CHAPTER THIRTY-FIVE: STRATIGRAPHIC ANALYSIS 3
Dipmeter/Image Log Case Histories

Table of Contents
35.00 Introduction to this Chapter
35.01 Case Histories
2. Channel Cut and Fill 1
3. Channel Cut and Fill 2
4. Channel Cut and Fill 3
5. Barrier Bar
6. Unconformities
7. Foreset Beds
8. Cross Bedding
9. Gouge
10. Shale Dome
11. Reef
12. Channel with Foreset Bedding
13. Sand Dunes
14. Barrier Bar Mapping
15. Unconformity
16. Deep Water Clastic
17. Channel Sand
18. Braided Channel
19. Sand Count
20. Laminated Shaly Sand
35.02 In Conclusion
35.03 Exercises for Chapter Thirty-Five
35.04: Bibliography for Chapter Thirty-Five

Continue to Chapter Thirty-Six

Publication History: This Chapter formed part of Chapter Seven of Volume Two of The Log Analysis Handbook, a series of course notes published by the author in 1978. Revised 1985 and 1993. Revised and re-organized for this electronic edition Oct 2002.

CHAPTER THIRTY-FIVE: STRATIGRAPHIC ANALYSIS 3
Dipmeter/Image Log Case Histories

35.00 Introduction To This Chapter
This Chapter covers case histories of depositional environment, sedimentary models, and bedding patterns from dipmeter and image log data. Depositional environment was covered in Chapter Thirty-Three. Interpretation of structure was covered beginning in Chapter Thirty-One. Dipmeter tool theory and data processing methods were described in Chapter Twenty-Six and will not be repeated here.

Formation microscanner image logs are gradually replacing standard dipmeters in many situations. The dip arrow plot, frequency azimuth plots, gamma ray, and resistivity correlation curves can be presented on a single log. This makes analysis much easier, as the visual impact of the bedding alongside the arrow plot is very powerful. The detailed dip information is ideal for stratigraphic work.

However, the computed dips can come from long interval HDT cluster and pool processing, SHDT mean square dip (MSD), continuous side-by-side (CSB) or local dip (LOC) processing. Or dips can be computed by FMS/FMI correlation or by digitizing the bedding planes seen on the image log. The choice of computation method depends on the particular requirements of the analyst. More than one computation may be required. Refer to Chapter Twenty-Six for details on this subject.

In many real cases, the processing method and parameters used are poorly described on the log heading. Try to be sure the dips presented are the dips you want or need. Figure 35.01 shows a comparison of different processing methods on the same data. Case histories and Exercises shown later give addition examples.

FIGURE 35.01: Dipmeter results from various computation methods

As with any log analysis technique, calibration and control by using core and sample descriptions is very beneficial. In addition, well to well correlation and mapping can be used to help confirm stratigraphic interpretation made from dipmeter and curve shape analysis.

35.01 Case Histories - Stratigraphic Analysis
In addition to the Classic Examples in Chapter Thirty-Four, review of case histories often assists in consolidating analysis rules for stratigraphic interpretation of dipmeters. A number of case histories have been gleaned from the literature and the author's files to illustrate some real life examples. Because of the inordinate detail available on many logs, most of these examples have been hand drafted by the original authors for clarity.

Figure 35.02 Channel Cut and Fill
This example illustrates a channel cut and fill situation. The dipmeter on Well B indicates high north dip appearing at the base of a 500 foot sand. This dip decreases upward in a typical cut and fill pattern. The north dip indicates an east west strike to the channel, with Well B positioned south of its axis. Well C shows a loss of 80 feet of sand at the base and Well D has only 50 feet of sand remaining. Well A also shows the cut and fill pattern, but bedding dips to the south, indicating that the channel axis is to the south, between Well A and Well B.

Figure 35.02: Channel Cut and Fill

Figure .35.03 Channel Cut and Fill
This is a more complicated sequence of cuts and fills. The gross interval appears to be a series of sand and shale interbeds on the SP log. The dip data shows Sand A dipping southeast so strike is SW - NE and the axis lies SE of the well. Sand B has the same strike, but opposite dip indicates the well is SE of the axis. Sand C shows no drape, so the well penetrated near the thickest part.

