archival analogue
DESCRIPTION
ARCHIVAL ANALOGUEGEOPHYSICAL LOGS – A NEW LIFEbyMarian KieltTRANSCRIPT
ARCHIVAL ANALOGUE
GEOPHYSICAL LOGS – A NEW LIFE by
Marian Kielt
Geofizyka Torun Sp. z o.o.
ARCHIVAL ANALOGUE GEOPHYSICAL LOGS – A NEW LIFE Geofizyka Torun Sp. z o.o. www.GTservices.pl 2 / 17
In Poland, the analogue geophysical logging in boreholes has been performed during 35
years. In the archives there are a lot of geophysical analogue data from thousands of wells.
The application of digital recording caused the necessity to make the data analysis again and
this way to prepare appropriate technical, pre-interpretation and interpretation procedures [8,
11].
INTRODUCTION
Basing on the analogue geophysical log analysis and well data from different parts of the world it was possible to create a catalogue of errors most often occurred. The catalogue helped to prepare the appropriate procedures that allowed speeding up the analysis of geo-physical logs. The errors are of a different genesis and frequency of occurrence. The arrange-ment of the database and verification of information contained there is often a time-consuming work and requires a lot of professional knowledge, many years’ experience, pa-tience and appropriate software. Most often such a work is considered by geologists and geo-physicists to be uninteresting. They forget the basic fact that they would work on such a data-base as they prepared or accepted before.
To discuss the digital archival geophysical databases one should consider two cases [7, 8]: - Scanning and converting the analogue geophysical logs into a digital form. - Work on a disordered database obtained from an outsider’s analogue-to-digital con-
version performer. In the first case it is possible to prepare the digital database according to uniform rules
given by the geophysical logs owner or interpreter. The second case is much more difficult, because the interpreter and earlier – the unconscious owner of geophysical logs receives a disordered database.
In this paper the conventional procedures applied in such situations are presented: - “Investigation” procedure in order to identify the content, - Quality control and evaluation of data usefulness, - Organisational procedure (assignation of geophysical logs to particular boreholes
and intervals), - Re-animation procedure (identification of types and places of errors, their removal
etc), - Reproduction procedure (search for a relation between particular geophysical pa-
rameters and its determination, construction of missing parameters), - Determination of lithotypes in a borehole plan, - Interval formational interpretation.
Sets of archival analogue geophysical logs
Taking into account a long period of time and modified sets of geophysical logs the archi-val logs should be understood as non-standardised logs recorded in an analogue form [1-6].
They can be divided into the following groups: - The first Schlumberger set containing SP and 3 x EL, applied till mid-forties, - Extended Schlumberger set containing SP and 5 x EL, continued and developed dur-
ing many years in the SU and countries using Russian-type recorders (GR, NGR, PS, 3 – 6 x EL, AL, CAL),
- Traditional set containing SP, GR, NG, 3 x EL and then AL.
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The amount and type of geophysical measurements do not play an important part for the scanning and analogue-to-digital transformation but they are essential for the interpretation work according to the rule that the lesser geophysical logs are to a disposal the lesser geologi-cal information can be obtained.
Characteristics of archival analogue geophysical logs The archival geophysical logs performed during tens of years are characterised by [9]:
- Common application of non-compensated tools, - Different and not complete logging sets, - Missing standardisation, - Not very clear relations between geophysical and petrophysical parameters and geo-
logical features, - Analogue recording (today often not understood by the users – fig.1).
For a long time the geophysical logs have been recorded and stored in an analogue form in different regions of the world. Beginning from the nineties they have been successively scanned and transformed into a digital form. However, their specific features cause a lot of errors in geophysical logs and because of that they are not suitable for interpretation in their original form.
Fig. 1 Example of archival diagrams containing original measurements (Poland).
Analogue-to-digital transformation
In 1991 the author of this paper initiated the work on formation of a complex digital data-
base instead of hitherto existing analogue database (fig. 2). Orlik J. and Podolak J. elaborated appropriate programs. The catalogues prepared contained the following data [8]: - Data related to borehole geophysics, - Geophysical logs together with identification codes, - Basic analogue characteristics of geophysical logs.
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Fig. 2 Schematic diagram of the pre-interpretation and interpretation procedures (Romaniuk W.).
