CN111157424A - Rock material pore size distribution measuring method - Google Patents
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- 239000011148 porous material Substances 0.000 title claims abstract description 59
- 238000000034 method Methods 0.000 title claims abstract description 55
- 239000011435 rock Substances 0.000 title claims abstract description 52
- 239000000463 material Substances 0.000 title claims abstract description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 82
- 238000001228 spectrum Methods 0.000 claims abstract description 45
- 238000005481 NMR spectroscopy Methods 0.000 claims abstract description 24
- 238000006243 chemical reaction Methods 0.000 claims abstract description 23
- 238000012360 testing method Methods 0.000 claims abstract description 23
- 230000018044 dehydration Effects 0.000 claims abstract description 4
- 238000006297 dehydration reaction Methods 0.000 claims abstract description 4
- 238000005119 centrifugation Methods 0.000 claims description 24
- 229920006395 saturated elastomer Polymers 0.000 claims description 19
- 230000001186 cumulative effect Effects 0.000 claims description 11
- 150000001875 compounds Chemical class 0.000 claims description 3
- 238000009736 wetting Methods 0.000 claims description 3
- 230000001133 acceleration Effects 0.000 claims description 2
- 238000004364 calculation method Methods 0.000 claims description 2
- 238000002474 experimental method Methods 0.000 claims description 2
- 238000000464 low-speed centrifugation Methods 0.000 claims description 2
- 229910052753 mercury Inorganic materials 0.000 description 11
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 10
- 238000001514 detection method Methods 0.000 description 8
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 6
- 238000001179 sorption measurement Methods 0.000 description 6
- 238000001225 nuclear magnetic resonance method Methods 0.000 description 5
- 238000002591 computed tomography Methods 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 229910052757 nitrogen Inorganic materials 0.000 description 3
- 238000004836 empirical method Methods 0.000 description 2
- 230000003044 adaptive effect Effects 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 238000003384 imaging method Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000012113 quantitative test Methods 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
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- G01N15/088—Investigating volume, surface area, size or distribution of pores; Porosimetry
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N24/00—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects
- G01N24/08—Investigating or analyzing materials by the use of nuclear magnetic resonance, electron paramagnetic resonance or other spin effects by using nuclear magnetic resonance
- G01N24/081—Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity
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Abstract
The invention discloses a method for measuring the pore size distribution of a rock material, which obtains a capillary pressure-water inflow accumulated saturation curve by adopting a centrifugal dehydration test, then obtains an optimal conversion coefficient by fitting the curve with nuclear magnetic resonance T2 spectrum inversion, and finally obtains the pore size distribution.
Description
Technical Field
The invention belongs to a method for measuring the pore size distribution of a rock material.
Background
Under the influence of a series of internal and external factors such as diagenesis, geological structure, weathering and the like, pore structures and defects with different scales exist in the rock material. The presence of these pore structures has different effects in different engineering contexts. For example, for a rock slope in a cold region, the existence of pores above the mesopores provides a good storage space and a water guide channel for water storage and permeation, and provides a foundation for freeze-thaw damage deterioration of the rock slope. However, for shale gas reservoirs and petroleum reservoirs, the more developed the pore structure, the greater the pore size of the reservoir and reservoir will be. In summary, the distribution characteristics of pore size have a significant impact on engineering. Therefore, the determination of the pore size distribution of the rock is of great engineering significance.
At present, the current measuring methods for the pore diameter of rock materials comprise a mercury pressure method, a nitrogen adsorption method and CO2Various methods such as an adsorption method, a CT scanning method, a nuclear magnetic resonance method, an electron microscope scanning method, and the like are used for the microscopic structure detection of the rock. The electron microscope scanning method is a qualitative detection method, and can only detect the pore structure on the surface of a sample. Mercury intrusion method, nitrogen adsorption method, CO2The adsorption method, CT scanning method, and nuclear magnetic resonance method belong to quantitative detection methods for pore structure, and can quantitatively detect the pore size distribution in a sample, but these methods also have their own disadvantages. The mercury intrusion method is the most commonly used quantitative test method, the pore diameter detection range is larger and is 100nm-100000nm, however, the mercury intrusion process damages the sample, and the original pore structure of the sample can be damaged, so that the test error is caused; nitrogen adsorption method, CO2Although the adsorption method can quantitatively detect the pore size distribution, the adaptive pore size range is less than 100 nm; the CT scanning method has long time for determining pore structures and relies on the identification of imaging pictures of each layer.
