Study on the impact of confining pressure on gas permeability of tight sandstone cores

Abstract Taking the tight sandstone core of Shengli Oilfield as the experimental sample, this paper studies the permeability variation of the tight sandstone under different confining pressures. The experimental results show that when the pore pressure is constant, the measured gas permeability of core decreases with the increase of confining pressure. Power function is more reasonable to describe the influence of confining pressure on permeability of tight sandstone between power function and exponential function. Analyze the impact of confining pressure on gas permeability of tight sandstone cores by using permeability change rate coefficient D and coefficient S.

Download Full-text

An Experimental Study on Stress Sensitivity of Tight Sandstones with Different Microfractures

Advances in Civil Engineering ◽

10.1155/2020/1865464 ◽

2020 ◽

Vol 2020 ◽

pp. 1-10

Author(s):

Xinli Zhao ◽

Zhengming Yang ◽

Zhiyuan Wang ◽

Wei Lin ◽

Shengchun Xiong ◽

...

Keyword(s):

Gas Permeability ◽

High Stress ◽

Confining Pressure ◽

Fracture Network ◽

Sensitivity Coefficient ◽

Stress Sensitivity ◽

Tight Sandstone ◽

The Core ◽

Before And After ◽

Tight Reservoirs

Aiming at the stress sensitivity problem of tight reservoirs with different microfractures, the cores of H oilfield and J oilfield with different microfractures were obtained through the fractures experiment, so as to study the change of gas permeability in tight sandstone core plug during the change of confining pressure. Besides, we use the nuclear magnetic resonance (NMR) spectra of the core before and after saturation to verify whether the core has been successfully fractured. Based on Terzaghi’s effective stress principle, the permeability damage rate (D) and the stress sensitivity coefficient (Ss) are used to evaluate the stress sensitivity of the core, which show consistency in evaluating the stress sensitivity. At the same time, we have studied the petrological characteristics of tight sandstone in detail using thin section (TS) and scanning electron microscope (SEM). The results show that the existence of microfractures is the main factor for the high stress sensitivity of tight sandstone. In addition, because of the small throat of the tight reservoir core, the throat closes when the overlying stress increases. As a result, the tight sandstone pore size is greatly reduced and the permeability is gradually reduced. Therefore, in the development of tight reservoirs, we should not only consider the complex fracture network produced by fracturing, but also pay attention to the permanent damage of reservoirs caused by stress sensitivity.

Download Full-text

Mechanism of Structural Damage in Low Permeability Coal Material of Coalbed Methane Reservoir under Cyclic Cold Loading

Energies ◽

10.3390/en13030519 ◽

2020 ◽

Vol 13 (3) ◽

pp. 519

Author(s):

Hewan Li ◽

Jianping Zuo ◽

Laigui Wang ◽

Pengfei Li ◽

Xiaowei Xu

Keyword(s):

Liquid Nitrogen ◽

Coalbed Methane ◽

Structural Damage ◽

Coal Sample ◽

Gas Permeability ◽

Confining Pressure ◽

Damage Degree ◽

Confining Pressures ◽

Coalbed Methane Reservoir ◽

The Relationship

The pore and fracture structure of coal is the main factor that affects the storage and seepage capacity of coalbed methane. The damage of coal structure can improve the gas permeability of coalbed methane. A coal sample with a drilled hole was kept inside of a custom-designed device to supply confining pressure to the coal sample. Liquid nitrogen was injected into the drilled hole of the coal sample to apply cyclic cold loading. Confining pressures varying from 0~7 MPa to the coal sample were applied to explore the relationship between the structural damage and confining pressure. The structural damage rules of coal samples under different confining pressure were revealed. The results showed that: (1) The structural damage degree of the coal sample increases with the increase of confining pressure; (2) The coal sample was broken after three cycles of cold loading under 7 MPa confining pressure; (3) Without confining pressure, the coal sample is more likely to be damaged or even destroyed by cold liquid nitrogen. (4) The fracture extends along the stratification direction of coal samples, which is significant for coal samples with original fractures, but not obvious for the coal sample without fracture. The research results provide a new method and theoretical basis for permeability improvement of the coal seam.

Download Full-text

Thermal Liability of Hyaloclastite in the Krafla Geothermal Reservoir, Iceland: The Impact of Phyllosilicates on Permeability and Rock Strength

Geofluids ◽

10.1155/2020/9057193 ◽

2020 ◽

Vol 2020 ◽

pp. 1-20 ◽

Cited By ~ 1

Author(s):

Josh Weaver ◽

Guðjón H. Eggertsson ◽

James E. P. Utley ◽

Paul A. Wallace ◽

Anthony Lamur ◽

...

