Integrated Sedimentological Analysis: a Key Approach for Volumetric Evaluation and Risk Assessment of Achimov Plays

Widely spread in Western Siberia Achimov deposits are represented by fan complexes in slope and basin parts of Neocomian clinoform formation. Stratigraphic trapping plays a key role especially in areas outside of structural highs. Sequence stratigraphy analysis together with defining fan relationship with slope allows predicting main and intermediate seals effectiveness as well as reservoir position inside the clinoforms. Prediction of reservoir facies distribution combined with regional and worldwide analogs analysis also a key element for volumetric reserves evaluation. Defining of architectural elements such as lobes, slumps and channels helps to estimate reservoir geometry and range of key parameters (Gross&Net thickness, NTG, Porosity and Permeability). Thus complex sedimentological model based on logs, seismic, core and analogs analysis allows evaluating uncertainty range of parameters and probability of success especially in poorly well constrained areas. Such detailed approach resulted in identification of areas with reserves density above economic threshold. As a consequence exploration well drilling is now considered to prove the presence of developable reservoirs within the considered license.