MXPA96002136A - Volumes of produced fluid in porososdeterminated media through magnetic resonance nuclearde gradiente de campo impuls - Google Patents

Abstract

The present invention relates to a method for obtaining at least one fluid transport property of a porous material comprising: (a) obtaining a porous material with a variable amount of fluid in the pore space, (b) applying pulses Radiofrequency that leads to a coherent precession of the nuclear fluid's spins for a preselected species of nuclear spins in the molecules in the fluid, (c) apply magnetic field gradients to encode the displacement of the fluid molecules over a period of time (d) repeat step (c) for different values of the magnetic field gradient intensities, (e) register the Nuclear Magnetic Resonance signal in step (d) for each intensity of the magnetic field gradient; determine the fluid transport property of the Nuclear Magnetic Resonance signal

Description

"VOLUMES OF FLUID PRODUCIBLE IN POROUS MEDIA DETERMINED THROUGH NUCLEAR MAGNETIC RESONANCE IMPROVED FIELD GRADIENT " The present invention relates to methods for determining the transport properties of fluids and porous media, using nuclear magnetic resonance (NMR) in combination with driven magnetic field gradients (PFG). Examples of transport properties include, but are not limited to measurements of the self-diffusion coefficients and displacements of quadratic media of fluid molecules, the relative amounts of fluid molecules that have a self-diffusion coefficient specific to the displacement of half quadratic, respectively, and the pore size distribution of the porous medium. In particular, the present invention relates to measuring the volume fractions of retained and free fluid, also known as the Fluid Index in rocks by measuring the self-diffusion coefficients and displacements of the quadratic medium of both fluid fractions as a function of the observation time and / or fluid saturation in the nuclear magnetic resonance experiment of the boosted field gradient (PFG NMR).

The free fluid index (FFI) refers to the fraction of fluid in a rock pore space, which can occur under typical deposit production conditions. The FFI is also sometimes referred to as the "movable" fluid fraction. The retained fluid index (BFI) is the fraction of fluid that can not be recovered from the reservoir rock. The normal petrophysical method to determine the FFI and BFI in laboratory measurements in reservoir core seals, is the determination of the capillary pressure curve of the fluid in the pore space, by means of progressive saturation of the core obturator using successive rotation speeds Higher core shutter in a centrifuge. The BFI is the fraction of fluid that remains in the pore space of the rock core at a certain capillary pressure, that is, at a certain speed of rotation of the centrifuge. The FFI is the fraction of fluid that has been removed from the core of the rock at this rotation speed. Alternatively, the capillary pressure curve and therefore the BFI and the FFI can be obtained from mercury injection experiments which also measures the pore size distribution of the rock. Another approach to determine BFIs and FFIs in rocks is the measurements of the nuclear magnetic relaxation times transverse (T2) or longitudinal (T] _) of fluids in rocks [see from C. Straley and others "NMR in Partially Saturated Rocks: Laboratory Insights on Free Fluid Index and Comparison with Borehole Logs ", SPNLA 32nd Annual Logging Symposium, June 16-19, 1991]. It has been shown that under the condition of the fast diffusion limit, the nuclear magnetic relaxation times of fluids in a single pore depend only on the surface for the volume ratio of that pore and therefore it is a measure of the pore size [ see MH Cohen and KS Mendelson, "Nuclear Magnetic Relaxation and the Internal Geometry of Sedimentary Rocks," J. Appl. Phys. volume 53, page 1127, (1982)]. Since rocks are typically described by a wide variety of pore sizes, the magnetization decline observed in the nuclear magnetic resonance experiment is multi-exponential. The distribution of relaxation times that describe this decline is a measure of the pore size distribution in the rock. In this approach, the BFI is the fraction of the fluid that has relaxation times less than a certain cutoff value of T2 of T] _. These actual cutoff values depend on the effectiveness of the surface relaxation, which is generally expected to be a function of detailed properties such as the mineralogy and roughness of rock surface.

