# ISRM Suggested Method for Achieving Full Water Saturation of Rock

J. Labuz<fnref n="1" /> ID · J. Sulem<fnref n="2" /> ID · F. Amann<fnref n="3" /> ID · P. Asem<fnref n="4" /> ID · P. Braun<fnref n="2" /> ID · P. Delage<fnref n="2" /> ID · E. Detournay<fnref n="1" /> ID · J. Fortin<fnref n="5" /> ID ·

S. Ghabezloo<fnref n="2" /> ID · D. Hart<fnref n="6" /> ID · R. Kiuru<fnref n="7" /> ID · R. Makhnenko<fnref n="8" /> ID · E. Papamichos<fnref n="9" />,<fnref n="10" /> ID · J. Sarout<fnref n="11" /> ID · J. Stenebråten<fnref n="10" /> ID ·

S. Vialle<fnref n="12" /> ID · R. Zimmerman<fnref n="13" /> ID

Received: 10 October 2025 / Accepted: 16 October 2025

© The Author(s) 2025

**Keywords** Saturation · Infiltration · Permeability · Poroelasticity

**List of Symbols**

B Skempton coefficient

k Permeability

K Drained bulk modulus

K_a Bulk modulus of bubble

K_f Bulk modulus of fluid

K_s Bulk modulus of solids

K_w Bulk modulus of water

p Pore (fluid) pressure

p_in Inlet pore pressure

p_out Outlet pore pressure

p_test Testing pore pressure

P Confining pressure or mean stress, if principal stresses are not equal

P' Differential pressure or Terzaghi effective confining pressure

S_w Degree of water saturation

T_i Temperature in pressure vessel

T_o Temperature outside but near pressure vessel

v_p Compressional or P-wave velocity

Δp Change in pore (fluid) pressure

ΔP Change in confining pressure

Δp/ΔP Undrained pore pressure coefficient

# 1 Introduction

## 1.1 Scope

The purpose of this suggested method (SM) is to present a set of unified recommendations for water (single-phase, wetting pore fluid) saturation of rock in laboratory experiments associated with a constant bulk modulus of fluid $K_f$. Full water saturation is usually not the end in itself; it is often a prerequisite for hydromechanical testing of rock. However, measuring material parameters, e.g., poroelastic properties described in the SM for uniaxial-strain compressibility testing for reservoir geomechanics (Dudley et al. 2016), is outside the scope of this SM. Apparatus, procedures, and calculations are described, with an emphasis on how they are adapted to the permeability of the rock sample. Water-rock chemical interactions, as well as rate dependence (e.g., creep), are assumed to be negligible at the time scale of the

<figure><img src="image_1.png" /></figure>

<footnote>J. Labuz
jlabuz@umn.edu</footnote>

<footnote n="1">¹ Department of Civil, Environmental, and Geo-Engineering, University of Minnesota, Minneapolis, USA</footnote>

<footnote n="2">² Laboratoire Navier, ENPC, IP Paris, Université Gustave Eiffel, CNRS, Champs-sur-Marne, France</footnote>

<footnote n="3">³ Department of Engineering Geology, RWTH Aachen University, Aachen, Germany</footnote>

<footnote n="4">⁴ University of Texas Permian Basin, Odessa, USA</footnote>

<footnote n="5">⁵ Laboratoire de Géologie, Ecole Normale Supérieure, PSL Research University, CNRS, Paris, France</footnote>

<footnote n="6">⁶ Wisconsin Geological and Natural History Survey, Madison, USA</footnote>

<footnote n="7">⁷ Aalto University, Espoo, Finland</footnote>

<footnote n="8">⁸ University of Illinois at Urbana-Champaign, Urbana, USA</footnote>

<footnote n="9">⁹ Aristotle University of Thessaloniki, Thessaloniki, Greece</footnote>

<footnote n="10">¹⁰ SINTEF Industry, Trondheim, Norway</footnote>

<footnote n="11">¹¹ Australian Resources Research Centre, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Perth, Australia</footnote>

<footnote n="12">¹² Discipline of Geophysics, Curtin University, Perth, Australia</footnote>

<footnote n="13">¹³ Department of Earth Science and Engineering, Imperial College, London, UK</footnote>
laboratory experiment, meaning that this SM applies to rock
with insignificant water sensitivity.

