Downhole apparatus

A double-acting compounder, 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 at an uphole end and a downhole end;
• a port extending through the outer housing and communicating between the fluid chamber and an exterior of the outer housing that, in operation is subject to hydrostatic pressure outside the outer housing;
• an equalizer, in contact with fluid from the fluid chamber, between the fluid chamber and the port for equalizing pressure between the fluid chamber and the hydrostatic pressure outside the outer housing at least when the double-acting compounder is not compounding;
• a movable seal assembly disposed within the fluid chamber and having a first end that defines the uphole end or the downhole end of the fluid chamber;
• the inner mandrel having an outer shoulder for contacting a second end of the movable seal assembly to move the movable seal assembly with the inner mandrel when the inner mandrel moves in a first direction relative to the outer housing to compresses fluid within the fluid chamber;
• and
• the outer housing having an inner shoulder for contacting the second end of the movable seal assembly to prevent the movable seal assembly from moving with the inner mandrel when the inner mandrel moves in a second direction relative to the outer housing to compresses fluid within the fluid chamber.