Chlorophyll: A Naturally Occurring Green Polymer Breaker for Hydraulic Fracturing

Abstract

Porphyrins produce free radicals in alkaline conditions. Chlorophyll is an Mg ϩϩ -containing tetrapyrrole formed from 4 porphyrin rings and is part of the photosynthetic reactions in plants (Arnoff, 1966). It catalyzes carbohydrate synthesis in the presence of light and carbon dioxide. Using the molecular structure of chlorophyll, we hypothesized that chlorophyll functions as a breaker by producing hydrogen peroxide or other radicals in the alkaline environments of borate-fracturing fluids.This study evaluated leaf extract containing chlorophyll as a potential polymer breaker. Leaves contain 1.5 to 2.5% of chlorophyll in their leaves and the ratio of chlorophyll a to b is 2.5-3.5 depending on growth conditions and light exposure (Willstaetter and Stoll, 1928). Chlorophyll samples were obtained from various plants and commercial sources, and their efficacy as polymer breakers was studied against guar-based fracturing fluids. The average molecular weight of treated fluids was measured by changes in intrinsic viscosity. Additionally, regain conductivity measurements were carried out. Results showed an 84% regain conductivity in proppant packs. Chlorophyll-treated cross-linked fluids showed a more than 90% viscosity reduction, without any viscosity rebound on cooling. The chlorophyll worked efficiently up to 250°F but the optimum temperatures are at 175 to 200°F with narrow pH range of 9.5 to 10. The chlorophyll-treated fluids also showed a reduction of molecular weights of the linear guar polymer from 1,472,000 to 138,000 as measured by the intrinsic viscosity method. The studies support the hypothesis that chlorophyll can function as a polymer breaker for alkaline fracturing fluids.

Grand Challenges and Opportunities for Greener Chemical Alternatives in Hydraulic Fracturing: A Perspective from the ACS Green Chemistry Institute Oilfield Chemistry Roundtable

“…Enzymes are ineffective in breaking acrylamide copolymers. For these systems, oxidizing breakers such as persulfate or peroxides are the most common break mechanism. − …”