This articles describes the mains guidelines and quality checks to be performed for successful logging operations
1. Preparation prior to logging operations:
- All wireline logging tools shall be checked and tested prior to rigging up.
- Logging operations shall commence when the hole conditions are stable. A check trip shall be required before running the formation pressure/sampling tool if there were hole problems during the previous run.
- The mud specifications shall meet the program specifications. The overbalance shall be at least 200 psi.
- Fishing equipment shall be available at the well site for all logging tools. All dimensions, lengths and connections of all the tools shall be recorded.
- For formation pressure/sampling logging a plot of expected pressures shall be prepared.
2. logging operations guidelines.
- The hole shall be circulated through the trip tank during logging operations. The hole shall be kept full throughout, and the trip tank volume shall be recorded every 15 minutes. The trend shall be monitored whilst running in and pulling out.
- The wireline logging depths shall be set to zero at surface and checked when pulling out to surface. Additional checks shall be made at casing depths and at TD.
- If a tool hangs up while running in and the section has not been logged before, log out of the well. If one of the detectors of a combination tool does not function properly, log the remaining detectors which have not been recorded before. When anticipating poor hole conditions, always log in as well as out of the hole to secure data.
- If a section has to be repeated, a 500 ft section shall be made on each logging run, and a 200 ft overlap with previous logging runs shall be made. The repeat section shall be made across an interval of interest.
- When running a calliper tool in a section where the top of the logged interval is below the casing shoe a 1 000 ft section over the shoe shall be run to check shoe depth and calliper gauge.
- Mud shall be sampled from both the pits and flowline immediately before the end of circulation prior to a logging job for analysis and resistivity measurement. This shall be repeated after check trips if resistivity tools are to be run.
- Check trips to bottom shall be required to ensure the hole and mud conditions.
- The weak-point tension limit and cable tension limit shall be checked and tool weight in mud calculated before entering open hole. Normal logging tension shall be checked every 1 000 ft in open hole. This is especially important in deviated holes where drag can be significant.
3. quality control guidelines
- The depth correlation of all the curves on the log must be checked with each other.
- The repeat section must be checked with the main log for agreement. The curves must be examined to see if they have sensible values. They shall be compared with logs in nearby wells, which must always be available on the rig.
- The correct logging speed must be verified. The speed can be determined from the breaks in the lines at the edges of the log which occur every minute. For example, if the distance is 60 ft, the logging speed was 60 ft/min. For resistivity logs the standard logging speed is 60 ft. Statistical nuclear tools require a speed of 30 ft/min. The acceptable range is +/- 10 %. Confirm this with the Logging Contractor in advance.
- Verification shall be made that there is 200 ft overlap between successive logging runs.
- The depth discrepancies between successive logging runs must be less than 2 ft.
- For the Cement Bond Log, a 300 ft section of the free pipe reading during logging must always be recorded (if uncemented sections exist).
4. Formation Pressure Tests guidelines
- When taking pressures the tool shall initially be set for two minutes only. If the pressure does not build up properly the tool shall be unseated and another attempt made.
- Plot both the formation pressure and mud pressures as they are taken. Inconsistencies in the mud gradient shall be checked immediately (a smooth mud gradient shall be regarded as a quality check).
5. Highly Deviated Wells guidelines
- Before entering open hole the normal logging tension shall be recorded. It shall be higher than that of a vertical hole and large stretch corrections shall be required.
- Checks shall be made to ensure that the tool is moving down the well as the wireline is being run into the hole.
- Short tool combinations are easier to get down the hole particularly in areas of high dogleg.
- For high deviations or particularly difficult holes, consideration shall be given to other techniques, eg., drillpipe (TLC) or coiled tubing (E-line) conveyed logging tools or the use of logging while drilling tools (LWD).
6. Horizontal Wells guidelines
- Horizontal wells shall be logged either with LWD or TLC techniques.
- The use of drilling jars are not recommended because of the risk of logging tool damage. It shall not be possible to run jars or HWDP because of ID restrictions for an extended length. This requires enough regular drillpipe at the well site to replace the HWDP’s, drill collars, jars, etc.
- The running in speed shall not exceed that used when running a packer on drillpipe. Below the kick-off point, the tools shall tend to lie on the low side of the hole and not be subject to so much bouncing as higher up. Obstructions downhole (eg., liner tops) shall be passed with caution. Break circulation at regular intervals (ie., every 10 stands).
- A down log shall be taken while running in. The Logging Contractor procedures shall recommend that the tools do not tag the bottom of the hole but stay a minimum 20ft above drillers depth. Depth control shall be checked with the drillpipe during in-run and out-run.
- Continuous communication is required between Driller and the wireline unit to ensuring the pulling speed and cable spooling speed are matched, and to minimise reaction time if the tool begins to stick. Minimise downward movement when setting slips, because the calliper will be in the open position.
- The cable shall not be slacked off to avoid the risk of damaging it at the side entry sub.
- A cable head tension/compression meter readout shall be made available to the Driller on the rig floor.
- The string to be spaced out to have latch point in cased hole.
- If circulating sub cannot be latched increase cable running speed and check for latching from logging unit.