The following procedures were also prepared:
- Organisation of scanning and analogue-to-digital transformation of geophysical logs (log identification, verification of measuring units, reading of maximum indications for par-ticular logs, determination of initial and final depth, division into measuring time inter-vals, determination of scale types, automatic coding of logs);
- Analogue-to-digital transformation of geophysical logs (controlled by an organisational procedure);
- Digital recording (with automatic division into measuring intervals in LAS format); - Creation of archives and catalogues of digital data sets for particular boreholes.
Such a routine (removal of errors before the transformation and organisational work)
makes it possible to obtain the databases ordered and prepared separately for each borehole. It enables management of the borehole data. The digitised geophysical logs may be presented identically (according to API rules) with logs recorded digitally (fig. 3).
Fig. 3. Examples of digitised geophysical logs.
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Creation of archival geophysical logs databases
Generally, the digital databases containing the geophysical logs can be divided into disor-
dered and ordered (arranged) ones. The disordered databases are not suitable for the direct interpretation work and require a
change into databases friendly for the user.
Disordered databases
The disordered analogue databases are most often a reason for the formation of disordered digital databases. Accidental people most often perform the scanning and analogue-to-digital transformation and this way the disordered and most often not verified databases are created containing thousands of various data sets. Though they do not occupy physically a lot of space, they are unclear for a potential user for two reasons. Firstly, they are not related to a catalogue (not a mathematical record of data sets with accidental names) and secondarily, the original analogue materials necessary for comparisons and graphical verification of digital data sets are missing. They also contain original errors, connected with recording, interpreta-tion variants, author’s approach, etc. Besides, there are also scanning and digitising errors (in case of several logs crossing) [9, 10].
Ordered databases
The other situation is when the scanning and digitising of analogue geophysical logs run
according to the prepared procedure called ORGANIZACJA. It enables verification of pro-files before scanning and transformation into a digital form.
The disordered databases require verification, catalogues, removal of errors and improperly prepared data, description of problems, etc. It is performed in the 2nd stage of the verified da-tabase construction (= verification stage). It requires several reports containing the data re-lated to [9, 10]: - Preliminary total and thematic contents, - Number and type of useless data sets, - Number and type of repaired data sets, - Number and type of missing data sets - Useful data sets, - Final recommendations.
Re-animation (detective) work
The digitised data sets are usually a “digital copy” of analogue geophysical logs. It means,
that they contain all original errors and limitations. Pretty often the digitising errors are added. It concerns particularly the disordered databases discussed earlier. Thus, the following opera-tions should be performed before using the geophysical logs [8]: - Quality and usability control (knowledge about the tool types, verification of scales, iden-
tification of acoustic cycle skips and recording of cavernous intervals, verification of zero records);
- Transformation of the physical units scale into pseudo-petrophysical one (API, porosity, resistivity) by means of lithological benchmarks;
- Pre-interpretation (removal of acoustic cycle skips, approximate elimination of the bore-hole diameter effects) (fig. 4 and 5);
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- Computation (interval time computation from original times and comparison with the measured interval time, computation of pseudo-laterologs of two penetration ranges based on at least 3 electric logs of different length) (fig. 5);
- Comparison of the scaled curves with skeleton values and verification of their consis-tency.
The above operations make it possible to obtain a set of geophysical logs useful for inter-pretation or to reject non-informative measurements.
Fig. 4. Graphical visualisation of corrected geophysical logs (GR, NGR and AL) using the
INZAL program (Furgal G.).
Fig. 5. Graphical visualisation of corrected geophysical logs (GR, NGR and EL) and pseudo-
laterologs computed by means of the INZAL program (Furgal G.).
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Geological standardisation of geophysical logs
On the way from physical parameters to information and geological features there are the
following “stops”: non-standardised geophysical logs – standardisation – standardised geo-physical logs – calibration of indications and geophysical images on models based on inter-preter’s experience – information and geological phenomena. During a long period of the borehole geophysics evolution the greater part of this way has been fully automatised, how-ever, the last part – calibration is only partly automatised. The theoretical and practical knowl-edge of the interpreter is still very important on this stage. The interpreter should have knowledge of borehole geophysics, petrophysics and geology [9, 11].
SET3.GR_2
GAPI0 17
SET3.SP_1
MV95 -5
4980
5000
5020
5040
5060
5080
5100
5120
5140
5160
DEPTHMETRES
SET3.EL02_1
OHMM0.2 200
SET3.EL03_1
0.2 200
SET3.EL07_1
0.2 200
SET3.EL14_1
0.2 200
SET4.DT_2
US/M350 150
SET3.NECN_2
0 25SET6.LL3_1
OHMM0.2 2000
SET6.LL3_2
OHMM0.2 2000
Fig. 6. Example of re-standardisation of selected geophysical logs (Poland, Miocene).
