Wells – Processes – Assembling well part
Reexamination Certificate
1999-04-13
2001-05-08
Tsay, Frank (Department: 3672)
Wells
Processes
Assembling well part
C166S231000
Reexamination Certificate
active
06227303
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a gravel pack well screen and in one of its aspects relates to (a) a well screen for gravel packing a well which has an internal, alternate flowpath formed between two concentric pipes for delivering gravel slurry to spaced points within the well annulus around the well screen and (b) a method for assembling the screen.
2. Background of the Invention
In producing hydrocarbons or the like from certain subterranean formations, it is common to produce large volumes of particulate material (e.g . . . sand) along with the formation fluids which must be controlled or it can seriously affect the economic life of the well. One of the most commonly-used techniques for controlling sand production is known as “gravel packing”. In a typical gravel pack completion, a screen is positioned within the wellbore adjacent the interval to be completed and a gravel slurry is pumped down the well and into the well annulus around the screen. As liquid is lost from the slurry into the formation and/or through the screen, gravel is deposited around the screen to form a permeable mass around the screen. This gravel is sized to allow produced fluids to flow therethrough but block the flow of any particulate material into the screen.
A major problem in gravel packing—especially where long or inclined intervals are to be completed—lies in adequately distributing the gravel over the entire completion interval, i.e. completely packing the well annulus along the length of the screen. Poor distribution of gravel (i.e. voids in the gravel pack) is often caused when liquid from the gravel slurry is lost prematurely into the more permeable portions of the formation thereby causing “sand bridge(s)” to form in the annulus before all of the gravel has been placed. These sand bridges effectively block further flow of the slurry through the annulus thereby preventing delivery of gravel to all parts of the completion interval.
To alleviate this problem, “alternate-path” well tools e.g . . . well screen) are now in use which provide good distribution of gravel throughout the entire completion interval even when sand bridges form before all of the gravel has been placed. Such tools include perforated shunts or by-pass conduits which extend along the length of the tool and which are adapted to receive gravel slurry as it enters the well annulus around the tool. If a sand bridge forms in this annulus, the slurry can still pass through the perforated shunt tubes (i.e. alternate-paths) to different levels in the annulus above and/or below the bridge. For a more complete description how such well tools (e.g . . . gravel-pack screens) operate, see U.S. Pat. No. 4,945,991, which is incorporated herein by reference.
In many prior-art, alternate-path well screens, the individual shunts tubes are carried externally on the outer surface of the screen; see U.S. Pat. Nos. 4,945,991; 5,082,052; 5,113,935; 5,417,284; and 5,419,394. While this arrangement has proven highly successful, externally-mounted shunts do have some disadvantages. For example, by mounting the shunts externally on the screen, the effective, overall outside-diameter of the screen is increased. This can be very important especially when a screen is to be run into a relatively small-diameter wellbore where even fractions of an inch in its outer diameter may make the screen unusable or at least difficult to install in the well.
Another disadvantage in mounting the shunts externally is that the shunts are thus exposed to damage during assembly and installation of the screen. If the shunt is crimped or otherwise damaged during installation, it can become totally ineffective in delivering the gravel to all of the levels in the completion interval which, in turn, may result in the incomplete packing of the interval. Several techniques have been proposed for protecting these shunts by placing them inside the screen; see U.S. Pat. Nos. 5,341,880, 5,476,143, and 5,515,915. However, this typically makes the construction of such screen more sophisticated, if not more complicated, which, in turn, normally results in substantially higher production costs.
SUMMARY OF THE INVENTION
The present invention provides a gravel-pack, well screen having an internal alternate flowpath for delivering gravel slurry to different levels within a well annulus during a gravel pack operation. The distribution of gravel directly to different levels within the annulus from the internal alternate flowpath provides a better distribution of gravel throughout the completion interval especially when sand bridges form in the annulus before all of the gravel has been placed. By placing the alternate flowpath inside the screen, it is protected from damage and abuse during handling and installation of the screen and does not increase the effective diameter of the screen which normally occurs when external alternate flowpaths are used.
More specifically, the well screen of the present invention is comprised of a larger-diameter, outer pipe which is concentrically positioned over a base pipe whereby an annulus is formed between the two pipes. Both of the pipes have perforations along their respective lengths but only through a radial portion of their respective circumferences which provides each pipe with a respective perforated, radial section and a non-perforated, radial section which, in turn, radially align, respectively, when the pipes are concentrically positioned.
A plurality of ribs are formed onto or are secured to the base pipe and extend longitudinally through the annulus to isolate that portion of the annulus which lies adjacent the perforated sections of the pipes from that portion of the annulus which lies adjacent the non-perforated sections of the pipes. The annulus adjacent the perforated sections forms the production side of the screen while the annulus adjacent the non-perforated section forms the alternate flowpath through the screen.
While at least one outlet is provided through the non-perforated section of the outer pipe, preferably there are a plurality of outlets (preferably with hardened inserts therein) vertically spaced along the length of the non-perforated section of the outer pipe to thereby provide outlets for the gravel slurry to flow from the alternate flowpath into the different levels of the well annulus. The upper and the lower ends of the annulus are closed with plates or the like and an inlet is provided through the upper plate to allow the gravel slurry to flow only into the alternate flowpath side of the screen.
In operation, the screen is assembled and lowered on a workstring down to the production formation within the wellbore. Gravel slurry is pumped down the workstring and out of a cross-over into the well annulus surrounding the screen. As the slurry flows into the well annulus, it also flows through the inlet in the upper end of the annulus and into the alternate flowpath within the screen (i.e. annulus adjacent the non-perforated sections of the concentric pipes). If a sand bridge forms in the well annulus before all of the gravel has been placed in the annulus, slurry can flow through the internal alternate flowpath and out the outlets therein into the different levels of the well annulus to finish gravel packing the completion interval.
Once the gravel pack is complete, the cross-over, etc., is removed and the well is put on production. Fluids, produced from the formation, flow through the gravel pack, the perforations in both the outer pipe and the base pipe, and into the base pipe and then to the surface through a tubing string connected to the base pipe.
REFERENCES:
patent: 4945991 (1990-08-01), Jones
patent: 4964464 (1990-10-01), Myers
patent: 5082052 (1992-01-01), Jones et al.
patent: 5113935 (1992-05-01), Jones et al.
patent: 5330003 (1994-07-01), Bullick
patent: 5341880 (1994-08-01), Thorstensen et al.
patent: 5355949 (1994-10-01), Sparlin et al.
patent: 5394938 (1995-03-01), Cornette et al.
patent: 5419394 (1995-05-01), Jones
patent: 5476143 (1995-12-01), Sparlin et al.
patent: 5505260
Mobil Oil Corporation
Tsay Frank
LandOfFree
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