Effect of polyacrylamide friction reducer on calcite dissolution rate at 25 °C and implication for hydraulic fracturing

Abstract

Hydraulic fracturing is widely used to create cracks and increase the size and connectivity of existing fractures, leading to higher permeability of shale rocks and production of unconventional hydrocarbon sources. The main chemicals used in hydraulic fracturing fluids can initiate fractures in shale reservoirs by acid induced carbonate dissolution, and minimise energy loss during the pumping process by friction reducer enhanced fluid viscosity. Here, using batch reactor experiments we investigate the effect of non-ionic polyacrylamide polymer (friction reducer) on the dissolution rate of calcite in acidic solutions (0.2 M buffer solution of sodium acetate/acetic acid) at 25 °C. The results demonstrate that polyacrylamide (from 0 to 30 mg) slows down the dissolution rate by a factor of 4. Hydrogen bonding and surface complexation between non-ionic polyacrylamide and calcite potentially trigger an adsorption mechanism that protects calcite from dissolving. This research provides new insights into friction reducer (polyacrylamide) influenced pore generation, enabling engineers to optimise the fracturing fluid design (amount of polyacrylamide) and to consider suitable actions to prevent the polymer from having a negative impact on productivity.