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Exercise Exercise Chapter 7 SUBSURFACE MAPPING AND CROSS SECTION 1/ Could the subsurface geologist use electric logs in correlating (a) Cenozoic units between coastal Gulf of Tonkin and coastal Gulf o[.]

SUBSURFACE MAPPING AND CROSS-SECTION

1/ Could the subsurface geologist use electric logs in correlating (a) Cenozoic units

between coastal Gulf of Tonkin and coastal Gulf of Southern?

2/ What are the subsea depths of Markers X, Y, and Z on Figure   1 ?

Figure 1

3/

Draw a structural contour map of marker surface P, using the subsurface data on subsea depths of markers, subsea depths of fault intersections, and magnitudes of fault cut-outs Assume fault surfaces dip 55 and use a contour interval of 100 ft ( Figure   1 and Figure   2 )

Figure 1

4/ A.) Figure   1 and Figure   2 are a subcrop map of Algerian Paleozoic units beneath a sub-Mesozoic unconformity Does this subcrop pattern indicate Pre-Mesozoic uplift? What is the evidence?

B.) Given that the principal period of structural trap formation in eastern Algeria was Cretaceous in age (Austrian orogeny), and given that the source of petroleum is Silurian shale, are the following statements true or false: Most of the petroleum in the eastern Algerian Sahara did not migrate from its source rock until Cretaceous or later time True or False?

Long-distance secondary migration is evident in this province True or False?

Figure 1

5/ How can an isopach map be construed as a structure map?

Figure 1

Succession: Liên tiếp, dãy, chuỗi

abut: tiếp giáp

6/ Using the following rough areal values, compute the approximate volume of

oil-saturated sand sketched in Figure   1

Mean areas of oil saturation

From OWC to 10' above OWC-1000 acres

From 10' to 20' above OWC-850 acres

From 20' to 30' above OWC-700 acres

From 30' to 40' above OWC-550 acres

7/ What type of cross section would you construct if:

(a) You were interested in the relationship of subsurface features 1 million years ago, and;

(b) you wanted to see how these features changed over a large region, and; (c) the features are thin and have a very gentle dip?

8/ What type of cross section would you construct if:

(a) You wished to know if a present-day surface feature was reflected in a similar subsurface structure, and;

(b) the area you were interested in was fairly small, and;

(c) it was important that the section not distort the thickness of the strata it depicted?

9/ What are common sources of error in cross sections and how are they avoided?

10/ (a) Using Equation 1, tandE = V tand , fill in the blanks in this table

(b) What general rule can you observe in 1a and b?

(c) in 2a and b?

(d) What can you observe in 3a, b and 4a, b?

11/ Once you have decided what type of cross section you need, what is the

construction procedure?

12/

Information is given below for four wells and one columnar section in northwestern Montana use the information to construct a stratigraphic cross section on top of the Mississippian You will need to know that the evaporitic Potlatch Formation is the eastern facies equivalent of the

Wabamun Dolomite All distance measurements are given in feet ( Figure 1 )

DISTANCES BETWEEN DATA POINTS

Outcrop to Well A: 26500 ft E

Well A to Well B: 21000 ft E

Well B to Well C: 10500 ft E

Well C to Well D: 10500 ft E

Well A

ELEVATION: 4291 (DF)

TOTAL DEPTH: 6642

LOG PICKS:

Mississippian (unconformity)        4622

Sun River       4622-4780

Lodgepole/Mission Canyon       4780-5850

Devonian (unconformity)        5850

Potlatch       5850-6070

Nisku       6070-6090

Duperow      

6090-REMARKS: D&A

Well B

ELEVATION: 4347 (DF)

TOTAL DEPTH: 4692

LOG PICKS:

Mississippian (unconformity)       2872

Sun River        2872-3023

Lodgepole/Mission Canyon        3023-4050

Devonian (unconformity)       4050

Three Forks       4050-4075

Potlatch       4075-4295

Nisku        4295-4338

Duperow       

4338-REMARKS: D&A

Well C

ELEVATION: 3750 (DF)

TOTAL DEPTH: 3450

LOG PICKS:

Mississippian (unconformity)        1910

Sun River       1910-1980

Lodgepole/Mission Canyon       1980-3050

Potlatch       3115-3290

Nisku        3290-3350

Duperow       

3350-REMARKS: 200 BOPD

Well D

ELEVATION: 3714 (DF))

TOTAL DEPTH: 3590

LOG PICKS:

Mississipian (unconformity)        1950

Lodgepole/Mission Canyon       1950-3070

Devonian (unconformity)        3070

ELEVATION: 3070-3158

Potlatch       3158-3298

Nisku       3298-3350

Duperow       3350-

REMARKS: D&A

13/ Information is given below for four wells Use the information to construct a structural cross section All distance measurements are given in feet

DISTANCES BETWEEN WELLS

Unit 1A to Unit 2:  3850 ft SE 

Unit 2 to Unit 3: 2250 ft SE 

Unit 3 to Unit 4: 2400 ft SE 

Vertical exaggeration= 5 (500 ft horizontal = 100

ft vertical) 

Well-Unit 1A

DRILLERS PICKS: 

REMARKS: D&A 

Well-Unit 2

A Sand  5317-5399  10 SE 

 REMARKS:  Possible fault at 6067 ft

 Gas @

5317-5377;  5725-5757 ft

Well-Unit 3

ELEVATION:  252 (KB)

TOTAL

A Sand  5617-5712 30 SE 

C Sand  6075-6162 7 SE 

G/W contact at

6102 ft

Well-Unit 4

ELEVATION:  398 (DF)

TOTAL

REMARKS: Slight show of Gas at 5518 ft

over part of the field

Figure 1

Only the porous core facies is productive in the reef section (see map) A deep-seated down-to-the-southwest fault extends upward along the southwest flank of the reef Oriskany production is from a small anticline on the upthrown side of the fault

Elevations and marked logs are provided for 6 wells in the Wyckoff Field ( Figure 2 ,

Figure 2

Figure 3 , Figure 4

, Figure 5

Figure 5

, Figure 6

, and Figure 7 )

Figure 3

Use this information to construct a northeast-southwest structural cross section from the Richards well to the Dibble well, showing the interval from top of Onondaga to bottom of Oriskany

15/ What are the benefits of a computerized cross section, and what are its

limitations?