Structural effects of the hydrolysis of poly(methylene oxide) and poly(glycolic acid) exposed to completion and acidizing fluids in an oil well environment

Abstract

Two hydrolyzable polymers, poly(methylene oxide) (PMO) and poly(glycolic acid) (PGA), were tested for association with mechanical systems to promote diversion of formation acid treatments in oil wells. Samples were confined to chemical products commonly employed in oil well completion processes, HCl 15% w/w and NaCl 23% w/w aqueous solutions, in separate metallic cylindrical cells, under conditions observed in southeastern Brazilian offshore fields (50 and 75°C and pressure of 41.4 MPa). Pristine samples were characterized by 13C‐NMR. Hydrolytic influences were evaluated by differential scanning calorimetry, scanning electron microscopy, wide angle X‐ray diffraction, and computerized microtomography. The intense effects observed showed a specific correspondence with each tested polymer and were evidenced by postexposure analysis. The results indicate that both polymers can be used in association with mechanical diverting systems to promote chemical treatment distribution and, therefore, improve oil well productivity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47362.

Viscosity-Reducing Agents (Breakers) for Viscoelastic Surfactant Gels for Well Stimulation

“…Polymers and viscoelastic surfactants (VES) are used to improve well productivity in carbonate and sandstone reservoirs. − These compounds are used in matrix acidizing and hydraulic fracturing. ,− In matrix acidizing, polymers and VES are used as chemical diverters and are known as self-diverting agents. ,− Using diverters ensures that the low viscosity acid pumped into the well goes into the low-permeability zones and not in the high-permeability zones, thus increasing the effectiveness of matrix acidizing. ,− , Diversion by gels replaces mechanical diversion techniques because mechanical diversion methods are not always recommended, especially for long horizontal or extended-reach wells. , In hydraulic fracturing, polymers and VES act as a fracturing fluid and a proppant transporter as a result of their high viscosity. ,,,, They are pumped at or above the formation fracturing pressure to create fractures in the wellbore, thus improving well productivity, especially in low-permeability zones . However, the usefulness of gels is not only based on their diversion or fracturing abilities.…”