## 1.2 Background

The deformation of earth materials and the transport of flu-
ids are often associated with fluid-saturated rock. The con-
stitutive relations of a fluid-filled porous rock are well estab-
lished (Biot 1941; Biot and Willis 1957; Rice and Cleary
1976; Detournay and Cheng 1993; Wang 2000; Coussy
2010), but an ISRM SM for achieving full water saturation
of rock has been lacking. The SM for determining water
content, porosity, density, absorption, and related proper-
ties (ISRM 1979) mentions wet-type vacuum “saturation,”
by placing the specimen under vacuum while submerged in
water. An alternative method is evacuating water under a
vacuum and then flooding the specimen with water. These
techniques, however, do not yield a degree of saturation S<sub>w</sub>
equal to one because they are limited by low water pressure.

To be successful in achieving and verifying full satura-
tion, i.e., infiltrating all connected cavities (pores) with water
and dissolving all air into the water or compressing air to an
insignificant volume, methods such as immersion or vacuum
must be complemented by a subsequent application of pore
(fluid) pressure *p* to realize K<sub>f</sub>=K<sub>w</sub>, according to 1/K<sub>f</sub>=S<sub>w</sub>/
K<sub>w</sub>+(1-S<sub>w</sub>)/K<sub>a</sub>, where K<sub>w</sub> is the bulk modulus of water and
K<sub>a</sub> is the bulk modulus of an air bubble (Wood 1930; Kon-
ing 1963; Schuurman 1966). As the air is removed and S<sub>w</sub>
approaches one, K<sub>f</sub> approaches K<sub>w</sub>.

A laboratory saturation procedure for soil using (greater
than atmospheric) pore pressure *p*, referred to as back pres-
sure, was promoted by Lowe and Johnson (1960), Wissa
(1969), and Black and Lee (1973). A similar method for
saturation of rock was adopted by Murrell (1965), Neff
(1966), Heck (1972), Todd and Simmons (1972), Cornet
and Fairhurst (1974), and Mesri et al. (1976), among others.
Applying *p* necessitates jacketing the specimen and applying
confining pressure *P* (or mean stress if the principal stresses
are not equal) in excess of *p*. The time required to reach
full saturation can range from several hours to many days,
depending on permeability.

Skempton (1954) checked the saturation of a jacketed soil
specimen within a pressure cell by monitoring, in undrained
isothermal conditions, Δp resulting from ΔP, where Δ is the
change or increment. The ratio Δp/ΔP, which can be called
the undrained pore pressure coefficient, provides a method
to evaluate saturation, as does measuring the compressional
or P-wave ultrasonic velocity v<sub>p</sub> (ISRM 1978b) for nearly
saturated rock (Wyllie et al. 1956; Nur et al. 1980). When
not fully saturated, the undrained pore pressure coefficient
is less than its value when fully saturated. The back pressure
is increased incrementally, and the change in pore pressure
Δp with the change in confining pressure ΔP is measured

at each stage of the saturation process. One criterion for
reaching full saturation is that each incremental ratio
Δp/ΔP remains constant because it implies that no high-
compressibility air occupies pore space. The undrained
pore pressure coefficient gradually approaches a constant
value with repeated iterations of increasing pore pressure
and confining pressure (Fig. 1). In soft, saturated soil with
low drained bulk modulus K, the solids Ks and water Kw bulk
moduli can be considered incompressible compared to the
soil skeleton so that K << Ks and K << Kw. Therefore, the
confining pressure increment ΔP is mainly transferred to the
pore water pressure, giving Δp/ΔP ≈ 1. Rock, on the other
hand, generally has K > Kw and Δp/ΔP < 1.

## 2 Methods

While different saturation procedures are in use by various
laboratories throughout the world (e.g., Papamichos et al.
1993; Hart and Wang 2001; Vialle and Vanorio 2011; Delle
Piane et al. 2015; Wild et al. 2017; Braun et al. 2019; Bor-
gomano et al. 2020; Kim and Makhnenko 2020; Asem et al.
2024), this SM presents a unified methodology for achieving
full water saturation of rocks, where both water and rock are
chemically inert (e.g., rock with less than a few percent of
reactive minerals).

