Oil giant BP Plc on Thursday completed its cementing job on the well that gushed oil for months into the Gulf of Mexico, dpa reported.
The cement followed the heavy drilling mud forced into the well this week to seal off the problem well.
"Monitoring of the well is underway in order to confirm the effectiveness of the procedure," BP said in an e-mail to media.
Closing off of the ruptured wellhead is only the first step towards permanent shut-down of the more than 100-day-old disaster that has threatened the ecology and economy of the Gulf region.
BP must also still complete the parallel relief well that will be used to pump another dose of cement into the bottom of the well 5 kilometres below the floor of the Gulf and mark the official closure of the well.
"Depending upon weather conditions, mid-August is the current estimate of the most likely date by which the first relief well will intercept the (opening at the bottom of the well)," BP said.