Andrew D. Carr¹, John E. A. Marshall²
(1) Advanced Geochemical Systems Ltd, Leics, United Kingdom
(2) School of Oceanographic Sciences, Hants, United Kingdom

Abstract: Spore transmittance (% St): Further Development of an optically based maturation parameter

Maturation in petroleum basins can be assessed by a number of parameters, all of which change in response to increasing temperature as sediments are buried. Vitrinite reflectance is the most widely used parameter, yet it has a number of disadvantages including its paucity as an autochthonous component in many of the marine source rocks responsible for oil generation and its sluggish response to increasing temperature during the immature and early mature stages. Spore colour has been developed as an alternative/supplementary parameter for maturation, but until recently it has suffered from the disadvantage of being a visual (subjective) assessment method.

A recently published study (Yule et al., 1999) showed that the colour of spores could be analysed using a scanning microspectrophotometer system, and based on the analysis of spore colour standards and laboratory matured samples, the parameter generated (% St) increased with maturity. In this study, %St results from wells containing Tertiary, Mesozoic and Palaeozoic strata are presented, and show that %St increases with depth of burial (and age), with the %St-depth gradient being an indicator of the thermal history. The method has the advantage that cavings can be easily identified, and while it is not proposed that St replaces vitrinite reflectance, it provides a powerful complementary technique.

Yule, B., Carr, A.D., Marshall, J.E.A. and Roberts, S. (1999) Spore transmittance (% St): a quantitative method for spore colour analysis. Organic Geochemistry, 30, 567-581.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana