drilling fluids selection
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Drilling Fluids Selection
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II. DRILLING FLUID SELECTION:
Fluid types
Water Base Muds
Invert Emulsion Muds
Drilling Fluid Selection
Section two of this Course discusses in general the relationship applicability of
water base and invert emulsion muds to the matters presented in Section one.
Section two also includes a brief discussion of the Economics of Drilling Fluid
Selection.
The most important function of drilling fluids is to provide a stable borehole.
Without that, nothing else is possible. Stability is a relative thing. The hole that is
going to be drilled and cased off in one day does not need the same inhibition as one
that will take a week to drill, and another week to log and run pipe on. Circulating
and conditioning, reaming and wiping holes is unproductive time. Cheap muds can
become very expensive when rig time becomes part of the mud cost.
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WBM Advantages and Disadvantages
& Higher frac pressure / fracgradient than SBM
&Good fracture sealing &healing ability
& Low gas solubility,promoting detection &handling of kicks
& Typically cheaper thanSBM
& Perceived to be moreenvironmentally friendlythan SBM
& Rheology / gels / densitynot as strongly affected byTemperature & Pressure.
' More accretion and bit-balling tendencies slower ROP
' Shale & boreholeinstability as a function ofopen-hole time
' Less lubricating than SBM
' More differential stickingpotential (fluid loss controlless tight)
' Hole cleaning in deviatedwells not as good as SBM
II. DRILLING FLUID SELECTION: Fluid Types
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Oil or Synthetic Base Muds
& Excellent ROP
& Excellent shale & hole
stability
& Thermally stable
& Excellent fluid losscontrol / low differentialsticking tendencies
& Excellent lubricity &
tubular wear
characteristics
& No hydrate formationproblems
' Low frac pressure & poorfracture healing ability
' Fluid Rheology stronglydependent on P,T
' Poor borehole stability whenformations are fractured in-situ
' High gas solubility,complicating kick detection &handling
' Expensive if losses are heavy
'Compliance requirements ofnew NPDES permit
II. DRILLING FLUID SELECTION: Fluid Types
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Shale Swell Testing
SHALE SWELLING TESTBHP, Zamzama 2, Pakistan
0
10
20
30
40
50
60
70
80
0 100 200 300 400 500 600 700 800 900 1000 11 00 1200TIME (MINUTES)
PERCENTEXPANSION
D I W A T E RV E R S A D R I LD i s p e r s e dK + S I L D R I LK C l \ S I L D R I LK C l \ P H P A
II. DRILLING FLUID SELECTION: Fluid Types
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Water Base Mud Systems
Dispersed / Deflocculated Non-Inhibitive
Freshwater / LignosulfonateDispersed / Deflocculated - Inhibitive
Lime / GYP
Seawater / Lignosulfonate
Non Dispersed Non-Inhibitive
Freshwater / Polymer
Non-Dispersed - Inhibitive Seawater & NaCl / Polymer Muds
KCl / Polymer Muds
Glycol & Amine Additive / Polymer Muds
II. DRILLING FLUID SELECTION
Water base muds may be classified on the basis of the groupings shown in the slide.
Fresh water / Lignosulfonate muds are probably the worst choice possible in a
drilling fluid. Lime muds have applications where high mud weights, and moderate
inhibition is required. Seawater / Lignosulfonate muds are only marginally betterthan Freshwater / Lignosulfonate. Freshwater / polymer muds can be run in certain
areas of low reactive clays. They are low solids fluids if run correctly, but only
provide a limited time for drilling and evaluation of a hole section. The non-
dispersed / inhibitive fluids are the peak of water base mud technology at the present
time.
