A new and superior gravel packing method called ALLPAK, for alternate path gravel packing, is reported here. It has been found that gravel packing problems associated with formation of sand bridges in the annulus outside the screen can be eliminated by adding alternate flow paths for slurry flow. The alternate paths are provided by perforated shunts or secondary piping placed provided by perforated shunts or secondary piping placed in the annulus, usually by attaching the tubes to the screen. Laboratory gravel pack simulator tests indicate that essentially complete annulus packs can always be obtained, even in cases where current methods provide very poor pack efficiencies. This paper describes the laboratory pack efficiencies. This paper describes the laboratory experiments and field tests which verify the advantages from this new concept.
A new completion method is described which solves the classical problem of sand bridging in conventional gravel packing. Provision of properly designed alternate slurry flow paths, through shunts or secondary piping placed in the annulus, eliminates almost all of the voids placed in the annulus, eliminates almost all of the voids seen with common gravel packing procedures. The results from laboratory testing done on a 30-ft full-scale gravel pack simulator indicate 95–100% gravel pack efficiencies pack simulator indicate 95–100% gravel pack efficiencies as compared to 65–80% obtained with conventional procedures, where both efficiencies are estimated by visual procedures, where both efficiencies are estimated by visual observations. In addition to providing superior gravel packs, the new method, called ALLPAK, for alternate packs, the new method, called ALLPAK, for alternate path gravel packing, also permits wider ranges in slurry path gravel packing, also permits wider ranges in slurry rheology and pumping rates. Field test results from U.S. Gulf Coast offshore wells validate and extend the laboratory observations.
The classical problem in gravel packing occurs when premature sand bridges form in the annulus between the sand retainer screen and the casing wall, for an in casing gravel pack, or the formation, for an open-hole gravel pack. The bridges usually form either at the top of the screen or adjacent to zones of higher permeability. Once a bridge forms, slurry flow past that point ceases, leaving an incomplete pack below the bridge.
Many mechanical variations for gravel packing apparatus have been developed or proposed for avoiding sand bridging, and a large body of literature exists reporting studies of the effects of gravel packing variables such as fluid rheology, pumping rates, sand density and concentration, etc. However, major problems still exist, especially where long intervals and/or highly deviated wells are involved.
This work describes apparatus and methodology for alternate path gravel packing which can eliminate bridging problems. The key to the new approach is the addition problems. The key to the new approach is the addition of alternate paths for slurry flow adjacent to the screen. These could either be inside or outside the screen, although the mechanical assembly is much simpler if the alternate paths are placed in the annulus. The alternate paths consist paths are placed in the annulus. The alternate paths consist of small separate tubes or pipes attached to the screen and perforated with small holes every few feet. Slurry can perforated with small holes every few feet. Slurry can either be injected directly into the tubes, or the tubes can be left open at the top of the annulus to act only as shunts.
Currently, our preferred arrangement is the shunt configuration because this permits running screens and placing gravel packs with little change from conventional placing gravel packs with little change from conventional equipment and procedures. Figures 1 and 2 illustrate the concept.