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Exercise CHAPTER 6 Exercise SUBSURFACE ENVIRONMENT 1/ List the four types of subsurface waters, and give a one sentence definition for each Meteoric water Infiltration of rainwater Distribution @ shal[.]

CHAPTER 6

Exercise SUBSURFACE ENVIRONMENT

1/

List the four types of subsurface waters, and give a one sentence

definition for each.

-Meteoric water

Infiltration of rainwater

Distribution @ shallow depth

Total mineralization: Low

Tens to be Oxidizing

pH: Often acidic due to dissolved humic, carbonic and nitrous acids

-Connate water

Ancient sea water which was trap in the sediment during burial

Differs from seawater both in concentration of dissolved salt and pH, and Eh

-Juvenile water

Primary of magmatic origin

Brought to near – surface environment dissolved in magma

Usually mixed with either connate or meteoric water

-Mixed water

Results from the commingling of meteoric, juvenile and connate waters

Usually between the near – surface meteoric water, juvenile and the deeper, more saline connate water

2/

a.) How does salinity vary with depth?

- Depth the salinity high

b.) What causes reversals of this vertical salinity trend?

- Causes reversals of this vertical salinity trend is : depth, high geopressure + high temperature => water vapor and water increased and moved up -> minerals ione were kept in porosity -> high concentration -> high salinity

3/

Below is a listing of rock types or groups, label each according to their thermal conductivity characteristics Use the terms "high" , "variable" ,

or "low"

3 Limestone :variable

7 Shale - normal pressured :low

8 Shale - overpressured :high

4

What are the three main causes of regional variations in geothermal gradients?

- First, there may be movements of deep, hot material to positions nearer the earth's surface These movements increase the thermal gradients and, therefore, the heat flow

- Second, there may be large-scale movements of relatively cool, originally shallow rocks, to deeper positions within the earth, displacing hotter rocks at depth and causing lower gradients and heat flow

- Third, there may he rock masses of great vertical extent but only limited lateral extent, which cause significant lateral contrasts In thermal conductivity, and so cause lateral variations in gradients and heat flow

5/ Why do high geothermal gradients favor oil production?

- Because, high geothermal gradients ( high temperature ) was ideal conditions for rock shale produced HC ( 150 – 2200C ), shales were changed to become material organic were original oil and primary porosity were preserved.

6/ There are two basic types of subsurface pressures which together

constitute the total overburden pressure What are they?

• The fluid pressure, often called "pore pressure" or "formation pressure", is

applied by the fluids within the pore spaces These fluids exert pressure against the grains

• Lithostatic pressure is due to the weight of the rock overburden It is transmitted

through the subsurface by grain-to-grain contacts in the rocks

7/ Below is a listing of causes of subnormal (under) or supernormal (over) pressures Label each with either the "underpressure" or overpressure" which they would cause.

_overpressure is caused by an artesian water system

overpressure _ is caused by diagenesis, where water is expelled

overpressure _ is caused by thermal expansion of water

underpressure _ is caused by an increase in pore volume by decompression or fracturing

overpressure _ is caused by under compaction of shale

underpressure _ is caused by an increase in pore volume due to dissolution of mineral cements

_underpressure is caused by a lowering of reservoir temperature

8*/

Sketch the potentiometric surface on the cross section ( Figure 1)

9*/

On this pressure/temperature graph for a crude oil/gas system, indicate the areas occupied by liquid, vapor, and liquid & vapor phase(s) Label the critical point, the bubble-point curve and the dew-point curve ( Figure   2)

10*/ Below is a listing of basin characteristics, each belonging to either a "juvenile", "intermediate", or "senile" basin Mark each with a J for juvenile, I for intermediate, S for senile.

Juvenile basin_ dynamic fluid system, strong marine influences.

_Senile basin_ widespread meteoric water in subsurface.

_ Intermediate basin _ meteoric water invasion at margins of basins.

_ Intermediate basin fluid pressures mostly hydrostatic, some artesian water systems _ senile basin generally only hydrostatic pressure gradients.

intermediate basin _ fluid movement compaction-induced, moving outwards towards

margins

_ juvenile basin invasion of meteoric water unimportant.

_ intermediate basin compaction of shales nearly complete.

_juvenile basin overpressured shales common.

_ juvenile basin still actively receiving sediments.

_ intermediate basin mostly removed from marine influences.

_ intermediate basin oil beginning to be degraded at basin margins.

_senile basin extensive degradation of oil.

11/

T here are 04 chemical composition relationships of ground water (classificated by Sulin-Russia) Determine the type and origin of them, What type would have most indication that relate to petroleum

acummulation?

