BAKER HUGHES - Drilling Fluids Reference Manual

BOREHOLE PROBLEMS
Temp 200º F 250º F 300º F
Density, lb//gal
H2O, bbl
X-LINK, sks
RTR, gal
MIL-BAR, sks
H2O, bbl
X-LINK, sks
RTR, gal
MIL-BAR, sks
H2O, bbl
X-LINK, sks
RTR, gal
MIL-BAR, sks
12 87 87 86 192 87 87 117 191 87 87 138 190
13 83 83 82 247 83 83 112 246 83 83 132 245
14 80 80 78 303 80 80 107 302 80 80 126 301
15 76 76 75 359 76 76 102 359 76 76 120 357
16 72 72 71 414 72 72 97 413 72 72 114 413
17 68 68 67 470 68 68 92 469 68 68 108 468
Table 7 - 6 Formulations to Build 100 Barrels of Weighted X-LINK Plug
Other Types of Remedial Techniques
Extremely severe drilling fluid losses, such as those encountered while drilling cavernous zones
and depleted reservoirs may require specialized techniques, such as drilling with air, drilling with
stiff foam, drilling with aerated fluid (using either an injection string run on outside of the casing
string or using concentric drillpipe), drilling with a mud-cap, or drilling blind until the loss zone
is cased off. With the exception of drilling blind, the methods noted above require special
equipment and preparation and should be planned before drilling operations begin.
It should be noted that severe corrosion problems may be encountered with aerated fluids if
preventive measures are not taken.
Lost Circulation Prevention by “Stress Cage” Technique
Induced losses occur when the drilling fluid density, required for well control and to maintain a
stable wellbore, exceeds the fracture resistance of the formations. A particular challenge is the
case of depleted reservoirs. There is a drop in pore pressure as the reserves decline, which
weakens hydrocarbon-bearing rocks, but neighboring or inter-bedded low permeability rocks
(shales) may maintain their pore pressure. This can make the drilling of certain depleted zones
virtually impossible – the drilling fluid density required to support the shale exceeds the fracture
resistance of the sands and silts. The potential prize is clear if a way can be devised to strengthen
the weak zones and thereby access these difficult reserves. In fact, the value of wellbore
strengthening is much more wide-ranging and includes the following applications/benefits:
• Access to additional reserves (depleted zones)
• Reduced drilling fluid losses in deepwater drilling
• Loss avoidance when running casing or cementing
BAKER HUGHES DRILLING FLUIDS
REFERENCE MANUAL
REVISION 2006 7-32