Well screen

A well screen is disclosed for positioning in a well bore to screen solid particles from the fluid produced by the well comprising a base pipe, a portion of the wall of which is perforated, and having threaded connections for connecting the base pipe into a pipe string, a wire screen surrounding the perforated portion of the base pipe, a thin porous membrane comprising two layers of woven cloth of ceramic fibers wrapped around the wire screen, means for holding the ends of the porous cloth membrane in sealing engagement with the base pipe, and a perforated tubular metal shroud surrounding the woven ceramic cloth membrane to protect the membrane from damage when lowered into a well bore.

This invention relates to well screens generally, and in particular, to 
well screens using thin, porous, flexible, membranes to screen solid 
particles from the well fluids flowing through the screens into a well 
bore. 
Recently Pall Well Technology came on the market with a new well screen 
under the trademark STRATA.TM. DOWNHOLE MEMBRANES. The screen includes 
an inner perforated base pipe covered by a drainage mesh, which, in turn 
is covered by four layers of Pall PMM.RTM. medium, which is described as 
being stainless steel powder sintered with a pore structure of stainless 
steel woven wire mesh. This screen is described in U.S. Pat. No. 
4,436,635, issued Mar. 13, 1984, entitled "Porous Metal Article and Method 
of Making". 
Also, U.S. Pat. No. 4,858,691, which issued Aug. 22, 1989 and is assigned 
to Baker Hughes Incorporated, describes a well screen that employs a wire 
mesh of woven metal wire positioned between a perforated inner tubular 
member and either a wire wrapped screen or a perforated cylindrical 
member. 
It is an object and feature of this invention to provide an improved thin 
porous, flexible membrane for use in well screens to remove all but the 
smallest of particles from the well fluid flowing through the membrane and 
a well screen that includes such a membrane. 
A further object and feature of this invention is to provide an improved 
well screen that employs, as such a porous membrane, a cloth made by 
weaving fibers of inert material. 
It is another object and feature of this invention to provide a well screen 
that includes a layer of woven fibers of inert material to provide a 
porous membrane that will screen extremely fine particles from the fluid 
flowing into a well bore. 
A further object and feature of this invention is to provide a porous 
membrane for use as a component of a well screen that consists of an 
elongated cloth woven from continuous ceramic fibers of 
alumina-boria-silica that is wrapped around a supporting screen for 
assembly in a well screen. 
It is another object and feature of this invention to provide a tubular 
screen for use in oil, gas, and water wells that includes a porous 
membrane comprising two layers of cloth made of woven ceramic threads that 
are wrapped around a metal supporting screen. 
It is a further object and feature of this invention to provide such a 
porous membrane where the edges of each wrap overlap and the overlaps of 
each layer are spaced apart. 
These and other objects, advantages, and features of this invention will be 
apparent to those skilled in the art from a consideration of this 
specification, including the attached drawings and appended claims.

The well screen of FIG. 1 includes base pipe 10 having a section between 
box 12 attached to one end and pin 14 at the other end that is provided 
with a plurality of spaced perforations 16. Formed around base pipe 10 is 
a conventional screen formed by wrapping wire around the outside of the 
base pipe. In the particular embodiment shown, the screen is a wire-based 
screen that includes a plurality of spaced parallel rods 18 that extend 
longitudinally along the outside of the base pipe around which 
trapezoidal-shaped wire 20 is wrapped in spaced coils. The wire is welded 
to the rods in accordance with the method taught in U.S. Pat. No. 
4,314,129 that issued Feb. 2, 1982 to Wilson, et al. and is assigned to 
the assignee of this application. 
In accordance with this invention, the rod base screen is covered by a 
porous membrane 22 made up of two wraps of ceramic cloth 24 and 26 made of 
woven fibers of ceramic material, such as alumina-boria-silica fibers. The 
cloth is applied to the well screen at an angle for pore openings and 
strength in case the screen collapses in a downhole situation. This 
configuration also enables flow after collapse. 
All edges of each wrap of the woven ceramic cloth overlap, as shown in FIG. 
3. The second layer of woven ceramic cloth 26 is wrapped with overlap 26a 
staggered from overlap 24a of an inner layer of woven material 24 to 
assure complete coverage without coinciding laps of the first and second 
layers. All fluid entering the base pipe must travel through the porous 
woven cloth so that all fluid entering the base pipe will have most of the 
solid particles screened from it by the cloth. The ends of the two layers 
of ceramic cloth are secured to the base pipe by clamps 30 and 32, as 
shown in FIG. 3. 
To protect the ceramic cloth from damage as the screen is handled at the 
surface and as it is run into the well bore, outer shroud 34 is positioned 
over the woven ceramic cloth sleeves. The shroud is mounted on the base 
pipe and attached to the base pipe by welds 38 and 40, which connect the 
shroud to mounting rings 42 and 44. The shroud is a tubular member in 
which louvers 46 are formed to allow fluid from the producing formation to 
flow from the well bore through the shroud and then to pass through layers 
24 and 26 of woven ceramic cloth where all but the smallest solid 
particles are screened from the fluid before it enters perforated base 
pipe or mandrel 10. In the embodiment shown, the louvers are spaced along 
a line diagonal to the longitudinal axis of the base pipe. 
Flow tests were performed on the screen of this invention by independent 
testing companies. Sand retention tests resulted in a rating of 80 
microns. Permeabillity was determined to be 39.82 Darcy with the pressure 
drop across the screen at a flow rate of 140 bpd/ft. at 1.68 psi. 
The screen tested comprised a base pipe (10) of 27/8" O.D., 6.4 lb/ft. 
tubing with an I.D. of 2.441". The inner screen included spaced parallel 
rods (18), 0.060" in diameter, and wire (20), trapezoidal in cross-section 
and 0.060" in height, wrapped around the rods, two layers of woven ceramic 
cloth having an O.D. of 3.195" stretched over rod based screen 18, and 
louvered outer shroud (34) having an O.D. of 3.595". 
From the foregoing it will be seen that this invention is one well adapted 
to attain all of the ends and objects hereinabove set forth, together with 
other advantages which are obvious and which are inherent to the apparatus 
and structure. 
It will be understood that certain features and subcombinations are of 
utility and may be employed without reference to other features and 
subcombinations. This is contemplated by and is within the scope of the 
claims. 
Because many possible embodiments may be made of the invention without 
departing from the scope thereof, it is to be understood that all matter 
herein set forth or shown in the accompanying drawings is to be 
interpreted as illustrative and not in a limiting sense.