| Popis: |
When running casing in deepwater/subsea applications or in liner deployments, excessive surge pressure in the wellbore can occur when drilling fluid in auto-filled casing is forced through the drillpipe landing string to surface. The resulting friction losses can increase the equivalent mud weight (EMW) sufficiently to exceed the fracture gradient of the formation and often results in fluid losses that could lead to well-control issues. Surge reduction tools mitigate this problem by introducing ports in the drillpipe above the casing or liner running tools. The auto-filled fluid can then be diverted through the ports into the annulus, allowing the casing or liner to be run much faster without the risk of surging the formation excessively. Until recently surge tools have been run in the open position, allowing the tool to divert fluid at all times; however this prevents circulation in the event that the casing or liner needs to be washed down upon encountering an obstruction downhole. Furthermore, should a well-control situation occur, the tool must be closed permanently by intervention from surface and can no longer divert fluid once wellbore control is achieved. To address this shortcoming, a multiple-opening diverter tool has been developed that is initially run into the wellbore in the closed-port position, allowing the system to have complete pressure integrity. The ports are covered by an unbalanced sleeve, which, as auto filling occurs, is opened by a small differential pressure created within the tool, diverting fluid as necessary. Once auto filling stops, the sleeve returns to its original position, and the ports are automatically closed off, enabling the string to be circulated without permanently deactivating the tool. In addition, the ports remain closed should a well-control situation occur. In this paper the authors will review the evolution of casing fill control equipment, discuss the issue of controlling losses while running a tubular, and describe the features of this new multiacting surge-control tool. They will conclude with a case study of its use and effectiveness. |
