CN114858683B - Method for evaluating pore structure change of gas storage core after salt precipitation - Google Patents
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- 150000003839 salts Chemical class 0.000 title claims abstract description 70
- 238000003860 storage Methods 0.000 title claims abstract description 38
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- 239000011435 rock Substances 0.000 claims abstract description 103
- 238000005481 NMR spectroscopy Methods 0.000 claims abstract description 43
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 36
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- 229920006395 saturated elastomer Polymers 0.000 claims abstract description 17
- 238000002474 experimental method Methods 0.000 claims abstract description 8
- 239000008398 formation water Substances 0.000 claims description 54
- 230000015572 biosynthetic process Effects 0.000 claims description 34
- 238000000151 deposition Methods 0.000 claims description 19
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical class [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 claims description 11
- 150000001875 compounds Chemical class 0.000 claims description 11
- 238000001035 drying Methods 0.000 claims description 10
- 238000013507 mapping Methods 0.000 claims description 9
- 238000005553 drilling Methods 0.000 claims description 8
- 238000005259 measurement Methods 0.000 claims description 8
- 239000008367 deionised water Substances 0.000 claims description 7
- 229910021641 deionized water Inorganic materials 0.000 claims description 7
- 238000005406 washing Methods 0.000 claims description 6
- 238000004457 water analysis Methods 0.000 claims description 6
- 238000004140 cleaning Methods 0.000 claims description 5
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical class O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 5
- 238000001228 spectrum Methods 0.000 claims description 5
- 238000005520 cutting process Methods 0.000 claims description 4
- 239000012153 distilled water Substances 0.000 claims description 4
- 238000006073 displacement reaction Methods 0.000 claims description 3
- 238000011161 development Methods 0.000 abstract description 3
- 230000018109 developmental process Effects 0.000 abstract description 3
- 239000007789 gas Substances 0.000 description 34
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 8
- 239000013078 crystal Substances 0.000 description 5
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- 230000008020 evaporation Effects 0.000 description 4
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- 239000003345 natural gas Substances 0.000 description 4
- 238000009826 distribution Methods 0.000 description 3
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Abstract
The invention relates to the technical field of oil and gas field development engineering, in particular to a method for evaluating salt deposition of a core of a gas storage reservoirMethod for changing pore structure based on NMR principle and combined with NMR transverse relaxation time T 2 Radius of pore throat r c A relation model is established for nuclear magnetic resonance T 2 The change of the pore structure of the rock core is reflected visually by the change relation of the map curve along with the water mineralization of the stratum; the saturated rock core is used for displacing the rock core, the problem that the rock core pore structure change cannot be observed through a nuclear magnetic resonance experiment when salt is dissolved in water is solved, and the method is simple to operate, easy to popularize and simpler and more reliable in result.
Description
Technical Field
The invention relates to the technical field of oil and gas field development engineering, in particular to a method for evaluating changes of pore structures of gas storage core after salt deposition.
Background
At present, the dependence of natural gas in China is as high as 43.41%, while the working gas volume of underground gas storage reservoirs in China only accounts for 4% of annual consumption, is lower than the average 12% in the world, and is far lower than 17% in the United states and 25% in the European Union, so that the natural gas storage and peak regulation capacity is further improved to be urgent.
For a gas reservoir type gas storage reservoir with limited formation water, in the multi-period operation process, the formation water can be evaporated by injecting dry natural gas, so that the gas storage reservoir may have a reservoir drying phenomenon after injection and production cycles are repeated year after year. Particularly, when the initial mineralization of formation water in a reservoir is high, the reservoir is dried after multi-period injection and production circulation, the problem of reservoir salt deposition and blockage also occurs, and potential safety hazards are brought to stable operation of a gas storage.
At present, the research on the stratum salt formation law mainly aims at the damage influence of salt crystallization after evaporation of stratum water on the physical properties of stratum rocks, and mainly concentrates the sealing and storing of CO in an underground saline water layer 2 The technical field is as follows. Giacomo and Bacci et al (2013) by drying CO 2 The study was performed by injection into a core saturated with brine. Kim and Sell et al (2013) developed a lab-on-a-chip method to study saline aquifers at CO 2 Salt formation dynamics at the pore scale during sequestration, but changes in the core pore structure were not further explored. The research on the microcosmic distribution of salt crystals after evaporation of formation water and the like is less under the condition of multi-period strong injection and strong extraction of natural gas in the underground gas storage. Particularly, the research on the change of the pore structure by salt crystals after evaporation and salt deposition of formation water in a reservoir is less, and a method capable of measuring the influence of evaporation and salt deposition of formation water with different mineralization on the pore structure of a rock core is urgently needed to be designed and established, and a relevant chart is established to provide basic parameters for accurately simulating and predicting the operation dynamic state of the gas storage so as to reduce or even eliminate potential safety hazards caused by salt deposition blockage to the efficient operation of the underground gas storage.