The nuclear magnetic resonance method is a new type pore structure test method, it is H in water+Pore characteristics of rock material are detected for the detection medium. The pore size range which can be detected by the method is large, and the pore structure with the pore size range of 1-100000nm can be detected; the detection speed of nuclear magnetic resonance is high, the detection of the internal pores of the sample can be completed in only a few minutes, and the sample is not damaged; it has great application potential in microscopic detection and pore size distribution determination of material. However, by nuclear magnetic resonanceThe acquired parameter T2 (transverse relaxation time) representing the aperture size needs to be converted into the actual aperture by a conversion coefficient, which is a parameter depending on lithology and is not a constant. The nuclear magnetic resonance method is adopted to measure the pore size distribution of the sample, and the conversion coefficient is mainly determined by an empirical method or a combined mercury intrusion method. However, due to different lithologies of various rock materials, the conversion coefficient obtained by an empirical method is difficult to accurately describe the pore size distribution in the rock materials, and the method for measuring the conversion coefficient by the nuclear magnetic resonance combined mercury intrusion method is time-consuming.
Therefore, the method for determining the pore size distribution of the rock by improving the existing nuclear magnetic resonance method has practical application requirements and great theoretical significance.
Disclosure of Invention
The invention aims to provide a method for measuring the pore size distribution of a rock material, which is simple and convenient and has accurate result.
The invention relates to a method for measuring the pore size distribution of a rock material, which comprises the following steps:
(1) preparing a rock material to be measured into a regular cylindrical sample, placing the rock sample in a vacuum water saturation device for vacuum water saturation until the sample is completely saturated with water, and obtaining a water retention sample;
(2) performing nuclear magnetic resonance testing on the water saturation sample in the step (1) to obtain a T2 spectrum of the water saturation sample, and performing inversion on the T2 spectrum to obtain a capillary pressure-water inflow accumulated saturation curve of the rock sample;
(3) and (3) carrying out centrifugal dehydration on the water-saturated sample tested in the step (2) at different rotating speeds, wherein: the first centrifugal rotating speed is minimum, and then the centrifugal speed is increased by the set acceleration until the set maximum centrifugal rotating speed is reached; after each rotation speed is centrifuged, performing nuclear magnetic resonance testing to obtain the water content under the centrifugal action at different rotation speeds; centrifuging the sample each time, converting the centrifugal force into capillary pressure, converting the water content of the sample into water inlet saturation, and acquiring a capillary pressure-water inlet accumulated saturation curve of the sample;
(4) and (3) fitting the capillary pressure-inflow accumulated saturation curve obtained by T2 spectrum inversion in the step (2) and the capillary pressure-inflow accumulated saturation curve obtained by the centrifugal method in the step (3), and performing inversion calculation on the pore size distribution of the sample.
In the step (1), the negative pressure of the vacuum saturated water is-0.1 MPa, and the vacuum saturation time is 4-6 h.
In the step (2), the specific method for obtaining the capillary pressure-inflow accumulated saturation curve of the rock sample by T2 spectrum inversion comprises the following steps:
2-1 according to the bore diameter r of the rock samplepAnd the relationship between the T2 spectra (equation 1) and capillary pressure PcAnd the aperture rpThe functional relationship between capillary pressure and nuclear magnetic resonance T2 spectrum can be found from the relationship (2) between (equation 3):
rp＝cT (1)
Pc＝2σw×cosθ/rp(2)
Pc＝2σw×cosθ/rp＝2σw×cosθ×c×T (3)
in the formula, rpIs the pore diameter; t is the T2 value in the T2 spectrum; c is a conversion coefficient; pcIs capillary pressure; sigmawIs the interfacial tension of water; theta is the wetting contact angle;
2-2 calculating the water inlet saturation of the rock sample through the T2 spectrum of the water saturated rock sample, wherein the functional relation between the water inlet cumulative saturation and the nuclear magnetic resonance T2 spectrum can be expressed by the formula (4):
in the formula (I), the compound is shown in the specification,
Swcumulative saturation for water inflow,%; phi is acPorosity component,%; phi is the saturated porosity,%; t isnIs the maximum of the T2 spectrum.