Figure .35.03: Channel Cut and Fill

Figure 35.04 Channel Cut and Fill
This is an east west cross section through the well in the previous example (Well 3). Each sand pinches out at a different elevation, so the oil water contact is different in each sand, as indicated by the high resistivity kicks in each sand. Dipmeter patterns can help identify isolated sands, and explain anomalies in oil water contacts between wells.

Figure 35.04: Channel Cut and Fill

Figure 35.05 Barrier Bar
In Well B, the increase of dip with depth above the sand body is drape over a sand bar. Dip is 12 degrees ENE so strike is at right angles to this, or WNW - SSE. The well lies to the east of the thickest sand and the sand shales out in direction of drape (ENE). Well A found thicker sand to the west as predicted.

Figure 35.05: Barrier Bar

The dipmeter run on Well "B" exhibits the pattern of increasing dip with depth, with the maximum dip being located just above 11,000 feet. Since the maximum, dip (12 degrees ENE) is recorded at the top of a sand, this sand is a buried bar which strikes WNW-SSE and shales out to the ENE. Well "A", the West offset to Well "B", has the same sand which has thickened to 50 feet.

Figure 35.06 Unconformities
Two unconformities are shown; with no weathering pattern on the left example and severe weathering on the right. Change in dip direction and amount is pretty obvious.

Figure 35.06: Unconformities

Figure 35.07 Foreset Beds
Four sets of foreset beds dipping SSE and a coarsening upward sequence is typical of a barrier bar, distributary mouth bar, or prograding delta front. Dips are to the SSW so sand body strikes ENE - WSW. Sand will shale out to the SSW.

Figure 35.07: Foreset Beds

Figure 35.08 Cross-bedding
Constant dip cross-bedding in cylindrical shaped sand represents delta distributary channel fill. Sand below 7200 feet dips SE so sand body strike is NW - SE. Sand at 7000 feet dips SW so strike is NE - SW. Steep cross-bedding shows high energy, coarse grain deposits, confirmed by SP log. Regional dip removal would accentuate patterns.

Figure 35.08: Cross-bedding

Figure 35.09 Gouge
Regular dips disappear at top of gouge zone, and slight drape occurs due to differential compaction or structural deformation. The pattern is similar to a reef, but lack of carbonate rocks is the key distinguishing feature. Random dips are common in both cases below the contact.

Figure 35.09: Gouge

Figure 35.10 Shale Dome
Similar to the previous example in many ways, the shale dome shows consistent dips below the contact instead of random dips. Again, lack of carbonate differentiates this case from a reef.

Figure 35.10: Shale Dome

Figure 35.11 Reef
Drape over reef indicates direction to reef crest. Drape is to SW so reef thickens to NW. Well 16-19 has about 160 feet of pay above oil water contact. Well 4-29 missed the pay and shows drape to NE, so thicker reef could be found by whipstocking or drilling to the SW of Well 4-29.

Figure 35.11: Reef

Figure 35.12 Channel with Foreset Bedding
This example shows the difference in detail that can be achieved by SHDT processing. Note depth scale change between different panels of the illustration. Detailed bedding analysis is shown, along with core description.

Figure 35.12: Channel with Foreset Bedding

Figure 35.13 Sand Dunes
This sand dune series is from a southern North Sea well. Constant steep foresets and decreasing bottom set dips are characteristic of dune and wadi environment.

Figure 35.13: Sand Dunes

Figure 35.14 Barrier Bar Mapping
Combining dipmeter with seismic mapping always makes for a good argument. Initial seismic mapping placed a high striking NW - SE and well control showed no hydrocarbons on downdip edges (Figure 35.14A). Dipmeter in NE well showed foresets dipping SE so strike of sand body is SW - NE (Figure 35.14C), at right angles to the seismic assumption. A well drilled on crest found pay and its dipmeter showed confirmation of the foresets and strike direction (Figure 35.14D). Pool was developed as in Figure 35.14B.

