The Role of Geochemical Correlations in Establishing Hydrocarbon Origin and Migration Patterns

B. J. Katz

Organic geochemistry provides several tools and techniques for the petroleum explorationist. Among these techniques is the ability to establish a genetic link between oils and oils and their sources. Such geochemical correlations provide information on the geographic and spatial limits of a petroleum system including the relationship between specific generative sub-basins, hydrocarbon accumulations and migration pathways.

These linkages can define regional exploration concepts. For example, in rift basins, such as the North Sea, correlations can establish the importance of vertical migration. In foreland basins, such as in western Canada, correlations cam confirm the presence of a single disassociated source, and establish an exploration fairway between the generative sub-basin and known accumulations.

Potentially of greater importance are those situations where geochemical correlations alter accepted exploration concepts based largely on geologic inference. For example, in the Sub-Andean region of northern South America much of the reserve base has been attributed to the La Luna Fm. and its stratigraphic equivalents. Exploration would focus on regions which are in communication with mature La Luna source rock. Detailed analysis of the region's oils has, however, shown that a number of geochemical families exist, with each family having a different source. Thus exploration is not limited to those regions where mature La Luna was in communication with potential targets but may be expanded.

Geochemical correlations can also define which portion of a source rock may be an effective contributor to a region's reserve base. Oils derived from both the Bucomazi Fm. of West Africa and the Napo Fm. of Ecuador show distinct linkages to only a discrete stratigraphic portion of the total potential source rock interval. Thus volumetric estimates should be based only on the net volume of the effective source facies.

Reliable correlations although based on expanded geochemical databases, must also take into consideration variations in such factors thermal maturation, expulsion, migration effects and post-emplacement alteration. Correlations need also to take into consideration sampling problems and biases and should be performed only within a geologic framework.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995