2-3 using T2 as bridge, combining P in step 2-1cAnd S in step 2-2wThe expression (2) can obtain a capillary pressure-inflow accumulated saturation curve of the rock sample based on T2 spectrum inversion。
In the step (3), the rotating speed of the first centrifugation is 200r/min, the speed increasing is 200r/min, the maximum centrifugation rotating speed is 4000r/min, and the time of each centrifugation is 90-180 min.
In the step (3), the method for obtaining the capillary pressure-inflow accumulated saturation curve through a centrifugal experiment specifically comprises the following steps:
3-1, carrying out low-speed centrifugation on the saturated water sample until the porosity of the sample is changed stably, wherein the centrifugal force and capillary pressure of the sample are balanced, and the expression when the centrifugal force in the rock sample is balanced with the capillary pressure during centrifugation is shown as a formula (5):
in the formula, PrIs centrifugal force, △ rho is density difference between water and air, omega is angular speed of rotary disk of centrifugal machine, r1、r2The distances from the inner end and the outer end of the sample to the axis of the centrifuge respectively;
3-2, performing nuclear magnetic resonance test on the centrifuged rock sample to obtain porosity, and calculating the water inflow accumulated saturation S of the sample by dividing the porosity of the centrifuged sample by the water saturation porosity of the rock samplew；
And 3-3, continuously increasing the rotation speed of the centrifuge, calculating capillary pressure and water inlet accumulated saturation of the sample at different centrifugal rotation speeds, and obtaining a capillary pressure-water inlet accumulated saturation curve based on the centrifugation method after statistics.
The specific method of the step (4) comprises the following steps:
4-1, fitting a capillary pressure-water inflow accumulated saturation curve obtained by T2 spectrum inversion and a capillary pressure-water inflow accumulated saturation curve obtained by a centrifugal method, and then improving the fitting degree between the capillary pressure-water inflow accumulated saturation curve and the water inflow accumulated saturation curve by continuously adjusting a conversion coefficient c by adopting a least square method, so that the fitting degree between 2 curves is the highest, wherein the conversion coefficient c is the optimal conversion coefficient between the pore size distribution of the rock sample and the T2 spectrum;
4-2, substituting the optimal conversion coefficient c into the relation between the pore diameter and the T2 spectrum, and obtaining the pore diameter distribution of the internal pores of the rock.
The invention has the beneficial effects that: according to the method, a capillary pressure-inflow accumulated saturation curve is obtained through a centrifugal dehydration test, then the optimal conversion coefficient is obtained through curve fitting with nuclear magnetic resonance T2 spectrum inversion, and finally the pore size distribution is obtained.
Drawings
FIG. 1 is a T2 spectrum distribution diagram of a similar sandstone sample in an example;
FIG. 2 is a capillary pressure-water inflow cumulative saturation curve of T2 spectrum inversion of a similar sandstone sample in an example;
FIG. 3 is a schematic diagram of the centrifugation of a quasi-sandstone sample in an example;
FIG. 4 is a capillary pressure-water inflow accumulated saturation curve obtained by a quasi-sandstone sample centrifugation method in the embodiment;
FIG. 5 is a graph comparing capillary pressure-cumulative saturation of feed water curves obtained by two methods in the examples;
FIG. 6 is a comparison graph of capillary pressure versus cumulative saturation of feed water curves by T2 inversion and mercury intrusion tests in the examples;
figure 7 is a pore size distribution plot for a sandstone-like sample of an example.
