Trace Coding
The objective of using different line types is to distinguish between different types of measurements plotted together in the same track (i.e., phase difference/attenuation resistivities, neutron porosity/formation density, or conductivity/weight on bit, etc.). Therefore, unless you are
Log Quality and Data Management Standards Log Preparation plotting more than one parameter together in any one track, all primary trace curves should be represented by solid lines only. The only exception to this is the back up scale for conductivity (see conductivity scale in RGD/
DPR log formats) Both short normal curves in track 2 on the correlation log format are plotted as solid lines. However, if you are plotting apparent resistivities with corrected resistivities, the corrected resistivity should be coded with a medium dashed line.
Pen-up Intervals
Pen-up intervals should not exceed 10 feet (3 meters). The only exception to this is when plotting TVD for a horizontal well or tool temperature (TCDX, TCDM). There is no reason to use a pen-up interval greater than 10 feet (3 meters), regardless of data density. You are strongly discouraged from doing so. Any data gaps and the reasons for their occurrence should be documented in the Remarks page of the Log Header (see “Main Header, Remarks” on page 3-10). Pen-up intervals are referred to as “Interpolation Limits” in 1.3x M-SERIES software.
Recommendations for Scales
Use standard scales for traces where possible. However, when secondary traces continuously interfere with the primary trace or curve, scale
adjustments may be necessary. When it does become necessary to change scales, always contact the geologist and/or engineer in the office who is watching the well and request preferred scales and formats. Always perform a scale change on secondary curves before primary curves. If scale changes are made to both secondary and primary curves and interference still exists, it may be necessary to move the secondary curve to another track or remove it from the log. Once again, consult the client for the preferred location of traces.
Rate of Penetration
The rate of penetration is included on all logs unless otherwise requested by the client. This includes morning and afternoon field logs as well. Rate of penetration is plotted on a linear grid but variable scale. It is typically presented with “Gamma Ray” in track 1 or with “Conductivity” or “Weight on Bit” in track 3. The scale should always begin with 0 on the right side of the track with increasing rate of penetration towards the left. This provides correlation of the sands and shales with “Gamma Ray” in track 1. The scale should be set up to allow minimum interference with the primary curve (gamma ray, conductivity, or weight on bit). This may require a scale of 1000 to 0 ft/hr if the rate of penetration is high. Also explore the “Scale Change” option when the rate of penetration decreases or increases (see page 2-12 and page 2-15).
Log Preparation Log Quality and Data Management Standards It is important to note that when using MPLOT, select 5DSH (for
correlation logs) and 2DSH (for quantitative logs) under the selection line type. Trace coding and curve averaging are provided automatically. For example, for 2DSH, a histogram will be plotted as a medium dashed line with a 2-foot average. This means that no additional averaging or smoothing should be selected under MPLOT when preparing to plot the rate of penetration.
Gamma Ray
It is important to set the scale range so that individual divisions on the trace scale are whole numbers (for example, each division on a scale from 25 to 225 API is equal to 20 units, each division on a scale from 50 to 150 API is equal to 10 units, etc., as opposed to a scale of 50 to 275 API, where each division would be equal to 22.5 units). This is an API industry standard because it simplifies reading the curve.
Your scale should be set up to accommodate recommended divisions of either 10, 15, 20, or 25 units. Anything beyond 25 is generally too large because the separation between the sand and shale base line may be too small for adequate differentiation of lithologies.
The scale should also be arranged so the gamma trace is centered in track 1.
If the curve becomes weighted to one side of the track (i.e., becomes increasingly sandy or shaly) as you increase in depth, it may be necessary to perform a scale change (see page 2-12 and page 2-15). If a scale change does not seem appropriate, pick the scale that works best through the zones of interest.
When plotting the gamma ray in track 1, you should set up your scaling to maximize the separation between the shale base line and the sand line.
Ideally, you would shoot for a 4 to 6 division separation. However, when plotting a secondary trace in the same track as gamma ray, such as rate of penetration, the above recommendations often cannot be adhered to. The gamma ray trace must be compressed in order to accommodate the secondary trace. The following suggestions may be helpful.
1. Compress the secondary trace (i.e., rate of penetration) scale as much as possible before compressing the gamma ray.
Remember, MPLOT will do scale changes on the fly for any trace.
