Synthesis and properties of organoboron functionalized nanocellulose for crosslinking low polymer fracturing fluid system

Starch microsphere silicon-boron crosslinker for low concentration hydroxypropyl guar gum based fracturing fluid

Hydroxypropyl guar gum (HPG) is a critical thickener to increase viscosity and lubrication to improve the water-based hydraulic fracturing efficiency. However, current crosslinkers require a large amount of HPG (>0.3 wt%) to form gel with sufficient viscosity, and high concentrations of HPG may cause adverse effects to the production and the environment. In this study, a novel starch microsphere silica‑boron crosslinker (SMSB) was developed using starch microspheres as a carrier and γ-aminopropyl triethoxy silane (KH550) as a modifier with an in-house method. Both the rheology and surface reactions of the SMSB-HPG crosslinking system were studied using multiple laboratory experiments and molecular dynamics simulation. The results showed that SMSB crosslinker caused multi-site cross-linking with low concentration (only 0.2 wt%) of HPG molecules, reducing the twisting of single molecular chain in the crosslinking system, enhancing the cross-linking strength between molecular chains, and making HPG molecular chains stretcher in the aqueous solution. The apparent viscosity and viscoelasticity of the HPG system were substantially higher than the organoboron crosslinker, and the temperature resistance of the SMSB-HPG crosslinking system was up to 140 °C. This study provides an alternative green crosslinker for more sustainable industrial applications and provides theoretical basis for the modification of biomaterials.

Experimental investigation on the high-pressure sand suspension and adsorption capacity of guar gum fracturing fluid in low-permeability shale reservoirs: factor analysis and mechanism disclosure

Guar fracturing technology has been considered as a kind of popular EOR technology, but the weak static suspension capacity becomes a challenge due to the poor temperature resistance and stability of guar fracturing fluid. The main goal of this investigation is to explore the effect of different factors on the high-pressure static sand suspension of guar gum fracturing fluid by a synthetic efficient nano-ZrO₂ cross-linker. In particular, a mechanism of static suspended sand of nano-ZrO₂ cross-linker is analyzed by microscopic simulation. The adsorption performance of guar fracturing fluid on the shale surface is also studied for analyzing the environmental pollution and damage of guar gum fracturing fluid to shale reservoirs after cross-linking in this investigation. The results obtained that the inclusion of a small content of nano-ZrO₂ cross-linker (0.4%) leads to an apparent increase of fracturing fluid viscosity and decrease in the falling quality of gravel (104 mPa·s and 0.3 g) compared to the classical cross-linker (63 mPa·s and 3.5 g). The lower adsorption capacity of guar fracturing fluid containing nano-ZrO₂ cross-linker on the shale surface means that it has a weaker pollution ability to the shale reservoir than the commercially available cross-linker. Meanwhile, the grid structure density formed by nano-cross-linker and guar gum is considered to be the key factor to significantly change the suspended sand capacity. The investigation of nano-cross-linker cannot only provide necessary theoretical technology and data support for the stability of water-based fracturing fluid, efficient sand carrying, and the development of water-based fracturing technology, but also effectively protect the underground shale reservoir.

The one-step synthesis of B,N co-doped carbon dots as a fracturing crosslinker and fluorescent tracer in flowback fluid and their performance

The carbon dot crosslinker has a unique crosslinking mechanism, that each crosslinking point can crosslink multiple guar gum molecular chains.