Laboratory measurement of compaction-induced permeability change in porous rocks: Implications for the generation and maintenance of pore pressure excess in the crust

1994 ◽  
Vol 143 (1-3) ◽  
pp. 425-456 ◽  
Author(s):  
Christian David ◽  
Teng-Fong Wong ◽  
Wenlu Zhu ◽  
Jiaxiang Zhang
Keyword(s):  
Pore Pressure ◽  
Laboratory Measurement ◽  
Permeability Change ◽  
Porous Rocks

Modeling Laboratory Permeability in Coal Using Sorption-Induced Strain Data

2007 ◽  
Vol 10 (03) ◽  
pp. 260-269 ◽  
Author(s):  
Eric P. Robertson ◽  
Richard L. Christiansen
Keyword(s):  
Pore Pressure ◽  
Fractured Reservoirs ◽  
Permeability Change ◽  
Coal Seams ◽  
Overburden Pressure ◽  
Change Models ◽  
Coal Permeability ◽  
Coal Matrix ◽  
Strain Data ◽  
The Matrix

Summary Sorption-induced strain and permeability were measured as a function of pore pressure using subbituminous coal from the Powder River basin of Wyoming, USA, and high-volatile bituminous coal from the Uinta-Piceance basin of Utah, USA. We found that for these coal samples, cleat compressibility was not constant, but variable. Calculated variable cleat-compressibility constants were found to correlate well with previously published data for other coals. Sorption-induced matrix strain (shrinkage/swelling) was measured on unconstrained samples for different gases: carbon dioxide (CO2), methane (CH4), and nitrogen (N2). During permeability tests, sorption-induced matrix shrinkage was demonstrated clearly by higher-permeability values at lower pore pressures while holding overburden pressure constant; this effect was more pronounced when gases with higher adsorption isotherms such as CO2 were used. Measured permeability data were modeled using three different permeability models that take into account sorption-induced matrix strain. We found that when the measured strain data were applied, all three models matched the measured permeability results poorly. However, by applying an experimentally derived expression to the strain data that accounts for the constraining stress of overburden pressure, pore pressure, coal type, and gas type, two of the models were greatly improved. Introduction Coal seams have the capacity to adsorb large amounts of gases because of their typically large internal surface area (30 to 300 m2/g) (Berkowitz 1985). Some gases, such as CO2, have a higher affinity for the coal surfaces than others, such as N2. Knowledge of how the adsorption or desorption of gases affects coal permeability is important not only to operations involving the production of natural gas from coalbeds but also to the design and operation of projects to sequester greenhouse gases in coalbeds (RECOPOL Workshop 2005). As reservoir pressure is lowered, gas molecules are desorbed from the matrix and travel to the cleat (natural-fracture) system, where they are conveyed to producing wells. Fluid movement in coal is controlled by diffusion in the coal matrix and described by Darcy flow in the fracture (cleat) system. Because diffusion of gases through the matrix is a much slower process than Darcy flow through the fracture (cleat) system, coal seams are treated as fractured reservoirs with respect to fluid flow. However, coalbeds are more complex than other fractured reservoirs because of their ability to adsorb (or desorb) large quantities of gas. Adsorption of gases by the internal surfaces of coal causes the coal matrix to swell, and desorption of gases causes the coal matrix to shrink. The swelling or shrinkage of coal as gas is adsorbed or desorbed is referred to as sorption-induced strain. Sorption-induced strain of the coal matrix causes a change in the width of the cleats or fractures that must be accounted for when modeling permeability changes in the system. A number of permeability-change models (Gray 1987; Sawyer et al. 1990; Seidle and Huitt 1995; Palmer and Mansoori 1998; Pekot and Reeves 2003; Shi and Durucan 2003) for coal have been proposed that attempt to account for the effect of sorption-induced strain. Accurate measurement of sorption-induced strain becomes important when modeling the effect of gas sorption on coal permeability. For this work, laboratory measurements of sorption-induced strain were made for two different coals and three gases. Permeability measurements also were made using the same coals and gases under different pressure and stress regimes. The objective of this current work is to present these data and to model the laboratory-generated permeability data using a number of permeability-change models that have been described by other researchers. This work should be of value to those who model coalbed-methane fields with reservoir simulators because these results could be incorporated into those reservoir models to improve their accuracy.

