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The geological and reservoir properties of sedimentary rocks depend upon an interplay of tectonics, sea level, sediment supply, physical and biological processes of sediment transport and deposition, and climate. At the basin scale, these processes interact to produce the geometric arrangement of different depositional environments or systems tracts through time, known as the stratigraphic architecture of the basin<ref name=pt06r88>Miall, A. D., 1984, Principles of Sedimentary Basin Analysis: New York, Springer-Verlag, 490 p.</ref>. At smaller scales, these processes control the external geometry and internal “anatomy” of clastic sediment bodies (see “[[Geological heterogeneities]]”). It is at this smaller scale that lithofacies analysis and interpretation of depositional environments become important for reservoir evaluation.

The geological and reservoir properties of sedimentary rocks depend upon an interplay of tectonics, sea level, sediment supply, physical and biological processes of sediment transport and deposition, and climate. At the basin scale, these processes interact to produce the geometric arrangement of different depositional environments or systems tracts through time, known as the stratigraphic architecture of the basin.<ref name=pt06r88>Miall, A. D., 1984, Principles of Sedimentary Basin Analysis: New York, Springer-Verlag, 490 p.</ref> At smaller scales, these processes control the external geometry and internal “anatomy” of clastic sediment bodies (see [[Geological heterogeneities]]). It is at this smaller scale that lithofacies analysis and interpretation of depositional environments become important for reservoir evaluation.

==Data requirements==

==Data requirements==

Basic data requirements for facies analysis of subsurface rocks are listed in Table 1. Data associated with wells are most often used, but seismic data, particularly three-dimensional data, are becoming increasingly important in defining sandstone body geometries (e.g., see <ref name=pt06r17>Brown, A. R., 1986 Interpretation of three-dimensional seismic data: AAPG Memoir 42, 194 p.</ref>; also see the chapter on “[[Three-dimensional seismic method]]s for Reservoir Development” in Part 7). Conventional core is perhaps the most diagnostic for sedimentological interpretation of vertical sequences (see “[[Core description]]”). However, wireline tools such as [[dipmeters]] and formation imaging devices can provide electrical images suitable for sedimentological interpretation with the added ability to determine paleocurrent directions in appropriate cases (see “[[Dipmeters]]” and “[[Borehole imaging devices]]”).

Basic data requirements for facies analysis of subsurface rocks are listed in Table 1. Data associated with wells are most often used, but seismic data, particularly three-dimensional data, are becoming increasingly important in defining sandstone body geometries (e.g., see <ref name=pt06r17>Brown, A. R., 1986 Interpretation of three-dimensional seismic data: AAPG Memoir 42, 194 p.</ref>; also see [[Three-dimensional seismic methods for reservoir development]]). Conventional core is perhaps the most diagnostic for sedimentological interpretation of vertical sequences (see [[Core description]]). However, wireline tools such as [[dipmeters]] and formation imaging devices can provide electrical images suitable for sedimentological interpretation with the added ability to determine paleocurrent directions in appropriate cases (see [[Dipmeters]] and [[Borehole imaging devices]]).

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===Lithofacies===

===Lithofacies===

One of the first steps in the facies analysis of a clastic reservoir is the description and interpretation of available conventional core<ref name=pt06r119>Siemers, C. T., Tillman, R. W., 1981, Recommendations for the proper handling of cores and sedimentological analysis of core sequences, in Siemers, C. T., Tillman, R. W., Williamson, C. R., eds., Deep-Water Clastic Sediments—A Core Workshop: SEPM Core Workshop, n. 2, p. 20–44.</ref>. An important result of [[core description]] is the subdivision of cores into ''lithofacies'', defined as subdivisions of a sedimentary sequence based on lithology, grain size, physical and biogenic sedimentary structures, and stratification that bear a direct relationship to the depositional processes that produced them. Lithofacies and lithofacies associations (groups of related lithofacies) are the basic units for the interpretation of depositional environments.

