Wells – Means for forming filter beds
Reexamination Certificate
1999-02-08
2001-01-23
Bagnell, David (Department: 3672)
Wells
Means for forming filter beds
C166S276000, C166S278000
Reexamination Certificate
active
06176307
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to underground well completion devices and processes. More specifically, the invention is concerned with an improved tool and method for gravel packing an underground well.
BACKGROUND OF THE INVENTION
When drilling and completing a well in an underground formation, a fluid or fluid-like substance having a density greater than water is typically used, e.g., a heavy weight drilling mud and water mixture. The dense mixture produces overbalanced hydrostatic pressures (i.e., pressures in excess of the formation pore pressures) in the well, e.g., to help prevent wellbore wall caving, to consolidate loose formations, or to control well pressure by minimizing the risk of excessive gas from the formation entering the wellbore.
However, the dense mixture tends to intrude into permeable portions of the formation, such as a productive interval. This intrusion can damage the productive interval, e.g., penetration of a water-based drilling fluid into a clay-containing formation can cause swelling and a loss of permeability. Damage to a productive interval may only be shallow (e.g., “skin” damage) and relatively easy to correct, but the damage may also be more extensive and permanent.
In a conventional well completion that includes a gravel pack (e.g., for sand control of a productive formation), a viscous as well as dense fluid (such as brine) may be used to entrain gravel particles and carry the stabilizing particles as a slurry into the face of the sandy formation to form the gravel pack. But the entraining fluid may cause further damage to the formation. Fluid loss control measures may also be required during a conventional gravel packing process, e.g., adding LCM “pills” or other fluid additives to control lost circulation when using a work string and backflushing tools to remove excess sand or gravel slurry. Coiled tubing and associated tools may also have to be run and nitrogen injected through the coiled tubing to bring a conventionally gravel packed well into production, adding still more risk of formation or other damage.
Significant costs are typically required for a drilling rig or other well intervention unit to be on-site during a conventional gravel packing process. The rig is typically used periodically throughout the conventional gravel packing process, e.g., to place, support, reposition, activate, and/or remove gravel packing tools downhole. The rig may be required to be on-site for many days during a conventional gravel packing process.
Use of a rig allows one or more packers attached to a work string to isolate a productive interval or zone during gravel packing. The isolated zone and work string allow a pressurized, but less dense fluid to be used to entrain the sand or gravel without exposing other portions of the wellbore to the pressurized fluid. But backflushing steps and means for removing excess slurry are typically required when a packer is used. In addition, placing, backflushing, and removing packers and other tools add costly rig time and entail other damage risks.
SUMMARY OF THE INVENTION
Such added rig costs and damage risks of gravel packing a productive wellbore interval are minimized by using a gravel packing assembly attached to a production tubing string that can be used without a rig after it is placed in a well. One embodiment of the inventive assembly uses an upper axial-flow plug to divert a pumped-down slurry from the interior of the production tubing to an annulus through a radial-flow port located above the upper axial-flow plug, and allow some of the entraining fluid portion of the slurry in the annulus to enter an interior passage through a first radial-flow screen located below the upper axial-flow plug. Initially, a lower axial-flow plug located below the first radial-flow screen prevents the flow of screen-separated entrainment fluid through the interior passage to a second radial-flow screen located below the second plug proximate to a productive interval. But when slurry continues to be pumped downhole and sufficient slurry particles are de-entrained in the annulus proximate to the productive interval, the resulting axial differential pressure across the de-entrained particles is transmitted through the screens and ruptures the lower plug, allowing screen-separated entrainment fluid to flow out of the second radial-flow screen and excess slurry to be displaced by a displacement fluid before the first plug is ruptured and formation fluids produced.
In addition to avoiding the need for a rig after emplacing the apparatus, the inventive process also avoids the need for a work string. Still further, the inventive process clears the production tubing of excess or residual sand slurry without the need for complex process steps to backflush or reverse the pumped slurry flow.
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Danos Joe C.
Schmalz Arlen R.
Bagnell David
Dougherty Jennifer R
Jacobson William O.
Union Oil Company of California
Wirzbicki Gregory F.
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