AN ACCOUNTING OF STRUCTURAL UNCERTAINTIES FOR A PROBABILISTIC ASSESSMENT OF HYDROCARBON RESOURCES
V.V. Lapkovsky, M.V. Lebedev, E.A. Ianevits
1Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, Novosibirsk, Russia
2OOO Tyumen Petroleum Research Center, Tyumen, Russia
3Branch of Lukoil-Engineering LLC "KogalymNIPIneft",Tyumen, Russia
Keywords: Stochastic modeling of structural uncertainties; probabilistic estimation of resources; estimation of seismic velocity anomalies, probability distribution of structural trap areas, lognormal distribution of structural trap areas
Abstract
In the new paradigm of the Russian oil and gas industry, much attention is paid to small hydrocarbon fields. This statement increases the requirements for the accuracy of forecasts of total hydrocarbon reserves in small-scale anticlinal traps. Such forecasts can be made by probabilistic estimation of resources, taking into account the probabilities of the field existence. The objective of the present research is the development of the scientific approach to quantifying the uncertainties associated with the existence and geometric parameters of small-scale anticlinal hydrocarbon traps mapped by modern 3D seismic exploration. The main method of solving this problem is stochastic modeling of structural uncertainties based on errors of structural mapping. The results of the study are summarized as follows. The type and parameters of the probability functions of the structural area are determined by the intensity and size of the velocity anomalies, as well as the parameters of the trap itself and the nature of its structural environment. The distributions of the structural closure areas can be described by functions in which the Mean value is greater than the quantile P50 value, the Mean value is approximately equal to the P50 value, and the Mean value is less than the P50 value. The lognormal distribution, which is commonly used to model structural uncertainty, is just one of the possible options. For small-scale hydrocarbon traps, their amplitude is comparable to the thickness of a productive reservoir; therefore, a change in the amplitude of the trap determines a change in the weighted average oil-gas-saturated thickness. As a result of the modeling, a positive relationship was established between variations in the anticline traps areas and their amplitudes. Accordingly, this relationship must be taken into account during the probabilistic assessment of the resources of this kind of the hydrocarbon traps. Otherwise, there may be a significant reduction in the range of uncertainty in resource estimates. Stochastic modeling of structural uncertainties is also a method of estimating the probability of the existence of anticlinal traps mapped by seismic exploration.
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