One of the first steps in the facies analysis of a clastic reservoir is the description and interpretation of available conventional core.<ref name=pt06r119>Siemers, C. T., Tillman, R. W., 1981, Recommendations for the proper handling of cores and sedimentological analysis of core sequences, in Siemers, C. T., Tillman, R. W., Williamson, C. R., eds., Deep-Water Clastic Sediments—A Core Workshop: SEPM Core Workshop, n. 2, p. 20–44.</ref> An important result of [[core description]] is the subdivision of cores into ''lithofacies'', defined as subdivisions of a sedimentary sequence based on lithology, grain size, physical and biogenic sedimentary structures, and stratification that bear a direct relationship to the depositional processes that produced them. Lithofacies and lithofacies associations (groups of related lithofacies) are the basic units for the interpretation of depositional environments.

===Depositional environments===

===Depositional environments===

Interpretation of the environment in which lithofacies were deposited from analysis of cored sequences involves relating the identified lithofacies to the physical and biological processes that produced them. This process-response relationship identifies the specific processes responsible for the sequence and, by inference, the depositional setting in which these processes occurred. The application of the process-response approach relies primarily on depositional models constructed through study of both modern and ancient analogs.

Interpretation of the environment in which lithofacies were deposited from analysis of cored sequences involves relating the identified lithofacies to the physical and biological processes that produced them. This process-response relationship identifies the specific processes responsible for the sequence and, by inference, the depositional setting in which these processes occurred. The application of the process-response approach relies primarily on depositional models constructed through study of both modern and ancient analogs.

Depositional models are important for predicting the distribution of [[permeability]] and porosity within different reservoir types. These models are never exact matches to a reservoir; rather, they serve as guides to aid in the interpretation of any one reservoir<ref name=pt06r147 />). Reservoir properties are generally observed to be correlative with lithofacies types to one degree or another (see “Geological Heterogeneities”). This reflects the fundamental control on permeability and porosity by grain size, sorting, and spatial distribution of different lithofacies types. Even where rocks have experienced later physical and chemical diagenesis, permeability and porosity relationships are controlled, in large part, by the original sedimentary fabric of the rock.

Depositional models are important for predicting the distribution of [[permeability]] and porosity within different reservoir types. These models are never exact matches to a reservoir; rather, they serve as guides to aid in the interpretation of any one reservoir.<ref name=pt06r147 /> Reservoir properties are generally observed to be correlative with lithofacies types to one degree or another (see [[Geological heterogeneities]]). This reflects the fundamental control on permeability and porosity by grain size, sorting, and spatial distribution of different lithofacies types. Even where rocks have experienced later physical and chemical diagenesis, permeability and porosity relationships are controlled, in large part, by the original sedimentary fabric of the rock.

===Wireline log calibration and correlation===

===Wireline log calibration and correlation===

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 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 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” in Part 5) and (2) establishing a relationship between lithofacies associations and 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 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.

For reservoirs in which no core is available, wireline log shape must be used to interpret sandstone body type and identify depositional environments. If closely spaced cuttings or sidewall cores are available, these can sometimes aid rock to log calibration. Log shapes are deduced from the expected wireline log response of the different environments combined with a knowledge of the paleogeography of the area in which the field is situated. Wireline log shapes are often described as “upward coarsening,” “upward fining,” or “blocky.” However, log shape as determined from a gamma ray or SP log in siliciclastic rocks is related more to argillaceous content than to grain size. Upward coarsening log patterns exhibit an upward decrease in argillaceous content. Upward fining log patterns exhibit the reverse trend. Blocky or cylindrical log patterns exhibit relatively little vertical variation in argillaceous content and are typical of siliciclastic rocks that have low overall argillaceous content. Various publications and reference charts are available to aid in this practice (e.g., <ref name=pt06r132>Spearing, D. R., 1974, Summary sheets of sedimentary deposits: Geological Society of American Publication MC-8.</ref><ref name=pt06r18>Cant, D. J., 1984, Subsurface facies analysis, in Walker, R. G., ed., Facies Models: Geoscience Canada, Reprint Series 1, p. 297–319.</ref><ref name=pt06r110>Rider, M. H., 1986, Geological interpretation of well logs: New York, John Wiley, 175 p.</ref>. However, without core control, curve shape analysis is fraught with hazards (e.g., see <ref name=pt06r125>Snedden, J. W., 1987, Validity of the use of the spontaneous potential curve shape in the interpretation of sandstone depositional environments, in White, B. R., Kier, R. eds., Transactions of the 34th annual meeting of the Gulf Coast Association of Geological Societies and 31st annual meeting of the Gulf Coast Section of SEPM, v. 34, p. 255–263.</ref>; also see the chapter on “Quick-Look Lithology from Logs” in Part 4).