<figure><img src="image_2.png" /><figcaption>**Fig. 1** Full water saturation of rock is achieved by increasing pore pressure *p* at a given *P'* = *P* – *p*, where *P* is confining pressure. As the bulk modulus of the fluid becomes constant, Δ*p*/Δ*P* and P-wave velocity *v*<sub>p</sub> become constant for small changes in *p*</figcaption></figure>

<figure><img src="image_3.png" /></figure>
**2.1 Concept**

To achieve full saturation, a specimen must be subjected to elevated pore pressure for a given duration of time to (i) infiltrate all interconnected pores with water and (ii) force air into solution, governed by air solubility and diffusivity in water, or compress air to an insignificant volume. It is noted that for tight rock, e.g., permeability $k < 10^{-16} m^2$ (~0.1 md), achieving full water saturation is further complicated by the wettability and potential capillary entry pressure in the smallest pores. Thus, adequate pore pressure and time are necessary components in the saturation process. Applying pore pressure in isothermal conditions at constant differential pressure, $P'=P-p$, also known as Terzaghi effective confining pressure, then evaluating $\Delta p/\Delta P$ (or $v_p$) under isothermal undrained conditions shall be used to ensure full water saturation. Once the specimen is saturated, hydromechanical testing should be conducted at a pore pressure $p_{test}$ greater than or equal to $p$ at saturation so that the dissolved air is not released.

In a standard apparatus, perfectly undrained conditions cannot be easily achieved due to the parasitic effects of the dead volume (tubing, valves, transducers) that result in the measured undrained pore pressure coefficient $\Delta p/\Delta P$ being smaller than the “material” coefficient; i.e., the measured $\Delta p/\Delta P$ combines both material and system response. To extract the material parameter known as Skempton’s B, some calibrations and corrections are necessary for most

apparatus (Wissa 1969; Bishop 1976; Zimmerman et al. 1985; Ghabezloo and Sulem 2010; Tarokh et al. 2018). Note that the P-wave velocity is not affected by the dead volume of the apparatus, as $v_p$ is governed by the saturation state and the microstructure of the rock through which the P-wave propagates. Changes in $v_p$ measured along the axis of the nearly saturated specimen at constant $P'$ during the saturation procedure can be attributed to changes in the degree of saturation (Si et al. 2016; Horikawa et al. 2021).

**2.2 Apparatus**

As presented schematically in Fig. 2, full water saturation in a rock mechanics laboratory involves a pressure vessel or cell and manual or syringe-type hydraulic pumps capable of applying pore pressure (pump A) independent of confining pressure (pump C) and regulating pore and confining pressures to within 1% or better; pump A should be capable of measuring flow volume and rate. For tight rock ($k < 10^{-16} m^2$), two-pore pressure pumps, A and B, connected to the inlet and outlet ends of the specimen, respectively, accelerate saturation. Two pore pressure transducers D and E at the inlet and outlet ends are suggested to evaluate pore pressure equilibrium. For permeable rock, one pressure transducer is sometimes used, but two are recommended; if one transducer is used, it should be placed at the pore water inlet of the sample. Pressure transducer F measures confining pressure. Pressure capacity needed for the pumps is dependent on

<figure><img src="image_4.png" /><figcaption>**Fig. 2** Schematic diagram of equipment for achieving full water saturation of rock. Arrangement (1) with one-pore pressure pump A. Arrangement (2) with two-pore pressure pumps, A (inlet) and B (outlet), to accelerate the saturation process</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Fig. 3** a Jacketed specimen with platens containing P-wave sensors, which are optional; b pore pressure platens with grooves to distribute pore fluid pressure, if porous stones or screens are not used</figcaption></figure>

the rock (e.g., permeability and pore size), where a highly permeable rock can be fully saturated with pore pressure of 1–2 MPa, while a tight rock of low permeability may require 10 MPa or more. A vacuum pump and vacuum bell are optional.

The jacketed specimen is illustrated in Fig. 3a, where it is shown that the water can only be injected or withdrawn through the drainage system, which includes inlet and outlet platens, drainage lines or tubing, valves, and pressure transducers. It is preferable to use the bottom platen as the inlet of the specimen. Temperature in the cell $T_i$ and/or outside but near the cell $T_o$ should be measured periodically (e.g., every hour or two) and maintained constant within ±0.5 °C. The interfaces between the platens/ drainage lines and the specimen shall be designed to allow fluid distribution over the specimen’s cross-section, e.g., machined grooves on the platens’ surface (Fig. 3b), disks made of porous and permeable stones, metals, or fine-mesh screens. Sharp bends in drainage lines should be avoided to enhance air-bubble migration and/or diffusion. It is recommended to use de-aired water to decrease the saturation time, although representative pore fluid, i.e., with the same chemical composition as the in situ pore fluid, can be substituted if required by the project.

For applications involving poroelastic experiments, minimizing system compliance and dead volume should be considered in designing the drainage lines and accessories. Specimen size and geometry are dependent on the application, as is the use of strain gages, which are recommended to evaluate completion of the diffusion process. Specimen size should reflect a representative

volume element, e.g., smallest dimension at least ten times the grain size, and a regular geometry such as a right-circular cylinder is recommended for ease of jacketing (sealing) the specimen, although other geometries have been used with success, e.g., a quarter of a right-circular cylinder (Asem et al. 2024).

## 3 Procedures

A flow chart of the procedure is shown in Fig. 4. The details are as follows:

(a) *Specimen geometry and tolerances.* Select a specimen with a convenient geometry. The ends of the specimen shall be flat to 0.02 mm and shall not depart from perpendicularity to the longitudinal axis of the specimen by more than 0.001 rad (about 3.5 min) or 0.05 mm in 50 mm (ISRM 1978a).

(b) *Rock characteristics.* Measure mass to the nearest 0.1 g and dimensions to the nearest 0.1 mm. For a right-circular cylinder, determine the diameter of the specimen by averaging two diameters measured at orientations 90° apart at about the upper height, mid-height, and lower height of the specimen; use the average diameter for calculating the cross-sectional area. Estimate porosity based on the mass–volume relation and specific density of the dominant mineral, or average the specific density if several minerals are present in non-negligible proportions. Measure P-wave velocity along the axis of the dry specimen if proper equipment is available.

<figure><img src="image_6.png" /></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 4** Flow chart of the saturation process</figcaption></figure>

(c) *Specimen setup.* Assemble the specimen, disks made of porous stones or screens if end platens are not grooved, end platens with P-wave velocity sensors if available, and jacket (membrane), and place the assembly within the cell. Connect the drainage tubes and pumps; the exact procedure will depend on the specimen geometry and cell design. Flush the tubing at the inlet and outlet ends with de-aired water or apply a vacuum prior to injecting de-aired water; representative pore fluid can be substituted if required by the project. Fill the cell with confining fluid (e.g., hydraulic oil), and with valves H and I open (the specimen is in a drained condition), apply a small confining pressure (P=1.0–1.5 MPa) so as not to significantly reduce the permeability. In selecting *p* and *P*', consider that once the specimen is saturated, hydromechanical testing should be conducted at a pore pressure *p*test greater than or equal to *p* at saturation so that the dissolved air is not released.

(d) *Permeability estimation.* Knowing the rock type, estimate permeability *k* from Fig. 5 (Brace 1980). The threshold of 10<sup>-16</sup> m<sup>2</sup> is a guide rather than a strict boundary based on the time for flow through within 8–16 h (1–2 workdays) associated with typical testing conditions. If *k* > 10<sup>-16</sup> m<sup>2</sup>, then proceed to step (e). If *k* ≤ 10<sup>-16</sup> m<sup>2</sup>, then proceed to step (f).

(e) *Permeable rock and infiltration by flow through.* With P=1.0–1.5 MPa, apply pore pressure p<sub>in</sub>=0.2–1.0 MPa to the inlet end while keeping atmospheric pressure on the outlet end p<sub>out</sub>=0 (valve I open). The pore pressure p<sub>in</sub> should be at least 0.5 MPa smaller than the confining pressure P (or the minimum principal stress). Once outflow is established, inflow volume should be measured from pump A and outflow volume measured through outlet valve I; the details will depend on the plumbing arrangement. Maintain p<sub>in</sub> until inflow and outflow volumes are approximately equal. Close the outlet valve I and wait for the pore pressure to equilibrate, typically in 10–20 min; proceed to step (g). If after an elapsed time of 8–16 h flow through has not occurred, close the outlet valve and allow the pore pressure to equilibrate; proceed to step (f).

