Preparation Of Organoboron Zirconium Crosslinker And Its Application In High Temperature Resistant Fracturing Fluid Systems

Fracturing is an effective method to transform high temperature and low permeabiliy reservoir. High temperature resistance fracturing fluid system is the key technique for successful transformation. Crosslinking agent is the crucial component of high temperature resistance fracturing fluid and organic boron zirconium complex is an effective crosslinking agent being applied in high temperature resistance fracturing fluid system. There are some shortcomings in preparing organic boron zirconium complex crosslinking agent which limit its use in fracturing fluid system. Also, there is still no deep study into the crosslinking characteristics of organic boron zirconium complex. Therefore, using simple method to prepare organic boron zirconium complex crosslinking agent with good performace and studying its crosslinking characteristics and application performace are meaningful for the development of high temperature resistance fracturing fluid system.In this paper, an organic boron zirconium complex crosslinking agent was synthesized using one-pot method as follow steps:first, zirconium oxychloride reacted with isopropanol to form zirconium tetraisopropyl ester; second, zirconium tetraisopropyl ester reacted with organic ligands to form organic zirconium complex; third, organic zirconium complex reacted with borax to form organic boron zirconium complex.The raw materials for preparing organic boron zirconium complex crosslinking agent were zirconium oxychloride and borax. The solvent was a mixture of water and isopropanol. Single factor experiment method was used to optimize synthesis conditions. The best synthesis condition was as follows:organic ligands were consist of polyol YC, alpha-hydroxycarboxylic acid LS and compound alkanolamine TF; the initial pH value of the reaction was 2.0; the reaction temperature was 55?; the mass ratio of the mixture solvent was 1:1.75:the mole ratio of boron and zirconium was 2:1; the dosage of compound alkanolamine was 2molTF/1molZr; the dosage of alpha-hydroxycarboxyiic acid was 1.5molLS/lmolZr; the dosage of polyol YC was 10molYC/1molZr; the reaction time was 5h. Infrared spectrum confirmed the structure of organic boron zirconium complex. The pH value of organic boron zirconium complex crosslinking agent solution was between 7.3?7.5 and the desity of it was between 1.05?1.10.Dynamic light scattering experiment results demonstated that there were nano particles exsisting in organic boron zirconium complex crosslinking agent solution. Environmental scanning electron microscope images indicated that the gel formed by organic boron zirconium complex crosslinking agent crosslinking with HPG showed film network structure whose crosslinking density was higher than the gel formed by borax or organic boron complex crosslinking agent crosslinking with HPG. Viscoelasticity test also showed that the gel formed from organic boron complex crosslinking agent crosslinking with HPG possessed higher crosslinking density and crosslinking intensity. Compared with borax and organic boron complex crosslinking agent, the initial pH value needed for organic boron zirconium complex crosslinking agent to crosslink with HPG was higher. Organic boron zirconium complex crosslinking agent displayed delayed crosslinking property and the gel formed by it showed secondary crosslinking property under high temperature shearing.Organic boron zirconium crosslinking agent showed good adaptability with most fracturing fluid addtives. According to the adaptation experments from the crosslinking agent to the addtives, a high temperature resistance fracturing fluid system formula was formed as follows:0.55% thickening agent JK101+0.5% organic boron zirconium crosslinking agent+1% temperature stabilizer heterocyclic compound BDT+1% clay stabilizer KC1+0.5% cleanup additive CF-5A+0.05% fungicide formaldehyde+0.04% pH modifier NaOH. These addtives showed good compatibility in this system.The comprehensive performance evaluations for the high temperature resistance fracturing fluid system formed above came to following conclusions:this system was suitable for 140? reservoir transformation; using 0.08% gel breaker could make it completely break; the average damage rate from the gel breaking liquid to low permeability core matrix permeability was 34.5%; the liquid showed good compatibility with formation water; the settling velocity of proppants in this system was low, which demonstated this fracturing fluid system possessed good proppant carrying capacity.