This chapter provides instructions on gathering and processing measurements for Short Normal Resistivity Service. Log presentations are included at the back of the chapter.
Introduction
The Short Normal Resistivity Service represents a basic and relatively inexpensive alternative in Formation Evaluation Logging Services. Prior to the commercial release of 2 MHz electromagnetic wave propagation tools (DPR), this was the only MWD formation evaluation logging tool available on the market. This is a current emitting resistivity device coupled with either a geiger-mueller or scintillator gamma ray detector. Since the resistivity sensor is a current device, it is severely limited in the mud types it can effectively operate in. However, it can be used quite effectively in water-based muds with a chloride content below 20,000 ppm. It cannot be used in oil-based muds. Although this service does have the capability to store data in the MTC memory, a commercial rigsite memory (RWD) service is not available at this time. The RGD Service's principal applications are wellsite log correlation, casing point selection,
conventional core point selection, preliminary evaluation of potential pay zones, and most importantly, realtime abnormal pore pressure detection.
Mud Types
Freshwater mud systems.
Short Normal Resistivity Log Quality and Data Management Standards
Borehole Correction Inputs
Gamma Ray
Tool size, hole size, mud weight, %K (potassium content), sensor type, gamma API correction factor.
Short Normal Resistivity
Tool size, hole size, resistivity of the mud (Rm).
Data Editing
Editing of Realtime Data
Because of occasional decoding problems that can introduce bad data into the database, it is necessary to edit periodically. Editing should be prudent.
Obvious bad data should be removed from the database. Under no circumstances should the data be replaced or altered. It is preferred that questionable data remain in the database. This data should be identified and referenced on the log with a remark.
Depth Shifts
Make sure logging depths are as accurate as possible. Make depth shifts in the database where necessary. Anytime depths differ at a depth at kelly down by 1.0 foot (0.45 meters) or greater, a depth shift should be performed. Depth shifts can be minimized by frequently calibrating the Kelly Height sensor at kelly down and updating the depth at kelly down at every connection.
Data Management
M-SERIES
A raw database file should be stored on the hard disk (Winchester) and an edited database file backed up on disk. If a Winchester is not used on the rigsite, a raw database file also should be backed up to disk. Provide all necessary information on every disk label, and use an easy to follow sequential numbering scheme for labeling disks.
P-SERIES
The database file should be backed up to tape periodically during the job.
Both edited and raw data are maintained in the same database, so there is no distinction between the two like M-SERIES.
Log Quality and Data Management Standards Short Normal Resistivity HPUTIL
When M-SERIES (MWD data) or P-SERIES XFER files (MWD data) are converted to binary files for plotting with MPLOT, then several file types should be backed up to disk. These are as follows:
• binary.* (includes .fil, .apd, .uni, .idx),
• *.cfg (HPUTIL Rev. 2.1 or greater)
• setup.fil (Mplot/Wplot formats...formally newplot.fil)
• log.fil (Makelog/Head/Minihead formats)
• tvddata.fil
• newplot.fil (use with HPUTIL versions earlier than Rev. 2.1)
• header.fil (use with HPUTIL versions earlier than Rev. 2.1)
• comment.fil
Rigsite Data Processing
Smoothing and/or Averaging M-SERIES
None applied to the database. User selective smoothing or averaging applied when plotting (see log formats for recommended curve smoothing).
P-SERIES
None applied to the realtime database. User selective smoothing or
averaging can be applied when plotting (see log formats for recommended curve smoothing).
HPUTIL
If Squeeze is applied to the binary.fil, backplots are removed and data is averaged on a 0.25 feet (0.1 meter) interval. User selective smoothing can also be applied when plotting (see log formats for recommended curve smoothing).
Filtering None.
Short Normal Resistivity Log Quality and Data Management Standards Other
Borehole Corrections
Automatically applied by surface software (see “Borehole Correction Inputs” on page 6-2).
Squeeze
Squeeze is required for non-P-SERIES databases (HPUTIL binary files).
Apply to binary files before plotting final logs with Gulton plotters.
Squeeze compresses the data file by removing all backplots, then averages the data on a 0.25 feet (0.1 meter) average. (For more information, see
“Squeeze” on page 1-5.) Quicken
Quicken is not required but highly recommended for non-P-SERIES databases (HPTUIL binary files). Apply to binary files after Squeeze is performed. This application sets up indices for every 100 feet (50 meters) of log, which speeds up the depth search routine for the MEDIT editor.
(For more information, see “Quicken” on page 1-5).
ADDTSD
ADDTSD is required for non-P-SERIES databases (HPUTIL binary files).
Apply to binary file as needed during job. This application calculates the time since drilled and data density curves for MWD and RWD data.
Calculate from the short normal resistivity (RSAX) unless otherwise requested. (For more information, see page 2-7.)
ADDTVD
ADDTVD is required on every horizontal well. This routine calculates and arranges directional data (true vertical depth) so it can be plotted as a curve.
This is an HPUTIL utility program. (For more information, see “True Vertical Depth” on page 2-8.)
Note: No other rigsite data processing is required unless incorrect borehole corrections have been entered into the database. If this occurs, enter the correct correction factors and recalculate the database.
Log Quality and Data Management Standards Short Normal Resistivity
Postwell Data Processing
Before Final Logs None.
