Changes

====Procedures to Capture Mudstone Description in Cores and Outcrops====

====Procedures to Capture Mudstone Description in Cores and Outcrops====

Millimeter-to-centimeter-scale observations of mudstone strata and their stacking patterns are recorded keeping track of the abundance of each physical, biological, and chemical attribute. One can then recognize laminae, laminasets, beds, and bedsets, and aggregate these observations into facies, facies associations, and facies-association successions<ref name=Bhcsea2014 /><ref name=Lzrea2015a /><ref name=Lzrea2015b />. An example of a description form and symbols we use to capture lamina-to-bedset-scale observations in mudstone successions is given in [[:file:M126CH3-Figure2.jpeg|Figure 2]]. Such a form clearly separates observations from interpretations, along with differentiating the various levels of interpretations; it captures observations on the left side; first to the right are lower level interpretations (e.g., sedimentary structures) and then higher level interpretations (e.g., benthic-energy and oxygen levels, depositional environments; [[:file:M126CH3-Figure2.jpeg|Figure 2]]).

Millimeter-to-centimeter-scale observations of mudstone strata and their stacking patterns are recorded keeping track of the abundance of each physical, biological, and chemical attribute. One can then recognize laminae, laminasets, beds, and bedsets, and aggregate these observations into facies, facies associations, and facies-association successions<ref name=Bhcsea2014 /><ref name=Lzrea2015a /><ref name=Lzrea2015b />. An example of a description form and symbols we use to capture lamina-to-bedset-scale observations in mudstone successions is given in [[:file:M126CH03-Figure2.jpeg|Figure 2]]. Such a form clearly separates observations from interpretations, along with differentiating the various levels of interpretations; it captures observations on the left side; first to the right are lower level interpretations (e.g., sedimentary structures) and then higher level interpretations (e.g., benthic-energy and oxygen levels, depositional environments; [[:file:M126CH03-Figure2.jpeg|Figure 2]]).

[[file:M126CH3-Figure2.jpeg|thumb|300px|{{figure number|2}}2A. Example of a form that we recommend using to capture the key attributes of mudstones observed in cores. 2B. Example of symbols useful for capturing mudstone observations in cores and hand specimens (after Lazar et al. <ref name=Lzrea2015b /> used with permission).

[[file:M126CH03-Figure2.jpeg|thumb|300px|{{figure number|2}}2A. Example of a form that we recommend using to capture the key attributes of mudstones observed in cores. 2B. Example of symbols useful for capturing mudstone observations in cores and hand specimens (after Lazar et al. <ref name=Lzrea2015b /> used with permission).

=====Observations=====

=====Observations=====

Key attributes to capture include the following (see also [[:file:M126CH3-Table2.jpeg|Table 2]] and [[Mudstone nomenclature]] and [[Laminasets, beds, and bedsets]]:

Key attributes to capture include the following (see also [[:file:M126CH03-Table2.jpeg|Table 2]] and [[Mudstone nomenclature]] and [[Laminasets, beds, and bedsets]]:

[[file:M126CH3-Table2.jpeg|thumb|300px|’’Table 2.’’ Mudstone Attributes Most Useful for Sequence-stratigraphic Analyses.]]

[[file:M126CH03-Table2.jpeg|thumb|300px|’’Table 2.’’ Mudstone Attributes Most Useful for Sequence-stratigraphic Analyses.]]

* Depth or elevation

* Depth or elevation

=====Interpretations=====

=====Interpretations=====

It is important to comment on the following (see also [[:file:M126CH3-Table2|Table 2]] , [[Laminasets, beds, and bedsets]], and [[Parasequences]]<ref>Bohacs, K. M., O. R. Lazar, and T. M. Demko, 2022a, Parasequences, in K. M. Bohacs and O. R. Lazar, eds., Sequence stratigraphy: Applications to fine-grained rocks: AAPG Memoir 126, p. 107–148.</ref>):

It is important to comment on the following (see also [[:file:M126CH03-Table2|Table 2]] , [[Laminasets, beds, and bedsets]], and [[Parasequences]]<ref>Bohacs, K. M., O. R. Lazar, and T. M. Demko, 2022a, Parasequences, in K. M. Bohacs and O. R. Lazar, eds., Sequence stratigraphy: Applications to fine-grained rocks: AAPG Memoir 126, p. 107–148.</ref>):

