Wellhead apparatus

Wellhead apparatus, comprising

• a housing having
• a bore therethrough and a lower end connectible to an outer casing string for extension within a well bore,
• an upwardly facing shoulder in the bore,
• a locking groove in the bore above the shoulder and having an upwardly facing load surface, and
• a lower fluid bypass means connecting with the bore above and below the groove, a casing hanger including
• a mandrel having a bore therethrough and a lower end connectible to an inner casing string for suspension within the outer casing string,
• a recess about the outer diameter of the mandrel,
• a radially expandable and contractible locking ring carried within the recess,
• a downwardly facing cam surface above the recess, and
• means connected to the mandrel for landing on the shoulder in the housing bore to locate the locking ring opposite the locking groove therein, and being releasable, in response to downward force on the mandrel, to permit the mandrel to move downwardly with respect to the housing and locking ring so as to move the locking ring outwardly into and hold it in an expanded position within the groove in which a downwardly facing load surface on the ring is adapted to seat upon an upwardly facing load surface on the groove to support downward loads,
• said housing bore and mandrel forming an annular space between cylindrical seal surfaces thereon which form an upward continuation of the fluid bypass means, and
• a sleeve carrying a seal ring and connected about the casing hanger mandrel for vertical movement within the housing bore, in response to lowering of the sleeve, between an upper position in which the seal ring is above the annular space to form upward continuation of the fluid bypass means, and a lower position in which the ring is in sealing engagement with the seal surfaces to close the space,
• the bore of the housing having a second fluid bypass means outside the sleeve to form an upward continuation of the space.