DD218681A1 - METHOD AND DEVICE FOR THE LABORATORY DETERMINATION OF POROSITAET PARAMETERS - Google Patents

Abstract

The invention relates to a laboratory method and a device for determining the perforated and non-perforated porosity of disturbed or undisturbed samples of porous media as a function of their fluid saturation. The aim of the invention is to ensure the reliable determination of these parameters with little effort. According to the invention, this object is achieved by the fact that a device in method step I brings a tracer into the thermodynamic equilibrium in the purged and non-purged pore space of a fluid-perfused sample. In method step II, the fluid is supplied with altered tracer concentration (eg, tracer-free) until it has largely displaced the end of I in the pore space that has been pervaded. Subsequently, in the process step III the system is circulated a circulation of the flowing fluid and maintained until the setting of the renewed thermodynamic equilibrium. The sought parameters are determined from a mass balance equation of the tracer of method steps I, II and III and a mathematical model for the Tracerkonzentrationsverlauf at the end of the process step II. Fig. 1

Description

-1- 244 765

Method and device for the iaborative determination of porosity parameters Field of application of the invention

The invention relates to a laboratory method and a device for determining the flowed through and non-perfused porosity of disturbed or undisturbed samples of porous media as a function of the saturation of the sample with the fluid under consideration. These parameters are z. B. needed for the investigation of heat and mass transport with the flowing soil and groundwater.

Characteristic of the known technical solutions

For the purpose of the Iaborative determination of the flowed through and non-perfused porosity, column run tests on samples with L> 5 O (L-length, 0-diameter of the sample) using conservative tracers are known. From the measured values of the tracer concentration C (z, t) (t-time, 0 <ζ <L), the desired porosity characteristics n ₀ and n _st are determined from the process-describing equations (1) by computer-aided parameter identification:

^D ϊ? ~ ~ ^V s7 - ⁽ⁿ ° ^{+ k3)} δ7 ~ ^{klC + k2Cst}

'"""""" 5C _s ~ _t "

0 = (n _St + l <4) TTt + ^ ₁ C - coCst D - dispersion coefficient

ν - filter speed (flow per area)

n ₀ - porosity flowed through

n _St ^: - imperforate porosity (P. with stagnant fluid)

k · ,, k ₂ - Velocity coefficient of the kinetic exchange reaction I. Order between the tracer in the pore space k3, k _{4 which is} traversed and does not flow through - Storage coefficients of the solid phase The disadvantages of this method are shown

- from the high computational effort,

- out of necessity 4 of the 8 parameters of Eq. (1)

(D, v, n ₀ , n _St , k ,, k ₂ , k ₃ , k ₄ ) must be determined by other methods, since from Eq. (1) only 4 independent "parameters are identifiable

- from the difficulties encountered in taking undisturbed L> 5 0 soil samples.

Object of the invention

The aim of the invention is to determine the flowed through and non-perfused porosity with little effort. Explanation of the essence of the invention

The object of the invention is to provide a method and a device with which all variables which are required to determine the aforementioned porosity parameters, both disturbed and undisturbed samples taken can be determined by laboratory. According to the invention, the object is achieved in that, when flowing through the sample with a tracer fluid, the quantities listed below are determined successively in three process steps:

Process step I:

The disturbed or undisturbed sample taken from the porous medium to be examined is incorporated into the device according to the invention. It is flowed through with the fluid to be examined, to which a conservative tracer is admixed, at about constant velocity ν until this tracer is in thermodynamic equilibrium in the flow-through and non-perfused fluid-filled pore space. This state is reached when the tracer concentration in the process is the same as in the feed (C _A = C _z = Q). The desired total fluid saturation of the porous medium n _s = n ₀ + n _St is produced by placing the phase which wets the porous medium in the pore space under appropriate negative pressure or the non-wetting under appropriate pressure

 The sample contains the following amount of tracer when the thermodynamic equilibrium is reached:

M, = C, η _Σ V

with C, = C _A The tracer concentrations in the inlet and outlet as well as the volume V of the sample are to be measured.

Process step II:

At the inlet of the sample, the fluid to be examined with an altered tracer concentration (eg tracer-free) is now supplied, the pressure conditions (capillary pressure) and the flow rate remaining unchanged compared to method step I. In the case of using a tracer-free fluid, which is considered below, the tracer is washed out of the perfused pore space. The flow of tracer-free fluid takes place until the concentration of the conservative tracer has reached approximately the value of 0.8 to 0.5 C in the course. The flow rate must be as constant as possible in this process step. The tracer concentration decrease as a function of time (at the times ti) at the outlet (AC _A = C ₁ -C _M [L, t] = AC _n [tj], the washed-out tracer quantity Mn and the fiiter speed v.

Process step III:

The sample is then fed into the inlet of the outlet (creation of a closed fluid circuit). The pressure conditions (capillary pressure) and the flow rate remain unchanged compared to the method steps I and II. The closed fluid circuit is operated until, in turn, a thermodynamic equilibrium has been established between the tracer fluid fractions of the flow-through and non-perfused pore space. This is achieved if ^ z = C _A = Cm. The sample then contains the amount of tracer

M, ι, _m = C n V _s (3)

Measurement technology is the tracer concentration in the inlet and outlet and C ... 711 "rfa" s <! S

Evaluation:. *.