* Origin of grains

* Origin of grains

* Transportation, depositional, and reworking processes

* Transportation, depositional, and reworking processes

=====Consistency of Marine Substrate=====

=====Consistency of Marine Substrate=====

Organisms bioturbating fine-grained sediments may produce different burrows depending on substrate consistency<ref name=LbzSchbr><ref name=Schbr2003 /><ref name=WtzlUchmn /><ref>Wetzel, A., 1991, Ecologic interpretation of deep-sea trace fossil communities: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 85, p. 7–69.</ref><ref>Bromley, R. G., 1996, Trace fossils biology, taphonomy and applications, 2nd ed.: London, Chapman and Hall, 361 p.</ref><ref>Brett, C. E., and P. A. Allison, 1998, Paleontological approaches to the environmental interpretation of marine mudrocks, in J. Schieber, W. Zimmerle, and P. Sethi, eds., Shales and mudstones I.: Stuttgart, Germany, E. Schweizerbart’sche Verlagsbuchhandlung (Nagele u. Obermiller), p. 301–349.</ref>. Five levels of substrate consistency can be inferred from ichnofossil analysis—from “soupground” to “hardground” ([[file:M126CH3-Table3]]).

Organisms bioturbating fine-grained sediments may produce different burrows depending on substrate consistency<ref name=LbzSchbr><ref name=Schbr2003 /><ref name=WtzlUchmn /><ref>Wetzel, A., 1991, Ecologic interpretation of deep-sea trace fossil communities: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 85, p. 7–69.</ref><ref>Bromley, R. G., 1996, Trace fossils biology, taphonomy and applications, 2nd ed.: London, Chapman and Hall, 361 p.</ref><ref>Brett, C. E., and P. A. Allison, 1998, Paleontological approaches to the environmental interpretation of marine mudrocks, in J. Schieber, W. Zimmerle, and P. Sethi, eds., Shales and mudstones I.: Stuttgart, Germany, E. Schweizerbart’sche Verlagsbuchhandlung (Nagele u. Obermiller), p. 301–349.</ref>. Five levels of substrate consistency can be inferred from ichnofossil analysis—from “soupground” to “hardground” ([[file:M126CH03-Table3]]).

[[file:M126CH3-Table3.jpeg|thumb|300px|’’Table 3.’’ Inferred Substrate Consistency Based on Ichnofossils Analysis.]]

[[file:M126CH03-Table3.jpeg|thumb|300px|’’Table 3.’’ Inferred Substrate Consistency Based on Ichnofossils Analysis.]]

=====Rock-Color Charts=====

=====Rock-Color Charts=====

====Total Organic Carbon Content====

====Total Organic Carbon Content====

Vertical and lateral profiles of total organic carbon (TOC) content have been used for rapid screening of the quality and distribution of mudstones as source, reservoirs, and seals of hydrocarbons ([[:file:M126CH3-Table4.jpeg|Table 4]]). The TOC content of a rock is the result of the nonlinear interaction of the rates of organic-matter production, destruction, and dilution<ref name=Bhcsea2005 /><ref name=Lzr2007 /><ref name=Sgmnea2003 /><ref name=Rmmrea2004 /><ref name=Tsn1995>Tyson, R. V., 1995, Sedimentary organic matter: Organic facies and palynofacies: Amsterdam, the Netherlands, Springer, 615 p.</ref><ref>Tyson, R. V., 2001, Sedimentation rate, dilution, preservation and total organic carbon: Some results of a modelling study: Organic Geochemistry, v. 32, p. 333–339.</ref><ref>Tyson, R. V., 2005, The “productivity versus preservation” controversy: Cause, flaws, and resolution, ‘’in’’ N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 17–33.</ref><ref name=Bhcsea2000>Bohacs, K. M., A. R. Carroll, J. E. Neal, and P. J. Mankiewicz, 2000, Lake-basin type, source potential, and hydrocarbon character: An integrated sequence-stratigraphic-geochemical framework, in E. Gierlowski-Kordesch, and K. Kelts, eds., Lake basins through space and time: AAPG Studies in Geology 46, p. 3–37.</ref><ref>Harris, N. B., 2005, The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences-introduction, in N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 1–5.</ref><ref> Katz, B. J., 2005, Controlling factors on source rock development-a review of productivity, preservation, and sedimentation rate, in N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 7–16.</ref>. High TOC contents record the optimized combinations of moderately high production, low destruction, and low dilution rates. Low TOC contents can be the result of low production, high dilution, or high destruction rates, as well as high thermal maturity. As referenced in the section on Well-Log Tools (and discussed in [[Sequence sets and composite sequences]]<ref name=Bhcs22b>Bohacs, K. M., O. R. Lazar, T. M. Demko, J. Ottmann, and K. Potma, 2022b, Sequence sets and composite sequences, in K. M. Bohacs and O. R. Lazar, eds., Sequence stratigraphy: Applications to fine-grained rocks: AAPG Memoir 126, p. 195–222.</ref>), the vertical profile of TOC has been related to physiographic setting and sequence-stratigraphic units (i.e., parasequence, parasequence set, sequence, and sequence-set scale; see discussions in Creaney and Passey<ref>Creaney, S., and Q. R. Passey, 1993, Recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework: AAPG Bulletin, v. 77, p. 386–401.</ref>, Bohacs<ref name=Bhcs1998 />, and Bohacs et al.<ref name=Bhcsea2005 />).

