COVENANT UNIVERSITY, CANNANLAND
OTA, OGUN STATE.
DEPARTMENT OF PETROLEUM ENGINEERING
POROSITY (USING POROSIMETER)
EMORDI CHIKA JESSICA
Table of Contents
EXPERIMENTAL APPARATUS 6
SAFETY MEASURES 7
Precaution Taken 7
Porosity is an important property of a reservoir rock that determines the economic relevance of the reservoir to the operator/owner, it is important therefore to determine the porosity of the reservoir rock. The porosity of a material can be determined in different way but in this experiment i would be looking at the use of the Ofite model 350 core porosimeter.
This report contains the procedures i used to carry out the experiment, the dimensions of my core sample, my results and conclusions.
Porosity is one of the most important parameters for the reservoir rock. It describes the storage capacity of the rock (Dandekar, 2013), and is described as the part of a rock that does not consists of solid grains but consists of open pores. Porosity is defined as the ratio of the pore volume (PV) to bulk volume (BV). The porosity may be divided into total porosity and effective porosity. The total is the ratio of all the pore spaces in a rock to the BV of the rock,
'= (Total pore volume)/(Total or bulk volume) ............ (1)
This illustrates that the reservoir rock total porosity may be very high with no conductivity to fluids residing in the ores due to the lack of interconnectivity. While the effective porosity is the ratio of all interconnected pore spaces in a rock to the BV.
Figure 1: conceptual representation of different types of pores in a reservoir rock
It may be classified according to its origin as either primary or secondary porosity. The primary porosity is also called the original porosity and is developed during the deposition of the rock. Secondary porosity is described as porosity that has developed after the deposition of the sediments, mainly due to geological activities. Porosity can range from less than 1% for solid granite to more than 50% for peat and clay, and it ranges from 15% to 25% in normal reservoirs. Several parameters influence the porosity, such as grain shape, grain size, sorting, packing and compaction. Porosity is measured as a fraction or most commonly as percentage [%].
'=PV/BV ...................... (1)
BV=''HR^2 ............... (2)
' = Porosity, %
PV = Pore volume, cm3
BV = Bulk volume, cm3
H=Height of the core, cm
R= Radius of the core, cm
The OFITE Model 350 Core Porosimeter:
This equipment if=s used for measuring effective porosity of a core sample using Nitrogen gas as a source of pressure
Figure 2 : porosimeter
Figure '': veneer calliper
This is used to take measurements of the core samples for more accuracy
1. Before starting a test, I placed all valves in the vertical position.
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. I measured and recorded the diameter and length of the core with the calipers included with the unit.
4. I unscrewed the sample holder and insert the core specimen. I screwed the sample holder back into place just until it stops.
5. I turned the 'P2 Test' valve to the 'Off' position.
6. I rotated the regulator clockwise until the pressure reads approx. 180 psi (1,242 kPa).
7. I turned the 'P1 Lock In' valve to the 'Off' position.
8. I allowed P1 to stabilize and recorded the value.
The O-ring contained within the sample holder should be periodically checked and replaced.
By applying a thin film of typical bearing grease to the O-ring its life can be prolonged.
I ensured that the connection to the gas source (cylinder was tightly fixed to prevent the evacuation of gas).
I made sure that the pressure values stabilized before taking my readings of pressure.
I ensured that I turned off the pressure test to off position before opening the core holder to avoid accident due to high pressure.
Length of the Core Sample = 20.5mm
Diameter of the Core Sample = 20.5mm
P1, psi = 153
P2, psi =57.18
V1 = 60.18cm3
V2 = 165.31cm3
Core bulk volume (cm3) VB='''D/4'^2*L
Core Grain Volume, VG (cm3) = V2-V3 = 165.31-161.027
Core Pore Volume, VP = VB-VG = 6.766-4.283
Porosity,'' = V_P/V_B ''100%
''=2.483/6.766'' 100% = 36.698%
Based on the calculated porosity of 36.698% using the porosimeter and gas the core is considered sufficiently porous.
There were errors that might happened during the experiment and might caused in data inaccuracy and miscalculation of the result
The experiment can only count effective porosity (interconnected pores). We cannot determine the whole porosity due to possibility of isolated pores.
Human errors also might happen, i.e. mistake at diameter and length measurement (wrong start, too tight or loose in measurement)
The porosity of the core plug sample can be determined by the OFITE model 350 core porosimeter with gas saturation method, making sure that no empty space in the matrix cup is necessary to make the measurement more accurate. At the end of this experiment i got the porosity of my core sample to be 36.698%
James A. Craig; O. D. Orodu. Reservoir/Core Analysis Laboratory Manual, February 2015
Dandekar, Y. A. (2013). POROSITY. In Y. A. Dandekar, Petroleum Reservoir Rock and Fluid Properties (pp. 19-23). CRC press..
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