Liquid and pressure communication between a formation and a wellbore is often established or enhanced by perforation tunnels in the formation. Perforation tunnels are traditionally made using shaped charges of chemical explosives that inject a material into the formation, creating the tunnel.
In conventional perforating, the explosive nature of the process shatters sand grains of the formation. A layer of “shock damaged region” having a permeability lower than that of the virgin formation matrix is typically formed around each perforation tunnel. The process may also generate a tunnel full of rock debris mixed in with the perforator charge debris. The shock damaged region and loose debris in the perforation tunnels are known to impair the productivity of production wells, or the injectivity of injector wells, and hence negatively impact upon the flow of liquids between the formation and the well.
The peak pressure exerted by an explosive shape charge is typically in the magnitude of 10k’s MPa, while only in the range of 10’s to 100’s MPa when exerted by the “qWave Pulser” technique. Therefore, the use of focused acoustic shock waves will cause significantly less damage to the formation, compared to using shaped explosive charges, while still exerting sufficient energy for a gradual, and gentle, excavation of new perforation tunnels. The relatively low energy excavation implies that the virgin permeability of the formation will not be compromised. Optionally keeping the wellbore in an underbalanced condition during all or parts of the perforation operation, and/or creating the perforation tunnels with an upwardly inclination may ensure cleaning of debris out from the perforation tunnels, having the advantage that debris will not impair the propagation of subsequent shock waves into the perforation tunnel thus leading to a more efficient excavation of the perforation tunnel.
Areas of Application
- Open hole perforation of water injection wells in hydrostatic pressure reservoirs: I.e. little to no option to backflush the formation prior to start of injection.
- Open hole perforation – production wells: For improved/enhanced fluid and pressure communication, especially in low permeability reservoirs, by generating tunnels/perforations bridging the area with drilling induced formation damage prior to setting lower completion, sand screens etc.
- Cased hole perforation: To perforate a cased hole section using the “qWave Pulser” technique would required the pre-step of a casing cutting member (such as a high energy laser, plasma cutting, water jet, mechanical tool etc.), to penetrate the steel casing, prior to using the “qWave Pulser” technique to generate a tunnel through the cement and into the formation.