A prepack well screen assembly for separating particulate material from formation fluid has inner and outer screens concentrically mounted in radially spaced relation around a perforated mandrel, thereby defining a prepack annulus in which a plurality of spherical plastic members are disposed. The concentric inner screen includes longitudinally extending rib wires spaced circumferentially around the mandrel, and a screen wire wrapped externally about the rib wires in a longitudinally spaced pattern to define spaced screen apertures for conducting formation fluids through the inner screen. The outer screen is a cylindrical fluid-porous, particulate-restricting member which is radially spaced from the inner screen to form the prepack annulus. The particulate-restricting member includes rib wires which are spaced circumferentially around the inner screen within the prepack annulus, and an outer screen wire wrapped externally about the rib wires to define the annulus. The outer screen wire is wrapped about the rib wires in a longitudinally spaced pattern to delineate spaced screen apertures for conducting formation fluids through the outer screen. The spherical plastic members are disposed within the prepack annulus and heated until the spherical plastic members become tacky and bond to each other to form a sintered, homogenous mass.

Sintered spherical plastic bead prepack screen aggregate

A prepack well screen assembly has a resistance welded outer screen concentrically mounted in radially spaced relation on a perforated mandrel, thereby defining an annulus in which a sintered metal prepack sleeve is loaded. The longitudinal spacing distance between adjacent turns of the outer screen selectively exclude sand fines of a predetermined minimum size. The porosity of the sintered metal prepack sleeve is selected to pass sand fines in the size range of from about 10 microns to about 150 microns. The effective inlet flow area through the sintered metal prepack sleeve is substantially greater than the effective inlet flow area through the outer screen. The sintered metal prepack screen excludes sand fines from inflowing formation fluid during the initial production phase following a gravel pack operation, without limiting production of formation fluid.

Sintered metal substitute for prepack screen aggregate

A sand screen having a plurality of sintered, substantially spherical plastic members covering a perforated mandrel is releasably suspended from a packer mandrel by a locking mandrel and a landing nipple. The sand screen and locking mandrel are retrievable with the assistance of a running tool which is insertable into the bore of the locking mandrel. According to this arrangement, the sand screen can be removed and replaced without retrieving the packer or the production tubing. In one embodiment, the sand screen is enclosed within the bore of a sliding side valve. The sliding side valve can be opened and closed as desired for selectively admitting production from various producing zones, or for isolation of a damaged screen. In another embodiment, an auxiliary sand screen having a plurality of sintered, substantially spherical plastic members covering a perforated mandrel is inserted into the bore of a primary screen, for example, a conventional wire-wrap sand screen. The auxiliary sand screen is thus interposed in the flow path for screening out sand fines which may be conducted through the wire-wrap screen because of screen damage caused by corrosion or sand erosion.

Sand screen completion

A process used during manufacture of printed circuit boards comprises protecting metal pads and/or through-holes to provide a tarnish-resistant and solderable coating. In the method, the pads and/or through-holes are bright-etched, metal plated, preferably by an immersion process, and treated with a tarnish inhibitor. The tarnish inhibitor may be incorporated into the immersion plating bath. The metal plating is usually with silver or bismuth and the pads and/or through-holes comprise copper.

Printed circuit board manufacture

A method for enhancing the solderability of a metallic surface is disclosed where the metallic surface is plated with an immersion silver plate prior to soldering, which immersion silver plate is treated with an additive selected from the group consisting of fatty amines, fatty amides, quaternary salts, amphateric salts, resinous amines, resinous amides, fatty acids, resinous acids, ethoxylated derivatives of any of the foregoing, and mixtures of any of the foregoing. The immersion silver deposits created are resistant to electromigration.

Method for enhancing the solderability of a surface

Methods for depositing metals on or removing metals from substrates are provided which involve the use of electrolytic cells comprising an anode and cathode, sulfuric acid, and a chalcogen-containing compound soluble in said bath and having the empirical formula ##STR1## wherein X is a chalcogen, each of R1 and R2 is selected from hydrogen, NR3 R4 and NR5, at least one of R1 and R2 is other than hydrogen, each of R3 and R4 is hydrogen or a monovalent organic radical, and R5 is a divalent organic radical, in which the molar ratio of the chalcogen compound to sulfuric acid is about 1 or more, and the molar ratio of water to the combination of acid and chalcogen compound is about 20 or less. These methods enable the use of higher concentrations of strong acids than would otherwise be possible, minimize hydrogen and/or oxygen evolution at the electrodes with attendant advantages, and are useful for electroplating (including immersion plating), electroforming, electrolytic machining, electropolishing, electrolytic roughening, anodizing and electrowinning among others.

Donald C. Young

Papers

Processes for the deposition or removal of metals