Pore Fluid Pressure Evolution Research Articles

Hydro-mechanical earthquake cycles in a poro-visco-elasto-plastic fluid-bearing fault structure

A major goal in earthquake physics is to derive a constitutive framework for fault slip that captures the dependence of shear strength on fault rheology, sliding velocity, and pore-fluid pressure. In this study, we present H-MEC (Hydro-Mechanical Earthquake Cycles), a newly-developed two-phase flow numerical framework — which couples solid rock deformation and pervasive fluid flow — to simulate how crustal stress and fluid pressure evolve during the earthquake cycle. This unified, continuum-based model, incorporates a staggered finite difference–marker-in-cell method and accounts for inertial wave-mediated dynamics and fluid flow in poro-visco-elasto-plastic compressible medium. Global Picard-iterations and an adaptive time stepping allow the correct resolution of both long- and short-time scales, ranging from years to milliseconds. We present a comprehensive in-plane strike-slip setup in which we test analytical poroelastic benchmarks of pore-fluid pressure diffusion from an injection point along a finite fault width. We then investigate how pore-fluid pressure evolution and solid–fluid compressibility control sequences of seismic and aseismic fault slip. While the weakening phase is controlled by localized compaction of pores and dynamic self-pressurization of fluids inside the undrained fault zone, the subsequent propagation of dynamic ruptures is driven by pore-pressure waves. Furthermore, pore-fluid pressure conditions on the fault and shear strength weakening associated with rapid self-pressurization of fluids control the characteristic slip-weakening distance, the final size of seismic events, and the scaling between slip and fracture energy observed for large earthquakes. Our modeling results demonstrate that fault failure can occur due to poroelastic coupling on a finite-width shear zone, thus highlighting the importance of considering the realistic hydro-mechanical structure of faults to investigate fluid-driven seismic and aseismic slip, either as a natural process or induced by human activities.

On the role of pore-fluid pressure evolution and hypoplasticity in debris flows

Abstract For debris flows, two characteristics play a crucial role in their behaviors: (i) the non-linear deformational behavior that stems from the internal contact stress between grains, and (ii) the pore-pressure feedback, which reduces the intergranular friction and, therefore, enhances the mobility of the whole mixture. In a previous work, the constitutive equations of a general grain–fluid multiphase mixture are deduced by exploiting the entropy principle based on the formulation of Muller and Liu. In the work at hand, this thermodynamically consistent and general model is applied to a two-phase debris flow. For this, it is scaled, depth-integrated, compared with other known models and employed for numerical investigations. The extra pore-fluid pressure and the hypoplastic stress are described as internal variables that are, respectively, governed by a pressure diffusion equation and a transport equation related to the hypoplastic material. Numerical investigation of a grain–fluid material, sliding down a slope into a runout, is carried out using a non-oscillatory, shock-capturing central-upwind scheme with the total variation diminishing property. Comparison of the obtained results with those from classical debris flow models shows that the proposed thermodynamic model provides a phenomenological insight into the influence of the pore-pressure feedback and intergranular friction in the flow dynamics. The extra pore-fluid pressure enhances the flow dynamics, while the effect of the intergranular stress is more significant during the settling of the flow and affects the shape of the granular bulk.

Hydromechanical Impacts of Pleistocene Glaciations on Pore Fluid Pressure Evolution, Rock Failure, and Brine Migration Within Sedimentary Basins and the Crystalline Basement

