Rock porosity evaluation method and system based on mineral ion concentration
1. A rock porosity evaluation method based on mineral ion concentration, comprising the steps of:
collecting nuclear magnetic signals of soft rock minerals;
obtaining a first sample based on the soft rock mineral, and collecting a first characteristic peak intensity and a first mineral component of the first sample;
performing dry-wet cycle test on the first sample, drying and grinding to obtain a second sample, and collecting a second characteristic peak intensity, a second mineral component and a cation mass concentration of an aqueous solution used for the dry-wet cycle test of the second sample;
evaluating the internal pore space change rule of the soft rock mineral under the action of dry and wet circulation based on the first characteristic peak intensity, the nuclear magnetic signal and the second characteristic peak intensity;
evaluating the internal chemical reaction law of the soft rock mineral under the action of the dry-wet circulation based on the first mineral composition, the second mineral composition and the cation mass concentration;
and evaluating the evolution law of the rock porosity of the soft rock mineral according to the internal pore change law and the internal chemical reaction law.
2. A method of rock porosity estimation based on mineral ion concentration according to claim 1,
in the process of drying and grinding the soft rock mineral to obtain the first sample, the soft rock mineral is dried and ground, then is sieved by using a sieve with the aperture of 0.0074mm, about 3g of the sieved soft rock mineral is selected by a quartering method, and then is tableted to prepare the sample, so that the first sample is obtained.
3. A method of rock porosity estimation based on mineral ion concentration according to claim 2,
and in the process of obtaining a second sample, quantitatively analyzing the aqueous solution generated in the dry-wet cycle test by using an inductively coupled plasma mass spectrometer to obtain the mass concentration of the cations.
4. A method of rock porosity estimation based on mineral ion concentration according to claim 3,
before the process of collecting the nuclear magnetic signals, the soft rock minerals are made into a cylindrical sample of 50mm multiplied by 100mm, then vacuumized and saturated for 12 hours, and the nuclear magnetic signals are obtained through a nuclear magnetic resonance imaging analyzer.
5. A method of rock porosity estimation based on mineral ion concentration according to claim 4,
in the process of evaluating the internal pore change rule, analyzing the characteristic peak change rule of the mineral composition of the soft rock mineral according to the first characteristic peak intensity and the second characteristic peak intensity;
according to the nuclear magnetic signal, a standard scale sample is used for scaling to obtain the porosity of the soft rock mineral;
and evaluating the internal pore change rule according to the characteristic peak change rule and the porosity.
6. A method of rock porosity estimation based on mineral ion concentration according to claim 5,
in the process of evaluating the internal chemical reaction rule, obtaining the first mineral component and the first chemical component content of the first sample according to the first mineral component;
obtaining the second mineral component and the second chemical component content of the second sample according to the second mineral component;
and evaluating the internal chemical reaction law according to the first mineral composition, the second mineral composition, the first chemical composition content, the second chemical composition content and the cation mass concentration.
7. A method of rock porosity estimation based on mineral ion concentration according to claim 6,
acquiring a first ion mass variation, a mass concentration variation, dry-wet cycle times, a soaking solution volume and a first molar mass of the second sample to obtain a first ion mass variation rate of the second sample;
obtaining a second ion mass change rate of the first sample according to the first ion mass change rate and the stoichiometric number of the second sample, wherein the second ion mass change rate at least comprises a second ion mass change amount and a second molar mass of the first sample;
obtaining a volume of the first sample reacted with water for assessing the porosity of the soft rock mineral from the constituent mass density of the first sample based on the second rate of ion mass change;
and evaluating the evolution law of the rock porosity of the soft rock mineral according to the volume and the internal pore change law for evaluating the mesoscopic damage of the soft rock.