Disclosure of Invention
The invention aims to provide a method for evaluating the change of a pore structure of a gas storage core after salt deposition, which is suitable for researching the change rule of the pore structure of the gas storage core after salt deposition.
In order to achieve the purpose, the invention provides a method for evaluating the change of a pore structure of a gas storage core after salt formation, which specifically comprises the following steps:
the method comprises the following steps: obtaining a target reservoir standard rock core: obtaining a target reservoir rock sample, drilling a standard rock core by using a rock core drilling machine and a cutting machine, cleaning the rock core, and dissolving soluble salt in the rock core;
step two: measuring nuclear magnetic resonance T of rock core under water-saturated condition 2 And (3) atlas: will be fullTaking out the core of the formation water, and placing the core into a nuclear magnetic resonance instrument to measure nuclear magnetic resonance T 2 Mapping, measuring nuclear magnetic resonance T after rock core saturates formation water 2 The atlas is used as T under the original condition of the rock core 2 Map morphology;
step three: washing the core by deionized water: taking out original condition T after measurement 2 Washing a rock core by using saturated formation water of the atlas, and taking out the rock core when the formation water reaching the rock core is completely displaced out of the rock core;
step four: drying the core: putting the core into an oven, and drying the moisture in the core;
step five: preparing stratum water samples with different degrees of mineralization: preparing stratum water samples with different mineralization degrees according to stratum water analysis data of a target reservoir;
step six: injecting formation water with different mineralization degrees into the rock core: putting the core into a core holder, performing an experiment in an oven, and using compound formation water to displace the core;
step seven: measurement of nuclear magnetic resonance T after saturated brine displacement of rock core 2 And (3) atlas: using saturated saline water to displace the rock core, and measuring the nuclear magnetic resonance T of the rock core after the rock core is filled with the saturated saline water 2 A spectrum is used for observing the change of the pore structure of the rock core after salt formation damage occurs in the rock core;
step eight: repeating the third step to the seventh step: changing the concentration of the water and the salt in the compound formation, and repeating the steps three to seven times;
step nine: analyzing the change of the pore structure of the rock core after the formation water with different mineralization degrees is salted: under the condition that the rock saturated with water is in a uniform magnetic field, transverse relaxation time T is determined according to nuclear magnetic resonance 2 Radius of pore throat r c And (5) judging the change of the pore structure of the rock core by using a relation model.
Wherein deionized water is used to displace the core 20PV in the first step.
And in the third step, the core holder is used for displacing the core 20PV with distilled water when the core is cleaned.
And setting the temperature of the oven as the target formation temperature in the sixth step.
And the concentration of the salt of the compound formation water in the step eight is 1/3 multiplied by the actual formation water mineralization degree, 2/3 multiplied by the actual formation water mineralization degree and the actual formation water mineralization degree in sequence.
Wherein, in the step nine: transverse relaxation time T of nuclear magnetic resonance 2 Radius of pore throat r c The relation model is as follows:
calculating a formula according to the average pore radius of the core:
According to the method for evaluating the pore structure change of the gas storage core after salt deposition, the method for evaluating the pore structure change of the gas storage core after salt deposition based on the nuclear magnetic resonance principle can simulate a real formation environment, and the method for performing the nuclear magnetic resonance experiment after the saturated strong brine is used for displacing the core for the first time overcomes the problem that the pore structure change of the core cannot be observed through the nuclear magnetic resonance experiment when the salt is dissolved in water. The method is favorable for deepening the recognition and understanding of the stratum salt deposition and blockage problem in the exploitation process of the gas reservoir type gas storage, so that basic parameters are provided for accurately simulating the stratum salt deposition process, the scientific development technical scheme is favorably formulated, and the stratum salt deposition and blockage problem in the exploitation process of the gas reservoir type gas storage is solved.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.
FIG. 1 is a flow chart of a method for evaluating changes of pore structures after salt formation of a core of a gas storage according to the invention.
FIG. 2 is a nuclear magnetic resonance T under original rock sample conditions of the method for evaluating changes of pore structures after salt formation of gas storage core according to the invention 2 And (4) mapping.
