| 摘要 |
1. A casing assembly (20) for a well, the casing assembly comprising: an essentially cylindrical inner pipe (22) extending along a casing axis (25) for the entire length of the casing assembly, the inner pipe having a series of perforations (40) formed through its surface along a first length segment (42) of the casing axis; an essentially cylindrical outer member (24) radially spaced from and concentrically located about the inner pipe (22) and also extending along the casing axis (25), the outer member having a series of perforations (50) formed through its surface along a second length segment (52) of the casing axis; a screen (60) mounted over an outer circumferential surface of the inner pipe and over the series of perforations (40) formed on the inner pipe; wherein the first length segment (42) and the screen (60) mounted over its surface and the second length segment (52) along the casing axis are substantially offset with respect to one another, characterized in that an open annular space is formed between the outer member (24) and the inner pipe (22) whereby fluid entering the perforations (50) in the outer member will flow in an axial direction (70,70') in a substantially unobstructed manner through said open annual space and then through said screen (60) with lessened force and greatly reduced velocity and ' through the series of perforations (40) on the inner pipe (22) which underlie the screen. 2. The casing assembly of claim 1, wherein the first length segment (42) and the second length segment (52) are substantially non-overlapping. 3. The casing assembly of claim 1, further comprising at least one flow control member (80) located in an annular space formed between the outer member (24) and the inner pipe (22) at one end of the screen (60), said at least one flow control member having apertures (82) therein for allowing fluid to flow in said axial direction (70, 70') from the first length segment to the second length segment. 4. The casing assembly of claim 3, wherein the open flow areas of said apertures (82) are less than the open cross-sectional area of said annular space which is upstream of said at least one flow control member (80) so as to produce a pressure drop which will tend to even out the flow of fluid reaching the screen (60), thereby further protecting the screen from erosion. 5. The casing assembly of claim 1, wherein each end of the inner pipe (22) has means (22') thereon to permit the casing assembly (20) to be attached to another casing assembly. 6. The casing assembly of claim 1, wherein the series of perforations (40) formed along the first length segment (42) of the inner pipe (22) are positioned in a middle portion of the length of the inner pipe and the series of perforations (50) which are formed through the outer member (24) along the second length segment (52) of the casing axis (25) are positioned at one end of the length of the outer member, said outer member (24) further having an additional series of perforations (50) along a third length segment (52') which is positioned at a second end of the outer member. 7. The casing assembly of claim 6, wherein the first length segment (42), the second length segment (52) and the third length segment (52') are substantially non-overlapping. 8. The casing assembly of claim 7, wherein the first length segment (42) has an axial length substantially equal to the combined length of the second length segment (52) and the third length segment (52'). 9. The casing assembly of claim 7, further comprising a pair of flow control members (80) located in annular spaces formed between the outer member (24) and the inner pipe (22) at each end of the screen (60), said flow control members having apertures (82) therein for allowing fluid to flow in said axial direction (70,70') from the second length segment (52) and the third length segment (52') to the first length segment (42). 10. The casing assembly of claim 1, wherein the screen is mounted at each of its ends over an outer circumferential surface of the inner pipe (22) by a pair of attachment rings (66) which have an outer portion (67) which is larger in diameter than the outer surface of the screen (60), whereby fluid flow over said rings (66) will be diverted from the surface of the screen (60). 11. The casing assembly of claim 10, wherein each of said attachment rings (66) has an annular recessed portion (68) located under said outer portion (24) which receives and retains one end portion of the screen (60). 12. The casing assembly of claim 10, wherein said screen (60) comprises a plurality of longitudinally extending support rods (62) over which a profiled wire (64) is helically wrapped and welded at every intersection. |
