Chemostratigraphy: A new tool for the correlation of ancient sequences

Chemostratigraphy involves the application of major and trace-element geochemistry to the characterization and correlation of strata in petroleum basins, particularly where biostratigraphic control is poor. The geochemistry of sediments is highly variable and sensitive to subtle changes in composition and uniform succession may show primary differences in the chemistry of their constituent minerals or in the proportions of accessory phases. Geochemical data are acquired by analysis using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS). These techniques enable the rapid acquisition of high-quality data on approximately 30 elements for a large number of samples. Data are used to characterize a geochemical [open quotes]fingerprint[close quotes] both for individual beds and sedimentary units and to recognize long-term geochemical trends. Chemostratigraphic correlations between wells are established on the identification of similar geochemical characteristics. Geochemical data can differentiate between successions of sedimentary units having repetitious lithological and E-Log characteristics. Core-based chemostratigraphies have the potential for high-resolution fingerprinting and correlation of individual beds and small-scale sedimentary units. Cuttings-based chemostratigraphies can be used to differentiate between thick sedimentary units and to identify long-term geochemical trends. Geochemical data can define marker horizons which can be utilized as a basis for E-Log correlations. Othermore » applications can determine changes in sediment provenance, which is important in modeling depositional system and reservoir geometry, fingerprint and predict the extent of claystone permeability barriers in reservoirs, investigate the geochemical controls responsible for E-log signatures, aiding research into interpretation of the responses of downhole geochemical tools, and investigate diagenetic histories.« less