AbstractThe effects of Pleistocene glacial loading on rock failure, permeability increases, pore pressure evolution, and brine migration within two linked sedimentary basins were evaluated using a multiphysics control volume finite element model. We applied this model to an idealized cross section that extends across the continent of North America from the Hudson Bay to the Gulf of Mexico. Our analysis considered lithosphere geomechanical stress changes (σyy > 35 MPa) in response to 10 cycles of ice sheet loading. Hydrologic boundary conditions, lithosphere rheological properties, and aquifer/confining unit configuration were varied in a sensitivity study. We used a Coulomb Failure Stress change metric (ΔCFSp > 0.1 MPa) to increase permeability by a factor of 100 in some simulations. Results suggest that a buildup of anomalous pore pressures up to about 3 MPa occurred in confining units during periods of glaciations, but this had only a second‐order effect on triggering rock failure. In regions prone to failure, permeability increases during glaciations help to explain observations of brine flushing in sedimentary basin aquifers. During the Holocene to present day, deglaciation resulted in underpressure formation in confining units primarily along the northern margin of the northern basin. Holocene‐modern geomechanical stress fields were relatively small (<0.6 MPa). However, pore pressure increases associated with postglacial rebound, especially when a basal sedimentary basin aquifer is present, induced rock failure and seismicity up to 150 km beyond the terminus of the ice sheet. Sedimentary basin salinity patterns did not equilibrate after 10 simulated glacial cycles.

The evolution of pore-fluid pressure and its causes in the Sinian-Cambrian deep carbonate gas reservoirs in central Sichuan Basin, southwestern China

Reconstructing the evolution of paleofluid pressure in carbonate reservoirs is a challenging problem, particularly when no oil-bearing fluid inclusions are available to provide barometric constraints on the fluid system. To recover the paleofluid pressure in the Sinian Dengying Formation (Z2dn) and the Cambrian Longwangmiao Formation (Є1l) of the central paleo-uplift of the Sichuan Basin, we conducted a comprehensive analysis combining the inclusion pressure-volume-temperature simulation, inclusions in situ Raman shifts, and basin modeling. The results showed that the evolution of the pore pressure could be divided into four stages. Prior to the end of the late Triassic, the whole central paleo-uplift was in a normal pressure state. During the Jurassic, a moderate overpressure prevailed in the dolomitic reservoirs of the Gaoshiti-Moxi area and decreased in the adjacent units. At the end of the early Cretaceous, the overpressure reached a maximum in the whole region and was strongest in the Longnüsi area, decreasing to the west. From the late Cretaceous to the present day, the central area of the basin has uplifted rapidly with the overpressure significantly decreasing. Z2dn has been restored to normal pressure during the Neogene, while Є1l remains moderately overpressurized. Based on an analysis of the structural background and preservation conditions, the types of sedimentary facies, the preservation condition of the traps, and the differential weathering process are the primary reasons for the different pressure states in Z2dn and Є1l during the last stages.

A finite volume method for two-phase debris flow simulation that accounts for the pore-fluid pressure evolution

The temporal and spatial evolution of pore-fluid pressure exerts strong control on debris flow motion because it can counteract normal stresses at grain contacts, reduce friction, and enhance bulk flow mobility. In Iverson’s two-phase debris flow model, the depth-averaged pore pressure equation, which takes into account the effect of shear-induced dilatancy, was combined with a previous model to describe the simultaneous evolution of flow velocity and depth, solid mass, and pore-fluid pressure. In this work, a high-resolution scheme based on the finite volume method was used to solve the system of equations. Several numerical tests were performed to verify the ability of the presented model and the accuracy of the proposed numerical method. Numerical results were compared with experimental data obtained in a laboratory, and the effectiveness of the proposed numerical method for solving practical problems has been proven. Numerical results indicated that increases of the pore-fluid pressure could enhance the motion of debris flow and expand the spread area. Furthermore, results showed that the debris shear-induced dilatancy could affect the evolution of pore-fluid pressure, thus further influencing the motion of debris flow.