Nuclear magnetic resonance has been used for a long time to study the fluid diffusion flow [P. T. Callaghan, Principies of Nucl ear Magnetic Resonance, Clarendon Press, Oxford 1991]. In general, the molecular displacements of the molecules of the fluid can be quantified with nuclear magnetic resonance, using impelled magnetic field gradients. With the application of the magnetic field gradient G, the precession or ega frequency of a nuclear magnetic moment in an external magnetic field B = (0,0, Bo) is a function of the projection of the position r of the magnetic moment of the magnetic field. Direction of the applied field gradient: omega = gamma (B0 + G-r) In the NMR PFG experiment, the amplitude of the nuclear magnetic resonance signal, such as a spin echo, is measured as a function of the intensity of the applied magnetic field gradients applied. The pulse time diagrams for the applied radiofrequency pulses and the magnetic field pulses are shown in Figure 1. The position of each fluid molecule is encoded by the first magnetic field gradient pulse of delta duration and the resistance g . After a time has elapsed, a second gradient pulse is applied during the refocus period. The latter is defined by the time period after the second radiofrequency pulse in the time diagram in Figure 1. The detected signal is the echo of the nuclear magnetic resonance spin that is formed and then the end of the refocus period . For stationary spins, the phase acquired during the first impulse of the gradient is inverted by means of the second impulse that must be matched in gdelta intensity. To move the spins, the phase inversion is incomplete depending on the distance in which the molecule has moved during the time between the two impulses of the gradient. A displacement causes a change in the resonance frequency of the nuclear magnetic resonance, or equivalently, a change in the phase of the signal that leads to an attenuation of the amplitude of the spin echo observed. Repeating the experiment and systematically increasing the intensity of the coincident field gradient pulses has a set of spin echo amplitudes M (gdelta,?) With an attenuation? (gdelta, J) which is characteristic for the displacement of the espins. Echo spin attenuation in PFG NMR is provided by [P. T. Callaghan, Principi is of Nuclear Magneti c Resonance, Clarendon Press, Oxford 1991]: (gdelta,?) Exp [igam a deltagír ^ - r)] drldr 2) where P (r | r1,?) dr1! represents the conditional probability (propagator) of finding a molecule initially in the position?, after a while? in the volume element r ^ a r ^, and p (r) is the initial density of the spin. In a homogeneous medium, the propagator P (r | r,?) Is a Gaussian displacement function (r1 - r). Therefore, the spin echo attenuation becomes an exponential function of the square of the intensity of the field gradient pulses applied with the self-diffusion coefficient D as the declination regime: ú > (gdelta,?) = exp [- (gam adeltag) 2D?] (3) For self-diffusion in restricted geometries it has been shown that deviations from the pattern predicted by equation [3] occur at high intensities of applied field gradients where the spin echo amplitude has already been attenuated by 2- 3 orders of magnitude [P. T. Callaghan et al., Nature, 351 467 (1991)].

With an increased observation time these effects become more pronounced since a greater number of molecules will experience restrictions of their movement of movement, due to the walls of the pore. The pore geometry and a measure of the pore sizes can be calculated from this non-exponential spin echo attenuation [see for example from P.S. Sen and M. D. Hurlimann, J Chem Phys. , 101, 5423 (1994). However, to a small (gammadeltag) ^ equation [3] can still be applied by yielding an observation time that depends on the coefficient D, of self-diffusion evident, which contains information on pore sizes of the porous medium. The present invention provides a method for obtaining at least one property of transporting fluids in porous media, by coding the self-diffusion of fluid molecules in the pore space by PFG NMR. In one embodiment of the present invention, the time dependence of the quadratic mean displacements of the fluid molecules are obtained, which demonstrate that a fraction of the molecules undergo highly restricted self-diffusion (low transfer mobility) during the time scale of the NMR PFG experiment while the other fraction demonstrates a high transfer mobility with only slight deviations from the coefficient of self-diffusion of bulk fluid. The relationship of the fluid with the low mobility of transfer to the total fluid is shown as being the BFI. The pore size of the rock as seen by both fractions of fluid can be calculated from the time dependence of the displacements of the quadratic medium.

