|
|
Line 1: |
Line 1: |
| High pressure/high temperature (HP/HT) wells are those where the undisturbed bottom hole temp at prospective reservoir depth or total depth is greater than 300°F or 150°C, and either the maximum anticipated pore pressure of any porous formation to be drilled through exceeds a hydrostatic gradient of 0.8 psi/ft, or a well requiring pressure control equipment with a rated working pressure in excess of 10000 psi. Drilling wells with these characteristics pose special challenges. | | High pressure/high temperature (HP/HT) wells are those where the undisturbed bottom hole temp at prospective reservoir depth or total depth is greater than 300°F or 150°C, and either the maximum anticipated pore pressure of any porous formation to be drilled through exceeds a hydrostatic gradient of 0.8 psi/ft, or a well requiring pressure control equipment with a rated working pressure in excess of 10000 psi. Drilling wells with these characteristics pose special challenges. |
|
| |
|
| ==Drilling fluid considerations== | | == Drilling fluid considerations == |
| | |
| Where possible, high temperature wells are drilled with oil-based fluids (OBFs) or synthetic-based fluids (SBFs), because of the thermal limitations of most water-based fluids (WBFs). Such limitations of WBFs include: | | Where possible, high temperature wells are drilled with oil-based fluids (OBFs) or synthetic-based fluids (SBFs), because of the thermal limitations of most water-based fluids (WBFs). Such limitations of WBFs include: |
| * Temperature-induced gelation
| |
| * High risk of CO<sub>2</sub> contamination from the formation being drilled and/or from the degradation of organic mud additives
| |
| * Increased solids sensitivity that is related to high temperatures
| |
|
| |
|
| Historically, WBFs have relied on bentonite clay for both rheology and filtration control. When tested at temperatures ≥ 300°F under laboratory conditions, bentonite slurries begin to thermally flocculate. Under HP/HT conditions with significantly elevated temperatures, a traditional WBF such as the lignosulfonate system might thicken so much that it no longer is usable or requires drastic and costly dilution and conditioning. | | *Temperature-induced gelation |
| | *High risk of CO<sub>2</sub> contamination from the formation being drilled and/or from the degradation of organic mud additives |
| | *Increased solids sensitivity that is related to high temperatures |
| | |
| | Historically, WBFs have relied on bentonite clay for both rheology and filtration control. When tested at temperatures ≥ 300°F under laboratory conditions, bentonite slurries begin to thermally flocculate. Under HP/HT conditions with significantly elevated temperatures, a traditional WBF such as the lignosulfonate system might thicken so much that it no longer is usable or requires drastic and costly dilution and conditioning. |
| | |
| | The ability to maintain bentonite and other active solids in a deflocculated state is the key to obtaining acceptable rheological and fluid-loss properties for WBFs exposed to high temperatures.<ref name="r1">Mason, W. and Gleason, D. 2003. System Designed for Deep, Hot Wells. American Oil and Gas Reporter 46 (8): 70.</ref> Bentonite can be used in relatively low concentrations, if it is supplemented with a high-temperature, high-molecular-weight synthetic polymer for additional carrying capacity. This combination helps to make it possible to maintain 6% by weight of low-gravity solids and a particle-size-distribution (PSD) of these solids in an acceptable micron range. Adding polymeric deflocculant at depths where elevated temperatures are expected assists in rheology control. |
|
| |
|
| The ability to maintain bentonite and other active solids in a deflocculated state is the key to obtaining acceptable rheological and fluid-loss properties for WBFs exposed to high temperatures.<ref name="r1"/> Bentonite can be used in relatively low concentrations, if it is supplemented with a high-temperature, high-molecular-weight synthetic polymer for additional carrying capacity. This combination helps to make it possible to maintain 6% by weight of low-gravity solids and a particle-size-distribution (PSD) of these solids in an acceptable micron range. Adding polymeric deflocculant at depths where elevated temperatures are expected assists in rheology control.
| | An HP/HT viscometer typically is used to monitor the temperature stability of the drilling fluid, and to evaluate its rheological properties at up to 500°F and 20,000 psia. This test is especially useful for determining whether high-temperature flocculation occurs in water-based muds. The test results can be presented graphically by plotting the change in viscosity with respect to temperature over the heating and cooling cycle, which establishes a baseline for recognizing indicators of temperature instability. |
|
| |
|
| An HP/HT viscometer typically is used to monitor the temperature stability of the drilling fluid, and to evaluate its rheological properties at up to 500°F and 20,000 psia. This test is especially useful for determining whether high-temperature flocculation occurs in water-based muds. The test results can be presented graphically by plotting the change in viscosity with respect to temperature over the heating and cooling cycle, which establishes a baseline for recognizing indicators of temperature instability.
| | There are a number of ways to minimize problems with temperature gelation, including: |
|
| |
|
| There are a number of ways to minimize problems with temperature gelation, including:
| | *Eliminating lignite and lignite derivatives from the WBF formulation |
| * Eliminating lignite and lignite derivatives from the WBF formulation | | *Lowering the bentonite concentration |
| * Lowering the bentonite concentration | | *Supplementing the high-temperature water-based system with synthetic polymers and copolymers |
| * Supplementing the high-temperature water-based system with synthetic polymers and copolymers | |
|
| |
|
| OBFs and SBFs are subject to temperature thinning. Surface density should be corrected on the basis of downhole pressure data from a PWD tool. Hydraulics-modeling software that accurately accounts for fluid compressibility and the effect of temperature can improve the performance of the SBF system by allowing more precise surface conditioning. | | OBFs and SBFs are subject to temperature thinning. Surface density should be corrected on the basis of downhole pressure data from a PWD tool. Hydraulics-modeling software that accurately accounts for fluid compressibility and the effect of temperature can improve the performance of the SBF system by allowing more precise surface conditioning. |
|
| |
|
| ==References== | | == References == |
| | |
| | <references /> |
|
| |
|
| <references>
| | == See also == |
| <ref name="r1">Mason, W. and Gleason, D. 2003. System Designed for Deep, Hot Wells. ''American Oil and Gas Reporter'' '''46''' (8): 70.</ref>
| |
| </references>
| |
|
| |
|
| ==See also==
| | [[PEH:Drilling_Fluids]] |
| [[PEH:Drilling Fluids]] | | |
| | == Noteworthy papers in OnePetro == |
|
| |
|
| ==Noteworthy papers in OnePetro==
| |
| Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read | | Use this section to list papers in OnePetro that a reader who wants to learn more should definitely read |
|
| |
|
| ==External links== | | == External links == |
| | |
| Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro | | Use this section to provide links to relevant material on websites other than PetroWiki and OnePetro |
|
| |
|
| [[Category: 1.6 Drilling Operations]] | | ==Category== |
| | [[Category:1.6 Drilling operations]] [[Category:YR]] |