(f) *Tight rock and infiltration by pore pressure.* For unsuccessful flow through or tight rock (*k* < 10<sup>-16</sup> m<sup>2</sup>), this infiltration step may take many days, depending on the rock specimen and plumbing arrangement (Fig. 2), with two options: (1) with one-pore pressure pump A, or if the outlet pump B does not have flow rate control, air can be released through outlet valve I or go into solution; (2) with two-pore pressure pumps A and B having flow rate control, the time to full saturation is reduced in comparison to one pump, but all air must go into solution. Select a constant value of *P*=*P* − *p* that is
<figure><img src="image_8.png" /><figcaption>**Fig. 5** Laboratory measurements of rock and soil permeability, reproduced from Brace (1980)</figcaption></figure>

small; $P' = 1.0$ MPa is recommended. The plumbing arrangement of one or two-pore pressure pumps should consider $p_{test}$. If $p_{test} < 5$ MPa, then some air will need to be bled during infiltration because the solubility of air in water at 5 MPa and 20 °C is approximately 1, i.e.,

0.02 air volume can be dissolved in 1 water volume at 0.1 MPa and 20 °C (Schuurman 1966; Black and Lee 1973).

<figure><img src="image_9.png" /></figure>
<figure><img src="image_10.png" /><figcaption>**Fig. 6** Infiltration of water into a tight, dry rock for constant inlet pressure *p*<sub>in</sub> and zero initial outlet pressure *p*<sub>out</sub>, with the outlet valve closed and constant confining pressure *P*. After some time (near *t*<sub>2</sub>), the outlet pressure begins to increase, and eventually (near *t*<sub>d</sub>) the inlet and outlet pressures are approximately equal</figcaption></figure>

(f1) *One pore pressure pump, or outlet pump without flow rate control, or p<sub>test</sub> < 5 MPa.* Apply and maintain *P* = *P*' + 1.0 MPa, say *P* = 2.0 MPa, and close outlet valve I. Consistent with *P*' and *P*, apply an inlet pore pressure, say *p*<sub>in</sub> = 1.0 MPa, and monitor (e.g., sampling rate = 1–2 data points per hour) the outlet pressure transducer E. Water infiltrates from the inlet at constant inlet pressure, and after a few days, *p*<sub>out</sub> will begin to increase (Fig. 6). If some air needs to be released (*p*<sub>test</sub> < 5 MPa), open outlet valve I when *p*<sub>out</sub>=0.5±0.2 MPa, releasing the pressure, and then close outlet valve I; repeat this process a few (2–3) times. Upon release of sufficient air volume or if no air needs to be released, keep outlet valve I closed and monitor the outlet pore pressure. Allow time, several days or longer, for pore pressure equilibrium within a few percent (e.g., 2%) between *p*<sub>in</sub> and *p*<sub>out</sub>, as measured by pressure transducers D and E. Continue to step (g).

(f2) *Two pore pressure pumps with flow rate control and p<sub>test</sub> ≥ 5 MPa with no release of air.* Apply and maintain *P* = *P'* + 2.0 MPa, say 3.0 MPa, and *p*<sub>in</sub> = 2.0 MPa. At the outlet end, apply *p*<sub>out</sub> = 0.9*p*<sub>in</sub> and monitor flow rate, with a suggested accuracy of 0.1 mm³/min, into the specimen. Water infiltrates from both ends with constant inlet *p*<sub>in</sub> and outlet 0.9*p*<sub>in</sub> pressures. When the inlet pressure reaches the fluid front advancing from the outlet end, the flow from the pore

pressure pump B at the outlet end will change
direction to maintain the 0.9p_in; shut outlet valve
I to remove the outlet pore pressure pump B from
communicating with the specimen. Allow time,
several days or longer, for pore pressure equilib-
rium of a few percent (e.g., 2%) between p_in and
p_out, as measured by pressure transducers D and
E. Continue to step (g).

