Complex Permeable Flow Unit Models are developed using all available conventional and statistical analysis techniques in LOGMAP and use core analysis and other geological and reservoir data to support the final interpretations.
The contour crossplot below shows a composite trend of the analysis porosity versus conventional water saturation for a carbonate reservoir. Overlaid on this crossplot are a series of lines labeled Buckle's lines and Permeability Equation lines. Buckle's lines are lines of constant porosity * water saturation and represent lines of constant pore geometry. The higher the Buckle's number the finer the pore throat size of the rocks. The permeability equation lines are based on modified versions of published theoretical equations comparing porosity to irreducible water saturation. The cross plot displayed in this example uses conventional water saturation and not irreducible and is used for illustration purposes only. In a true reservoir study the statistical irreducible water saturation would be used. The intersection of the two sets of lines form a series of polygons, which can be related to permeable flow units as each polygon is bounded by a range of pore geometry based on Buckle's lines as well as bounded by a range of permeability based on the permeability equation lines. The following crossplot is the same as the previous crossplot except that representative polygons have been drawn based on the intersection of the Buckle's lines and Equation Permeability lines and guided by the underlying contour trends of the porosity and water saturation data. The next crossplot below is the same crossplot as previously shown, except that this time the observed core permeablity spectra have been overlaid for the represenative polygons. As can be observed, the polygons to the lower right have the observed highest range of core permeability and lowest Buckle's numbers (larger pore throats) as compared to the data to the upper left, which shows lower/poorer permeability range and higher Buckle's numbers (finer pore throats). The figure below is an enlargement of the display of the permeability spectra. Note that this is an observed spectra display. If the polygons are defined as outlined, then when all the core data are scanned these are the observed core permability maximum spectra that result. In a multiple well sense this observed permeability information can be translated to net pay information on each well, derivation of apparent core permeability for wells where core permeability was not available and to mapping of apparent reservoir flow units based on the reference polygons previously discussed. The display below shows an example of how a cross plot distribution can be translated to depth to define apparent net pay. For a given depth, there exists a porosity-water saturation data pair. That data pair is crossplotted to find which, if any, of the interpreted polygons the data pair lies within. At that depth, a line is drawn with a line length proportional to the polygon number and a color to match the polygon outline. Generally, the polygon interpretation and colors used are designed to that the brightest color and longest line represent the best characterisitics. In the case of this example, the best permeable flow unit based on the best Buckle's-permeability polygon is shaded bright red and has the longest line length on the depth display to the right of the main crossplot. The display below shows an analysis comparison to the core data. Column 1 show the analysis porosity as compared to the core porosity. The second column show a bulk volume display. The third column shows the statistically predicted permeability based on the observed core data versus the actual core data. The fourth column shows the polygon flow units discussed previously. The map below shows the porosity curve plotted for each well. The shading of each porosity curve is based on the polygon interpretation of a porosity vs. water saturation cross plot where the polygons relate to apparent permeable flow units as described previously. |
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hitchner@nucleus.com |
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