Laboratory measurement of Biot's coefficient and pore pressure influence on poroelastic rock behaviour

2018 ◽  
Vol 58 (1) ◽  
pp. 182 ◽  
Author(s):  
Hossein Salemi ◽  
Stefan Iglauer ◽  
Ali Rezagholilou ◽  
Mohammad Sarmadivaleh
Keyword(s):  
Pore Pressure ◽  
Volumetric Strain ◽  
Local Stress ◽  
Confining Pressure ◽  
Hydrocarbon Reservoirs ◽  
Biot’S Coefficient ◽  
Geomechanical Analysis ◽  
Loading System ◽  
Pressure Changes ◽  
Stress Variations

Understanding rock behaviour as a function of pore pressure and confining pressure is crucial for petroleum and geomechanical analysis. Indeed, deformation and local stress variations within hydrocarbon reservoirs and their surroundings occur due to pore pressure changes. Theoretically, pore pressure changes coupled with stress variations in hydrocarbon reservoirs are a function of the Biot’s coefficient, the elastic properties of the rock and the reservoir shape. Thus, in this study, the Biot’s coefficient was measured as a function of porosity, permeability, and volumetric strain for five Gosford sandstone samples. A triaxial loading system was used to measure rock volumetric strain while pore pressure and confining pressure were varied. The constant deformation technique was employed for these experiments; i.e. the variation of pore pressure created a volumetric strain, and the confining pressure required to restore the original volumetric strain was measured to calculate Biot’s coefficient. For the investigated samples, measured liquid permeabilities were in the range of 7–10 mD and Biot’s coefficients were 0.84–0.91. This is consistent with similar investigations by other researchers in which measured Biot’s coefficients were in the range of 0.65–0.90. This study thus illustrates how liquid permeability and the Biot’s coefficient decrease as a function of confining pressure.

Experimental investigation of the effect of compliant pores on reservoir rocks under hydrostatic and triaxial compression stress states

2019 ◽  
Vol 56 (7) ◽  
pp. 983-991
Author(s):  
Hua Yu ◽  
Kam Ng ◽  
Dario Grana ◽  
John Kaszuba ◽  
Vladimir Alvarado ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Triaxial Compression ◽  
Matrix Material ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Differential Pressure ◽  
Sandstone Sample ◽  
Stress States ◽  
Rock Springs ◽  
Stage 1

The presence of compliant pores in rocks is important for understanding the stress–strain behaviors under different stress conditions. This paper describes findings on the effect of compliant pores on the mechanical behavior of a reservoir sandstone under hydrostatic and triaxial compression. Laboratory experiments were conducted at reservoir temperature on Weber Sandstone samples from the Rock Springs Uplift, Wyoming. Each experiment was conducted at three sequential stages: (stage 1) increase in the confining pressure while maintaining the pore pressure, (stage 2) increase in the pore pressure while maintaining the confining pressure, and (stage 3) application of the deviatoric load to failure. The nonlinear pore pressure – volumetric strain relationship governed by compliant pores under low confining pressure changes to a linear behavior governed by stiff pores under higher confining pressure. The estimated compressibilities of the matrix material in sandstone samples are close to the typical compressibility of quartz. Because of the change in pore structures during stage 1 and stage 2 loadings, the estimated bulk compressibilities of the sandstone sample under the lowest confining pressure decrease with increasing differential pressure. The increase in crack initiation stress is limited with increasing differential pressure because of similar total crack length governed by initial compliant porosity in sandstone samples.

On: “The influence of pore pressure and confining pressure on dynamic elastic properties of Berea sandstone,” by N. I. Christensen and H. F. Wang (GEOPHYSICS, 50, 207–213, February 1985).

