Spore coloration and thermal alteration indices (SCI and TAI): usage

Exploring for Oil and Gas Traps
Series	Treatise in Petroleum Geology
Part	Critical elements of the petroleum system
Chapter	Evaluating source rocks
Author	Carol A. Law
Link	Web page
Store	AAPG Store

How to use SCI and TAI

SCI (spore coloration index) and TAI (thermal alteration index) are maturation indicators that measure the color of palynomorphs. Color changes as a function of maturity.

There are a number of scales for both SCI and TAI within the exploration industry. The SCI and TAI scales have been standardized to the vitrinite reflectance (R_o) maturity scale. Users of SCI and TAI data need to have access to the maturation relationship used by the lab supplying the data, and users should be aware of how the scales compare from one lab to another in order to apply the data correctly. These relationships should be available from the vendor performing the analysis.

Correlation of SCI & TAI with other parameters

The table below shows a very generalized correlation of kerogen maturity parameters with SCI and TAI (after).

Vitrinite reflectance (%Ro)	Spore coloration index (SCI)	Thermal alteration index (TAI)	Pyrolysis Tmax (°C)	Generalized hydrocarbon zone
0.40	4.0	2.0	420	Immature
0.50	5.0	2.3	430	Immature
0.60	6.0	2.6	440	Oil
0.80	7.4	2.8	450	Oil
1.00	8.1	3.0	460	Oil
1.20	8.3	3.2	465	Oil & wet gas
1.35	8.5	3.4	470	Wet gas
1.50	8.7	3.5	480	Wet gas
2.00	9.2	3.8	500	Methane
3.00	10	4.0	500+	Methane
4.00	10+	4.0	500+	Overmature

See also

• Evaluating source rock maturity
• Maturation
• Tmax
• Vitrinite reflectance
• Apatite fission track analysis
• Hydrogen Index (HI)
• Production Index (PI)

External links

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thermal alteration index