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| | part = Critical elements of the petroleum system | | | part = Critical elements of the petroleum system |
| | chapter = Formation fluid pressure and its application | | | chapter = Formation fluid pressure and its application |
− | | frompg = 5-1 | + | | frompg = 5-33 |
− | | topg = 5-64 | + | | topg = 5-35 |
| | author = Edward A. Beaumont, Forrest Fiedler | | | author = Edward A. Beaumont, Forrest Fiedler |
| | link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm | | | link = http://archives.datapages.com/data/specpubs/beaumont/ch05/ch05.htm |
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| ==RFT tool== | | ==RFT tool== |
| | | |
− | [[file:formation-fluid-pressure-and-its-application_fig5-16.png|thumb|300px|{{figure number|1}}Formation pressure is measured by the formation sampler when it is extended from the tool to contact the formation.<ref name=ch05r5>Dahlberg, E., C., 1994, Applied Hydrodynamics in Petroleum Exploration, 2nd ed.: New York, Springer-Verlag, 295 p.</ref> Copyright: Springer-Verlag.]] | + | [[file:formation-fluid-pressure-and-its-application_fig5-16.png|thumb|350px|{{figure number|1}}Formation pressure is measured by the formation sampler when it is extended from the tool to contact the formation.<ref name=ch05r5>Dahlberg, E., C., 1994, Applied Hydrodynamics in Petroleum Exploration, 2nd ed.: New York, Springer-Verlag, 295 p.</ref> Copyright: Springer-Verlag.]] |
| | | |
− | The repeat formation tester (RFT) tool was designed to measure formation pressure quickly and accurately. It measures pressure at specific points on the borehole wall. The diagram below shows a typical RFT tool. Formation pressure is measured by the formation sampler ([[:file:formation-fluid-pressure-and-its-application_fig5-16.png|Figure 1]]) when it is extended from the tool to contact the formation. Fluid samples from the formation can also be taken with the tool. | + | The [[Wireline formation testers|repeat formation tester (RFT)]] tool was designed to measure formation pressure quickly and accurately. It measures pressure at specific points on the borehole wall. The diagram below shows a typical RFT tool. Formation pressure is measured by the formation sampler ([[:file:formation-fluid-pressure-and-its-application_fig5-16.png|Figure 1]]) when it is extended from the tool to contact the formation. Fluid samples from the formation can also be taken with the tool. |
| | | |
| ==Differences between RFTs and DSTs== | | ==Differences between RFTs and DSTs== |
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| {| class = "wikitable" | | {| class = "wikitable" |
| |- | | |- |
− | ! Consideration | + | ! Consideration || RFTs || DSTs |
− | ! RFTs
| |
− | ! DSTs
| |
| |- | | |- |
− | | Time to take one measurement | + | | Time to take one measurement || Less than 5 minutes for permeable formations || More than 90 minutes |
− | | Less than 5 minutes for permeable formations | |
− | | More than 90 minutes | |
| |- | | |- |
− | | Drilling delay to run test | + | | Drilling delay to run test || About one logging run (wireline conveyed) || About equal to two trips with drillstring |
− | | About one logging run (wireline conveyed) | |
− | | About equal to two trips with drillstring | |
| |- | | |- |
− | | Sampling interval | + | | Sampling interval || Small || Several feet or more; generally tests multiple flow units |
− | | Small, | |
− | | Several feet or more; generally tests multiple flow units | |
| |- | | |- |
− | | Samples per run | + | | Samples per run || Many || Few |
− | | Many | |
− | | Few | |
| |- | | |- |
− | | Expense per test | + | | Expense per test || Small || Large |
− | | Small | |
− | | Large | |
| |- | | |- |
− | | Purpose of tool | + | | Purpose of tool || Pressure measurement || Fluid recovery and pressure |
− | | Pressure measurement | |
− | | Fluid recovery and pressure | |
| |- | | |- |
− | | Survey problems | + | | Survey problems || |
− | | * Getting good seat to measure pressure * Screen plugging with material in drilling mud
| + | * Getting good seat to measure pressure |
− | | + | * Screen plugging with material in drilling mud |
− | | * Packer failure * Depth determination
| + | | |
− | | + | * Packer failure |
| + | * Depth determination |
| |- | | |- |
− | | Fractured reservoir | + | | Fractured reservoir || May be unreliable || Good if fractures intersect wellbore |
− | | May be unreliable | |
− | | Good if fractures intersect wellbore | |
| |- | | |- |
