Dipmeter Image Repair Notes A

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Dipmeter/ Image Repair______________________________________________________________ 1

Dipmeter / Image Repair Notes

Bill Newberry

Version 1.0 - Jan., 1998

This is a work in progress and will be updated and expandedperiodically.


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Dipmeter/Image Repair

When there is an apparent problem with a set of image or dipmeter data there is a logical path

to follow in trying to locate the specific cause. The following checklist can be used a starting point in analyzing the problem. Relatively straightforward fixes exist for many of the common problems. The most common problems involve poor image quality or inclinometry channelswhich are incorrect. Many of these bad jobs can be repaired with a high degree of confidence;others are hopelessly bad. The term repair often means not so much the fixing of bad data asit does the determination of processing parameters which will permit the computation of reasonable and usable dip results.

Apparent Problem

Images Look Bad

Check Speed CorrectionTurn on sticking logic, tune with thresholding

Check for oil or gas in the borehole, particularly in horizontal wells

Check for mirror imaging of pad and/or flap images

Check EMEX Voltage

Turn off EMEX correction ( output = input / EMEX Voltage )

Check for sections of bad dataRun BorEID in sections, omitting the bad zones

Change Equalization Parameters

Dips are Bad

Check Inclinometry using GPIT Survey

Rescale or recompute bad accelerometers or magnetometersIf more than one magnetometer and/or accelerometer are bad, use well deviationsurvey and process on VAX

Calipers are badSet to Bit Size in BorDip or process on VAX, using MAPUTL to fix calipers

Change BorDip parameters


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MSD Parameter Selection for BorDip

BorDip is a very effective dip analysis program. However it is not CorDip under a new name.It was completely rewritten from the ground up. In order to get good consistent dips fromBorDip parameters must be selected in a slightly different manner than you are accustomed towith CorDip. What follows is a discussion of my findings after looking at a large number of SHDT, FMS and FMI jobs from a variety of geographical locales with differing geologicalformations and mud conditions. There is no magic bullet set of parameters that will universally

provide the best results. There is a straightforward methodology which will take care of all butthe most extreme data sets. When there is no prior knowledge as to what sort of dips to look for, I make a pass of BorDip run on default settings. If this does not produce reasonable results,i.e. good quality, consistent dips with recognizable patterns, I go directly into BorView andmanually pick a few dips to get the overall trend. I then rerun BorDip using the dip trend foundfrom the manual picks as a focusing plane. Also, since I already know the general trend, I lower the search angle from 60 to 40 . The results of this pass should show at least moderate qualitydip patterns. Next, I hang a second BorDip module under the first. Here I change theCorrelation Cutoff (under Correlation Parameters ) from 0.5 to 0.25, under FocusingPlane Parameters ; change the search angle to 20 , set the Type of Focusing Plane toVariable Plane and select the output from the previous run in Select Previous Dip Results for Variable Focus. If the input data is of reasonable quality, the results should be good. If theinput data is of poor quality, (oil-based mud, poor pad contact, ovalized hole, etc.) there is anadditional procedure which can often dramatically improve the dip calculations. This schemeinvolves serious changes to the button-to-button correlations. In general, better correlations areseen on opposing pads than on adjacent ones. After eliminating the adjacent pad correlations,the dips improve greatly. Figure 1 shows the standard MSD button correlations. Figure 2

shows the correlation links I use, all are two way links.

Figure 1 Figure 2


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Figure 3 shows the results of 3 passes of BorDip using marginal FMI data from a highlydeviated well in the Gulf of Mexico. The first tadpole track shows the dips computed by runningBorDip with default parameters. The second set of tadpoles were computed using a fixed planefor focusing. The third tadpole track is from a pass using the results from the previous pass as avariable focus and using the modified correlation links. The dips drastically improved and theyare correct as compared to manually picked dips.

