A sequential model of shale gas transport under the influence of fully coupled multiple processes

Martian habitats are ideally constructed using only locally available soils; extant attempts to process structural materials on Mars, however, generally require additives or calcination. In this work we demonstrate that Martian soil simulant Mars-1a can be directly compressed at ambient into a strong solid without additives, highlighting a possible aspect of complete Martian in-situ resource utilization. Flexural strength of the compact is not only determined by the compaction pressure but also significantly influenced by the lateral boundary condition of processing loading. The compression loading can be applied either quasi-statically or through impact. Nanoparticulate iron oxide (npOx), commonly detected in Martian regolith, is identified as the bonding agent. Gas permeability of compacted samples was measured to be on the order of 10−16 m2, close to that of solid rocks. The compaction procedure is adaptive to additive manufacturing.

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Direct Formation of Structural Components Using a Martian Soil Simulant.

Sandstone is encountered in many hydropower projects in China, and its permeability evolution characteristics during the deformation process are one of the most important issues in engineering design. In this study, microstructure observation and mineral content analysis of a sandstone are performed, and triaxial flow experiments under different fluid pressures are carried out. The experiment results show that the permeability evolution with volumetric strain is associated with microcrack development in the process of rock deformation and failure. The volumetric strain is closely related to the permeability and fluid pressure, and it plays a role of linking the flow field and the stress field. A conceptual model is suggested to describe the permeability evolution of the rock. Scanning electron microscope analysis results on some failed specimen pieces illustrate that the fluid pressure plays a role in the development of microcracks. A high fluid pressure can accelerate crack propagation and rock f...

Experimental Research on Permeability Evolution with Microcrack Development in Sandstone under Different Fluid Pressures

The permeability and porosity of a porous sandstone under cyclic loading–unloading conditions are measured using an integrated permeability and porosity measurement system. Mineral content analysis of the rock is performed. The rock contains open microcracks and pores, which can be closed after cyclic loading–unloading; as a result, the permeability and porosity decrease. Based on the test results, the empirical relations of confining stress-dependent sandstone permeability and porosity are derived. A power law is suggested to describe the relationship between the stress-dependent porosity and permeability of the sandstone under both loading and unloading conditions within the stress range used in the experiment. The permeability of the sandstone is more sensitive to stress than to porosity. It is inferred from the test results that the evolution of sandstone porosity and permeability is related to the relative movement of particles and the closure of microcracks.

Gas Permeability and Porosity Evolution of a Porous Sandstone Under Repeated Loading and Unloading Conditions

The seepage property of low-permeability rock is of significant importance for the design and safety analysis of underground cavities. By using a self-developed test system, both permeability and porosity of granite from an underground oil storage depot were measured. In order to study the influence of rock types on permeability, a tight sandstone was selected as a contrast. The experimental results suggested that the porosity of this granite is less than 5% and permeability is low to 10–20 m2 within the range of effective stress. During the loading process, both exponential relationship and power law can be utilized to describe the relationship between effective stress and permeability. However, power law matches the experimental data better during the unloading condition. The stress dependent porosity of granite during loading process can be described via an exponential relationship while the match between the model and experimental data can be improved by a power law in unloading paths. The correlation of permeability and porosity can be described in a power law form. Besides, granite shows great different evolution rules in permeability and porosity from sandstone. It is inferred that this difference can be attributed to the preparing of samples and different movements of microstructures subjected to effective stress.

Stress dependent permeability and porosity of low-permeability rock

Testing device and measuring and calculating method for gas permeability of compact rock material

Natural compact rocks, such as sandstone, granite, and rock salt, are the main materials and geological environment for storing underground oil, gas, CO 2, shale gas, and radioactive waste because they have extremely low permeabilities and high mechanical strengths. Using the inert gas argon as the fluid medium, the stress-dependent permeability and porosity of monzonitic granite and granite gneiss from an underground oil storage depot were measured using a permeability and porosity measurement system. Based on the test results, models for describing the relationships among the permeability, porosity, and confining pressure of rock specimens were analyzed and are discussed. A power law is suggested to describe the relationship between the stress-dependent porosity and permeability; for the monzonitic granite and granite gneiss (for monzonitic granite (A-2), the initial porosity is approximately 4.05%, and the permeability is approximately 10 −19  m 2 ; for the granite gneiss (B-2), the initial porosity is approximately 7.09%, the permeability is approximately 10 −17  m 2 ; and the porosity-sensitivity exponents that link porosity and permeability are 0.98 and 3.11, respectively). Compared with moderate-porosity and high-porosity rocks, for which φ > 15%, low-porosity rock permeability has a relatively lower sensitivity to stress, but the porosity is more sensitive to stress, and different types of rocks show similar trends. From the test results, it can be inferred that the test rock specimens’ permeability evolution is related to the relative particle movements and microcrack closure.

Compact rock material gas permeability properties

Gas flow in small pore throats in compact rocks is usually affected by the gas slippage effect due to the dense structure and low porosity of the rocks. In this study, permeability and porosity of two granitic gneiss specimens under different pore and confining pressures are measured. Petrographic studies are also performed using X-ray diffraction, optical microscopy, and scanning electron microscopy coupled with an energy-dispersive spectrometer. Test data indicate that the gas flow in the compact rock does not follow Darcy’s law due to the effect of gas slippage, and the measured permeability needs to be corrected by the gas slippage effect. The test results show that the gas slippage effect increases subsequently when the pore pressure is low, which leads to the measured permeability higher than the absolute permeability. The influence of confining pressure on the impact rate of the slippage effect appears to approach an upper limit symptomatically. It is found that a power law describes well the relationship between the absolute permeability and the effective porosity. A correlation of the slippage factor and the absolute permeability is provided. When the confining pressure is high and the pore pressure is low, the flows are slip flow and transitional flow and traditional fluid dynamics N–S equations are not applicable and Knudsen’s diffusion equations should be used.

An Experimental Study on the Slippage Effect of Gas Flow in a Compact Rock

The invention discloses a device and method for measuring the effective porosity of a low-permeability rock on the basis of an inert gas experiment. The device comprises a pressure chamber (1), an air pressure loading system (2), a confining pressure loading system (3), the to-be-measured low-permeability rock (4) and a high-precision pressure gauge (5) which are communicated through a communicating pipeline, wherein the to-be-measured low-permeability rock (4) is placed in the pressure chamber (1); the air pressure loading system (2) loads air pressure to the upper and lower surfaces of the to-be-measured low-permeability rock (4); the high-precision pressure gauge (5) is used for measuring the air pressure in the communicating pipeline; the confining pressure loading system (3) loads confining pressure to the periphery of the to-be-measured low-permeability rock (4). According to the method, after air pressure loading, the high-precision pressure gauge is used for measuring pressure changes of inert gas so as to derive the effective porosity of the rock sample under different confining pressure. The device has the advantages that the operation is simple, the range of confining pressure measured in the experiment is wide, the measuring accuracy is high, the experiment period is short, and the final result is easy to convert.

Zuo Jing

Papers

Testing device and measuring and calculating method for gas permeability of compact rock material

Compact rock material gas permeability properties

An Experimental Study on the Slippage Effect of Gas Flow in a Compact Rock

Device and method for measuring effective porosity of low-permeability rock on basis of inert gas experiment