New methods are presented for analyzing (1) laminated, (2) dispersed, and (3) total shale models. The techniques involve the use of log-log crossplots of effective porosity vs. true resistivity as 'affected by a shale group (As h).

Response equations for the above models have been written in such a way as to allow the generation of log-log plots from which values of water saturation can be readily calculated.

Three key advantages of the proposed methods are: (1) the value of m does not have to be assumed equal to 2.0; in fact, it can be determined from this analysis by trial and error, (2) water resistivity does not have to be known in advance provided that the reservoir contains some water-bearing intervals, and (3) all shaly intervals being analyzed can be displayed in a single log-log plot that includes porosity and water saturation even if shale volumes are changing continuously. An application is presented in detail.

It is concluded that log-log crossplots provide powerful evaluation techniques for the analysis of laminated, dispersed and total shale models. These methods can be readily extended to the analysis of naturally fractured reservoirs.

You can access this article if you purchase or spend a download.