From the balance equation of the tracer quantity of the three method steps, it follows:

Mi = Μ ,, + M

III

(4)

and thus the fluid-saturated total porosity of the porous medium n ₂ to:

Μ ... ;

 (5)

η _Σ =

V (C ₁ -C ₁

The determination of n ₀ is based on the assumption that for the front tip of the tracer-free water particles emerging at the outlet for v / L> k _{2 the} following equation is sufficiently accurate the decrease in concentration of the tracer at the outlet of the

_ Sample: hf erf

-10 =

 L

(6)

To determine n _o from Eq. (6) the measured values Cn (tnj) are graphically represented in an X, Y-Ko ordinate η system

, 2C ₁

Y = inferf

(7a)

X = in tu (t, | - time since the beginning of method step I

YW

Y (α)

γ "

0.00 0.05 0.10 0.15 0.20

0.00 0.04 0.09 0.13 0.18

0.25 0.30 0.35 0.40 0.45

0.23 0.27 0.32 0.37 0.42

0.50 0.55 0.60 0.65 0.70

0.48 0.54 0.60 0.66 0.73

0.75

0.775

0,800

0.825

0,850

0.81 0.85 0.90 0.97 1.02

0.875 0.900 0.925 0.950 0.975

1.07 1.15 1.25 1.40 1.65

hf erf ( - = Ο = - inf erf

To inf (oc) = oo

plotted and the values Y, starting from the smallest Xj values starting from a straight line according to Eq. (6) Y? = A-BX. · (8th)

balanced. For increasing values X ₁ , the Y _r values may be above the alignment line. The flow through and non-perfused porosity result from this: _λ

ⁿ o ~

With: . t _o ; _s = exp X (C _n = 0.5 C,) (9a)

and .-

n _St - η _Σ - n ₀ = '- ) ~ ^{(v / L>} - ^, s -Ob)

For carrying out the method, the device according to the invention can be used. On a sample chamber filled with sample material are connected:

- lateral means for adjusting the capillary pressure in the sample; Elements which can be flowed through at the ends of the sample and which ensure the maintenance of the capillary pressure. -

- from below the inlet with a three-way stopcock, from above the Abiauf with another three-way stopcock,

- two adjustable height Boyle-Mariottesche vessels on the inlet two-way valve, each with one stopcock,

- on the drainage tap a drain and a standpipe,

Between the three-way valves a connection closed by a pump with a standpipe connected between the inlet two-way valve and the pump,

- Between the front sides of the sample chamber and the three-way valves each a measuring cell for determining the Tracerkonzentration.

embodiment

In the drawing, a device according to the invention is shown. The sample chamber is completely filled with a soil sample 1. It is acted upon laterally with a constant overpressure Δρ with respect to the atmospheric pressure p _atm . At the front, the sample chamber is bounded by ceramic plates 5. Fluid and tracer flow through the ceramic plates (lower end side) and out (upper end side). At the inlet two Boyle-Mariottesche vessels 2 and 3 are connected. In Fig. 2 is tracer-free water; in 3 water and NaCl as a tracer. The vessels are height adjustable for adjusting the flow rate. They can be connected via the inlet tap 11 separately to the line to the inlet two-way cock 10Z.

The position of the taps in the three process steps is shown. At the drain are connected via a three-way tap 10 A, a drain pipe and a standpipe 7. Between 10A and 10Z there is another line with which the drain can be returned to the inlet. For this purpose, a pump 6 and a standpipe 7 is connected in the line. Both are used to set the constant Ftltergeschwindigkeit to about the value previously set with the adjusted height of the Boyle-Mariottesian vessels. In each of the supply and discharge a measuring cell 8 is connected for measuring the Tracerkonzentration. A burette 9 is used to determine the flow rate. The individual measuring steps and their evaluation were used

Claims (2)

Invention claims: 1. A method for determining porosity parameters by flowing a sample with a fluid and a tracer, z. B. NaCl, characterized in that the sample is traversed at certain capillary pressure to be set by the fluid at a constant velocity ν and successively set or measured in three process or measuring steps, the following parameters: I) A quantity of tracer is added to the fluid. The sample is traversed by the fluid and tracer until the tracer concentration in the inlet C _{2 is} equal to that in the outlet C _A. This value is set equal to Q. Measured are C _A , C ₂ and the sample volume V. II) An altered amount of tracer, preferably no tracer, is added to the fluid. The feed is as long as maintained until the tracer concentration in the outlet has become approximately C _A = 0.5 / C ₂ -Q /. The tracer concentration change over the time C _A (tj, which is set equal to C _n (t,)), the washed-out tracer quantity Mn and the filter speed v are measured. III) The outlet is fed to the inlet in a closed circuit. The circulation is maintained until the tracer concentration in the inlet C _{2 is} equal to that in the outlet C _{A again} . This value is set equal to Cm. Measured are C _A and C ₂ . 2. A device for determining porosity parameters, characterized in that are connected to a completely filled with sample material sample chamber: Lateral means for adjusting the capillary pressure in the sample; components which can be flowed through at the end faces of the sample and which ensure the maintenance of the capillary pressure, - from below the inlet with a three-way stopcock, from above the drain with another three-way stopcock, - two adjustable height Boyle-Mariottesche vessels on the inlet two-way valve, each with one stopcock, - on the drainage tap a drain and a standpipe, Between the three three-way valves a connection closed by a pump with a standpipe connected between the inlet two-way valve and the pump, - Between the end faces of the sample chamber and the three-way valves each have a measuring cell for determining the Tracerkonzentration. For this 1 page drawings