− | | Layered reservoir | + | | Layered reservoir || Not representative || Good if many layers are included in tested interval |
− | | Not representative | |
− | | Good if many layers are included in tested interval | |
| |- | | |- |
− | | Skin damage | + | | Skin damage || Can be major error || Can be measured and corrected for |
− | | Can be major error | |
− | | Can be measured and corrected for | |
| |} | | |} |
| | | |
| ==Example: comparing RFT to DST== | | ==Example: comparing RFT to DST== |
| | | |
− | [[file:formation-fluid-pressure-and-its-application_fig5-17.png|thumb|{{figure number|2}}Plot of reservoir pressure vs. depth from a low-[[permeability]] chalk reservoir.<ref name=ch05r9 /> Courtesy JPT.]] | + | [[file:formation-fluid-pressure-and-its-application_fig5-17.png|300px|thumb|{{figure number|2}}Plot of reservoir pressure vs. depth from a low-[[permeability]] chalk reservoir.<ref name=ch05r9 /> Courtesy JPT.]] |
| | | |
| [[:file:formation-fluid-pressure-and-its-application_fig5-17.png|Figure 2]] is a plot of reservoir pressure vs. depth from a low-[[permeability]] chalk reservoir. The RFT data clearly show the hydrostatic gradient, the gas gradient, and the gas-water contact. Making the same interpretation from the DST data in this example is very difficult because data are from a low-permeability chalk reservoir. Reliable pressures are difficult to obtain in low-permeability reservoirs with DSTs. Extrapolated DST shut-in pressures from a partial buildup may not reflect actual fluid pressures. As rock quality increases, extrapolated pore pressure from DST buildup falls more and more closely to actual fluid pressure. | | [[:file:formation-fluid-pressure-and-its-application_fig5-17.png|Figure 2]] is a plot of reservoir pressure vs. depth from a low-[[permeability]] chalk reservoir. The RFT data clearly show the hydrostatic gradient, the gas gradient, and the gas-water contact. Making the same interpretation from the DST data in this example is very difficult because data are from a low-permeability chalk reservoir. Reliable pressures are difficult to obtain in low-permeability reservoirs with DSTs. Extrapolated DST shut-in pressures from a partial buildup may not reflect actual fluid pressures. As rock quality increases, extrapolated pore pressure from DST buildup falls more and more closely to actual fluid pressure. |
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| ==RFT pressure profile== | | ==RFT pressure profile== |
| | | |
− | [[file:formation-fluid-pressure-and-its-application_fig5-18.png|thumb|{{figure number|3}}Typical RFT pressure-time profile..]] | + | [[file:formation-fluid-pressure-and-its-application_fig5-18.png|thumb|300px|{{figure number|3}}Typical RFT pressure-time profile..]] |
| | | |
| [[:file:formation-fluid-pressure-and-its-application_fig5-18.png|Figure 3]] is a typical RFT pressure-time profile. Points are similar to points on a DST pressure profile. | | [[:file:formation-fluid-pressure-and-its-application_fig5-18.png|Figure 3]] is a typical RFT pressure-time profile. Points are similar to points on a DST pressure profile. |
| | | |
| ==Operating an RFT survey== | | ==Operating an RFT survey== |
− | The table below explains how to operate an RFT survey (see Gunter & Moore<ref name=ch05r9>Gunter, J., M., Moore, C., V., 1987, Improved use of wireline testers for reservoir evaluation: Journal of Petroleum Technology, p. 635–644.</ref>). | + | The list below explains how to operate an RFT survey (see Gunter & Moore<ref name=ch05r9>Gunter, J., M., Moore, C., V., 1987, Improved use of wireline testers for reservoir evaluation: Journal of Petroleum Technology, p. 635–644.</ref>). |
| | | |
− | {| class = "wikitable"
| + | # Use well logs to pick permeable zones for formation pressure measurements. Look for an invasion profile. |
− | |-
| + | # Plot mud hydrostatic and formation pressure at the well site to recognize anomalies or tool errors and to optimize station coverage. |
− | ! Step
| + | # Occasionally repeat formation pressure measurements at the same depth to check for consistency. |
− | ! Action
| + | # Repeat at some of the same depths for multiple surveys to help normalize the different surveys. |
− | |-
| + | # Sample both water- and hydrocarbon-bearing intervals to establish both the water and hydrocarbon pressure gradients. |
− | | 1
| + | # Plot pressures at the same scale as well logs to aid in interpretation. |
− | | Use well logs to pick permeable zones for formation pressure measurements. Look for an invasion profile.