8. A rock porosity evaluation system based on mineral ion concentration, comprising,
the device comprises a first characteristic acquisition module, a second characteristic acquisition module and a third characteristic acquisition module, wherein the first characteristic acquisition module is used for acquiring first characteristic peak intensity and first mineral composition of a first sample, and the first sample is used for representing a first product prepared according to soft rock minerals;
the second characteristic acquisition module is used for acquiring the nuclear magnetic signals of the soft rock minerals, the second characteristic peak intensity of a second sample and second mineral components, wherein the second sample is used for representing a second product obtained after the first sample is subjected to dry-wet circulation;
the first operation module is used for generating a characteristic peak change rule curve graph according to the first characteristic peak intensity and the second characteristic peak intensity;
the second operation module is used for obtaining the porosity of the second sample according to the nuclear magnetic signal;
a third operation module; the system is used for generating an internal chemical reaction rule table according to the first mineral composition and the second mineral composition;
the first evaluation module is used for generating a first evaluation result according to the characteristic peak change rule curve graph and the porosity, and the first evaluation result is used for representing an internal pore change rule;
the second evaluation module is used for generating a second evaluation result according to the internal chemical reaction rule table, and the second evaluation result is used for expressing the internal chemical reaction rule;
and the third evaluation module is used for obtaining a third evaluation result according to the first evaluation result and the second evaluation result, wherein the third evaluation result is used for expressing the evolution rule of the rock porosity of the soft rock mineral.
9. The system of claim 8, wherein the porosity of the rock is estimated based on the concentration of mineral ions,
the system also comprises a third characteristic acquisition module for acquiring the cation mass concentration of the aqueous solution after the first sample is subjected to the dry-wet cycle test;
the third operation module comprises a dry-wet cycle number counting unit, a soaking solution volume recording unit, a molar mass unit, a stoichiometric number unit, a mass density unit and a volume generating unit;
the dry-wet cycle number counting unit is used for recording the cycle number of the first sample after a dry-wet cycle experiment;
the soaking solution volume recording unit is used for recording the volume of the soaking solution in the process of the dry-wet cycle experiment;
the molar mass unit is used for providing the molar mass of the soft rock mineral;
the mass density unit is used for providing the mass density of the soft rock mineral;
the stoichiometric number unit is used for providing the first sample to generate the stoichiometric number of the second sample;
the volume generating unit is used for obtaining the generating volume of the first sample and the second sample based on the cycle number according to the volume of the soaking solution, the cycle number, the molar mass, the mass density and the stoichiometric number.
10. The system of claim 9, wherein the porosity of the rock is estimated based on the concentration of mineral ions,
the third evaluation module is connected with the second evaluation unit and the first evaluation unit and is used for generating a third evaluation result according to the cycle number, the generated volume and the internal pore change rule.
Background
The evolution of the mesoscopic structure of the carbonaceous mudstone under the action of the dry-wet cycle is a complex water-rock interaction process, the internal pore volume of the rock is quantitatively calculated from the mineral ion concentration angle, and the method has important significance for knowing the mesoscopic structure characteristics of the rock and accurately evaluating the mechanical property of the rock.
In the past, most researches are related to the microscopic structure change, disintegration form, particle structure evolution, mechanics and deformation characteristics of water injection-rock interaction, the evolution rule of mineral components of soft rock is discussed less based on chemical analysis, particularly the pore evolution equation of rock is established less from the perspective of water-rock chemical reaction, and a method and a system for quantitatively describing the damage evolution process of the soft rock under the action of dry-wet circulation are urgently needed to meet the existing technical requirements.
Disclosure of Invention
The invention aims to analyze the chemical reaction of minerals according to the mineral reaction principle by testing the ion concentration of a solution in the dry-wet cycle action process of the rock, establish the functional relationship between the ion concentration of the minerals and the porosity by utilizing the ion conservation principle, and quantitatively calculate the porosity of the carbonaceous mudstone.
In order to solve the above problems, the present invention provides a rock porosity evaluation method based on mineral ion concentration, comprising the steps of:
collecting nuclear magnetic signals of soft rock minerals;
obtaining a first sample based on soft rock minerals, and collecting first characteristic peak intensity and first mineral components of the first sample;
carrying out dry-wet cycle test on the first sample, drying and grinding to obtain a second sample, and collecting a second characteristic peak intensity, a second mineral component and a cation mass concentration of an aqueous solution for the dry-wet cycle test of the second sample;
evaluating the internal pore change rule of the soft rock mineral under the action of dry and wet circulation based on the first characteristic peak intensity, the nuclear magnetic signal and the second characteristic peak intensity;
evaluating the internal chemical reaction rule of the soft rock mineral under the action of dry-wet circulation based on the first mineral component, the second mineral component and the cation mass concentration;
and evaluating the evolution law of the rock porosity of the soft rock mineral according to the internal pore change law and the internal chemical reaction law.