SUMMARY OF THE INVENTION The present invention is a method for obtaining at least one fluid transport property of a porous material. The steps of the method include obtaining a porous material with a variable quantity of fluid in the pore space, applying radiofrequency pulses that lead to a coherent precession of the nuclear spins for a species of pre-selected nuclear spins in the molecules in the fluid, apply magnetic field gradients to encode the displacement of the molecules of the fluid during a time interval, repeat the application of the radiofrequency and magnetic field gradient pulses for values different from the intensities of the magnetic field gradient, record the resonance signal Nuclear magnetic (NMR) for each intensity of the magnetic field gradient, and determine the fluid transport property of the nuclear magnetic resonance signal. In a preferred embodiment, the transport property is the volume of fluid retained which is also known as the fluid index retained.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: Nuclear magnetic resonance time plot of the driven field gradient for diffusion (and flow) coding. The amplitude of the spin echo is measured as a function of the gdelta intensity of the driven field gradient. (a) shows a simple version using the echo of the primary spin. (b) shows a version using stimulated spin echo. This sequence is useful to increase the time? of observation for systems where T2 < ^. (c) is a variation of (b) that includes ff pulses and the reversal of the polarity of the gradient to reduce the effects of internal magnetic field gradients [see RM Cotts et al., "Pulsed Field Gradient Stimulated Echo Methods for Improved NMR Diffusion Measurements is Heterogeneous Systems ", J. Magn. Reson. , volume 83, 252 (1989)]. Internal magnetic field gradients are often found when heterogeneous media such as rocks are placed in a magnetic field. Reading and deterioration gradients can be added in these sequences. The reading gradients are used for encoding the spatial information and / or to help match the intensities of the driven field gradient if the reading gradient is parallel to the driven gradient. Figure 2 shows the spin echo attenuations "-f (gdelta,?) As a function of the square of the intensity of the applied field gradient applied (gdelta) 2 at different observation times? For a water saturation at 100 The continuous lines represent the adjustment of the experimental data to the Two Fluid Model Figure 3a) shows the dependence of the observation time of the displacements of the quadratic medium of the water with high and low transfer mobilities respectively in the limestone The continuous line represents the time dependence of the displacement of the quadratic medium of the bulk water, b) represents the dependence of the observation time of both fractions of fluid in these limestones, a) and b) are obtained by adjusting the model of Two Fluids (equation [5] to the experimental data as provided in Figure 2. Figure 4 shows the amplitude of the spin echo M (gdelta,?) As a function of the square of the intensity of the applied field gradient applied (gdelta) 2 to 30 ms of observation time for different water saturation s in the limestone itself. The solid lines represent the fit of the experimental data using the Two Fluid Model for a partially saturated rock according to (equation [14]).

DESCRIPTION OF THE PREFERRED MODALITY In the PFG NMR movement movement of the molecules is encoded with driven field gradients. Using the Einstein relation for the Brownian movement, the displacement of the quadratic mean < r2 (A) > of the fluid molecule can be determined from the observation time dependence of the coefficient D () of self-diffusion defined according to equation 3. In an isotropic medium: (D (? Is equal to the bulk diffusion coefficient of the fluid if self-diffusion is not restricted. [3] it is retained only if all the molecules of the fluid that carry the nuclear spin under investigation remain in the same characteristics in their mobility of transfer. The necessary (but not necessarily sufficient) conditions for this to be the case are that the fluid comprises only one chemical type and is in a physical state and that all molecules experience the same restriction of their diffusion trajectory due to collisions or collisions with the wall of the pore. If there are several populations of the same fluid molecule in the pore space that are distinguishable by their quadratic half displacements during the time scale of the PFG NMR experiment, the amplitude of the spin echo consequently the spin echo attenuation consists of a superposition of the exponential functions of the shape of the equation [3] [see from J. Kaerger, H. Pfeifer, W. Heink, Advances in Magnetic Resonance, 12, 1 (1988)]. For two distinguishable fluid components, the spin echo attenuation can be described by: H- '(gdelta,?) = Ph exp [- (gammadeltag) D]?] + Pi exp [- (gammadeltag) 2Dx / \] (5) 1 = ph + Pl (6) where P (l) represents the fraction of fluid that has the self-diffusion coefficient D ^ (i). The indices h and 1 refer to fluid molecules with high and low transfer mobilities respectively. Using equation [4], the corresponding quadratic displacements for both fractions of fluid are obtained. The time dependence of r (?) > h (l) is used to identify the characteristics of fluid transport through the pore space. If the displacement of half a square of the fluid with low transfer mobility is independent of the observation time (< r2 (?)? = < r2 > _), the diffusion of this fluid fraction is greatly restricted in space of the pore. The displacement of quadratic means is limited by the maximum size of the pores that contain that fraction of the fluid. It can be used to calculate an upper limit of the pore radius. It is supported by the fluid that has a low mobility of transfer: R < low < r > ? For self-diffusion on a sphere with a radius Resfera: 5 R2esfera = - < r2 (? = «9) > ? (8) 6 The capillary pressure for the fluid in a pore of the radius R is calculated by the Young-Laplace equation: 2gammacos -? - Pe = (9) R where gamma is the air / fluid interfacial tension and -? - is the contact angle between the fluid and the air at the pore surface. Therefore, the pressure Pmini required to move the fluid with low transfer mobility out of the pores by centrifugation of the rock sample is provided by: 2gamma cos 2gamma cos =? - mm Rbai a < r > ? 0.5;? O; In rock samples, R-low is usually within the order of a few microns. Consequently, for a wetting fluid (e.g., Qr = 0.25 T, gamma = 60 dyne / cm), Pm n is typically in the order of 3.52 kilograms per square centimeter to 7.03 kilograms per square centimeter. This scale of values corresponds reasonably well to the capillary cut pressure used to determine the fraction of retained fluid (BFI) in rocks by centrifugation of the sample. Since the relative quantity of the moving fluid with low transfer Pl measured by PFG NMR and the BFI obtained by centrifugation of the rock sample measures the fraction of fluid in the small pores, we can make the following associations: BFI = F1 and FFI = Ph (11) For small observation times, the displacement of the quadratic medium of the fluid with high transfer mobility < r2 (?) > h is to be expected to coincide with the corresponding value of the bulk fluid. Only long enough observation time periods >; A considerable part of these molecules undergo restrictions of their diffusion path due to collisions or collisions with the pore wall. At observation times greater than AR, < r2 (? R) > n deviates clearly from the displacement of the quadratic mean < r2 (_?) Bulk bulk fluid. Consequently, the displacement of the quadratic mean of the root of the fluid a? R represents the calculation for the minimum radius of the pores containing the fluid with high transfer mobility: High Ralta can be considered as the lower limit of the mean free diffusion path of fluid molecules with high mobility of movement until they bounce against the pore wall.

