Wells – Means for forming filter beds
Reexamination Certificate
1999-08-19
2001-04-24
Schoeppel, Roger (Department: 3672)
Wells
Means for forming filter beds
C166S233000, C166S236000, C166S278000
Reexamination Certificate
active
06220345
ABSTRACT:
DESCRIPTION
1. Technical Field
The present invention relates to a well screen and in one of its aspects relates to a well screen for fracturing/gravel packing a well having an internal, alternate flowpath which, in turn, is formed between the aligned, blank sectors of two pipes.
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, especially when the formation has been fractured to improve flow therefrom. This sand production 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 within the well annulus to form a permeable mass around the screen. This gravel (e.g. sand) is sized to allow the produced fluids to flow therethrough while blocking the flow of most particulate material into the screen.
A major problem in fracturing/gravel packing a well-especially where long or inclined intervals are to be completed lies in adequately distributing the fracturing fluid/gravel slurry (hereinafter referred to as “gravel slurry”) over the entire completion interval. That is, in order to insure an adequate “frac-pac” of a long completion and/or inclined interval, it is necessary for the gravel slurry to reach all levels within that interval. Poor distribution of the gravel slurry throughout the interval (i.e. along the entire length of the screen) typically results in (a) only a partial fracturing of the formation and (b) a gravel pack having substantial voids therein.
Poor distribution of the gravel slurry is often caused when carrier fluid from the slurry is lost prematurely into the more permeable portions of the formation and/or into the screen, itself, thereby causing “sand bridge(s)” to form in the well annulus around the screen before the formation has been adequately fractured and all of the gravel has been placed. These sand bridges effectively block further flow of the gravel slurry through the well annulus thereby preventing delivery of gravel to all levels within the completion interval.
To alleviate this problem, “alternate-path” well tools (e.g. well screens) have been proposed and are now in use which provide for the good distribution of gravel throughout the entire completion interval even when sand bridges form before all of the gravel has been placed. Such tools typically include perforated shunts or by-pass conduits which extend along the length of the tool and which are adapted to receive the gravel slurry as it enters the well annulus around the tool. If a sand bridge forms before the operation is complete, the gravel slurry can still be delivered through the perforated shunt tubes (i.e. “alternate-paths”) to the different levels within the annulus, both above and/or below the bridge. For a more complete description of a typical alternate-path well screen and how it operates, see U.S. Pat. No. 4,945,991, which is incorporated herein by reference.
In many prior-art, alternate-path well screens of the type described above, the individual shunts tubes are carried externally on the outer surface of the screen; see U.S. Pat. No. 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 lies in the fact that the shunts are 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 fracturing/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 can make the construction of such screens more sophisticated, if not more complicated, which, in turn, normally results in substantially higher production costs.
Recently, another alternate-path screen is disclosed and claimed in co-pending and commonly assigned, US patent application Ser. No. 09/290,605, filed Apr. 13, 1999 which simplifies the construction of a screen having an internal alternate flowpath. The screen disclosed therein is comprised of two concentric pipes, i.e. an inner base pipe and an outer pipe. A portion of the annulus which is formed between the two concentric pipes provides the alternate flowpath(s) for conveying gravel slurry to different levels within the completion interval.
Dividers (e.g. ribs) extend longitudinally within the annulus between the pipes to separate the alternate flowpath portion of the annulus from a perforated, production portion of the annulus. The outer surface of the outer pipe is wrapped with wire or the like to prevent sand from flowing into the production portion of the annulus. Openings are longitudinally-spaced along the outer pipe to provide outlets for the alternate flowpath whereby gravel slurry can be delivered from the alternate flowpath to different levels within the completion interval.
SUMMARY OF THE INVENTION
The present invention provides still another well screen which has an internal, alternate flowpath for delivering fracturing fluid/gravel slurry to different levels within a well annulus during a fracturing/gravel pack or “frac-pac” operation. The delivery of gravel directly to several different levels within the well annulus provides a much better distribution of the 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 the handling and installation of the screen and does not increase the effective diameter of the screen.
More specifically, the well screen of the present invention is comprised of a larger-diameter, outer pipe which is positioned over a base pipe whereby an annulus (e.g. preferably less than about one inch in width) is formed between the two pipes. Preferably, the pipes are substantially concentric but in some instances they may be positioned slightly off-center wherein the annulus is slightly larger on one side than the other. The circumference of each pipe has a perforated sector (i.e. sector having openings therein) which subtends a central angle of “&agr;” and a blank sector (i.e. sector which is devoid of openings) which extend along the lengths of the respective pipes. When the well screen is assembled and the base pipe is positioned within the outer pipe, the respective perforated sectors are radially aligned to form a perforated, production sector within the annulus between the pipes and the respective blank sectors are radially aligned to form a blank, alternate flowpath sector within the annulus.
The base pipe is wrapped with wire to allow the flow of fluids through the openings in the base pipe while blocking the flow of solids therethrough. An inlet is provided through the upper end of the annulus to allow gravel slurry to flow into the annulus between the pipes. The slurry flows into the blank, alternate flowpath sector of the annulus but, since there are no openings in this sector, the slurry can not e
Hurst Gary D.
Jones Lloyd G.
Tibbles Raymond J.
Mobil Oil Corporation
Schoeppel Roger
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