Poromechanics of stick‐slip frictional sliding and strength recovery on tectonic faults

AbstractPore fluids influence many aspects of tectonic faulting including frictional strength aseismic creep and effective stress during the seismic cycle. However, the role of pore fluid pressure during earthquake nucleation and dynamic rupture remains poorly understood. Here we report on the evolution of pore fluid pressure and porosity during laboratory stick‐slip events as an analog for the seismic cycle. We sheared layers of simulated fault gouge consisting of glass beads in a double‐direct shear configuration under true triaxial stresses using drained and undrained fluid conditions and effective normal stress of 5–10 MPa. Shear stress was applied via a constant displacement rate, which we varied in velocity step tests from 0.1 to 30 µm/s. We observe net pore pressure increases, or compaction, during dynamic failure and pore pressure decreases, or dilation, during the interseismic period, depending on fluid boundary conditions. In some cases, a brief period of dilation is attendant with the onset of dynamic stick slip. Our data show that time‐dependent strengthening and dynamic stress drop increase with effective normal stress and vary with fluid conditions. For undrained conditions, dilation and preseismic slip are directly related to pore fluid depressurization; they increase with effective normal stress and recurrence time. Microstructural observations confirm the role of water‐activated contact growth and shear‐driven elastoplastic processes at grain junctions. Our results indicate that physicochemical processes acting at grain junctions together with fluid pressure changes dictate stick‐slip stress drop and interseismic creep rates and thus play a key role in earthquake nucleation and rupture propagation.

Evolution of pore fluid pressures in a stimulated geothermal reservoir inferred from earthquake focal mechanisms

AbstractThis paper proposes an inversion method to estimate the evolution of pore fluid pressure fields from earthquake focal mechanism solutions. Application of the method to induced seismicity in the Basel enhanced geothermal system in Switzerland shows the evolution of pore fluid pressure in response to fluid injection experiments. The pore fluid pressure in the reservoir was less than the minimum principal stress at each depth, indicating that hydraulic fracturing did not occur during the stimulation. This suggests that seismic events may play an important role in promoting the development of permeable channels, particularly southeast of the borehole where the largest seismic event (Mw 2.95) occurred. This is not directly related to a drastic decrease in fault strength at the hypocenter but rather to positive feedback between permeability enhancement and elastic/poroelastic stress loading from slipping interfaces.

Evolution of pore-fluid pressure during folding and basin contraction in overpressured reservoirs: Insights from the Madison–Phosphoria carbonate formations in the Bighorn Basin (Wyoming, USA)

Reconstructing the evolution of paleofluid (over)pressure in sedimentary basins during deformation is a challenging problem, especially when no hydrocarbon-bearing fluid inclusions are available to provide barometric constraints on the fluid system. This contribution reports the application to a natural case (the Bighorn Basin) of recent methodological advance to access fluid (over)pressure level prevailing in strata during sub-seismic fracture development. The fluid pressure evolution in the Mississippian-Permian Madison–Phosphoria limestone reservoir is tentatively reconstructed from the early Sevier Layer Parallel Shortening to the Laramide folding in two basement-cored folds: the Sheep Mountain Anticline and the Rattlesnake Mountain Anticline. Results point out that supra-hydrostatic pressure values prevail in the limestone reservoir during most of its whole Sevier–Laramide history. The comparison of the reconstructed fluid overpressure values within situ measurements in various overpressure reservoirs in other oil-producing basins highlights that the supra-hydrostatic fluid pressure gradually reaches the lithostatic value during the whole basin contraction and fold development. During most of the LPS history, however, overpressure level can be defined by a mean gradient. Among the factors that control the pressure evolution, the mechanical stratigraphy, the stress regime under which fractures developed and regional fluid flow are likely dominating in the case of the Bighorn Basin, rather than classical factors like disequilibrium compaction or fluid generation during burial. A coeval evolution between fluid overpressure and differential stress build-up is also emphasized. The approach presented in this paper also provides estimates of strata exhumation during folding.

