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CO2 ENHANCED FRACTURING OF GAS SHALES

Summary of a paper by Middleton et al: ‘Shale Gas and Non-Aqueous Fracturing Fluids: Opportunities and Challenges for Supercritical CO2’ (Reference: Applied Energy – June 2015)

Key Points from the paper:

  • CO2 should dramatically increase production while lowering environmental impacts thru the following physical mechanisms;

  • Low viscosity and thermal fracturing creates more complex fractures;

  • Miscibility with hydrocarbons, minimizes flow blockage in small pore networks;

  • Preferential adsorption of CO2 vs. methane in organic rich shales;

  • CO2 sequestration during the fracturing phase (adsorption in organics, dissolution into connate waters);

  • Physical blocking of tight pores and flow channels with water does not occur with CO2.

Primary Gas Storage Sites in Shale

Diagram showing fracturing system showing three primary gas-in-place origins of methane

Primary Gas Storage Sites in Shale

Chart showing production to timeline in years with four different mechanisms

Chart showing production to timeline in years with the same four mechanisms with CO2 fracturing

CO2 Fracturing Enhances Gas Production by 3 Mechanisms:

  • Enhanced fracturing;

  • Preferential desorption;

  • Reduced flow blocking of pores (capillary effects).

5 year cumulative production may be increased by as much as 80%.

Issues with Water Use Solved with CO2 Fracturing

Current concerns with water use in hydraulic fracturing include:

  • Huge volumes of mainly fresh water required for large multi-stage completions (20,000 to 30,000 m3/well);

  • Fresh water availability issues related to drought, public concerns;

  • Treatment and / or disposal of contaminated flow-back water is costly;

  • Induced seismicity has been linked to deep disposal of flow-back water;

  • Potential for fresh water contamination during injection / production phases as well as with water disposal.