Preferably, in the process of drying and grinding the soft rock mineral to obtain a first sample, the soft rock mineral is dried and ground, then is sieved by using a sieve with the aperture of 0.0074mm, about 3g of the sieved soft rock mineral is selected by a quartering method, and then is tableted to prepare the sample, so that the first sample is obtained.
Preferably, in the process of obtaining the second sample, the mass concentration of the cations is obtained by analyzing the aqueous solution generated in the dry-wet cycle test by using an inductively coupled plasma mass spectrometer.
Preferably, before the process of acquiring the nuclear magnetic signals, after the soft rock mineral is made into a 50mm × 100mm sample and vacuumized and saturated for 12 hours, the nuclear magnetic signals are acquired by a nuclear magnetic resonance imaging analyzer.
Preferably, in the process of evaluating the internal pore change rule, analyzing the characteristic peak change rule of the mineral composition of the soft rock mineral according to the first characteristic peak intensity and the second characteristic peak intensity;
according to the nuclear magnetic signal, utilizing a standard scale sample to carry out calibration to obtain the porosity of the soft rock mineral;
and evaluating the internal pore change rule according to the characteristic peak change rule and the porosity.
Preferably, in the process of evaluating the internal chemical reaction law, the first mineral composition and the first chemical composition content of the first sample are obtained according to the first mineral composition;
obtaining the second mineral component and the second chemical component content of a second sample according to the second mineral component;
and evaluating the internal chemical reaction rule according to the first mineral component, the second mineral component, the content of the first chemical component, the content of the second chemical component and the cation mass concentration.
Preferably, acquiring a first ion mass change amount, a mass concentration change amount, a dry-wet cycle number, a soaking solution volume and a first molar mass of a second sample to obtain a first ion mass change rate of the second sample;
obtaining a second ion mass change rate of the first sample according to the first ion mass change rate and the stoichiometric number of the second sample, wherein the second ion mass change rate at least comprises a second ion mass change amount and a second molar mass of the first sample;
obtaining the volume of the first sample according to the component mass density of the first sample based on the second ion mass change rate;
and (4) evaluating the evolution law of the rock porosity of the soft rock mineral according to the volume and internal pore change law, and evaluating the mesoscopic damage of the soft rock.
A rock porosity evaluation system based on mineral ion concentration includes,
the device comprises a first characteristic acquisition module, a second characteristic acquisition module and a third characteristic acquisition module, wherein the first characteristic acquisition module is used for acquiring first characteristic peak intensity and first mineral composition of a first sample, and the first sample is used for representing a first product prepared according to soft rock minerals;
the second characteristic acquisition module is used for acquiring a nuclear magnetic signal of the soft rock mineral, a second characteristic peak intensity of a second sample and a second mineral component, wherein the second sample is used for expressing a second product obtained by the first sample after dry-wet circulation;
the first operation module is used for generating a characteristic peak change rule curve graph according to the first characteristic peak intensity and the second characteristic peak intensity;
the second operation module is used for obtaining the porosity of the second sample according to the nuclear magnetic signal;
a third operation module; the system is used for generating an internal chemical reaction rule table according to the first mineral composition and the second mineral composition;
the first evaluation module is used for generating a first evaluation result according to the characteristic peak change rule curve graph and the porosity, and the first evaluation result is used for expressing the internal pore change rule;
the second evaluation module is used for generating a second evaluation result according to the internal chemical reaction rule table, and the second evaluation result is used for expressing the internal chemical reaction rule;
and the third evaluation module is used for obtaining a third evaluation result according to the first evaluation result and the second evaluation result, wherein the third evaluation result is used for expressing the evolution rule of the rock porosity of the soft rock mineral.
Preferably, the system further comprises a third characteristic acquisition module for acquiring the cation mass concentration of the aqueous solution after the first sample is subjected to the dry-wet cycle test;
the third operation module comprises a dry-wet cycle number counting unit, a soaking solution volume recording unit, a molar mass unit, a stoichiometric number unit, a mass density unit and a volume generating unit;
the dry-wet cycle number counting unit is used for recording the cycle number of the first sample after a dry-wet cycle experiment;
the soaking solution volume recording unit is used for recording the volume of the soaking solution in the process of the dry-wet cycle experiment;
a molar mass unit for providing the molar mass of the soft rock mineral;
a mass density unit for providing a mass density of the soft rock mineral;
a stoichiometry unit for providing a first sample to generate a stoichiometry of a second sample;
and the volume generating unit is used for obtaining the generation volume of the first sample and the second sample based on the cycle number according to the volume of the soaking solution, the cycle number, the molar mass, the mass density and the stoichiometric number.
