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==Production logs==
==Production logs==
Production logs are run in a producing well to determine downhole flow rates and to evaluate reservoir sweep ([[:file:M91Ch6FG45.JPG|Figure 6]]; Table 10). They give the subsurface team an understanding of how the reservoir is behaving under production. For example, if a well is producing water, the logs can then be analyzed to determine which perforated intervals are sourcing the water. The perforations can then be isolated to restore the well to dry oil production (Smolen, 1992b).
Production logs are run in a producing well to determine downhole flow rates and to evaluate reservoir sweep ([[:file:M91Ch6FG45.JPG|Figure 6]]; Table 4). They give the subsurface team an understanding of how the reservoir is behaving under production. For example, if a well is producing water, the logs can then be analyzed to determine which perforated intervals are sourcing the water. The perforations can then be isolated to restore the well to dry oil production (Smolen, 1992b).
{| class = "wikitable"
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|+ {{table number|4}}The main production log types
|-
! Production log || How it works || What it is used for
|-
| Flowmeter log || Flow from the reservoir turns a spinner; the faster the flow, the faster the spinner turns || The flow rates and flow profile of a reservoir interval can be derived from the spin rate
|-
| Shut-in flowmeter log || The well is shut in; the tool measures fluid flowing from high- to low-pressured reservoir intervals via the wellbore || Can be used to pick out vertical permeability barriers
|-
| Pulsed neutron log || The tool bombards the pore fluid with high-energy neutrons that pass through the well casing; the neutrons are captured typically by chlorine atoms, and the gamma radiation emitted in response is measured; the log is sensitive to chlorine abundance and hence the water saturation and the salinity of the pore fluids || Fluid saturations are determined from the log results and hence the degree of sweep behind the casing can be calculated
|-
| Fluid density log || A variety of tools measure the fluid density by recording either the pressure gradient, the bulk density, or the capacitance of the flowing mixture in the well || Where more than one flowing phase is present, the fraction of a particular fluid flowing can be calculated, i.e., water, oil, or gas
|-
| Temperature log || Records a temperature profile || For example, can determine which interval is taking (cold) injection water in an injection well
|-
| Gamma-ray spectrometer log || Measures element concentrations, especially carbon/oxygen ratios || Indication of hydrocarbon saturations, particularly in low-salinity, clean sandstones
|}
The geologist uses production-log data to determine the flow geology characteristics of the reservoir and to help establish where there may be unswept oil and gas targets.
The geologist uses production-log data to determine the flow geology characteristics of the reservoir and to help establish where there may be unswept oil and gas targets.