Nowadays petrophysical uncertainty is taken into account by major western companies for the field evaluation alongside with existing geological uncertainties. Several published papers review and generalize the main theoretical aspects. However, for Russian companies this idea of stochastic well log interpretation is rather innovative. Thus, the main objective of this paper is to represent the Monte-Carlo simulation method, frequently used in Total for the petrophysical interpretation, on the example of Termokarstovoye field. The stochastic interpretation was performed on two cored wells (providing the uncertainty reduction by the presence of core measurements), logged with wireline PEX tool.

Basically the stochastic interpretation follows the deterministic one and tells how much results vary around the deterministic result. Furthermore, the proposed methodology allows the interpreter to determine the most relevant uncertain parameters on which additional measurements or justifications are required to reduce the petrophysical uncertainty.

Following the described methodology it was identified that the main uncertainty on Termokarstovoye field is saturation. Its influence on the final HCPV (cumulative hydrocarbon pore volume) distribution can be decreased by providing the additional analysis on formation water salinity and by resistivity log inversion, which are the two main impacting parameters.

Thus, experience while running the Termokarstovoye practical case highlighted that, firstly, the final petrophysical uncertainty can be explained and justified. Secondly, further recommendations can be made on new acquisitions to later decrease the uncertainty.

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