2. Since a 6 division separation between sand and shale may not be feasible, shoot for a 4 division separation (anything less than 4 divisions is not recommended). This may require using scales that we are not accustomed to, but still allow for divisions that are divisible by whole numbers. For example, with a scale from 30 to 180 or 80 to 230, each division equals 15.
Log Quality and Data Management Standards Log Preparation Note: Note the different smoothing intervals for the gamma ray
MWD API trace on the 1-, 2-, and 5-inch logs. Always use a smaller smoothing interval for the higher rates of penetration.
Resistivity
The scale for both correlation and quantitative logs will vary for different locations. Consult the client for preferred scales and formats. As a standard, plot apparent resistivities on all logs for RGD services unless specifically requested by the customer. For the DPR service, plot corrected phase difference and amplitude ratio resistivities.
In the event that you need to change your resistivity scale due to anomalous readings that obscure the trace, use the following standards:
For correlation logs, your amplified measurement is always 1/5 the unamplified scale. For example:
Default scale: Change scale to:
unamplified = 0.0 to 10.0 unamplified = 0.0 to 20.0 amplified = 0.0 to 2.0 amplified = 0.0 to 4.0 Or:
unamplified = 0.0 to 50.0 amplified = 0.0 to 10.0
Note: An X10 scale is available (on MPLOT) as a back up scale. This is typically used for linear resistivity scales (common in the Western Region) on all correlation logs for the 0 to 10 scale (see correlation log formats for the RGD and DPR Services). When the 0 to 10 scale wraps around (when resistivity exceeds 10 ohm-m) the back-up scale automatically switches to 0 to 100 scale. The back-up trace will begin at the first division beyond the left-hand track edge (this division equals 10 ohm-m).
If the X-10 scale is used, a remark should be provided that explains that the back-up scale is a “X-10 scale.”
Although this is a typical format for wireline 1- or 2-inch logs, it is new to our MWD/RWD logs. A remark will avoid any confusion for anyone reading the log.
For a quantitative log, the resistivity trace is ordinarily plotted on a two cycle semi-logarithmic scale. In order to increase the scale, increase from 2 cycles to 4 cycles. This is a standard procedure in the logging industry. For example:
Log Preparation Log Quality and Data Management Standards Increase from 2 to 4 cycles: 2-cycle = 0.2 - 20.0
4-cycle = 0.2 - 2000.0
A 4-cycle semi-logarithmic format should always occupy both tracks II and III (this will require you to sacrifice any other traces in track III). This prevents the scale from becoming too compressed in only one track. To do this, just set up track II with a 2-cycle semi-log scale from 0.2 to 20.0, and track III with a 2-cycle semi-log scale from 20.0 to 2000.0.
Note: Make note of the change from +/- wrap to the over option for the resistivity trace in track 2 for quantitative logs.
This option is now available on MPLOT and should be used wherever possible.
Conductivity
This trace is plotted commonly in areas characterized by low resistivity formations such as the Gulf Coast. This scale will also vary for different locations. It is always plotted on a linear grid, a default scale of which is typically 4000 to 0000 mmhos. Where space permits (i.e., extra traces are available for plotting), plot a back-up trace for conductivity (typically this would be 8000 to 4000 mmhos-meter). This trace is coded as a medium dashed line. If no space is available for extra traces, use the wrap or back-up feature for plotting. In either case, the back-back-up trace should be annotated as CSAX back up or CPCM back up on your logs (see “Back Up Trace Labels” on page 2-10).
Neutron Porosity
This scale is variable but always on a linear grid. In clastic formations (sand and shale), the scale is typically 60 to 0 porosity units. In carbonates (limestones), the scale is 45 to -15 porosity units. On correlation logs, this trace is plotted in track 3. On quantitative log scales, the trace is either plotted across tracks 2 and 3, or only in track 3. This trace is plotted as a solid line in double combo presentations (because it is a primary curve) and as a medium dashed line for triple combo presentations. Consult the client for preferred scales and formats.
Bulk Density
This scale is variable, but always on a linear grid. The default scale is 2.0 to 3.0 g/cc (for a limestone matrix). Scales for clastic formations will vary for each region but a default scale that matches the neutron porosity 60 to 0 porosity units scale is 1.65 to 2.65 g/cc. Bulk density on correlation logs is typically plotted only in track 3. On quantitative logs, it is typically plotted across tracks 2 and 3 or only in track 3. This trace is plotted as a solid line.
Consult the client for preferred scales and formats.
