ABSTRACT

 

One
of the most important factor that considers an hydrocarbon reserve technically
and economically viable is porosity. Its therefore important to estimate the
porosity of the reservoir rock. In doing this, experimental analysis is done on
core samples or logging operations, for better results, direct measurement
using cores is performed.

This report contains the
experimental procedure done to estimate the porosity of a core sample using the
porosimeter equipment. This equipment operates under the principle of Boyle’s
law. Contained in this report is the procedures taken, the result analysis,
observations made.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CHAPTER 1

 

INTRODUCTION

 

A
reservoir rock considered to have to the ability to store fluids is very
important property. The reservoir rock contains small pores which can be a
porous media. Fluids are held in this small pores until they are produced,
hence the amount of pore spaces in a rock makes a good reservoir rock.
Therefore, one very important reservoir parameter is porosity. There are
different methods in which porosity can be measured; It can be measure either
from core obtained during drilling operation or from log analysis. To measure
porosity directly from core, it of importance estimate porosity from core
samples. Porosity is therefore the ability of a reservoir rock to store fluid.
Mathematically, it is said to be the ratio of pore volume to the bulk volume.

The
relationship is given below;

Porosity
 =

It is measured in
percentage or as a fraction.

Stated are some
classifications of porosity, based on the mode of formation.

–         
Primary/Original
porosity

–         
Secondary/Induced
Porosity

Based on the pore
connection;

–    
Absolute
Porosity =

–       

The equipment used in
this experiment works on the principle of Boyles Law.

According
to Boyle’s Law, the pressure exerted by the gas in a container of known volume
is inversely proportional to the volume of the gas. This can be mathematically
expressed as:

,

where,

P
= Pressure of the gas

V
= Volume of the gas

This
implies that,

 

EXPERIMENT

Apparatus

Figure 1
– The OFITE Model 350 Core Porosimeter.

 

This Instrument is used for measuring the
effective porosity of a core sample. This work based on the principle of
Boyle’s Law. However the pressure applied for this experiment was 180psi.

Figure 2
– Placement of Core Sample.

 

Figure 3
– Front Panel of Model 350 Porosimeter.

 

Included
Instrument used are; namely; Core samples, Veneer Calipers

 

PROCEDURE

 

Procedure A – Without a Vacuum
(Normal Porosity Sample)

1.     
Before starting my experiment, I placed
all the valves (P1,P2) in vertical position. Also rotated counter clockwise the
regulators on the front panel.

2.     
I turned the unit on and allowed it
to warm up for 5 to 10 minutes. After the unit warms up, the display read zero.

3.     
The length and diameter of the core
used were measured and documented using a veneer caliper.

4.     
I loosened the sample holder to insert
my core for analysis, and I tightened it back.

5.     
I turned the “P2 Test” valve to the
“Off” position.

6.     
I rotated the regulator in a clockwise
direction, until I reached the required pressure, 180 psi

7.     
I turned the “P1 Lock In” valve to
the “Off” position.

8.     
I made sure the P1 stabilized and recorded
the value

 

 

 

 

 

 

 

 

 

 

CHAPTER 2

RESULTS AND
ANALYSIS

Data
Records

Length of the Core Sample = 6.3 cm3

Diameter of the Core Sample = 3.7 cm3

Current Porosimeter Calibration =
40psi

V1 = 60.18cm3

V2 = 165.31cm3

P1 = 180.65 psi (off
before P1)

P2 = 96.5 psi

 

Data
analysis

Core bulk volume (cm3) VB
 

V1 = 60.18 cm3
and V2 = 165.31

Core Grain Volume, VG (cm3)
= V2-V3 = 165.31 – 112.66 = 52.65cm3

Core Pore Volume, VP = VB-VG
= 67.75 – 52.65 = 15.1cm3

Porosity =

× 100% = 22.28%

PRECAUTIONS

1.    
I ensured that the connection to the gas
source (cylinder was tightly fixed to prevent the evacuation of gas).

2.    
I made sure that the pressure values
stabilized before taking my readings of pressure.

3.    
I avoided parallax error by reading the
pressure gauge values directly (perpendicular to the gauge).

 

MAINTENANCE

 

1.     I
checked the O-ring contained within the sample holder to ensure it did not need
replacement and ensured there was no foreign particles in the sample holder.

 

 

 

 

 

 

 

 

 

 

 

 

 

OBSERVATIONS,
CONCLUSIONS AND RECOMMENDATIONS

 

Observations

1.    
I observed that the Porosimeter did not
have sufficient pressure to induce the required volume of gas to the core to
perform the experiment and hence, the output of the pressure readings was not
coherent with the calibrated values of V1 and V2.

2.    
The direction/orientation of the core plug
when placed in the sample holder does not affect the values of P1
and P2.

 

Conclusions

1.    
Since a large value was obtained for the
porosity, it can be concluded that the core plug is from a highly porous
formation such as unconsolidated sandstone or a vugular carbonate rock with
vugs.

2.    
From the experiment and analysis of the
results obtained, the values of the core grain volume, core pore volume and
porosity have been greatly altered by the calibration of the apparatus
(Porosimeter). However, the determination of the porosity of the reservoir rock
is fundamental to ascertaining the quantity of reservoir fluids in place so as
to establish the technical and economic limits of the field development plan.

 

Recommendations

Sufficient
pressure should be provided in the gas cylinder so as to enable students obtain
accurate values of porosity that they can relate with. This can be achieved by
using alternative sources of gas such as CO2 and O2.