Geophysics ◽  
1986 ◽  
Vol 51 (4) ◽  
pp. 1016-1016
Author(s):  
G. H. F. Gardner
Keyword(s):  
Pore Pressure ◽  
Confining Pressure ◽  
Hysteresis Curve ◽  
Hysteresis Cycle ◽  
Berea Sandstone ◽  
Experimental Accuracy ◽  
Confining Pressures ◽  
History Of ◽  
Pressure Changes ◽  
Dynamic Elastic Properties

The authors present their results as if Berea sandstone were an elastic material; that is, velocities are given as functions of confining and pore pressure. In fact, most rocks are inelastic and velocities depend on the history of the confining and pore pressure, and not just on the present values. Some measurements of hysteresis were reported by Gardner et al. (1965). The confining pressure was cycled between two pressures [Formula: see text] and [Formula: see text] for a fixed pore pressure [Formula: see text], following a fixed schedule of pressure changes, until repeatable values of velocity were obtained. (At any intermediate pressure the velocity measured for increasing pressure was different from the value for decreasing pressure, giving rise to a hysteresis cycle). When the same schedule of pressure changes for the differential pressure [Formula: see text] was followed by holding [Formula: see text] fixed and varying [Formula: see text], the measured velocities followed the same hysteresis curve within the limits of experimental accuracy. In brief, when hysteresis was taken into account, changes in pore and confining pressures were equally effective in changing velocity. In their article, Christensen and Wang do not refer to hysteresis; perhaps they would like to comment on its relevance.

scholarly journals Experimental Investigation of the Liquefaction Properties and Post-Liquefaction Volumetric Strain of Calcareous Sand in Dredger Fill Site

2020 ◽  
Vol 2020 ◽  
pp. 1-15 ◽  
Author(s):  
Shenghua Zhao ◽  
Yanlin Zhao ◽  
Jiang He ◽  
Zhenzhong Cao ◽  
Lei Wang
Keyword(s):  
Relative Density ◽  
Pore Pressure ◽  
Volumetric Strain ◽  
Confining Pressure ◽  
Cyclic Stress ◽  
Calcareous Sand ◽  
Liquefaction Resistance ◽  
Modified Method ◽  
Pressure Development ◽  
Dredger Fill

In this study, dynamic triaxial cyclic tests were conducted to examine the liquefaction properties and post-liquefaction volumetric strain of calcareous sand from a dredger fill site in the midst of the islands and reefs of the South China Sea. The test results indicated that there were some differences in micromorphology and composition between the calcareous sand obtained via dredging and natural calcareous sand. Axial cyclic stress attenuation can lead to higher cyclic vibration than actual liquefaction vibration, and the modified method can eliminate the effect of axial cyclic stress attenuation. Saturated calcareous sand liquefies under undrained and cyclic loading conditions, and the liquefaction resistance of the calcareous sand decreases with an increase of the effective confining pressure in the dense state. Calcareous sand obtained via dredging exhibited a higher liquefaction resistance compared with other types of calcareous sand. Furthermore, the proposed pore pressure development modified model better describes the pore pressure growth of the calcareous sand from the filling site. The fitting parameters of this model exhibited a high correlation with the relative density. Moreover, the post-liquefaction volumetric strain of the calcareous sand is larger than that of quartz sand, exhibiting a linear relationship with relative density.

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

2003 ◽  
Vol 217 (3) ◽  
pp. 233-241 ◽  
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.

scholarly journals Experimental Study on the Effects of Stress Variations on the Permeability of Feldspar-Quartz Sandstone

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-15 ◽  
Author(s):  
Fugang Wang ◽  
Zhaoxu Mi ◽  
Zhaojun Sun ◽  
Xufeng Li ◽  
Tianshan Lan ◽  
...  
Keyword(s):  
Injection Pressure ◽  
Confining Pressure ◽  
Repeated Loading ◽  
Micropore Structure ◽  
Injection Process ◽  
Reservoir Permeability ◽  
Stress Changes ◽  
Cyclic Variations ◽  
Loading And Unloading ◽  
Stress Variations

The multistage and discontinuous nature of the injection process used in the geological storage of CO2 causes reservoirs to experience repeated loading and unloading. The reservoir permeability changes caused by this phenomenon directly impact the CO2 injection process and the process of CO2 migration in the reservoirs. Through laboratory experiments, variations in the permeability of sandstone in the Liujiagou formation of the Ordos CO2 capture and storage (CCS) demonstration project were analyzed using cyclic variations in injection pressure and confining pressure and multistage loading and unloading. The variation in the micropore structure and its influence on the permeability were analyzed based on micropore structure tests. In addition, the effects of multiple stress changes on the permeability of the same type of rock with different clay minerals content were also analyzed. More attention should be devoted to the influence of pressure variations on permeability in evaluations of storage potential and studies of CO2 migration in reservoirs in CCS engineering.