IMPLEMENTATION Application of the Two Fluid Model for Self-Diffusion Studies of PFG NMR of Fluids in Rocks.

The diffusion (and flow) measurements with the NMR PFG technique are carried out by generating a stimulated primary spin echo using an appropriate rf pulse sequence (a combination of ///2 and // pulse) and the application of at least two separation-induced magnetic field gradients for diffusion coding. Examples for pulse sequences are given in Figure 1. The figure is an example for an appropriate pulse sequence for measuring the diffusion of fluids in the presence of internal magnetic field gradients caused by differences in susceptibility between the fluid and the material of grain in a porous medium. The pulses // rf in this sequence constantly refocus the phase shifts of nuclear magnetic moments due to internal magnetic field gradients but allow the co-addition of phase shifts due to impelled magnetic field gradients of opposite polarity + g . Therefore, the effect of the diffusion of the fluid molecules and the internal magnetic field gradients in the spin echo attenuation is canceled [R. M. Cotts, M. J. R. Hoch, T. Sun and J. T.

Markert, Journal of Magneti c Resonance, 83, 252-266 (1989)]. Due to the finite delta duration of the driven magnetic field gradients, the observation time that enters equations [2-5] is related to their separation / ^ ' deta? =? ' - - - (13) where it is equal to zero in sequences a) and b). A number of variations of PFG pulse sequences NMR shown in Figure 1 have also been described by Cotts to measure fluid self-diffusion in heterogeneous systems. For measurements of PFG NMR diffusion of fluids in rocks (or other porous materials) in a laboratory nuclear magnetic resonance spectrometer, rock sample cores typically 1 centimeter in diameter and 2 centimeters in length are those that are use However, its size is limited only by the excitation volume of the rf coil and the volume where the constant field gradients are generated by the gradient coil system. The samples should be filled with fluid using an appropriate procedure (eg, pressure saturation to imbibe the fluid through an evacuated sample) with the desired fluid. To avoid fluid loss during nuclear magnetic resonance measurements, rock samples saturated with fluid must be coated or sealed. It is beneficial for the interpretation of the measurements that the material used for the coating or sealing does not exhibit an echo signal of the nuclear magnetic resonance spin using the PFG NMR sequence selected for the measurement of fluid diffusion in the sample. As an example, for the measurements of PFG NMR H of self-diffusion of water in rocks, the samples could be sealed by a Teflon tape since it does not contain hydrogen (H) or by a layer of an epoxy resin that usually does not show a stimulated or primary spin echo during observation times that exceed a few 10 ~ 3 seconds. An example of the results for measurements of PFG NMR diffusion with water in the rocks is given in Figure 2. Shows the saturations of the spin echo? (gdelta, A.) as a function of the square of the intensity of the applied field gradient applied (gdelta) 2 for a fully saturated limestone (porosity f = 23.9 percent, air permeability k = 1276md). The sequence of the pulse used is given in Figure 1. The parameters were delta = 1.41 ms, 7"= 1.81 ms and the observation time was changed between 25 ms and 600 ms The resistance + g of the driven field gradient was linearly increased to gma? = 0.8T / m, and for each value of g, the The amplitude of the spin echo was measured in the presence of a small reading gradient of approximately 2mT / m oriented parallel to G. The reading gradient was used to help match the intensities (gdelta) of the successive pairs of gradient pulses. of bipolar field [see v.gr., by F. Stallmach, J. Kaerger and H.Peifer, Journal of Magnetic Resonance, A102,270 (1993)] In contrast to bulk water, spin echo attenuation for water in limestone rocks found to be non-exponential with (gdelta) 2. However, as shown by solid lines in Figure 2, the experimental data points can be well represented by a double-exponential function which is provided in equation [5] .The adjustment of this call "Two Fluid Model" to the attenuation of the experimental spin echo yields the self-diffusion coefficients Dh (l) the pn (l) fractions of water molecules with high and low mobility, respectively. According to the equation [4], the dependence of the observation time of the displacement of quadratic means for both fractions of fluid can be calculated. The results for water in the limestone are shown in Figure 3a. For comparison, the time dependence of the displacement of half a square of bulk water is also shown in the Figure. The displacement of half a square water with high transfer mobility <; r2 (\) > ^ it is found to increase through the whole scale of observation time. However, this increase is not linear and is slower than for bulk water. The clear deviations of bulk water mobility occur during observation times? > 50ms, which means that in this rock, most water molecules with high mobility of movement experience restriction of their diffusion path due to collisions or collisions with the pore wall only after a diffusion time of approximately 50 ms . This corresponds to root mean square shifts < r2 (R = 50ms) > h ^ * ^ of approximately 25 micrometers. Consequently, according to the equation

[12] The minimum radius of the pores containing the fluid with high transfer mobility is 25 micrometers.

The mean square displacement of the water with low transfer mobility < r2 > ^ in the limestone is within the order of 20 micrometers2. In particular, it does not increase with the time of increasing observation. This is evidence for restricted diffusion and possibly originates from the fluid in the small pores. According to equation [7], the radius of the RDaja pore can be seen by water molecules with low transfer mobility is less than 5 micrometers. The fractions P_ and P ^ of fluid are plotted in the Figure 3b as a function of observation time, P ^ is roughly 0.21 (or 21 percent) in the? short and decreases only slightly longer observation times. Since nuclear magnetic relaxation in small pores is more effective than in large pores, the relative contribution of small pores to the spin echo amplitude decreases with an increased observation time. This effect is called "relaxation weighting" and has to be taken into account for the calculation of BFI and FFI of the PFG NMR diffusion data, if there are observational dependencies of intense observation time of Pl and P ^. The relaxation weight is negligible for limestone according to equation [11] of the BFI is predicted from the measurements of PFG NMR diffusion and the application of the two fluid model is to be expected to be approximately 21 percent. Table 1 shows a comparison of BFI that is determined by two methods of Nuclear Magnetic Resonance and for comparison of a normal core analysis procedure. A Nuclear Magnetic Resonance method used was based on the multi-exponential analysis of the transverse magnetization decline measured using the CPMG technique [see MN Miller et al., "Spin Echo Magnetic Resonance Logging: Porosity and Free Fluid Index Determination"]. SPE 20561 presented at the 65th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, New Orleans, LA, September 23-26, 1990; see also R.L. Kleinberg et al., "Nuclear Magnetic Resonance of Rocks: TI vs. T2", document SPE 26470, presented at the 65th Annual Technical Conference and Exhibition of the Society of Petroleum Engineers, in Houston, TX, from October 3 to 6, 1993 ] The PFG NMR BFI data in Table I is determined using the new Two Fluid Model analysis of the PFG NMR data: These Nuclear Magnetic Resonance methods to determine BFI are compared with the abnormal petrophysical method of measuring water saturation. residual at a capillary pressure of 3.52 kilograms per square centimeter (CAP PRE). The fluid fraction of the low transfer mode as obtained by applying the Two Fluid Model proposed to the self-diffusion measurements of NMR PFG of the fluids in the rock is found to be well suited to the index of the fluid retained (or fraction). of "non-producible" fluid) of the normal petrophysical method. These results confirm the validity of the assumptions that lead to the equation [11].

Table 1: retained fluid index (BFI) as a percentage of total porosity determined by different methods for water in limestone rocks.

Properties of BFI Rock in% by Porosipermea TypeCPMG PFG CAPABILITY NMR NMR PRE MD 30ms T2 pl 3.52 kg / cm2 silver 30.2 21,000 19 marsmg 23.9 1,276 33 21 11.19 ++ nava or red 23.6 1,138 21 ++: results for core shutters Measures for dissemination of data can also be carried out PFG NMR if the porous material has only been partially saturated with the fluid or if more than one type of fluid occupies the pore space (eg, oil and water). In the case where more than one type of fluid occupies the pore space, if the molecules of each type of fluid contribute to the observed signal of PFG NMR, the observed signal is then superimposed on the Nuclear Magnetic Resonance signals of the components individual The amplitude of the spin echo is then provided by: M (gdelta,?) = I = l pj_i exp [- (gammadeltag) 2D] _j_?]} (14) 1 = Phi + PU (15) where IHJ is the total contribution of the ith fluid component to the spin echo amplitude (proportional to the number of those fluid molecules) adpü (hi and Dli (hi) represent the fractions and self-diffusion coefficients of the fluid with low and high transfer mobility of the itn fluid component, respectively To simplify the multi-exponential analysis of the spin echo decline in multi-component systems, Nuclear Magnetic Resonance techniques for signal separations can be employed. are: (i) The Fourier transformation of the spin echo signal recorded in the time domain if the different fluid components contain the same nuclei under investigation but have different chemical shifts so that their Nuclear Magnetic Resonance signals in the domain of frequency appears at different Larmor frequencies.The attenuation of each component of f Individual resistance with the intensity of the increasing field gradient can then be analyzed according to equation [11]. (ii) The selective excitation of a part of the fluid components using configured rf pulses. This technique also requires that the individual fluid components be able to be distinguished by their chemical shifts. Only an echo of the spin of the excited components of all the molecules of the fluid is obtained. (iii) Using isotopes irradiated in fluid mixtures. The diffusion of the irradiated isotopes of the fluid molecules can be observed without interference of all the other components of the fluid, if the component taken into account only confines the isotope of Nuclear Magnetic Resonance under investigation. As an example, in a mixture of water and oil, the diffusion of the oil can be observed by means of H PFG NMR without the superposition of the Nuclear Magnetic Resonance signal of the water, deuterated water is used. The self-diffusion measurements of NMR PFG described herein can also be applied to porous samples where the pore space is only partially occupied by the fluids. The data for a rock at different water saturations is shown in Figure 4. With a decreased water saturation, the amplitude of the signal in (gdelta) 2 = 0 decreases corresponding to a decreased number of fluid molecules in the pore space of the rock. Within the range of 100 percent to approximately 32 percent water saturation, the rapidly declining component of the signal amplitude disappears in the attenuation of the signal indicating that water with high transfer mobility is removed from the space of the pore. For saturations less than 32 percent only simple exponential spin echo attenuation has been observed and for saturations less than 24 percent without declination of the spin echo amplitude with the intensity of the applied field gradients applied.

Claims (9)

R E I V I N D I C A C I O N E S;

1. A method for obtaining at least one fluid transport property of a porous material comprising: (a) obtaining a porous material with a variable amount of fluid in the pore space. (b) applying radiofrequency pulses that lead to a coherent precession of the nuclear fluid spins for a preselected species of nuclear spins in the molecules in the fluid; (c) apply magnetic field gradients to encode the displacement of the fluid molecules during a time interval. (d) repeating step (c) for values different from the intensities of the magnetic field gradient; (e) register the Magnetic Resonance signal

Nuclear in step (d) for each intensity of the magnetic field gradient; (f) determining the fluid transport property of the Nuclear Magnetic Resonance signal. 2. The method according to claim 1, wherein the transport property is the index of the retained fluid.

3. The method according to claim 1, wherein the method is repeated for different time intervals.

4. Claim 3 and wherein the transport property is the index of the retained fluid. The method according to claim 1, wherein the variable amount of fluid varies from 5 to 100. 6. The method according to claim 3, wherein the fluid varies from 5 in the type of porous material. The method according to claim 1, wherein the porous material with the variable amount of fluid is obtained by inserting the fluid into the material. 8. The method of compliance with the claim 1, wherein the porous material with the amount of variable fluid is obtained in its natural state. The method according to claim 1, wherein the fluid includes more than one type of fluid.