PC2-a porosity code for personal computers

A novel method has been developed for the prediction of environmental corrections for dual-spaced thermal neutron porosity tools. The method is based on a three-dimensional formulation of an enhanced diffusion theory model which uses two-linked multigroup diffusion operators in each space/energy mesh. It is sufficiently fast to be executed on personal computers and the user image is greatly improved by using the combinatorial geometry technique to specify the configuration of the borehole and formation. A stochastic routine is used to map this model automatically onto the three-dimensional orthogonal mesh. Initial validation has been accomplished by comparing calculations for a generic tool with Monte Carlo predictions. The examples include homogeneous formations with various lithologies and pore fluids using standard bore hole conditions and the effect of changes in borehole size and salinity. The ability to deal with formation and heterogeneities is demonstrated by predicting the effect of drilling fluid invasion on the detection of gas-oil contacts, and the response to bed boundaries and thin beds.<>