Subsurface Hydrocarbon Migration: Steady-State Model,Sensitivity Analysis and Field Example,Green Canyon Block,North Central Gulf of Mexico.

Abstract

Recent studies of exploration wells from offshore Louisiana and Trinidad suggest fine-grained authigenic carbonates with negative carbon isotopic signatures act as geochemical recorders or tracers of hydrocarbon movement. A flux of hydrocarbons through an aquifer then produces a “mixed” δ¹³C signal, impacted on by flow speed, microbial degradation and the presence of biogenic or detrital calcite. Mapping of δ¹³C anomolies could be used to determine hydrocarbon migration pathways. By measuring the mixed signal as a function of position along the aquifer, it should be possible to extract both the amount and speed of the hydrocarbon flow by “inverting” the measurements — due allowance being made for thermal effects which “kill” microbes or alter their biodegradation rate, and for the thermal degradation of oil to gas. Preliminary measurements in offshore Louisiana strongly suggest this process is operative in Plio-Pleistocene sands.

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