Keyword(s):

Compressive Strength ◽

Thermal Treatment ◽

Elevated Temperatures ◽

Gas Permeability ◽

Temperature Fluctuations ◽

Confining Pressure ◽

Bulk Rock ◽

Geothermal Fields ◽

Triaxial Compressive Strength ◽

The Impact

Geothermal fields are prone to temperature fluctuations from natural hydrothermal activity, anthropogenic drilling practices, and magmatic intrusions. These fluctuations may elicit a response from the rocks in terms of their mineralogical, physical (i.e., porosity and permeability), and mechanical properties. Hyaloclastites are a highly variable volcaniclastic rock predominantly formed of glass clasts that are produced during nonexplosive quench-induced fragmentation, in both subaqueous and subglacial eruptive environments. They are common in high-latitude geothermal fields as both weak, highly permeable reservoir rocks and compacted impermeable cap rocks. Basaltic glass is altered through interactions with external water into a clay-dominated matrix, termed palagonite, which acts to cement the bulk rock. The abundant, hydrous phyllosilicate minerals within the palagonite can dehydrate at elevated temperatures, potentially resulting in thermal liability of the bulk rock. Using surficial samples collected from Krafla, northeast Iceland, and a range of petrographic, mineralogical, and mechanical analyses, we find that smectite dehydration occurs at temperatures commonly experienced within geothermal fields. Dehydration events at 130, 185, and 600°C result in progressive mass loss and contraction. This evolution results in a positive correlation between treatment temperature, porosity gain, and permeability increase. Gas permeability measured at 1 MPa confining pressure shows a 3-fold increase following thermal treatment at 600°C. Furthermore, strength measurements show that brittle failure is dependent on porosity and therefore the degree of thermal treatment. Following thermal treatment at 600°C, the indirect tensile strength, uniaxial compressive strength, and triaxial compressive strength (at 5 MPa confining pressure) decrease by up to 68% (1.1 MPa), 63% (7.3 MPa), and 25% (7.9 MPa), respectively. These results are compared with hyaloclastite taken from several depths within the Krafla reservoir, through which the palagonite transitions from smectite- to chlorite-dominated. We discuss how temperature-induced changes to the geomechanical properties of hyaloclastite may impact fluid flow in hydrothermal reservoirs and consider the potential implications for hyaloclastite-hosted intrusions. Ultimately, we show that phyllosilicate-bearing rocks are susceptible to temperature fluctuations in geothermal fields.

Download Full-text

A modified approach for determination of nonlinear properties in seismic response analyses for 200 m high core rock-fill dams

Canadian Geotechnical Journal ◽

10.1139/t08-045 ◽

2008 ◽

Vol 45 (8) ◽

pp. 1064-1072 ◽

Cited By ~ 7

Author(s):

Hongjun Li ◽

Shichun Chi ◽

Gao Lin ◽

Hong Zhong

Keyword(s):

Site Response ◽

Confining Pressure ◽

In Situ Stress ◽

Nonlinear Properties ◽

Rock Fill ◽

Equivalent Linear ◽

Wide Range ◽

Confining Pressures ◽

The Impact

Equivalent linear analyses are widely used for estimation of site response and safety status of rock-fill dams subjected to strong earthquakes. However, the average normalized curves incorporated in the equivalent-linear iterative process cannot precisely depict the variations of dynamic parameters with shearing strain for one type of soil material under a wide range of confining pressures. Thus, a modified approach for the determination of nonlinear properties for soil elements confined under a broad range of effective pressures in site response analyses for high rock-fill dams (>200 m) is proposed. In this approach, the normalized confining-pressure-interpolating curves (CPI curves) of each soil element under different effective stress are obtained by linearly interpolating or extrapolating by its in situ stress. By comparing the results obtained by equivalent linear analyses incorporating the average curves and the CPI curves, respectively, the impact of utilizing the recommended curves when determining nonlinear soil properties on site response analyses of high rock-fill dams (>200 m) is discussed. It is shown that the refinement in the determination of nonlinear properties during site response can be utilized in the near future by incorporating the results of this study in practice.

Download Full-text

Numerical Simulation of SHPB Test for Concrete under Confining Pressure

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.580-583.3144 ◽

2014 ◽

Vol 580-583 ◽

pp. 3144-3148 ◽

Cited By ~ 1

Author(s):

Hua Zhang ◽

Ao Yu Xie ◽

Yu Wei Gao

Keyword(s):

Strain Rate ◽

Split Hopkinson Pressure Bar ◽

Dynamic Properties ◽

Confining Pressure ◽

Hopkinson Pressure Bar ◽

Stress Strain ◽

Confining Pressures ◽

Stress States ◽

Pressure Bar ◽

The Impact

Using the HJC dynamic constitutive model, the Split Hopkinson Pressure Bar (SHPB) impact test with confining pressure for concrete was simulated in the software ANSYS/LS-DYNA. The confining pressure was simulated by applying constant pressure around the specimen. The triangle velocity wave, which has less diffusion, is used as loader in the simulation. The confining pressures used were 0MPa, 2MPa, 4MPa, 8MPa and 16MPa and the stress-strain curves were presented. The influence of confining pressure on the dynamic properties was analyzed by comparing the stress-strain curves of concrete under different stress states. The strain rate decreases sensitively as long as the confining pressure increases. By debugging the impact velocity, the stress-strain curves under the similar strain rate were obtained, which indicate the toughening and reinforcing effect with the increase of confining pressure.

