Patent ID: 8695696
Filing Date: 2014-04-15
Classification: E21B

Abstract:
1. A jar comprising: an outer housing; an inner mandrel at least partially disposed telescopically within the outer housing to define a fluid chamber between the inner mandrel and the outer housing, the fluid chamber containing fluid and being sealed; a valve disposed within the fluid chamber, the valve having a restriction surface facing, during setting, a cooperating restriction surface on one of the inner mandrel and the outer housing and a pressure surface facing the other of the inner mandrel and the outer housing, the valve being movable between a seated position in which the valve seats against the other of the inner mandrel and the outer housing and an unseated position; the cooperating restriction surface cooperating with the restriction surface to set the jar for a jar in a first direction; the pressure surface being exposed to fluid within the fluid chamber when the jar is set and pressuring up for a jar in the first direction; the pressure surface being indented to cause uneven radial movement, in a plane perpendicular to a jar axis, of the restriction surface towards the cooperating restriction surface, to define fluid metering gaps between peaks on the restriction surface, when the jar is set and pressuring up for a jar in the first direction, the fluid metering gaps being sized to control a metering rate between a downhole end and an uphole end of the restriction surface; and jarring surfaces on the inner mandrel and the outer housing respectively for jarring contact with each other during a jar in the first direction.