For reservoirs in which no core is available, wireline log shape must be used to interpret sandstone body type and identify depositional environments. If closely spaced cuttings or sidewall cores are available, these can sometimes aid rock to log calibration. Log shapes are deduced from the expected wireline log response of the different environments combined with a knowledge of the paleogeography of the area in which the field is situated. Wireline log shapes are often described as “upward coarsening,” “upward fining,” or “blocky.” However, log shape as determined from a gamma ray or SP log in siliciclastic rocks is related more to argillaceous content than to grain size. Upward coarsening log patterns exhibit an upward decrease in argillaceous content. Upward fining log patterns exhibit the reverse trend. Blocky or cylindrical log patterns exhibit relatively little vertical variation in argillaceous content and are typical of siliciclastic rocks that have low overall argillaceous content. Various publications and reference charts are available to aid in this practice (e.g., <ref name=pt06r132>Spearing, D. R., 1974, Summary sheets of sedimentary deposits: Geological Society of American Publication MC-8.</ref><ref name=pt06r18>Cant, D. J., 1984, Subsurface facies analysis, in Walker, R. G., ed., Facies Models: Geoscience Canada, Reprint Series 1, p. 297–319.</ref><ref name=pt06r110>Rider, M. H., 1986, Geological interpretation of well logs: New York, John Wiley, 175 p.</ref>). However, without core control, curve shape analysis is fraught with hazards (e.g., <ref name=pt06r125>Snedden, J. W., 1987, Validity of the use of the spontaneous potential curve shape in the interpretation of sandstone depositional environments, in White, B. R., Kier, R. eds., Transactions of the 34th annual meeting of the Gulf Coast Association of Geological Societies and 31st annual meeting of the Gulf Coast Section of SEPM, v. 34, p. 255–263.</ref>; also see [[Quick-look lithology from logs]]).

Correlation sections that will be used for establishing sandstone body geometry should have a depositionally flat datum (such as a bentonite 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 bentonite 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.

==Clastic depositional lithofacies and environments==

==Clastic depositional lithofacies and environments==

Clastic depositional environments range from alpine to abyssal settings (Figure 3 and Table 2). Detailed reviews of these are given by Galloway and Hobday<ref name=pt06r36>Galloway, W. E., Hobday, D. K., 1983, Terrigenous Clastic Depositional Systems Applications to Petroleum, Coal, and Uranium Exploration: New York, Springer Verlag, 423 p.</ref>, Walker<ref name=pt06r147 />), Berg<ref name=pt06r14>Berg, R. R., 1986, Reservoir Sandstones: Englewood Cliffs, N., J., Prentice-Hall, 481 p.</ref>, Reading<ref name=pt06r107>Reading, H. G., ed., 1986, Sedimentary Environments and Facies, 2nd ed.: Boston, MA, Blackwell Scientific Publications, 615 p.</ref>, Beaumont and Foster<ref name=pt06r11>Beaumont, E. A., Foster, N. H., 1987, Reservoirs II—Sandstones: AAPG Treatise of Petroleum Geology Reprint Series, n. 4, 573 p.</ref>, and others. The following review is a cursory summary of the origin, lithofacies, geometry, and reservoir properties of major clastic environments and deposits. The reader should be aware that the remarks offered here for each depositional environment are necessarily of a highly generalized and idealized nature. Siliciclastic reservoirs are typically composed of multiple bodies deposited (and eroded) through time under varying tectonic, sealevel, and climatic conditions. Corresponding geometry, vertical sequence, wireline log character, and [[reservoir quality]] trends for a given reservoir may be, and often are, different from the generalized “single environment” models. In addition, subsequent diagenesis (see “[[Evaluating diagenetically complex reservoirs]]”) may alter the permeability and porosity structure created by depositional (and erosional) processes. However, it has been often observed that in siliciclastic rocks, diagenesis generally follows depositional fabric (see “Geological Heterogeneities”). Complex structural patterns can reduce reservoir continuity as well.

Clastic depositional environments range from alpine to abyssal settings (Figure 3 and Table 2). Detailed reviews of these are given by Galloway and Hobday,<ref name=pt06r36>Galloway, W. E., Hobday, D. K., 1983, Terrigenous Clastic Depositional Systems Applications to Petroleum, Coal, and Uranium Exploration: New York, Springer Verlag, 423 p.</ref> Walker,<ref name=pt06r147 /> Berg,<ref name=pt06r14>Berg, R. R., 1986, Reservoir Sandstones: Englewood Cliffs, N., J., Prentice-Hall, 481 p.</ref> Reading,<ref name=pt06r107>Reading, H. G., ed., 1986, Sedimentary Environments and Facies, 2nd ed.: Boston, MA, Blackwell Scientific Publications, 615 p.</ref> Beaumont and Foster,<ref name=pt06r11>Beaumont, E. A., Foster, N. H., 1987, Reservoirs II—Sandstones: AAPG Treatise of Petroleum Geology Reprint Series, n. 4, 573 p.</ref> and others. The following review is a cursory summary of the origin, lithofacies, geometry, and reservoir properties of major clastic environments and deposits. The reader should be aware that the remarks offered here for each depositional environment are necessarily of a highly generalized and idealized nature. Siliciclastic reservoirs are typically composed of multiple bodies deposited (and eroded) through time under varying tectonic, sealevel, and climatic conditions. Corresponding geometry, vertical sequence, wireline log character, and [[reservoir quality]] trends for a given reservoir may be, and often are, different from the generalized “single environment” models. In addition, subsequent diagenesis (see “[[Evaluating diagenetically complex reservoirs]]”) may alter the permeability and porosity structure created by depositional (and erosional) processes. However, it has been often observed that in siliciclastic rocks, diagenesis generally follows depositional fabric (see [[Geological heterogeneities]]). Complex structural patterns can reduce reservoir continuity as well.

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[[file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig3.png|thumb|{{figure number|3}}Models of major depositional environments. The curve on the left shows the SP or gamma ray response and the curve on the right shows the relative grain size profile. The size of the dots next to the vertical profile indicates the relative magnitude of permeability expected in such a sequence. (Parts c and d are from <ref name=pt06r147 />, and parts f, h, and i are from <ref name=pt06r36 />.)]]

[[file:lithofacies-and-environmental-analysis-of-clastic-depositional-systems_fig3.png|thumb|{{figure number|3}}Models of major depositional environments. The curve on the left shows the SP or gamma ray response and the curve on the right shows the relative grain size profile. The size of the dots next to the vertical profile indicates the relative magnitude of permeability expected in such a sequence. (Parts c and d are from <ref name=pt06r147 />, and parts f, h, and i are from <ref name=pt06r36 />.]]

===Alluvial fan deposits===

===Alluvial fan deposits===

Gamma ray, SP, and resistivity logs through braided channel complexes generally have a blocky character, whereas individual meandering channels have an upward-fining signature except where stacked and cross-cut, where they may exhibit more complex wireline log signatures.

Gamma ray, SP, and resistivity logs through braided channel complexes generally have a blocky character, whereas individual meandering channels have an upward-fining signature except where stacked and cross-cut, where they may exhibit more complex wireline log signatures.

The upward-fining character of fluvial channels tends to produce sandstone bodies that have their greatest permeability at the base of the body. However, the common stacking and cross-cutting of channels in both braided and meandering river deposits often produces a complex spatial distribution of permeability within the braided or meander belt. Preferred permeability pathways, and consequently, fluid flow, can be expected to follow the paleochannel direction<ref name=pt06r104>Qiu, Yinan, 1984, Depositional model, heterogeneous characteristics, and waterflood performance of sandstone reservoirs in a lake basin case study of oilfields, eastern China: Proceedings of the 11th World Petroleum Congress, v. 3, p. 113–125.</ref>.

The upward-fining character of fluvial channels tends to produce sandstone bodies that have their greatest permeability at the base of the body. However, the common stacking and cross-cutting of channels in both braided and meandering river deposits often produces a complex spatial distribution of permeability within the braided or meander belt. Preferred permeability pathways, and consequently, fluid flow, can be expected to follow the paleochannel direction.<ref name=pt06r104>Qiu, Yinan, 1984, Depositional model, heterogeneous characteristics, and waterflood performance of sandstone reservoirs in a lake basin case study of oilfields, eastern China: Proceedings of the 11th World Petroleum Congress, v. 3, p. 113–125.</ref>

===Eolian deposits===

===Eolian deposits===

Eolian sands develop in arid settings and commonly form extensive, blanket-like deposits (Figure 3b). Wind transport removes fines and produces rounded and extremely well sorted grains often leading to favorable reservoir quality.

Eolian sands develop in arid settings and commonly form extensive, blanket-like deposits (Figure 3b). Wind transport removes fines and produces rounded and extremely well sorted grains often leading to favorable reservoir quality.

This combination of widespread occurrence and good reservoir properties makes eolian sandstones attractive exploration targets and many hydrocarbon accumulations have been discovered in such deposits (see <ref name=pt06r2>Ahlbrandt, T. S., Fryberger, S. G., 1982, Introduction to eolian deposits, in Scholle, P. A., Spearing, D. eds., Sandstone Depositional Environments: A APG Memoir 31, p. 11–47.</ref>.

This combination of widespread occurrence and good reservoir properties makes eolian sandstones attractive exploration targets and many hydrocarbon accumulations have been discovered in such deposits (see <ref name=pt06r2>Ahlbrandt, T. S., Fryberger, S. G., 1982, Introduction to eolian deposits, in Scholle, P. A., Spearing, D. eds., Sandstone Depositional Environments: AAPG Memoir 31, p. 11–47.</ref>).

Eolian deposits include dune, interdune, sand sheets (marginal to dune complex), and extradune (noneolian) lateral deposits<ref name=pt06r2 />). Dune deposits comprise the major sedimentary bodies in eolian successions. All are characterized by large scale cross stratification in which foreset dips range up to 35°. Associated deposits may include those of wadi (fluvial), playa (lacustrine), and sabkha (arid tidal flat) origin.

Eolian deposits include dune, interdune, sand sheets (marginal to dune complex), and extradune (noneolian) lateral deposits.<ref name=pt06r2 />) Dune deposits comprise the major sedimentary bodies in eolian successions. All are characterized by large scale cross stratification in which foreset dips range up to 35°. Associated deposits may include those of wadi (fluvial), playa (lacustrine), and sabkha (arid tidal flat) origin.

In the subsurface, eolian sandstones generally comprise thickly bedded sequences with few major interstratified shales. The sequences tend to be uniform and lack discernible coarsening- or fining-upward trends and, thus, exhibit blocky to weakly serrated gamma ray, SP, and resistivity log profiles The well-bedded and high angle cross stratified nature of eolian sandstones promotes reliable results from dipmeter logs. Dune and interdune deposits can often be distinguished and paleowind directions inferred using correctly processed dipmeter data (<ref name=pt06r80>Lupe, R., Ahlbrandt, T. S., 1979, Sediments of the ancient eolian environment—reservoir inhomogeneity, in McKee, E., D., ed., A Study of Global Sand Seas: U., S. Geological Survey Professional Paper 1052, p. 241–252.</ref>.

In the subsurface, eolian sandstones generally comprise thickly bedded sequences with few major interstratified shales. The sequences tend to be uniform and lack discernible coarsening- or fining-upward trends and, thus, exhibit blocky to weakly serrated gamma ray, SP, and resistivity log profiles The well-bedded and high angle cross stratified nature of eolian sandstones promotes reliable results from dipmeter logs. Dune and interdune deposits can often be distinguished and paleowind directions inferred using correctly processed dipmeter data.<ref name=pt06r80>Lupe, R., Ahlbrandt, T. S., 1979, Sediments of the ancient eolian environment—reservoir inhomogeneity, in McKee, E., D., ed., A Study of Global Sand Seas: U., S. Geological Survey Professional Paper 1052, p. 241–252.</ref>

Eolian sandstones generally comprise excellent reservoir intervals but often possess complex porosity and permeability variations. They are commonly anisotropic with regard to the flow of fluids and exhibit greater horizontal than vertical permeability because of their pronounced lamination<ref name=pt06r154>Weber, K. J., 1987, Computation of initial well productivities in aeolian sandstone on the basis of a geological model, Leman Gas field, U., K., in Tillman, R. W., Weber, K. J., eds., Reservoir Sedimentology: SEPM Special Publication 40, p. 335–354.</ref>.

