The disclosed devices relate to sucker rod components, tubing drains and downhole tooling, assuring that components will detach at an applied pre-determined tensile load or pressure while eliminating the effects of torsion and bending on the shearing mechanism.
In a producing oil or gas well a rotating downhole pump is driven from the surface by a sucker rod string. The pump typically consists of a rotor which is attached to the sucker rod string and spins inside a stator. Sometimes it is necessary to remove the sucker rod string from the rotor. The shear coupling is threaded onto the sucker rod string near the pump and when a pre-determined axial load is applied to the shear coupling it separates allowing the sucker rod string to be removed.
Similar to sucker rod strings tubing string are formed of segments of tubing. The sucker rod and pump lie within the tubing string. Tubing drains thread between segments of tubing near the bottom of the string. The tubing drain is activated prior to removing the tubing from the well and is necessary to avoid lifting the weight of the fluid column and to avoid fluid contamination of the surface at the well site.
Presently most shear couplings are comprised of two components, one male component which mates with a female component, and a number of shear pins inserted into holes drilled transversely through both components of the shear coupling [U.S. Pat. No. 4,422,508]. Alternatively some shear couplings are comprised of single or multiple components with a reduced cross sectional area designed to shear when a pre-determined tensile load is applied [U.S. Pat. No. 2004/0202521 A1, U.S. Pat. No. 5,470,118]. Known shear mechanisms in shear couplings at this time are subject to combined axial, bending and torsion loading experienced in typical downhole production, and the bending and torsional loading is much greater in deviated wells than vertical wells because of well deviation and friction along the tubing string. The combined stress from axial, bending and torsion loading may result in early activation of the shear mechanism below the designed pre-determined axial load disrupting production. Additionally the bending and torsion loading fatigues the shear mechanism leading to early failure and disrupting production. Even designs utilizing keyways and shear pins are subject to torsional and bending loads at the pins. Not all circumferential displacement is taken up by the key and this displacement travels down through the male component of the shear coupling and is then transferred to the shear pins.
In a typical shear coupling comprising one male component, one female component, and multiple shear pins, the pins fit tightly or are press fit into the transverse thru holes and typically the key and keyway have a looser fit than the pins. The pins are typically aligned in a single plane through the axis of the shear coupling. If the shear coupling is bent downhole, this one plane is significantly stiffer than the rest of the shear coupling. When the shear coupling rotates, the uneven stiffness of the shear coupling exposes the shear coupling to undesirable loading conditions which lead to fatigue damage. As torque is applied to this type of shear coupling, the pins are subject to shear loads before the keyway experiences torsional loading because it takes less circumferential displacement for the pins to be loaded than the keyway. Additionally, a typical keyway has a small bearing area where the male and female halves of the keyway make contact. As the bearing area deforms additional torsion is applied to the pins. The combined tensile loading from string weight, torsion and bending loads can cause fatigue at the pins and keyway and may lead to premature activation of the shear mechanism. Accidental activation of the shear mechanism is costly at producing well sites.