In case of the interpretation of non-standardised geophysical logs the interpreter must go this way unaided, using his knowledge and experience (fig. 6).
It should be emphasised, that a presentation of geophysical logs in petrophysical units (API, bulk density, porosity, resistivity) is only a preparation of the parameters measured in standardised (comparable) units for the formational and geological interpretation [1 – 17].
Interpretation methods applied Types of interpretation work There are three basic groups of the interpretation work:
- General interpretation including a construction of selected profiles of combined geophysi-cal logs, scaled in pseudo-petrophysical units (natural gamma-ray intensity, neutron porosity, interval time, resistivity) and computation of acoustic interval times for seismic purposes, unless such measurements have been performed or thy are of poor quality;
- Geological interpretation enabling the basic lithofacies and lithophysical units of different types to be determined and computation of synthetic interval times and bulk pseudo-density, based on a known lithology.
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- Formational interpretation, which makes it possible to evaluate the properties and satura-tion of collector horizons with fluids.
The following interpretation methods are very useful [11]: - Macroscopic analysis of geophysical logs; - Analysis of petrophysical parameters variability with depth; - Sequential analysis of petrophysical parameters; - Analysis of cross-plots; - Analysis of clay and pure sands line; - Analysis of the bed boundary variability gradient; - Analysis of log shapes; - Analysis of functional relations between petrophysical parameters; - Analysis of petrophysical parameters magnitude.
Modelling During the re-animation and interpretation work the modelling of lithology, fluid types as
well as continuous correcting and comparing of modelled lithofacial profiles with geophysical logs are very useful. Another possibility is a comparison of the obtained results with testing and other geological data. Unfortunately, such data are accessible only in some intervals.
The modelling play an important part, especially when the interpreter has a limited set of geophysical logs at his disposal. In such a situation one should assume different types of lithology and saturation with fluids (hydrocarbons, water) [11].
Software
When the geophysical logs are prepared according to the rules mentioned above, the inter-
pretation does not create a problem. However, one should remember of a limited amount of geological information contained in logs and of their vertical resolution.
When we have a limited set of logs we cannot expect that the results will be the same as in case of modern sets of geophysical logs, in accordance with the rule, that the number of un-known quantities must not exceed the number of known ones.
The INZAL program (Zalayev N.) was applied to the re-animation and some part of inter-pretation work. During the pre-interpretation and interpretation in a borehole scale the GE-OLOG program was used.
Selected results of geological and reservoir interpretation
The interpretation of geophysical logs includes a wide range of geological and reservoir problems. It depends on quantity and quality of accessible geophysical logs, interpretation methods and computation procedures as well as on the interpreter’s knowledge and experi-ence. The interpretation enables localisation and determination of - horizons with a resistivity anisotropy, - basic lithofacies, including horizons saturated with hydrocarbons (fig. 8), - basic lithofacies, porosity class and identification of fluids, - coal horizons (fig. 9), - fault surface and zone (fig. 10), - basic lithofacies (fig. 11).
The interpretation makes it possible to construct the borehole profiles based on selected geophysical logs (fig. 12 and 13).
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The formational interpretation is also possible in different litho-stratigraphic units (fig. 14-67) as well as presentation of results of a complex interpretation of borehole geophysical logs in the time and depth scales (fig. 17).
WIRE4.NGR_1IMP/MIN1800 2500
WIRE4.NEGR_1IMP/MIN20000 26000
2450
2475
2500
2525
DEPTHMETRES
WIRE4.EN64_1OHMM0.15 20
WIRE4.EL18_20.2 20
WIRE4.EN16_10.15 15
WIRE4.EL18_2OHMM0.2 20
WIRE4.NGR_1IMP/MIN2500 1800
WIRE4.EN16_1OHMM0 3
WIRE4.ELSP_110 28
WIRE4.NEGR_1IMP/MIN20000 26000
Fig. 7 Horizons with anisotrophy.
SET3.GR_2
GAPI0 17
SE
T3.
GR
_2
SET3.SP_1MV-25 130
SE
T3.
SP
_1
4980
5000
5020
5040
5060
5080
5100
5120
5140
5160
DEPTHMETRES
SET3.EL14_1
OHMM2 200
SE
T3.
EL1
4_1
SET4.DT_2
US/M350 150
SE
T4.
DT
_2
SET3.NECN_2
C/MN0 25
SE
T3.
NE
CN
_2
SET6.LL3_2
OHMM2 2000S
ET
6.LL
3_2
ilowce
piaskowce zailone
GAS
ilowce
PIC
KS
_1.T
AB
LE_1
Fig. 8 Basic lithofacies.
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DESCRIPTION:
- SHALE
- CLAY
- SAND
- C L A Y E Y S A N D - LIGNITE
- SHALE 1 - PROBABLY 70% L IGNITE , 3 0 % S H A L E e t c .
- ANHYDRITE
WIRE_12.GR_1GAPI15 150
WIRE_12.RHOB_1G/C31 4
1450
DEPTHMETRES
WIRE_12.RHOB_1G/C31.1 2.8
WIRE_12.PE_1B/E10 0
WIRE_12.RHOB_1G/C31.1 2.9
WIRE_12.DT_1US/F165 75
LITHOLOGY MODEL RHOB
G/C31.05 2.75
WIRE_13.GR_1GAPI0 150
WIRE_13.RHOB_1G/C31 3
WIRE_2.CAL2_1IN8 18
WIRE_2.CAL2_1IN8 18
WIRE_13.GR_1GAPI10 65
WIRE_13.RHOB_1G/C31 3
WIRE_2.CAL2_1IN8 18
WIRE_2.CAL2_1IN8 18
1650
1700
1750
DEPTHM
ETE
R
WIRE_13.DT_2G/C3215 0
WIRE_13.GR_1GAPI0 80
LITHOLOGY
Fig. 9 Coal horizon localisation (India).
Fig. 11 shows a unique example. The analogue geophysical measurements (GR, NGR, 6 x
EL) and digital ones (dipmeter logs, SGR) have been performed in a borehole. Such a combi-
nation of non-standardised and standardised geophysical measurements made it possible to
verify and combine the information obtained from two sources. The Rotliegende conglomer-
ates of different geophysical characteristics (also in other boreholes) could be attributed to the
inter-dune deposit environment and the sandy deposits represent the dune environment. The
combination of the analogue and digital measurements caused an increase in geological in-
formativity of the first ones.
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3380
3400
3420
DE
PT
HM
ET
RE
S
WIRE5.EL28_2OHMM0.3 500
WIRE.GR_2GAPI20 80
WIRE5.NTCN_114000 40000
WIRE.POTA_1
%2 0WIRE.URAN_1
PPM0.5 2.5
WIRE.THOR_2
PPM0 4WIRE5.EL28_2
OHMM0.03 500
WIRE5.EL14_10.06 300
WIRE5.EN20_10.07 200
WIRE5.NTCN_18000 40000
WYKRES WEKTOROWYSHIVA 6: 0.5 M X 0.25 M X 45
3387UNCONFORMITY
3389
dune sand16
3405
inter-dune sand19
3424
COMMENTARY
3525
3550
3575
3600
3625
DE
PT
HM
ET
RE
S
WIRE.POTA_1
%0 5
WIRE.THOR_1
PPM0 10
WIRE.URAN_1
PPM0 5
WIRE.GR_2
GAPI0 200
WIRE6.GGDN_1
10000 0
WIRE.GR_2GAPI20 200
WIRE.DT_1US/F120 30
WIRE6.EL28_12 17
WIRE6.EL28_1OHMM0 20
WIRE6.EL14_10 25
WIRE6.LL3_1OHMM0 10
WYKRES WEKTOROWYSHIVA 6: 0.5 M X 0.25 M X 45
WYKRES WEKTOROWYSHIVA 6: 1 M X 0.5 M X 45
MO
DE
LO
WY
WY
KR
ES
KR
AW
ED
ZI
PL
AS
ZC
ZY
ZN
TN
AC
YC
H
Fig. 10. Localisation of a tectonic zone and unconformity in the Rotliegendes deposits (Poland).