Detailed Description
Example testing pore size distribution of sandstone-like samples
(1) Preparing a sandstone sample to be detected into a standard cylindrical sample with the diameter of 5cm and the height of 2.5cm, placing the sample in a vacuum saturation device, and vacuumizing under negative pressure of-0.1 MPa for 4 hours until the sample is saturated with water.
(2) Carrying out nuclear magnetic test on the saturated water sandstone-like sample, wherein the parameters of the nuclear magnetic resonance tester are as follows: the magnet strength is 0.52T, the center frequency is 21MHz, O1 is 2691500Hz, TW is 1500, and NECH is 6000. The saturated porosity of the sandstone-like sample is 6.329% by obtaining a T2 spectrum curve through nuclear magnetic resonance, the T2 spectrum is shown in figure 1, the maximum value of T2 is 471.375ms, and the minimum value of T2 is 0.012 ms. And inverting a capillary pressure-inflow accumulated saturation curve of the sandstone-like sample according to the T2 spectrum, wherein the method comprises the following steps:
2-1, obtaining a T2 spectrum of the water-saturated rock sample by adopting a nuclear magnetic resonance test, and describing the relationship between the pore size of the rock sample and the T2 spectrum as follows:
rp＝cT (1)
in the formula, rpIs the pore diameter, um; t is the T2 value, ms, in the T2 spectrum; c is the conversion coefficient, um/ms.
2-2 the relationship between capillary pressure and pore diameter is as follows:
Pc＝2σw×cosθ/rp(2)
in the formula, PcCapillary pressure, MPa; sigmawIs the interfacial tension of water, 7.2N/cm2(ii) a θ is the wetting contact angle, 0 °;
2-3 combining the formula (1) and the formula (2), the functional relation between the capillary pressure and the nuclear magnetic resonance T2 spectrum is expressed as:
Pc＝2σw×cosθ/rp＝2σw×cosθ×c×T (3)
2-4, calculating the water inlet cumulative saturation of the rock sample through the T2 spectrum of the saturated sandstone sample, wherein the functional relation between the water inlet cumulative saturation and the nuclear magnetic resonance T2 spectrum is expressed by the following formula:
in the formula (I), the compound is shown in the specification,
Swcumulative saturation for water inflow,%; phi is acPorosity component,%; phi is the saturation porosity, 6.329%; t isnIs the maximum of the T2 spectrum and is 471.375 ms.
2-5 for directly displaying the form of the capillary pressure-water inflow accumulated saturation curve, T2 is taken as a bridge and combined with PcAnd SwWhen the conversion coefficient c is selected to be 0.32um/ms, a rock test based on T2 spectrum inversion is drawnThe capillary pressure-water inlet cumulative saturation curve is shown in the attached figure 2.
(3) And (3) centrifugally dewatering the saturated water sample after the nuclear magnetic resonance test, setting the rotation speed of an initial centrifugal machine to be 200r/min, keeping the porosity of the sample constant after the sample is centrifuged for 90min, and setting the centrifugation time to be 90min, thus obtaining one-time centrifugation after the centrifugation is finished. After the first centrifugation is finished, performing nuclear magnetic resonance testing on the sample subjected to the first centrifugation, after the testing is finished, putting the sample into a centrifugal machine, increasing the rotating speed to 400r/min, and performing second centrifugation for 90 min; performing a nuclear magnetic resonance test after the centrifugation is finished; according to the rule, the increase range of the centrifugal rotating speed is set to be 200r/min, and the centrifugation is continued until the peak rotating speed reaches 4000 r/min. The structure of the centrifugal device is schematically shown in figure 3. And after each centrifugation, performing nuclear magnetic resonance test on the sample to obtain the water content under the centrifugation at different rotating speeds. The centrifugal force is converted into capillary pressure, the water content of the sample is converted into water inlet saturation, and a capillary pressure-water inlet accumulated saturation curve is constructed according to the result of the sandstone-like sample centrifugal test, wherein the steps are as follows:
3-1, according to the balance of centrifugal force and capillary pressure, the expression of the capillary pressure in the sandstone-like sample during centrifugation is as follows:
in the formula, PrIs centrifugal force, MPa, △ rho is density difference of water and air, about 1000kg/m3(ii) a Omega is the angular speed of the centrifuge turntable, rad/s; r is1、r2The distances r from the inner and outer ends of the sample to the axis of the centrifuge1Is 0.125m, r2Is 0.15 m;
3-2 performing nuclear magnetic resonance test on the sandstone-like sample after each centrifugation to obtain porosity, and calculating the water inflow accumulated saturation S of the sample by dividing the porosity of the centrifuged sample by the porosity of saturated waterw。
3-3, counting capillary pressure and water inlet accumulated saturation of the sample at different centrifugal speeds to obtain a capillary pressure-water inlet accumulated saturation curve based on a centrifugal method as shown in the attached figure 4.
