1. OBMI Processing and Structural Interpretation Well: E16-4 GDF SUEZ E&P Nederland B.V
Nadege Bize, Geologist,
Schlumberger, CEU

2. Outline
- Introduction, Scope of the study and Input Data ………..page Service Details and Workflow of the processing … page Quality Control (GPIT and OBMI image)………….…… page Interpreted Features in the OBMI image …………….…page Overview……………………………….…...…..page Bed boundaries………………………… …page Structural Analysis…………………..…………page Sedimentary dips ………………………...……page Cross beddings……………………………..….page 24 - Unconformable beds………………..….….…..page 27 - Resistive fractures………………………....…..page 32 - Drilling Induced fractures ……………………..page Statistics per formation…………………………………….page Conclusions …………………………..…………….…….. page 63 2

3. Introduction Scope of the study
This report covers log processing, quality control and interpretation of Schlumberger’s Oil-Base Micro-Imager tool (OBMI), which was acquired in the 5.875” open hole section of well E16-4, E16 Field, offshore Netherlands. This study has been conducted at the request of GDFSUEZ E&P Nederland B.V. The OBMI log was acquired while logging up from 4200 to m MD.
Scope of the study
OBMI PROCESSING
- Load the OBMI image log data into GeoFrame; Perform thorough log quality control;
Speed correct and normalize Image logs;
OBMI INTERPRETATION
- Carry out an interactive analysis by manually picking dips, finding their orientation and classifying all geological features (beddings, sedimentary features, natural and induced fractures).
- Determine the Structural dip; make a structural zonation and a stereographic analysis of the dip data sets.
Input data - GDFSUEZ_E16-4_RUNB1_MAIN_7JUN09_057PUP.DLIS - GDFSUEZ_E16-4_MainPass_069PUP.DLIS 3

4. Services Details
121.2 deg
UBI
UBI
UBI
UBI 4

5. Static and Dynamic images
Workflow of the processing
Data processing was carried out using Schlumberger's GeoFrame platform (Gf 4.4, linux). Standard techniques have been applied to the processing and interpretation of this FMI data set.
The processing chain applied to the main FMI file 007 pup is :
Data Load: To load DLIS acquisition data into a GeoFrame project.
BHGeol Formatter: To create collections for Borehole Geology modules.
GPIT Survey: To check the inclinometer/navigation data and eventually repair them.
BorEID: To apply basic corrections to raw borehole image data (speed correction).
BorNor: To create a Dynamic and Static normalization of corrected image data.
BorView: To set of interactive graphic tools and perform image interpretation;
Statpack: To provide dip vector plots.
SediView: To extract the structural dip and eventually remove it.
Speed corrections
GPIT Checks
Automatic dip picking
Static and Dynamic images
Manual Dip picking
Dip Vector Plots
Structural Dip 5

6. Quality Control – Inclinometer/Navigation (GPIT) data
The geomagnetic components (declination, inclination, field strength) derived from log values (averaged log) appear to be correct and within tolerance in comparison to those from the Interim Geomagnetic Model (IGM) with less than 1% difference.
The navigation survey cross-plots show a normal pattern for a low deviated well in which the tool does several rotations. The accelerometers and magnetometers were operating properly. 6

7. Quality Control – Tool Dynamics data7 4 6 8 2 3 5 7

8. Quality Control – Lithology and OBMI signatures
OBMI Static
Maur
There is a good correspondence between sand layers defined in the lithology column by GR cut of and highly resistive intervals on the OBMI. Then limits between the Carboniferous or Permian formations are clearly seen on the image. 8

9. Quality Control – Tool Dynamics data
Caliper Data (track 1): From the OBMI (RC1-RC2) derived calipers, borehole quality is good from TD to 3775m but shows washouts above 3775m which are affecting the quality of the image
For the whole section, small and short variations of the hole diameter drives to a high rugosity of the walls.
OBMI image (track 2): The overall quality of the OBMI image is good to medium due to high rugosity of the borehole with long stick and slip events of the tool and due to borehole enlargements above 3775m. OBMI Image was reconstructed using the speed correction in BorEID module. Conductivity contrasts are well matching with the GR changes: Clean Sand layers, with low GR are well correlated to Highly resistive intervals.
Tool Sticking (track 4 and 5): Cable tension, tool velocity and tool acceleration show abundant tool sticking events that adversely affected the image quality. 3. Cable speed (CS, average 500 m/h) was always below the maximum recommended logging speed (~1100m/h).
Tool Rotation (track 6) : P1AZ (Pad 1 azimuth) and RB (relative bearing) curves indicate several rotations below 3800m (less than the limit of one turn per 10 m) and only one rotation in the washout interval. This is a normal behavior when one of the tool arms is following the longest hole diameter.
Gravity and Magnetic Field (track 6) : Log-derived ANOR (gravitational norm) and FNOR (magnetic field norm) are both straight and within tolerance compared to IGM values. They do not show any excessive noises or defects. 9

10. Quality Control – Tool Dynamics data
Washout
Signal Saturation
The OBMI image was successfully reconstructed following speed correction. The LQC display (track 5) shows mainly events of Poor Signal (yellow dots) to Signal Saturation (blue dots) where the image quality is locally decreased. In the interval m one of the pad readings are saturated but image still can be analyzed with three other pads information. Lower part of the interval was logged with severe sticking events, and some intervals are also unreliable to pick dips. Upper part is of better quality excluding washed out zone around m MD. 10

11. Example of good image quality showing numerous cross beddings (orange plus tadpoles).1 4 3 2
Example of low confidence interval where only one bed can be picked. 1 to 4 represent the 4 OBMI pads. For this interval, pad 4 was not touching the formation; pad 2 and 3 show also bad readings. In these conditions, no dips are reliable. 11

12. Interpreted features – Overview
OBMI borehole image covers 50% of the borehole in a 5.875” borehole. All the 2945 dips interpreted across the 625 m of OBMI image were assigned into 9 dip sets. The high number of dips represents a good data base to carry out a detailed structural dip analysis and a fracture characterization.
1265 bed boundaries, 548 sedimentary beds, 679 cross-beddings, 219 unconformable bed boundaries, 128 resistive fractures, 55 Drilling Induced fractures have been picked.
Permian
Beds
Fractures
Carboniferous
Beds
Sedimentary dips
Fractures 12

13. Interpreted features – Bed boundaries
Bed Boundary (1284 green tadpoles) are planar features identified as bedding planes, deposited in a low energy environment with abundant claystones or fine grained sediments. They are considered as indicators of the structural dip.
Their distribution is uniform throughout the whole interval except between 3950m and 4050m where the poor quality of the image does not allow to pick reliable dips and above 3700m where sets of cross beddings are well developed.
They show a general SSW azimuth trend and low magnitude (<5 deg).
Deposits are dated from Carboniferous to Permian. The Major Saalian unconformity is visible on the Image as an erosive surface at 3844m. The general SSW azimuth trend for the beds is not changing between Carboniferous and Permian.
Permian
the
3844m
Saalian Unconformity
Carboniferous 13

14. Interpreted features – Beddings and Structural information
Whole interval m-4200m a) c)
190 – 220 deg b) d)
a) General Distribution of the bed boundaries for the whole interval.
b) Rosette azimuth clearly shows a main dip direction towards SSW.
c) Dip azimuth histogram confirms this direction with a maximum of dip distribution between 190 deg and 220 deg.
d) Dip frequency indicates that 90 % of magnitudes are less than 5 deg. 14

15. Example of Bed Boundary-Structural dip- Upper HPLGRD
Example of beds consistently dipping S with 2 deg average magnitude in silt/fine sandstone formations. Sands layers are perfectly matching with low GR (black box). 15

16. Example of Bed Boundary-Structural dip - LSILCL
Most of the bed boundaries are picked in Shales and Silt formations. Here, they are consistently dipping SSW with less than 5 deg magnitude. Static Image shows conductive sediments and the good quality of the image allows to pick thin layers less than 3 cm thick. 16

17. Interpreted features – Beddings and Structural information
Whole interval m-4200m
Dip Vector Plot
SSW
Saalian Unconformity TD
Top
Dip Vector Plot for Dip Magnitude shows magnitude less than 5deg (red line).
Azimuth is consistently towards SSW for Carboniferous and Permian formations.
Dip Vector Plots have been computed per formations, see page 39.
SediView
Structural analysis was performed assuming that the manually picked ‘Bed Boundary’ dip category with 1289 data points would best represent the structural dip.
The projection of these dips on an Upper Hemisphere Steronet shows a general structural dip angle of 3.4 deg for deg azimuth with a 1.2 deg fit.
The small 1.2 deg fit indicates that the all section corresponds to only one structural unit even if a stratigraphical unconformity separates Carboniferous to Permian formations at 3844m. 17

18. Structural dip information per formations
Permian
Carboniferous
Maur
For North sea basins, final phase of Variscan folding and thrusting uplifted carboniferous sediments and resulted in the formation of a marked erosional boundary: the Saalian unconformity. On the OBMI image, this unconformity can be seen at 3844m but there is no drastic change for dip orientation or magnitudes between Carboniferous and Permian deposits. They are in concordance. Structural dips computed per formation show similar values, from 3.1 to 5.4 deg magnitude with 197 to 207 deg azimuth. 18

19. Seismic section oriented SW-NE with Formation Tops
BZECH
CARB
HPLGRD
MAURTS
Structural cross section has been displayed using a mega green model for dips and with a SW-NE orientation, SE point of view. 19

20. Seismic section oriented NW-SE with Formation Tops
BZECH
CARB
HPLGRD
MAURTS
Structural cross section has been displayed using a mega green model for dips and with a NW-SE orientation, SW point of view. 20

21. Carboniferous- Permian unconformity (Saalian Uconf.)
Saalian Unconformity between Carboniferous and Permian corresponds to an erosional surface at 3844m separating silts (Carb.) with low angle dips to sands (Perm.) with cross beddings. Within continental deposits, numerous erosional surfaces are visible on the OBMI and it is not easy without regional information to classify them.
First Permian deposits are highly resistive and are a good marker for further well correlations. they correspond to the base of LSILCL formation.
Top Carboniferous depth map (Saalian unconformity) 21

22. Interpreted features – Sedimentary dips
The red color code has been used for planar features known as sedimentary dips and characterized by high dip magnitudes (10-30 deg) and constant azimuths.
448 sedimentary dips were manually picked across sandstone/silt lithologies. They were mostly deposited in a relatively high energy environment and are considered as indicators of depositional currents.
Set of sedimentary dips with high magnitudes but same azimuth are indicators of unidirectional currents. Constant magnitudes indicate also vertical accretion common in fluvial braided environments. It is confirming GDF’s paleo-environments interpretation for these deposits.
For vertical accretion, direction of the dips is directly the direction of the paleo-current.
They are mainly concentrated in the lower section of the well (4040m-4160m) in the carboniferous formations (HPLGRD).
Next pages correspond to their statistical analysis for the whole interval. Analysis per formations are displayed page 39.
Permian
Carboniferous
HPLGRD 22

23. Interpreted features – Sedimentary dips Whole interval 3520m – 4200m
10 – 90 deg
a) General Distribution of the sedimentary dips for the whole interval. Results are displayed without structural dip removal.
b) Rosette azimuth shows dip directions from North to East.
c) Dip azimuth histogram confirms this direction with a maximum of dip distribution between 10 deg and 90 deg.
d) Dip frequency indicates that 60 % of magnitudes are more than 10 deg. N E
3990
4060
4090
3930
3880
Dip vector for sedimentary dips
Top
3182
Dip vector for sedimentary dips indicates a general NE trend (blue arrow) with some local variations between 4090m and 3990m. Results are displayed without structural dip removal. TD 23

24. Example of Sedimentary dips- U-STGRAB
Erosional surface
Example of sedimentary dips consistently dipping NNE in a sand body (low GR, red box). All sedimentary dips have higher magnitudes (more than 10 deg) and different azimuths than the structural dips below (green tadpoles). They are surrounding an erosional surface and correspond to vertical accretion deposits (same azimuths, same high magnitudes). 24

25. Example of Sedimentary dips - Lower HPLGRD
Erosional surface
Erosional surface
Example of 3 sets of sedimentary dips with North to East azimuth trends. They are separated by erosional surfaces (red circles) and correspond to high energy level deposits in a braided fluvial system. 25

