Wells – Processes – Material placed in pores of formation to treat resident...
Reexamination Certificate
2000-08-22
2002-10-15
Bagnell, David (Department: 3672)
Wells
Processes
Material placed in pores of formation to treat resident...
C166S235000
Reexamination Certificate
active
06464007
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to gravel packing a wellbore and in one of its aspects relates to a method and well tool for gravel packing a long interval within a wellbore using a low viscosity fluid wherein a good distribution of gravel is achieved across the entire interval.
BACKGROUND
In producing hydrocarbons or the like from loosely consolidated and/or fractured subterranean formations, it is not uncommon to produce large volumes of particulate material (e.g. sand) along with the formation fluids. As is well known, these particulates routinely cause a variety of problems and must be controlled in order for production to remain economical. Probably the most popular technique used for controlling the production of sand from a producing formation is one which is commonly known as “gravel packing.”
In a typical gravel pack completion, a screen or the like is lowered into the wellbore and positioned adjacent the interval of the well which is to be completed. Particulate material, collectively referred to as “gravel,” is then pumped as a slurry down a workstring and exits above the screen through a “cross-over” or the like into the well annulus around the screen. The liquid in the slurry is lost into the formation and/or through the openings in the screen thereby resulting in the gravel being deposited or “screened out” in the annulus around the screen. The gravel is sized so that it forms a permeable mass or “pack” between the screen and the producing formation which, in turn, allows flow of the produced fluids therethrough and into the screen while substantially blocking the flow of any particulate material therethrough.
A major problem associated with gravel packing, especially where thick or inclined production intervals are to be completed, is insuring good distribution of gravel throughout the completion interval. That is, if gravel is not distributed over the entire completion interval, the gravel pack will not be uniform and will have voids therein which reduces its efficiency. Poor distribution of gravel across an interval is often caused by the premature loss of liquid from the gravel slurry into the formation as the gravel is being placed. This loss of fluid can cause “sand bridges” to form in the annulus before all of the gravel has been distributed within the annulus. These bridges block further flow of the slurry through the well annulus thereby preventing the placement of sufficient gravel (a) below the bridge for top-to-bottom packing operations or (b) above the bridge, for bottom-to-top packing operations.
Recently, well tools have been developed which provide a good distribution of gravel throughout the desired interval even where sand bridges form in the annulus before all the gravel has been deposited. These tools (e.g. well screens) include a plurality of “alternate flowpaths” (e.g. shunts or perforated conduits) which extend along the screen and receive gravel slurry as it enters the wellbore annulus. If a sand bridge forms before all of the gravel is placed, the slurry will by-pass the sand bridge and will flow out through the shunt conduits to different levels within the annulus to thereby complete the gravel packing of the annulus above and/or below the bridge. For complete details of such well tools; see U.S. Pat. Nos. 4,945,991; 5,082,052; 5,113,935; 5,515,915; and 6,059,032; all of which are incorporated herein by reference.
Well tools having alternate flowpaths such as those described above have proved successful in completing relatively thick wellbore intervals (i.e. 100 feet or more) in a single operation. In such operations, the carrier fluid in the gravel slurry is typically comprised of a highly-viscous gel. However, it is often advantageous to use low-viscosity fluids (e.g. water, thin gels, or the like) as the carrier fluid for the gravel slurry since such slurries are less expensive, do less damage to the producing formation, give up the gravel more readily than do those slurries formed with more viscous gels, and etc.
Unfortunately, however, the use of low-viscosity slurries may present some problems when used in conjunction with “alternate path” screens for gravel-packing long intervals of a wellbore. This is primarily due to the low-viscosity, carrier fluid being prematurely “lost” through the spaced outlets (i.e. perforations) in the shunt tubes thereby causing the shunt tube(s), themselves, to “sand-out” at one or more of the perforations therein, thereby blocking further flow of slurry through the blocked shunt tube. When this happens, there can be no assurance that slurry will be delivered to all levels within the interval being gravel packed.
SUMMARY OF THE INVENTION
The present invention provides a method and a well tool for gravel packing a completion interval within a wellbore which provides for a good distribution of gravel across the interval while using a gravel slurry having a low-viscosity carrier fluid, e.g. water. Basically, the gravel packing tool of the present invention is comprised of a well screen which has at least one alternate flowpath which extends along the screen. The alternate flowpath is initially closed to flow by a valve means which is adapted to open at a predetermined pressure. When a sand bridge forms in the annulus adjacent the completion interval, the pressure on the pumped slurry increases to open the valve means to thereby allow the slurry to flow through the alternate flowpath to complete the gravel packing of the completion interval.
More specifically, the gravel pack tool is comprised of a screen which is positioned adjacent the completion interval by a workstring. Preferably, a plurality of alternate flowpaths (i.e. unperforated or blank shunt tubes) of different lengths are positioned along the screen. Each of the tubes is open at its upper end to form an inlet and is open at its bottom end to form an outlet. A valve means, e.g. rupture disk, check valve, etc., is positioned at the inlet of each tube to initially block flow therethrough. Each of the valve means is adapted to open at a different pressure so that the tubes will be opened sequentially as successive sand bridges are formed in the annulus which, in turn, cause the pressure on the pumped slurry to increase in the annulus.
By providing shunt tubes of different lengths and having only one outlet (i.e. open lower end), blank shunt tubes (i.e. unperforated along their lengths) can be used to deliver slurry to different levels within the completion interval. By being able to use blank shunt tubes, the risk of a particular tube “sanding-out” at a spaced outlet along its length is alleviated. Further, by initially closing each tube to flow, flow of the low-viscosity fluid through a particular shunt tube will only occur after a sand bridge has been formed in the annulus and the pressure of the slurry in the annulus has substantially increased. This results in a higher flowrate through the now-open shunt tube which is highly beneficial in keeping the gravel suspending in the low-viscosity carrier fluid as the slurry flows through the tube.
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Bagnell David
ExxonMobil Oil Corporation
Gay Jennifer H
LandOfFree
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