Profiling Drilling Fluid’s Invasion Using Scanning Electron Microscopy: Implications for Bridging and Wellbore Strengthening Effects

摘要

Wellbore stability issues are continually plaguing the industry and it is important to understand the mud properties that contribute to these issues.The effects of mud cake build up and filtration with time aids the understanding of formation damage and wellbore stability.The increase of drilling in high temperature and pressure zones(HTHP)necessitates studies that can predict filtrate invasion,and particle bridging. The most common hydraulically challenged zones are:depleted sands or intervals with very low pore pressure and fracture pressure,wellbore ballooning zones encountered in deep water drilling where surge and swab pressures could be a serious challenge,and complete lost circulation/no return zones. Filtrate invasion and mud cake build up can be considered as primary factors controlling wellbore stability while drilling.Decreasing the near wellbore permeability by forming an ultra low mud cake can strengthen the wellbore and mitigate further lost circulation problems.Very few studies have investigated filtration and filter cake build up under HPHT situations where effect of different mud particles and bridging solids can be analyzed. This paper focuses on experimental methods quantifying water based muds used by the industry and investigating effects on particle bridging,filtrate invasion and permeability.Then adding lost circulation material(LCM)to optimize the particle size distribution of bridging solids as needed.To show the particle bridging effect,high temperature and pressure(HTHP)filtration tests were conducted at different time steps on sandstone cores of 50 mD and 750 mD.The Scanning Electron Microscope(SEM)analysis conducted on the cores presents an expected trend of particle invasion with depth and time,internal mud cake formation in the porous media,and pore plugging.