Figure 35.14: Barrier Bar Mapping

Figure 35.15 Unconformity With SYNDIP
The Cretaceous - Mississippian unconformity stands out in several ways. Resistivity shading is white for high resistivity carbonate, and Cretaceous sands and silts are shown gray or black. Bubble coding shows poor correlations and some nonplanar dips in Cretaceous contrasts with little bubble coding but numerous nonplanar dips in Mississippian.

Figure 35.15: Unconformity With SYNDIP

Figure 35.16 Deep Water Clastic With SYNDIP
This is a deep water prodelta sequence grading upward from shale to finely bedded sandstones. Long coarsening upward trends are indicated. Full clean sand is never reached. Foresets dip northwest so cleaner sand should be to southeast.

Figure 35.16: Deep Water Clastic With SYNDIP

Figure 35.17 Channel Sand With SYNDIP
SYNDIP in three wells shows variations in channel sand from well to well. Shale is well bedded and sands less so, evident from more bubble coding in the sands. Cross-bedding is often nonparallel indicating some erosion at base of each channel fill. Fining upward ramps indicate energy level decreasing as channels filled and delta prograded outward.

Figure 35.17: Channel Sand With SYNDIP

Figure 35.18 Oil Base Dipmeter in Braided Channel
Compressed scale dipmeter with computed log analysis shows thick sand section successfully logged with oil base dipmeter. Cylindrical curve shape with moderate dip spread indicates braided channel. Regional dip is ESE at about 4 degrees. Bedding in the sands is not clear on the small scale presentation. On Figure 7.92A, the detailed GEODIP presentation shows numerous red patterns, and an interpretation of the channels.

Figure 35.18A: Oil Base Dipmeter in Braided Channel – Correlation Scale

Figure 35.18B: Oil Base Dipmeter in Braided Channel – Detail Scale

1. Abandoned channel sequence (shale with thin sandy or silty beds)
2. Abrupt lower contact
3. Channel lag (soft clay pebbles)
4. Active channel sequence (massive sand and isolated events)
5. Scour and fill deposit
6. Longitudinal mud-channel bars (small foreset beds). Direction of transport: SSW. Channel elongation: NNE-SSW.
7. Lateral or transverse bar (more silty); a well-developed foreset towards the top. Channel axis towards ESE.
8. Longitudinal bar
9. Scour and fill deposit

Figure 35.19 to 35.21 Sand Count Using FMS Image Examiner
Both SYNDIP and the FMS Image Examiner can be used for sand counts by using resistivity cutoffs for both the shale (low resistivity) and tight (high resistivity) ends of the spectrum. The SYNDIP approach was used in Figure 35.17. The FMS screens for choosing cutoffs and assessing results are shown here. The histogram in Figure 35.19 shows the lime (tight) cutoff chosen in a known lime streak. Similarly, the shale cutoff is chosen in Figure 35.20. Remaining rock is shown in Figure 35.21 with a sand count of 15.4 meters or 64 percent of the analyzed interval.

Figure 35.19: Sand Count Using FMS Image Examiner

Figure 35.20: Sand Count Using FMS Image Examiner

Figure 35.21: Sand Count Using FMS Image Examiner

Figure 35.22 to 35.24 The Ultimate Dipmeter Analysis
By combining all dipmeter presentations, a maximum evaluation, total analysis approach to stratigraphy is achieved. A combination of DUALDIP, STRATIM, and SYNDIP with detailed core description is shown here. Note core data is on a smaller scale than dip data and is 8 feet off depth.

Figure 35.22: The Ultimate Dipmeter Analysis

Figure 35.23: The Ultimate Dipmeter Analysis

Figure 35.24: The Ultimate Dipmeter Analysis

35.02 In Conclusion
Case histories are an excellent source of knowledge. Review the Bibliography for more examples. Although dipmeter analysis can be ambiguous, sufficient geological constraints, local knowledge, and experience serve to improve skills and speed analysis. Modern computer processing, in particular dip-removed arrow plots and stick plots, are essential ingredients.

35.03 Exercises for Chapter Thirty-Five
Exercise 35.01: CLUSTER and GEODIP
Draw the dip patterns. What sedimentary features can you see? (20 marks)

Exercise 35.02: FMS Image With MSD Dips (20 marks)
1. Are the MSD dips representative of the true dip of the clay beds? Why (not)?

