Drilling Fluid Losses and Gains: Case Histories and Practical Solutions

摘要

Identification and resolution of drilling fluid losses and gainsrnwhile drilling have gained in importance due to the high costrnof deepwater drilling focusing concern on any delays. Drillingrnfluid losses and gains, or wellbore breathing, can be attributedrnto several factors. These include the local geological setting,rninherent natural fractures in the formation, well trajectory,rndrilling operations, equivalent mud weight, mud rheology andrnchemistry, etc. Recurring observations of formation influxrnwhile drilling or during connections oftentimes are interpretedrnas a potential well control situation. Therefore significant rigrntime can be lost to insure this is not the case. There have beenrnrecent developments in the area of monitoring drilling fluidrnlosses and gains. A fundamental understanding of the reasonsrnfor mud losses and gains, along with the implementation ofrnthese recent monitoring techniques, would greatly improvernmanaging this problem.rnIn this work, mechanisms are provided to explain drillingrnfluid losses and gains. Loss and gain situations can occur in arnvariety of drilling scenarios: examples would be while drillingrnin deeper waters, where the operating window between thernpore pressure and fracture gradient is narrow; drillingrnextended reach wells where the problem may be encounteredrnat higher hole inclination angles; drilling though formationsrnwith abnormally high geothermal gradients, etc. In addition,rncase histories are provided where drilling fluid losses andrngains were diagnosed during a borehole stability analysis,rnfollowed by implementation of recommended remedialrnmeasures that resulted in better management of the problem onrnlater wells. Sometimes potential for mud losses and gains arerninterpreted from formation leak-off tests. New solutions,rnwhich include alterations to the drilling fluid composition andrnlost circulation sweeps, are proposed to help mitigate thernoccurrence of drilling fluid losses and gains.