Vertical and lateral profiles of total organic carbon (TOC) content have been used for rapid screening of the quality and distribution of mudstones as source, reservoirs, and seals of hydrocarbons ([[:file:M126CH03-Table4.jpeg|Table 4]]). The TOC content of a rock is the result of the nonlinear interaction of the rates of organic-matter production, destruction, and dilution<ref name=Bhcsea2005 /><ref name=Lzr2007 /><ref name=Sgmnea2003 /><ref name=Rmmrea2004 /><ref name=Tsn1995>Tyson, R. V., 1995, Sedimentary organic matter: Organic facies and palynofacies: Amsterdam, the Netherlands, Springer, 615 p.</ref><ref>Tyson, R. V., 2001, Sedimentation rate, dilution, preservation and total organic carbon: Some results of a modelling study: Organic Geochemistry, v. 32, p. 333–339.</ref><ref>Tyson, R. V., 2005, The “productivity versus preservation” controversy: Cause, flaws, and resolution, ‘’in’’ N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 17–33.</ref><ref name=Bhcsea2000>Bohacs, K. M., A. R. Carroll, J. E. Neal, and P. J. Mankiewicz, 2000, Lake-basin type, source potential, and hydrocarbon character: An integrated sequence-stratigraphic-geochemical framework, in E. Gierlowski-Kordesch, and K. Kelts, eds., Lake basins through space and time: AAPG Studies in Geology 46, p. 3–37.</ref><ref>Harris, N. B., 2005, The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences-introduction, in N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 1–5.</ref><ref> Katz, B. J., 2005, Controlling factors on source rock development-a review of productivity, preservation, and sedimentation rate, in N. B. Harris, ed., The deposition of organic-carbon-rich sediments: Models, mechanisms, and consequences: SEPM Special Publication 82, p. 7–16.</ref>. High TOC contents record the optimized combinations of moderately high production, low destruction, and low dilution rates. Low TOC contents can be the result of low production, high dilution, or high destruction rates, as well as high thermal maturity. As referenced in the section on Well-Log Tools (and discussed in [[Sequence sets and composite sequences]]<ref name=Bhcs22b>Bohacs, K. M., O. R. Lazar, T. M. Demko, J. Ottmann, and K. Potma, 2022b, Sequence sets and composite sequences, in K. M. Bohacs and O. R. Lazar, eds., Sequence stratigraphy: Applications to fine-grained rocks: AAPG Memoir 126, p. 195–222.</ref>), the vertical profile of TOC has been related to physiographic setting and sequence-stratigraphic units (i.e., parasequence, parasequence set, sequence, and sequence-set scale; see discussions in Creaney and Passey<ref>Creaney, S., and Q. R. Passey, 1993, Recurring patterns of total organic carbon and source rock quality within a sequence stratigraphic framework: AAPG Bulletin, v. 77, p. 386–401.</ref>, Bohacs<ref name=Bhcs1998 />, and Bohacs et al.<ref name=Bhcsea2005 />).

  [[file:M126CH3-Table4.jpeg|thumb|300px|’’Table 4.’’ Essential Attributes of Mudstones as Hydrocarbon Sources, Reservoirs, and Seals.]]

  [[file:M126CH03-Table4.jpeg|thumb|300px|’’Table 4.’’ Essential Attributes of Mudstones as Hydrocarbon Sources, Reservoirs, and Seals.]]

TOC content can be measured through direct combustion, modified direct combustion, indirect (by difference), and pyrolysis plus combustion products. Each method has advantages and disadvantages; see Peters and Cassa<ref name=PtrsCss1994>Peters, K. E., and M. R. Cassa, 1994, Applied source rock geochemistry, in L. B. Magoon, and W. G. Dow, eds., The Petroleum system—From source to trap: AAPG Memoir 60, p. 93–120.</ref> for a detailed discussion. We recommend the direct combustion method for most mudstones.

