Analysis of lost circulation on the Norwegian Continental Shelf
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- Studentoppgaver (TN-IEP) 
Lost circulation (downhole losses of drilling fluid) is defined by the absence or reductionof drilling fluid pumped through the drill string while drilling the wells, which filtrates theformation instead of flowing up to the surface. The Lost circulation is a costly and challengingproblem for the industry, and an extensive amount of money is used to prevent and mitigatethis. Lost circulation can occur at any formation drilled and any well sections where a pressureimbalance is present, and the formation breakdown pressure is less than the total hydrostaticpressure in the well.There are different strategies and methods used in the Oil and Gas industry to prevent lostcirculation. Lost Circulation Material (LCM) is used as a wellbore strengthening strategy toprevent and cure downhole losses. The LCM treatment is either a remedial or a preventativetreatment and can be added continuously into the wellbore or be spotted as a concentrated LCMpill.Environmental emission considerations are closely monitored and crucial if the Oil andGas industry shall be up and running in the years to come. Lost circulation issues contribute toa higher environmental discharge.This thesis aims to investigate the LCM methods used and their cost, the cost of lostcirculation and environmental impact caused by lost circulation. This was studied by analyzingdifferent final well reports from different operators. In addition, drilling professionals have beeninterviewed to get further insight and information. Where severe downhole losses had occurred,the wells were in-depth analyzed to find the cost of total drilling fluid lost, LCM used,environmental discharge, and NPT due to lost circulation.The analysis' main findings indicated that graphite and CaCO3 as an LCM were used, incombination or alone, in 74% of the wells where severe losses had occurred. Furthermore, thecost of NPT in wells with severe downhole losses was, in average, 50 times larger than theaverage LCM cost. The average cost of LCM used approximately equaled the cost of one hourof NPT. Finally, a standardized LCM testing, reporting, and decision flow chart is stronglyrecommended to easier draw suitable conclusions. This will give a good basis for furtherdevelopment.