Changes

[[file:production-logging_fig2.png|thumb|{{figure number|2}}Noise log responses to fluid movement downhole.]]

[[file:production-logging_fig2.png|thumb|{{figure number|2}}Noise log responses to fluid movement downhole.]]

Temperature surveys are the most common surveys to locate fluid movement downhole. Small entries and even flow in channels behind pipe can be detected. Generally, if a well is not flowing, the temperature of the fluid in the borehole will eventually approach the formation temperature, called the ''geothermal gradient''. When a well is produced, formation fluids enter the borehole and move uphole. Gasses typically cool when entering the borehole while liquids do not. In either case, their movement uphole is easily detected by deviations of the borehole temperature from the geothermal gradient. [[:file:production-logging_fig1.png|Figure 1]] illustrates a typical temperature survey response to two gas entries into a well.

Temperature surveys are the most common surveys to locate fluid movement downhole. Small entries and even flow in channels behind pipe can be detected. Generally, if a well is not flowing, the temperature of the fluid in the borehole will eventually approach the formation temperature, called the ''geothermal gradient''. When a well is produced, formation fluids enter the borehole and move uphole. Gasses typically cool when entering the borehole while liquids do not. In either case, their movement uphole is easily detected by deviations of the borehole temperature from the geothermal gradient. [[:file:production-logging_fig1.png|Figure 1]] illustrates a typical temperature survey response to two gas entries into a well.

Noise logs are also used to evaluate fluid movement downhole. Unlike temperature surveys, noise logs are not run continuously across the interval of interest. Instead, a number of stationary readings are taken at different depths downhole. The movement of fluids, especially gasses, generates turbulence or noise, which gets louder as the flow rate or pressure drop increases. [[:file:production-logging_fig2.png|Figure 2]] shows how a noise log can be effective at detecting movement downhole. In this schematic diagram, a source, sink, and restriction to flow are the noise sources. The frequency spectrum of the noise is also observed to further improve the understanding of flow downhole.

Noise logs are also used to evaluate fluid movement downhole. Unlike temperature surveys, noise logs are not run continuously across the interval of interest. Instead, a number of stationary readings are taken at different depths downhole. The movement of fluids, especially gasses, generates turbulence or noise, which gets louder as the flow rate or pressure drop increases. [[:file:production-logging_fig2.png|Figure 2]] shows how a noise log can be effective at detecting movement downhole. In this schematic diagram, a source, sink, and restriction to flow are the noise sources. The frequency spectrum of the noise is also observed to further improve the understanding of flow downhole.

Quantitative evaluation of flow profiles in injection or producing wells is common. Injection wells are most often evaluated with radioactive tracer techniques, while producing wells, where multiphase flow may be encountered, are evaluated using flowmeters with fluid identification devices.

Quantitative evaluation of flow profiles in injection or producing wells is common. Injection wells are most often evaluated with radioactive tracer techniques, while producing wells, where multiphase flow may be encountered, are evaluated using flowmeters with fluid identification devices.

The most effective technique with radioactive tracers is the ''velocity shot'' technique, illustrated in [[:file:production-logging_fig3.png|Figure 3]]. The tool is stationary during such a test, and the gamma count rate is recorded at the surface. In Figure 3, tests were made above, between, and below the perforations, and the surface recordings are shown to the right of the well sketch. The highest velocity and flow rate are recorded above the perforations, while zero flow is detected in the lowest interval. By measurement of the traveltime between detectors, Δt, and using the known spacing between detectors D₁ and D₂, the flow rates can be calculated and an injection profile constructed, as shown on the right of the figure.

The most effective technique with radioactive tracers is the ''velocity shot'' technique, illustrated in [[:file:production-logging_fig3.png|Figure 3]]. The tool is stationary during such a test, and the gamma count rate is recorded at the surface. In [[:file:production-logging_fig3.png|Figure 3]], tests were made above, between, and below the perforations, and the surface recordings are shown to the right of the well sketch. The highest velocity and flow rate are recorded above the perforations, while zero flow is detected in the lowest interval. By measurement of the traveltime between detectors, Δt, and using the known spacing between detectors D₁ and D₂, the flow rates can be calculated and an injection profile constructed, as shown on the right of the figure.

