ABSTRACT which the pore spaces are interconnected.

ABSTRACT

 

Porosity
is one of the two most important properties of a reservoir rock, of which the
other is permeability. Porosity determines a reservoirs storage capacity. It may
be defined as the ratio of void space, commonly called pore volume, to bulk
volume and is usually reported as either fraction or a percentage.

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The
OFITE MODEL 350 porosimeter was designed to rapidly and accurately measure the
effective porosity of a core sample. The effective porosity is the percentage
of void within a solid media in which the pore spaces are interconnected. It is
imperative to accurately measure the effective porosity of a petroleum
reservoir when estimating the amount of recoverable oil within a producing
formation.

In
this experiment, OFITE MODEL 350 porosimeter was used to estimate the effective
porosity of a core sample. The core sample had a diameter of 3.7cm and was 6.3cm
long. The effective porosity was later estimated to be 22.2%.

 

CHAPTER 1: INTRODUCTION

 

Porosity
can be defined as the percentage of void within a solid media. Almost all
hydrocarbon reservoirs are composed of sedimentary rocks in which porosity
values 10 to 40% in sandstones and 5 to 25%in carbonates (M. Peter
Cone & Kersey).

Discrepancies
often exist between laboratory determined porosity values and porosities
derived from downhole logs. Many of these discrepancies can however be
explained by noting differences in the definition and assessment of porosity (M. Peter Cone & Kersey).

Porosity
can be categorized as total or effective porosity. Total porosity is the ratio
of all the pore spaces in the rock to the bulk volume of the rock, while
effective porosity is the ratio of interconnected void spaces to the bulk
volume (Torsaeter & Abtahi, 2000). Thus, only the
effective porosity contains fluids that can be produced from wells (Torsaeter & Abtahi, 2000).

Figure
1: Sketch of Cross Section of Reservoir Rock

 

CHAPTER 2: EXPERIMENTAL
APPARATUS & MATERIALS

2.0 INTRODUCTION

For
the purpose of this experiment, the equipment used includes the core porosimeter
and the Vernier caliper, while the material used was a core plug.

 

2.1 CORE POROSIMETER

The
porosimeter is an instrument used for measuring the pore volume, and hence the
porosity of a core sample. Pore volume is obtained from the
difference between bulk volume and grain volume (Schlumberger Oilfield Glossary, n.d.).

                           

Figure
2: Core porosimeter (OFITE MODEL 350 CORE POP)

 

2.2 VERNIER CALIPER

This
is a measuring instrument that consists of an L-shaped frame with a linear
scale along its longer arm and an L-shaped sliding attachment with a vernier, used
to read directly the dimension of an object (in this case, the core plug)
represented by the separation between the inner or outer edges of the two
shorter arms (American Heritage Dictionaries, 2011).

Figure
3: Vernier Caliper

2.3 CORE PLUG

This
is a plug or sample taken from conventional core for analysis. Core plugs are
typically 2.5 to 3.8cm in diameter and about 5cm long or more (Schlumberger oilfield glossary, n.d.).

                  

Figure
4: Core plugs

CHAPTER 3: EXPERIMENTAL PROCEDURE

 

The
procedure for this experiment (Porosity determination using core porosimeter)
was as follows:

1.      Before
commencement of experiment, I placed all the valves in a vertical condition and
made sure the regulator in the front panel was rotated fully clockwise.

2.      I
turned the unit on and allowed it to warm up for 5-10 minutes.

3.      I
then measured and recorded the diameter and length of the core using a vernier
caliper.

4.      I
unscrewed the sample holder and inserted the core specimen. I then screwed the
sample holder back into place.

5.      Next,
I turned the P2 test valve to the off position.

6.      I
then rotated the regulator clockwise until the pressure read 180psi.

7.      I
then turned the P1 lock in valve to the off position and allowed P1 to
stabilize before recording the value.

 

CHAPTER 4: RESULT DISCUSSION

 

4.1 CONSTANTS OF THE
POROSIMETER

V1 = 60.18cm³

V2 = 165.31cm³

 

4.2 RECORDED PARAMETERS

Initial Pressure Value, P1
= 180.65psi

Final Pressure Value and
Expansion, P2 = 96.5psi

Diameter, D = 3.7cm

Length, L = 6.3cm

 

4.3 CALCULATED PARAMETERS

4.3.1 CORE BULK VOLUME, VB

VB
=

………………………………………………………………………………….. (4.1)

Where:

VB
= Bulk Volume

D
= Diameter

L
= Length

 VB =

 = 67.7cm³

 

4.3.2 V3

V3
=

 ………………………………………………………………………………… (4.2)

Where:

P1 = Initial Pressure
Value

P2 = Final Pressure Value
and Expansion

V1 = Constant of
Porosimeter

 V3 =

 =
112.7cm³

 

4.3.3 CORE GRAIN
VOLUME, VG

VG  = V2-V3 …………………………………………………………………………………..
(4.3)

Where:

VG
= Core Grain Volume

V2
= Constant of the Porosimeter

 

VG  = 165.31 – 112.7 = 52.7cm³

 

4.3.4 CORE PORE VOLUME, VP

VP  = VB – VG
…………………………………………………………………………………. (4.4)

Where:

VB
= Bulk Volume

VG = Core
Grain Volume

VP  = 67.7 – 52.7 = 15cm³

 

4.3.5 POROSITY,

 =

 * 100 …………………………………………………………………………………
(4.5)

Where:

VB
= Bulk Volume

VP
= Core Pore Volume

 =

 * 100
=
22.2%

CHAPTER 5: CONCLUSION

 

In
conclusion, the porosimeter rapidly and accurately measures the effective
porosity of a core sample, which was measured as 22.2% for a core sample of
length 6.3cm and diameter 3.7cm.

The knowledge of the
effective porosity which has been gained is imperative to accurately measure the
effective porosity of a petroleum reservoir when estimating the amount of
recoverable oil within a producing formation