TOC content can be measured through direct combustion, modified direct combustion, indirect (by difference), and pyrolysis plus combustion products. Each method has advantages and disadvantages; see Peters and Cassa<ref name=PtrsCss1994>Peters, K. E., and M. R. Cassa, 1994, Applied source rock geochemistry, in L. B. Magoon, and W. G. Dow, eds., The Petroleum system—From source to trap: AAPG Memoir 60, p. 93–120.</ref> for a detailed discussion. We recommend the direct combustion method for most mudstones.

====Rock-Eval® Pyrolysis: Hydrogen and Oxygen Indices====

====Rock-Eval® Pyrolysis: Hydrogen and Oxygen Indices====

Rock-Eval® pyrolysis is a rapid screening method for estimating the hydrogen and oxygen content of organic matter and provides insights into (1) the character of the original organic material (algal versus land plant), (2) the preservational conditions in the depositional environment<ref name=Ptrsea2005>Peters, K. E., C. C. Walters, and J. M. Moldowan, 2005, The biomarker guide: Biomarkers and isotopes in the environment and human history, 2nd ed.: Cambridge, U.K., Cambridge University Press, 1155 p.</ref>, and (3) the quality and distribution of hydrocarbon sources and reservoirs ([[:file:M126CH3-Table4.jpeg|Table 4]]). Vertical profiles of hydrogen indices (HIs) have been related to physiographic setting and sequence-stratigraphic units and surfaces<ref name=Bhcs1998 /><ref name=CrnyPssy1993 /><ref>Bohacs, K. M., O. R. Lazar, J. Ottmann, K. Potma, and T. M. Demko, 2013, Shale-gas-reservoir families—translating sequence stratigraphy into robust predictions of reservoir distribution and potential: AAPG Search and Discovery article #90163.</ref>. For more information on the Rock-Eval method and parameters, see Espitalié et al.<ref>Espitalié, J., G. Deroo, and F. Marquis, 1985, La pyrolyse Rock-Eval et ses applications: Review Institut Français du Pétrole, Partie 1 and 2, v. 40, p. 563–784, Partie 3, v. 41, p. 73–89.</ref><ref>Espitalié, J., J. L. Laporte, M. Madec, F. Marquis, P. Lepat, J. Paulet, and A. Boutefeu, 1977, Méthode rapide de caractérisation des roches mères, de leur potentiel petrolier et leur degré d’évolution: Review Institut Français du Pétrole, v. 32, p. 23–42.</ref>, Lafargue et al.<ref>Lafargue, E., F. Marquis, and D. Pillot, 1998, Rock-Eval 6 applications in hydrocarbon exploration, production, and soil contamination studies: Institut Français du Pétrole, v. 53, p. 421–437.</ref>, Peters<ref>Peters, K. E., 1986, Guidelines for evaluating petroleum source rock using programmed pyrolysis: AAPG Bulletin, v. 70, p. 329.</ref>, and Tissot and Welte<ref name=TsstWlt>Tissot, B. P., and D. H. Welte, 1984, Petroleum formation and occurrence: Berlin, Springer-Verlag, 699 p.</ref>.

Rock-Eval® pyrolysis is a rapid screening method for estimating the hydrogen and oxygen content of organic matter and provides insights into (1) the character of the original organic material (algal versus land plant), (2) the preservational conditions in the depositional environment<ref name=Ptrsea2005>Peters, K. E., C. C. Walters, and J. M. Moldowan, 2005, The biomarker guide: Biomarkers and isotopes in the environment and human history, 2nd ed.: Cambridge, U.K., Cambridge University Press, 1155 p.</ref>, and (3) the quality and distribution of hydrocarbon sources and reservoirs ([[:file:M126CH03-Table4.jpeg|Table 4]]). Vertical profiles of hydrogen indices (HIs) have been related to physiographic setting and sequence-stratigraphic units and surfaces<ref name=Bhcs1998 /><ref name=CrnyPssy1993 /><ref>Bohacs, K. M., O. R. Lazar, J. Ottmann, K. Potma, and T. M. Demko, 2013, Shale-gas-reservoir families—translating sequence stratigraphy into robust predictions of reservoir distribution and potential: AAPG Search and Discovery article #90163.</ref>. For more information on the Rock-Eval method and parameters, see Espitalié et al.<ref>Espitalié, J., G. Deroo, and F. Marquis, 1985, La pyrolyse Rock-Eval et ses applications: Review Institut Français du Pétrole, Partie 1 and 2, v. 40, p. 563–784, Partie 3, v. 41, p. 73–89.</ref><ref>Espitalié, J., J. L. Laporte, M. Madec, F. Marquis, P. Lepat, J. Paulet, and A. Boutefeu, 1977, Méthode rapide de caractérisation des roches mères, de leur potentiel petrolier et leur degré d’évolution: Review Institut Français du Pétrole, v. 32, p. 23–42.</ref>, Lafargue et al.<ref>Lafargue, E., F. Marquis, and D. Pillot, 1998, Rock-Eval 6 applications in hydrocarbon exploration, production, and soil contamination studies: Institut Français du Pétrole, v. 53, p. 421–437.</ref>, Peters<ref>Peters, K. E., 1986, Guidelines for evaluating petroleum source rock using programmed pyrolysis: AAPG Bulletin, v. 70, p. 329.</ref>, and Tissot and Welte<ref name=TsstWlt>Tissot, B. P., and D. H. Welte, 1984, Petroleum formation and occurrence: Berlin, Springer-Verlag, 699 p.</ref>.