Figure 3


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Recommendations:

If you do not know what sort of dips to expect, start by making a reconnaissance pass of BorDip run on defaults. If necessary, use BorView to find the dip trend to use as a focusing

plane.

If you are not expecting high dips or you are using a focusing plane, set the Search Angle to40 and use Fixed Plane.

Make a second pass using:

Correlation Cutoff = 0.25Search Angle = 20

Variable PlanePrevious output for focusingChange the correlation links if you have poor input data

Hints:

BorDip does not work well when bad buttons are included. It is good practice to kill obviously bad or flaky buttons.

BorDip does not have the double angle search option. In CorDip you could input a search angle

value of something like 135

, which would tell CorDip to first search 35

and if no dip weredetected then search out an additional 35 to try to find a dip. In BorDip, if you put in 135 , itinterprets that literally and will most likely give trash results. If you really want a 70 searchangle, put in 70 not 135 .


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GPIT_Survey

The GPIT_Survey module is invaluable for determining the quality of the inclinometry data aswell as for performing some of the more common fixes to GPIT data. It is the only means of validating the usability of the inclinometry data and should be run on EVERY job. The earthsmagnetic field is changes with your location on the earths surface and also varies slowly over time. By default, GPIT_Survey picks up the date, latitude and longitude from the input data file.If Date was not set in the raw data file, GPIT_Survey will probably crash. If this happens, usethe Data Manager to set an appropriate Date, then restart the module. In the middle of the

panel, there 3 columns of data. The first or Used are the earth constants as read from the rawdata. The second column or IGM contains the constants as determined from a lookup table

based on the values of date, latitude and longitude. These two columns should closely agree andshould conform to known values for the local area. It is not uncommon for latitude and longitudevalues to get mistyped. The third column, Averaged log, has the calculated values for theearth constants based on the accelerometer and magnetometer data. If the tool is operating

properly, these Averaged log values should be close to know values. GF3.0 even alerts youhen these values are out of tolerance. In the example below, there is an obvious problem withthe accelerometer and magnetometer data.

Averaged log values are obviously bad.


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first icon on the left, we can rescale the X and Y data to make them centered. A little bit of arithmetic will give you the offsets that need to be applied to each component.

Calculated offsets needed

Accelerometers MagnetometersX -0.190785 0.09733Y 0.016910 0.05085

Xplots after offsets have been applied to accelerometers and magnetometers.

After each fix is applied, the Averaged log values are updated so that you can see if thecalculated values are now within tolerance. The reconstructed values now look good for thenorms.


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If a single magnetometer or accelerometer is dead, it is often possible to use the recomputeoption to fix it. In this procedure, the 5 good components and the known values for the earthnorms are used to calculate the missing channels. This option must be used carefully since thecalculation can sometimes fail. Look at the results closely.

When more than one of the 6 components are dead, GPIT_Survey cannot be used to producea fix ( as of GF3.0). However, there is a LOGOS program named GPIPRE which allows oneto do more extensive repairs when an independent deviation survey is available. Use GPIPREto rebuild the inclinometry using only the accelerometers and the independent HAZI channel.Run BorEID and other processing on the VAX. If all the magnetometers are good and theaccelerometers are bad, you will need both DEVI and HAZI data for GPIPRE to be able toreconstruct the inclinometry. Sometimes the customer supplied deviation information is not in aconvenient form. Below is a rather extreme case where only the latitude and longitude values for the well at various depths is given.


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Typical LOGOS GPIPRE Dialogue


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GPIT Speed Correction

I am a firm believer in using the sticking detection logic in BorEID under GPIT Parameters.This option can often significantly improve the speed correction results in sticky holes. However,you have to use a little caution when using this feature. In very smooth holes where there is littleactivity on the Z-accelerometer the sticking logic can be activated erroneous depth shiftscreated. Also in very sticky holes, the Kalman filter can blow up, producing some very badoutputs. Unfortunately, these incorrect shifts are often not noticeable on the images. It isnecessary to check the playback to make sure that the depth correction did not do anythingstrange. There should be some reasonable correlation between the computed stuck sections andthe values seen on the cable tension.