(g) *Back pressure application.* Once infiltration is com-
plete, in the sense that pore pressure is equilibrated at
the two ends, with inlet valve G open and outlet valve I
closed, increase confining pressure ΔP = 1.0 MPa and
pore pressure on the inlet side Δp_in = 1.0 MPa to main-
tain P'=constant. Wait for pore pressure equilibrium
within a few percent (e.g., 2%) between p_in and p_out,
as measured by pressure transducers D and E. Continue
to step (h).

(h) Δp/ΔP and/or vₚ measurement. Close inlet valve G; if closure of the valve generates an increase in water pressure, allow additional time for pore pressure equilibrium. With inlet G and outlet I valves closed, increase the confining pressure by a small increment, ΔP = 0.5 MPa (or less). Note that ΔP changes P'. For permeable rock with one-pore pressure transducer, wait 10–20 min for equilibrium of pore pressure. For setups with two-pore pressure transducers D and E, allow time for equilibrium within a few percent (e.g., 2%) and record the change in pore pressure Δp. If equipment is available, measure P-wave velocity vₚ along the
specimen axis. Compute $\Delta p/\Delta P$, $v_p$, and record pore pressure $p$. Continue to step (i).

(i) Repeat back pressure application and measurement. With inlet valve G open and outlet valve I closed, increase the confining pressure in increments of 1.0 or 2.0 MPa, i.e., add 0.5 or 1.5 MPa to the 0.5 MPa increase from step (h), and increase the pore pressure on the inlet side by an appropriate amount $\Delta p_{in}$ to maintain $P'=constant$. Repeat step (h). The cycle shall continue until at least three consecutive $\Delta p/\Delta P$ or $v_p$ values are equal within a few percent (e.g., 2%) for a given $P'$, as shown in Fig. 1.

## 4 Calculations

The calculations shall conform to the following.

(a) Record the confining pressure $P$ (or mean stress if the principal stresses are not equal) and change in confining pressure $\Delta P$.

(b) Calculate the pore pressure $p$ and change in pore pressure $\Delta p$: if one-pore pressure transducer is used (D in Fig. 2), record $p$; if two-pore pressure transducers are used (D and E in Fig. 2), record and average the values.

(c) Record temperature in the cell and/or outside but near the cell.

(d) Compute $\Delta p/\Delta P$ and/or P-wave velocity $v_p$ for the given pore pressure $p$ and differential pressure, $P'=P-p$, also known as Terzaghi effective confining pressure.

## 5 Reporting

The report shall include the following.

(a) Source of sample, including geological setting, depth and orientation, date, and method of sampling (if known).

(b) Lithologic description of rock, including approximate grain size and mineralogy.

(c) Details of specimen preparation.

(d) Description of apparatus, including pumps, drainage lines, valves, pressure transducers or gauges, and dates of testing.

(e) Specimen dimensions, mass, volume, density, estimated porosity, and P-wave velocity $v_p$ if equipment is available.

(f) Temperature variation, test duration, and rates at which pressures are applied

(g) Values of $\Delta p/\Delta P$ and/or $v_p$ (optional) as a function of $p$ at a given $P'=P-p$.

## 6 Notes

(a) The SM describes procedures to achieve full water saturation of a rock sample, with no regard to the experiment associated with the saturated sample.

(b) Water immersion procedures conducted at atmospheric pressure conditions cannot achieve full saturation even though rock density may not change appreciably.

(c) Full saturation involves only the connected pore space; isolated pores are considered part of the solid phase (e.g., in poroelasticity).

(d) Water-rock interaction, other than mechanical, and rock that exhibits rate dependence are not considered. Therefore, only rock that is not water sensitive (Rhett and Lord 2001) is covered by this SM. For the impact of osmotic pressure in clay-rich rocks, see Sarout and Detournay (2011).

(e) The water used to saturate the rock should be de-aired, including (if practical) any representative pore fluid pertaining to the project.

(f) For a rock sample containing another fluid besides water (e.g., oil), cleaning chemicals and procedures depend on the nature of the rock and the other fluid, but these details are beyond the scope of the SM.

