Deep water Drilling – Low Fracture Gradients

•In deepwater drilling, challenges exist that are related to formation pore pressures and fracture gradients being very close at shallow depths. •For deepwater applications, the fracture gradient and equivalent pore pressure decrease as water depth increases. •At extreme water depths (±10,000 ft), this low fracture gradient (due to the lack of overburden) and low equivalent pore pressure make drilling impractical, even with unweightedmud, due to annular pressure losses increasing the Equivalent Circulating Density (ECD). •The typical deepwater well uses frequent shallow casing strings to seal off low fracture-gradient formations. •The low fracture gradients also present lost circulation problems from both surge and swab pressures. •This is especially true with synthetic, mineral oil and diesel systems, which are compressible and tend to reduce the allowable fracture gradients •Surge, swab and ECD pressures are a significant concern for all deepwater drilling operations, particularly while running and cementing casing. •Understanding the effects of temperature and pressure on hydraulics and drilling fluid rheology is very important in deepwater •Low water temperatures and the resulting low riser temperatures can result in elevated fluid rheology and high surge and swab pressures.