Os Exercícios Petrofísica

Lista P1 Petrofísica

Nome do Aluno:

1) Show that the porosity of a porous medium is given by

φ = 1 – ( ρb / ρs )

where φ = fractional porosity ρb = bulk density of the rock ρs = grain density of the rock Describe experimentally how you would use the above equation to determine the porosity of a consolidated cylindrical core plug sample. Does your experimental procedure measure effective or total porosity? Explain.

1) Mostre que a porosidade de um meio poroso é dada por

φ = 1 - (ρb / ρs)

onde :

φ = porosidade fracionária

ρb = densidade aparente da rocha

ρs = densidade granular da rocha

Descreva experimentalmente como você usaria a equação acima para determinar a porosidade de uma amostra cilíndrica consolidada do obturador do núcleo. Seu procedimento experimental mede a porosidade efetiva ou total? Explicar.

 

2) Calculate the porosity and the grain density of a core sample given the following data:

 Weight of dry core = 26.725 g

Weight of core saturated with kerosene = 27.575 g

Weight of saturated core immersed in kerosene = 16.385 g

API gravity of kerosene = 44°

Calcule a porosidade e a densidade dos grãos de uma amostra nuclear, dados os seguintes dados:

 Peso do núcleo seco = 26.725 g

Peso do núcleo saturado com querosene = 27,575 g

Peso do núcleo saturado imerso em querosene = 16,385 g

Gravidade API de querosene = 44 °

3) FIGURE bellow shows a Boyle’s law porosimeter normally used to determine grain volume in routine core analysis. The operation of the instrument is as follows:

[pic 1]

• The sample is placed in the sample chamber and vented to the atmosphere.

• The sample chamber is sealed.

• The reference chamber is pressurized by means of helium.

• The shut-off valve is closed.

• Once the system comes to equilibrium, the gauge pressure in the reference changer (P1g) is recorded.

• The three-way valve is opened between the reference chamber and the sample chamber.

• Once the system has re-equilibrated, the gauge pressure (P2g) is recorded.

• The instrument was calibrated with steel spheres with the results shown in the table bellow.

[pic 2]

a) Starting from ideal gas law, derive the following equation for the grain volume of the sample:

where

Vs     = grain volume of the sample

Vc     = volume of sample chamber

Vr     = volume of reference chamber In applying ideal gas law, be sure to use the absolute pressures (P1g+Pa) and (P2g+Pa) in your derivation, where Pa is the atmospheric pressure.

If your derivation is correct, Pa will drop out of the equation at the end. If it does not, then you are doing something wrong.

b) Plot an appropriate calibration curve for the porosimeter.

c) Determine the volumes of the chambers, Vc and Vr.