FIG. 3 shows the nuclear magnetic resonance T of a rock sample obtained by the method for evaluating the pore structure change after salt formation of the gas storage core according to the invention after salt formation of the formation water with the salinity of 100000mg/L 2 And (4) mapping.
FIG. 4 shows the nuclear magnetic resonance T of a rock sample obtained by evaluating the change of the pore structure of a rock core after salt formation in a gas storage reservoir according to the method of the invention after salt formation in formation water with a mineralization degree of 200000mg/L 2 And (4) mapping.
FIG. 5 shows the nuclear magnetic resonance T of a rock sample obtained by the method for evaluating the pore structure change of the rock core of the gas storage after salt formation in formation water with the mineralization degree of 300000mg/L in the invention 2 And (4) mapping.
Detailed Description
Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, and the embodiments described below with reference to the accompanying drawings are exemplary and intended to be illustrative of the present invention and should not be construed as limiting the present invention.
Referring to fig. 1 to 5, fig. 1 is a flow chart illustrating a method for evaluating a change in a pore structure of a gas storage core after salt formation according to the present invention, and fig. 2 is a flow chart illustrating a nuclear magnetic resonance T under original conditions of a rock sample according to the method for evaluating a change in a pore structure of a gas storage core after salt formation according to the present invention 2 FIG. 3 is a graph of nuclear magnetic resonance T of a rock sample obtained by evaluating the change of a pore structure after salt formation of a rock core of a gas storage according to the method for evaluating the change of the pore structure after salt formation of the rock sample in the reservoir, wherein the rock sample is subjected to salt formation in a formation water with a mineralization degree of 100000mg/L 2 FIG. 4 is a graph of nuclear magnetic resonance T of a rock sample obtained by evaluating the change of the pore structure of a rock core after salt formation in a gas storage reservoir according to the method for evaluating the salt formation of the rock core of the gas storage reservoir after salt formation in formation water with the mineralization degree of 200000mg/L 2 FIG. 5 is a graph of a rock sample 30000 of the method for evaluating the pore structure change of the rock core of the gas storage after salt formationNuclear magnetic resonance T after salt precipitation of 0mg/L mineralization formation water 2 And (4) mapping. The invention provides a method for evaluating pore structure change of a gas storage core after salt precipitation, which specifically comprises the following steps:
s1: obtaining a target reservoir standard rock core: obtaining a target reservoir rock sample, drilling a standard rock core by using a rock core drilling machine and a cutting machine, cleaning the rock core, dissolving soluble salt in the rock core, and displacing the rock core 20PV by using deionized water;
s2: measuring nuclear magnetic resonance T of rock core under water-saturated condition 2 And (3) atlas: taking out the core of saturated formation water, and placing the core into a nuclear magnetic resonance instrument to measure nuclear magnetic resonance T 2 Mapping, measuring nuclear magnetic resonance T after rock core saturates formation water 2 The spectrum is used as T under the original condition (salt formation does not occur) of the rock core 2 Map morphology;
s3: washing the core by deionized water: taking out original condition T after measurement 2 Washing a core by using a saturated formation water core of the atlas, displacing the core 20PV by using distilled water by using a core holder when the core is washed, and taking out the core when the formation water reaching the core is completely displaced out of the core;
s4: drying the core: putting the core into an oven, and drying the moisture in the core;
s5: preparing stratum water samples with different degrees of mineralization: preparing stratum water samples with different degrees of mineralization according to stratum water analysis data of a target reservoir;
s6: injecting formation water with different mineralization degrees into the rock core: putting the core into a core holder, performing an experiment in an oven, wherein the oven temperature is the target formation temperature, displacing the core by using compound formation water, and taking out the core after displacing by 10 PV;
s7: measurement of nuclear magnetic resonance T after saturated brine displacement of rock core 2 Mapping: using saturated saline to displace the rock core 10PV, preventing the salt crystals deposited in the rock core from dissolving in water, and measuring the nuclear magnetic resonance T of the rock core after the rock core is filled with the saturated saline 2 A map is used for observing the pore structure change of the rock core after salt formation damage occurs;
s8: repeating S3 to S7: repeating S3 to S7 for three times by changing the concentration of the compound formation water salt, wherein the concentration of the salt of the compound formation water is 1/3 multiplied by the actual formation water mineralization, 2/3 multiplied by the actual formation water mineralization and the actual formation water mineralization in sequence;
s9: analyzing the change of the pore structure of the rock core after the formation water with different mineralization degrees is salted: under the condition that the rock saturated with water is in a uniform magnetic field, transverse relaxation time T is determined according to nuclear magnetic resonance 2 Radius of pore throat r c And (5) judging the change of the pore structure of the rock core by using a relation model.
