Field Performance of the Double-Wall Multicell Liner
Authors: Richardson Robert L. 
Published: December 2007

Abstract
The unique double-wall, multicell construction of the Fether liner incorporates many features not possible with the conventional single-wall, straight liner. These features provide assurance of getting the liner in place without plugged perforations, added support to the wall of the hole and greater resistance to collapse. The staging of production flow through two sets of large perforations provides control over excessive sand production. The Fether liner has been used to advantage in two areas of severe sand and liner problems, the Sisquoc at East Cat Canyon and the Ventura Avenue D-8 zone. The history of these two areas and their related production problems show that sustained production cannot be obtained with conventional liners or variations of straight-wall liners involving gravel and sand packs. The considerable reduction of sand content in Fether liner completions at East Cat Canyon has made possible the recovery of oil from an area where production formerly could not be economically sustained. At Ventura Avenue in the D-8 zone, where 80 per cent of the wells have required re-drilling due to liner failures, the Fether liner is out-performing previous liner types.

Introduction
The completion of oil wells has a long and varied history. First came early "barefoot" completions, then ripped casing and star perforators through round holes, inserts, slots, undercut slots, wire wraps, prepacks and float packs with gravel, sand, glass beads and plastic-coated walnut shells. The much-sought-after ideal behind each new device in this long history has been the desire to obtain maximum oil production with a minimum of sand. Oilwell liners are referred to in our literature as "oil-well screens" or "screen pipe" and appropriately so. The proper mesh for liners has long been a function of the grain size and distribution of the sand to be kept from entering the well. Prepacked and float-packed liners are filters which provide a physical restriction to screen out sand. This paper presents a discussion of the design and added features of a new concept in oilwell liners which does not depend on positive restrictions for sand control the Fether liner. The performance of this liner in several of California's most difficult areas is also summarized.

Design
The Fether liner was designed by Don Fether some six years ago. As a manufacturer of brake lining for the automotive and oil industries, Fether acquired a basic understanding of frictional forces. The Fether liner was designed to make use of the frictional characteristics of sand and the basic design does not incorporate mechanical screening. Recommended perforation sizes are 180 and 200 mesh, hardly capable of screening. Reference to Fig. 1, a cut-away section of the Fether liner, shows its unique construction. Conventional tubular stock makes up the straight inner wall of the liner. Onto this straight stock are placed convexed forged shapes resembling opposed bells of minimum diameter on each end and maximum diameter at the center. They are placed continuously along the length of the joint and, regardless of the outside diameter of the straight stock, are always 8-in. long with a maximum diameter 2-in. greater than the straight stock. The welding of these shapes both to the straight stock and to each other provides the multicell construction. Prior to assembly, the straight tubular stock is perforated with 200-mesh, 2-in. slots and 4-in. centers. The number of rows is governed by the pipe size. Although not readily apparent in the cut-away section, Fig. 2 shows the pattern of perforations in the convex outer shapes which are perforated only on their top reclining surface. These perforations are 180-mesh 2-in. slots on 8-in. centers, with the same number of rows, but they laterally offset from those on the inside wall. This construction provides several features which are not possible with straight-wall liners, including:added resistance to collapse from the truss-like construction,protection to the perforations against plugging while running in,added support to the wellbore by the convex outer shapes andstaging of the production through two sets of perforations.
Increased resistance to collapse is provided by the outer bell shapes.
JPT
P. 483^