26. Interpreted features – Cross beddings
612 orange tadpoles correspond to cross beddings with varying magnitudes (10 deg to 30 deg) and high range of azimuths.
They are multi-directional current deposits and indicators of a medium to high energy environment.
They are more present in the upper carboniferous (upper STGRAB) and all Permian formations above 3840m.
They are common in braided fluvial systems when water level is high and they can alternate with vertical accretion.
Permian
Carboniferous 26

27. Interpreted features – Cross beddings
Whole interval 3520m – 4200m
a) General Distribution of the Cross beddings for the whole interval.
b) Rosette azimuth does not show a main dip direction. Azimuths are highly variable.
c) Dip azimuth histogram confirms the spread distribution of direction.
d) Dip frequency indicates that 85 % of magnitudes are more than 10 deg.
Erosional surface
On the image, cross beddings correspond to thin layers with different azimuths in silt/fine sand bodies. For some intervals, the OBMI coverage with less than 50% limits their interpretation and then it is difficult to differentiate, cross bedding from low angle resistive fractures or artifacts. Sets of cross beddings are generally limited by 2 unconformable bed boundaries (minor erosional surface in red circle). 27

28. Examples of Cross beddings
Erosional surface
Erosional surface
Cross beddings have scattered dip azimuths and magnitudes varying between 15 and 30 deg. Sets are generally limited by 2 unconformable bed boundaries (red circles) corresponding to minor erosional surfaces. Deposits are resistive clean sands or more conductive silty sands. 28

29. Interpreted features – Unconformable Bed boundaries
211 Unconformable bed boundaries correspond to highly variable angle surfaces showing a non conformance appearance with respect to surrounding bed boundaries. As seen from rosette plot in track 4 there is no dominant azimuth direction for these surfaces in this well.
Carboniferous and Permian formations correspond to continental deposits and the majority of these surfaces are erosional surfaces at the base of sedimentary dip or cross bedding sets.
They are well spread from Carboniferous to Permian.
They can be minor erosional surfaces, internal to sedimentary dips / cross bedding sets, or major (pink square tadpoles), separating different types of deposits and highlighting a change in energy level deposition.
Unconformities, as Saalian unconformity (3844m) appear as major erosional surfaces (major unconformable bed but since we do not see a change of structural dip, from the image they can not be classify as Unconformity.
Permian
Carboniferous 29

30. Unconformable beds=minor erosional surfaces
Interpreted features – Unconformable Bed boundaries
a) General Distribution of the Unconformable beds for the whole interval.
b) Rosette azimuth shows variable dip azimuth.
c) Dip azimuth histogram confirms there is no main azimuth trends
d) Dip frequency indicates that 80 % of magnitudes are more than 10 deg.
Unconformable beds=minor erosional surfaces
Example of unconformable beds corresponding to sand arrivals in silt/shale deposits. These erosional surfaces have higher magnitudes than the bed boundaries below but can not be classified as disconformities/unconformities. 30

31. Examples of Unconformable beds - LSILCL2 2 2 1
In red circles: example of erosional surfaces separating different sets of cross beddings.
Surface 1: major erosional surface separating 2 different types of sedimentation. Environment energy level changed from quiet with shales /silts deposition to multidirectional flows with sand cross beddings deposition. Surface 2: minor erosional surface, internal to cross bedding sediments do not show variation of environment. 31

32. Examples of Unconformable beds Lower STGRAB
In this example, a major erosional surfaces is separating two different types of sedimentation (conductive silt/shales form resistive clean sands). 32

33. Interpreted features – Resistive Fractures
Density
Azimuth
Strike
Permian
Carboniferous
128 resistive Fractures correspond to high amplitude and bright sinusoids. Since the drilling fluid is non-conductive, they could be assumed both as closed/cemented or opened to fluid flow. Their mean dip magnitude is 40 deg and strikes are varying along the section.
Fracture density in track 6 indicates that they are mainly concentrated in the Permian from 3650m to 3705m and from 3720m to 3740m (SILEV formation). 33

34. Interpreted features – Resistive Fractures
Magnitude
75%
Strike
Azimuth
Strike
NNW NE
ENE
WNW
WSW
ESE
Dip histogram shows that 60% of the Resistive fracture magnitudes are between 40 and 60 deg. Rosette strike plot confirms several strike orientation NNW-SSE / WNW-ESE / NE-SW SW
SSE 34