The nuclear magnetic resonance measurement core pore structure principle is as follows:
in the formula (1), T 2 Is transverse relaxation time in ms; t is 2n Transverse volume (free) relaxation time in ms; rho 2 The transverse surface relaxation strength of the rock is expressed in the unit of mu m/ms; s is the pore surface area in cm 2 (ii) a V is the pore volume in cm 3 (ii) a D is the diffusion coefficient in mum 2 (ms); gamma is the gyromagnetic ratio of proton, and the unit is Hz/T; g is magnetic field gradient with unit of T/cm; t is E Is the echo interval, and the unit is ms;
t of fluid 2n Ratio T 2 Much larger, therefore T 2n Has a negligible reciprocal of (1) and a negligible right term, whereas in NMR spectroscopy the magnetic field is uniform and T E Very small, so the right term 3 is also negligible, and the above equation reduces to:
as can be seen in equation (2), since the surface area to volume ratio of a pore is related to the pore radius and the shape factor, for a pore with a regular shape, the transverse relaxation time can be derived from the above equation, and then:
in the formula (3), F S Is a pore geometry factor; r is c Pore throat radius in μm;
let C = 1/(ρ) 2 F S ) Then when the rock saturated with water is in the condition of uniform magnetic field, the rock core T 2 The change of the map is consistent with the change of the pore structure of the rock core, and the nuclear magnetic resonance transverse relaxation time T 2 Radius of pore throat r c In a proportional relationship:
T 2 ＝Cr c (4)
calculating a formula according to the average pore radius of the core:
in the formula (5), T 2i Is the ith component T 2 A value in ms;
is the average pore radius in μm; fi is the ith component pore radius frequency;
thus, it is possible to provide
The change of (4) is consistent with the change amplitude of the average pore radius of the rock core and can be used>
The magnitude of the increase or decrease evaluates the change in the average pore radius of the core.
Example (b):
the core samples used were from Wen 23 reservoir sand four groups.
Obtaining a target reservoir rock sample, drilling a standard rock core by using a rock core drilling machine and a cutting machine, cleaning the rock core, and cleaning soluble salt in the rock core, wherein the basic parameters of the rock core are shown in the following table 1, and the formation water analysis data of a target stratum is shown in the following table 2; taking out the core of the saturated formation water, and putting the core into a nuclear magnetic resonance instrument to measure a nuclear magnetic resonance spectrum, wherein the measurement result is shown in figure 3;
| core numbering | Length/cm | Diameter/cm | Porosity/%) | permeability/ |
| 1 | 3.40 | 2.53 | 12.41 | 0.39 |
TABLE 1 core basic parameters
TABLE 2 formation water analysis data
And taking out the saturated formation water core after the basic data is measured, using the core holder to displace the core 20PV by using distilled water of the first intermediate container, and taking out the core after the deionized water of the core is completely displaced out of the core. And putting the core into an oven, and drying the moisture in the core. Preparing stratum water samples with different degrees of mineralization according to stratum water analysis data of a target reservoir, wherein the concentrations of the prepared stratum water samples are 100000mg/L, 200000mg/L and 300000mg/L respectively;
setting the temperature of the oven to a target formation temperatureAnd (3) slowly displacing the core by using the compound formation water, and taking out the core after displacing 10 PV. In order to prevent the salt crystals deposited in the core from dissolving in water, the core 10PV is displaced by saturated saline, and the nuclear magnetic resonance T is measured after the core is filled with the saturated saline 2 And (3) a spectrum is obtained, the pore structure change of the rock core is observed after salt deposition damage occurs in the rock core, the steps are repeated for three times, images obtained by sequentially setting the salt concentration of the compound formation water to be 100000mg/L, 200000mg/L and 300000mg/L are respectively shown in the figures 3, 4 and 5, and the images obtained by calculating after drying and salt deposition are performed on the formation water under the original condition (no salt deposition occurs), 100000mg/L, 200000mg/L and 300000mg/L
13.85, 11.34, 10.95 and 10.59, respectively.