Three‐dimensional earthquake sequence simulations with evolving temperature and pore pressure due to shear heating: Effect of heterogeneous hydraulic diffusivity

A new methodology for three‐dimensional (3‐D) simulations of earthquake sequences is presented that accounts not only for inertial effects during seismic events but also for shear‐induced temperature variations on the fault and the associated evolution of pore fluid pressure. In particular, the methodology allows to capture thermal pressurization (TP) due to frictional heating in a shear zone. One‐dimensional (1‐D) diffusion of heat and pore fluids in the fault‐normal direction is incorporated using a spectral method, which is unconditionally stable, accurate with affordable computational resources, and highly suitable to earthquake sequence calculations that use variable time steps. The approach is used to investigate the effect of heterogeneous hydraulic properties by considering a fault model with two regions of different hydraulic diffusivities and hence different potential for TP. We find that the region of more efficient TP produces larger slip in model‐spanning events. The slip deficit in the other region is filled with more frequent smaller events, creating spatiotemporal complexity of large events on the fault. Interestingly, the area of maximum slip in model‐spanning events is not associated with the maximum temperature increase because of stronger dynamic weakening in that area. The region of more efficient TP has lower interseismic shear stress, which discourages rupture nucleation there, contrary to what was concluded in prior studies. Seismic events nucleate in the region of less efficient TP where interseismic shear stress is higher. In our model, hypocenters of large events do not occur in areas of large slip or large stress drop.

A 48 m.y. history of fracture opening, temperature, and fluid pressure: Cretaceous Travis Peak Formation, East Texas basin

Research Article| July 01, 2010 A 48 m.y. history of fracture opening, temperature, and fluid pressure: Cretaceous Travis Peak Formation, East Texas basin S.P. Becker; S.P. Becker * 1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924, USA *Current address: ExxonMobil Upstream Research Company, P.O. Box 2189, Houston, Texas 77252-2189, USA. Search for other works by this author on: GSW Google Scholar P. Eichhubl; P. Eichhubl † 1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924, USA †E-mail: peter.eichhubl@beg.utexas.edu Search for other works by this author on: GSW Google Scholar S.E. Laubach; S.E. Laubach 1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924, USA Search for other works by this author on: GSW Google Scholar R.M. Reed; R.M. Reed 1Bureau of Economic Geology, The University of Texas at Austin, University Station Box X, Austin, Texas 78713-8924, USA Search for other works by this author on: GSW Google Scholar R.H. Lander; R.H. Lander 2Geocosm LLC, 3311 San Mateo Drive, Austin, Texas 78738, USA Search for other works by this author on: GSW Google Scholar R.J. Bodnar R.J. Bodnar 3Department of Geosciences, 4044 Derring Hall, Virginia Tech, Blacksburg, Virginia 24061, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2010) 122 (7-8): 1081–1093. https://doi.org/10.1130/B30067.1 Article history received: 05 Apr 2009 rev-recd: 03 Aug 2009 accepted: 24 Aug 2009 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation S.P. Becker, P. Eichhubl, S.E. Laubach, R.M. Reed, R.H. Lander, R.J. Bodnar; A 48 m.y. history of fracture opening, temperature, and fluid pressure: Cretaceous Travis Peak Formation, East Texas basin. GSA Bulletin 2010;; 122 (7-8): 1081–1093. doi: https://doi.org/10.1130/B30067.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Quartz cement bridges across opening-mode fractures of the Cretaceous Travis Peak Formation provide a textural and fluid inclusion record of incremental fracture opening during the burial evolution of this low-porosity sandstone. Incremental crack-seal fracture opening is inferred based on the banded structure of quartz cement bridges, consisting of up to 700 cement bands averaging ∼5 μm in thickness as observed with scanning electron microscope–cathodoluminescence. Crack-seal layers contain assemblages of aqueous two-phase fluid inclusions. Based on fluid inclusion microthermometry and Raman microprobe analyses, we determined that these inclusions contain methane-saturated brine trapped over temperatures ranging from ∼130°C to ∼154°C. Using textural crosscutting relations of quartz growth increments to infer the sequence of cement growth, we reconstructed the fluid temperature and pore-fluid pressure evolution during fracture opening. In combination with published burial evolution models, this reconstruction indicates that fracture opening started at ca. 48 Ma and above-hydrostatic pore-fluid pressure conditions, and continued under steadily declining pore-fluid pressure during partial exhumation until present times. Individual fractures opened over an ∼48 m.y. time span at rates of 16–23 μm/m.y. These rates suggest that fractures can remain hydraulically active over geologically long times in deep basinal settings. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Pore pressure development beneath the décollement at the Nankai subduction zone: Implications for plate boundary fault strength and sediment dewatering