1 1 Loại nước sunphat natri có nguồn gốc rửa lũa đại lục, được đặc trưng bằng:

>1; < 1 and <0

2 Loại nước bicabonat natri (nước kiềm) có nguồn gốc đại lục, khí quyển được đặc trưng bằng: >1; > 1 and <0

3 Loại nước clorua magie liên quan với nguồn gốc biển và được đặc trưng

4 Nước clorua canxi (nước cứng) có nguồn gốc biến chất sâu (liên quan với các mỏ dầu khí) được đặc trưng bằng:

CHAPTER 7

Exercise

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

- Marker X : -1773

- Marker Y : -3020

- Marker Z : -5311

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 ).

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?

True

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?

True

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

- An isopach value, a, is the thickness of a horizontal stratigraphic unit measured in a vertical hole An iso-chore value, b, is the thickness of an inclined unit measured in a vertical hole and not corrected for dip (i.e., deviation of strata from horizontal) Again, an iso-chore value, b', is the thickness of an inclined unit measured in a non-vertical hole and corrected for deviation of the hole from non-vertical but not corrected for dip

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

Figure 1

 Total volume of oil : 31000 acro fort

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?

Stratigraphic cross sections

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?

Structure cross sections

9/

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

o Input data

o Line of section

o Scale

o Datum

10/

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

  EXAGGERATION VERTICAL   TRUE DIP EXAGGERATED DIP

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

- V=const -> E < d

(c) in 2a and b?

- V=const -> E < d

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

- V=const -> E > d

11/

Once you have decided what type of cross section you need, what is the construction procedure?

- First, a horizontal datum line is established along the wall Well locations are scaled off horizontally according to the relative distances between wells on the line of section Each log is positioned over its well location by matching the horizontal datum line and the corresponding elevation or horizon on the log This procedure is called "hanging" the log

on the datum line Correlatable strata on each log can be marked with colored push pins and the geology can be further highlighted by stretching string or elastic bands between the pins It is easy to change correlations or to substitute new logs into the diagram Many rough cross sections can be constructed in this manner while the geologist begins to visualize the geology of the area

15/

What are the benefits of a computerized cross section, and what are its limitations?

- Benefits: accuracy and quickly, including manage data

- Limitations: difficulty is building new software according to events of present

CHAPTER 8

THE HABITAT OF HC IN SEDIMENT BASINS

1/

Give one example in which a basin's depocenter, its topographic low point, and its point of maximum basement subsidence will not, in all likelihood, coincide.

2/

Relate the following features to either convergent or divergent plate tectonic processes:

A divergent plate upwelling in the asthenosphere

B _convergent plate _ suture zone

C _divergent plate _ failed arm rift

D _convergent plate _ large-scale transcurrent (strike-slip) fault motion

E _convergent plate _ active continental margin

F _divergent plate _ passive continental margin

3/ What is the sequence of events which leads to the development of a new ocean basin

and the splitting apart of continents?

4/

  Name the two basin types, among the ten developed in our classification scheme, that dominate world's conventional petroleum reserves

Downwarp basin

Foreland basin

2   Name the three basin types that only rarely have yielded giant-field

production and which do not occur among the world's most petroleum-rich basins

- interior basin

- Pullapart basin

- Fore arc basin

5/

5.1 What two major groups of basins, each containing several of our ten basin types, yield petroleum mostly from shallow wells, at depths of less than 2 kilometers?

- cool, eroded cratonic basin ( foreland, interior )

- hot, young convergent margin basin (non arc, back arc, collision )

5.2Which two of the ten basin types usually produce petroleum from depths exceeding 3 kilometers or more?

- pull apart basin

- deltas basin

6/

What two basinal settings lead to enrichment in natural gas?

- reservoir have to large capacity and depth which is temperature effect to

production of oil-gas

- reservoir of original Kerogen have to large volume ( deltas, pullapart )

7/

What is required in order to obtain giant gas fields in a basin?

- evaporate barrier and hydrate barrier were opened

8/

Using the classification scheme developed in Sections 7.6 to 7.11, name the basin type(s) associated with each of these regions:

A — California

B _ — the continental shelf off eastern North and South America

C — small oceans and inland seas

D — Precambrian shield areas with low, peneplained topography

E — both the Andes Mountains of South America and the Tethyan trend (Alpine Mountains to Himalayas)

F — point where a failed arm rift meets an ocean basin

G — the Pacific "Ring of Fire" island-arcs

9/

Name the two types of cratonic basins

interior

foreland

Which of the two usually has the greater petroleum potential?

foreland