Salinity‐ and Heat‐Tolerant VES (Viscoelastic Surfactant) Clean Fracturing Fluids Strengthened by a Hydrophobic Copolymer with Extremely Low Damage

Abstract

As good thickeners for clean fracturing fluids, high salt‐tolerant surfactants have received increasing attention. Based on previous studies, we have further studied the performances of four surfactants, EDAS (JS‐SO), EHSB (JS‐OH‐SO), ETAC (JN) and EDHB (JS‐OH), in monovalent (NaCl) and divalent (CaCl2) salts. This is of great significance for the application of high‐salinity formation water to directly prepare fracturing fluids. The results showed that in high‐salinity aqueous solutions, both zwitterionic surfactants and cationic surfactants can exhibit extremely strong salt tolerance. The addition of the counter ion salt can destroy the internal salt, thus increasing water solubility of zwitterionic surfactants. Cationic surfactants have strong water solubility, and the counter ion Cl− will weaken the electrostatic shielding effect between the head groups. Surfactants can still maintain excellent network structures under high‐salinity conditions. This is mainly owing to the extreme insensitivity of zwitterionic surfactants to salts and the large initial head group area of cationic surfactants. In actual applications, the formation water from the Tahe Oilfield was used directly to prepare the fracturing fluids. Testing the rheological properties of fracturing fluid systems found that adding a small amount of hydrophobic associating polymers can increase the temperature resistance from 100 °C to 140 °C, and the final viscosity can be maintained above 30 mPa S. At the same time, they all showed excellent proppant suspension properties and extremely low core damage rates. The results indicated that even in high‐salinity formation water and high‐temperature formation, these fracturing fluid systems still have good performances, extremely low damage and meet fracturing fluid industry standards.

Preparation of a salt‐responsive Gemini viscoelastic surfactant for application to solids‐free drilling fluids

“…The decrease in the strength of the composite network structure of "polymer chains + surfactant micelles" led to a decrease in the rheological properties of the system. 51,52 This result shows that NT-1 exhibits clear salt-responsive properties in solids-free drilling fluids. Figure 11d shows that the salinity significantly affected the API fluid loss of the base slurry.…”

“…As an excessive salt concentration can cause some NT‐1 worm‐like micelles to grow into capsule‐like micelles, some micellar networks were destroyed. The decrease in the strength of the composite network structure of “polymer chains + surfactant micelles” led to a decrease in the rheological properties of the system 51,52 . This result shows that NT‐1 exhibits clear salt‐responsive properties in solids‐free drilling fluids.…”

Preparation and viscoelasticity of a novel hydrophobic associating polymer with salt stimulation responsiveness by functional monomer modification for fracturing fuids

“…Although natural plant-gum fracturing uid has good thickening ability, biodegradability, and biocompatibility, it has poor temperature resistance and greatly damages the reservoir [7][8] . Clean fracturing uids are low-molecular-weight surfactants that have the advantages of facile preparation, low friction, low amount of residue, and strong sand-carrying capacity; however, they are expensive and have poor temperature and salt resistance [9][10][11][12][13] . Synthetic-polymer fracturing uids not only demonstrate good thickening ability, high gel-breaking performance, and high thermal stability, but can also be exibly designed according to different requirements [14][15][16][17][18][19][20] .…”

Rheological behavior of a novel fracturing fluid formed from amine oxide surfactants

“…However, the wormlike micelle structure of surfactant is prone to dissociate at high temperatures, which greatly restricts the application in high‐temperature reservoirs. At present, the researches on high‐temperature resistant VES fracturing fluid mainly focus on cationic surfactant (Tian et al, 2021; Zhao et al, 2018), anionic surfactant (Khair et al, 2011), and new Gemini surfactant (Mao, Yang, et al, 2018; Mao, Zhang, et al, 2018; Xiong et al, 2018; Yang et al, 2017; Zhang et al, 2018). Due to the electrostatic repulsion between the ionic head groups, it is necessary for these surfactants to add counter‐ion salts or cosurfactants to stimulate micellar growth.…”