Abstract: Log Based Petroleum Geochemistry of World Wide Tertiary through Precambrian Source Rocks

LANCASTER, JAMES R. and JAMES C. ENGSTROM

An innovative approach to determine petroleum geochemistry values using traditional wireline logs is presented. The computed values include total organic carbon (TOC), S1, S2, S3, oxygen and hydrogen indices (OI and HI), equivalents of atomic oxygen/carbon

and hydrogen/carbon ratios, and the transformation ratio S1 / (S1+S2) (TR). TR is used to compute the level of organic metamorphism (LOM), thermal alteration index (TAI), Tmax, time-temperature index (TTI), and vitrinite reflectance (Ro%).

Comparisons of laboratory and computed data are presented using crossplots and analog plots.

The petroleum geochemical values are displayed on a composite log using global wide case history data of Tertiary through Precambrian source rocks. Paleodepths range from 9000 to 21000 feet and paleotemperatures range from about 100 to greater than 230 degrees C. TOCs range from less than 1 to less than 10 Wt%, HI ranges from greater than 10 to greater than 700, and OI ranges from 20 to about 300. Kerogen types are I, II, III, and possibly IV. Thermal maturity ranges from early mature to well beyond the "oil window".

Map views of quantities, kerogen type, and maturation levels are compared to production history over an established oil producing field. Organic facies can be inferred from a van Krevelen diagram and used with seismic cross sections and sequence stratigraphic profiles.

AAPG Search and Discovery Article #90946©1997 AAPG Rocky Mountain Section Meeting, Denver, Colorado