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Sticking Detection - ON , Recovery Speed Factor = 20

Another commonly encountered problem in processing GPIT data occurs when sections of thedata are bad. This can cause BorEID to fail completely or produce very long pulls on theimages. Sometimes a bad pull over say 20 feet may cause the speed corrected images to showa pull of 200 feet or in some cases the entire section above the pull will be bad. Since the GPITdata is processed over the entire logged interval, changing the Start and Stop depths in BorEIDwill not cure the problem. The cleanest way to handle this is to first locate the sections of gooddata, then go back to Data_Load and load only the good sections. This way BorEID sees onlygood data and should run fine.


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FMS Tools Logged in an Incorrect Mode

There are three types of FMS tools:

MESTA - 2 pad toolMESTB - Slim hole toolMESTC - 4 pad tool

If the logging engineer inputs the wrong sonde type during acquisition, you will have to intervenein the processing to get correct results. The processing software, both LOGOS and GeoFrame,key off of some of the tool parameters. If these are incorrect, the output will not be right. Thefollowing should help you repair the two most common problems.

--------------------------------------------------------------------------

MESTB tool logged as a MESTC , LOGOS Processing

After the data has been loaded, in MAPUTL, change the "BUTTON SPACING" from 0.15 to0.12 . Otherwise the processing is the same.

--------------------------------------------------------------------------

This is to change a MEST tool that was ran in (2)pad mode to (4)pad mode. The job has to be

processed in LOGOS on the VAX. If you have a DLIS file, first convert it to LIS. Thefollowing steps will produce an LIS file which will load and process correctly on the VAX.

$ASSIGN SYS$OUTPUT FOR$PRINT$DS/GO LISU$ASSIGN/BLOCKSIZE=8192 SAMDI0.DAT$ASSIGN/BLOCKSIZE=8192 SAMDI2.DAT/WRITE$TEMP/BUILD/MEDIT! You will be in edit mode .! At the first of each line of a "CONS" file, replace the first! character ( Usually an "L" ) with a "*"$TEMP/ANA/SHOW$TEMP/BUILD/APPLY/TEDIT! You will be in edit mode .! Search for "MLM", then change (FSCA to 4SCA) or (1800 TO 4180)$TEMP/GO/ANAL$EXIT


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CALIPER Problems with SHDT/FMS/FMI Tools-------------------------------------------------------------

The most common caliper problem is one of simple miscalibration. The tool is actually working properly but the output values are incorrect. This is a relatively straight-forward problem to fix. If the calipers are not operating correctly, it is usually necessary use the caliper information fromother tools.

Assuming that the calipers have been miscalibrated, it is first necessary to obtain a good set of calibrations for that tool from the field and to read the bad set of calibrations from the data tape.Then the bad calibration has to be removed and the good calibration applied. This is basically asimple algebra problem of solving two equations for two unknowns.

y1 = m1 * x1 + b1

y2 = m2 * x2 + b2

where:

x1 = Raw C1 readingx2 = Raw C2 readingy1 = Calibrated C1 readingy2 = Calibrated C2 readingm1 = Gain applied to Raw C1 readingm2 = Gain applied to Raw C2 readingb1 = Offset applied to Raw C1 reading

b2 = Offset applied to Raw C2 reading

If we use subscripts of "b" for the original bad calibration and "g" for the new, good calibrations,the following transforms should provide the desired results.

( y1b - b1b )y1g = m1g * (--------------) + b1g

( m1b )

( y2b - b2b )y2g = m2g * (--------------) + b2g

( m2b )

These transforms can be applied in LOGOS by using MAPUTL or in GeoFrame through "DataFunctioning" in the Playback module.