=====Sample Selection and Analytical Considerations=====

=====Sample Selection and Analytical Considerations=====

Well-log analysis is the most complete and least expensive method of characterizing mudstones down-hole. This method provides robust characterization of the stratigraphic distribution of potential source, reservoir, and seal rocks. It is particularly valuable where sample data are not available or for lake strata where thin-bedded source rocks are common. Few well-log types, however, directly measure the rock properties sought to evaluate source, reservoir, or seal potential—it is essential to understand the assumptions made, and caution must be used in interpretation.

Well-log analysis is the most complete and least expensive method of characterizing mudstones down-hole. This method provides robust characterization of the stratigraphic distribution of potential source, reservoir, and seal rocks. It is particularly valuable where sample data are not available or for lake strata where thin-bedded source rocks are common. Few well-log types, however, directly measure the rock properties sought to evaluate source, reservoir, or seal potential—it is essential to understand the assumptions made, and caution must be used in interpretation.

The three main categories of well logs are electric, radioactive, and structural; most well logs were originally designed and mainly used for estimating lithology, porosity, rock strength, pressure, hydrocarbon presence and type, and structural characteristics (fractures, faults, folds, in situ stress). [[:file:M126CH3-Table5.jpeg|Table 5]] summarizes the principles of well-logs commonly used for sequence-stratigraphic analysis and provides helpful tips and traps of log applications to mudstone successions. Many excellent textbooks provide more detail on well-logs and their interpretation<ref name=Srr>Serra, O., 1984, Fundamentals of well-log interpretation: Developments in Petroleum Science, v. 15, Part A, p. iii–vii, 1–423.</ref><ref name=Schlmbrgr1991>Schlumberger Limited, 1991, Log interpretation principles/applications: Houston, Texas, Schlumberger Educational Services, 142 p.</ref><ref name=EmryMyrs>Emery, D., and K. J. Myers, 1996, Sequence stratigraphy: Oxford, Blackwell Science, 297 p.</ref><ref name=Rdr2002>Rider, M., 2002, The geological interpretation of well logs: Marsa, Malta, Interprint, 280 p.</ref><ref name=Evnck2008>Evenick, J. C., 2008, Introduction to well logs and subsurface maps: Tulsa, Oklahoma, PennWell, 236 p.</ref>. A few general tips and traps to have in mind when using well logs are as follows:

The three main categories of well logs are electric, radioactive, and structural; most well logs were originally designed and mainly used for estimating lithology, porosity, rock strength, pressure, hydrocarbon presence and type, and structural characteristics (fractures, faults, folds, in situ stress). [[:file:M126CH03-Table5.jpeg|Table 5]] summarizes the principles of well-logs commonly used for sequence-stratigraphic analysis and provides helpful tips and traps of log applications to mudstone successions. Many excellent textbooks provide more detail on well-logs and their interpretation<ref name=Srr>Serra, O., 1984, Fundamentals of well-log interpretation: Developments in Petroleum Science, v. 15, Part A, p. iii–vii, 1–423.</ref><ref name=Schlmbrgr1991>Schlumberger Limited, 1991, Log interpretation principles/applications: Houston, Texas, Schlumberger Educational Services, 142 p.</ref><ref name=EmryMyrs>Emery, D., and K. J. Myers, 1996, Sequence stratigraphy: Oxford, Blackwell Science, 297 p.</ref><ref name=Rdr2002>Rider, M., 2002, The geological interpretation of well logs: Marsa, Malta, Interprint, 280 p.</ref><ref name=Evnck2008>Evenick, J. C., 2008, Introduction to well logs and subsurface maps: Tulsa, Oklahoma, PennWell, 236 p.</ref>. A few general tips and traps to have in mind when using well logs are as follows:

[[file:M126CH3-Table5.jpeg|thumb|300px|’’Table 5.’’ Well-logs: Applications, Tips, and Traps. See, for Example, Serra<ref name=Srr />, Schlumberger><ref name=Schlmbrgr1991 />, Emery and Myers<ref name=EmryMyrs />, Rider<ref name=Rdr2002 />, and Evenick<ref name=Evnck2008 /> for More Detail on Well-log Interpretations, Applications, and Caveats.]]

