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1
Drilling Fluids
Offshore Drilling Operations Agenda
Monday Tuesday Wednesday Thursday Friday
AM
Introduction
HSEMetocean
Geology
Rig Typesand
Wellbore Construction Sequences
Casing and Cementing
Design
Drill Strings and Bits
Lunch Exercise Exercise Exercise Exercise Exercise
PM
Offshore Systems
and Structures
Well PlanningAnd Rig Selection
Wellbore Stability
and Drilling Fluids
Directional Drilling
MacondoReview
Exam
2
Why WBM or OBM?
• Cost benefit ratio.
• Temperature.
• Formation reactivity.
• Required additives.
• Environmental sensitivity.
• It is important to look at the big picture when choosing a fluid type. What problems are expected.
3
Water Based Mud Advantages Disadvantages
Higher frac pressure / frac gradient than OBM
Good fracture sealing & healing ability
Low gas solubility, promoting detection & handling of kicks
“Typically” cheaper than OBM
Perceived to be more environmentally friendly than OBM
Rheology / gels / density not as strongly affected by Temperature & Pressure.
More accretion and bit-balling tendencies –slower ROP
Shale & borehole instability as a function of open-hole time
Less lubricating than OBM More differential sticking
potential (fluid loss control more difficult to manage)
Hole cleaning in deviated wells not as good as OBM
Oil or Synthetic Base Muds (NAFs)ADVANTAGES
Excellent ROP
Excellent shale & hole stability
Thermally stable Excellent fluid loss
control / low differential sticking tendencies
Excellent lubricity & tubular wear characteristics
No hydrate formation problems
DISADVANTAGES
Low frac pressure & poor fracture healing ability
Fluid Rheology strongly dependent on P,T
Poor borehole stability when formations are fractured in-situ
High gas solubility, complicating kick detection & handling
Expensive if losses are heavy
Compliance requirements of new NPDES permit
4
Measurable Working Fluid Properties
• Density• Viscosity• Filtration• pH• Temperature stability• Chemical and physical composition• Corrosivity• Additive compatibility• Formation compatibility• Environmental compatibility
Density
• Mass per unit volume.– ppg, g/cc, kg/m3, lb/ft3
• Important to wellbore stability.– Pressure Control– Formation Stability
• Measured With:– Mud Balance– True Mud Balance– Hydrometer
5
Mud Density Measurement• In the field, mud density is measured with
a mud balance.
Electrostatic Charges on Clay Platelets
• Clays have (+) charges on platelet faces and (-) charges on platelet edges
• Face-to-face and edge-to-edge repel
• Edge-to-face attracts
6
Structures and Behaviors of Clay•Clay (shale rock) is sedimentary
•Layers deposited in water
•Water is baked and squeezed out of clay structure with deeper burial
•When exposed to water, clay draws water back into structure
Yield Point (YP)
• YP driven by electrostatic structure• Particle charges• Concentration
• More charged particles means more structure
• More internal resistance to shear
7
Other Fluids
Drill-in fluids• Designed to drill into and through
productive zones.
• Formulated to have;– Very low solids
– Limited fluid loss
– Acidizable components
– Usually water-based with a polymer viscosifier
– Good flow back characteristics of filter cake
• Displace the mud system currently in use and are only used for drill-in.
8
Completion Fluids• Contacts a producing formation after the well
is drilled.– Perforating
– Gravel packing
– Pay-zone drilling or underreaming
– Casing repair
– Zone-sensitive operations
– Chemical treatments
– Cleanout of sand and foreign objects,
– Well killing
– Tubing and hardware replacement
Packer Fluids
• Fluid placed in the tubing annulus.
• Purpose– Inhibit Corrosion and other production chemistry and
temperature issues.
– High enough density to assist in controlling wellbore pressure.
– Low enough density to prevent a differential packer failure at late stages of production.
• Usually a salt based solution.