(4) Fitting a capillary pressure-inflow cumulative saturation curve obtained by T2 spectrum inversion with a capillary pressure-inflow cumulative saturation curve obtained by a centrifugal method, as shown in figure 5, finding that the optimal conversion coefficient of a T2 spectrum and pore size distribution is 0.475um/ms by adjusting c by adopting a least square method, and obtaining a pore size distribution diagram as shown in figure 7 by substituting into a T2 spectrogram.
(5) And (3) carrying out mercury intrusion test on the sandstone-like sample to verify the result of the method. Fitting a capillary pressure-mercury inlet accumulated saturation curve obtained by a mercury intrusion test and a capillary pressure-water inlet accumulated saturation curve obtained by T2 inversion, wherein the conversion coefficient with the minimum fitting error is 0.55um/ms as shown in the attached figure 6; compared with the common value range of the empirical value of the conversion coefficient of the porous rock-like material, which is 0.01-30um/ms, the conversion coefficient of the invention is very similar to the conversion coefficient obtained by the mercury pressing method, and the accuracy of the invention is verified.
The present embodiment is only for illustrating the technical concept and features of the present invention, so as to further understand the content of the present invention and implement the same, and the protection scope of the present invention is not limited thereby. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.
Claims (6)
1. A rock material pore size distribution determination method comprises the following steps:
(1) preparing a rock material to be measured into a regular cylindrical sample, placing the rock sample in a vacuum water saturation device for vacuum water saturation until the sample is completely saturated with water, and obtaining a water retention sample;
(2) performing nuclear magnetic resonance testing on the water saturation sample in the step (1) to obtain a T2 spectrum of the water saturation sample, and performing inversion on the T2 spectrum to obtain a capillary pressure-water inflow accumulated saturation curve of the rock sample;
(3) and (3) carrying out centrifugal dehydration on the water-saturated sample tested in the step (2) at different rotating speeds, wherein: the first centrifugal rotating speed is minimum, and then the centrifugal speed is increased by the set acceleration until the set maximum centrifugal rotating speed is reached; after each rotation speed is centrifuged, performing nuclear magnetic resonance testing to obtain the water content under the centrifugal action at different rotation speeds; centrifuging the sample each time, converting the centrifugal force into capillary pressure, converting the water content of the sample into water inlet saturation, and acquiring a capillary pressure-water inlet accumulated saturation curve of the sample;
(4) and (3) fitting the capillary pressure-inflow accumulated saturation curve obtained by T2 spectrum inversion in the step (2) and the capillary pressure-inflow accumulated saturation curve obtained by the centrifugal method in the step (3), and performing inversion calculation on the pore size distribution of the sample.
2. The method for measuring the pore size distribution of the rock material as claimed in claim 1, wherein in the step (1), the negative pressure of vacuum saturated water is-0.1 MPa, and the vacuum saturation time is 4-6 h.
