Sub-Surface Plug Release Assembly

An apparatus for cementing casing in a borehole, the apparatus comprising:

• a subsurface tool configured to connect on the casing, the subsurface tool having a bore;
• a subsurface plug disposed in the bore of the subsurface tool, the subsurface plug having a passage therethrough;
• a wiper plug configured to pass through the casing and configured to engage with the subsurface plug as a plug unit;
• and
• a support configured to hold the subsurface plug at least temporarily in the bore of the subsurface tool, the support being configured to release the subsurface plug in response to pressure in the casing behind the plug unit.

A system used on casing in a borehole and being operated by a wiper plug, the system comprising:

• a float valve connected to the casing;
• a cementing collar connected to the casing uphole of the float valve and being configured to pass the wiper plug therethrough;
• a subsurface tool connected to the casing between the cementing collar and the float valve, the subsurface tool having a bore;
• a subsurface plug disposed in the bore of the subsurface tool, the subsurface plug having a passage therethrough, the passage configured to engage the wiper plug deployed down the casing;
• a support disposed in the bore of the subsurface tool and configured to hold the subsurface plug at least temporarily in the bore of the subsurface tool, the support being configured to release the subsurface plug with the engaged wiper plug as a plug unit in response to pressure in the casing behind the plug unit;
• and
• a locator tool connected to the casing between the subsurface tool and the float valve, the locator tool being configured to locate the plug unit at least temporarily at a location in the casing.