Download Full-text

Gas permeability of a compacted bentonite–sand mixture: coupled effects of water content, dry density, and confining pressure

Canadian Geotechnical Journal ◽

10.1139/cgj-2014-0371 ◽

2015 ◽

Vol 52 (8) ◽

pp. 1159-1167 ◽

Cited By ~ 26

Author(s):

Jiang-Feng Liu ◽

Frédéric Skoczylas ◽

Jean Talandier

Keyword(s):

Water Content ◽

Gas Permeability ◽

Confining Pressure ◽

Degree Of Saturation ◽

Dry Density ◽

Sand Mixture ◽

Compacted Bentonite ◽

High Confining Pressure ◽

Confining Pressures ◽

Gas Tightness

The gas-tightness of compacted bentonite–sand mixtures is important to the total sealing efficiency of geological repositories. The initial aim of this work was to determine whether the combination of a high confining pressure (Pc) and incomplete saturation could cause a bentonite–sand mixture to become gas-tight. The results show that the physical characteristics of the materials (degree of saturation, Sr; porosity, [Formula: see text]; and dry density, ρd) are very sensitive to changes in the applied confining pressures and their own swelling deformation (or shrinkage). The combination of these changes affects the sample’s effective gas permeability (Keff). For materials prepared at a relative humidity (RH) of 98%, Keff decreased from 10−16 to 10−20 m2 when Pc increased from 1 to 7 MPa. This means that gas-tightness can be obtained for a compacted bentonite–sand mixture when the materials experience a series of changes (e.g., w, Sr, [Formula: see text], and ρd). In addition, larger irreversible deformation (or hysteresis) was observed during the loading–unloading cycle for the sample with higher water content. This phenomenon may be attributed to larger interactions between the macrostructural and microstructural deformations and the decrease of preconsolidation pressure during hydration.

Download Full-text

Mechanical behaviour of powders using a medium pressure flexible boundary cubical triaxial tester

Proceedings of the Institution of Mechanical Engineers Part E Journal of Process Mechanical Engineering ◽

10.1243/095440803322328881 ◽

2003 ◽

Vol 217 (3) ◽

pp. 233-241 ◽

Cited By ~ 11

Author(s):

F Li ◽

V M Puri

Keyword(s):

Shear Modulus ◽

Mechanical Behaviour ◽

Triaxial Compression ◽

Three Dimensional ◽

Volumetric Strain ◽

Confining Pressure ◽

Alumina Powder ◽

Medium Pressure ◽

Mean Pressure ◽

Confining Pressures

A medium pressure (<21 MPa) flexible boundary cubical triaxial tester was designed to measure the true three-dimensional response of powders. In this study, compression behaviour and strength of a microcrystalline cellulose powder (Avicel® PH102), a spray-dried alumina powder (A16SG), and a fluid-bed-granulated silicon nitride based powder (KY3500) were measured. To characterize the mechanical behaviour, three types of triaxial stress paths, that is, the hydrostatic triaxial compression (HTC), the conventional triaxial compression (CTC), and the constant mean pressure triaxial compression (CMPTC) tests were performed. The HTC test measured the volumetric response of the test powders under isostatic pressure from 0 to 13.79MPa, during which the three powders underwent a maximum volumetric strain of 40.8 per cent for Avicel® PH102, 30.5 per cent for A16SG, and 33.0 per cent for KY3500. The bulk modulus values increased 6.4-fold from 57 to 367MPa for Avicel® PH102, 3.7-fold from 174 to 637 MPa for A16SG, and 8.1-fold from 74 to 597MPa for KY3500, when the isotropic stress increased from 0.69 to 13.79 MPa. The CTC and CMPTC tests measured the shear response of the three powders. From 0.035 to 3.45MPa confining pressure, the shear modulus increased 28.7-fold from 1.6 to 45.9MPa for Avicel® PH102, 35-fold from 1.7 to 60.5MPa for A16SG, and 28.5-fold from 1.5 to 42.8MPa for KY3500. In addition, the failure stresses of the three powders increased from 0.129 to 4.41 MPa for Avicel® PH102, 0.082 to 3.62 MPa for A16SG, and 0.090 to 4.66MPa for KY3500, respectively, when consolidation pressure increased from 0.035 to 3.45MPa. In addition, the shear modulus and failure stress values determined from the CTC test at 2.07, 2.76, and 3.45MPa confining pressures are consistently greater than those from the CMPTC test at the same constant mean pressures. This observation demonstrates the influence of stress paths on material properties. The CTT is a useful tool for characterizing the three-dimensional response of powders and powder mixtures.