The effect of pore pressure depletion and injection cycles on ultrasonic velocity and quality factor in a quartz sandstone

Geophysics ◽  
2007 ◽  
Vol 72 (2) ◽  
pp. E43-E51 ◽  
Author(s):  
P. Frempong ◽  
A. Donald ◽  
S. D. Butt
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Axial Strain ◽  
Fluid Pressure ◽  
Porous Rocks ◽  
Confining Stress ◽  
Viscoelastic Deformation ◽  
Experimental Conditions ◽  
Pore Pressures ◽  
Pressure Depletion

Passing seismic waves generate transient pore-pressure changes that influence the velocity and attenuation characteristics of porous rocks. Compressional ultrasonic wave velocities [Formula: see text] and quality factors [Formula: see text] in a quartz sandstone were measured under cycled pore pressure and uniaxial strain conditions during a laboratory simulated injection and depletion process. The objectives were to study the influence of cyclical loading on the acoustic characteristics of a reservoir sandstone and to evaluate the potential to estimate pore-fluid pressure from acoustic measurements. The values of [Formula: see text] and [Formula: see text] were confirmed to increase with effective stress increase, but it was also observed that [Formula: see text] and [Formula: see text] increased with increasing pore pressure at constant effective stress. The effective stress coefficient [Formula: see text] was found to be less thanone and dependent on the pore pressure, confining stress, and load. At low pore pressures, [Formula: see text] approached one and reduced nonlinearly at high pore pressures. The change in [Formula: see text] and [Formula: see text] with respect to pore pressure was more pronounced at low versus high pore pressures. However, the [Formula: see text] variation with pore pressure followed a three-parameter exponential rise to a maximum limit whereas [Formula: see text] had no clear limit and followed a two-parameter exponential growth. Axial strain measurements during the pore-pressure depletion and injection cycles indicated progressive viscoelastic deformation in the rock. This resulted in an increased influence on [Formula: see text] and [Formula: see text] with increasing pore-pressure cycling. The value [Formula: see text] was more sensitive in responding to the loading cycle and changes in pore pressures than [Formula: see text]; thus, [Formula: see text] may be a better indicator for time-lapse reservoir monitoring than [Formula: see text]. However, under the experimental conditions, [Formula: see text] was unstable and difficult to measure at low effective stress.

scholarly journals Analysis of Damage and Permeability Evolution for Mudstone Material under Coupled Stress-Seepage

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3755
Author(s):  
Bin Liu ◽  
Jinlan Li ◽  
Quansheng Liu ◽  
Xuewei Liu
Keyword(s):  
Finite Element ◽  
Pore Pressure ◽  
Permeability Coefficient ◽  
Minimum Energy ◽  
Coupling Model ◽  
Capacity Expansion ◽  
Permeability Change ◽  
Permeability Evolution ◽  
Finite Element Software ◽  
Coupled Stress

Mudstone material in a deep roadway is under the coupled stress-seepage condition. To investigate the permeability change and damage development during rock excavation in roadways, a stress-seepage damage coupling model has been proposed. In this model, damage capacity expansion of mudstone material is considered as the initiation and propagation of micro-cracks and the fracture penetration. A damage variable is introduced into the proposed model based on the principle of minimum energy consumption. As a result, an elastoplastic damage constitutive equation is established. Then, the permeability evolution equation describing the micro-macro hydraulic behavior of mudstone is deduced via percolation theory, which can describe the characteristics of sudden permeability change after rock capacity expansion. Furthermore, a finite element model is established based on commercial finite element software-ABAQUS. The numerical model was firstly verified by comparison between experimental and simulation results. On the basis of it, numerical investigation of the temporal and spatial evolution law of pore pressure, damage and permeability coefficient during roadway excavation is undertaken. The numerical results indicate that with increase of construction time, pore pressure first increases and then decreases, while the damage zone and permeability coefficient increase gradually and finally nearly keep constant. The proposed coupling model and finite element method can describe damage and permeability evolution for mudstone material under coupled stress-seepage well.

