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Submitted on 8 Jul 2015
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SEISDIP: Dip and Azimuths from 3 Component Vertical Seismic Profiles (3C -VSP).
Charles Naville, Sylvain Serbutoviez, Josette Bruneau, Alexandre Throo, Hubert Japiot, Renaud Daures, Jean-Yves Gaborit
To cite this version:
SEISDIP
TM
: Dip and Azimuths from 3 Component
Vertical Seismic Profiles (3C
-
VSP)
C. Naville, S. Serbutoviez, J. Bruneau, A. Throo
Institut Français du Pétrole, Rueil-Malmaison, France
H. Japiot, R. Daures, J.Y. Gaborit
Compagnie Générale de Géophysique, Massy, France
3C oriented with a hardwave device and 3C isotropic recording processing P-wave polarization measurement and application of the Snell-Descartes law
Principle of the method
Application
of Snell-Descartes law VSP imaging in deviated well Uncorrect VSP interpretation
Conventional VSP-CDP stack built from monocomponent processing and monoclinal
interface modelling of the well vicinity
TD at 900m offset, 2150m Vert. Depth Geophone Illuminated zone Probable lateral extention of the reflector Probable lateral extention Impossible lateral extention of the reflector, because there is Impossible lateral extention of the reflector HT HR Z Source, 600m offset no corresponding reflected energy
Well Source, 600m offset
TD at 900m offset, 2150m Vert. Depth Geophone
Accident in the well vicinity accounting for the observed
interference and reflector interuption, from unknown relative azimuth Well D = Direct wave R = Reflected wave
N= Normal to the reflector, defining Dip & Azimuth
N is obtained as the bisector of ( D , R ) angle for a reflector right under the geophone G, corresponding to the VSP corridor stack domain
Source Well G N D Dipping reflector
Sketch of geological flexure Vertical plane of well deviation
Picked horizons Interfered reflections Erroneous interpretation as an accident H1 H3 H4 H2
P-wave 3C-ISOTROPIC reflected wavefield
Z component HT component HR component
When source is above VSP tool, energy on HR or HT denotes strong dips
Monocomponent Standard Processing
Dip determination on 4 key reflectors
by inversion of time and polarization
Application 1
Mirror point location in horizontal plane Mirror point location in vertical plane of deviation
DIP/Azimuth Crossplot
500 6°W 10°W 20°W -1700 -1900 -2100 Depth (m) from GL W ell trajector y Flexured layers Source offset TD 700 900 1100 Offset (m) from well head
Dip on H3 ( ) 0 -400 -200 Source location Well trajector y North East 800 1000 6°W 10°W 20°W Dip on H3 ( ) 0 90 180 270 360 North South West Dip (degree) Azimuth (degree) East 0 10 20 30 H1 H2 H3 H4 Picked horizons H1 H3 H4 H2
P-wave 3C-ISOTROPIC reflected wavefield
When source is above VSP tool, energy on HR or HT denotes strong dips
H1 H2
H3
H4 Well
Dip determination along the borehole by polarization
inversion in the VSP corridor stack domain
Application 2
VSP dipmeter" results ( ) compared with conventional microresistivity Dipmeter log ( )
Courtesy of PETROREP, France
DIP ANGLE AND DIRECTION
140 BCS T 40
H3 H3
H3 (2330 m):10°/260°E
DIP ANGLE AND DIRECTION
140 BCS CAVING Cycle Skipping True value T 40 H4 H4 H4 (2427 m):7°/290°E
DIP ANGLE AND DIRECTION
H1 (2022 m):6°/280°E
140 BCS T 40
H1 H1
BCS : Borehole Compensated Sonic 6 arm Dipmeter results on Tad pole plot
DIP ANGLE AND DIRECTION
140 BCS T 40
H2 H2
H2 (2022 m):5°/310°E
• yields to the structural dip of seismic interfaces in the well vicinity
• is unsensitive to caves, OBM, casing • can see below the well bottom
The VSP "dipmeter"
• restitutes the dip at high vertical resolution, locally on the borehole wall only
• works in open hole only, with good borehole conditions
for the orientation of 3 Component VSP data
Suggestions
Orientation using the direct P-wave arrival polarization at processing stage is cumbersome, time consuming, often unreliable, sometimes impossible in case of interfered direct arrival
Thus a hardware orientation device is systematically recommended in combination with the VSP tool at acquisition stage:
In the BINNACLE setting, one gimbal is free to rotate around the (Xarm) axis orthogonal to the tool axis (W) in the plane of arm opening, but with an unknown orientation; the other gimbal is free to rotate around the horizontal axis (YT).
Recorded orthogonal components : Zup (vertical), XT, YT (horizontal)
in deviated well (vertical deviation angle DEV > 8°) cased or open hole, double Gimbal mounted geophones with Trunnion setting, complemented with knowledge of the well trajectory, allow for unequivocal orientation of the 3 Components
The Binnacle double gimbal setting does not allow for complete knowledge of the 3C orientation as the Relative Bearing (RB) angle of the VSP tool is needed, thus the Binnacle
setting is not recommended •
in near vertical well (DEV< 8°), an orientation accessory such as a gyroscope or a inclinometer/
magnetometer has to be combined with the VSP tool, without deteriorating the mechanical VSP tool coupling to the formation or generating unwanted power induced seismic noise on the tool
geophones. Commercial inclinometer/magnetometers are widely used in wireline logging, and
are efficient down to very small well deviations (DEV < 1°- 2°) in cased hole
• Zup well axis W YH X - HAZI Zup W XT YT Xarm Zt=W RB DEV Vertical RBO Xarm Yarm
Description of the gimbal mounted geophone settings
:
In the TRUNNION setting, one gimbal is free to rotate around the VSP tool axis (W), the o t h e r g i m b a l i s f r e e t o r o t a t e a r o u n d t h e horizontal axis (YH) orthogonal to the well deviation vertical plane. X-HAZI is oriented toward Hole AZimuth direction ( 360°).
Recorded orthogonal components : Zup (vertical), X-HAZI, YH (horizontal)
Recorded orthogonal components are fixed in the tool : Zt (tool axis), Xarm, Yarm. Receivers are omnitilt.
Xarm orthogonal to well axis W in the plane of arm opening. RBO is in the vertical plane and orthogonal to tool axis W.
Where
?
Warning
How
?
High cost wells in areas where the results from conventional methods are unsatisfactory due to : • surface seismic image blurred at target level, not necessarily at large depth
• difficult borehole conditions affecting the acquisition of wireline logs or the quality of their measurement: logging tool sticking to the borehole wall, irregular logging speed, caving, OBM, etc ...
The SEISDIP technique represents an independent and reliable method to obtain the
structural dip/azimuth in the well vicinity, potentially up to a distance of a few hundred meters
away from the well and below Total Depth, based on oriented 3C VSP data and isotropic
processing
The "VSP dipmeter" SEISDIP method complements the dip results obtained by other methods, such as surface seismic and wireline microresistivity dipmeter log
The "VSP dipmeter" SEISDIP method offers an alternative solution to attain the dip when the other methods fail
Conclusion
Recommendations for the application of the SEISDIP method
By combining a hardware orientation device to the VSP tool for acquisition of single run/single rig source VSP's in vertical/deviated well, especially if the well is vertical over and above the target depth interval
If gimbal mounted geophones are to be used in deviated wells (DEV>8°), gimbal geophones need
to be mounted on a Trunnion setting in the VSP tool
If a inclinometer/magnetometer tool or a Gyroscope has to be combined with a VSP tool, it is
highly recommended to contact your VSP contractor 15 days prior to VSP acquisition in order
