structure and pattern recognition

7/27/2019 Structure and Pattern Recognition

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Structure and Pattern Recognition

Structure and Pattern RecognitionObjec t ive o f t h i s Chap te r :

Recognition the basic dip patterns of:

Red - downdip thickening Blue - downdip thinning Green - constant section

These patterns will be used to define:

Structural dip from the green patterns.

Copyright 1999

Schlumberger Oilfield Services

4100 Spring Valley Road, Suite 600, Dallas, Texas 75251

Reproduction in whole or in part by any process , including lecture, is prohibited.

Printed in U.S.A.

Version 9.2


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Structural AnalysisStructural analysis consists of defining the structural dip and the evaluation of unconformities andfaults.

Dipmeter ProcessingDipmeter processing of the data recorded with the electrical images is an excellent quick look fordetermining structural dip as well as for locating some faults and unconformities. Dipmeterprocessing is very useful in resolving low structural dip.

Structural DipDip computation of either the borehole images or dipmeter processing is a measurement of structuraldip and not regional dip. Regional dip, as determined from multiple well logs is an area, can bedifferent from structural dip resolved from a single well. Dips computed from either boreholeimages or from dipmeter can be influenced by compaction or structural changes. The figure oppositeillustrates the influence of compaction and structural uplift.

Structural dip is a n average of many dip co mputations ; therefore, a dipme ter plot will yield thestructural dip more accurately than a point by point manual computation in low structural dipsituations. A long correlation length, eight feet, will usually yield an accurate dip. In higherstructural dips, image analysis can provide higher confidence data. The two types of processing docompliment each other. Structural dip and mega-patterns from dipmeter processing will be presentedfirst.

Regional Dip vs. Structural Dip

R e g i o n a l D i p

Rule : Structural dip may be projected horizontally as far asthe green pattern extends vertically.

S t r u c t u r a l D i

p


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Structural Dip v s. Regional Dip ExampleAn example opposite illustrates the importance of structural dip determination. Well No. 1penetrated a carbonate at 3814 ft. There was a strong oil show. Regional dip was 1SSW. Well No.2 was located 2210 ft to the NNE and did penetrate the carbonate in a much better structural positionas 3754 ft. This was the expected depth from regional dip projection. Well No. 2 produced oil atthe rate 55 BOPD but with 120 BWPD. A dipmeter was run in Well No. 2. The structural dip wasdetermined to be 2 NNE. This indicated a closure to the SSW, which is regionally downdip. WellNo. 3 was located 736 ft WSW of Well No. 2 and along the WNW-ESE structural strike. Final welllocation was 100 ft to the ESE of Well No. 2. (A well located only 736 ft from a marginal well wasnot deemed to be politically sound). Well No. 3 produced oil at the rate of 200 BOPD with no waterproduction. Structural dip determination is very important in locating potential closur es.

Example of Regional vs. Structural Dip

Subsea at Pay Zone Production Structural Dip

No. 22NNE

No. 1Assumed

1SSW

No. 3

Flat Dip

2/3

1/3

N

2210 f t

Re giona l Dip = 1 SSW

Structu ral D ip

Well No. 3 3 7 54200 BOPD0 BW P D

Well No. 2 37 7 65 5 B O P D + 1 2 0 B W P D2 N NE

Regiona l DipWell No. 1

38 1 4Oi l Show?


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Dip PatternsThere are four basi c groups of dip pat terns defined b y Al Gilreath:

Downdip thinning Blue

Constant downdip Green Downdip thicken ing Red

Random Bedding Yellow

All patterns must have a constant azimuth, but the dips either increase upward, decrease upward, orremain constant.

0

NWSEN

Blue Pattern:Constant Azimuth

Increasing Upward MagnitudeDowndip Thinning

N

E

W

S

0 30 60 90

Downdip to NE

or zonta ert ca

45

Dipmeter

Dip AngleFrom Horizontal

Borehole

0

SENWS

Red Pattern:Con stant Azimuth

Decreasing U pward Magnit udeDowndip Th icken ing

NE

WS

DipmeterBorehole

FMS

0

NWSEN

Green Pattern:Con stant Azimuth

Constant Magn itude

Constant Downdip Section

N

E

W

S

DipmeterBorehole

FMS - BORMAP

ConstantSectio n

DowndipThickening

Blue:Downdip Thinning

Green:Constant Thickness

Red:Downdip Thickening


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Pattern Recognition Exercise 1Objec t ive : Determination of dips and mega -patterns from arrow plots.

Ques t ions : Complete the blanks opposite.

Pattern Recognit ion Exercise 1

7 2 0 0

7 0 0 0

6 8 0 0

6 6 0 0

6 4 0 0

0 90Tad pol e ( de g )

Magnitude Azimuth

Construct Arrow Plot of

45 10017 34575 335

Mark the patterns (red, blue, green)


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Borehole Drif tUnless controlled, the magnitude and direction of borehole drift is a useful indication of structuralevents. The borehole deviation is presented much as the dipmeter arrow plot. The body of thetadpole indicates the magnitude of the borehole deviation and is measured with reference to gravity.The arrow points in the direction of borehole drift and is measured with reference to magnetic northbut presented as true north.

