PfEFFER Version 2.0

(Petrofacies Evaluation of Formations for Engineering Reservoirs)

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Synopsis of PfEFFER features

The minimum log data required by the spreadsheet-based software are a porosity and resistivity log. Old logs are well suited to this analysis once they are digitized or simply typed into the spreadsheet. Toolbars and menus perform most operations through the utilization of nearly 8,000 lines of Visual Basic code. PfEFFER v. 1 reads standard LAS log data files such as those obtained from a logging truck or permits manual entry, organizes digital data by well and zone, and creates a "Super Pickett" crossplot, depth plots, and lithology solutions (if sufficient logs are available).

The software is focused on interpreting and analyzing reservoir pore type, permeability trends, and variations in mineral composition. PfEFFER v. 1 provides procedures for optimal estimation of bulk volume water and water saturation (including irreducible values) to better evaluate potential production, reservoir quality, and heterogeneity. Also capillary pressure data can be incorporated to further calibrate well log data with pore size or to assess depth to the free water level. The program will assemble zonal information from well workbooks into a project workbook and can automatically generate map and 3-D visualizations of key parameters as defined by the user. "Hot links" are maintained in the project workbook to each well workbook to aid in data management.

In addition to revising the appearance of the spreadsheet and refining the modules as described above, PfEFFER v. 2.0 contains new modules including pay flag cutoffs, a flow unit column, depth-constrained cluster analysis, moveable oil plots and calculations, shaly log analysis, Hough transform for simultaneous solution of Archie equation constants and formation water resistivity, secondary porosity, and petrophysical forward modeling.

Three additional modules (add-ins) are available as PfEFFER Pro. These modules include color cross section generation, map coordinate conversion (longitude-latitude to UTM x-y), and software to help build an input file for a reservoir simulator based on the petrophysical characterization. DOE's freeware reservoir simulation software, BOAST 3, was used in the development and testing.

All of the standard EXCEL features continue to be available to users for independent analysis and data exploration. The simplicity of hardware and software requirements means that PfEFFER is an attractive option for companies of all sizes. The range and versatility of module capabilities makes them powerful tools for the analysis of both old log suites and the latest generation of logging measurements.

Open LAS

Reads log ASCII standard (LAS) digitial files, establishes new worksheets including header information, reads specified depth intervals, names zone, and appends new log data to old workbook.

Log Display

Depth-related information can be displayed as vertical depth EXCEL charts. Log traces can be combined on a single chart. Standard EXCEL features permit stretching the log(s) to change image size; scales; annotation of logs; and size adjustment, type, and color of the log traces. Charts can be printed separately or grouped and cut and pasted into other Windows applications, e.g., building cross sections.

Calculation of Porosity

Porosity can be calculated using density, neutron, density/neutron, or sonic with and without correction for shale volume. Secondary porosity can also be calculated.

"Super Pickett" Crossplot

The focal point of the analytical routines and graphical displays is the "Super Pickett" crossplot, an extension of the standard log-log porosity/resistivity plot. The special features in this crossplot include:
  1. tracking the pattern of data points by depth,
  2. annotation of the crossplot with bulk volume water and permeability lines in addition to the standard water saturation lines.

Distinctive depth-related trends and patterns on the crossplots have been recognized from hundreds of examples, initially "fingerprinting" an individual reservoir, tracking subtle variations among sets of wells in the same reservoir, and comparing stacked reservoirs. Specific parameters obtained from the crossplots include minimum bulk volume water and associated porosity and water saturations, permeability estimates, resistivity gradients reflecting hydrocarbon transition zones and depth of possible free water levels, and reservoir zonation/permeability barriers and associated heterogeneities. Comparisons of crossplots in the same reservoir among several wells can be used to evaluate reservoir connectedness (conformance).

Color is used in the data shown on the "Super Pickett" crossplot to display attributes such as well log data, completion information, and other derived data described below. Color ranges are automatically or manually selected to highlight and emphasize reservoir components, adding new perspectives to the reservoir.

Shaly Sand Models for Sw Calculation

Sw model menu permits selection of Archie water-saturation model (the default) and two shaly sand modeld, the Simandoux model and the Dual-Water model.

Moveable Hydrocarbon

Based on the assumption that the zone near the well is permeated with mud filtrate, the Archie equation is used to compute Sxo, the filtrate saturation of this flushed zone. Sxo is used to compute moveable and residual hydrocarbon saturations. PfEFFER generates a moveable oil plot consisting of bulk volume water, bulk volume fluid, and porosity. Difference between BVF and BVW represents the moveable hydrocarbons saturation.

Pay-flag Cutoffs

Button can be activated to add color to cells of selected variables used to determine pay including porosity, BVW, Sw, and/or Vsh. A pay column reveals computed fractional hydrocarbon volumnes based on cutoff selection.

Lithological Analysis

Includes two options in PfEFFER v. 2.0, one based on the RHOMAA-UMAA plot and the other allowing a more general selection of logs and system components. The general option allows the user to compute up to six components based on up to five logs. Any log can be employed and the component selection is at the discretion of the user.

Capillary Pressure

The "CAP" module overlays capillary pressure curves as contoured surfaces on the "Super Pickett" crossplot. The overlay utilizes capillary pressure data from samples analyzed from the reservoir (presented as water saturation and porosity vs. capillary pressure for various pore types). The resulting capillary pressure contours can serve as templates in the distinction of separate pore-type petrofacies, determination of pore-throat sizes, and prediction of elevation above free-water level, when integrated with digital log data.

Zonation by Depth-constrained Cluster Analysis

Analysis can be employed to segment the entire spreadsheet into subintervals based on a user-specified set of logs. A heirarchical cluster (Ward's method) is used to produce subintervals that are as homogeneous as possible and distinct as possible from each other, in terms of their log characteristics. With output including columns of class membership and average log values in these classes, the option is useful in designating flow units and can be used as a quick and simple blocking function.

Forward Modeling

Implements equations developed by Pittman to predict values of rx (radius of smallest pore-throat), capillary pressure, and hydrocarbon column height for a range of water-saturation values based on specific values of permeability and porosity.


The Mapping module produces a "first-look" map to examine spatial variability/continuity among wells, assess reservoir heterogeneity, and evaluate the consistency of the variables being mapped. A commercial mapping package is needed if a more complete spatial analysis is desired. PfEFFER plot files can be easily exported to most mapping programs using standard features of EXCEL. The "mapping" or project workbook is electronically linked to "well" workbooks and associated "reservoir" worksheets. Information changed in a reservoir worksheet level is reflected in the mapping workbook. Griding, base map generation, 2-D and 3-D visualization of the parameters are accomplished automatically as selections from the mapping menu. A series of dialog boxes lead the user through assembling wells, reservoirs, and defining mapping parameters.

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Kansas Geological Survey, PfEFFER software
Comments to
Updated August 7, 1998