[[file:M126CH03-Table5.jpeg|thumb|300px|’’Table 5.’’ Well-logs: Applications, Tips, and Traps. See, for Example, Serra<ref name=Srr />, Schlumberger><ref name=Schlmbrgr1991 />, Emery and Myers<ref name=EmryMyrs />, Rider<ref name=Rdr2002 />, and Evenick<ref name=Evnck2008 /> for More Detail on Well-log Interpretations, Applications, and Caveats.]]

* Direct measurement of rock properties from samples is always the most accurate information you can obtain and is invaluable for calibrating well-log estimates. Sample coverage, however, tends to be sparse and unevenly distributed; hence, calibrated well-logs are essential for evaluating the entire section under examination.

* Direct measurement of rock properties from samples is always the most accurate information you can obtain and is invaluable for calibrating well-log estimates. Sample coverage, however, tends to be sparse and unevenly distributed; hence, calibrated well-logs are essential for evaluating the entire section under examination.

* Well-log analyses of mudstones require special attention to the standard procedures for depth alignment in combined log techniques, tool calibration, and tool baseline. Pay particular attention to the caliper log, for some mudstones tend to wash out, whereas others drill “gunbarrel straight.”

* Well-log analyses of mudstones require special attention to the standard procedures for depth alignment in combined log techniques, tool calibration, and tool baseline. Pay particular attention to the caliper log, for some mudstones tend to wash out, whereas others drill “gunbarrel straight.”

For source evaluation, TOC depth profiles estimated from well-log data can be used to calculate TOC thickness, organic-matter volume, and the amount of hydrocarbon generated from a source rock over a particular area of a basin. The TOC profile also helps to interpret mudstone depositional environments and to correlate stratigraphic sequences<ref name=Bhcs1998 /><ref name=CrnyPssy1993 /><ref>Bessereau, G., and F. Guillocheau, 1995, Stratgraphie sequentielle et distribution de la matiere organique dans le Lias du bassin de Paris: Comptes Rendu de l’Académie des Sciences, v. 316, p. 1271–1278.</ref>. Mudstone reservoir and seal character can be estimated through analogous analyses using combinations of various well-logs<ref>Spears, R. W., and S. L. Jackson, 2009, Development of a predictive tool for estimating well performance in horizontal shale gas wells in the Barnett Shale, North Texas, USA: Petrophysics, v. 50, p. 19–31.</ref> (see [[:file:M126CH3-Table5.jpeg|Table 5]]); the vertical profiles generated also provide useful insights for constructing sequence-stratigraphic frameworks<ref name=Bhcs1998 />.

For source evaluation, TOC depth profiles estimated from well-log data can be used to calculate TOC thickness, organic-matter volume, and the amount of hydrocarbon generated from a source rock over a particular area of a basin. The TOC profile also helps to interpret mudstone depositional environments and to correlate stratigraphic sequences<ref name=Bhcs1998 /><ref name=CrnyPssy1993 /><ref>Bessereau, G., and F. Guillocheau, 1995, Stratgraphie sequentielle et distribution de la matiere organique dans le Lias du bassin de Paris: Comptes Rendu de l’Académie des Sciences, v. 316, p. 1271–1278.</ref>. Mudstone reservoir and seal character can be estimated through analogous analyses using combinations of various well-logs<ref>Spears, R. W., and S. L. Jackson, 2009, Development of a predictive tool for estimating well performance in horizontal shale gas wells in the Barnett Shale, North Texas, USA: Petrophysics, v. 50, p. 19–31.</ref> (see [[:file:M126CH03-Table5.jpeg|Table 5]]); the vertical profiles generated also provide useful insights for constructing sequence-stratigraphic frameworks<ref name=Bhcs1998 />.

===Seismic Tools===

===Seismic Tools===

====Seismic-Stratigraphy Procedure====

====Seismic-Stratigraphy Procedure====

The first step in seismic stratigraphy is to identify seismic terminations, and then use those terminations to recognize surfaces and delineate them. Next, key surfaces such as sequence boundaries and maximum flooding surfaces (maximum transgressive surfaces) are traced on the intersecting lines in a grid of seismic lines or propagated through a seismic-data volume until the boundaries have been correlated and tied within the entire dataset. This is intended to verify the regional extent of major discontinuity surfaces and to identify which other potentially significant surfaces are local in nature. [[:file:M126CH3-Table6.jpeg|Table 6]] outlines the workflow for seismic stratigraphy. [[:file:M126CH3-Table7.jpeg|Table 7]] details the criteria for identifying key stratigraphic surfaces.