Effect of Overburden Pressure on Some Properties Of Sandstones

1962 ◽  
Vol 2 (04) ◽  
pp. 360-366 ◽  
Author(s):  
Valery M. Dobrynin
Keyword(s):  
Experimental Data ◽  
Physical Properties ◽  
Pore Pressure ◽  
Clay Minerals ◽  
Elastic Waves ◽  
Water Saturation ◽  
Porous Rocks ◽  
Overburden Pressure ◽  
Pore Compressibility ◽  
Internal Pore

Abstract Experimental data demonstrate that physical properties of porous rocks change under pressure. In this paper an assumption is made and proved that under pressure the changes of physical properties such as porosity, density, permeability, resistivity and velocity of elastic waves are controlled to a large extent by the pore compressibility of rocks. It is also shown that the pore compressibility of rocks can be determined, within the range of pressures from 0 to 20,000 psi, by knowing the maximum pore compressibility and the magnitude of the pressure. Mathematical equations were developed which permit one to define changes in physical properties of porous rocks under pressure. These equations were verified by experimental data obtained from the study of sandstones. Introduction In studying the behavior of porous rocks under pressure in the field of petroleum technology, the most interesting aspect is the observation of those properties which characterize the rocks as possible reservoirs for example, porosity, permeability, resistivity, density and be velocity of elastic waves. The literature dealing with this problem mainly contains data concerning the study of only one or at most two of these parameters, but not of the group as a whole. An attempt is made in this paper to find general equations involving each of these parameters, which will permit the study of the behavior of rocks under pressure. All experimental data used here were obtained from the investigation of consolidated sandstones. EXPERIMENTAL In addition to the use of published experimental data, an experiment was carried out which studied the main physical properties of sandstones under pressure. Two homogeneous quartz sandstones were chosen for this purpose:the Torpedo sandstone bona Kansas, andthe Medina sandstone from Ohio. The porosity of the Torpedo sandstone was 20.2 per cent, and that of the Medina 8.7 per cent. Permeabilities were 45 md and less than 1 md, respectively. Each sandstone contained about 5 per cent clay minerals, consisting mostly of kaolinite and chlorite, which were distributed quite evenly throughout the samples. One cylindrical sample 2 in. in diameter and 5 in. in length was cut from each sandstone and then saturated in a vacuum with a 3N solution of NaCl. This high concentration was used in order to obtain true formation factors and to decrease the swelling of the clay minerals. The methods of mounting the samples and measuring the changes in porosity and resistivity were practically the same as those described by Fatt and Mann. Changes of resistivity under pressure were studied for sandstones with 100 per cent water saturation, and for sandstones with the irreducible water saturation. The irreducible saturation was obtained by enclosing the saturated rock samples in relatively fine silicate powder so as to remove the water by capillary action. This procedure is described by Orkin and Kuchinski. Changes of permeability with pressure were determined at room temperature using nitrogen as the flowing medium. In studying the effects of pressure, one series of measurements was made using an internal pore pressure Pi equal to the atmospheric pressure, while the overburden pressure P. ranged from 0 to 20,000 psi. A second series of measurements was used over the same range of overburden pressure, but with an internal pore pressure of 1,800 psi When the results were compared on the basis of net overburden pressure (P, - 0.85 Pi ), there was practically no difference for these two sandstones. The origin of the factor 0.85 in the expression for net overburden pressure is given by Brandt, Fatt and Geertsma. SPEJ P. 360^

Solid-phase bulk modulus and microinhomogeneity parameter from quasistatic compression experiments

Geophysics ◽  
2014 ◽  
Vol 79 (6) ◽  
pp. A51-A55 ◽  
Author(s):  
Tobias M. Müller ◽  
Pratap N. Sahay
Keyword(s):  
Bulk Modulus ◽  
Pore Pressure ◽  
Solid Phase ◽  
Additional Parameter ◽  
Direct Measure ◽  
Porous Rocks ◽  
Complete Set ◽  
Pore Pressure Build Up

Quasistatic deformation experiments in the laboratory are key to determining the poroelastic moduli of rocks. For microinhomogeneous porous rocks, it is a challenge to determine a complete set of poroelastic parameters. This is because an additional parameter is required that quantifies the effect of microinhomogeneities because then the unjacketed bulk and pore moduli are no longer the same as the bulk modulus of the solid phase. We found that measurements for the drained and unjacketed bulk moduli together with Skempton’s pore-pressure build-up coefficient were sufficient to determine the solid-phase bulk modulus and the microinhomogeneity parameter. The latter served as a direct measure for the deviation from Biot-Gassmann prediction for the undrained bulk modulus. We applied the results to a set of measured poroelastic moduli in which microinhomogeneities have been made responsible for a non-Gassmann rock behavior. Accordingly, our estimate for the microinhomogeneity parameter quantified the deviation from the Biot-Gassmann prediction.

