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A rock physics modelling approach for time-lapse monitoring and characterization of fluid–rock interactions in hydrocarbon reservoirs.

One of the research gaps is to understand the development of seismic characteristics of gas-saturated rock along with the change in rock properties because of chemical reactions. We suggest a method to explain the change in elastic properties brought on by CO2 injection in a rock by capturing the physico-chemical interactions observed in the laboratory in a theory of rock physics. We adapt the theory such that it can be applied to the field data and calibrate the theory using water-saturated well log data from the Ankleswar field, an established oil field in the Cambay basin, western India. This study demonstrates that, for a uniform model, velocity decreases by up to 18% as CO2 saturation increases from 0% to 20% (ignoring the chemical effect), and that, for a specific saturation, say 20%, chemical effects result in a 17% decrease in velocity from the present to the end of 60 years. Whereas, for patchy model, velocity decreases maximum by 14% and 16% due to varying saturation and chemical reaction. This research contributes to make strategy for CO2-sequestration in a designated field.

(a) Simulated stratigraphic column: Grey and yellow denote shale and sand layers, respectively with water-saturated velocity and density logs from Ankleshwar field, (b) time-lapse synthetic seismic data at different CO2 saturation (SCO2) and time (t) in year (c) Time-lapse synthetic logs at 80% CO2 saturation

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