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WELL LOG ANALYSIS
DRILLING MEASURED FROM:
LOGS MEASURED FROM:
LOGS MEASURED BY:
LONGITUDE:
LATITUDE:INTERVAL PLOTTED:
SCALE:
PROBABLY GROUND LEVEL
SCHLUMBERGER
W 3 DEGREE 13.38 MINUTES
N 55 DEGREE 1.53 MINUTES1820.00-2353.10 METRES
1:500
PERMANENT DATUM: PROBABLY GROUND ELEVATION
GROUND ELEVATION:
KB:
173 FTSTATE / PROVINCE: DENMARK
COUNTY:
WELL:
COMPANY:
ABENRA-1UAB MINIJOS NAFTA,LITHUANIA
FIRST RECORDED DEPTH:
LAST RECORDED DEPTH:
ANALYSIS DATE:
ANALYSIS PLACE:
JANUARY 2003
WELL LOG ANALYSIS DEPARTMENT
MARIAN KIELT MEASUREMENT DATE:
7700 FT
JULY 04, 1953WITNESSED BY:
PLOT NO 2
CHROBREGO 50 ST.87-100 TORUN, POLAND
LOGS.GRAPI0 500
GAMMA RAY AND SP LOGS
LOGS.SPMV0 150
1900
2000
2100
2200
2300
DEPTHMETRES
DEPTHMETRES
LOGS.L10INOHMM0.05 500
RESISTIVITY LOGS
LOGS.L38INOHMM0.05 500
LOGS.L16FTOHMM0.05 500
GR
PS
EU
DO
-IM
AG
ING
0 2 0 0
1852A 8 ?
1855
A 540
1895
A 418
1913A 3
1915
B 563
1978B 4
41982
B 328
2010B 1
2012
C 87
2019
C 561
2080
C 412
2092
C 39
2101
C 222
2123
D 457
2181
D341
2222
E 916
2238
E 454
2293
E 315
2307
E 226
2333E 1
2335
PRE-ZECHSTEIN13
2349
LIT
HO
ST
RA
TY
GR
AP
HY
LT
HO
LO
GIC
AL
CO
LU
MN
clayey anhydrite
salt
anhydrite
salty anhydrite
salt
anhydrite
dolomite
dolomitic shale
anhydrite
salt
dolomitic anhydrite
dolomite
ooitic limestone
dolomite (breccia)
dolomitic anhydrite
dolomite
anhydritic dolomiteanhydrite
dolomitic anhydrite
anhydrite
limy dolomite
limy anhydrite
anhydrite
dolomite
limestone
dolomite
limestone
dolomitic limestone
limy dolomite
shale breccia
argillite
LIT
HO
LO
GY
DE
SC
RIP
TIO
N
WELL LOG ANALYSIS
DRILLING MEASURED FROM:LOGS MEASURED FROM:LOGS MEASURED BY:
LONGITUDE:LATITUDE:
INTERVAL PLOTTED:SCALE:
PROBABLY ROTARY TABLESCHLUMBERGER
W 3 DEGREE 40.175 MINUTESN 55 DEGREE 10.863 MINUTES1920.00-2500.00 METRES1:500
PERMANENT DATUM: PROBABLY ROTARY TABLEELEVATION:
KB: 3.88 M
32.38 MSTATE / PROVINCE: DENMARK
COUNTY:
WELL:COMPANY:
HONNING VILLAGE
HONNING-1UAB MINIJOS NAFTA,LITHUANIA
FIRST RECORDED DEPTH:LAST RECORDED DEPTH:
ANALYSIS DATE:ANALYSIS PLACE:
JANUARY 2003WELL LOG ANALYSIS DEPARTMENTMARIAN KIELT MEASUREMENT DATE:
2489.5 MOCTOBER 19, 1958WITNESSED BY:
PLOT NO 1
CHROBREGO 50 ST.87-100 TORUN, POLAND
LOGS.GRUR/H0 10
GAMMA RAY LOG
1940
1960
1980
2000
2020
2040
2060
2080
2100
2120
2140
2160
2180
2200
2220
2240
2260
2280
2300
2320
2340
2360
2380
2400
2420
2440
2460
2480
DEPTHMETRES
DEPTHMETRES
LOGS.NEUTIMP/MIN0 600
NEUTRON LOG
LOGS.LLOHMM0.25 2500
LATEROLOG
GR PSEUDO-IMAGING
0 5
1924
BUNTER71
1995
Z468
2064
Z3107
2170
Z2236
2406
Z168
2474
PRE-ZECHSTEIN23
2497
LITHOSTRATYGRAPHY
LITHOLOGICAL COLUMN
claystone
anhydrite
salt
salty shalestone
salt
anhydrite
salt
anhydritic dolomite
limy shalestone
anhydrite
salt
shalestone
limy shalestone
shalestone
limy shalestone
clayey anhydrite
shalestone
limy shalestone
anhydrite
shalestone
clayey dolomiteanhydrite
shalestone
limy shalestone
shalestone
limy shalestone
clayey dolomite
limy shalestone
dolomite
anhydrite
dolomiteanhydrite
dolomite
anhydrite
dolomite
shaly breccia
argillite
LITHOLOGY DESCRIPTION
Fig. 11
Determination of basic lithofacies in the Zechstein formation (Denmark).
