Lithology and Fluid Uncertainties from Deterministic Inversion

Deterministic simultaneous inversion provides us with a representation of the subsurface in terms of P-impedance and S-impedance. In the case where we have excellent results it can still prove difficult to interpret these impedances in terms of lithologies and fluids for a number of reasons. Often the properties of the rocks are not unique indicators of the type of rock or fluid even when the beds are fully resolved. When the beds are below seismic resolution there is even more uncertainty. Under such conditions of overlapping properties and sub-resolution beds, it is often recommended that some form of geostatistical inversion is considered to quantify and reduce the uncertainty. However, such inversions are often difficult and time consuming. It is often advantageous to have an estimate of uncertainty without having to go to a full geostatistical inversion. There are various methods to convert a combination of P-impedance and S-impedance to lithology probability. However, the implementation of such methods can be hampered by a lack of control data. In this paper we present a method based on geostatistical simulation to enhance the input data and provide a guide to the interpretation of the estimated probabilities.