drilling fluids selection

7/29/2019 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



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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



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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


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



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Invert Emulsion Mud Systems

Balanced Activity Water Phase

High Salinity Water Phase


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.


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.


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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drilling fluids selection