DRILLING FLUID SYSTEMS

&

FUNCTIONS

1

All-oil muds Invert emulsion

Oil-based Muds(diesel, mineral, synthetic)

non-damaging

Polymer muds

dispersed non-dispersed

Clay (gel) muds

Water-based Muds

Drilling Muds

inhibitive

Drilling Mud Classification

2

Primary Functions of a Drilling Fluid

3

Some Water-based Muds

• Freshwater bentonite (gel)• Seawater bentonite• Extended bentonite• Attapulgite (salt water gel)• Gypsum• Lime• Potassium/Lime

• Polymer• KCl/polymer• KCl/Polymer/PHPA• KCl/glycol• Mixed Metal Hydroxide• Silicate• Low invasion• Cationic

4

Bentonite-based WBM

• Bentonite used for viscosity and fluid loss control

• Polymer (eg CMC) often used for additional fluid loss control• Thinner (dispersant) added to improve rheology, fluid loss

control & thermal stability (eg lignosulphonate, lignite, synthetic polymer)

• Bentonite must be pre-hydrated• Muds sensitive to calcium & magnesium contamination• Unless properly treated, muds undergo irreversible thermal

gelation

• Poor level of shale inhibition• Bentonite can cause high levels of formation damage

• Cheap

5

Polymer-based WBM

• Polymers used for viscosity and fluid loss control

• Many polymers tolerant of contamination by salts

• Can formulate to high salinities (eg. sat’d NaCl, formates etc)

• Moderate thermal stability, depending on composition

• Shale inhibition provided by salts, polymers & glycols

• Less formation damaging than bentonite muds

• More expensive than bentonite muds

• More lubricating than bentonite muds

• Flexible systems - properties adjusted via polymer selection

• Lower solids content than bentonite muds - can increase ROP

6

Functions of Common WBM Additives

7

Functions of Common WBM Additives (II)

8

Functions of Common WBM Additives (III)

9

Oil-based Muds

10

Oil-based Muds

11

Some Measured Mud Properties

• Funnel viscosity (Marsh Funnel) (seconds/quart)• Yield point (lb/100 ft sq)• Plastic viscosity (cPoise)• 6 and 3 rpm Fann viscometer readings• Gel strengths (10 second & 10 minute) (lb/100 ft sq)• API fluid loss (WBM) (ambient temperature, 100 - 150 psi)

• HTHP fluid loss (OBM and WBM) (250’F, 500 psi)• pH (WBM)• Oil:water ratio (OBM)• Density (pcf, ppg or sg)• High gravity & low gravity solids content (HGS / LGS) (from density & retort)

• Salt content - usually as chlorides (WBM & OBM)• Emulsion stability (OBM)• Inhibitor concentrations - K+, PHPA, glycol etc (WBM)

12

Comparative Drilling Fluid Performance

Formation damage avoidance

Wellbore stability

Lubricity

Tolerance tocontaminants

Environmental acceptability

Overall drilling performance

Corrosivity

Thermalstability

Mineral OBM

Ester

Glycol WBM

KCl / PHPA

SBM

Bentonite WBM

13