Computes Clay Volume

For all water saturation models, except for Waxman-Smits, an accurate value of clay volume is essential for obtaining reliable results.  SSA provides users with the means to compute these values based upon different log suites. Vcl can be computed from the gamma ray log, spectra log, density log, density-neutron logs, neutron-sonic logs, density-sonic logs, resistivity logs, and SP log. Users may refer to technical online notes for selecting the best calculation method.

If lab data is available for a well, the clay volume from the lab can be compared with values from each log method. Linear regressions can be performed and a transformation equation selected based upon the best fit. For nearby wells without lab data, these computed transformations can be recalled and used to compute clay volume.

SSA displays a table of clay volumes computed by different methods and a graph comparing values.

Computes Total and Effective Porosities

Porosity can be computed from porosity logs (density-neutron, density, neutron, sonic, density-sonic) or from resistivity logs. Results are presented in a table giving columns of total porosity, effective porosity, and clay volume and two graphs.  One graph presents the percent volume of shale, sand, and pore space while the other graph shows the total porosity line and effective porosity line and shades the clay effect between the two lines.

From the porosity calculation screen, two crossplots can be viewed, the density-neutron crossplot and a Q-plot. The density-neutron crossplot shows the sand and shale lines, dispersed shale line, and the laminar-structural shale envelope. The crossplot can also be displayed giving the percent porosity and clay volumes lines with a shaded region for the gas crossover points. The Q-plot is a crossplot of q versus effective porosity. Values is the lower right portion of the triangle indicate a productive formation, shown in red on the screen.

Generate Crossplots

Crossplots offer analysts a unique ability to view data. SSA offers several crossplots which aid users in characterizing their reservoir and predicting producibility. The available crossplots include: a Q-plot for indicating producibility of a formation, a neutron-density crossplot for predicting shale type and presence of gas, Resistivity porosity vs total porosity for indicating hydrocarbons, the Low Vcl plot for suggesting the special problem of low clay volume, high Sw shaly sands, Archie's water saturation vs resistivity water saturation plot for indicating hydrocarbon presence, Bulk volume water plot for seeing if Sw is at irreducible water saturation, Dew plot for indicating hydrocarbon presence, Vcl from gamma ray vs Vcl from SP plot for predicting shale type and log Rt vs log porosity plot for indicating hydrocarbons. These crossplots provide SSA users a visual look at their data to help determine if a zone is a possible producer.