Validation

Check our numbers against the literature

A calculation you cannot check is a calculation you cannot sign off. Below, each core method runs through the same engine code the app uses, next to the value worked by hand from the published equation.

How this page is built

The engine column is not typed in. The page calls the production engine functions when it is built. An automated test runs the same cases on every change and fails if any result drifts outside its stated tolerance. If the page shows a match, the code shipped with it produces that match.

Engine results against published references

Method	Inputs	Reference value	Engine result	Difference
Water saturation Archie water saturation Archie (1942); Asquith & Krygowski, Basic Well Log Analysis (2004)	Rt 10 ohm·m, φ 0.20, Rw 0.05 ohm·m, a 1, m 2, n 2	0.3536 v/v	0.3536 v/v	< 0.000001
Water saturation Archie water saturation, non-unit constants Archie (1942); Humble formation factor, Winsauer et al. (1952)	Rt 10 ohm·m, φ 0.20, Rw 0.05 ohm·m, a 0.62, m 2.15, n 1.8	0.2762 v/v	0.2762 v/v	< 0.000001
Water saturation Indonesia (shaly-sand) water saturation Poupon & Leveaux (1971)	Rt 10 ohm·m, φ 0.20, Rw 0.05 ohm·m, Vsh 0.10, Rsh 2 ohm·m, a 1, m 2, n 2	0.3247 v/v	0.3247 v/v	< 0.000001
Water saturation Indonesia water saturation, non-unit constants Poupon & Leveaux (1971)	Rt 10 ohm·m, φ 0.20, Rw 0.05 ohm·m, Vsh 0.10, Rsh 2 ohm·m, a 0.62, m 2.15, n 1.8	0.2539 v/v	0.2539 v/v	< 0.000001
Organic matter ΔlogR total organic carbon Passey et al. (1990), AAPG Bulletin 74(12)	ΔlogR 1.0, level of organic metamorphism (LOM) 10	4.064 wt%	4.064 wt%	0.000033
Organic matter ΔlogR total organic carbon, second point Passey et al. (1990), AAPG Bulletin 74(12)	ΔlogR 1.7, LOM 10.5	5.689 wt%	5.689 wt%	0.000030
Geomechanics Eaton sonic pore pressure Eaton (1975), SPE 5544	Sv 10,000 psi, hydrostatic 4,650 psi, Δt ratio 0.8, exponent 3	7,260.8 psi	7,260.8 psi	< 0.000001
Geomechanics Eaton fracture gradient Eaton (1969), JPT 21(10)	Sv 10,000 psi, Pp 4,650 psi, Poisson's ratio 0.25	6,433.3 psi	6,433.3 psi	0.0033
Geomechanics Bowers effective stress (loading curve) Bowers (1995), SPE 27488	Vp 7,500 ft/s, A 5, B 1	500.0 psi	500.0 psi	< 0.000001
Geomechanics Bowers effective stress, Gulf of Mexico coefficients Bowers (1995), SPE 27488	Vp 7,500 ft/s, A 4.4567, B 0.8168	2,320.0 psi	2,320.0 psi	0.0040
Fluid properties Standing oil formation volume factor Standing (1947), API Drilling & Production Practice	Rs 500 scf/STB, gas gravity 0.8, 35 °API, 180 °F	1.2927 rb/STB	1.2927 rb/STB	0.0000074
Production forecasting Arps exponential decline, one-year cumulative Arps (1945), Trans. AIME 160	qi 1,000 bbl/d, Di 0.001 /day, t 365 days	305,803 bbl	305,803 bbl	0.35
Production forecasting Arps hyperbolic decline, one-year cumulative Arps (1945), Trans. AIME 160	qi 1,000 bbl/d, Di 0.002 /day, b 0.5, t 365 days	267,399 bbl	267,399 bbl	0.27
Economics Net present value Standard discounted cash flow, end-of-period convention	Cash flows −100, 50, 50, 50 at a 10% discount rate	24.34 $	24.34 $	< 0.000001
Economics Internal rate of return Standard discounted cash flow	Cash flows −100, 50, 50, 50	23.38 %	23.38 %	0.0000071
Formation water Rw from NaCl-equivalent salinity Bateman & Konen (1977), The Log Analyst 18(5)	100,000 ppm NaCl equivalent, 75 °F	0.0735 ohm·m	0.0735 ohm·m	0.0000044
Formation water Rw to formation temperature (Arps) Arps (1953), Trans. AIME 198	Water analysis Na 39,300 + Cl 60,700 ppm (100,000 ppm NaCl eq.), formation 200 °F	0.0291 ohm·m	0.0291 ohm·m	< 0.000001
Porosity Secondary porosity index Schlumberger Log Interpretation Principles; Asquith & Krygowski (2004)	Crossplot φ 0.12, sonic φ 0.08	0.040 v/v	0.040 v/v	< 0.000001

Blind tests on synthetic wells

We also forward-model synthetic wells from a known answer: invented lithology, porosity, fluids, organic content and pressure, turned into the log curves a logging tool would record. The engine then interprets those logs without seeing the answer. On the organic-rich test well, density and uranium TOC each recover the designed zone average to within 0.6 wt%, ΔlogR (sonic overlay) recovers the TOC above the background shale to within 0.6 wt%, and kerogen volume comes within 0.015 v/v. These checks run on every build. Synthetic wells contain no client data, and one of them is free to download so you can run the full workflow yourself.

Download a synthetic well (RRS-SYN-0001, LAS)

What this page does not prove

Matching a published equation proves the equation is coded correctly. It does not prove the equation suits your rock. Parameter choice, calibration to core and pressure data, and judgement remain the interpreter's job, and the app shows every parameter so that judgement can be reviewed.

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