scholarly journals Permeability Evolution of Fractured Rock Subjected to Cyclic Axial Load Conditions

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-12 ◽  
Author(s):  
Zilong Zhou ◽  
Jing Zhang ◽  
Xin Cai ◽  
Shanyong Wang ◽  
Xueming Du ◽  
...  
Keyword(s):  
Axial Load ◽  
Fractured Rock ◽  
High Amplitude ◽  
Axial Displacement ◽  
Testing System ◽  
Permeability Evolution ◽  
Permeability Enhancement ◽  
Axial Forces ◽  
Dynamic Forces ◽  
Load Conditions

Permeability experiments on saw-cut fractured rock subjected to cyclic axial load conditions were conducted on the MTS815 rock mechanics testing system. The influence of the frequency and amplitude of cyclic axial forces on axial displacement and permeability evolution of fractured rock was experimentally investigated. Results show that the increasing frequency under the same amplitude of axial load leads to a reduction in axial displacement, but a drop followed by an increase in permeability, while the permeability values oscillated sharply under high amplitude of cyclic loads, which can be attributed to the production of gouge materials. Besides, the increase in axial displacement roughly contributed to the permeability reduction, and excessive amplitude of cyclic load posed limited boost to the permeability enhancement. By comparing with the quasistatic function, we found that it did not completely correspond to the trend of the permeability evolution subjected to cyclic axial forces, and sensitivity coefficients evolving with frequency and amplitude should be considered. A new function of the permeability evolution subjected to the amplitude and frequency of cyclic axial forces was derived and verified by the experimental data. This study suggests that small amplitude and high frequency of dynamic forces have the potential for enhancing the permeability of fracture and triggering the disaster of fractured rock.

scholarly journals The influence of fault reactivation on injection-induced dynamic triggering of permeability evolution

2020 ◽  
Vol 223 (3) ◽  
pp. 1481-1496
Author(s):  
Elif Cihan Yildirim ◽  
Kyungjae Im ◽  
Derek Elsworth
Keyword(s):  
Pore Pressure ◽  
Fluid Pressure ◽  
Fault Reactivation ◽  
Permeability Evolution ◽  
Fracture Permeability ◽  
Permeability Enhancement ◽  
Pressure Pulses ◽  
Fracture Sealing ◽  
Permeability Increase ◽  
Pressure Driven

SUMMARY Mechanisms controlling fracture permeability enhancement during injection-induced and natural dynamic stressing remain unresolved. We explore pressure-driven permeability (k) evolution by step-increasing fluid pressure (p) on near-critically stressed laboratory fractures in shale and schist as representative of faults in sedimentary reservoirs/seals and basement rocks. Fluid is pulsed through the fracture with successively incremented pressure to first examine sub-reactivation permeability response that then progresses through fracture reactivation. Transient pore pressure pulses result in a permeability increase that persists even after the return of spiked pore pressure to the null background level. We show that fracture sealing is systematically reversible with the perturbing pressure pulses and pressure-driven permeability enhancement is eminently reproducible even absent shear slip and in the very short term (order of minutes). These characteristics of the observed fracture sealing following a pressure perturbation appear similar to those of the response by rate-and-state frictional healing upon stress/velocity perturbations. Dynamic permeability increase scales with the pore pressure magnitude and fracture sealing controls the following per-pulse permeability increase, both in the absence and presence of reactivation. However, initiation of the injection-induced reactivation results in a significant increase in the rate of permeability enhancement (dk/dp). These results demonstrate the role of frictional healing and sealing of fractures at interplay with other probable processes in pore pressure-driven permeability stimulation, such as particle mobilization.

scholarly journals Experimental Study on Seepage Characteristics of Fractured Rock Mass under Different Stress Conditions

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Ma Haifeng ◽  
Yao Fanfan ◽  
Niu Xin’gang ◽  
Guo Jia ◽  
Li Yingming ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Permeability Coefficient ◽  
Fractured Rock ◽  
Axial Strain ◽  
Strain Curve ◽  
Confining Pressure ◽  
Strain Effect ◽  
Permeability Evolution ◽  
Hoop Strain ◽  
Permeability Characteristics

In order to obtain the mechanical behavior and permeability characteristics of coal under the coupling action of stress and seepage, permeability tests under different confining pressures in the process of deformation and destruction of briquette coal were carried out using the electrohydraulic servo system of rock mechanics. The stress-strain and permeability evolution curves of briquette coal during the whole deformation process were obtained. The mechanical behavior and permeability coefficient evolution response characteristics of briquette coal under stress-seepage coupling are well reflected. Research shows that stress-axial strain curve and the stress-circumferential strain curve have the same change trend, the hoop strain and axial strain effect on the permeability variation law of basic consistent, and the permeability coefficient with the increase of confining pressure and decreases, and the higher the confining pressure, the lower the permeability coefficient, the confining pressure increases rate under the same conditions, and the permeability coefficient corresponding to high confining pressure is far less than that corresponding to low confining pressure. The confining pressure influences the permeability of the briquette by affecting its dilatancy behavior. With the increase of the confining pressure, the permeability of the sample decreases, and the permeability coefficient decreases with the increase of the confining pressure at the initial stage, showing a logarithmic function. After failure, briquette samples show a power function change rule, and the greater the confining pressure is, the more obvious the permeability coefficient decreases.