Log Quality and Data Management Standards Log Preparation Density Porosity
This scale is variable (but always on a linear grid) to match the neutron porosity scale. In clastics (sands and shales), the scale is 60 to 0 porosity units. In carbonates (limestones), the scale is 45 to -15 porosity units. On correlation logs, this trace is plotted in track 3 with neutron porosity. On quantitative logs, the trace is plotted either across tracks 2 and 3 or only in track 3 with neutron porosity. This trace is plotted as a solid line. Consult the client for preferred scales and formats.
Photoelectric Cross Section
The default scale is 0 to 10 barnes/electron, which is plotted on a linear grid. The scale may be manipulated to move the trace out of the way of the primary curves (keep track divisions as whole numbers). This trace is generally reserved for quantitative logs. It is plotted as a heavy dashed line in track 3 (when “Bulk Density” or “Density Porosity” is plotted across tracks 2 and 3), or in track 3 as a half track presentation (when “Bulk Density” or “Density Porosity” is plotted only in track 3). This currently is not a commercial measurement!
Delta Rho Correction
The default scale is - 0.25 to 0.25 g/cc, which is plotted on a linear grid.
Although the scale can be manipulated to move it out of the way of the primary curves, the same sensitivity should be maintained (i.e., - 0.5 to 0.20 g/cc). This curve is generally reserved for quantitative logs. It is plotted in track 3 as a medium spot line (when “Bulk Density” or “Density Porosity” is plotted across tracks 2 and 3), or in track 3 as a half track presentation (when “Bulk Density” or “Density Porosity” is plotted in only track 3). Consult the client for preferred scales and formats.
Time Since Drilled
“Time Since Drilled” is a trace that is automatically calculated in P-SERIES and MDMS software systems and is referred to as “Elapsed Time.” This trace is also calculated from the executable ADDTSD in the HPUTIL main menu (run ADDTSD after the binary file in HPUTIL has been constructed). It is important to note that there are differences between these traces. Most notably P-SERIES/MDMS calculates elapsed time on a run-by-run basis, which means the trace is interrupted at the end and beginning of runs. Use this trace only if HPUTIL and MPLOT are not available for generating logs. The ADDTSD executable calculates “Time Since Drilled” continuously from top to bottom so there are no
interruptions in the trace. The ADDTSD executable also gives you much more flexibility in selecting traces you can calculate TSD from, such as phase difference resistivity, gamma ray, etc. This is the trace of choice. Be careful when selecting mnemonics for plotting. Use mnemonics that are
Log Preparation Log Quality and Data Management Standards defined as “Time Since Drilled” (for example, RPTM - Time Since Drilled from Phase Difference Resistivity [RWD]).
This trace is plotted on linear grids only and reserved for quantitative logs.
The default track for “Time Since Drilled” is track 3. However, it may be moved over to the first track for Triple Combo presentations to avoid competition with other traces or when a logarithmic grid is used in track 3.
The default scale from 0 to 300 minutes (increasing from left to right should be used in conjunction with a medium spot line type. It is not recommended to use a scale smaller than 0 600 minutes. Since a medium spot line type is similar to a medium dashed line (the back up scale for conductivity), make sure to identify the back up conductivity trace as CSAX back up or CPCM back up.
Note: Plot “Time Since Drilled” with the “X-10 Mode” (see Note in “Resistivity” on page 2-5) to avoid multiple trace wraps where bit trips and long periods of circulation occur.
Data Density
Data density is another data type that is automatically calculated by the P-SERIES/MDMS software systems. This trace is also calculated with
“Time Since Drilled” from the ADDTSD executable in the HPUTIL main menu (run ADDTSD after the binary file in HPUTIL has been
constructed). The “Data Density” calculated from ADDTSD is the trace of choice for plotting. Data density should be plotted as tick marks on the left side of the depth track on quantitative logs. Make sure to move any
annotated “Run Markers” to the right side of the depth track.
True Vertical Depth
True vertical depth is another new trace added for horizontal wells. It is calculated from the ADDTVD executable in the HPUTIL main menu. It should be plotted on both correlation and quantitative logs in track 1 as a heavy spot line type with a variable scale (the scale will depend on the true vertical depths calculated in the lateral portion of the hole), which should increase from right to left. If scaled appropriately, the TVD trace can be used in conjunction with the gamma ray and/or resistivity traces to identify when the bit enters and exits the objective zone.
Log Quality and Data Management Standards Log Preparation