The first step in seismic stratigraphy is to identify seismic terminations, and then use those terminations to recognize surfaces and delineate them. Next, key surfaces such as sequence boundaries and maximum flooding surfaces (maximum transgressive surfaces) are traced on the intersecting lines in a grid of seismic lines or propagated through a seismic-data volume until the boundaries have been correlated and tied within the entire dataset. This is intended to verify the regional extent of major discontinuity surfaces and to identify which other potentially significant surfaces are local in nature. [[:file:M126CH03-Table6.jpeg|Table 6]] outlines the workflow for seismic stratigraphy. [[:file:M126CH03-Table7.jpeg|Table 7]] details the criteria for identifying key stratigraphic surfaces.

[[file:M126CH3-Table6.jpeg|thumb|300px|’’Table 6.’’ Seismic-stratigraphy Workflow.]]

[[file:M126CH03-Table6.jpeg|thumb|300px|’’Table 6.’’ Seismic-stratigraphy Workflow.]]

[[file:M126CH3-Table7.jpeg|thumb|300px|’’Table 7.’’ Surface Definitions With Translation Terms, and Primary and Secondary Recognition Criteria.]]

[[file:M126CH03-Table7.jpeg|thumb|300px|’’Table 7.’’ Surface Definitions With Translation Terms, and Primary and Secondary Recognition Criteria.]]

====Seismic Facies Analysis====

====Seismic Facies Analysis====

=====Seismic-Facies Parameters: Internal Form=====

=====Seismic-Facies Parameters: Internal Form=====

Seismic-facies units are mappable, 3-D seismic units composed of groups of reflections whose parameters differ from those of adjacent facies units<ref name=Mtchmea1977 />. These parameters include the configuration or geometry, continuity, amplitude, frequency, and interval velocity ([[:file:M126CH3-Table8.jpeg|Table 8]]). Each parameter provides considerable information on the geology of the subsurface ([[:file:M126CH3-Table8.jpeg|Table 8]]). Reflection configuration reveals gross stratification patterns from which depositional processes, erosion, and paleotopography can be interpreted. In addition, fluid contact reflections (flat spots) are commonly identifiable. Reflection continuity is closely associated with continuity of strata; continuous reflections suggest widespread, uniformly stratified deposits. Reflection amplitude contains information on the velocity and density contrasts of individual bedding interfaces and their spacing. It is used to predict lateral bedding changes and hydrocarbon occurrences. “Frequency” (reflection spacing), although a characteristic of the seismic pulse, is also related to such geologic factors as the spacing of reflectors or lateral changes in interval velocity (because of organic-matter or hydrocarbon content or lithofacies changes).

Seismic-facies units are mappable, 3-D seismic units composed of groups of reflections whose parameters differ from those of adjacent facies units<ref name=Mtchmea1977 />. These parameters include the configuration or geometry, continuity, amplitude, frequency, and interval velocity ([[:file:M126CH03-Table8.jpeg|Table 8]]). Each parameter provides considerable information on the geology of the subsurface ([[:file:M126CH03-Table8.jpeg|Table 8]]). Reflection configuration reveals gross stratification patterns from which depositional processes, erosion, and paleotopography can be interpreted. In addition, fluid contact reflections (flat spots) are commonly identifiable. Reflection continuity is closely associated with continuity of strata; continuous reflections suggest widespread, uniformly stratified deposits. Reflection amplitude contains information on the velocity and density contrasts of individual bedding interfaces and their spacing. It is used to predict lateral bedding changes and hydrocarbon occurrences. “Frequency” (reflection spacing), although a characteristic of the seismic pulse, is also related to such geologic factors as the spacing of reflectors or lateral changes in interval velocity (because of organic-matter or hydrocarbon content or lithofacies changes).

[[file:M126CH3-Table8.jpeg|thumb|300px|’’Table 8.’’ Seismic-reflection Characteristics of Seismically Definable Rock Bodies.]]

[[file:M126CH03-Table8.jpeg|thumb|300px|’’Table 8.’’ Seismic-reflection Characteristics of Seismically Definable Rock Bodies.]]

Grouping these seismic parameters into mappable seismic-facies units facilitates their interpretation in terms of depositional environment, sediment provenance, and geologic setting. Seismic-reflection configuration or geometry is the most obvious and directly analyzable seismic parameter. Stratal configuration or geometry is interpreted from seismic-reflection configuration and refers to the geometric patterns and relations of strata within a stratigraphic unit. These commonly indicate depositional setting and processes as well as later structural movement.

