An annular groove is formed in {TAIL ~ the bore} of the wellhead housing above {HEAD ~ the casing hanger} 
An annular groove is formed in { TAIL ~ the bore } of the wellhead housing above { HEAD ~ the casing hanger }
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD