Constants & Standard Values
Physical constants and typical correlation-parameter defaults used across BauerCalc's calculators, organized by physical category. Looking for unit conversions instead? See the .
Fluid / PVT
gStandard GravityStandard
9.80665 m/s² (32.174 ft/s²)
SI-defined standard value
Universal physical constant, used throughout the platform to convert fluid density directly into a hydrostatic pressure gradient (ρ×g).
Used in:
ρwFresh-Water Density (standard conditions)Standard
62.4 lbm/ft³ (≈1.000 g/cc)
Standard reference density of water at ~60°F/15.6°C
Universal physical constant — the reference density behind the black-oil density formula's 350 lbm/STB constant (350 = 62.4 lbm/ft³ × 5.615 ft³/bbl).
Used in:
ρairAir Density (standard conditions)Standard
0.0764 lbm/scf
Standard reference density of air at standard temperature/pressure
Universal physical constant, scaled by gas specific gravity to weigh the dissolved gas contribution in the black-oil density formula.
Used in:
MairApparent Molecular Weight of AirStandard
28.97 g/mol
Standard atmospheric composition value
Universal physical constant, multiplied by gas specific gravity to get a gas's apparent molecular weight for real-gas density calculations.
Used in:
141.5 / 131.5API Gravity ↔ Specific GravityStandard
γo = 141.5 / (131.5 + °API)
API (American Petroleum Institute) gravity scale definition
Defined by the API gravity scale itself, not an empirical correlation — converts stock-tank oil API gravity to specific gravity.
Used in:
0.433 psi/ftFresh-Water Hydrostatic GradientStandard
0.433 psi/ft ≈ 9.807 kPa/m
Derived directly from fresh-water density × standard gravity (ρ×g)
Derived, not independently defined — this is standard_gravity and fresh_water_density expressed as a pressure gradient. The real normal (hydrostatic) formation gradient in a given basin varies 0.433–0.465 psi/ft with water salinity, so this is the fresh-water baseline, not a universal formation-pressure value.
Used in:
Electrical / Resistivity
aArchie Tortuosity FactorPrimary
1.0 (Humble formula) or 0.62 (Archie's original)
Typical default — not a universal value
Archie, G.E. (1942) — The electrical resistivity log as an aid in determining some reservoir characteristics
Empirical tortuosity constant in the Archie formation-factor relation. Regional values vary — e.g. Permian Basin Wolfcamp/Spraberry typically use a≈1.0 — always calibrate from core SCAL where available.
Used in:
mArchie Cementation ExponentPrimary
≈2 for clean sandstone; varies in carbonates
Typical default — not a universal value
Archie, G.E. (1942) — The electrical resistivity log as an aid in determining some reservoir characteristics
The source calc's own limitations flag that the default m=n=2 "may not apply in carbonates with vuggy or fracture porosity; calibrate from core SCAL when possible."
Used in:
nArchie Saturation ExponentPrimary
≈2
Typical default — not a universal value
Archie, G.E. (1942) — The electrical resistivity log as an aid in determining some reservoir characteristics
Subject to the same "calibrate from core SCAL when possible" caveat as the cementation exponent m — not a fixed value across lithologies.
Used in:
Mechanical / Friction
μByerlee Fault-Friction CoefficientPrimary
0.6–1.0 for most crustal rock; as low as 0.3–0.4 for clay-rich gouge or serpentinite-bearing faults
Typical default — not a universal value
Byerlee, J.D. (1978) — Friction of Rocks
"Byerlee's Law" is unusually rock-type-insensitive compared to most rock-mechanical properties, but documented exceptions exist. The source calc explicitly recommends calibrating μ to known regional fault behavior rather than relying on the default range alone.
Used in:
φAngle of Internal FrictionTextbook
25–35° for shale; 30–45° for sandstone and carbonate
Typical default — not a universal value
Jaeger, J.C., Cook, N.G.W., Zimmerman, R.W. (2007) — Fundamentals of Rock Mechanics
From triaxial testing — the ranges shown are typical starting points by lithology, not universal values. Always calibrate against local core/triaxial data where available.
Used in:
Elastic
EminRickman Brittleness — Young's Modulus Lower BoundPrimary
≈1 Mpsi (Barnett Shale calibration)
Typical default — not a universal value
Rickman, R., Mullen, M.J., Petre, J.E., Grieser, W.V., Kundert, D. (2008) — A Practical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clones of the Barnett Shale
Reasonably well corroborated across secondary literature.
A basin-specific calibration constant from Rickman et al.'s own Barnett Shale dataset — NOT a universal physical limit. The cited paper's own thesis is that other shale plays "are not clones of the Barnett Shale"; using this default outside a Barnett-like play is likely wrong. Recalibrate locally from the target play's own core or log population.
Used in:
EmaxRickman Brittleness — Young's Modulus Upper BoundPrimary
≈8 Mpsi (Barnett Shale calibration)
Typical default — not a universal value
Rickman, R., Mullen, M.J., Petre, J.E., Grieser, W.V., Kundert, D. (2008) — A Practical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clones of the Barnett Shale
Reasonably well corroborated across secondary literature.
A basin-specific calibration constant from Rickman et al.'s own Barnett Shale dataset — NOT a universal physical limit. Recalibrate locally from the target play's own core or log population.
Used in:
νminRickman Brittleness — Poisson's Ratio Lower BoundPrimary
≈0.15 (Barnett Shale calibration)
Typical default — not a universal value
Rickman, R., Mullen, M.J., Petre, J.E., Grieser, W.V., Kundert, D. (2008) — A Practical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clones of the Barnett Shale
LOWER confidence than the E bounds — this specific value could not be traced to an authoritative primary-source confirmation (the primary paper, SPE-115258, was paywalled and not directly accessible during this project's research).
A basin-specific calibration constant reported in secondary literature alongside Rickman et al.'s method — NOT a universal physical limit, and carries lower sourcing confidence than the E bounds above. Recalibrate locally wherever possible rather than trusting this default.
Used in:
νmaxRickman Brittleness — Poisson's Ratio Upper BoundPrimary
≈0.4 (Barnett Shale calibration)
Typical default — not a universal value
Rickman, R., Mullen, M.J., Petre, J.E., Grieser, W.V., Kundert, D. (2008) — A Practical Use of Shale Petrophysics for Stimulation Design Optimization: All Shale Plays Are Not Clones of the Barnett Shale
LOWER confidence than the E bounds — this specific value could not be traced to an authoritative primary-source confirmation (the primary paper, SPE-115258, was paywalled and not directly accessible during this project's research).
A basin-specific calibration constant reported in secondary literature alongside Rickman et al.'s method — NOT a universal physical limit, and carries lower sourcing confidence than the E bounds above. Recalibrate locally wherever possible rather than trusting this default.
Used in:
Thermal
GGeothermal Gradient (typical onshore default)Textbook
1.0–1.5 °F/100ft onshore; 1.5–1.8 °F/100ft common in Gulf of Mexico salt-withdrawal basins
Typical default — not a universal value
Bourgoyne, A.T., Millheim, K.K., Chenevert, M.E., Young, F.S. (1986) — Applied Drilling Engineering
A regional default, not a universal constant — geothermal gradient varies significantly by basin and structural setting. Always use a locally measured or offset-well-calibrated value where available.
Used in:
Porosity by Rock Type
φUnconsolidated / Recent SandTextbook
35 – 45%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
Loosely packed, recently deposited sand at or near the high end of what grain packing alone allows — cementation and compaction during burial reduce this substantially as the sediment becomes sandstone.
φSandstoneTextbook
15 – 35%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
Spans moderately consolidated sandstone (higher end) to tight, well-cemented sandstone (lower end, as low as ~15%). Sorting and cementation, not grain size itself, are the dominant controls.
φLimestoneTextbook
5 – 20%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
Dominated by original depositional (interparticle/intercrystalline) texture — see the Dunham and Folk classification schemes above. Vuggy or oomoldic limestone can run well above this range; densely recrystallized limestone can run near zero.
φDolomiteTextbook
10 – 30%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
Typically more porous than limestone — dolomitization commonly creates secondary intercrystalline/vuggy porosity on top of (or in place of) the original limestone fabric, giving dolomite its characteristic reservoir quality.
φShaleTextbook
Total up to ≈40%; effective typically < 2%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
A different kind of range than the other rows: shale can carry high total porosity (fine-grained, water-filled pore space), but that pore space is so poorly interconnected that effective (producible) porosity is usually near zero — the same total-vs-effective distinction behind the neutron-density "shale effect" in log analysis.
φChalkTextbook
5 – 40%
Typical default — not a universal value
Tiab, D., Donaldson, E.C. (2004) — Petrophysics: Theory and Practice of Measuring Reservoir Rock and Fluid Transport Properties
Secondary-source-corroborated, not page-verified against the cited textbook directly.
An unusually wide range even for this table — chalk can retain very high porosity (North Sea chalk reservoirs) if burial compaction was limited, or be tightly compacted to a low-porosity, low-permeability rock elsewhere.
Sedimentary Rock Classification
Sedimentary rocks fall into four broad groups, distinguished by how they form. The two carbonate-specific schemes below (Dunham 1962, Folk 1959/1962) give a much more detailed breakdown of the Carbonate group specifically.
Siliciclastic
Detrital fragments of preexisting rocks and minerals, classified by grain size.
Conglomerate / Breccia · Sandstone · Siltstone · Mudrock (shale, claystone, mudstone)
Carbonate
Limestone and dolomite — see the detailed Dunham and Folk classification schemes below.
Limestone · Dolomite
Chemical / Evaporite
Precipitated directly from solution rather than deposited as detrital grains.
Rock salt · Gypsum · Chert
Organic
Formed largely from accumulated organic (carbonaceous) material.
Coal · Oil shale
Boggs, S., Jr. (2012) — Principles of Sedimentology and Stratigraphy, 5th ed., Pearson Prentice Hall
Standard textbook consensus rather than one author's original scheme — there is no single pinned academic paper defining this division the way Dunham or Folk's own papers define carbonate texture.
Carbonate Classification — Dunham (1962)
Classifies carbonate rocks by depositional texture — mud presence, grain support, and evidence of organic binding. The scheme most used for reservoir-fabric work; still the dominant carbonate texture classification in petroleum geology today, not superseded.
ClassSupportGrain contentBinding
MudstoneMud-supported< 10% grainsNot organically bound at deposition
WackestoneMud-supported> 10% grainsNot organically bound at deposition
PackstoneGrain-supportedLime mud presentNot organically bound at deposition
GrainstoneGrain-supportedLime mud absentNot organically bound at deposition
Boundstone—AnyOrganically bound at deposition
Crystalline——Original depositional texture not recognizable (recrystallized)
Dunham, R.J. (1962) — Classification of Carbonate Rocks According to Depositional Texture, in Ham, W.E., ed., Classification of Carbonate Rocks — A Symposium, AAPG Memoir 1, pp. 108-121
"Crystalline" (unrecognizable original depositional texture) is part of Dunham's own 1962 scheme. Embry & Klovan (1971)'s later extension (floatstone/rudstone/bafflestone/bindstone/framestone) is a separate, distinctly-cited addition and is not included here.
Carbonate Classification — Folk (1959, 1962)
Classifies carbonate rocks by detailed petrographic composition — the proportion of allochems (grains), micrite (mud matrix), and sparite (sparry cement). The scheme most used for detailed petrographic and diagenetic work; a genuinely distinct, still-used alternative to Dunham, not a superseded scheme. Folk's 1959 paper establishes the core allochem/matrix/cement framework and biomicrite/biosparite naming; the 1962 paper refines it into the energy-ordered spectrum below.
TypeAllochem contentMatrix / cement
Micrite< 1% allochemsMicrite (mud) matrix
Fossiliferous micrite1 – 10% allochemsMicrite (mud) matrix
Sparse biomicrite10 – 50% allochemsMicrite (mud) matrix
Packed biomicrite> 50% allochemsMicrite (mud) matrix
Poorly washed biospariteAllochems + micrite + spar mixedMicrite + sparry calcite cement
Unsorted biosparitePoorly sorted allochemsSparry calcite cement
Sorted biospariteWell-sorted allochemsSparry calcite cement
Rounded biospariteRounded, abraded allochemsSparry calcite cement
Folk, R.L. (1959) — Practical Petrographic Classification of Limestones, AAPG Bulletin, Vol. 43(1), pp. 1-38
Folk, R.L. (1962) — Spectral Subdivision of Limestone Types, in Ham, W.E., ed., Classification of Carbonate Rocks — A Symposium, AAPG Memoir 1, pp. 62-84
Grain-Size Classification
The Udden–Wentworth scale, universally adopted across sedimentology and well-log lithology description since 1922 — unlike the correlation entries above, these class boundaries are a fixed definitional standard, not a typical default.
ClassΦ (phi) rangeSize range (mm)
Gravel
Boulder< −8> 256
Cobble−8 to −664 – 256
Pebble−6 to −24 – 64
Granule−2 to −12 – 4
Sand
Very coarse sand−1 to 01 – 2
Coarse sand0 to 10.5 – 1
Medium sand1 to 20.25 – 0.5
Fine sand2 to 30.125 – 0.25
Very fine sand3 to 40.0625 – 0.125
Silt & Clay
Silt4 to 80.0039 – 0.0625
Clay> 8< 0.0039
Wentworth, C.K. (1922) — A Scale of Grade and Class Terms for Clastic Sediments, The Journal of Geology, Vol. 30(5), pp. 377-392
Φ = −log₂(size in mm); the phi notation shown here was introduced later by Krumbein (1934) as a log-linear relabeling of Wentworth's original millimeter boundaries, not part of the 1922 paper itself.
