Changes

===Orientation and layout of the cross section===

===Orientation and layout of the cross section===

[[file:geological-cross-sections_fig2.png|thumb|{{figure number|2}}Schematic stratigraphic cross section along part of the north flank of the Wilmington anticline in the Long Beach unit showing log displays. Distance scale is irregular to make the cross section more compact. The left track of each log is an SP or gamma ray trace and the right track is a resistivity trace. (From Slatt et al.<ref name=pt06r122 />)]]

[[file:geological-cross-sections_fig2.png|thumb|{{figure number|2}}Schematic stratigraphic cross section along part of the north flank of the Wilmington anticline in the Long Beach unit showing log displays. Distance scale is irregular to make the cross section more compact. The left track of each log is an [[Basic open hole tools#Spontaneous potential|SP]] or [[Basic open hole tools#Gamma ray|gamma ray]] trace and the right track is a resistivity trace. (From Slatt et al.<ref name=pt06r122 />)]]

The orientation of a cross section must be chosen to balance the need for a clear representation of the features of interest with the availability of appropriate information. In development geology, this information comes largely from well data (geophysical logs, mudlogs, and cores), but in some places, outcrops and seismic reflection data can be used to constrain interpretations (see [[Wellsite methods]], [[Wireline methods]], [[Laboratory methods]], and [[Geophysical methods]]).

The orientation of a cross section must be chosen to balance the need for a clear representation of the features of interest with the availability of appropriate information. In development geology, this information comes largely from well data (geophysical logs, mudlogs, and cores), but in some places, outcrops and seismic reflection data can be used to constrain interpretations (see [[Wellsite methods]], [[Wireline methods]], [[Laboratory methods]], and [[Geophysical methods]]).

If the object of the cross section is to show lateral and vertical details of the stratigraphy, log properties are of utmost importance.

If the object of the cross section is to show lateral and vertical details of the stratigraphy, log properties are of utmost importance.

Typically the SP or gamma ray log and one resistivity log are displayed ([[:file:geological-cross-sections_fig2.png|Figure 2]]). [[Porosity]] logs may also be important, and if seismic data are part of the cross section, the sonic log is a critical tool to demonstrate the velocity structure, and consistency of conversion of time to depth.

Typically the [[Basic open hole tools#Spontaneous potential|SP]] or [[Basic open hole tools#Gamma ray|gamma ray]] log and one resistivity log are displayed ([[:file:geological-cross-sections_fig2.png|Figure 2]]). [[Porosity]] logs may also be important, and if seismic data are part of the cross section, the sonic log is a critical tool to demonstrate the velocity structure, and consistency of conversion of time to depth.

Lines connecting correlative formation or zone tops between wells will show the lateral variation in thickness of these units. If it is important for the display to show exact correlations on logs, these lines should be drawn horizontally across the log display and angled between the edges of adjacent well displays, such as shown in [[:file:geological-cross-sections_fig2.png|Figure 2]]. Straight lines connecting the centers of the well displays may be more appropriate to provide a better representation of the thickness variations of units between wells. If thickness variations or the geometry of units is paramount in importance, then the logs can be reduced in scale so as to form a background or overlay to the formation data. Alternatively, they can be omitted entirely, and well courses can be represented as line segments, as shown in [[:file:geological-cross-sections_fig1.png|Figure 1b]].

Lines connecting correlative formation or zone tops between wells will show the lateral variation in thickness of these units. If it is important for the display to show exact correlations on logs, these lines should be drawn horizontally across the log display and angled between the edges of adjacent well displays, such as shown in [[:file:geological-cross-sections_fig2.png|Figure 2]]. Straight lines connecting the centers of the well displays may be more appropriate to provide a better representation of the thickness variations of units between wells. If thickness variations or the geometry of units is paramount in importance, then the logs can be reduced in scale so as to form a background or overlay to the formation data. Alternatively, they can be omitted entirely, and well courses can be represented as line segments, as shown in [[:file:geological-cross-sections_fig1.png|Figure 1b]].