Borehole drift in a consolidated formation will vary with the structural dip and with the boreholefluid. The bit will drift updip in mud drilled boreholes and downdip in air drilled boreholes. Themagnitude of drift reflects the structural dip in the lower dip ranges but does not respond when thestructural dip exceeds approximately 60.

Borehole Deviation Borehole Drifts - Consolidated

Updip in mud drilled boreholes Downdip in air drilled boreholes

Borehole Drifts - Unconsolidated and Flat Dip

Tend to spiral Doglegs may occur at

Faults Unconformities

Structural dip changes

Borehole Drift

0 10

Drift is to the NE at

5 from ver tical

Calipers Pseudo-Images 0 Dips 90 Drift0 20


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Pattern Recognition Exercise 2Objec t ive : Pattern recognition.

Ques t ions : Mark the dip patterns.

AzimuthFan

Plot

BoreholeDrift


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Ques t ions : Mark the patterns.


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Ref: True~ 445 samples ~

: All

900 Tadpole (deg)

10300

10400

10500

10600

~ Scale 1 : 388 ~

CAUTION:If a fracture/dip belongs toseveral sets it will be codedaccording to the latestShow selection.

Well Overview: 10300.0 - 10600.0 ft - FracView 1. 3A


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Pattern Recognition Exercise 4Objec t ive : Pattern recognition with structural dip.



: All

900 Tadpole (deg )

10300

10400

10500

10600

~ Scale 1 : 388 ~

CAUTION:If a fracture/dipbelongs toseveral sets itwill be codedaccording tothe latestShow selection.

Well Overview: 10300.0 - 10600.0 ft - FracView 1.3A

Ref: Relative~ 124 samples ~

: All

900 Tadpole (deg )

10300

10400

10500

10600

~ Scale 1 : 388 ~

CAUTION:If a fracture/dipbelongs toseveral sets itwill be codedaccording tothe latestShow selection.


If structural dip greater than 4 then always use the structural dip subtract (relative) when markingdip patterns.


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Structural Dip Exercise 1Objec t ive : Determination of structural dip from arrow plots.

Ques t ions : What is the structural dip?

An offset located 1000 structurally up dip should gain ____________ feet.

1000

Structural gain = ___________ ft.


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8400

8300

8250

8200

0 9 0Tadpo le (deg )

G R (A PI) 1 5 0

Ref : T rue~ 3 4 5 S a m p le s ~

: A l l

~ S c a l e 1 : 3 2 1 ~

CAUTION:If a frac ture/ dip belongsto several s ets i t wil l becoded acco rd ing t o thelatest 'Show' selection.

W el l O v e r v ie w : 5 0 0 0 .0 f t - 9 0 0 0 . 0 ft - F r a c Vi e w 1 .3 A

8350

0


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0 60 120 180 240 300Orientation: North

TD:67/260

TD:10/95TD:15/90TD:13/90

TD:3/350

TD:51/71

TD:65/250

TD:27/259

TD:26/256

TD:62/87

TD:12/301

TD:10/329TD:6/325

TD:15/256

TD:11/313

TD:11/302

TD:10/253

TD:60/75

8262

8260

8258

8256

8254

8252

8250

82482514

2515

2516

2517

2518

Display 1 ; scale 1/20


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0 90Tadpole

(deg)


: All6750

6800

6850

6900

~ Scale 1:221 ~

Caution: If a fracture/dip belongs to severalsets it will be codedaccording to the latestShow selection.



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: E x a m p l e s e

t

: A l l o t

h e r s

A z i m u t

h H i s t o g r a m

R e f : T r u e ,

N . H

e m i s p h e r e

~ 1 5 0 s a m p l e s ~

S t e r e o n e t : 6

7 5 0 . 0 - 6

9 0 0 . 0 f t - F r a c V

i e w

1 . 3 A

S t e r e o n e t : 6

7 5 0 . 0 - 6

9 0 0 . 0 f t - F r a c V

i e w

1 . 3 A

: E x a m p l e s e

t

: A l l o t

h e r s

W u l

f f S t e r e o n e t

( U p p e r

H e m

i s p h e r e )

P o l e s

t o p l a n e s

R e f : T r u e ,

N . H e

m i s p h e r e

~ 1 5 0 s a m p

l e s ~

E x a m p l e s e

t :

2 . 1 / 3 1 4

M e a n o r

i e n t . : d i p

/ a z i m u t

h

: E x a m p l e s e

t

: A l l o t

h e r s

R e f : T r u e

~ 1 7 2 s a m p l e s ~

F L I P V e r s

i o n

4 . 4 A

( C ) S c

h l u m

b e r g e r

1 9 9 0

C A U T I O N :

I f a

f r a c

t u r e

/ d i p

b e l o n g s

t o s e v e r a

l

s e t s i t w

i l l b e c o

d e d

a c c o r d

i n g

t o t h e

l a t e s t

S h o w

s e l e c t

i o n .

