Schlumberger

Technical Paper: An Innovative Inert Material to Cure the Losses in the Brent Depleted Reservoirs—North Sea Case Histories

Society: SPE
Paper Number: 100934
Presentation Date: 2006
 Download: An Innovative Inert Material to Cure the Losses in the Brent Depleted Reservoirs—North Sea Case Histories (0.30 MB PDF) Login | Register

 

Abstract

Drilling in the Brent field began to experience severe lost circulation problems after the start of depressurisation in 1998. The losses occurred in the reservoir sections, which were penetrated by extended reach and near-horizontal wells. In contrast, wells drilled before the onset of depressurisation experienced few losses.

The lost circulation problems resulted from a narrowing of the drilling operating window as reservoir depletion gradually reduces the fracture gradient. Numerous interbedded reservoir shales, which were sub-seismic in thickness, required a minimum mud weight to maintain stability, especially in the subhorizontal sections. Problems became acute when the fracture gradient was reduced to a level below the equivalent circulating density (ECD) required to successfully drill the shales.

The rate of decline in the fracture gradient was much lower than would have been predicted from conventional geomechanics estimation, and this extended the duration of the Brent drilling programme during depressurisation. Drilling and cementing the Brent reservoir with no losses has proven very difficult in the past 2 years.

This paper will describe the lost circulation problems when drilling and cementing the Brent reservoir and the new approach used during cementing to cure losses without adding constraints to the offshore operation.

Request More Information