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Inhibition in Water Base Mud
Inhibitive Additives: Potassium Chloride
GLYCOLS (High Molecular Weight)
Amines
Inhibitive Systems:
KCl / PHPA
Lime Muds
Cationic Polymer Muds
Calcium Chloride Muds
Aluminum Complex Muds Formate Based Muds
II. DRILLING FLUID SELECTION: Fluid Types
Water base muds may be formulated with inhibitive additives. Some of these work
better than others. Usually these muds use combinations of polymers and inhibitors
such as KCl to delay hydration and maintain hole stability for a long enough period
for the hole to be drilled, evaluated and cased off. A number of inhibitive mudsystems are on the market now. Some of them more in the realm of the
experimental and exotic than a tried and true system.
KCl / PHPH muds are probably the best all around proven inhibitive water base
system. KCl may no longer be used offshore in the Gulf of Mexico.
No current water base mud can provide total inhibition. This is only possible when
water is eliminated as the continuous phase of the drilling fluid. Another limitation
of water base muds is in ROP. Drilling rates with oil muds far surpass that of water
base fluids.
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Cuttings from GOM Using
CaCl2 Mud in 4500 Water
SPE 59186
II. DRILLING FLUID SELECTION: Fluid Types
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Invert Emulsion Mud Systems
Balanced Activity Water Phase
High Salinity Water Phase
II. DRILLING FLUID SELECTION
Diesel Base Fluids
Mineral Oil Base Fluids
Synthetic Base Fluids
Lime Based Emulsifiers
Lime Free Emulsifier Package
100 % Oil Systems
Several Invert Emulsion systems may also be defined on the basis of base fluid
utilized, emulsifier package, and some specialty applications
Invert Emulsion Drilling Fluids provide far superior performance to water basefluids. As shown previously, calcium chloride must be added to the water phase of
an invert emulsion mud to provide an osmotic force that will prevent water being
sucked from the mud into the cuttings and borehole wall. There is still some
controversy about whether it is correct to merely balance the forces in the formation,
or whether it is better to run a high enough WPS to exceed the hydrational forces.
Unocal has found in our operations that higher water phase salinities are better. In
general we run water phase salinities of above 30 % by weight CaCl2, or 300,000
ppm CaCl2. Applying a dehydrating force on the formation, particularly on the
cuttings, allows for better hole cleaning and reduced hole problems.
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Hole Stabilization with Invert
Emulsion Drilling Fluids
OIL IS THE CONTINUOUS PHASE IN THE MUD
Calcium Chloride added to the water phase of
the mud generates osmotic force and may be
used to dehydrate formation clays.
II. DRILLING FLUID SELECTION
Invert Emulsion drilling fluids are far superior to any water base fluid for inhibition
and ROP, and usually would be the fluid of choice for most Unocal operations.
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High Temperatures and Pressures
Normal water base muds have temperature
limitations of + / - 300 F.
High temperature water base muds (+/- 400 F) may be
formulated using special additives.
Invert emulsion drilling fluids may be formulated to be stable
to temperatures in excess of 400F by increasing
concentrations of standard products, and may be converted
into higher temperature formulations during the course of a
well as conditions dictate.
II. DRILLING FLUID SELECTION
High temperature drilling fluids require special formulations. Water base fluids
require special products. Oil base fluids usually just require higher concentrations
of normal emulsifiers and fluid loss agents.
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Economics
Price per Sack
Price per Barrel
Mud Price per Well
Total Well Cost
Total Well Cost per BOE/Day (production)
II. DRILLING FLUID SELECTION: ECONOMICS
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Ship Shoal Wells SBF vs WBMShip Shoal Wells SBF vs WBM
0
2,000
4,000
6,000
8,000
10,000
12,000
14,000
16,000
0 2 4 6 8 10 12 14 16 18 20 22 24
DAYS
DEPTH(MD)
12-1/4" WBM (M-2)12-1/4" SBF (H-7)12-1/4" SBF (H-8)
8-1/2" SBF (H-9)12-1/4" SBF (H-10)8-1/2" SBF (H-11)8-1/2" SBF (H-12)
II. DRILLING FLUID SELECTION: ECONOMICS
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