Abstract
A novel approach, based on geotracer compositional correlation analysis is reported, which reveals the oil charge sequence and migration pathways for five oil fields in Saudi Arabia. The geotracers utilised are carbazoles, a family of neutral pyrrolic nitrogen compounds known to occur naturally in crude oils. The approach is based on the concept that closely related fields, with respect to filling sequence, will show a higher carbazole compositional correlation, than those fields that are less related. That is, carbazole compositional correlation coefficients can quantify the charge and filling relationships among different fields. Consequently, oil migration pathways can be defined based on the established filling relationships. The compositional correlation coefficients of isomers of C1 and C2 carbazoles, and benzo[a]carbazole for all different combination pairs of the five fields were found to vary extremely widely (0.28 to 0.94). A wide range of compositional correlation coefficients allows adequate differentiation of separate filling relationships. Based on the established filling relationships, three distinct migration pathways were inferred, with each apparently being charged from a different part of a common source kitchen. The recognition of these charge and migration pathways will greatly aid the search for new accumulations.
Highlights
Occurring geotracers are usually measured in reservoired oils
Comparing the migration pathways and filling relationships defined from the carbazole compositional correlation analysis (Fig. 7b) with those derived from the basin modeling analysis (Fig. 8) shows that conclusions derived from the two approaches are basically the same
The conclusions derived from the carbazole compositional correlation analysis are supported by the basin modeling analysis, these two approaches are totally different
Summary
Occurring geotracers (such as carbazoles) are usually measured in reservoired oils. The concentration of carbazoles in oils represents the difference between the initial concentration expelled from the source rock and the amount removed during oil migration and accumulation[11]. Loss of carbazoles during migration and accumulation processes is complicated and depends on a variety of factors including migration channel size, host rock porosity, specific surface area and adsorption capacity, volume of reservoired oil and relative migration distance[11]. We report a novel method for locating oil charge and migration pathways using carbazole compositional correlations between different fields. Five oil fields, located in the Summan exploration area in the north-eastern part of Saudi Arabia (Fig. 2), were utilised as a case study to test the proposed methodology and illustrate the general procedure for assessing oil migration pathways
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