(g) The $\Delta p/\Delta P$ values are dependent on $P' = P - p$ as well as temperature $T$, and both $P'$ and $T$ should be maintained relatively constant during the saturation procedure.

(h) For non-isotropic loading (principal stresses are not equal) to generate $P$ and $\Delta P$, the value of $\Delta p/\Delta P$ can be dependent on the magnitudes and directions of the principal stresses, so the way $\Delta P$ is applied should be consistent throughout the saturation procedure.

**Acknowledgements** R. Ulusay and the ISRM Commission on Testing Methods supported the efforts of the Working Group and provided helpful suggestions. M. Aldin, J. Dudley, K. Hashiba, R. Holt, and H. Wang are thanked for their thorough reviews and insightful comments.

**Funding** No funding was received for conducting this study.

**Data Availability** Not applicable.

## Declarations

**Conflict of Interest** The authors have no relevant financial or non-financial interests to disclose.
**Open Access** This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

## References

Asem P, Detournay E, Huang H, Labuz JF (2024) Saturating a tight rock and measuring its hydromechanical response. Rock Mech Rock Eng 57:10385-10398

Biot MA (1941) General theory of three-dimensional consolidation. J Appl Phys 12(2):155-164

Biot MA, Willis DG (1957) The elastic coefficients of the theory of consolidation. J Appl Mech 24:594-601

Bishop AW (1976) The influence of system compressibility on the observed pore-pressure response to an undrained change in stress in saturated rock. Geotechnique 26(2):371-375

Black DK, Lee KL (1973) Saturating laboratory samples by back pressure. J Soil Mech Found Div 99(1):75-93

Borgomano J, Gallagher A, Sun C, Fortin J (2020) An apparatus to measure elastic dispersion and attenuation using hydrostatic- and axial-stress oscillations under undrained conditions. Rev Sci Instrum 91(3):034502

Brace WF (1980) Permeability of crystalline and argillaceous rocks. Int J Rock Mech Min Sci Geomech Abstr 17(5):241-251

Braun P, Ghabezloo S, Delage P, Sulem J, Conil N (2019) Determination of multiple thermo-hydro-mechanical rock properties in a single transient experiment: application to shales. Rock Mech Rock Eng 52:2023-2038

Cornet FH, Fairhurst C (1974) Influence of pore pressure on the deformation behavior of saturated rocks. Proc. 3rd ISRM Congress. Denver 2:538-544

Coussy O (2010) Mechanics and Physics of Porous Solids. Wiley, Chichester

Delle Piane CD, Arena A, Sarout J, Esteban L, Cazes E (2015) Micro-crack enhanced permeability in tight rocks: an experimental and microstructural study. Tectonophysics 665(8):149-156

Detournay E, Cheng AHD. 1993. Fundamentals of poroelasticity. Fairhurst C, editor, Comprehensive Rock Engineering: Principles, pp 113-171.

Dudley JW, Brignoli M, Crawford BR, Ewy RT, Love DK, McLennan JD, Ramos GG, Shafer JL, Sharf-Aldin MH, Siebrits E, Boyer J, Chertov MA (2016) Suggested method for uniaxial-strain compressibility testing for reservoir geomechanics. Rock Mech Rock Eng 49:4153-4178

Ghabezloo S, Sulem J (2010) Effect of the volume of the drainage system on the measurement of undrained thermo-poro-elastic parameters. Int J Rock Mech Min Sci 47:60-68

Hart DJ, Wang HF (2001) A single test method for determination of poroelastic constants and flow parameters in rocks with low hydraulic conductivities. Int J Rock Mech Min Sci 38(4):577-583

Heck WJ. 1972. Development of equipment for studying pore pressure effects in rock. Gray KE, editor, Basic and Applied Rock

Mechanics, Proc. 10th Symp. Rock Mech., Austin, Texas. AIME, New York, pp 243-266.

