A Novel Viscoelastic Surfactant Fluid System Incorporating Nanochemistry for High-Temperature Gravel Packing Applications

摘要

Viscoelastic Surfactant (VES) fluids have been used in many openhole gravel packing applications with the shunt tube technique as they offer several advantages over polymeric fluids. However, existing VES fluids have temperature limitations. The objective of this work was to develop a new viscoelastic surfactant (VES) based fluid for gravel packing wells with temperature up to 325°F while retaining the advantages of existing VES fluids. The new fluid system consists of a surfactant, a cosurfactant, and a nanoadditive. The performance of the new fluid system was evaluated in laboratory experiments up to 325°F. The properties studied and discussed in this paper are shear recovery time, rheology (viscosity versus shear rates), gravel suspension, and core retained permeabilities. The optimization of the final fluid formulation based on sensitivity of the target properties to concentration of each component is also detailed in the paper. The new VES-based gravel pack carrier fluid incorporating a nanoadditive showed significantly improved performance at elevated temperatures compared with conventional fluids. In particular, while the conventional VES fluids do not meet the gravel suspension requirement, the new fluid system is able to suspend the gravel under static conditions up to 325°F. In addition, the viscosity at low shear rates is improved while the viscosity at high shear rates is comparable to existing VES fluids. Tests with outcrop cores of varying permeabilities demonstrated the fluid's minimal formation damage. The complete VES fluid system with nanoadditive was found to be compatible with both monovalent and divalent brines at densities up to 14.0 lbm/gal. As such, it is a more cost-effective alternative to xanthan-based carrier fluids, which are incompatible with inexpensive calcium brines and thus necessitate sodium bromide or formate brines depending on the density requirements. Based on the extensive laboratory study, it can be concluded that the new fluid system outperforms conventional VES gravel pack carrier fluids at high temperatures while retaining the benefits of the conventional VES fluids. The new fluid system significantly extends the temperature limit of VES-based gravel packing carrier fluids. The fluid system can also be used with many completion brines and mixed at a wide density range, making it an excellent alternative to conventional polymeric fluids used in gravel packing applications.