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Fig. 12. Construction of selected geophysical logs profiles (Poland, Miocene). The diameter effects were not taken into account.
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The verification and correction of the acoustic interval time is practically very important (removal of cycle skips and borehole diameter effects). Such corrected measurements help to identify seismic velocities.
6
Czw
artorzed +
T
rzeciorzed
24
8
25
4
Ka
jp
er d
ln
38
29
2
Wapien m
uszlow
y
21
0
50
2
Re
t
14
8
65
0
Pstry piaskow
iec srodkow
y
23
6
88
5
Pstry piaskow
iec dolny
32
2
12
08
Le
in
e
57
12
64S
tassfurt
29 12
93
Anhydryt gorny
55
13
48
Sol najstarsza
86
14
34
Wapien podstaw
ow
y
21
2
WIRE1.GR_2GAPI0 5000
WIRE3.GR_2GAPI0 3500
WIRE1.GR_2GAPI0 5000
WIRE1.CALI_1MM0 700
WIRE1.CALI_1MM700 0
WIRE3.CALI_1MM0 700
WIRE2.GR_1GAPI0 5500
WIRE3.CALI_1MM700 0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
425
450
475
500
525
550
575
600
625
650
675
700
725
750
775
800
825
850
875
900
925
950
975
1000
1025
1050
1075
1100
1125
1150
1175
1200
1225
1250
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1300
1325
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1375
1400
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1475
1500
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1550
1575
1600
1625
DEPTHMETRES
WIRE1.DTC1_2US/M500 0
WIRE1.NEGR_11000 100000
WIRE3.NENE_1MSEC20000 500000
WIRE1.EL28_2OHMM2.5 250
WIRE1.EL14_31 100
WIRE1.DTC2_1US/M500 0
Fig. 13. Verification and change of selected geophysical measurements scale (Poland, the Zechstein, Bunter Sandstone and Muschelkalk formations).
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The INZAL procedure (Zalayev N.) is very essential. It is applied to a formational interpre-tation of geophysical logs recorded in an analogue form. The procedure has several options that support the interpretation process (fig. 14 – 16).
GAMMA RAY LOGCALIPER LOG
FLUIDS FORMATION VOLUMETRICSRESISTIVITYSPONTANEOUS POTENTIAL LOG
LOGS.CALIIN-4 16
LOGS.GRUR/H0 30
LOGS.SPMV150 50
4740
4760
4780
4800
DEPTHMETRES
INZAL.RTOHMM0.1 10000
INZAL.R0OHMM0.1 10000
INZAL.KPBW%0 50
INZAL.KPW1%0 50
INZAL.KPW%0 50
INZAL.KPT%0 50
INZAL.KCL%0 100
INZAL.SAND%0 100
INZAL.KPH1%100 0
INZAL.KPH%100 0
INZAL.KPEF%100 0
Fig. 14 Formational interpretation (Poland, Miocene) (Furgal G.).
Fig. 15 Results of the formational interpretation (Poland, the Miocene and Carboniferous formations) (Furgal G.).
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Fig. 16 Results of the formational interpretation (Poland, the Zechstein and Miocene formations) (Furgal G.).
The next, very important and useful type is the interpretation of well logs performed in
the whole well and presented in depth and time scales. The results are lithological bench-marks, which also enable identification of seismic reflecting horizons.
Fig. 17 Results of a complex interpretation in a depth scale (Majak S., Pabian M., Smiechowska E.).
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Conclusions The experience acquired during the analogue and digital interpretation of well logs, knowl-
edge of the digital recording properties together with appropriate programs and methods of interpretation make it possible to recover a lot of valuable geological information, which is coded in the analogue measurements. Thus, the opinions of some geologists about a direct loss of numerous geological data contained in the analogue geophysical logs are wrong.
The conception of archives as well as accessible methodical and technical tools allows the data to be stored in databases recorded on compact and magneto-optical discs (fig. 18). This way, the analogue data archives change into ones recorded on different media.
Fig. 18. Digital database.
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