Controlled weak point for wireline cable

DETAILED DESCRIPTION The present invention operates such that once a first "weak point" is cut or separated, a backup prevents its liberation.
Meanwhile, it remains electrically connected, sending signals and able to resist considerable stresses until such time as the operator slackens the force applied to the cable.
At this moment, a second "weak point", whose resistance can be calculated so as to make it either the same as or different from the first, takes effect for continuing the tool unhooking and recovery operation, or to be cut if necessary.
The controllable weak point apparatus is mounted within two tubular steel sections that are interconnected with one section firmly connected to the steel cable and a lower section connected to the surface readout tool.
The upper and lower tubes are joined in such a way that they can be easily separated; however, an internal, tubular mechanism functions to not allow any separation until a predetermined force shears the pins of a weak point.
The internal mechanism consists of an inner tube carrying the cable therethrough and extending axially within a slotted mandrel which is disposed within a slotted limit sleeve which, in turn, is reciprocally received within upper and lower external sleeves.
The inner tube is connected via shear pins to an upper crossover housing as an upper spring is compressed between the crossover housing and an adjusting nut threadedly received over the slotted mandrel.
A support block secured within the lower external sleeve is secured by plural shear pins to the lower end of the slotted mandrel, and a lower spring is compressed between the lower end of the support block and an adjustable nut secured on the bottom of the inner tube.
The upper and lower shear pin arrays provide the respective second and first weak points.
Therefore, it is an object of the present invention to provide a controllable weak point device for enabling wider use of surface readout tools.
It is also an object of the present invention to provide a connective device that provides greater safety in those wireline operations performed at greater depths