The experimental results show that: the porosity of the core is gradually reduced along with the experiment (based on the peak area of the nuclear magnetic resonance T2 spectrum under the original condition), the pore throat radius distribution of the sample is in a single-peak form, the single peak of the pore throat radius distribution of the sample is shifted to the right along with the experiment and the increase of NaCl salt crystals deposited in the core, and the shift amplitude and the shift sum of the single peak are obtained in the process of depositing the formation water under the original condition of 100000mg/L mineralization
The calculated value has the largest change range and has the most obvious influence on the pore structure, so the optimal stage for controlling the salt deposition condition is the early salt deposition stage, namely, measures should be taken immediately when the salt deposition condition of the gas storage occurs.
While the above disclosure describes one or more preferred embodiments of the present invention, it is not intended to limit the scope of the claims to such embodiments, and one skilled in the art will understand that all or a portion of the processes performed in the above embodiments may be practiced without departing from the spirit and scope of the claims.
Claims (6)
1. A method for evaluating pore structure change of a gas storage core after salt deposition is characterized by comprising the following steps:
the method comprises the following steps: obtaining a target reservoir standard rock core: obtaining a target reservoir rock sample, drilling a standard rock core by using a rock core drilling machine and a cutting machine, cleaning the rock core, and dissolving soluble salt in the rock core;
step two: measuring nuclear magnetic resonance T of rock core under water-saturated condition 2 And (3) atlas: taking out the core of saturated formation water, and placing the core into a nuclear magnetic resonance instrument to measure nuclear magnetic resonance T 2 Mapping, measuring nuclear magnetic resonance T after rock core saturates formation water 2 The atlas is used as T under the original condition of the rock core 2 Map morphology;
step three: washing the core by deionized water: taking out original condition T after measurement 2 Washing a rock core by using saturated formation water of the atlas, and taking out the rock core when the formation water reaching the rock core is completely displaced out of the rock core;
step four: drying the core: putting the core into an oven, and drying the moisture in the core;
step five: preparing stratum water samples with different degrees of mineralization: preparing stratum water samples with different degrees of mineralization according to stratum water analysis data of a target reservoir;
step six: injecting formation water with different mineralization degrees into the rock core: putting the core into a core holder, performing an experiment in an oven, and using compound formation water to displace the core;
step seven: measurement of nuclear magnetic resonance T after saturated brine displacement of rock core 2 And (3) atlas: using saturated saline water to displace the rock core, and measuring the nuclear magnetic resonance T of the rock core after the rock core is filled with the saturated saline water 2 A spectrum is used for observing the change of the pore structure of the rock core after salt formation damage occurs in the rock core;
step eight: repeating the third step to the seventh step: changing the concentration of the water and the salt in the compound formation, and repeating the steps three to seven times;
step nine: analyzing the change of the pore structure of the rock core after the formation water with different mineralization degrees is salted: under the condition that the rock saturated with water is in a uniform magnetic field, transverse relaxation time T is determined according to nuclear magnetic resonance 2 Radius of pore throat r c And (5) judging the change of the pore structure of the rock core by using a relation model.
2. The method for evaluating the pore structure change of the gas storage core after salt formation according to claim 1,
deionized water was used to displace the core 20PV in the first step.
3. The method for evaluating the pore structure change of the gas storage core after salt formation according to claim 2,
and in the third step, the core holder is used for displacing the core 20PV with distilled water when the core is cleaned.
4. The method for evaluating the pore structure change of the gas storage core after salt formation according to claim 3,
and setting the temperature of the oven as the target formation temperature in the sixth step.
5. The method for evaluating the pore structure change of the gas storage core after salt formation according to claim 4,
and the concentration of the salt of the compound formation water in the step eight is 1/3 multiplied by the actual formation water mineralization degree, 2/3 multiplied by the actual formation water mineralization degree and the actual formation water mineralization degree in sequence.
6. The method for evaluating the pore structure change of the gas storage core after salt formation according to claim 5,
in the step nine: transverse relaxation time T of nuclear magnetic resonance 2 Radius of pore throat r c The relation model is as follows:
wherein: rho 2 Is the transverse surface relaxation strength of the rock, in μm/ms, F S Is a pore geometry factor;
calculating a formula according to the average pore radius of the core:
wherein: c = 1/(ρ) 2 F S )，T 2i Is the ith component T 2 Values in ms, fi is the ith component pore radius frequency;
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| CN113504171A (en) * | 2021-07-13 | 2021-10-15 | 西南石油大学 | Device and method for measuring reservoir salt deposition damage and evaluating salt dissolving agent effect |
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