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The volume of rock which is located between the oil/water contact and the gas/oil contact is determined by 3D seismic and logging ,the oil/water contact determination depends on correct depth of seismic travel times.
The volume of rock which is located between the oil/water contact and the gas/oil contact is determined by 3D seismic and logging ,the oil/water contact determination depends on correct depth of seismic travel times.


&nbsp; It is difficult to determine the average porosity ,so it is determined in a range by using porosity log and core data analysis . The saturation of oil or gas is determined from logging interpretation and core data analysis too.<ref name="1">Knut, B. 2010. Petroleum Geoscience:from sedimentary environment to rock physics:Springer-Verlag Berlin Heidelberg.</ref>
&nbsp; It is difficult to determine the average porosity ,so it is determined in a range by using porosity log and core data analysis . The saturation of oil or gas is determined from logging interpretation and core data analysis too.<ref name="a">Knut, B. 2010. Petroleum Geoscience:from sedimentary environment to rock physics:Springer-Verlag Berlin Heidelberg.</ref>


The volume of oil or gas in place (Vp ) is calculated from:
The volume of oil or gas in place (Vp ) is calculated from:
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== '''The effect of rock type on production rate''' ==
== '''The effect of rock type on production rate''' ==


The change in rock type is an important reason for changing the production rate, as it controls the rock properties such as porosity and permeability which control the production rate.'''<ref name="2">1.3 Resevoirs-Clas User. http://users.clas.ufl.edu/jbmartin/petroleum_geology/reservoirs.html</ref>'''
The change in rock type is an important reason for changing the production rate, as it controls the rock properties such as porosity and permeability which control the production rate.'''<ref name="b">1.3 Resevoirs-Clas User. http://users.clas.ufl.edu/jbmartin/petroleum_geology/reservoirs.html</ref>'''


The effect of many types of rock on the production as the following&nbsp;:
The effect of many types of rock on the production as the following&nbsp;:

Revision as of 15:48, 1 December 2015

It is a branch of petroleum engineering which study the geology of reservoir to manage the production for a field and get more hydrocarbons out of it.

The work of production geologists is understanding the reservoir from the geological side and creating a model for it by using computer software ,the model provides the all information which is needed for hydrocarbons production.

Determination of Petroleum Reserves and it's relationship with geology

After detecting of oil from exploration well , the reserve estimation must be made to know the amount of oil which will be produced .

The volume of rock which is located between the oil/water contact and the gas/oil contact is determined by 3D seismic and logging ,the oil/water contact determination depends on correct depth of seismic travel times.

  It is difficult to determine the average porosity ,so it is determined in a range by using porosity log and core data analysis . The saturation of oil or gas is determined from logging interpretation and core data analysis too.[1]

The volume of oil or gas in place (Vp ) is calculated from:

                   Vp = Vr · N/G · ϕa · Sat

In which:

-(Vp) = The total initial volume of oil in place.

- (Vr) = The volume of rock above the oil/water contact (OWC) and below the cap rock.

- (N/G) = Net to gross volume ,the ratio between the volume which have sufficient amount of oil to produce (N) and the total volume of rock (G).

- (ϕa) = The average porosity.


The effect of rock type on production rate

The change in rock type is an important reason for changing the production rate, as it controls the rock properties such as porosity and permeability which control the production rate.[2]

The effect of many types of rock on the production as the following :

 Sand stone rocks

  • Porosity decreases with depth, the decreasing of rate depends on sand stone type:

    - Immature sands lost porosity faster than well sorted sands.

    - Poorly sorted sands lost porosity faster than well sorted sands.     

  • Pressure and temperature affect on porosity as:

    -When the temperature increases ,it causes faster cementation and decreasing porosity.

    -When the pressure increases ,it reduces compaction and increasing porosity.

 Carbonate sand rocks

 The depositional environment may change the quality of carbonate reservoirs.

  • Reefs:

Reefs have high porosity as they are initially cemented ,and it is necessary that hydrocarbons migrate into the pore space early to keep the porosity.

  • Carbonate mud rock:

The common deposits are aragonite .When aragonite re-crystallize to calcite, the porosity is destroyed by it.

Chalk is a type of carbonate mud rocks which have high porosity and low permeability because of  it's small size .When they are fractured , they can make a good reservoirs.

  •     Dolomite rock:

A good reservoirs are formed by dolomites. The volume of Mg atoms is 13% smaller than Ca atoms ,so after dolomitization happens ,the total volume of material decreases by 13% and generates 13% porosity.

 Other types of rocks

The two major reservoir types around the world are sand stones and carbonates of  about 90% of the world's production from them . Other types of rocks take around 10% of the world's production.

  • Dissolution:

The dissolution of feldspars in granites forms a good reservoir rock and it is called granite wash.

  •  Fracturing:

Making fractures in igneous and metamorphic rocks generates a good porosity and permeability in these rocks and makes it a good reservoir.

Changes of rock properties During Production

During production ,the changes of reservoir rock happens which have a bad effect on reservoir properties such as reservoir damage. This takes place in two ways:

 Chemical reactions

During drilling or water injection ,the minerals and drilling liquids may react and damage the reservoir.

This damage is treated by chemicals injection to improve the permeability.

Mechanical damage

Clay minerals or small grains are carried toward the well by fluids and blocking the pores around the well.

This damage is treated by lowering the production rate.

Monitoring Production

During production, the information about fluid properties in reservoir is provided from the comparison between production and injection pressures .These data is very important for reservoir simulation models.  

Conclusion

-The effect of geology on the hydrocarbon reserve.

-The properties of rock changes the production rate, as changing the rock type.

-During production, the reservoir properties may be changed.

-The important of  monitoring production.

References

  1. Knut, B. 2010. Petroleum Geoscience:from sedimentary environment to rock physics:Springer-Verlag Berlin Heidelberg.
  2. 1.3 Resevoirs-Clas User. http://users.clas.ufl.edu/jbmartin/petroleum_geology/reservoirs.html