SHEAR DILATION DIAGNOSTICS—A NEW APPROACH FOR EVALUATING TIGHT GAS STIMULATION TREATMENTS

2007 ◽  
Vol 47 (1) ◽  
pp. 221 ◽  
Author(s):  
S.T. Chipperfield ◽  
J.R. Wong ◽  
D.S. Warner ◽  
C.L. Cipolla ◽  
M.J. Mayerhofer ◽  
...  
Keyword(s):  
Simulation Model ◽  
Shear Failure ◽  
Fractured Rock ◽  
Fracture Network ◽  
Diagnostic Tools ◽  
Order Effects ◽  
Tight Gas ◽  
Gas Reservoirs ◽  
Shear Dilation ◽  
Permeability Enhancement

Many tight gas reservoirs require fracture stimulation to achieve commercial outcomes. These reservoirs can often be characterised geologically and geomechanically by high deviatoric stresses and hard, naturally fractured rock. Stimulation treatments in such reservoirs may create complex fracture networks from a combination of shear and tensile failures. Water fracs can be used where shear failure is anticipated to dominate; however, in these environments few practical modelling tools exist to determine: the level of permeability enhancement; the degree of permeability retainment during draw-down; and, the stimulated rock volume (SRV). This paper seeks to provide the engineer with a suite of tools capable of achieving these goals.This paper presents a dual porosity, pressure-dependent permeability reservoir simulation model that was devised to honour shear failure mechanisms (also called shear dilation) using basic geological characterisation. The assumptions of this model and the pragmatic selection of first-order effects are discussed. Using the results of this simulation model, three families of diagnostic tools are presented. The first category is that of treatment diagnostics, which includes bottom hole pressure evaluation, injectivity and fall-off analysis. The second approach is called seismic-based reservoir characterisation (SBRC), which uses the microseismic to determine the SRV as well as provide estimates of the initial and stimulated fracture network properties. The third category is post-treatment diagnostics, which incorporates the evaluation of pressure draw-down characteristics.Finally, this paper compares these individual approaches and provides a workflow to evaluate data on future wells.

Effect of Elastomeric Snubber Properties on Seismic Response of Vibration-Isolated Mechanical Equipment: An Experimental Study

2008 ◽  
Vol 24 (2) ◽  
pp. 387-403 ◽  
Author(s):  
Saeed Fathali ◽  
André Filiatrault
Keyword(s):  
Seismic Response ◽  
Contact Surface ◽  
High Amplitude ◽  
Relative Displacement ◽  
Mechanical Equipment ◽  
Gap Size ◽  
Displacement Response ◽  
Dynamic Forces ◽  
Centrifugal Chiller ◽  
Input Motion

Earthquake-simulator experiments were conducted on a liquid centrifugal chiller supported by four isolation/restraint systems with built-in elastomeric snubbers. The test plan incorporated variations of input motion amplitudes and snubber properties to investigate their effect on three response quantities: peak dynamic forces induced into the snubbers, peak acceleration, and peak relative displacement response of the equipment. The elastomeric snubbers limited the displacement responses of the vibration-isolated equipment at the expense of excessive dynamic forces and amplification of the equipment acceleration response. The snubber gap size was the most influential property on the response quantities. For high-amplitude input motions, all the response quantities increased with an increase of the gap size. Due to the compressibility of the snubber elastomeric contact-surface, the actual gap size was always larger than the nominal gap size. Even with a nominal gap size less than 0.25 in., the seismic response of the equipment was substantially different from the seismic response of rigidly mounted equipment. Compared to snubbers with constant contact-surface, snubbers with expanding contact-surface resulted in lower dynamic forces. The thicker and softer contact-surface could lower the dynamic forces induced into the snubbers but resulted in larger relative displacement response of the equipment.

scholarly journals Permeability Evolution During Shear Zone Initiation in Low-Porosity Rocks

2021 ◽  
Author(s):  
Christian Kluge ◽  
Guido Blöcher ◽  
Auke Barnhoorn ◽  
Jean Schmittbuhl ◽  
David Bruhn
Keyword(s):  
Shear Zone ◽  
Shear Zones ◽  
Shear Displacement ◽  
Affine Scaling ◽  
Permeability Evolution ◽  
Thin Sections ◽  
Fracture Surface Roughness ◽  
Permeability Enhancement ◽  
Reservoir Conditions ◽  
The Difference

AbstractUsing an innovative experimental set-up (Punch-Through Shear test), we initiated a shear zone (microfault) in Flechtingen sandstone and Odenwald granite under in situ reservoir conditions while monitoring permeability and fracture dilation evolution. The shear zone, which has a cylindrical geometry, is produced by a self-designed piston assembly that punches down the inner part of the sample. Permeability and fracture dilation were measured for the entire duration of the experiment. After the shear zone generation, the imposed shear displacement was increased to 1.2 mm and pore pressure changes of $$\pm 5$$ ± 5 or $$\pm 10$$ ± 10  MPa were applied cyclically to simulate injection and production scenarios. Thin sections and image analysis tools were used to identify microstructural features of the shear zone. The geometry of the shear zone is shown to follow a self-affine scaling invariance, similar to the fracture surface roughness. The permeability evolution related to the onset of the fracture zone is different for both rocks: almost no enhancement for the Flechtingen sandstone and an increase of more than 2 orders of magnitude for the Odenwald granite. Further shear displacement resulted in a slight increase in permeability. A fault compaction is observed after shear relaxation which is associated to a permeability decrease by a factor more than 3. Permeability changes during pressure cycling are reversible when varying the effective pressure. The difference in permeability enhancement between the sandstone and the granite is related to the larger width of the shear zones.

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