35. Interpreted features – Resistive Fractures
Unclassified
Unclassified
Examples of well developed resistive bright fractures showing several strike directions. With 50% coverage of the borehole some features are difficult to picked or classify. For this interval, we may have more fractures. With double coverage a dual OBMI will add more information. 35

36. Interpreted features – Resistive Fractures
Erosional surface
Examples of well developed resistive bright fractures showing several strike directions. 36

37. Interpreted features – Drilling Induced Fractures
Permian
Carboniferous
Mostly present in Carboniferous formations (Lower HPLGRD and upper STGRAB), these features are representative of the direction of the present day NNW-SSE maximum horizontal stress in a near-vertical well. Several drilling induced fractures have been identified across the whole interval showing a unique character: en-echelon shear discontinuous white traces. They are the result of the stress under balance in the borehole between the mud pressure, formation pressure and the stress regime in a near-vertical well. 37

38. Interpreted features – Drilling Induced Fractures
From the rosette plot maximum horizontal stress direction is NNW-SSE ( deg.). It is matching to the general direction of the stress for this area (see stress World Map bellow).
SSE
NNW
Magnitudes
Drilling Induced fractures appear as parallel in echelon resistive sinusoids (red arrows).
E16-4

39. Statistics per formations
TD-4168m MD Maurits Fm.
OBMI Static
Sedimentary dips
Beds
Fracture density
m: Unconformity 39

40. Resistive Fracture Strikes
TD-4168m MD Maurits FM.
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 4.5 deg for 207 deg azimuth (SSW) with a 1.3 deg fit.
Resistive Fracture Strikes 40

41. Unconformable bed boundaries
TD-4168m MD Maurits Fm.
Sedimentary dips
4197m
Unconformable bed boundaries
At m an erosive surface may be the upper limit of Maurits formation. It separates conductive siltstones to more resistive clean sandstones. 41

42. Resistive fracture strikes
Statistics per formations
4168m – 4060m MD Lower HPLGRD
OBMI Static
Cross beddings
Sedimentary dips
Resistive fracture strikes
Beds
4060m
Fracture density
4168m 42

43. Resistive Fracture Strikes
4168m – 4060m MD Lower HPLGRD
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 3.4 deg for 200 deg azimuth (SSW) with a 1.2 deg fit.
Resistive Fracture Strikes

44. Unconformable bed boundaries
4168m – 4060m MD Lower HPLGRD
Sedimentary dips
4080m
4111m
4127m
4145m
Unconformable bed boundaries 44

45. Resistive fracture strikes
Statistics per formations
4060m MD Upper HPLGRD
OBMI Static
Cross beddings
Sedimentary dips
Resistive fracture strikes
Beds
4037m
Fracture density
4060m 45

46. Resistive Fracture Strikes
4060m MD Upp HPLGRD
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 2.3 deg for deg azimuth (SSW) with a 1.3 deg fit.
Resistive Fracture Strikes 46

47. Unconformable bed boundaries
4060m MD Upp HPLGRD
Sedimentary dips
4043m
4050m
4055m
Unconformable bed boundaries
4037m
Upper limit of HPLGRD formation is an erosive surface at m surrounding by a 2m thick clean sand interval. 47

48. Resistive fracture strikes
Statistics per formations
m MD- Lower-STGRAB
OBMI Static
Cross beddings
Sedimentary dips
Resistive fracture strikes
Beds
Fracture density
3960m
4037m 48

49. Resistive Fracture Strikes
m MD- Lower-STGRAB
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 3.3 deg for 208 deg azimuth (SSW) with a 1.1 deg fit.
Resistive Fracture Strikes

50. Unconformable bed boundaries
m MD- Lower-STGRAB
Sedimentary dips
3990m
Unconformable bed boundaries
There is no evidence of a major unconformity on the top of the Sand layer between 3966 m and 3958m. It may correspond to an unconformable bed at m. However, at the base of the clean sand interval, a sharp erosive surface at 3955,5m is picked. 50

51. Resistive fracture strikes
Statistics per formations
3960m-3844m MD- Upper-STGRAB
OBMI Static
Cross beddings
Sedimentary dips
Resistive fracture strikes
Beds
3844m
3960m
Fracture density 51

