Composite sucker rod assembly for underground wells

Abstract

A composite sucker rod assembly is provided for use in down-hole wells. The sucker rod assembly includes a plurality of parallel composite strands forming an elongate rod. Preferably, both ends of the rod are fitted with metallic terminus fittings. Each terminus fitting has a tapered cavity with a proximal opening to receive a rod end. The cavity is tapered so as to flare outwardly from said cavity's proximal opening toward the cavity's distal end. The sucker rod assembly further includes a spreader plate, preferably made up of a plurality of pieces, which has holes to receive and splay out the plurality rod strands. A hardened material, such as a hardened resin, is introduced into the cavity and allowed to harden to affix the rod to the terminus fitting. Preferably the hardened resin is compressed by a connection member.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates generally to sucker rod engineering and design. More particularly, the present invention relates to a composite sucker rod assembly for use in down-hole vertical lift oil extraction.[0002]Sucker rods for use with vertical lift rod pumps, also referred to as surface units, rocking horse, or pump jacks are typically made from individual lengths of steel rod sections that are connected together by threaded couplings. The individual sucker rods are typically 25 feet, 30 feet or 37.5 feet in length and are connected together with couplings to form a sucker rod string. A typical sucker rod string is from 700 to 10,000 feet or more in length. The sucker rod string connects the vertical lift surface device to the down-hole pump unit. Traditional metal sucker rods are heavy and subject to corrosion and fatigue failure, particularly at the threaded connections or due to stress corrosion cracking. An unexpected broken sucker rod du...

AI Technical Summary

Benefits of technology

The present invention is a sucker rod assembly for use in oil wells that is made of carbon fiber strands. These strands are made by pultrusion or other methods and are designed to have high strength and stiffness. The assembly is optimized for tensile strength and durability. The carbon fiber strands are bundled together and splayed out at the ends to hold the assembly in place. The assembly is connected to other equipment using a connection member that engages a tapered wedge. The assembly is lightweight and has pumping performance and service life advantages over conventional steel or monolithic fiberglass sucker rods. The assembly is also designed to be rotated in the well tubing to prevent wear. The carbon fiber strands are wrapped with a composite material to hold them together and provide stiffness and dampening. The assembly is designed to be strong and durable while also being lightweight.

Problems solved by technology

Traditional metal sucker rods are heavy and subject to corrosion and fatigue failure, particularly at the threaded connections or due to stress corrosion cracking.

An unexpected broken sucker rod due to corrosion and / or fatigue is expensive to remove and replace.

Further, the weight of a metal sucker rod string limits its strength and fatigue life and can limit the depth which even large surface units can pump.

The weight of a steel sucker rod string can also overload and reduce the life of the surface unit and its components.

Fiberglass sucker rods do offer a weight reduction and corrosion resistance but have significant stretch and are prone to splitting and failing due to transient compression in the rod string.

Steel sucker rods are stiff and often cause excessive wear on the inside of the well casing where the well is not straight.

Additionally, the flex in the string induced by pumping causes metal fatigue which can cause the sucker rod to fail.

The highly corrosive environment worsens the frequency of rod failures.

Fiberglass sucker rods are lighter than steel but have been known to suffer premature failure if subjected to any compression loading during the pumping cycle.

A carbon fiber composite sucker rod pultruded as a monolithic bar and meeting the typical requirements of a sucker rod would not be attractive because it would be subject to compression failures similar to fiberglass and it would be difficult to make the terminus end fitting match the strength potential of the carbon fiber composite mid-section since it would be merely glued on the outside of the monolithic rod versus tying into the majority of the fibers.

Continuous steel sucker rods are limited in the length that can be practically used due to weight, transportation and handling issues.

Continuous length steel sucker rods are heavy, corrode, and are subject to fatigue failure.

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