Changes

[[file:predicting-reservoir-system-quality-and-performance_fig9-54.png|300px|thumb|{{figure number|1}}Example of regression porosity–depth plots for different formations along the U.S. Gulf Coast. From Loucks et al.;<ref name=Loucks>Loucks, R. G., M. M. Dodge, and W. E. Galloway, 1984, [http://archives.datapages.com/data/specpubs/sandsto2/data/a059/a059/0001/0000/0015.htm Regional controls on diagenesis and reservoir quality in Lower Tertiary sandstones along the Texas Gulf Coast], in D. A. McDonald and R. C. Surdam, eds., Clastic Diagenesis: AAPG Memoir 37, p. 15–45.</ref> courtesy AAPG.]]

[[file:predicting-reservoir-system-quality-and-performance_fig9-54.png|300px|thumb|{{figure number|1}}Example of regression porosity–depth plots for different formations along the U.S. Gulf Coast. From Loucks et al.;<ref name=Loucks>Loucks, R. G., M. M. Dodge, and W. E. Galloway, 1984, [http://archives.datapages.com/data/specpubs/sandsto2/data/a059/a059/0001/0000/0015.htm Regional controls on diagenesis and reservoir quality in Lower Tertiary sandstones along the Texas Gulf Coast], in D. A. McDonald and R. C. Surdam, eds., Clastic Diagenesis: AAPG Memoir 37, p. 15–45.</ref> courtesy AAPG.]]

A pitfall of using porosity–depth plots for porosity prediction is that regression relationship averages out anomalies and complicates predictions of unusually porous sandstones. Use porosity–depth plots for porosity prediction with caution. If enough porosity data are available to make a meaningful plot, keep the “data cloud” on the plot in order to view the ranges of porosity at different depths. In a frontier exploration setting, the usefulness of porosity–depth plots may be limited if global data sets must be used.

A pitfall of using porosity–depth plots for porosity prediction is that [[Correlation and regression analysis|regression]] relationship averages out anomalies and complicates predictions of unusually porous sandstones. Use porosity–depth plots for porosity prediction with caution. If enough porosity data are available to make a meaningful plot, keep the “data cloud” on the plot in order to view the ranges of porosity at different depths. In a frontier exploration setting, the usefulness of porosity–depth plots may be limited if global data sets must be used.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-54.png|Figure 1]] is an example of regression porosity–depth plots for different formations along the U.S. Gulf Coast. Unfortunately it does not include the raw data, so we cannot see porosity variations within each formation. Formations on the left side of the plot, like the Vicksburg, tend to be quartz cemented. Formations on the right side, like the Frio (areas 4-6). tend to be clay cemented.

[[:file:predicting-reservoir-system-quality-and-performance_fig9-54.png|Figure 1]] is an example of regression porosity–depth plots for different formations along the U.S. Gulf Coast. Unfortunately it does not include the raw data, so we cannot see porosity variations within each formation. Formations on the left side of the plot, like the Vicksburg, tend to be quartz cemented. Formations on the right side, like the Frio (areas 4-6). tend to be clay cemented.