2. Are the FMS dips on the next page better or worse? What else can be seen on the FMS dip presentation?

3. What is the sand/shale ratio in the interval shown? What is regional dip?

Exercise 35.03: Point Bar Example (20 marks)
1. How many bar sequences were penetrated? What direction is the stream migrating? Can you tell which way the stream is traveling? Draw a hypothetical GR log for this example.

Exercise 35.04: Channel Fill Example (20 marks)
1. How many channel sequences were penetrated? What direction is the stream axis? Can you tell which way the stream is traveling? Draw a hypothetical GR log for this example.

Exercise 35.05 Sand/Shale Ratio On FMS (20 marks)
1. How thick are sand beds A through E? What is sand/shale ratio. Which sands are clean and which have shale laminations? On the lower illustration, what could be done to the FMS image to improve it?

2. Why do the shales in the upper half of the log look different than those at the bottom?

Exercise 35.07: Dipmeter Study (30 marks)
1. Draw stick diagrams and give a written analysis for this dipmeter. Would the presence of other logs help you? What causes the scattered dips at the base of the log?

35.05 Bibliography for Chapter Thirty-Five
Dipmeter Applications

1: Application of dipmeter surveys; Stratton,E.F., Hamilton,R.G.; American Institute of Mining Metallurgical Engineers Meeting, 21 p., 1947

2: Application of the continuous dipmeter to reef study; Schlumberger; Schlumberger News, 9 p., 1961

3: Continuous dipmeter survey can be an important exploration tool; Thompson,J.D.; The Oil and Gas Journal, 4 p., 1961

4: Diplog; Hammack,G.W.; Dresser Atlas Tech Bulletin, 15 p., 1964

5: Determining true formation thickness from the dipmeter; Norman,J.L., Thibodaux,J.B.; Pan Geo Atlas Corporation, 6 p., 1964

6: Interpretation of continuous dipmeter surveys; Schlumberger; Schlumberger Training Aid, 26 p., 1964

7: Detailed stratigraphic control through dip computations; Gilreath,J.A., Maricelli,J.J.; American Association of Petroleum Geologists Bulletin, v. 48, no. 12, p. 1902-1910, 1964

8: How to compute dips quickly from dip log correlations; Walker,T., Robertson,E.; World Oil, p. 135-140, 1964

9: Stratigraphic interpretation of continuous dipmeter survey data; Schlumberger; Interpretation Bulletin, 6 p., 1966

10: Log interpretation in Bolivia; Salisch,J.A., Brown,H.D.; Society of Professional Well Log Analysts, 20 p., 1966

11: A review of log interpretation methods used in the Niger delta; Poupon,A., Strecker,I., Gartner,J.; 53 p., 1966

12: Applications of the continuous dipmeter in Western Canada; Goetz,J.; The Journal of Canadian Petroleum Technology, 5 p., 1966

13: Dipmeter - Middle East; WEC, 13 p., 1967

14: Logging programs in northeastern South America; Brown,H.D., Salisch,H.A.; Society of Professional Well Log Analysts, 27 p., 1967

15: The continuous dipmeter as a tool for studies in directional sedimentation and directional tectonics; Rodriquez,A.R., Pirson,S.J.; Society of Professional Well Log Analysts 9th Annual Logging Symposium, 25 p., 1968

16: Stratigraphic applications of dipmeter data in mid-continent; Campbell,R.L.,Jr.; American Association of Petroleum Geologists Bulletin, v. 52, no. 9, p. 1700-1719, Sept 1968

17: Interpretation of dipmeter data in the Devonian carbonates and evaporites of the Rainbow and Zama areas; Cox,J.W.; 19th Annual Technical Meeting of Petroleum Society of Canadian Institute of Mining, Paper No. 6820, 1968

18: Depositional environments defined by dipmeter interpretation; Gilreath,J.A., Healy,J.S., Yelverton,J.N.; Transactions - Gulf Coast Association of Geological Societies, v. 19, p. 101-111 , 1969

19: Geological application of well logs; Fons,L.,Jr.; Society of Professional Well Log Analysts 10th Annual Logging Symposium, 44 p., 1969

