Many of the technical challenges of drilling in deepwater have been well documented in the literature. One of the primary concerns is the narrow operating window between pore pressure and fracture gradient that often results in major fluid losses when drilling, running casing, and cementing. Deepwater fracture gradients are typically much lower than those encountered onshore or in shallow water (Fig. 1) thus preventing losses in deepwater can be more difficult.

Failure to minimize lost circulation can greatly increase the already high cost of drilling, as well as risking loss of the well. Successful management of lost circulation in deepwater should incorporate identification of potential loss zones, optimization of drilling hydraulics, and clear, easy to follow procedures should lost circulation be encountered.

The aim of this paper is to review the top 10 concerns associated with lost circulation in deepwater environments. This top 10 list addresses the causes of lost circulation and recommended solutions for managing these problems. Based on experience in various deepwater basins around the world, including the Gulf of Mexico, Brazil, and West Africa, the top 10 concerns are (1) sub-salt rubble zones, (2) locating loss zones, (3) seepage losses, (4) drilling, running casing and cementing with synthetic-based drilling fluid, (5) drilling practices, excessive rate of penetration and hole conditions, (6) wellbore breathing (ballooning), (7) low temperature drilling fluid rheology, (8) inadequate shoe tests, (9) synthetic-based fluid compressibility, and (10) well control.

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