Lecture 2 - Specialty fluids.ppt - SPECIALTY FLUIDS Specialty Fluids • These are fluids for the following • Wellbore Stability(already discussed •

Lecture 2 - Specialty fluids.ppt - SPECIALTY FLUIDS...

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SPECIALTY FLUIDS
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Specialty Fluids These are fluids for the following: Wellbore Stability (already discussed) High Temperature-High Pressure Drill-In Slimhole Coring Deep Water
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HPHT Definition HPHT wells are generally considered to be those which encounter bottom hole temperatures in excess of 300°F (150°C) and pressures which require a mud weight of 16.0 ppg (1.92 SG) or more to maintain well control.
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Water-based mud additive - temperature limits Bentonite ≈ 350°F Water dispersible polymers - 250-275°F Lignite ≈ 400°F Lignosulfonate ≈ 350°F High Temperature Systems
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High temperature drilling fluid products Bentonite ≈ 350°F Plant derived resins ≈ 400°F Synthetic polymers 500°F High Temperature Systems
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Synthetic polymers Derived from Hydrocarbon Feedstock Acrylate Polyacrylamide Sulfonated styrene Vinylsulfonate High Temperature Systems
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Formulations Convert Existing WBM to HT System Lower solids content Add temperature stable polymers Test at temperatures 25°F higher than bottom-hole temperature (BHT) Perform pilot test continually High Temperature Systems
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HPHT Drilling Fluids At high temperatures, conventional drilling fluid additives thermally degrade at appreciable rate Majority of mud treatment chemicals begin to degrade between 250 and 275 o F Degradation leads to loss of product function Clay and Lignite-Lignosulphonate-based systems stable up to 350 o F System maintenance becomes difficult above 350 o F
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Thermal Degradation Thermal degradation can be simplistically thought of as the result of putting so much energy into a chemical substance that some portion of its structure can break off or change form. Similar results can be effected at lower temperatures by the presence of certain chemicals. Oxygen (from air) can promote oxidation, water (present in the mud) can promote hydrolysis.
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Bentonite Muds High temperatures disperse and flocculate bentonite suspensions Hydration of Montmorillonite (the major constituent of commercial bentonite) increases with temperature and pressure An increased number of clay platelets are split from aggregated stacks. The combination of increased surface area and drop in pH will tend to increase the flocculation within the suspension. Under downhole conditions this creates a demand for alkali and deflocculant additves. If sufficient deflocculant is not present, or the deflocculant itself is thermally degrading, severe flocculation or gelation can occur.
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Bentonite Muds Figure shows effects of temperature on the gelling characteristics of a simple bentonite suspension Excessive gelation occurs at 250 O F Actual temperature limit depends on the mud composition
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Polymer Muds Temperature effects mainly due to constituent polymers Polymer muds are generally low solids fluids with a degree of inhibition to clay hydration Increased clay hydration not a big problem in polymer muds
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  • Fall '18
  • James Bonifacio

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