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FMI Pad/Flap Overlap

The relative positions of the FMI Pads and Flaps change azimuthally around the borehole

depending on hole diameter. The flaps are offset vertically from the pads by a constant distance( 5.7" ). The flaps are NOT offset azimuthally by a constant distance. This offset or gap changeswith borehole diameter.

------------------------------| || PAD || |

--- | o o o o o o o o o o o o || | o o o o o o o o o o o o|| | || | || | || ------------------------------| | |

5.7 inches ->| |


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GEOL_SLG_BLD to build the sidefiles, this computation will be taken care of for you. If youuse "canned" sidefiles, it will be necessary to edit them appropriately.


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For display on the workstation, changes need to be made in the"HEADER_FORMATS.DAT" file before running VAXSUN. The default assumesa pad/flap gap of 0.0 .

HEADER_FORMATS.DAT

/* FMI FLAP A */TYPE3 5

NAMEFMI FLAP ACHAN_NAMES

UNITS_NAMES

OFFSET_ANGLE0.00OFFSET_DISTANCE2.4 Add the appropriate gap ( from the following table )

to the 2.4 to get the flaps positioned correctly.For instance, for a 6.5" hole, 2.4 + 0.501 = 2.901 .For a 10" hole, 2.4 + 0.332 = 2.732 .This value should be the same as the "Arc Dist" entryin the GAP table.There are 4 flaps, so remember to set thisOFFSET_DISTANCE for all flaps.

==========================================================


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GAP TABLE

Bit size Gap Arc Dist Coverage Overlap

inches inches inches % inches---------- -------- --------- -------- --------6.000 0.547 2.947 88.387 0.6356.500 0.501 2.901 90.183 0.1967.000 0.463 2.863 87.308 0.0007.500 0.431 2.831 81.487 0.0008.000 0.400 2.800 76.394 0.0008.500 0.380 2.780 71.901 0.0009.000 0.363 2.763 67.906 0.0009.500 0.346 2.746 64.332 0.000

10.000 0.332 2.732 61.115 0.00010.500 0.319 2.719 58.205 0.00011.000 0.306 2.706 55.560 0.00011.500 0.295 2.695 53.144 0.00012.000 0.285 2.685 50.930 0.00012.500 0.276 2.676 48.892 0.00013.000 0.267 2.667 47.012 0.00013.500 0.259 2.659 45.271 0.00014.000 0.252 2.652 43.654 0.00014.500 0.245 2.645 42.149 0.00015.000 0.239 2.639 40.744 0.00015.500 0.233 2.633 39.429 0.00016.000 0.227 2.627 38.197 0.00016.500 0.222 2.622 37.040 0.00017.000 0.217 2.617 35.950 0.00017.500 0.212 2.612 34.923 0.00018.000 0.208 2.608 33.953 0.00018.500 0.204 2.604 33.035 0.00019.000 0.200 2.600 32.166 0.00019.500 0.196 2.596 31.341 0.00020.000 0.193 2.593 30.558 0.00020.500 0.189 2.589 29.812 0.00021.000 0.186 2.586 29.103 0.000

=======================================


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FMS sensor array FLIC processing numbering convention

+-------------------------------+row 4 | 4| 8 12 16 20 24 | ---+

| | | | 0.4"row 3 | 3 | 7 11 15 19 23 27 | ---+| | | | 0.4"

row 2 | 2 |6 10 14 18 22 26 | ---+| | | | 0.4"

row 1 | 1 5 9 13 17 21 25 | ---++-------------------------------+

| | | | | | |+---+---+---+---+---+---+.4" .4 .4" .4" .4" .4"

4-pads FMS tool MEST-C, MEST-B (PTYP=MEC)

+----------------------------------+row 2 | 2 |4 6 8 10 12 14 16 | ---+

| | | | 0.3"row 1 | 1 3 5 7 9 11 13 15 | ---+

+-----------------------------------+| | | | | | | | |

+--+- -+--+--+---+---+---+--+.3" .3 .3" .3" .3" .3" .3" .3"