Stratigraphic Column Lithology Symbols
The standard area-fill patterns used to represent common lithologies on a stratigraphic column, cross-section, or geologic map, per the FGDC's official Digital Cartographic Standard for Geologic Map Symbolization. A curated 7-lithology subset — several of these lithologies have multiple bedding- or composition-specific pattern variants in the full standard; the plainest, most generic variant was chosen for each (see each card's own note where a choice had to be made). Swatches below reproduce each pattern's defining visual device at legend scale — not the standard's literal printed line art, drawn for large-format map sheets — see this platform's `stratColumnSymbols.js` for the full disclosure of that choice.
Sandstone
FGDC 607 — Massive sand or sandstone
Fine, evenly scattered dots.
Shale
FGDC 620 — Clay or clay shale
Short, staggered horizontal dashes.
Limestone
FGDC 627 — Limestone
Regular, evenly-sized offset brick courses.
Dolomite
FGDC 642 — Dolostone or dolomite
Coarser, more irregular offset brick courses than limestone, with diagonal rhomb-like accents.
Coal
FGDC 658 — Coal
Solid fill (renders in the page’s foreground color — black on light theme, light on dark theme).
Anhydrite / Evaporite
FGDC 667 — Gypsum (representative — see note)
Diagonal cross-hatch.
FGDC-STD-013-2006 has no distinct anhydrite pattern; Gypsum (667), the standard’s nearest evaporite-mineral symbol, is used here as a disclosed representative substitution, not a naming variant of the same lithology.
Conglomerate
FGDC 601 — Gravel or conglomerate (1st option)
Large, irregular scattered circles ("pebbles"), coarser than sandstone’s fine dot pattern.
Federal Geographic Data Committee (2006) — FGDC Digital Cartographic Standard for Geologic Map Symbolization (FGDC-STD-013-2006; also published as USGS Techniques and Methods 11-A2)
Sandstone (607), shale (620), limestone (627), dolomite (642), and conglomerate (601) each have several additional bedding- or composition-specific pattern variants in the full standard not shown here. Coal (658) is unambiguous. The standard has no distinct anhydrite pattern — Gypsum (667) is used as a disclosed representative evaporite symbol, not a naming variant of the same lithology.
Geologic Time Scale
The International Chronostratigraphic Chart, down to Epoch level for the Phanerozoic (the interval virtually all subsurface work touches) and a coarser Era/undivided-Eon level for the rarely-relevant Precambrian. Ages are millions of years (Ma) before present, at the base of each unit; "~" marks a boundary the chart itself flags as an approximate, unconstrained numerical age.
Chart v2026/06 · last verified 2026-09-10 — the ICS revises this chart's numeric ages periodically; check stratigraphy.org/chart for anything newer.
PeriodEpochBase age (Ma)
Phanerozoic — Cenozoic
QuaternaryHolocene0.0117
QuaternaryPleistocene2.58
NeogenePliocene5.333
NeogeneMiocene23.04
PaleogeneOligocene33.9
PaleogeneEocene56.0
PaleogenePaleocene66.0
Phanerozoic — Mesozoic
CretaceousLate (Upper) Cretaceous100.5 ±0.1
CretaceousEarly (Lower) Cretaceous143.1 ±0.6
JurassicLate (Upper) Jurassic161.5 ±1.0
JurassicMiddle Jurassic174.7 ±0.8
JurassicEarly (Lower) Jurassic201.4 ±0.2
TriassicLate (Upper) Triassic~237
TriassicMiddle Triassic247.0*
TriassicEarly (Lower) Triassic251.902 ±0.024
Phanerozoic — Paleozoic
PermianLopingian259.857 ±0.084*
PermianGuadalupian274.4 ±0.4
PermianCisuralian298.9 ±0.15
Carboniferous (Pennsylvanian)Late (Upper) Pennsylvanian307.0 ±0.1
Carboniferous (Pennsylvanian)Middle Pennsylvanian315.2 ±0.2
Carboniferous (Pennsylvanian)Early (Lower) Pennsylvanian323.4 ±0.4
Carboniferous (Mississippian)Late (Upper) Mississippian330.3 ±0.4
Carboniferous (Mississippian)Middle Mississippian346.7 ±0.4
Carboniferous (Mississippian)Early (Lower) Mississippian358.86 ±0.19
DevonianLate (Upper) Devonian382.31 ±1.36
DevonianMiddle Devonian393.47 ±0.99
DevonianEarly (Lower) Devonian419.62 ±1.36
SilurianPridoli422.7 ±1.6
SilurianLudlow426.7 ±1.5
SilurianWenlock432.9 ±1.2
SilurianLlandovery443.1 ±0.9
OrdovicianLate (Upper) Ordovician458.2 ±0.7
OrdovicianMiddle Ordovician471.3 ±1.4
OrdovicianEarly (Lower) Ordovician486.85 ±1.5
CambrianFurongian~497.0