20: East Cameron block 270, a Pleistocene field; Holland,D.S., Sutley,C.E., Bertlitz,R.E., Gilreath,J.A.; 24th Annual Symposium of Gulf Coast Association of Geological Societies Symposium, 9 p., 1970

21: Dipmeter - Libya; WEC, 13 p., 1970

22: Fundamentals of Dipmeter Interpretation; Schlumberger; Schlumberger Training Aid, 145 p., 1970

23: Distributary front deposits interpreted from dipmeter patterns; Gilreath,J.A., Stephens,R.W.; Transactions - Gulf Coast Association of Geological Societies, 8 p., 1971

24: Deficiencies of computer correlated dip logs; Robertson,J.M.; Society of Professional Well Log Analysts 13th Annual Logging Symposium, 15 p., 1972

25: Structural geologic considerations in diplog interpretation; Holt,O.R.; Society of Professional Well Log Analysts 13th Annual Logging Symposium, 30 p., 1972

26: Geological aids; Schlumberger; Society of Professional Well Log Analysts 14th Annual Logging Symposium, p. 5-18, 1973

27: Dipmeter outlines petroleum entrapment on flaks of diapiric shale done; Franke,M., Hepp,V.; Society of Professional Well Log Analysts 14 Annual Logging Symposium, 20 p., 1973

28: Dipmeter interpretation in the southern and northern North Sea basin; WEC, p. 56-59, 1974

29: Vermilion block 16 field: a study of irregular gas reservoir performance related to non-uniform sand deposition; Seal,W.L., Gilreath,J.A.; Transactions - Gulf Coast Association of Geological Societies, v. 29, 1975

30: Interpretation of log responses in a deltaic environment; Gilreath,J.A., Stephens,R.W.; American Association of Petroleum Geologists Marine Geology Workshop, 31 p., 1975

31: Quick interpretation of the high resolution dipmeter; Okitsu F.; Society of Professional Well Log Analysts 17th Annual Logging Symposium, 10 p., 1976

32: Reservoir delineation by wireline techniques; Goetz,J.F., Prins,W.J.; Society of Professional Well Log Analysts: The Log Analyst, p. 12-40, 1977

33: Preplatform exploration of High Island Blocks A-560 and A-561; Lund,J.W., King,J.S., Berlitz,R., Gilreath,J.A.; The Oil and Gas Journal, p. 254-273, 1979

34: Dipmeter Workbook; Schlumberger; Workbook, 72 p., 1980

35: Schlumberger dipmeter interpretation; Schlumberger; Manual, 58 p., 1981

36: Application of dip related measurements to a complex carbonate clastic depositional environment; Bigelow,E.L.; Society of Professional Well Log Analysts: The Log Analyst, p. 9-30, 1982

37: Diplog analysis and practical geology; Dresser Atlas; Manual, 57 p., 1983

38: Applications of the SHDT stratigraphic high resolution dipmeter to the study of depositional environments; Chauvel,Y., Seeburger,D.A., Orjuela,A.C.; Society of Professional Well Log Analysts 25th Annual Logging Symposium, 23 p., 1984

39: Geological evaluation of high resolution dipmeter data; Nurmi,R.D.; Society of Professional Well Log Analysts 15th Annual Logging Symposium, 24 p., 1984

40: Comparative results of quantitative laminated sand shale analysis in Gulf Coast wells using maximum diplog microresistivity information; Quinn,T.H., Sinha,A.K.; Society of Professional Well Log Analysts 26th Annual Logging Symposium , 25 p., 1985

41: The use of dipmeter synthetic data to determine rock texture and depositional environment; Standen,E.; 10th Canadian Well Logging Society, 12 p., 1985

42: A fundamental approach to dipmeter analysis; Enderlin,M.B., Hansen,D.K.T.; 10th Canadian Well Logging Society, 14 p., 1985

43: Making more intelligent use of log derived dip information; Bigelow,E.L.; Society of Professional Well Log Analysts: The Log Analyst, p. 26-42, 1985

44: Schlumberger sedimentary environments from wireline logs; Serra,O.; Manual, 210 p., 1985