Eolian sandstones generally comprise excellent reservoir intervals but often possess complex porosity and permeability variations. They are commonly anisotropic with regard to the flow of fluids and exhibit greater horizontal than vertical permeability because of their pronounced lamination.<ref name=pt06r154>Weber, K. J., 1987, Computation of initial well productivities in aeolian sandstone on the basis of a geological model, Leman Gas field, U., K., in Tillman, R. W., Weber, K. J., eds., Reservoir Sedimentology: SEPM Special Publication 40, p. 335–354.</ref>

===Deltas===

===Deltas===

* ''Tidally dominated deltas'' (such as the Gulf of Papua delta) are those in which the tidal energy exceeds that of either wave or fluvial processes. Sand deposited by the distributaries is reworked by tidal currents into elongate sand ridges that are generally perpendicular to the regional coastline.

* ''Tidally dominated deltas'' (such as the Gulf of Papua delta) are those in which the tidal energy exceeds that of either wave or fluvial processes. Sand deposited by the distributaries is reworked by tidal currents into elongate sand ridges that are generally perpendicular to the regional coastline.

Rarely do deltas conform perfectly to these end-members. In general they are transitional, giving rise to complexity and variability in the geometry and reservoir heterogeneities of resulting sandstone bodies (e.g., <ref name=pt06r130>Sneider, R. M., Tinker, C. N., Meckel, L. D., 1978, Deltaic environment reservoir types and their characteristics: Journal of Petroleum Technology, Nov., p. 1538–1546.</ref>.

Rarely do deltas conform perfectly to these end-members. In general they are transitional, giving rise to complexity and variability in the geometry and reservoir heterogeneities of resulting sandstone bodies (e.g., <ref name=pt06r130>Sneider, R. M., Tinker, C. N., Meckel, L. D., 1978, Deltaic environment reservoir types and their characteristics: Journal of Petroleum Technology, Nov., p. 1538–1546.</ref>).

Distributary mouth bars and channel deposits (Figure 3h) comprise the best reservoir quality bodies within a delta system. The general upward-coarsening character of distributary mouth bars tends to produce sandstone bodies that have their greatest permeability at the top. Conversely, distributary channel sandstone bodies are usually upward-fining and have their greatest permeability at the base<ref name=pt06r130 />). Preferred orientation of flow may be expected to follow paleochannel trends.

Distributary mouth bars and channel deposits (Figure 3h) comprise the best reservoir quality bodies within a delta system. The general upward-coarsening character of distributary mouth bars tends to produce sandstone bodies that have their greatest permeability at the top. Conversely, distributary channel sandstone bodies are usually upward-fining and have their greatest permeability at the base.<ref name=pt06r130 />) Preferred orientation of flow may be expected to follow paleochannel trends.

Distributary mouth bars typically contain a high percentage of interstratified clay that reduces vertical permeability. Hartman and Paynter<ref name=pt06r50>Hartman, J. A., Paynter, D. D., 1979, Drainage anomalies in Gulf Coast Tertiary sandstones: Journal of Petroleum Technology, Oct., p. 1313–1322.</ref> document an example of such behavior from a Gulf Coast deltaic reservoir undergoing natural waterdrive. After several years of production, the better quality channel sands watered out, whereas oil remained in the poorer quality delta fringe deposits. In this field, by-passed oil was accessed by recompleting wells only in the delta fringe interval.

Distributary mouth bars typically contain a high percentage of interstratified clay that reduces vertical permeability. Hartman and Paynter<ref name=pt06r50>Hartman, J. A., Paynter, D. D., 1979, Drainage anomalies in Gulf Coast Tertiary sandstones: Journal of Petroleum Technology, Oct., p. 1313–1322.</ref> document an example of such behavior from a Gulf Coast deltaic reservoir undergoing natural waterdrive. After several years of production, the better quality channel sands watered out, whereas oil remained in the poorer quality delta fringe deposits. In this field, by-passed oil was accessed by recompleting wells only in the delta fringe interval.

