Adaptive Option in Geological Modeling of Petroleum Reservoirs

Abstract

The adaptive geological model differs from the deterministic one in that it takes into account the uncertainty of the initial data, has a degree of detail corresponding to the level of accuracy of the geological information, and reproduces the main regularities of the structure of the oil and gas object under consideration, primarily for the purpose of predicting its geology in undeveloped zones. At the first stage, adaptive geological models of separate layers identified by the results of detailed correlation of the considered object are constructed independently from each other, and then the single-layer models are summed up into a multilayer adaptive geological model of the object as a whole. With the adaptive approach, traditional methods of interpolation of geological and production data are not applied. The basis of adaptive geological modeling is the seismic data. The essence is that the seismic data vector is available both at the wells and at the points of the inter-well spacing, so any geological parameter can be calculated from this vector using a special fuzzy-logic function. At the same time, such function cannot be the same for the whole model polygon, so an additional so-called fuzzy-grid is developed. A grid with large cells, which contain local fuzzy-logic functions. Since fuzzy-logical functions are formed on the basis of geological and production information of the considered object, they can differ substantially for other objects. Thus, the mathematical apparatus of a geological model automatically modifies to the specific initial data, and therefore it is called adaptive. The calculated parameters of the adaptive geological model cells through which the wells pass are not necessarily the same as the actual well data. The reason is that these parameters are calculated using functions in which the initial data of neighboring wells participate. Deviations of calculated results from actual data characterize the degree of "defectiveness" of geological and production information. Thus, the adaptive geological model in comparison with the deterministic one gives a more meaningful result both about the geological structure of the considered object and the degree of reliability of its representation.