Multi-layer well screen

Abstract

This is a special downhole multi-layer sand screen for oil and other fluids containing sand. The preferred embodiment of the sand filter includes an outer screen, an intermediate screen and an inner screen although another embodiment may have only an outer and an inner screen. The outermost screen is of larger spacing to retain only the coarser sand particles and the openings in the inner two screens are progressively smaller to retain the less coarse sand material. The coarser sand particles bridge about the larger openings in the outer screens and progressively finer sand materials bridge across the intermediate and inner screens.

We claim:  .[.1. A sand screen filter assembly for use in a well bore which comprises: 
     
        .Iadd. .  A sand screen filter assembly for use in a wellbore which comprises: a slotted section of pipe;   a first layer of wire screen concentrically positioned about said pipe and having a fixed spacing "c" between wires of said first layer;   a second layer of wire screen positioned about and spaced from said first layer and having fixed spacing "b" between wires of said second layer, said spacing "b" being greater than said spacing "c";   a third layer of wire screen positioned about and spaced from said second layer and having a spacing "a" between wires of said third layer, said spacing "a" being greater than said spacing "b";   a plurality of longitudinal rods secured between and to said layers of wire screens to give fixed radial spacing with such spacing having no filtering material therein; and   the radial distance between said first layer and said second layer of wire screen is at least as great as said spacing "b" and the radial distance between said second and third layers of wire screen is at least as great   
     
     
        as said spacing "a". .Iaddend. .Iadd.10.  A sand screen filter assembly for use in a wellbore which comprises: a slotted section of pipe;   a first layer of wire screen concentrically positioned about said pipe and having a fixed spacing "c" between wires of said first layer;   a second layer of wire screen positioned about and spaced from said first layer and having a fixed spacing "b" between wires of said second layer, said spacing "b" being greater than said spacing "c";   a third layer of wire screen positioned about and spaced from said second layer and having a spacing "a" between wires of said third layer, said spacing "a" being greater than said spacing "b";   a plurality of longitudinal rods secured between and to said layers of wire screens to give fixed radial spacing with such spacing having no filtering material therein; and   said spacing "a" is equivalent to a mesh size capable of capturing approximately 50% wt. of formation sand, said spacing "b" is equivalent to a mesh size capable of capturing approximately 20% wt. of formation sand, and said spacing "c" is equivalent to a mesh size capable of capturing   
     
     
        approximately 5% wt. of formation sand..Iaddend. .Iadd.11.  A sand screen filter assembly as in claim 9 wherein said spacing "a" is equivalent to a mesh size capable of capturing approximately 50% wt. of formation sand, said spacing "b" is equivalent to a mesh size capable of capturing approximately 20% wt. of formation sand, and said spacing "c" is equivalent to a mesh size capable of capturing approximately 5% wt. of formation sand.