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Drilling fluids
This document discusses drilling fluid systems and their functions. It describes the classification of drilling muds as water-based or oil-based. Water-based muds can be further broken down and include bentonite muds, polymer muds, and muds with additives like gypsum, lime, potassium/lime, and mixed metal hydroxide. Oil-based muds include invert emulsion and mineral/synthetic oil-based muds. Key functions of drilling fluids are cooling and lubricating the drill bit, carrying cuttings to the surface, controlling formation pressure, and maintaining wellbore stability. Common measurements of mud properties are also outlined.
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Drilling fluids
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- 2. All-oil muds Invert emulsion Oil-basedMuds (diesel, mineral, synthetic) non-damaging Polymer muds dispersed non-dispersed Clay (gel) muds Water-based Muds Drilling Muds inhibitive Drilling Mud Classification 2
- 3. Primary Functions ofa Drilling Fluid 3
- 4. 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
- 5. Bentonite-based WBM • Bentoniteused 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
- 6. Polymer-based WBM • Polymersused 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
- 7. Functions of CommonWBM Additives 7
- 8. Functions of CommonWBM Additives (II) 8
- 9. Functions of CommonWBM Additives (III) 9
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- 12. Some Measured MudProperties • 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
- 13. Comparative Drilling FluidPerformance Formation damage avoidance Wellbore stability Lubricity Tolerance to contaminants Environmental acceptability Overall drilling performance Corrosivity Thermal stability Mineral OBM Ester Glycol WBM KCl / PHPA SBM Bentonite WBM 13