52. Resistive Fracture Strikes
3960m-3844m MD- Upper-STGRAB
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 3.1 deg for deg azimuth (SSW) with a 0.9 deg fit.
Resistive Fracture Strikes 52

53. Unconformable bed boundaries
3960m-3844m MD- Upper-STGRAB
Sedimentary dips
3990m
Unconformable bed boundaries 53

54. Statistics per formations
3844m-3750m MD LSILCL
OBMI Static
3750m
3844m
Fracture density 54

55. Resistive Fracture Strikes
3844m-3750m MD LSILCL
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 3.4 deg for deg azimuth (SSW) with a 1.5 deg fit.
Resistive Fracture Strikes 55

56. Unconformable bed boundaries
3844m-3750m MD LSILCL
Sedimentary dips
Unconformable bed boundaries 56

57. Resistive fracture strikes
Statistics per formations
3750m-3637m MD- SILEV
OBMI Static
Cross beddings
Sedimentary dips
3637m
Resistive fracture strikes
Beds
3750m
Fracture density 57

58. Resistive Fracture Strikes
3750m-3637m MD- SILEV
Bed Boundaries
3650
Bed Boundaries – Structural dip
Structural dip: 3.1 deg for deg azimuth (SSW) with a 0.9 deg fit.
Resistive Fracture Strikes 58

59. Unconformable bed boundaries
3750m-3637m MD- SILEV
Sedimentary dips
3990m
Unconformable bed boundaries
Two unconformable beds, at m and m can correspond to the upper limit of SILEV formation. 59

60. Resistive fracture strikes
Statistics per formations
3637m MD-Top - USILCL
OBMI Static
Cross beddings
Sedimentary dips
Resistive fracture strikes
3637m
Beds
Fracture density
With only 3 dips statistic for sedimentary dips have no value 60

61. Resistive Fracture Strikes
3637m MD-Top - USILCL
Bed Boundaries
Bed Boundaries – Structural dip
Structural dip: 3.8 deg for deg azimuth (SSW) with a 1deg fit.
Resistive Fracture Strikes

62. Conclusions
The overall quality of the OBMI image is medium to good due to high rugosity of the borehole with stick and slip events of the tool and due to borehole enlargements above 3775m. However 2761 dips could be picked with a high level of confidence for the 625m of OBMI.
1265 bed boundaries representative of the structural dip indicate a main SSW azimuth direction of dipping with low magnitudes. For the whole interval, their projection on a Stereonet shows only one structural unit dipping 3.4 deg for deg azimuth. Here, Carboniferous layers seems in concordance with the Permian bed boundaries.
In these continental deposits, Sedimentary dips (548 layers picked) are recognized mainly in coarser-grained sandstone sections (from meter to few meter thick) of the Carboniferous. They correspond to high energy environment dominated by unidirectional currents (vertical accretion).
Cross beddings (675 layers picked) with varying magnitudes (10 deg to 30 deg) have been also interpreted as multidirectional current deposits and indicate medium to high energy environments. They are more concentrated in the Permian formations. Sedimentary dips and cross beddings are common in braided fluvial environments.
219 Unconformable bed boundaries correspond to minor erosive surfaces (211 dips), internal to sedimentary dips / cross bedding sets, or major erosion surfaces (8 dips), separating different types of deposits and highlighting a change of the deposition energy level. Limits between the different formations are:
m : between Maurits Fm and lower HPLGRD
m: between lower HPLGRD and Upper HPLGRD
m: between Upper HPLGRD and Lower STGRAB
- 3844m: Saalian Unconformity between Carboniferous and Permian
m: between LSILCL and SILEV.
128 resistive fractures are mainly concentrated in the Silverpit evaporates (SILEV) from 3650m to 3705m and from 3720m to 3740m. They show 3 strike trends: NNW-SSE / WNW-ESE / NE-SW.
Strikes are consistent with E17 fractures strikes, but does not allow to discriminate opened and closed fractures because of the nature of the mud (Oil Based Mud). In this particular logging environment, we would recommend a sonic tool such as UBI to be able to distinguish opened from closed fractures.
Only one syn-sedimentary micro-faults have been interpreted from OBMI image.
55 Drilling induced fractures present in Carboniferous formations indicate a NNW-SSE maximum horizontal stress in this near-vertical. 62