3. The method for determining the pore size distribution of the rock material as claimed in claim 1, wherein in the step (2), the specific method for obtaining the capillary pressure-water inflow cumulative saturation curve of the rock sample by the T2 spectrum inversion comprises the following steps:
2-1 according to the bore diameter r of the rock samplepAnd the relationship between the T2 spectra (equation 1) and capillary pressure PcAnd the aperture rpThe relationship between capillary pressure and nuclear magnetic resonance T2 spectrum (equation 3) can be found as follows:
rp＝cT (1)
Pc＝2σw×cosθ/rp(2)
Pc＝2σw×cosθ/rp＝2σw×cosθ×c×T (3)
in the formula, rpIs the pore diameter; t is the T2 value in the T2 spectrum; c is a conversion coefficient; pcIs capillary pressure; sigmawIs the interfacial tension of water; theta is the wetting contact angle;
2-2 calculating the water inlet saturation of the rock sample through the T2 spectrum of the water saturated rock sample, wherein the function relation between the water inlet cumulative saturation and the nuclear magnetic resonance T2 spectrum can be expressed as the following formula 4:
in the formula (I), the compound is shown in the specification,
Swcumulative saturation for water inflow,%; phi is acPorosity component,%; phi is the saturated porosity,%; t isnIs the maximum of the T2 spectrum;
2-3 using T2 as bridge, combining P in step 2-1cAnd S in step 2-2wThe capillary pressure-water inflow accumulated saturation curve of the rock sample based on T2 spectrum inversion can be obtained.
4. The method for measuring the pore size distribution of the rock material as claimed in claim 1, wherein in the step (3), the rotation speed of the first centrifugation is 200r/min, the speed increase is 200r/min, the maximum centrifugation rotation speed is 4000r/min, and the time of each centrifugation is 90-180 min.
5. The method for determining the pore size distribution of the rock material as claimed in claim 1, wherein in the step (3), the method for obtaining the curve of capillary pressure-water inflow cumulative saturation through a centrifugal experiment specifically comprises the following steps:
3-1, carrying out low-speed centrifugation on the saturated water sample until the porosity of the sample is changed stably, wherein the centrifugal force and capillary pressure of the sample are balanced, and the expression when the centrifugal force in the rock sample is balanced with the capillary pressure during centrifugation is shown as a formula 5:
in the formula, PrIs centrifugal force, △ rho is density difference between water and air, omega is angular speed of rotary disk of centrifugal machine, r1、r2The distances from the inner end and the outer end of the sample to the axis of the centrifuge respectively;
3-2 performing nuclear magnetic resonance test on the centrifuged rock sample to obtain porosity, and separatingCalculating the water inlet accumulated saturation S of the sample by dividing the porosity of the sample behind the core by the water saturation porosity of the rock samplew；
And 3-3, continuously increasing the rotation speed of the centrifuge, calculating capillary pressure and water inlet accumulated saturation of the sample at different centrifugal rotation speeds, and obtaining a capillary pressure-water inlet accumulated saturation curve based on the centrifugation method after statistics.
6. The method for determining the pore size distribution of a rock material as claimed in claim 1, wherein the specific method of the step (4) is as follows:
4-1, fitting a capillary pressure-water inflow accumulated saturation curve obtained by T2 spectrum inversion and a capillary pressure-water inflow accumulated saturation curve obtained by a centrifugal method, and then improving the fitting degree between the capillary pressure-water inflow accumulated saturation curve and the water inflow accumulated saturation curve by continuously adjusting a conversion coefficient c by adopting a least square method, so that the fitting degree between 2 curves is the highest, wherein the conversion coefficient c is the optimal conversion coefficient between the pore size distribution of the rock sample and the T2 spectrum;
4-2, substituting the optimal conversion coefficient c into the relation between the pore diameter and the T2 spectrum, and obtaining the pore diameter distribution of the internal pores of the rock.
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| CN112284999A (en) * | 2020-10-26 | 2021-01-29 | 中国石油大学(华东) | Sandstone pore size distribution determination method and application thereof |
| CN113945497A (en) * | 2020-07-15 | 2022-01-18 | 中国石油天然气股份有限公司 | Evaluation method for mobility of reservoir fluid of oil and gas reservoir |
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