Below is a picture of the Micromeritics, AutoPoreII  Hg capillary pressure system and the sample holders, glass penetrometers.

Below is a very simple interpretation frame work for mercury injection data. In this cartoon, the rock is made of 3 pores. Hg does not want to go into any of the pores since it is a nonwetting fluid. However, it can be forced in a pore at pressures greater than or equal to the capillary pressure. Capillary pressure is given by the following formula:

variables are defined in picture below.

As the Hg is injected, it fills the largest available pores/cavities first. Increasing pressure forces the Hg into smaller and smaller pores. Actually access is thought to be accommodated by "pore throats". Thus the volume injected at any pressure is actually a measure of the pore volume accessible at a particular pore throat size. Extremely high pressures therefore correspond to extremely small pores. There are a number of ways to present Hg injection data.

Mercury data can be delivered three ways: 1) no corrections (raw data); 2) formula correction or 3) blank corrected. The corrections attempt to correct for the change in volume of the glass penetrometers and mercury as a function of pressure.  Formula correction are based on the well known properties of mercury and glass while the blank correction is actually an empirical correction made by subtracting the response of completely empty penetrometer (100% Hg) from the observed data with sample present. This difference it performed in a piecewise fashion at each pressure. There are a number of ways to present Hg injection data. One standard presentation is shown below, a pressure versus the fraction Hg injected.

Here we see the fraction of Hg injected at each pressure. Often these curves are normalized by the total pore volume and not simply by the total injected Hg volume as was done here.  A cartoon of the major features of these plots is shown in the Figure below:

Another common presentation is that of incremental injection volume versus injection pressure or equivalently pore throat radius. This is shown below:

This presentation gives us an view of the distribution of pore throats in our samples. Larger pore throats correspond to high permeabilities and lower irreducible water saturations.

One classical use of this information is to assess rock type. Since the injection curves capture more of the microstructural variation than say permeability or porosity, they provide a more reliable means of identifying rock types and flow units. Below is a crude plot of multiple injection curves taken from the same reservoir showing a bimodal distribution of rock types.

A corresponding incremental injection plot is shown below which clearly shows those zones with the better rocks.

With measurements of permeability and porosity, one can generate the classical Leverett J-Functions and examine this space for variations in rock types.

Mercury data can easily be converted to equivalent height above free water for use in predicting possible hydrocarbon column heights as well as transition zone extents.

Send mail to csondergeld@ou.edu with questions or comments about this web site.
Last modified: 08/14/04