After Final Logs - LIS ASCII File and Tape
Performed using either WDS, LOGWORKS, or P-SERIES.
Rigsite Calibration Verification
Currently, none is required.
Quality Control
Quality Control Curves Data Density
Data density (integrated) should be calculated from the short normal resistivity (RSIX) and plotted on the quantitative log as tick marks in the depth track on the left-hand side.
Time Since Drilled
Time since drilled (RSTX) should be plotted on the quantitative log with a linear grid, preferably in track III with conductivity, weight on bit, etc. The line type should be a medium spot.
Log Quality Control
You are responsible as a logging engineer to periodically evaluate the data quality of your logs. Generate quantitative logs and inspect the curves for areas that might suggest a compromise in quality. If areas characterized by poor quality are detected, notify the office (Teleco) and the client
immediately. Under these circumstances, the client should be given the opportunity to recover either lost or poorly recorded data.
Typical Log Response
Gamma Ray
The gamma ray sensor is primarily a lithology indicator. It measures the natural gamma ray radiation that is emitted from naturally occurring
Short Normal Resistivity Log Quality and Data Management Standards radioactive elements (uranium, thorium, and potassium) deposited within the surrounding formations. As it turns out, shale generally contains much higher quantities of these radioactive substances than sandstones and carbonates (limestone and dolomite). Therefore, the gamma ray sensor can in most cases easily distinguish between shales and non-shale formations.
• Shales are generally identified by high gamma ray readings (greater than 100 MWD-API units).
• Non-shale formations (sandstones and carbonates) are identified by relatively low gamma ray readings (lower than 60 MWD-API units).
Short Normal Resistivity
The short normal resistivity measurement is very sensitive to conductive muds (very low Rm), high formation resistivities, and increasing borehole size relative to tool size. Therefore, when the ratio Ra / Rmis large, the borehole correction is large and can result in anomalously high corrected formation resistivities (Rcorr). This is compounded with increasingly larger boreholes relative to the tool size. The responses below assume an
appreciable amount of invasion. If there is little to no invasion, Rashould read close to Rt.
Permeable Zones (No Hydrocarbons)
1. When Rmf< Rw , then Rais lower than Rt and Rcorrmay be higher than Rt(this depends on Ra / Rmand borehole size relative to tool size).
2. When Rmf> Rw, then Rais higher than Rt and Rcorrmay be lower than Rabut probably still higher than Rt(this depends largely on the depth of invasion and Rw).
Impermeable Zones
1. If mud is fresh (high Rm), then Rashould read close to Rt , if Rtis not too high (greater than 20 to 50 ohmm).
2. If mud is conductive (low Rm), then Rawill read lower than Rt .
Other Requirements for This Service
Surface measurement of Rmand Rmfcorrected for bottom-hole circulating temperature required on a daily basis. This data should be supplied on the header of each daily log with BHCT (see “Main Header, Environmental Parameters” on page 3-8 for additional mud information and measurement procedures).
Log Quality and Data Management Standards Short Normal Resistivity
Log Presentation
North and South America Log Presentations
1:600 AND 1:1200 ENGLISH DEFAULT LOG FORMATS (correlation)
1:240 ENGLISH DEFAULT LOG FORMAT (quantitative)
1. TVD: Optional trace used specifically for horizontal well applications. Scale should increase from left to right.
2. TCDX: Scale should increase from left to right.
3. RSIX: The output and presentation of this trace are predetermined. However, you must input a number in these parameters to prevent MPLOT from crashing.
Presentation is in the depth track.
Track 1: Linear Track 2: Linear Track 3: Linear
Trace Track Param Ledge Redge Line Mode Smooth Pen Up Notes
1
Track 1: Linear Track 2: 2 Cycle Log Track 3: Linear
Trace Track Param Ledge Redge Line Mode Smooth Pen Up Notes
1
Short Normal Resistivity Log Quality and Data Management Standards International Log Presentations
1:500 METRIC DEFAULT LOG FORMAT (correlation)
1:200 METRIC DEFAULT LOG FORMAT (quantitative)
1. TCDX: Default units are Celsius. Other default units and scales are 0 - 250°°F.
2. TVD: Optional trace used specifically for horizontal well applications. Scale should increase from left to right.
3. ROPS: Default units are ft/hr. Other default units and scales are 100 -0 m/hr, 60 - 0 min/ft, 60 - 0 min/m, 10 - 0 ft/min, 10 - 0 m/min. Default for averaging is also feet.
Metric equivalent is 2.0 (for 1:500) and 1.0 (for 1:200).
4. WBCS: Default units are K-lbs. Optional units and scales are 0 - 50 Tonnes, 0 - 500 KN.
5. RSIX: The output and presentation of this trace are predetermined. However, you must input a number in these parameters to prevent MPLOT from crashing.
Presentation is in the depth track.
Note: Pen up intervals are in feet. Metric equivalent is 3 meters (for 10 feet) and 30 meters (for 100 feet).
Track 1: Linear Track 2: 2 Cycle Log Track 3: Linear
Trace Track Param Ledge Redge Line Mode Smooth Pen Up Notes
1
Track 1: Linear Track 2: 2 Cycle Log Track 3: Linear
Trace Track Param Ledge Redge Line Mode Smooth Pen Up Notes
1
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