45: Geologic interpretation of alternative dipmeter analyses from a permocarboniferous glaciogene sequence in the Fitzroy Graben Canning Basin, Western Australia; Golstein,B.A.; Society of Professional Well Log Analysts: The Log Analyst, p.6-26, 1986

46: Schlumberger dipmeter interpretation; Schlumberger; Manual, 76 p., 1986

47: Depositional environment determination using SSP resistivity method; Mitchell Tapping,H.J.; Society of Professional Well Log Analysts: The Log Analyst, p.15-20, 1986

48: Strategies for dipmeter interpretation; Gilreath,J.A., Adams,J.; The Technical Review, v.35, no.4, p.28-41, 1987

49: Dipmeter interpretation rules; Gilreath,J.A.; The Technical Review, 6 p., 1987

50: A practical method of identifying and exploiting clastic depositional environments using wireline parameters; Fett,T.H.; Society of Professional Well Log Analysts 28th Annual Logging Symposium, 19 p., 1987

51: New angles and dimensions in dipmeter interpretation opened by the six arm dipmeter; Goetz,J.F., Garat,J.; Society of Professional Well Log Analysts 28th Annual Logging Symposium, 25 p., 1987

52: Application of an interactive statistical classification system to the analysis of high resolution dipmeter curves; Keskes,N., Le Tendre,L., Schein,F., Benamou,N., et al; Society of Professional Well Log Analysts 28th Annual Logging Symposium, 24 p., 1987

53: Program helps determine structure from dipmeter data; Elphick,R.Y.; Geobyte, p. 57-75, 1988

54: Obtaining structural and stratigraphic dip information using segmentation trees and optimization; Kerzner,M.G.; Society of Petroleum Engineers Formation Evaluation, p. 47-54, 1988

55: The evolution of a dipmeter analysis: a case study from Pakistan; Waterhouse,M.; Society of Professional Well Log Analysts 30th Annual Logging Symposium, 22 p., 1989

56: Wellbore breakout stress analysis within the central and eastern continental United States; Dart,R.L., Richard,L.; Society of Professional Well Log Analysts: The Log Analyst, p. 12-30, 1989

57: Reconnaissance mapping of stratigraphic traps in sandstones: depositional energy maps, diagenetic maps; Sheir,D.E.; Society of Professional Well Log Analysts: The Log Analyst, p. 225-242, 1989

58: Heterogeneties and geometry of sedimentary bodies in a fluvio-deltaic reservoir; Ravenne,C., Eschard,R., Galli,A., Mathieu,Y., et al; Society of Petroleum Engineers Formation Evaluation, p. 239-246, 1989

59: Types of channel fills interpreted from dipmeter logs in the McMurray formation northeast Alberta; Muwais,W., Smith,D.G.; Bulletin of CPG, v. 38, no. 1, p. 53-63, 1990

60: Methods for improved dip determination in water based mud with the six arm dipmeter; Chemali,R., Su,S.M., Goetz,J.F., Maute,R.E., Osborn,F.F.; Society of Professional Well Log Analysts 31st Annual Logging Symposium, 25 p., 1990

61: Interpretation of depositional systems in the lower Silurian Medina group of western New York; Davis,R.J., Johnson,C.A., Gilreath,J.A.; Society of Professional Well Log Analysts 31st Annual Logging Symposium, 25 p., 1990

62: A fundamental approach to dipmeter analysis; Enderlin,M.B., Hanse,D.K.T.; 14 p., 1990

ABOUT THE AUTHOR

E. R. (Ross) Crain, P.Eng. is a Consulting Petrophysicist and a Professional Engineer with over 35 years of experience in reservoir description, petrophysical analysis, and management. He has been a specialist in the integration of well log analysis and petrophysics with geophysical, geological, engineering, and simulation phases of oil and gas exploration and exploitation, with widespread Canadian and Overseas experience.

His textbook, "Crain's Petrophysical Handbook on CD-ROM" is widely used as a reference to practical log analysis. Mr. Crain is an Honourary Member and Past President of the Canadian Well Logging Society (CWLS), a Member of Society of Petrophysicists and Well Log Analysts (SPWLA), and a Registered Professional Engineer with Alberta Professional Engineers, Geologists and Geophysicists (APEGGA)