Preferably, the third evaluation module is connected with the second evaluation unit and the first evaluation unit and is used for generating a third evaluation result according to the cycle number, the generated volume and the internal pore change rule.
The invention discloses the following technical effects:
according to the invention, according to the principle of ion conservation, the microscopic pore evolution equation of the carbonaceous mudstone under the action of dry-wet circulation is established by taking the mass concentration of ions in a solution as a variable, and is contrastively analyzed with the low-field nuclear magnetic resonance test result through theoretical calculation, so that the established microscopic pore evolution equation can reflect the evolution rule of the porosity of the carbonaceous mudstone along with the dry-wet circulation frequency, and a new thought is provided for quantitatively researching the soft rock porosity test under the action of dry-wet circulation.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without creative efforts.
FIG. 1 is a flow chart of a method according to the present invention;
FIG. 2 is a block diagram of the system of the present invention;
FIG. 3 shows carbonaceous mudstone T under the action of the wet and dry cycle according to an embodiment of the present invention2The distribution of the map is changed;
FIG. 4 is a calibration curve of a NMR sample according to an embodiment of the invention;
FIG. 5 is a graph of the porosity of carbonaceous mudstone under the action of a wet and dry cycle according to an embodiment of the invention;
FIG. 6 is a graph illustrating incremental changes in porosity of carbonaceous mudstone under the action of a dry-wet cycle in accordance with an embodiment of the present invention;
FIG. 7 is a comparison of porosity test values and calculated values as described in examples of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1-7, the present invention provides a rock porosity evaluation method based on mineral ion concentration, comprising the steps of:
collecting nuclear magnetic signals of soft rock minerals;
obtaining a first sample based on soft rock minerals, and collecting first characteristic peak intensity and first mineral components of the first sample;
carrying out dry-wet cycle test on the first sample, drying and grinding to obtain a second sample, and collecting a second characteristic peak intensity, a second mineral component and a cation mass concentration of an aqueous solution for the dry-wet cycle test of the second sample;
evaluating the internal pore change rule of the soft rock mineral under the action of dry and wet circulation based on the first characteristic peak intensity, the nuclear magnetic signal and the second characteristic peak intensity;
evaluating the internal chemical reaction rule of the soft rock mineral under the action of dry-wet circulation based on the first mineral component, the second mineral component and the cation mass concentration;
and evaluating the evolution law of the rock porosity of the soft rock mineral according to the internal pore change law and the internal chemical reaction law.
In the process of drying and grinding the soft rock mineral to obtain a first sample, the soft rock mineral is dried and ground, then is sieved by using a sieve hole with the aperture of 0.0074mm, about 3g of the sieved soft rock mineral is selected by a quartering method, and then is tableted to prepare the sample, so that the first sample is obtained.
And in the process of obtaining the second sample, analyzing the aqueous solution generated in the dry-wet cycle test by using an inductively coupled plasma mass spectrometer to obtain the mass concentration of the cations.
Before the process of collecting nuclear magnetic signals, soft rock minerals are made into a sample of 50mm multiplied by 100mm, then vacuumized and saturated for 12 hours, and then the nuclear magnetic signals are obtained through a nuclear magnetic resonance imaging analyzer.
In the process of evaluating the internal pore change rule, analyzing the characteristic peak change rule of the mineral composition of the soft rock mineral according to the first characteristic peak intensity and the second characteristic peak intensity;
according to the nuclear magnetic signal, utilizing a standard scale sample to carry out calibration to obtain the porosity of the soft rock mineral;
and evaluating the internal pore change rule according to the characteristic peak change rule and the porosity.
Preferably, in the process of evaluating the internal chemical reaction law, the first mineral composition and the first chemical composition content of the first sample are obtained according to the first mineral composition;
obtaining the second mineral component and the second chemical component content of a second sample according to the second mineral component;
and evaluating the internal chemical reaction rule according to the first mineral component, the second mineral component, the content of the first chemical component, the content of the second chemical component and the cation mass concentration.