Seasonal trends of reservoir-triggered seismicity in Song Tranh 2 reservoir, Vietnam

2021 ◽  
Author(s):  
Grzegorz Lizurek ◽  
Konstantinos Leptokaropoulos ◽  
Jan Wiszniowski ◽  
Izabela Nowaczyńska ◽  
Nguyen Van Giang ◽  
...  
Keyword(s):  
Water Level ◽  
Pore Pressure ◽  
Seismic Activity ◽  
Water Level Fluctuations ◽  
Response Type ◽  
Seasonal Trends ◽  
Triggered Seismicity ◽  
Stress Orientation ◽  
Water Level Changes ◽  
Pressure Changes

&lt;p&gt;Reservoir-triggered seismicity (RTS) is the longest known anthropogenic seismicity type. It has the potential to generate seismic events of M6 and bigger. Previous studies of this phenomenon have proved that major events are triggered on preexisting major discontinuities, forced to slip by stress changes induced by water level fluctuations and/or pore-pressure changes in the rock mass in the vicinity of reservoirs. Song Tranh 2 is an artificial water reservoir located in Central Vietnam. Its main goal is back up the water for hydropower plant. High seismic activity has been observed in this area since the reservoir was first filled in 2011. The relation between water level and seismic activity in the Song Tranh area is complex, and the lack of clear correlation between water level and seismic activity has led to the conclusion that ongoing STR2 seismic activity is an example of the delayed response type of RTS. However, the first phase of the activity observed after impoundment has been deemed a rapid response type. In this work, we proved that the seismicity recorded between 2013 and 2016 manifested seasonal trends related to water level changes during wet and dry seasons. The response of activity and its delay with respect to water level changes suggest that the main triggering factor is pore pressure change due to the significant water level changes observed. A stress orientation difference between low and high water periods is also revealed. The findings indicate that water load and related pore pressure changes influence seismic activity and stress orientation in this area.&lt;/p&gt;&lt;p&gt;This work was partially supported by research project no. 2017/27/B/ST10/01267, funded by the National Science Centre, Poland, under agreement no. UMO-2017/27/B/ST10/01267.&lt;/p&gt;

scholarly journals Experimental Study of Stress-Seepage Coupling Properties of Sandstone under Different Loading Paths

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-21
Author(s):  
Xi Chen ◽  
Wei Wang ◽  
Yajun Cao ◽  
Qizhi Zhu ◽  
Weiya Xu ◽  
...  
Keyword(s):  
Elastic Modulus ◽  
Pore Pressure ◽  
Complex Loading ◽  
Friction Angle ◽  
Confining Pressure ◽  
Triaxial Tests ◽  
Compression Tests ◽  
Biot Coefficient ◽  
Cyclic Loading And Unloading ◽  
Loading And Unloading

The study on hydromechanical coupling properties of rocks is of great importance for rock engineering. It is closely related to the stability analysis of structures in rocks under seepage condition. In this study, a series of conventional triaxial tests under drained condition and hydrostatic compression tests under drained or undrained condition on sandstones were conducted. Moreover, complex cyclic loading and unloading tests were also carried out. Based on the experimental results, the following conclusions were obtained. For conventional triaxial tests, the elastic modulus, peak strength, crack initiation stress, and expansion stress increase with increased confining pressure. Pore pressure weakened the effect of the confining pressure under drained condition, which led to a decline in rock mechanical properties. It appeared that cohesion was more sensitive to pore pressure than to the internal friction angle. For complex loading and unloading cyclic tests, in deviatoric stress loading and unloading cycles, elastic modulus increased obviously in first loading stage and increased slowly in next stages. In confining pressure loading and unloading cycles, the Biot coefficient decreased first and then increased, which indicates that damage has a great impact on the Biot coefficient.

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