Grouping these seismic parameters into mappable seismic-facies units facilitates their interpretation in terms of depositional environment, sediment provenance, and geologic setting. Seismic-reflection configuration or geometry is the most obvious and directly analyzable seismic parameter. Stratal configuration or geometry is interpreted from seismic-reflection configuration and refers to the geometric patterns and relations of strata within a stratigraphic unit. These commonly indicate depositional setting and processes as well as later structural movement.

=====External Form and Internal Geometry: A-B/C Mapping=====

=====External Form and Internal Geometry: A-B/C Mapping=====

Seismic-facies mapping was definitively explained by Ramsayer<ref name=Rmsyr1979 />, based on 2-D seismic data. It is referred to as the “A-B/C” mapping approach, as observations are made upon the upper boundary (A), the lower boundary (B), and the internal reflection character (C). The A, B, and C categories of Ramsayer’s<ref name=Rmsyr1979 /> seismic facies codes each included five types initially, thus providing 15 different variations for a given seismic interval of interest ([[:file:M126CH3-Table9.jpeg|Table 9]]). For example, a prograding seismic package with oblique clinoforms, toplap at its upper surface, and downlap at its base would be noted as Tp-Dn/Ob. Subsequent work and incorporation of Campbell’s<ref name=Cmpbll1967> Campbell, C. V., 1967, Lamina, laminaset, bed and bedset: Sedimentology, v. 8, p. 7–26.</ref> approach to stratal description expanded the range of descriptors for “C” (internal character) to span continuity, reflection shape, reflection inter-relations, and amplitude ([[:file:M126CH3-Table9.jpeg|Table 9]], the lower part). We highly recommend using all these aspects of reflection character to describe the internal reflection configuration.

Seismic-facies mapping was definitively explained by Ramsayer<ref name=Rmsyr1979 />, based on 2-D seismic data. It is referred to as the “A-B/C” mapping approach, as observations are made upon the upper boundary (A), the lower boundary (B), and the internal reflection character (C). The A, B, and C categories of Ramsayer’s<ref name=Rmsyr1979 /> seismic facies codes each included five types initially, thus providing 15 different variations for a given seismic interval of interest ([[:file:M126CH03-Table9.jpeg|Table 9]]). For example, a prograding seismic package with oblique clinoforms, toplap at its upper surface, and downlap at its base would be noted as Tp-Dn/Ob. Subsequent work and incorporation of Campbell’s<ref name=Cmpbll1967> Campbell, C. V., 1967, Lamina, laminaset, bed and bedset: Sedimentology, v. 8, p. 7–26.</ref> approach to stratal description expanded the range of descriptors for “C” (internal character) to span continuity, reflection shape, reflection inter-relations, and amplitude ([[:file:M126CH03-Table9.jpeg|Table 9]], the lower part). We highly recommend using all these aspects of reflection character to describe the internal reflection configuration.

[[file:M126CH3-Table9.jpeg|thumb|300px|’’Table 9.’’ Seismic Facies A, B, and C (Expanded after Mitchum et al., <ref name=Mtchmea1977 />; Ramsayer<ref name=Rmsyr1979 />).]]

[[file:M126CH03-Table9.jpeg|thumb|300px|’’Table 9.’’ Seismic Facies A, B, and C (Expanded after Mitchum et al., <ref name=Mtchmea1977 />; Ramsayer<ref name=Rmsyr1979 />).]]

The A-B/C mapping is still necessary even with the most advanced and high-resolution 3-D datasets and visualization tools because seismic facies are most meaningful within their stratigraphic context—that is, when applied to genetically related strata (which is the whole point of sequence stratigraphy). Bounding surfaces provide important geological and stratigraphic information. Seismic facies are nonuniquely related to depositional environment and lithofacies (e.g., clinoform reflections can occur in deltaic sandstones, carbonate platforms, and mudstone-dominated shelves); hence, one needs more information from the stratigraphic context of the seismic facies—their relation to lower and upper bounding surfaces and position along the depositional profile.

The A-B/C mapping is still necessary even with the most advanced and high-resolution 3-D datasets and visualization tools because seismic facies are most meaningful within their stratigraphic context—that is, when applied to genetically related strata (which is the whole point of sequence stratigraphy). Bounding surfaces provide important geological and stratigraphic information. Seismic facies are nonuniquely related to depositional environment and lithofacies (e.g., clinoform reflections can occur in deltaic sandstones, carbonate platforms, and mudstone-dominated shelves); hence, one needs more information from the stratigraphic context of the seismic facies—their relation to lower and upper bounding surfaces and position along the depositional profile.