In producing wells, spinner flowmeters are used to measure the bulk flow rate, even in multiphase flow conditions<ref name=pt09r2>Anderson, R. A., Smolen, J. J., Laverdiere, L., Davis, J. A., 1980, A production logging tool with simultaneous measurements: Journal of Petroleum Technology, February, p. 191–198.</ref>. Two such flowmeters are shown in [[:file:production-logging_fig4.png|Figure 4]]. The ''full bore flowmeter'' in [[:file:production-logging_fig4.png|Figure 4(a)]] is run continously across the interval of interest, while the basket type flowmeter in [[:file:production-logging_fig4.png|Figure 4(b)]] uses stationary measurements. Although these devices can determine the bulk flow rate, fluid identification tools are required to evaluate the kinds of fluids present in the flow. These fluid identification instruments measure the pressure gradient, bulk density, or capacitance of the flowing mixture. The flowmeter and fluid identification devices are usually run as a combination on the same tool string. Results typical of such a tool string are shown in [[:file:production-logging_fig5.png|Figure 5]]. In this example, zone A produces water, while the zones above it are all gas producers. A plug set between zones A and B will be effective at eliminating the water production in this example.

In producing wells, spinner flowmeters are used to measure the bulk flow rate, even in multiphase flow conditions<ref name=pt09r2>Anderson, R. A., Smolen, J. J., Laverdiere, L., Davis, J. A., 1980, A production logging tool with simultaneous measurements: Journal of Petroleum Technology, February, p. 191–198.</ref>. Two such flowmeters are shown in [[:file:production-logging_fig4.png|Figure 4]]. The ''full bore flowmeter'' in [[:file:production-logging_fig4.png|Figure 4(a)]] is run continously across the interval of interest, while the basket type flowmeter in [[:file:production-logging_fig4.png|Figure 4(b)]] uses stationary measurements. Although these devices can determine the bulk flow rate, fluid identification tools are required to evaluate the kinds of fluids present in the flow. These fluid identification instruments measure the pressure gradient, bulk density, or capacitance of the flowing mixture. The flowmeter and fluid identification devices are usually run as a combination on the same tool string. Results typical of such a tool string are shown in [[:file:production-logging_fig5.png|Figure 5]]. In this example, zone A produces water, while the zones above it are all gas producers. A plug set between zones A and B will be effective at eliminating the water production in this example.

The well mechanical integrity survey logs include two groups. The first group, cement evaluation surveys, assesses the degree of cement fill around the casing and can be effective at locating potential channels for fluid movement. The second group is the casing inspection surveys, in which acoustic, mechanical, and electromagnetic measurements are used to evaluate internal and external casing conditions.

The well mechanical integrity survey logs include two groups. The first group, cement evaluation surveys, assesses the degree of cement fill around the casing and can be effective at locating potential channels for fluid movement. The second group is the casing inspection surveys, in which acoustic, mechanical, and electromagnetic measurements are used to evaluate internal and external casing conditions.

===Cement evaluation===

===Cement evaluation===

Cement evaluations are primarily done with cement bond logs or pulse-echo cement evaluation tools. These are acoustic devices whose main objectives are the measurement of cement annular fill around the casing.

Cement evaluations are primarily done with cement bond logs or pulse-echo cement evaluation tools. These are acoustic devices whose main objectives are the measurement of cement annular fill around the casing.