CambrianMiaolingian~506.5
CambrianSeries 2~521.0
CambrianTerreneuvian538.8 ±0.6
Proterozoic
—Neoproterozoic1000
—Mesoproterozoic1600
—Paleoproterozoic2500
Archean
—Archean (undivided)4031 ±3
Hadean
—Hadean (informal)~4567
Cohen, K.M., Finney, S.C., Gibbard, P.L., Fan, J.-X. (2013) — The ICS International Chronostratigraphic Chart (2013; updated), Episodes, Vol. 36, pp. 199-204
* Marks the 2 Epoch bases (Middle Triassic, Lopingian) whose numeric age changed in the chart's v2026/06 revision — hover for the pre-revision value. Precambrian time is shown at Era level (Proterozoic) or as a single undivided Eon (Archean, Hadean) rather than carried to the same Period/Epoch depth as the Phanerozoic, since it is essentially never a subsurface target on this platform.
Depositional Environments
The standard named depositional settings sedimentary rocks form in, each with distinct grain-size, sorting, and geometry characteristics that carry through to reservoir quality. A simple reference list, not a cross-section illustration — see each entry's reservoir-relevance note for how the setting typically behaves as an exploration/reservoir target.
Fluvial
Rivers and streams — channel, point-bar, and floodplain deposits, ranging from braided to meandering river systems.
Classic clastic reservoir target; channel sands can be excellent reservoirs, but stacking, connectivity, and lateral continuity are often complex and compartmentalized.
Deltaic
Where a river enters a standing body of water (sea or lake) and deposits its sediment load — distributary channels, mouth bars, and delta-front/prodelta sequences.
One of the most prolific reservoir settings worldwide (e.g., Niger Delta, Gulf of Mexico); typically produces well-sorted, laterally extensive sand bodies with predictable stacking patterns.
Shoreface
The nearshore marine zone between fair-weather and storm wave base, reworked by wave and current energy into well-sorted sand bodies.
Wave reworking produces clean, well-sorted, laterally continuous sands with generally good reservoir quality and predictable upward-coarsening trends.
Shelf
The broad, low-relief marine platform beyond the shoreface, generally below normal wave base but still within the photic/storm-influenced zone.
Reservoir quality is more variable than shoreface — storm-deposited sand sheets can form reservoirs, but background shelf mud deposition often dominates and can act as a seal or baffle.
Deep Marine / Turbidite
Sediment gravity flows (turbidity currents) transporting sand and mud down the continental slope onto the basin floor, forming submarine fans and channel-levee systems.
Major deepwater exploration target (e.g., Gulf of Mexico, offshore Brazil, West Africa); reservoir geometry is controlled by channel/lobe architecture and can be highly heterogeneous.
Eolian
Wind-blown deposits — dune and interdune sands, typically in arid, sediment-starved continental settings.
Very well-sorted, well-rounded sand grains give excellent primary porosity and permeability where preserved (e.g., Rotliegend, Navajo Sandstone), though internal dune cross-bedding creates strong permeability anisotropy.
Lacustrine
Lake deposits — ranging from nearshore clastic deltas and beaches to deep, quiet-water organic-rich mudstones.
Deep lacustrine mudstones are important source rocks in rift basins (e.g., China, West Africa rift systems); associated deltaic/turbidite sands within the same basin can form reservoirs.
Glacial
Deposits from ice sheets and glacial meltwater — poorly sorted till, and better-sorted glaciofluvial/glaciolacustrine outwash sands and gravels.
Least common hydrocarbon reservoir setting on this list; where present, reservoir quality is highly variable and controlled by whether the deposit is ice-contact (poorly sorted till) or meltwater-reworked (better-sorted outwash).
Boggs, S., Jr. (2012) — Principles of Sedimentology and Stratigraphy, 5th ed., Pearson Prentice Hall
Same textbook as the Sedimentary Rock Classification section above — its Depositional Environments chapters cover this exact 8-environment list (Continental: fluvial, eolian, lacustrine, glacial; Siliciclastic Marine / Marginal-Marine: deltaic, shoreface, shelf, deep marine/turbidite).