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[.]
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 of Southern? 2/ What are the subsea depths of Markers X, Y, and Z on Figure 1 ? Figure 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 Figure 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 Figure 5/ How can an isopach map be construed as a structure map? Figure Succession: Liên tiếp, dãy, chuỗi abut: tiếp giáp 6/ Using the following rough areal values, compute the approximate volume of oilsaturated 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 Figure 7/ What type of cross section would you construct if: (a) You were interested in the relationship of subsurface features 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 1a. VERTICAL EXAGGERATION TRUE DIP 65 b 2a b. 7 4 80 _ _ 3a _ b. _ 4a. 5 _ b 5 14 (b) What general rule can you observe in 1a and b? EXAGGERATED DIP _ _ 71 78 35 47 32 _ (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) Figure 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 6090REMARKS: 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 4338REMARKS: D&A Well C ELEVATION: 3750 (DF) TOTAL DEPTH: 3450 LOG PICKS: Mississippian (unconformity) 1910 Sun River 1910-1980 Lodgepole/Mission Canyon 1980-3050 Devonian (unconformity) 3050 10 Three Forks 3050-3115 Potlatch 3115-3290 Nisku 3290-3350 Duperow 3350REMARKS: 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 3350REMARKS: 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: Unit to Unit 3: Unit to Unit 4: Datum= -5000 ft. Vertical exaggeration= (500 ft horizontal = 100 ft vertical) ELEVATION: TOTAL DEPTH: 3850 ft SE 2250 ft SE 2400 ft SE Well-Unit 1A 234 (KB) 6154 11 DRILLERS PICKS: A Sand B Sand REMARKS: D&A 5634-5724 6102-6146 Well-Unit 127 (KB) TOTAL DEPTH: 6127 ELEVATION: DIPMETER READINGS: LOG PICKS: A Sand B Sand C Sand REMARKS: Gas @ 53175377; 5725-5757 ft Well-Unit ELEVATION: TOTAL DEPTH: 252 (KB) 6212 LOG PICKS: A Sand 5617-5712 B Sand Absent C Sand 6075-6162 REMARKS: Gas in C Sand; G/W contact at 6102 ft DIPMETER READINGS: 30 SE 7 SE Well-Unit ELEVATION: TOTAL DEPTH: 10 SE 15 SE _ 5317-5399 5725-5770 Absent Possible fault at 6067 ft 398 (DF) 6400 LOG PICKS: A Sand B Sand C Sand REMARKS: 5518-5598 5923-5961 6281-6370 Slight show of Gas at 5518 ft DIPMETER READINGS: 7 SE 7 SE 7 SE Figure ??? 12 14/ The Wyckoff Gas Field, located in Steuben County, N.Y., produces from Onondaga Limestone and/or Oriskany Sandstone ( Figure ) The Onondaga forms a thick biohermal reef over part of the field Figure Only the porous core facies is productive in the reef section (see map) A deep-seated down-tothe-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 wells in the Wyckoff Field ( Figure , 13 Figure Figure , Figure 14 Figure , Figure 15 Figure , Figure 16 Figure , and Figure ) 17 Figure 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 18 Figure 15/ What are the benefits of a computerized cross section, and what are its limitations? 19