Drilling Fluid Losses and Gains: Case Histories and Practical Solutions

Abstract Identification and resolution of drilling fluid losses and gains while drilling have gained in importance due to the high cost of deepwater drilling focusing concern on any delays. Drilling fluid losses and gains, or wellbore breathing, can be attributed to several factors. These include the local geological setting, inherent natural fractures in the formation, well trajectory, drilling operations, equivalent mud weight, mud rheology and chemistry, etc. Recurring observations of formation influx while drilling or during connections oftentimes are interpreted as a potential well control situation. Therefore significant rig time can be lost to insure this is not the case. There have been recent developments in the area of monitoring drilling fluid losses and gains. A fundamental understanding of the reasons for mud losses and gains, along with the implementation of these recent monitoring techniques, would greatly improve managing this problem. In this work, mechanisms are provided to explain drilling fluid losses and gains. Loss and gain situations can occur in a variety of drilling scenarios: examples would be while drilling in deeper waters, where the operating window between the pore pressure and fracture gradient is narrow; drilling extended reach wells where the problem may be encountered at higher hole inclination angles; drilling though formations with abnormally high geothermal gradients, etc. In addition, case histories are provided where drilling fluid losses and gains were diagnosed during a borehole stability analysis, followed by implementation of recommended remedial measures that resulted in better management of the problem on later wells. Sometimes potential for mud losses and gains are interpreted from formation leak-off tests. New solutions, which include alterations to the drilling fluid composition and lost circulation sweeps, are proposed to help mitigate the occurrence of drilling fluid losses and gains.