Acquiring first ion mass variation, mass concentration variation, dry-wet cycle times, volume of a soaking solution and first molar mass of a second sample to obtain first ion mass variation rate of the second sample;
obtaining a second ion mass change rate of the first sample according to the first ion mass change rate and the stoichiometric number of the second sample, wherein the second ion mass change rate at least comprises a second ion mass change amount and a second molar mass of the first sample;
obtaining the volume of the first sample according to the component mass density of the first sample based on the second ion mass change rate;
and (4) evaluating the evolution law of the rock porosity of the soft rock mineral according to the volume and internal pore change law, and evaluating the mesoscopic damage of the soft rock.
A rock porosity evaluation system based on mineral ion concentration includes,
the device comprises a first characteristic acquisition module, a second characteristic acquisition module and a third characteristic acquisition module, wherein the first characteristic acquisition module is used for acquiring first characteristic peak intensity and first mineral composition of a first sample, and the first sample is used for representing a first product prepared according to soft rock minerals;
the second characteristic acquisition module is used for acquiring a nuclear magnetic signal of the soft rock mineral, a second characteristic peak intensity of a second sample and a second mineral component, wherein the second sample is used for expressing a second product obtained by the first sample after dry-wet circulation;
the first operation module is used for generating a characteristic peak change rule curve graph according to the first characteristic peak intensity and the second characteristic peak intensity;
the second operation module is used for obtaining the porosity of the second sample according to the nuclear magnetic signal;
a third operation module; the system is used for generating an internal chemical reaction rule table according to the first mineral composition and the second mineral composition;
the first evaluation module is used for generating a first evaluation result according to the characteristic peak change rule curve graph and the porosity, and the first evaluation result is used for expressing the internal pore change rule;
the second evaluation module is used for generating a second evaluation result according to the internal chemical reaction rule table, and the second evaluation result is used for expressing the internal chemical reaction rule;
and the third evaluation module is used for obtaining a third evaluation result according to the first evaluation result and the second evaluation result, wherein the third evaluation result is used for expressing the evolution rule of the rock porosity of the soft rock mineral.
The system also comprises a third characteristic acquisition module for acquiring the cation mass concentration of the aqueous solution after the first sample is subjected to the dry-wet cycle test;
the third operation module comprises a dry-wet cycle number counting unit, a soaking solution volume recording unit, a molar mass unit, a stoichiometric number unit, a mass density unit and a volume generating unit;
the dry-wet cycle number counting unit is used for recording the cycle number of the first sample after a dry-wet cycle experiment;
the soaking solution volume recording unit is used for recording the volume of the soaking solution in the process of the dry-wet cycle experiment;
a molar mass unit for providing the molar mass of the soft rock mineral;
a mass density unit for providing a mass density of the soft rock mineral;
a stoichiometry unit for providing a first sample to generate a stoichiometry of a second sample;
and the volume generating unit is used for obtaining the generation volume of the first sample and the second sample based on the cycle number according to the volume of the soaking solution, the cycle number, the molar mass, the mass density and the stoichiometric number.
And the third evaluation module is connected with the second evaluation unit and the first evaluation unit and used for generating a third evaluation result according to the cycle number, the generated volume and the internal pore change rule.
Example 1: as shown in fig. 3-7, the test samples and test protocols provided by the present invention are as follows:
1. test protocol
1.1X-ray diffraction test (XRD)
After dry-wet circulation is carried out on a sample, a grinder is used for grinding the dry sample, the dry sample is sieved by a sieve with the aperture of 0.0074mm, the sample after the test is finished is selected by a quartering method to be about 3g of powder sample for tabletting and sample preparation, and then a D8 advanced X-ray diffractometer is used for carrying out X-ray diffraction test on the sample.
1.2 inductively coupled plasma emission spectroscopy quantitative analysis
An iCAPRQICP-MS inductively coupled plasma mass spectrometer is adopted to test the cation concentration of the aqueous solution in dry-wet circulation, and the principle is to analyze the element to be tested through the spectrum of specific wavelength according to the characteristic spectral line emitted when the atom of the element to be tested in an excited state returns to the ground state.
