Changes

[[file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig2.png|300px|thumb|{{figure number|2}}Gamma ray correlation (dip section) of a series of prograding shoreface sandstones. Note the imbricate nature of the sandstone bodies and the “non-layer cake” nature of the correlations.]]

[[file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig2.png|300px|thumb|{{figure number|2}}Gamma ray correlation (dip section) of a series of prograding shoreface sandstones. Note the imbricate nature of the sandstone bodies and the “non-layer cake” nature of the correlations.]]

Interpretations of depositional environment based on individual well data are transformed into a three-dimensional picture of the reservoir by wireline [[log correlation]] and, where possible, by [[3-D seismic: the data cube|three-dimensional seismic data]].

Interpretations of depositional environment based on individual well data are transformed into a three-dimensional picture of the reservoir by wireline log correlation and, where possible, by [[3-D seismic: the data cube|three-dimensional seismic data]].

Wireline logs to be used for facies analysis should, whenever possible, always be calibrated by core. This calibration involves (1) shifting core to log depths (see [[Preprocessing of logging data]] and [[Core-log transformations and porosity-permeability relationships]]) and (2) establishing a relationship between lithofacies associations and [[Quick-look lithology from logs|curve shape]]. [[Core gamma scans]], obtained by passing the core through a device that measures the natural radioactivity of the rock, are particularly useful for shifting cores to logs. The calibration of wireline log shape by core is particularly important for firmly establishing the log response and the identity of vertical sequences on these logs.

Wireline logs to be used for facies analysis should, whenever possible, always be calibrated by core. This calibration involves (1) shifting core to log depths (see [[Preprocessing of logging data]] and [[Core-log transformations and porosity-permeability relationships]]) and (2) establishing a relationship between lithofacies associations and [[Quick-look lithology from logs|curve shape]]. [[Core gamma scans]], obtained by passing the core through a device that measures the natural radioactivity of the rock, are particularly useful for shifting cores to logs. The calibration of wireline log shape by core is particularly important for firmly establishing the log response and the identity of vertical sequences on these logs.

Correlation sections that will be used for establishing sandstone body geometry should have a depositionally flat datum (such as a [[bentonit]]e bed, marine shale bed, or laterally persistent limestone). Sections should be oriented parallel and perpendicular to depositional [[strike]], if known, and represent as straight a line as possible given well density and placement.

Correlation sections that will be used for establishing sandstone body geometry should have a depositionally flat datum (such as a [[bentonit]]e bed, marine shale bed, or laterally persistent limestone). Sections should be oriented parallel and perpendicular to depositional [[strike]], if known, and represent as straight a line as possible given well density and placement.

The only sedimentologically significant correlation horizons are those that approximate [[time lines]] within and between sandstone bodies. This style of correlation requires an understanding of the succession of depositional environments and intervening [[Unconformity|unconformable surfaces]]. It often leads to nonparallel and nonhorizontal correlations. For example, in [[Lithofacies and environmental analysis of clastic depositional systems#Shoreline deposits|shoreface]] systems, time lines denoted by shale or silt breaks between shingled shoreface sheets and lenses are inclined in a seaward (depositional [[dip]]) direction ([[:file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig2.png|Figure 2]]).

The only sedimentologically significant correlation horizons are those that approximate time lines within and between sandstone bodies. This style of correlation requires an understanding of the succession of depositional environments and intervening [[Unconformity|unconformable surfaces]]. It often leads to nonparallel and nonhorizontal correlations. For example, in [[Lithofacies and environmental analysis of clastic depositional systems#Shoreline deposits|shoreface]] systems, time lines denoted by shale or silt breaks between shingled shoreface sheets and lenses are inclined in a seaward (depositional [[dip]]) direction ([[:file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig2.png|Figure 2]]).

This imbrication does not occur in a strike direction. This style of correlation is especially important for reservoir delineation since the large scale (interwell and field) architecture of the sandstone body exerts a control on the movement of fluids through the volume of the reservoir.

This imbrication does not occur in a strike direction. This style of correlation is especially important for reservoir delineation since the large scale (interwell and field) architecture of the sandstone body exerts a control on the movement of fluids through the volume of the reservoir.