Deepwater Drilling –Large Mud Volumes-Low Flow Line Temperatures

Large Mud Volumes

•Wells drilled in deep water require long risers and large diameter casing strings. –The riser, large-diameter casing and large hole sizes call for large mud system volumes. –A 20-in. ID riser in 2,500 ft of water has a volume of 972 bbl. –It is not uncommon for a deepwater drilling operation to have a circulating system of 4,000 bbl or more. –These large systems require proportionately larger quantities of mud additives for maintenance and treating. •Logistics –Inventory management is critical –Delivery time –Sea conditions –Changing hole conditions •Considerations –Bulk bags (1 ton or more) –Floating liquid storage for brines –Bulk handling systems –Proper estimates

Low Flow Line Temperatures

•As explained earlier, water temperature decreases with depth.
•Long risers surrounded by cold sea water will result in much colder mud temperatures and higher vicositiesin the riser and at the flow line.
•The increased viscosity from temperature, particularly in oilbaseand synthetic muds, may limit the shale shaker screens which can be used without losing mud to relatively large mesh sizes.
•Often, there is a temptation to treat the mud system to reduce the viscosity at the flow line, but this should be avoided, since it will reduce hole cleaning in the riser.
•Circulating a third “boost”mud pump on the riser will limit the amount of cooling that occurs in it.
•A Fann Model 70 HTHP viscometer can be used to provide a more accurate profile of the effects of cold and hot temperatures and pressures on a particular mud.