Abstract

A lithology model describes the geology of reservoir sequences in terms of basic rock types (e.g. limestone, sandstone, etc.). This lithology model can be used to correlate or develop geological models, to improve porosity calculations, or develop reservoir parameters.

The introduction of a cased-hole density and PE measurement to the pulsed-neutron data set have been described in recent publications. The cased-hole porosities and Pe factor form a basis for a multiple lithology model. Neutron-induced spectroscopy augments the measurement set through description of the chemical make-up of the formation. This cased-hole measurement forms the input data for an analytical and logical model to determine rudimentary rock constituents. The analytical terms in the model are adjusted to match core data or local geological knowledge.

The number of predicted constituents depends on the number of (statistically) strong independent measurements. The two log-analysis examples utilize a model structured with four-components. One of the log examples uses a model set consisting of dolomite, silt, sandstone, and anhydrite. The second example uses a model set of dolomite, limestone, chert and shale.