Experimental Investigation of the Evolution of Permeability and Porosity
173
The permeability test methods described by the scholars before are nearly all traditional steady-state methods, and the permeability of the tested oil shale specimens is
all parallel to the bedding orientation. The results of the previous studies show that the
temperature has a great influence on the permeability of the oil shale. But, this method
is time-consuming and inaccurate because the internal structure of oil shale at room
temperature is very dense. Besides, the effect of external in-situ stresses and the effect
perpendicular to the bedding orientation under actual buried geological conditions were
not considered during the test.
In this paper, the gas permeability test device developed based on the pressure pulse
attenuation method is used to test the permeability of oil shale perpendicular to the
bedding orientation under different temperature and volume stress conditions. Besides,
mercury intrusion porosimetry and weight loss tests were also conducted to investigate
the variation of porosity and weight loss with the temperature, and it can provide a better
explanation to the permeability variation with temperature and volumetric stress.
2 Testing Methods and Procedure
2.1 Specimen Preparation
In this test, the large pieces of oil shale specimens removed from the open-pit mine in
Fushun were immediately wrapped in plastic wrap and delivered to the Key Laboratory
of In-Situ Modified Mining of Ministry of Education at the Taiyuan University of Technology. A rock drilling machine was used to drill three cylindrical specimens with a
diameter of 50 mm along the direction perpendicular to the bedding of the oil shale. All
the specimens were processed and polished to a height of 15 mm by a grinder and some
sandpapers, and the parallelism of upper and lower ends was guaranteed to be within
0.05 mm. At the same time, six oil shale specimens with a size of 7 mm × 8 mm
were drilled perpendicular to the bedding direction to conduct a mercury intrusion test.
It should be noticed that all the specimens were drilled from the same oil shale rock.
2.2 Testing Apparatus
1. Pyrolysis device
The WYFI high-temperature and high-pressure pyrolysis reactor (in Fig. 1) developed by the Taiyuan University of Technology was used in the pyrolysis experiment. The
device is composed of pyrolysis reactor, constant pressure pump, temperature control
system, gas-liquid product, collection device, gas cylinder, and data collection system.
Through constant pressure pump and temperature control system, the device can achieve
a constant temperature and constant pressure environment of 20 °C to 600 °C, 0.1 to
20.0 MPa. The internal size of the reactor is 65 mm × 135 mm, which can be used
to simulate the in-situ stress environment pyrolysis test for rock specimens smaller than
this specification.
173
The permeability test methods described by the scholars before are nearly all traditional steady-state methods, and the permeability of the tested oil shale specimens is
all parallel to the bedding orientation. The results of the previous studies show that the
temperature has a great influence on the permeability of the oil shale. But, this method
is time-consuming and inaccurate because the internal structure of oil shale at room
temperature is very dense. Besides, the effect of external in-situ stresses and the effect
perpendicular to the bedding orientation under actual buried geological conditions were
not considered during the test.
In this paper, the gas permeability test device developed based on the pressure pulse
attenuation method is used to test the permeability of oil shale perpendicular to the
bedding orientation under different temperature and volume stress conditions. Besides,
mercury intrusion porosimetry and weight loss tests were also conducted to investigate
the variation of porosity and weight loss with the temperature, and it can provide a better
explanation to the permeability variation with temperature and volumetric stress.
2 Testing Methods and Procedure
2.1 Specimen Preparation
In this test, the large pieces of oil shale specimens removed from the open-pit mine in
Fushun were immediately wrapped in plastic wrap and delivered to the Key Laboratory
of In-Situ Modified Mining of Ministry of Education at the Taiyuan University of Technology. A rock drilling machine was used to drill three cylindrical specimens with a
diameter of 50 mm along the direction perpendicular to the bedding of the oil shale. All
the specimens were processed and polished to a height of 15 mm by a grinder and some
sandpapers, and the parallelism of upper and lower ends was guaranteed to be within
0.05 mm. At the same time, six oil shale specimens with a size of 7 mm × 8 mm
were drilled perpendicular to the bedding direction to conduct a mercury intrusion test.
It should be noticed that all the specimens were drilled from the same oil shale rock.
2.2 Testing Apparatus
1. Pyrolysis device
The WYFI high-temperature and high-pressure pyrolysis reactor (in Fig. 1) developed by the Taiyuan University of Technology was used in the pyrolysis experiment. The
device is composed of pyrolysis reactor, constant pressure pump, temperature control
system, gas-liquid product, collection device, gas cylinder, and data collection system.
Through constant pressure pump and temperature control system, the device can achieve
a constant temperature and constant pressure environment of 20 °C to 600 °C, 0.1 to
20.0 MPa. The internal size of the reactor is 65 mm × 135 mm, which can be used
to simulate the in-situ stress environment pyrolysis test for rock specimens smaller than
this specification.