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Line 63: − + − + − + − [[file:log-analysis-applications_fig1.png|thumb|{{figure number|1}}Interactive depth shifting. The user marks correlating inflection points and shifts off-depth traces to base trace depths.]] − − [[file:log-analysis-applications_fig2.png|thumb|{{figure number|2}}Interactive spontaneous potential (SP) baseline flattening. The user selects points on the raw SP curve, which represent zero deflection (that is, baseline = 100% shale). By projecting the baseline between two consecutive points, SP deflections are calculated and redisplayed as a baselined (or “static”) SP.]] − − [[file:log-analysis-applications_fig3.png|thumb|{{figure number|3}}A histogram display of a traces value range. Frequency nodes in a trace's data values (''x''<sub>1</sub>, and ''x''<sub>2</sub>) within a given formation are related to geology. Node values are usually consistent and mappable for that interval if observed in multiple wells in an area. If node values are atypical for a given well due to tool miscalibration, a correct distribution and range can be determined and the trace normalized.]]
Log analysis applications (view source)
Revision as of 19:02, 17 January 2014
, 19:02, 17 January 2014→Data editing
==Data editing==
==Data editing==
[[file:log-analysis-applications_fig1.png|left|thumb|{{figure number|1}}Interactive depth shifting. The user marks correlating inflection points and shifts off-depth traces to base trace depths.]]
[[file:log-analysis-applications_fig2.png|thumb|{{figure number|2}}Interactive spontaneous potential (SP) baseline flattening. The user selects points on the raw SP curve, which represent zero deflection (that is, baseline = 100% shale). By projecting the baseline between two consecutive points, SP deflections are calculated and redisplayed as a baselined (or “static”) SP.]]
Options for editing of the data include the following:
Options for editing of the data include the following:
[[file:log-analysis-applications_fig3.png|left|thumb|{{figure number|3}}A histogram display of a traces value range. Frequency nodes in a trace's data values (''x''<sub>1</sub>, and ''x''<sub>2</sub>) within a given formation are related to geology. Node values are usually consistent and mappable for that interval if observed in multiple wells in an area. If node values are atypical for a given well due to tool miscalibration, a correct distribution and range can be determined and the trace normalized.]]
* Merge various traces into a single trace.
* Merge various traces into a single trace.
* Discriminate against invalid data. Using this technique, the user specifies minimum and/or maximum value limits for a primary trace. Then, instead of modifying actual trace values, the trace is scanned, and at depths where data occur outside the limits, flags are set in a separate discriminator trace. When applying the discriminator trace during data displays or calculations, any depths containing flags will either be eliminated from the display or be assigned default calculation values.
* Discriminate against invalid data. Using this technique, the user specifies minimum and/or maximum value limits for a primary trace. Then, instead of modifying actual trace values, the trace is scanned, and at depths where data occur outside the limits, flags are set in a separate discriminator trace. When applying the discriminator trace during data displays or calculations, any depths containing flags will either be eliminated from the display or be assigned default calculation values.
* Apply depth corrections. These fall into two categories:
* Apply depth corrections. These fall into two categories:
*#Depth shifting traces against each other. To do this, the user visually compares base and unshifted traces, marks corresponding data points (Figure 1), and then shifts the off-depth data to the base trace depths.
*#Depth shifting traces against each other. To do this, the user visually compares base and unshifted traces, marks corresponding data points ([[:file:log-analysis-applications_fig1.png|Figure 1]]), and then shifts the off-depth data to the base trace depths.
*#Correct for true vertical depth (TVD), true vertical thickness (TVT), and/or true stratigraphic thickness (see [[Preprocessing of logging data]]).
*#Correct for true vertical depth (TVD), true vertical thickness (TVT), and/or true stratigraphic thickness (see [[Preprocessing of logging data]]).
* Baseline the spontaneous potential (SP). Interactively flattening the SP to a shale baseline at a single value (Figure 2) allows the user to look at SP values quantitatively in order to calculate water resistivity (''R''<sub>w</sub>) and estimate shale content.
* Baseline the spontaneous potential (SP). Interactively flattening the SP to a shale baseline at a single value ([[:file:log-analysis-applications_fig2.png|Figure 2]]) allows the user to look at SP values quantitatively in order to calculate water resistivity (''R''<sub>w</sub>) and estimate shale content.
* Convert data scales (both ways): conductivity to resistivity, raw data to porosities, neutron porosities to a different matrix, metric to English depth units, percent to decimal, and so on.
* Convert data scales (both ways): conductivity to resistivity, raw data to porosities, neutron porosities to a different matrix, metric to English depth units, percent to decimal, and so on.
* Data normalization. This procedure assumes the values in an individual data trace are credible but require some modification. This involves modifying data values with an atypical distribution and/or range to a “normal” distribution and range (see Figure 3 and discussion of histograms). Proper normalization must first account for borehole conditions during each run, ''and'' geological changes taking place across a wider geographic area. Normalization is accomplished by applying the equation:
* Data normalization. This procedure assumes the values in an individual data trace are credible but require some modification. This involves modifying data values with an atypical distribution and/or range to a “normal” distribution and range (see [[:file:log-analysis-applications_fig3.png|Figure 3]] and discussion of histograms). Proper normalization must first account for borehole conditions during each run, ''and'' geological changes taking place across a wider geographic area. Normalization is accomplished by applying the equation:
:<math>y = ax + b</math>
:<math>y = ax + b</math>
where
where