At a depth of 18,360ft fillers on the deepwater horizon encountered fluid at a reservoir pressure of 8900 psia. In order to keep this fluid from flowing up the well bore and riser, they should have pumped a mud solution into the well, filling it to the top. What should have been the weight density (pg) of this mud in order to keep the reservoir fluid from flowing up the bore to the surface? Suppose water was used instead of mud. What would the pressure differential be in this case?