Summary

The Petroleum Province of Anadarko Basin is one of many prolific hydrocarbon systems in North America. Diagenesis and hydrothermal processes in this area affected oil and gas migration pathways, inside the Mississippian stratigraphy. Chemostratigraphy allows a clear identification of such migration pathways; through the integration of inorganic geochemistry with mud gas data and drilling parameters, sweet points can be identified for reservoir depletion.

The combination of rock textures with the elemental patterns points out different diagenetic degrees. In carbonates, e.g. Osagean limestone, diagenetic degree depends primarily on water-carbonates interactions and on the presence of interstitial colloidal fluids. These dynamics can be easily recognized through the presence of particular vicarious elements inside carbonates, estimating the presence of cement and matrix for porosity assessment. The distribution of such elements, correlated with drilling parameters and mud gas data, gives valuable information about the position of porous layers.

When sediments temperature is high enough to trigger hydrothermal phenomena, it is also possible to detect fracture and fault systems, filled with a variety of mineral species related to the hydrothermal regime. Positive anomalies in minor and trace elements, depending on the different mineral species, can provide fracture's position and nature. If fractures assist the production permeability, the knowledge of their position, nature, related mud gas data and drilling parameters allows an optimized well completion, increasing the recovery factor of a reservoir. Finally, in a geo-steered well, drilling a siliciclastic sequence, e.g. in Meramecian thin bedded silty-shaly sandstone, the chemical signal makes possible an exhaustive and detailed reservoir characterization, also when the recognition of sedimentary facies becomes difficult because of low cuttings quality. Variations in some key elements and ratios related to transgressive/regressive cycles, paleo-productivity, paleo-salinity and anoxic conditions allow well trajectory assessment in a highly defined stratigraphic framework. This approach, combined with drilling parameters, allows significant savings, providing key information at low costs for a very effective geosteering process.

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