Despite its importance for plate boundary fault processes, quantitative constraints on pore pressure are rare, especially within fault zones. Here, we combine laboratory permeability measurements from core samples with a model of loading and pore pressure diffusion to investigate pore fluid pressure evolution within underthrust sediment at the Nankai subduction zone. Independent estimates of pore pressure to ∼20 km from the trench, combined with permeability measurements conducted over a wide range of effective stresses and porosities, allow us to reliably simulate pore pressure development to greater depths than in previous studies and to directly quantify pore pressure within the plate boundary fault zone itself, which acts as the upper boundary of the underthrusting section. Our results suggest that the time‐averaged excess pore pressure (P*) along the décollement ranges from 1.7–2.1 MPa at the trench to 30.2–35.9 MPa by 40 km landward, corresponding to pore pressure ratios of λb = 0.68–0.77. For friction coefficients of 0.30–0.40, the resulting shear strength along the décollement remains <12 MPa over this region. When noncohesive critical taper theory is applied using these values, the required pore pressure ratios within the wedge are near hydrostatic (λw = 0.41–0.59), implying either that pore pressure throughout the wedge is low or that the fault slips only during transient pulses of elevated pore pressure. In addition, simulated downward migration of minima in effective stress during drainage provides a quantitative explanation for down stepping of the décollement that is consistent with observations at Nankai.

Dissociation Behavior of CO2 Hydrate in Sediments during Isochoric Heating

As CO2 is sequestered into sediments in the oceanic environment, CO2 hydrate can form as a byproduct. This study explored the dissociation behavior of CO2 hydrate in sediments in relation to pore fluid pressure evolution and sediment particle size. We synthesized CO2 hydrate in three types of particulate sediments: glass beads, fine sand, and crushed silt. We then dissociated them through isochoric heating. We observed the excess pore fluid pressure build-up and self-preservation behavior, in which the pressure-temperature state evolves along the hydrate phase boundary until either it reaches the second quadruple point or all hydrates dissociate. The pore fluid pressure evolution is limited, however, by the CO2 vapor-liquid phase equilibrium boundary due to the liquefaction of CO2. The presence of CO2 liquid in sediments forces the pressure-temperature evolution to follow the CO2 vapor-liquid phase equilibrium boundary, regardless of hydrate formation and dissociation processes. CO2 hydrate in fine-grained sediments experiences capillary pressure-induced melting point depression, but this effect vanishes when the pores exceed approximately 1 microm, such as in coarse-grained sediments. In particular, any fracture generation in sediments which involves the local release of confinement eliminates the melting point depression induced by the capillary effect.

Evolution of boudins under progressively decreasing pore pressure A case study of pegmatites enclosed in marble deforming at high grade metamorphic conditions, Naxos, Greece

During ductile deformation of marbles under high grade metamorphic conditions on Naxos, Greece, pegmatites enclosed in the marbles were deformed in a brittle fashion forming blocky boudins with quartz crystallized in the interboudin zones. We studied the three-dimensional geometry of the boudins in the field and in two large samples. The first sample was serially sectioned to observe the structural and microstructural evolution; in the second sample we mapped the surface morphology of the deformed pegmatite. In profile, the boudins can be classified as symmetric torn type boudins, evolving towards asymmetric boudins with a later domino boudin component. In three dimensions, however, the morphology of the boudinaged pegma- tite is a simple set of normal faults with mode-I fractures in the fault tips and rotation of the fault blocks to accommodate the extension in the marble. Deformation history was constrained by petrology and microstructures in combi- nation with simple order of magnitude calculations of both the cooling and pore fluid pressure evolution. The dynamically recrystallized, coarse-grained calcite of the marble provides clear evidence that after the pegmatite intruded the marble and solidified, it was deformed at peak conditions of M2b metamorphism (� 670 °C and � 0.6 GPa). Such pegmatitic melts contain � 10 percent H2O which is released during crystalliza- tion. We infer that after crystallization of the pegmatite the pore fluid pressure in the pegmatite remained close to lithostatic due to the very low permeability of the surrounding marble, and the pegmatite was deformed at very low effective stress which led to brittle deformation of feldspar and mode-I fracturing of the pegmatite, forming torn type boudins. With time the pore fluid pressure slowly decreased, increasing the effective stress. Ongoing N-S extension thus resulted in slip along the quartz-filled interboudin zones and in block rotation, producing domino boudins.

Experimental Study of the Compaction of Phyllosilicate-Bearing Sand at Elevated Temperature and with Controlled Pore Water Pressure

Relative to the time-dependent compaction behavior of clean quartz sands, little experimental work has been carried out on phyllosilicate-rich siliciclastic rocks (mudstones). Compaction is expected to be produced by intracrystalline plastic deformation of the phyllosilicate matrix, coupled with pressure solution of embedded quartz grains and with silica reprecipitation in the adjacent pore spaces or loss from the system via an advective flux of pore water. Time dependence of compaction also arises in nature owing to the generation of excess pore pressure, which lowers effective stress and hence compaction rate until such pressure excess becomes dissipated by permeation. A suite of experiments was performed on synthetic mixtures of quartz sand in a matrix of fine grained illite + muscovite, hydrostatically compacted at a range of effective pressures between 10 MPa and 210 MPa, with a constant pore water pressure of 70 MPa and at temperatures ranging between 300 and 450°C. A small adjacent volume of porous quartz sand was provided as a precipitation sink for silica dissolved from the phyllosilicate + quartz mixture. Volume strains were measured by (a) direct measurement of sample length and (b) measurement of amount of pore water expelled at constant pore pressure, and interpreted with the aid of quantitative petrography on compacted samples. Control experiments were performed on (i) dry, clean sand, (ii) dry sand + phyllosilicate, and (iii) wet, clean sand. Dry, clean sand showed almost no compaction. Wet, clean sand showed a degree of compaction similar to dry phyllosilicate + sand, but wet phyllosilicate + sand showed dramatically more compaction. Compaction rate φ for the wet, mixed phyllosilicate/sand samples is described by ![Formula][1] in which σ is effective stress (MPa), φ is porosity (%), R is the gas constant, and T is temperature (K). Petrographic study showed interpenetration of grain contacts, formation of quartz overgrowths, a decrease in the amount of quartz embedded in the phyllosilicate matrix, and an increase in mean grain size of quartz with progressive compaction. These effects are attributed to solution and redeposition of quartz. The empirical compaction law was integrated over a natural burial history. The porosity evolution is extremely sensitive to the evolution of pore fluid pressure and relatively less to temperature gradient and burial rate. There is reasonable qualitative agreement when compared with porosity/depth relations reported in the literature. [1]: /embed/graphic-1.gif

Regional metamorphic dehydration and seismic hazard

We use a one‐dimensional model of coupled heat transport, fluid transport, porosity feedback, and metamorphism to investigate how dehydration reactions, proceeding during burial of hydrous rocks in the footwall of thrusts or the hanging wall of normal faults, may influence the temporal evolution of pore fluid pressure (Pf). Based on a new interpretation of existing kinetic data for the dehydration of model serpentinite, we advance the hypothesis that Pf buildup to tensile failure may be possible within decades of the onset of dehydration in low permeability metamorphic rocks of the middle crust. This model contrasts with both: 1) typical earthquake nucleation models which involve preexisting fluids that play a passive role, responding to tectonic stresses rather than generating them and 2) conventional treatments of Pf generation based on equilibrium thermodynamics and constant rates of dehydration, which require 10³–106 years to produce significant Pf increases. Our results suggest that repeated cycles dehydration‐induced seismicity are plausible in low permeability areas of the mid‐crust, and can be sustained throughout an orogenic episode if fresh hydrous minerals descend into the metamorphic zone along the downgoing face of a thrust‐ or normal‐fault system.