Download Full-text

Application of machine learning algorithms to predict permeability in tight sandstone formations

Nafta-Gaz ◽

10.18668/ng.2021.05.01 ◽

2021 ◽

Vol 77 (5) ◽

pp. 283-292

Author(s):

Tomasz Topór ◽

Keyword(s):

Machine Learning ◽

Oil And Gas ◽

Learning Algorithms ◽

Confining Pressure ◽

Machine Learning Algorithms ◽

Core Material ◽

Confining Stress ◽

Tight Sandstone ◽

Oil And Gas Exploration ◽

Better Than

The application of machine learning algorithms in petroleum geology has opened a new chapter in oil and gas exploration. Machine learning algorithms have been successfully used to predict crucial petrophysical properties when characterizing reservoirs. This study utilizes the concept of machine learning to predict permeability under confining stress conditions for samples from tight sandstone formations. The models were constructed using two machine learning algorithms of varying complexity (multiple linear regression [MLR] and random forests [RF]) and trained on a dataset that combined basic well information, basic petrophysical data, and rock type from a visual inspection of the core material. The RF algorithm underwent feature engineering to increase the number of predictors in the models. In order to check the training models’ robustness, 10-fold cross-validation was performed. The MLR and RF applications demonstrated that both algorithms can accurately predict permeability under constant confining pressure (R2 0.800 vs. 0.834). The RF accuracy was about 3% better than that of the MLR and about 6% better than the linear reference regression (LR) that utilized only porosity. Porosity was the most influential feature of the models’ performance. In the case of RF, the depth was also significant in the permeability predictions, which could be evidence of hidden interactions between the variables of porosity and depth. The local interpretation revealed the common features among outliers. Both the training and testing sets had moderate-low porosity (3–10%) and a lack of fractures. In the test set, calcite or quartz cementation also led to poor permeability predictions. The workflow that utilizes the tidymodels concept will be further applied in more complex examples to predict spatial petrophysical features from seismic attributes using various machine learning algorithms.

Download Full-text

Volume change behaviour and microstructure of stabilized loess under cyclic freeze–thaw conditions

Canadian Journal of Civil Engineering ◽

10.1139/cjce-2016-0052 ◽

2016 ◽

Vol 43 (10) ◽

pp. 865-874 ◽

Cited By ~ 18

Author(s):

Sheng-lin Wang ◽

Qing-feng Lv ◽

Hassan Baaj ◽

Xiao-yuan Li ◽

Yan-xu Zhao

Keyword(s):

Fly Ash ◽

Volume Change ◽

Cement Content ◽

Frost Heave ◽

Equivalent Diameter ◽

Surface Porosity ◽

Change Rate ◽

Freeze Thaw ◽

Significant Damage ◽

The Impact

Freeze–thaw action is considered to be one of the most destructive actions that can induce significant damage in stabilized subgrades in seasonally frozen loess areas. Laboratory tests including frost heave – thaw shrinkage and microstructure change during freeze–thaw cycles were conducted to evaluate the volume change rate of loess stabilized with cement, lime, and fly ash under the impact of cyclic freeze–thaw conditions. The loess specimens collapsed after eight freeze–thaw cycles (192 h), but most stabilized loess specimens had no visible damage after all freeze–thaw cycles were completed. All of the stabilized loess samples underwent a much smaller volume change than the loess alone after the freeze–thaw cycles. Although surface porosity and equivalent diameter of stabilized loess samples increased, the stabilized loess can retain its microstructure during freeze–thaw cycles when the cement content was less than 6%. To ensure freeze–thaw resistance of stabilized loess subgrades, the mix proportions of the three additives was recommended to be 4 to 5% cement, 6% lime, and 10% fly ash.

Download Full-text

Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

Mathematical Problems in Engineering ◽

10.1155/2021/8282493 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Zhiwei Cai ◽

Tongqing Wu ◽

Jian Lu ◽

Yue Wu ◽

Nianchun Xu

Keyword(s):

Shear Crack ◽

Rock Fracture ◽

Confining Pressure ◽

Particle Flow Code ◽

Shear Cracks ◽

Deformation And Failure ◽

Fracture Development ◽

Confining Pressures ◽

The Law ◽

Microcrack Growth

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.

Download Full-text