Hydraulic fracturing has become a common practice in the petroleum industry, and several systems have been developed to obtain a suitable crosslinked polymer for the treatment. However, each system has its strengths and weaknesses. This study aims to investigate the effect of three different ligand types attached to zirconium (Zr) on the performance of carboxymethylhydroxypropylguar (CMHPG) crosslinked with Zr-based crosslinkers with the different ligands. The shear recoverability and rapid viscosity buildup at the high pH of Zr-based crosslinkers were overcome by a new aluminum-zirconium (Al-Zr) dual crosslinker in this research.
The polymer used was CMHPG, and the tests were conducted at pH of 3.8 and 10.8. One of the factors that affects the gel performance is the type of ligand attached to the Zr. Because the Zr-based crosslinkers are shear-sensitive, ligands were introduced to delay the crosslinking until the fluid passes the high-shear environments (perforations). Therefore, in this study, lactate, propylene glycol, and triethanolamine (TEA) were studied as ligands attached to the Zr. Two Zr crosslinkers with almost the same concentration of Zr can display different performances if the ligand attached to the Zr is not the same.
The rapid viscosity buildup at high pH had always been a limitation of Zr crosslinkers; however, a new Al-Zr dual crosslinker was introduced in the present study to address this limitation. The Al-Zr crosslinker outperformed all the other crosslinkers examined in the present study. Immediate viscosity buildup at a high pH and a lack of shear recoverability of Zr-based crosslinkers was addressed through the Al-Zr crosslinker. The Al-Zr crosslinker introduced in this study is one compound that is easy to use in the field. The Al-Zr crosslinker performance was compared with the boron-zirconium (B-Zr) crosslinker: Both had lactate as a ligand attached to them. Among all the Zr-based crosslinkers in this study, the Zr crosslinker with lactate and propylene glycol as a ligand performed the best. The CMHPG crosslinked with each of the crosslinkers was tested for proppant-carrying purposes along with static leakoff rates. The results revealed gel-proppant-suspending capabilities and acceptable leakoff rates.
Extensive laboratory research is a key to a successful field treatment. These results indicate that fracturing fluids are complex, and the ligand type is one of the important factors in determining the final properties of fracturing fluids. Therefore, the results of this study will assist in developing Zr-based crosslinkers that address their current shortcomings.