===Shallow marine clastic deposits===

===Shallow marine clastic deposits===

The marine shelf is an environment affected by storm- and tidal-driven waves and currents and sometimes by oceanic currents. Although shelf sand ridges of either storm or tidal origin formed during transgression are the best known examples (Figure 3g), sand bodies associated with the marine shelf also include reworked delta front and barrier sands, amalgamated storm sheets, and oceanic current deposits<ref name=pt06r10>Barwis, J. H., 1989, The explorationist and shelf sand models—where do we go from here?: 7th Annual Research Conference Proceedings, Gulf Coast SEPM, p. 1–14.</ref>.

The marine shelf is an environment affected by storm- and tidal-driven waves and currents and sometimes by oceanic currents. Although shelf sand ridges of either storm or tidal origin formed during transgression are the best known examples (Figure 3g), sand bodies associated with the marine shelf also include reworked delta front and barrier sands, amalgamated storm sheets, and oceanic current deposits.<ref name=pt06r10>Barwis, J. H., 1989, The explorationist and shelf sand models—where do we go from here?: 7th Annual Research Conference Proceedings, Gulf Coast SEPM, p. 1–14.</ref>

Most marine sand bodies are upward coarsening with the best reservoir quality rocks at the top of the body. Gamma ray, SP, and resistivity logs have a corresponding upward-coarsening character. In the case of storm-deposited sheet sands either attached or detached from the shoreface, amalgamation of individual storm deposits at the top of the bodies produces the greatest permeability and porosity and the most laterally continuous units<ref name=pt06r8>Atkinson, C. D., Goesten, B. G., Speksnijder, A., vander Vlugt, W., 1986, Storm-generated sandstone in the Miocene Miri Formation, Seria Field, Brunei (N., W. Borneo), in Knight, R. J., McLean, J. R., eds., Shelf Sands and Sandstones: Canadian Society of Petroleum Geologists Memoir 11, p. 213–240.</ref><ref name=pt06r38>Gaynor, G. C., Scheihing, M. H., 1988, Shelf depositional environments and reservoir characteristics of the Kuparuk River Formation (Lower Cretaceous), Kuparuk field, North Slope, Alaska, in Lomando, A. J., Harris, P. M., eds., Giant oil and gas fields—A core workshop: Society of Economic Paleontologists and Mineralogists Core Workshop 12, p. 333–389.</ref>. In the case of tidal- and storm-generated shelf sand ridges, best reservoir quality is also at the top in the form of several different types of large scale cross bedding.

Most marine sand bodies are upward coarsening with the best reservoir quality rocks at the top of the body. Gamma ray, SP, and resistivity logs have a corresponding upward-coarsening character. In the case of storm-deposited sheet sands either attached or detached from the shoreface, amalgamation of individual storm deposits at the top of the bodies produces the greatest permeability and porosity and the most laterally continuous units.<ref name=pt06r8>Atkinson, C. D., Goesten, B. G., Speksnijder, A., vander Vlugt, W., 1986, Storm-generated sandstone in the Miocene Miri Formation, Seria Field, Brunei (N., W. Borneo), in Knight, R. J., McLean, J. R., eds., Shelf Sands and Sandstones: Canadian Society of Petroleum Geologists Memoir 11, p. 213–240.</ref><ref name=pt06r38>Gaynor, G. C., Scheihing, M. H., 1988, Shelf depositional environments and reservoir characteristics of the Kuparuk River Formation (Lower Cretaceous), Kuparuk field, North Slope, Alaska, in Lomando, A. J., Harris, P. M., eds., Giant oil and gas fields—A core workshop: Society of Economic Paleontologists and Mineralogists Core Workshop 12, p. 333–389.</ref> In the case of tidal- and storm-generated shelf sand ridges, best reservoir quality is also at the top in the form of several different types of large scale cross bedding.

===Deep water marine deposits===

===Deep water marine deposits===