Integrating Propellant and Shaped Charges to Improve Frac Efficiency

Abstract

Current perforating guns utilize shaped charges with high energy explosives (RDX, HMX, etc.) to shoot high velocity jets of metal in a direction that is perpendicular to the gun body (and casing), thus creating holes in casing and tunnels through cemented annulus and formation. The physics of shaped charge perforating (high velocity jet of metal penetrating casing and formation) results in a crushed zone of rock around the perforation tunnel. Rock crushing increases skin and lowers permeability in the near wellbore region, making formations more difficult to breakdown and increasing treating pressures. There have been many methods developed to overcome the perforation crushed zone and improve flow efficiency. These methods include underbalance, overbalance, propellants, charge orientation and reactive shaped charge liners. Propellants (energetic materials with slower burn rates than explosives shaped charges) have been utilized in a number of methods to create a delayed pressure pulse to break-up the crushed zone around perforation tunnels. Propellants have been added as solid sleeves over guns, solid sticks ignited across open sets of perforations and propellant discs within gun bodies. With each of these techniques, propellant is located within the wellbore when it burns, thus the pressure pulse builds within the casing and then flows into perforation tunnels. As the pressure pulse moves into perforations, it can disrupt the tunnel crushed zone and create fractures. The net effect is lower skin and improved perforation efficiency. Unfortunately, by burning propellant within the casing, the efficiency of the pressure pulse is reduced. To tackle the challenges above, a new method is proposed to place propellant in a molded cap that attaches to the face of individual shaped charges. This new method results in jets produced by shaped charges dragging the propellant material behind the high velocity jet as it penetrates casing, cement annulus and formation. As a result, most of the propellant burns sequentially within the perforation tunnel, thus delivering direct continuum pressure pulse to the perforating event. The propellant provides a secondary stream of energy, enlarging the perforation tunnel diameter, cleaning up the perforation tunnel and giving impetus to the shaped charge jet, resulting in deeper penetration. The result is very effective and efficient in disrupting crushed zones and creating fractures around the perforation tunnel.