Abstract
Rock porosity is a key physical parameter at room temperature and pressure that plays an important role in evaluating reserves of oil and natural gas. Research on rock porosity spans over a hundred years. However, in situ porosity under a high isostatic pressure has not been adequately explored, and the experimental conditions for measuring porosity remain unclear. To investigate the feasibility of porosity measurement under a high isostatic pressure and the optimal choice of experimental conditions for this, we design an experimental apparatus that can achieve isostatic pressure up to 200 MPa to fit the relationship between the void volume of a given sample and the drop in gas pressure in an empty standard chamber. The effect of experimental parameters, such as the initial gas pressure at the inlet, the time needed for the gas to reach equilibrium, and the time needed for vacuuming, on the porosity experiment was examined. A series of porosity experiments under different isostatic pressures of up to 200 MPa were carried out with this apparatus. The results quantitatively verify the degree to which porosity is related to isostatic pressure.
Highlights
The permeability of the two sandstones exhibited some differences, permeability measurements indicated that effective porosity can be adequately measured by the designed apparatus
To maximize the measurement accuracy of rock porosity, we selected the time within 1 min of when there was a drop of 0.2 kPa, and this was considered as the gas pressure equilibrium time
The rock porosity measuring apparatus that took the autoclave as the sample holder was built, which can achieve porosity determination under a high isostatic pressure of up to 200 MPa
Summary
The common reservoir rocks include limestone, dolomite, sandstone, and shale, all of which consist of a matrix and a void. The effective porosity includes only voids that are interconnected [30]. The porosity measured by the proposed apparatus is the effective porosity Where øe f f is the effective porosity, and Viv and Vb are the volume of the interconnected void and the bulk volume, respectively. The empty volume of the standard chamber is composed of capillary pore volume, valve passage volume, and the inner void volume of pressure sensor. Minerals 2022, 12, 127 and irregular volume of the standard and sample chambers of this platform, the empty volumes of the two parts could not be measured by the direct method. High-precision digital pressure sensor, manufactured by Xi‘an Holder Instrument Co., Ltd. (Xi’an, China), with an accuracy class of ±0.1% F-S., was a part of the platform
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