The ''cement bond log'' (CBL) measures the degree to which cement contacting the pipe on the outside attenuates an acoustic signal traveling along the pipe<ref name=pt09r21>Pardue, G. H., Morris, R. L., Gollwitzer, L. H., Moran, J. H., 1963, Cement bond log—a study of cement and casing variables: Journal of Petroleum Technology, May.</ref><ref name=pt09r9>Fitzgerald, D. D., McGhee, B. F., McGuire, J. A., 1983, Guidelines for 90% accuracy in zone isolation decisions: Richardson, TX, Society of Petroleum Engineers, SPE 12141.</ref><ref name=pt09r25>Western Atlas International, 1985, Acoustic Cement Bond Log and Prolog CBL: Houston, TX, n. 2206.</ref>. Figure 6 illustrates how the acoustic signal is affected by the presence of cement. The initial portion of the acoustic signal or signature indicates the amplitute of the signal traveling along the pipe. The a mplitude curve records the amplitude of this initial portion or pipe signal. A low amplitude indicates good bond, while a very high signal amplitude shows free pipe. This amplitude measurement can be converted to percent annular fill of cement. The ''variable density log'' (VDL) at the far right of Figure 6 is a contour map of the received wavetrain signature as it changes with depth.

The ''cement bond log'' (CBL) measures the degree to which cement contacting the pipe on the outside attenuates an acoustic signal traveling along the pipe<ref name=pt09r21>Pardue, G. H., Morris, R. L., Gollwitzer, L. H., Moran, J. H., 1963, Cement bond log—a study of cement and casing variables: Journal of Petroleum Technology, May.</ref><ref name=pt09r9>Fitzgerald, D. D., McGhee, B. F., McGuire, J. A., 1983, Guidelines for 90% accuracy in zone isolation decisions: Richardson, TX, Society of Petroleum Engineers, SPE 12141.</ref><ref name=pt09r25>Western Atlas International, 1985, Acoustic Cement Bond Log and Prolog CBL: Houston, TX, n. 2206.</ref>. [[:file:production-logging_fig6.png|Figure 6]] illustrates how the acoustic signal is affected by the presence of cement. The initial portion of the acoustic signal or signature indicates the amplitute of the signal traveling along the pipe. The a mplitude curve records the amplitude of this initial portion or pipe signal. A low amplitude indicates good bond, while a very high signal amplitude shows free pipe. This amplitude measurement can be converted to percent annular fill of cement. The ''variable density log'' (VDL) at the far right of [[:file:production-logging_fig6.png|Figure 6]] is a contour map of the received wavetrain signature as it changes with depth.

 

[[file:production-logging_fig6.png|thumb|{{figure number|6}}CBL logs and their response to various cement conditions.]]

 

The ''pulse-echo cement bond log'' (CET) operates in an entirely different acoustic mode than does the CBL<ref name=pt09r10>Froelich, B., Dumont, A., Pittman, D., Seeman, B., 1982, Cement evaluation tool—a new approach to cement evaluation: Journal of Petroleum Technology, August.</ref>. The pulse-echo tool is effective at measuring the compressive strength of cement behind pipe, as well as detecting the presence of liquid or gas behind pipe. The main presentation of the pulse-echo tool is the cement map shown on the right of Figure 7. The dark areas correspond to cement, and the white areas indicate the lack of it. With such a cement map, likely channels can be readily detected.

[[file:production-logging_fig7.png|thumb|{{figure number|7}}Pulse-echo cement bond log showing cement top and channel on the cement map presentations.]]

The ''pulse-echo cement bond log'' (CET) operates in an entirely different acoustic mode than does the CBL<ref name=pt09r10>Froelich, B., Dumont, A., Pittman, D., Seeman, B., 1982, Cement evaluation tool—a new approach to cement evaluation: Journal of Petroleum Technology, August.</ref>. The pulse-echo tool is effective at measuring the compressive strength of cement behind pipe, as well as detecting the presence of liquid or gas behind pipe. The main presentation of the pulse-echo tool is the cement map shown on the right of [[:file:production-logging_fig7.png|Figure 7]]. The dark areas correspond to cement, and the white areas indicate the lack of it. With such a cement map, likely channels can be readily detected.

===Casing inspection===

===Casing inspection===