polymer SMPT is embedded in the PHCA′s wormlike micelle through the association of another hydrophobic chain and form a highly branched supramolecular network structure.At the same time,the polymer chains and vermicular micelles make the physical crosslinking through the intermolecular forces form a three-dimensional″supramolecular honeycomb structure″.This study also analyzed the gelation process under different temperature and different PHCA concentration.As a result of this study we can conclude that the polylactic acid fiber goes through the internal“honeycomb structure”,can strengthen the network structure of SMGF,improving the rheological property of the supramolecular gel fracturing fluid.However this study also found that it could not change the Shear dilution behavior of the SMGF.The comprehensive influence factor related with consistency coefficient（K） reflects the rheological characteristics of fracturing fluid corresponding to the changes of the fiber concentration and temperature.The permeability recovery rate of the supramolecular gel fracturing fluid is 88.02%,and fluid flow conductivity of proppant packing layer damage rate is 13.09%.TEM reveals the low damage reason for this fracturing fluid.In summary,SMPT breaking liquid is without solid-phase particles.