1.3 low field NMR test
Preparing a carbonaceous mudstone rock block into a sample of 50mm multiplied by 100mm, vacuumizing and saturating the sample after the dry-wet cycle is completed for 12H, taking out the sample, wiping the surface moisture with a dry towel, wrapping the sample with a preservative film, tightly putting the sample into a sample cylinder, and conveying the sample into a MacroMR12-150H-I nuclear magnetic resonance imaging analyzer by using the sample cylinder for testing.
2. Analysis of test results
2.1 law of evolution of mineral composition
Recording XRD test results of carbon mudstone under the action of different dry and wet cycle times, wherein characteristic peaks of dry and wet cycle 0 are mainly distributed at 8.8 degrees, 12.36 degrees, 26.59 degrees and 28.07 degreesThe positions 29.41 degrees and 33.01 degrees, and the main mineral components of the carbonaceous mudstone are quartz, illite, kaolinite, calcite, feldspar, pyrite and mica by JADE software processing analysis. Comparing XRD results of the carbonaceous mudstone under the action of different dry and wet cycle times, the strength of the characteristic peak of the carbonaceous mudstone kaolinite is gradually increased along with the increase of the dry and wet cycle times, and the strength of the characteristic peak of the carbonaceous mudstone kaolinite is 697s at 0 time of the dry and wet cycle-1The peak intensity of the characteristic peak of the carbonaceous mudstone kaolinite is 1230s after 5, 10, 15, 20 and 25 times of dry and wet cycles-1、1830s-1、2059s-1、2135s-1And 2180s-176.47%, 162.55%, 195.41%, 206.31% and 212.77% respectively; the characteristic peak intensities of the feldspar and the calcite are gradually reduced along with the increase of the dry and wet cycle times, and the diffraction intensity of the carbonaceous mudstone feldspar in the dry and wet cycle time 0 is 2080s-1After 5, 10, 15, 20 and 25 times of dry-wet cycles, the characteristic peak intensity of the carbonaceous mudstone feldspar is 1200s respectively-1、836s-1、508s-1、182s-1And 166s-142.31%, 59.81%, 75.58%, 91.25% and 92.02% decrease, respectively; the characteristic peak intensity of the carbonaceous mudstone calcite in the dry-wet cycle for 0 time is 2353s-1The characteristic peak intensity of the calcite of the carbonaceous mudstone is 1701s after 5, 10, 15, 20 and 25 times of dry-wet cycles-1、810s-1、662s-1、452s-1And 164s-1A reduction of 27.71%, 65.58%, 71.87%, 80.79% and 93.03%, respectively.
The quantitative analysis of the mineral components of the carbonaceous mudstone with different dry and wet cycle times by using the JADE software is shown in Table 1. From table 1, it can be seen that: the content of the carbonaceous mudstone kaolinite is gradually increased along with the increase of the dry and wet cycle times; compared with the dry-wet cycle of 0 time, the content of the carbonaceous mudstone kaolinite in the dry-wet cycles of 5 times, 10 times, 15 times, 20 times and 25 times is respectively increased by 14.49%, 17.76%, 20.56%, 23.36% and 25.23%; the contents of feldspar and calcite decrease with the increase of the number of dry and wet cycles, the contents of feldspar and calcite in the dry and wet cycles of 5, 10, 15, 20 and 25 times are respectively reduced by 25.86%, 44.83%, 58.62%, 67.24% and 72.41% compared with the feldspar content in the dry and wet cycle of 0 time, and the contents of calcite in the dry and wet cycles of 5, 10, 15, 20 and 25 times are respectively reduced by 18.42%, 32.89%, 42.11%, 50.0% and 57.89% compared with the calcite content in the dry and wet cycle of 0 time. The illite, quartz, pyrite content increases to some extent, which may be the result of a decrease in the feldspar and calcite hydrolysis content, leading to an increase in the overall mineral proportion of illite, quartz, pyrite.