Horikawa T, Katsura M, Yokota T, Nakashima S (2021) Effects of pore water distributions on P-wave velocity-water saturation relations in partially saturated sandstones. Geophys J Int 226(3):1558-1573

ISRM (1978a) Suggested methods for determining the strength of rock materials in triaxial compression. Int J Rock Mech Min Sci Geomech Abstr 15:47-51

ISRM (1978b) Suggested methods for determining sound velocity. Int J Rock Mech Min Sci Geomech Abstr 15:53-58

ISRM (1979) Suggested methods for determining water content, porosity, density, absorption and related properties and swelling and slake-durability index properties. Int J Rock Mech Min Sci Geomech Abstr 16:141-156

Kim K, Makhnenko RY (2020) Coupling between poromechanical behavior and fluid flow in tight rock. Transp Porous Media 135:487-512

Koning HL. 1963. Some observations on the modulus of compressibility of water. Conference on Settlement and Compressibility of Soils, Wiesbaden, pp 33-36.

Lowe J, Johnson TC. 1960. Use of back pressure to increase degree of saturation of triaxial test specimens. Research Conference on Shear Strength of Cohesive Soils, ASCE, pp 819-836.

Mesri G, Adachi K, Ullrich CR (1976) Pore-pressure response in rock to undrained change in all-round stress. Geotechnique 26(2):317-330

Murrell SAF (1965) The effect of triaxial stress systems on the strength of rocks at atmospheric temperatures. Geophys J R Astron Soc 10:231-281

Neff TL (1966) Equipment for measuring pore pressure in rock specimens under triaxial load. Test Tech Rock Mech Am Soc Test Mater STP 402:3-17

Nur AM, Walls JD, Winkler K, DeVilbiss J (1980) Effects of fluid saturation on waves in porous rock and relations to hydraulic permeability. Soc Pet Eng J 20:450-458

Papamichos E, Vardoulakis I, Quadfel H (1993) Permeability reduction due to grain crushing around a perforation. Int J Rock Mech Min Sci Geomech Abstr 30(7):1223-1229

Rhett DW, Lord CJ. 2001. Water weakening in sedimentary rocks. Proc. 38th US Symp Rock Mech, Washington, D.C. ARMA-01-0121.

Rice JR, Cleary MP (1976) Some basic stress-diffusion solutions for fluid saturated elastic porous media with compressible constituents. Rev Geophys Space Phys 14(2):227-241

Sarout J, Detournay E (2011) Chemoporoelastic analysis and experimental validation of the pore pressure transmission test for reactive shales. Int J Rock Mech Min Sci 48(5):759-772

Schuurman E (1966) The compressibility of an air/water mixture and a theoretical relation between the air and water pressures. Geotechnique 16(4):269-281

Si W, Di B, Wei J, Li Q (2016) Experimental study of water saturation effect on acoustic velocity of sandstones. J Nat Gas Sci Eng 33:37-43

Skempton AW (1954) The pore-pressure coefficients A and B. Geotechnique 4(4):143-147

Tarokh A, Detournay E, Labuz JF (2018) Direct measurement of the unjacketed pore modulus of porous solids. Proc R Soc Lond A Math Phys Eng Sci 474:2219

Todd T, Simmons G (1972) Effect of pore pressure on the velocity of compressional waves in low-porosity rocks. J Geophys Res 77(20):3731-3743

Vialle S, Vanorio T (2011) Laboratory measurements of elastic properties of carbonate rocks during injection of reactive CO2-saturated water. Geophys Res Lett 38(1):L01302

Wang HF (2000) Theory of Linear Poroelasticity with Applications to Geomechanics and Hydrogeology. Princeton University Press, Princeton, New Jersey
Wild KM, Barla M, Turinetti G, Amann F (2017) A multi-stage triaxial testing procedure for low permeable geomaterials applied to Opalinus Clay. J Rock Mech Geotech Eng 9(3):519–530

Wissa AEZ (1969) Pore pressure measurement in saturated stiff soils. J Soil Mech Found Div 95(4):1063–1073

Wood AB (1930) A textbook of sound. G. Bell and Sons, London

Wyllie MRJ, Gregory AR, Gardner LW (1956) Elastic wave velocities in heterogeneous and porous media. Geophysics 21:41–70

Zimmerman RW, Haraden JL, Somerton WH (1985) The effects of pore pressure and confining pressure on pore and bulk volume compressibilities of consolidated sandstones. Meas Rock Prop Elev Press Temp ASTM, STP 869:24–36

**Publisher's Note** Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.