19-02-2011, 12:57 PM
Lesson 10 Flow Mudcap Snub Closed systems.ppt (Size: 3.84 MB / Downloads: 236)
Underbalanced Drilling (UBD)
Lesson 10 Flow Drilling ,Mudcap ,Drilling Snub Drilling ,Closed Systems
Flow Drilling
Flow drilling refers to drilling operations in which the well is allowed to flow to surface while drilling.
All UBD operations are really flow drilling operations, but the term is usually applied to drilling with a single phase mud, and no gas is injected except by the formation.
Drilling Fluid Selection
Density is determined by:
• Maximum pressure ≤ to formation pressure.
• Minimum pressure dictated by wellbore stability.
Pressure limitations of diverter and BOP equipment.
Sizing Flare Line
Weymouth’s equation can be used to predict the pressure drop for a gas, in steady-state, adiabatic, flow along the pipe:…
Surface Pits
Primary oil separation pit.
Secondary oil separation pit.
Skimmer system safety.
Drilling fluid pit.
Oil transfer tank.
Operating Procedures
Mechanical objectives during flow drilling are:
• To control the well.
• Minimize differential sticking problems.
• Minimize drilling fluids losses.
Maximum tolerable surfaces pressures should be established before drilling starts.
Mudcap Drilling
Utilized with uncontrollable loss of circulation during flowdrilling operations.
Higher pressures than can be safely handled with the rotating head or RBOP.
It is not strictly an underbalanced drilling technique.
Driller loads the annulus with a relatively high density high viscosity mud and closes the choke with surface pressure maintained.
Drilling is then continued “blind” by pumping a clear non-damaging fluid down the drillstring through the bit and into the thief zone.
Applications:
o Sustained surface pressures in excess of 2,000 psi.
o Sour oil and gas production.
o Small diameter wellbores.