Adding on-the-fly Digits to Logs

You can convert some rasterized logs to digits, which can then be used to calculate formation properties. The digitizing function is not intended for mass digitizing because a computer cannot replace human experience in all situations. Sometimes computer-digitized curves are acceptable, other times user-intervention is required to correct digits. AccuX digitizing functionality is intended only to fill some holes in the exploration area when no digits are available for short intervals associated with reservoir rocks.

To add on-the-fly digits to logs

1. Right-click the log and from the shortcut menu, select add raster log and on the fly digits from AXXSES.

The Raster Catalog dialog box appears.

2. Select a curve to load then click OK.

The digitized curve appears in the cross section. You may need to redraw portions of this curve.

Selecting a log for digitizing

Following are tips derived from testing different types of curves:

 Formation Resistivity. A good source of formation resistivity is an induction log with a depth scale around 1:600 and a conductivity curve (CILD) in the right track. AccuX digitizes the CILD curve and converts it to deep resistivity (RILD). The computer-generated CILD curve can then be manually edited and all changes are automatically applied to the RILD curve.

Note: AccuX digitizes CILD from 500 millisiemens (2 OHMM) to 1 millisiemen. You may need to manually edit low resistivity layers of less than 2 OHMM.

Another good source of formation resistivity is a Laterolog (LLD) curve with a depth scale around 1:600 because this log is usually recorded with conductivity CILD. Note that some LLD with a 1:600 scale is recorded without CILD.

AccuX can also digitize LLD recorded on the logarithmic track with a scale around 1:240.

AccuX will not automatically digitize an Induction log with a scale around 1:240 because the AccuX digitizing module cannot recognize ILD, ILM, and SFL. However, if the interest interval is not too large, you can add a blank curve, rename the curve ILD, set a scale of 0.2 – 2000 OHMM (or something else), and then manually digitize the desired portion.

 Spontaneous Potential. When you select an Induction log with a scale around 1:600, AccuX automatically digitizes the SP curve.

 Gamma Ray. When you select a Sonic log for digitizing with a scale around 1:240 or 1:600, AccuX automatically digitizes GR using a default scale of 0-150 GAPI. If the original scale is other than 0-150 GAPI (for example, 1:120 GAPI) you can later recalibrate the curve or set the specific clean rock and shale line for the well.

 Porosity Logs. A good source for getting computer-generated porosity curves is a Sonic log with a depth scale of 1:240 or 1:600. AccuX digitizes the DT curve using a default scale of 500 – 100 microseconds. For some wells the left - right scale can be changed from zone to zone. Because of this you may need to recalibrate some portions of the curve using individual scales for each segment.

Generally, digitize a Neutron-Density log with a depth scale around 1:600 or 1:240. In this case RHOB is created as the dominant curve (the Neutron curve is not digitized). You may need to manually correct some portions of the RHOB curve when there are multiple curves (RHOB, DCOR, NPHI, etc.) on the Neutron-Density track.

Related Topics

 Changing Global Online Settings for Raster Functionality

 Adding Curves to Logs

 Editing Spikes