Sorption-Induced Permeability Change of Coal During Gas-Injection Processes

2008 ◽  
Vol 11 (04) ◽  
pp. 792-802 ◽  
Author(s):  
Wenjuan Lin ◽  
Guo-Qing Tang ◽  
Anthony R. Kovscek
Keyword(s):  
Pore Pressure ◽  
Effective Stress ◽  
Gas Adsorption ◽  
Gas Production ◽  
Co2 Injection ◽  
Permeability Reduction ◽  
Permeability Change ◽  
Gas Composition ◽  
Adsorption Equilibria ◽  
Study Results

Summary Our study has two features. First, laboratory experiments measured the change of the permeability of coal samples as a function of pore pressure and injected-gas composition at constant effective stress. Second, adsorption-solution theory described adsorption equilibria and aided interpretation. The gases tested include pure methane (CH4), nitrogen (N2), and carbon dioxide (CO2), as well as binary mixtures of N2 and CO2 of different compositions. The coal pack was initially dry and free of gas, then saturated by each test gas at a series of increasing pore pressures at a constant effective stress until steady state was reached. Thus, the amount of adsorption varied, while the effective stress was held constant. Results show that, (i) permeability decreases with an increase of pore pressure at fixed injection-gas composition, and, (ii) permeability change is a function of the injected-gas composition. As the concentration of CO2 in the injection gas increases, the permeability of the coal decreases. Pure CO2 leads to the greatest permeability reduction among all the test gases. However, 10 to 20% by mole of N2 helps to preserve permeability significantly. According to the mixed-gas adsorption isotherms, adsorption and the selectivity of a particular gas species on coal surfaces is a function of pressure and the gas composition. Therefore, we conclude that loading coal surfaces with adsorbed gas at constant effective stress causes permeability reduction. Finally, gas adsorption and permeability of coal are correlated, simply to extend the usefulness of study results. Introduction Coalbed methane (CBM) has grown to supply approximately 10% of US natural-gas production and is becoming important worldwide as an energy source (EIA 2006). Conventional CBM-recovery procedures stimulate wells and produce CH4 by depressurizing the coalbed. A full understanding of the mechanisms underlying CBM production has yet to be established. Injection of CO2, N2, or mixtures of the two gases enhances CBM recovery significantly (Stevens et al. 1998; Stevens 2001). Coalbeds also present a potential sink for greenhouse gases (GHGs), such as CO2. One issue of particular interest for CO2 injection, and the subject of our study, is the sensitivity of coal permeability to the partial pressure of CO2 in the injection gas.

scholarly journals Failure in the Tension Zone around a Circular Tunnel Excavated in Saturated Porous Rock

2021 ◽  
Vol 11 (18) ◽  
pp. 8384
Author(s):  
Chiara Deangeli
Keyword(s):  
Compressive Strength ◽  
Pore Pressure ◽  
Uniaxial Compressive Strength ◽  
Numerical Models ◽  
Rock Properties ◽  
Far Field ◽  
Tension Zone ◽  
Porous Rocks ◽  
Circular Tunnel ◽  
Tunnel Excavation

Rock failure during tunnel excavation is still a matter of concern. The influence of groundwater is generally taken into account along discontinuities or in “soil-like” formations. However, brittle saturated porous rocks can be subject to undrained conditions during tunnel excavation. Negative effective stresses develop close to the tunnel boundary. This study aims at identifying a limit pore pressure in the rock around the tunnel, which induces failure in the tension zone. A discussion related to the strength parameters in the tension zone, with the Hoek and Brown criterion, is presented. A comparative analysis with different far-field stresses and rock properties indicates that the limit pore pressure decreases with the depth of the tunnel. The limit pore pressure is directly proportional to the uniaxial compressive strength and inversely proportional to the constant m. When the uniaxial compressive strength is close to the state of stress around the tunnel, the role of m reduces. Numerical models set up with FLAC indicate that the tension zone around the tunnel has a thickness of about 1 m. Due to uncertainties in the far-field stresses, hydro-mechanical behavior, and properties of the rock, the tension zone requires a careful investigation, in order to avoid stability problems.

