Murphy Montney has been implementing downhole chokes in a variety of successful applications that have resulted in both significantly improved well performance and facility equipment/chemical cost savings. The specific applications piloted have included:
Mitigating Sand Plugging
Surface Hydrate Elimination
The observed reservoir performance improvement and mitigation of downhole sand plugging is the result of minimizing the net pressure condition created within the induced fracture network. Restricted well drawdown minimizes the physical loss of the induced stimulation, loss which leads to the downhole plugging situation. In addition, Montney pressure dependent reservoir responses have demonstrated stimulated reservoir volume (SRV) flow capacity and fracture conductivity improvement/maintenance under higher flowing sandface pressure conditions, significantly enhancing the minimum-contacted-gas-in-place (CGIPmin). A conceptual reservoir model whereby early pressure maintenance and long-term pressure management is required to maximize the EUR and long-term production has been developed.
Downhole chokes are being used in lieu of surface line heaters and methanol injection in the mitigation of surface hydrate formation. By moving the point of pressure and temperature reduction downhole, the Joule-Thompson cooling response across the choke is geothermally regulated.
Success has also been observed in liquid unloading applications. Downhole choking can create a choked flow rate Venturi effect, which by definition is based upon a critical upstream to downstream pressure ratio, a function of the gas specific heat relationship. Choked flow accelerates gas to a sonic velocity across the flow restriction, imparting a sufficient velocity head upon an upstream fluid level to carry a water droplet to surface. The acceleration of fluid droplets across the downhole choke is equivalent to an infinite lowering of the liquid loading rate, limited only by the maintenance of the choked flow condition created across the downhole choke.
The downhole choke permits for a controlled and self-regulated drawdown, creating both improved reservoir performance and well operations. Mitigating surface hydrate formation and frac sand flowback has resulted in significant cost savings. A novel application specific to over-pressured reservoirs is the use of downhole chokes in liquid unloading applications, maintaining high flowing sandface pressure conditions while unloading liquid.