ABSTRACT: Applications of Sr and Pb Isotopes to Petroleum Production

Richard W. Hurst

Both the strontium and lead isotope systems have been applied to problems routinely encountered by production geologists. Sr isotopes have been very effective as a correlation tool, particularly when applied to rock-rock and water-rock systems.

The Pb isotope system may be used to discriminate fossil fuel-derived Pb (coal, petroleum, kerogen) from rock and gasoline-derived Pb. Lead isotope ratios of genetically related kerogens are virtually identical, indicating the potential use of Pb isotopes in oil-oil correlations.

Water-rock and rock-rock correlations using Sr isotopes will be discussed via examples from California (Kreyenhagen Formation, San Joaquin basin; Monterey Formation, southern California) and Argentina (Commodoro Rividavia Formation). The latter investigation also demonstrates the application of combined Sr-O isotope systematics to problems involving reservoir continuity in fluvial sands of the Commodoro Rividavia Formation. Strontium isotopes have also been used to assess the source of water when pipe casings fail; rapid identification of fluid sources is important since failures on the sea floor require far less remediation than subsurface leaks.

Pb isotope analyses of related oils indicate that oils (1) are radiogenic, (2) lie in a field defined by fossil fuels on a plot of ²⁰⁶Pb/²⁰⁴Pb vs. ²⁰⁶Pb/²⁰⁷Pb; and (3) are isotopically distinct from most of gasoline and rock Pb isotopic compositions. Although Pb isotopes have not been used by the petroleum industry to any great extent, the data suggest that oil-oil correlations may be improved using Pb isotope systematics.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990