An New Approach for Estimating Critical Injection Pressure and Fault Stability during Fluid Injection into Rock Reservoir

2011 ◽  
Vol 243-249 ◽  
pp. 3966-3974
Author(s):  
Jun Ping Zhou ◽  
De Guo Xiong ◽  
Xue Fu Xian ◽  
Yong Dong Jiang ◽  
Zhan Fang Liu ◽  
...  
Keyword(s):  
Pore Pressure ◽  
Oil Recovery ◽  
Temporal Distribution ◽  
Injection Pressure ◽  
Radial Symmetry ◽  
Fault Reactivation ◽  
Fluid Injection ◽  
Porous Rocks ◽  
Fault Stability ◽  
Natural Rock

It is a well-known fact that an injection of the borehole fluids into surrounding porous rocks often results in fault reactivation,such as during hydrocarbon production from a reservoir, fluid injection for enhanced oil recovery, hot dry rock geothermal energy extraction, and waste disposal or carbon dioxide sequestration. However, no rigorously derived method for the description of spatial and temporal distribution of seismic events and for the estimation of the critical value of pore pressure of a porous rock sufficient for the generation of an microseismic has ever been developed. There a model developed within the context of Biot’s theory of poroelasticity is used to obtain the distribution of pore pressure, then the pore pressure is substituted into a Mohr–Coulomb failure criterion to predict the fault stability and the spatio-temporal cluster of microseismic events in a reservoir. in this model, the Biot system of equations is formulated for the radial symmetry case and is supplemented by the relevant boundary conditions, Then the solution is constructed analytically. A key advantage and the novelty of the proposed approach is it allows one to monitor an influence of pressure applied at the borehole within and surrounding reservoir and to predict the lower and upper bounds for the critical state of a natural rock, and it can be used in different reservoirs.

A Reformation of the Equations of Anisotropic Poroelasticity

1991 ◽  
Vol 58 (3) ◽  
pp. 612-616 ◽  
Author(s):  
M. Thompson ◽  
J. R. Willis
Keyword(s):  
Pore Pressure ◽  
Constitutive Equations ◽  
Isotropic Material ◽  
Transverse Isotropy ◽  
Material Behavior ◽  
Solid Skeleton ◽  
Porous Rocks ◽  
Testing Procedures ◽  
Fluid Content ◽  
Mean Strain

The constitutive equations of linear poroelasticity presented by Biot (1955) and Biot and Willis (1957) extended the description of rock behavior into the realm of saturated porous rocks. For isotropic material behavior, Rice and Cleary (1976) gave a formulation which involved material constants whose physical interpretation was particularly simple and direct; this is an aid both to their measurement and to the interpretation of predictions from the theory. This paper treats anisotropic poroelasticity in terms of material tensors with interpretations similar to those of the constants employed by Rice and Cleary. An effective stress principle is derived for such anisotropic material. The material tensors are defined, rigorously, from the stress field and pore fluid content changes produced by boundary displacements compatible with a uniform mean strain and uniform pore pressure increments. Such displacements and pore pressure increments lead to homogeneous deformation on all scales significantly larger than the length scale of microstructural inhomogeneities. This macroscopic behavior is related to the microscopic behavior of the solid skeleton. The tensors which describe the microscopic behavior of the solid skeleton would be difficult, even impossible, to measure, but their introduction allows relationships between measurable quantities to be identified. The end product of the analysis is a set of constitutive equations in which the parameters are all measurable directly from well-accepted testing procedures. Relationships exist between measurable quantities that can be used to verify that the constitutive equations described here are valid for the rock under consideration. The case of transverse isotropy is discussed explicitly for illustration.

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