~ S c a l e

1 : 2 2 1 ~

W e l

l O v e r v

i e w : 6

4 7 7 . 0 - 7

0 0 6 . 5

f t - F r a c V

i e w

1 . 3 A

6 7 5 0

6 8 0 0

6 8 5 0

6 9 0 0

0

9 0

T a d p o

l e ( d e g

)


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Structural Dip Exercise 4Question: What is the structural dip?

RAB Images / Dips Electrical Images / Dips


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Structural Dip Exercise 5Quest ion: What is the structural dip?

1 1 2 2 4

1 1 2 2 5

1 1 2 2 6

1 1 2 2 7

1 1 2 2 8

1 1 2 2 9

1 1 2 3 0

1 1 2 3 1

I m a g e

1 1 2 1 9 -

1 1 7 3 5 F t -

F r a c

V i e w

1 . 3

L I P V e r s i o n

4 . 4 A - (

C ) S c h

l u m

b e r g e r

1 9 9 0

1 1 0 8 0

1 1 2 5 0

W

N S

E

S t e r e o n e t :

1 1 0 0 0 . 0 -

1 1 6 9 0 . 0 f t

. - F r a c V

i e w

1 . 9 A

W e l

l O v e r v

i 3 e w :

0 0 9 0

. 0 -

1 1 6 3 0 . 0 f t -

F r a c V

i e w

1 . 3 A

0

9 0

T a d p o l e

( d e g

)

R e f :

T r u e

~ 6 0 s a m p

l e s ~

: A l l

W u

l f f S t e r e o n e t

( U p p e r

H e m

i s p

h e r e )

P o

l e s

t o p l a n e s

R e f :

T r u e ,

N . h

e m i s p

h e r e

~ 5 3 s a m p

l e s ~

: G r e e n

S e t

G r e e n

S e t :

7 1

. 8 / 6 3

M e a n o r i e n

t : d i p / a z i m u t h


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Structural Dip Exercise 5 (continued)Quest ion: If the following information is used

1. Vert ical wel lbore; and

2. Measured thickness of pay sand is 202 ft.

then

1. What is the true sand thickness?

2. If 50 ft is a minimum thickness, is this a commercial well?

Measured

Thickness

202 ft.


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Structure and Pattern Recognition Exercise - AnswersPattern Recognition

Exercise 1

7200

7000

6800

6600

6400

0 9 0Tad pole (deg )

Magnitude Azimuth

17 4525 14029 2854 105

Construct Arrow Plot of

45 10017 34575 335

Mark the patterns (red, blue, green)


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Exercise 2

a. Structure Interpretat ion:

Blue from top to 320 ft

Green from 320 ft to 530 ft

Red from 530 ft to TD

b. Stratigraphic Interpretation

Many red/blue/green patterns

Exercise 3

1 . R ed Pa tte rn .

Exercise 4

1. Major red from 10400 f t to 10540 ft .

Structura l Dip

Exercise 1

1. 10.1 at 48.84; gain = tan 10.1*1000= 178

Exercise 2

1. 6.5 at 276 above 8248 ft

6.2 at 39 below 8248 ft

Exercise 3

1 . 2.1 at 314

Exercise 4

1. FMI: 56.97 magnitude at 115.55 azimuth, RAB: 59:25 magnitude at 110.26 azimuth.

Exercise 5

1 . 70.8 at 63

Yes, thickness is 66.43 ft

70.8 202

True Thickness

Cos 70.8 = True thickness/ 202= 66.43

T r u e T h i c k n e s s

If 80, then = 35.1

: Fractures: Faults: Structure below: Structure above: All others

Azimuth Histogram

Ref: True, N. Hemisphere~ 65 s amp le s ~

: Structure below fault: S t r u

S t e r eone t : 8168.1 - 8469 .0 ft - F r acV iew 1 .3A

8200

8300

8400

0

N

S

EW

N

S

EW

Wulff Stereonet(Upper Hemisphere)

Poles to planesRef: True, N. Hemisphere

~ 72 s amp le s ~

: Structure below fault: Structure above fault: Faults: Fractures

Structure below fault:6 . 2 /89

Structure above fault:6 . 5 /276

S te r eone t : 8168.1 - 8469 .0 ft - F r acV iew 1 .3A

Mean orient.:dip/azimuth

Wel l Ove rv i ew: 8168 .1 - 8469 .0 f t - F r acV iew 1 .3A

Ref: True~ 167 s amp le s ~

~ Scale 1:389 ~

CAUTION:If a fracture/dipbelongs toseveral sets itwill be codedaccording to thelatest 'Show'selection.

structure and pattern recognition

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