Abstract: A shock absorber for damping shock energy generated by downhole perforating guns or stimulation devices is described. The shock absorber includes a spring assembly including at least a first spring and a second spring, the first spring having a tension greater than the second spring; a damper assembly; and a housing retaining the spring assembly and the damper assembly and including ends adapted for connection into a casing perforation assembly. The provision of springs of increasing stiffness permits the force generated by the perforating gun to be absorbed gradually and smoothly.

Abstract: The universal joint arrangement includes a first adapter having two projecting support formations; a drive plate having a first pair of matching depressions or pockets is seated with these depressions on the projecting support formations of the first adapter and the drive plate has a second pair of pockets for the projecting support formations of a respective second adapter.

Abstract: The disclosure relates to downhole drilling motors which include seal arrangements and pressure control assemblies for staging the pressure between the two seal assemblies, with each pressure control assembly including a rotary element for displacing a piston, and the piston controlling one or several valves.