Fracturing Fluid and Rock: Best Friends or Sworn Enemies – Nano-Scale Chemical Reactions During Hydraulic Fracturing

Abstract

The US Department of Energy National Laboratory System is advancing the level of understanding of the physical and chemical interactions of unconventional resources and the practice of hydraulic fracturing so that hydrocarbon resources can achieve maximum recovery. One of the aspects of this research is the chemical interactions of fracturing fluids and the rock fractures and nanopores into which they are being injected. Oxygen and acid introduced to the formation causes complex inorganic and organic chemical reactions that cause permeability improvements and secondary reprecipitation. Using a combination of traditional analytical chemistry methods, highly advanced synchotron light source based imaging and an extensive industry technical steering committee, SLAC National Laboratory has designed, executed and published finding that show the dynamics and extent of this induced chemistry change in unconventional reservoirs. The findings have shown that minor amounts of acid used at the initiation of a frac stage can be carried throughout the rock matrix in the stimulated rock volume to create and occlude permeability. Oxygen in the fluids can act to reprecipitate mobilized iron and reduce nano-scale permeability. Barium in rock and drilling fluids can react with sulfate to clog pore throats. Other ingredients in the fracturing fluid like ammonium persulfate also contribute to barite precipitation in the nanopores. Pressure pulse permeability experiments with reacted cores from Marcellus Shale and Eagle Ford have been a challenge to test for permeability impacts but lesson learned in initial testing will establish new testing methods. The program will be extended to other shale basins in America so that state-of-the-art scientific equipment at the National laboratories can be used to determine additional chemical and physical alterations of shale reservoirs from the hydraulic fracturing process.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018