Resource calculation methods for multilayer traps:Case study of two-layer traps

Volumetric method is a formal way to predict the in-place or recoverable resources of a play or trap, including deterministic and probabilistic methods. Probabilistic evaluation is an optimal way for the assessment of resources in tectonic traps, but the resource assessment of targets with multiple strata is usually calculated by directly and simply cumulating the resources of individual targets using given specified success probability weights. This prediction generally does not correctly reflect actual geological conditions. Taking into account the risk of each target stratum in the trap, we analyzed the geological correlation between each target, including non-correlation, partial and complete geological correlation, and calculated the probability of in-place resources under different conditions. Then the risked resource in-place is divided by the probability of hydrocarbons existing in at least one of the targets to obtain the resource volumes of multilayer traps.