| |
− | |-
| |
− | | 2
| |
− | | Plot mud hydrostatic and formation pressure at the well site to recognize anomalies or tool errors and to optimize station coverage.
| |
− | |-
| |
− | | 3
| |
− | | Occasionally repeat formation pressure measurements at the same depth to check for consistency.
| |
− | |-
| |
− | | 4
| |
− | | Repeat at some of the same depths for multiple surveys to help normalize the different surveys.
| |
− | |-
| |
− | | 5
| |
− | | Sample both water- and hydrocarbon-bearing intervals to establish both the water and hydrocarbon pressure gradients.
| |
− | |-
| |
− | | 6
| |
− | | Plot pressures at the same scale as well logs to aid in interpretation.
| |
− | |}
| |
| | | |
| ==Controlling RFT quality== | | ==Controlling RFT quality== |
− | The table below describes how to control RFT quality. For details, see Gunter & Moore.<ref name=ch05r9 /> | + | The list below describes how to control RFT quality. For details, see Gunter & Moore.<ref name=ch05r9 /> |
| | | |
− | {| class = "wikitable"
| + | # Inspect the tool and check calibration before going in the hole. |
− | |-
| + | # Run quartz and strain gauges simultaneously. Record both readings independently. Normalize to one another after completing the survey. |
− | ! Step
| + | # Maintain a slight overflow of mud to keep the level in the borehole constant during the survey and to prevent mud hydrostatic pressure errors. |
− | ! Action
| + | # Take mud hydrostatic pressures while descending into the hole to give the instruments time to equilibrate to changing temperature and pressure and to provide a mud hydrostatic pressure profile. |
− | |-
| + | # Check for tool errors by calculating mud hydrostatic pressures at different depths from mud weight; check them against measured mud hydrostatic pressures at the same depths. |
− | | 1
| |
− | | Inspect the tool and check calibration before going in the hole.
| |
− | |-
| |
− | | 2
| |
− | | Run quartz and strain gauges simultaneously. Record both readings independently. Normalize to one another after completing the survey.
| |
− | |-
| |
− | | 3
| |
− | | Maintain a slight overflow of mud to keep the level in the borehole constant during the survey and to prevent mud hydrostatic pressure errors.
| |
− | |-
| |
− | | 4
| |
− | | Take mud hydrostatic pressures while descending into the hole to give the instruments time to equilibrate to changing temperature and pressure and to provide a mud hydrostatic pressure profile.
| |
− | |-
| |
− | | 5
| |
− | | Check for tool errors by calculating mud hydrostatic pressures at different depths from mud weight; check them against measured mud hydrostatic pressures at the same depths.
| |
− | |}
| |
| | | |
| ==See also== | | ==See also== |
| * [[Methods for obtaining formation fluid pressures]] | | * [[Methods for obtaining formation fluid pressures]] |
| * [[Determining formation fluid pressure from DSTs]] | | * [[Determining formation fluid pressure from DSTs]] |
| + | * [[Wireline formation testers]] |
| | | |
| ==References== | | ==References== |
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| [[Category:Critical elements of the petroleum system]] | | [[Category:Critical elements of the petroleum system]] |
| [[Category:Formation fluid pressure and its application]] | | [[Category:Formation fluid pressure and its application]] |
| + | [[Category:Treatise Handbook 3]] |