4-pads FMS tool MEST-B (PTYP=HR) - Slim hole tool

+-----------------------------------+row 2 | 2 |4 6 8 10 12 14 16| ---+

| | | | 0.3"row 1 | 1 3 5 7 9 11 13 15 | ---+

+----------------------------------+| | | | | | | | |

+--+--+--+---+---+---+---+---+.24 .24 .24 .24 .24 .24 .24 .24 (inches)

FMI tool

+-----------------------------------------------------+row 2 | 2 |4 6 8 10 12 14 16 18 20 22 24| ---+

| | | | 0.3"row 1 | 1 3 5 7 9 11 13 15 17 19 21 23 | ---+

+-----------------------------------------------------+| | | | | | | | | | | | |

+--+--+--+---+---+---+--+---+---+---+---+---+.2" .2" .2" .2" .2" .2" .2" .2" .2" .2" .2" .2"


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Order of FMS and SHDT buttons on the tool for the 2-pad FMS (toolseen from above) :

North27 1S11 1A* *

|||

1 4A * | * 2 27West --------O-------- East

27 4 * | * 2A S2 1||

|* *3A 31 27South

For the 4-pad FMS tool the scheme is the following (tool seenfrom above) :

North

16 1* *

|||

1 * | * 16West --------O-------- East

16 * | * 1|||

* *

1 16

South


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FMI Channels

channel names output file contents

standard tool :

SBi - DBi SHDTRB.x0n pseudo-SHDT fast channels(sampling 0.1")

FBA1 + FBA2 FMI1.x0n FMI fast channels, pad A, rows 1 and 2(24 channels - sampling 0.1")

FBA3 + FBA4 FMI5.x0n FMI fast channels, flap A, rows 3 and 4(24 channels - sampling 0.1")

FBB1 + FBB2 FMI2.x0n FMI fast channels, pad B, rows 1 and 2

(24 channels - sampling 0.1")

FBB3 + FBB4 FMI6.x0n FMI fast channels, flap B, rows 3 and 4(24 channels - sampling 0.1")

FBC1 + FBC2 FMI3.x0n FMI fast channels, pad C, rows 1 and 2(24 channels - sampling 0.1")

FBC3 + FBC4 FMI7.x0n FMI fast channels, flap C, rows 3 and 4(24 channels - sampling 0.1")

FBD1 + FBD2 FMI4.x0n FMI fast channels, pad D, rows 1 and 2(24 channels - sampling 0.1")

FBD3 + FBD4 FMI8.x0n FMI fast channels, flap D, rows 3 and 4(24 channels - sampling 0.1")

Order of FMI channels in the output file :

x101, x201, x102, x202, ...., x112, x212or x301, x401, x302, x402, ...., x312, x412

for x = A, B, C or D

Order of the pseudo-SHDT channels :

SB1, DB1, DB2, DB3A, DB4A, SB2, DB1A, DB2A, DB3, DB4


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Image files (FMS : MESTBi, FMI : FMIi) :

- header.I(6) = pad number i

- header.I(7) = number of pads on the tool(2 or 4 for FMS, 8 for FMI)- header.I(8) = number of rows on every pad

(4 for 2-pad FMS; 2 for 4-pad FMS; 2 for FMI)

- header.R(4) = distance between buttons (inches)0.1 = 2-pads FMS tool0.15 = 4-pads FMS tool MEST-C, MEST-B (PTYP=MEC)0.12 = 4-pads FMS tool MEST-B (PTYP=HR)0.1 = FMI tool

- header.R(5) = distance between rows (inches)0.4 = 2-pads FMS tool0.3 = 4-pads FMS tool

0.3 = FMI tool

SHDTRB file :

- header.I(9) = origin of data1 = standard SHDT2 = FMS 2-pad3 = FMS 4-pad4 = FMI

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Dipmeter Image Repair Notes A

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