Expanding the possibilities of synchronous inversion in carbonates using a sedimentological concept

Introduction. More than 50 % of the world’s oil and gas reserves are concentrated in carbonate reservoirs. At the same time, they are characterized by a complex structure and strong lateral variability of sediments, since their filtration-intensive properties (FES) can simultaneously depend both on the sedimentation structure of sediments, which is decisive in the formation of FES, and on secondary processes (recrystallization, dolomitization, leaching, etc.), which enhance facies heterogeneity. One of the most important tasks in modeling such deposits is to trace productive effective thicknesses in the inter-well space. For “complex” terrigenous reservoirs, inversion and its volumetric interpretation through Bayesian classification have proven themselves well. Such approaches make it possible to restore the values of elastic properties in the target intervals of the section and to make a forecast in the inter-well space of the distribution of reservoirs and their FES. The correctness of using this approach to carbonate rocks remains a topic for discussion.
Aim. In order to obtain a forecast of the distribution of reservoirs of carbonate deposits of the Osinsky horizon of Eastern Siberia, a method for constructing a low-frequency model was developed and the optimal interpretation was chosen.
Materials and methods. Considering the features of the carbonate section, various methods of constructing the NMF have been tested and an optimal technique has been developed to preserve the geological basis of the section and remove the influence of wells on the trend. Synchronous inversion was calculated, its interpretation was carried out by the Bayesian classification of cubes of elastic parameters, and the collector probability cube for each facial zone was obtained at the output.
Results. It is established that the classical approach to constructing a low-frequency trend through well interpolation is not suitable for carbonate reservoirs, it is necessary to use the trend for more correct propagation of elastic properties. When interpreting, facies changes in the formation should also be taken into account, since in different facies the reservoir can be represented by different FES, and therefore by different elastic parameters.
Conclusion. Seismic inversion as a tool for detailed geological modeling on the example of an oil field in Eastern Siberia has shown its effectiveness for predicting FES in the carbonate interval.

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