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Carbon–oxygen (C/O) log stratigraphy is a geostatistical method that helps in understanding the filling and response of upstream and downstream reservoirs, such as carbonates and shales. C/O logs are used in geophysical evaluation, providing a basis for determining fluid compositions in hydrocarbon systems, exploring hydrocarbon reservoirs and their associated sequences, and in stratigraphic interpretation.
Carbon–oxygen (C/O) logs provide a detailed stratigraphic section to integrate cored intervals in terms of depth and lithology. The C/O log is a versatile technique used in well logging. It is widely applied in field geological research, geological workstation evaluation, reservoir analysis and modeling, and production prediction.
The basic concept of carbon–oxygen (C/O) log stratigraphy is to measure the ratio of carbon and oxygen present within a rock formation. This ratio can be used to infer the likely composition of the rock formation and determine whether or not it contains hydrocarbon reserves. By obtaining core samples from multiple depths throughout the well, it is possible to create a detailed picture of the subsurface rock formations and gain an understanding of their composition.
In order to acquire an accurate measurement, carbon–oxygen (C/O) logs employ both electrochemical and nuclear magnetic resonance (NMR) detection techniques. Electrochemical detection is used to measure the oxygen content in each sample, while NMR is used to measure the carbon content. This data is then combined to determine the ratio of carbon to oxygen in each sample.
The interpretation of C/O log data requires a good understanding of the geological history of the formation and its response to diagenetic processes. By evaluating the history and re-evaluating the data in light of this history, it is possible to make more accurate predictions about the formation. Diagenetic processes can affect the C/O ratio, by increasing or decreasing the amount of oxygen available in the rock, potentially making a formation more or less resource-rich.
The evaluation of C/O log data is highly specialized and requires experience in understanding the relationship between the geological processes and their effect on the data. A good knowledge of the surrounding stratigraphic column as a whole is also important, as it allows better correlation between the data and its context.
Carbon–oxygen (C/O) log stratigraphy is a powerful tool for making predictions about the composition of subsurface reservoirs. With the right expertise in evaluating the data and the correct context, predictions can be made with a high degree of accuracy. This methodology has been used to great effect in the evaluation of hydrocarbon reservoirs and in predicting their future production rates.