TABLE 1
2.2 ion Change law of aqueous solution
The cation concentration in the solution after various dry and wet cycles is shown in table 2. From table 2, it can be seen that: the mass concentration of the cations in the aqueous solution gradually increases along with the increase of the dry-wet cycle times, and the sequence of the mass concentration of the cations is Ca2+、K+、Na+、Fe2+And Al3+(ii) a Dry and wet cycles 5, 10, 15, 20 and 25 times Ca2+The average rate of mass concentration increase is 36.69, 35.79, 32.19, 27.23 and 25.27mg/L respectively, wherein 0-5 times of dry-wet circulation Ca2+The average rate of mass concentration increase is 1.42 times of 20-25 times of dry-wet cycle; k+The average rate of mass concentration increase is 2.31, 2.67, 2.61, 1.64 and 0.77mg/L, wherein the dry-wet cycle K is 0-5 times+The average rate of mass concentration increase is 3.00 times of 20-25 times of dry-wet cycle; na (Na)+The average rate of mass concentration increase is 1.54, 0.53, 0.57, 0.44 and 0.41mg/L respectively, wherein the Na is circulated for 0-5 times in a dry-wet way+The average rate of mass concentration increase is 3.75 times of the dry-wet cycle of 20-25 times; fe2+The average rate of mass concentration increase is 1.17, 0.71, 0.30, 0.27 and 0.29 respectively, wherein the dry-wet cycle is 0-5 times2+The average rate of mass concentration increase is 3.97 times of 20-25 times of dry-wet cycle; al (Al)3+The average rate of mass concentration increase is 0.12, 0.04, 0.03, 0.02 and 0.04 respectively, wherein the Al content is 0-5 times of dry-wet cycle3+The average rate of mass concentration increase is 2.64 times of 20-25 times of dry-wet cycle. Ca2+Rate of increase of element content K+、Na+、Fe2+And Al3+Mass concentration one order of magnitude higher, wherein Al3+The rate of increase in mass concentration is lowest, for example, 25 cycles of dry and wet, Ca2+The rate of increase in mass concentration is K+32.82 times of Na, Na+61.63 times of element, Fe2+87.14 times of element and Al3+631.75 times of the element. In combination with mineral analysis of the carbonaceous mudstone, the dissolution rate of calcite in the carbonaceous mudstone is the fastest, and the dissolution rates of potassium feldspar and albite, pyrite and mica are low.
TABLE 2
2.3 porosity analysis
2.3.1、T2Spectral analysis
Partial T of carbonaceous mudstone sample under action of dry-wet circulation2The spectral distribution is shown in FIG. 3. The carbonaceous mudstone sample obviously has 3 peaks, the first peak and the second peak correspond to small holes, the third peak corresponds to a middle hole, the first peak and the second peak of the carbonaceous mudstone occupy most of the area, and the internal pores of the carbonaceous mudstone sample are mainly small pores; with the increase of the dry-wet cycle times, the areas of the three peaks are increased, which shows that the number of small pores and medium pores is gradually increased under the action of the dry-wet cycle; after 10 times of dry-wet cycle, the second peak and the third peak are increased obviously, and T is2The spectrum peak shifts to the right, which shows that the small pores of the carbonaceous mudstone gradually evolve to the large pores along with the increase of the dry and wet cycle times, and this may be the mineral erosion of the carbonaceous mudstone under the action of the dry and wet cycle, the gradual development of the pores in the rock, the expansion and communication, and the increase of the number and size of the pores.
Carbonaceous mudstone T under the action of dry-wet circulation2The spectral area calculation results are shown in table 3. T is2The total area, the first peak area and the second peak area of the spectrum are increased along with the increase of the dry-wet cycle number, and the increasing rate is gradually reduced; as the dry-wet cycle number increases, the ratio of the first peak area decreases, and the ratio of the second peak area to the third peak area increases; dry compared with dry-wet cycle 0 timesThe total area for wet cycles 5, 10, 15, 20 and 25 increased 32.23%, 58.06%, 75.90%, 88.40% and 97.6%, respectively, and the first peak area increased 26.26%, 51.03%, 64.16%, 74.33% and 81.30%, respectively; the second peak areas increased 244.69%, 250.48%, 327.24%, 409.54% and 460.25%, respectively, and the third peak areas increased 70.30%, 254.14%, 587.59%, 651.12% and 777.00%, respectively. The porosity of the carbonaceous mudstone is increased with the increase of the dry and wet cycle times, but the increasing rate is gradually reduced; the number and size of the pores are gradually increased, but the pores are mainly small.
TABLE 3
2.3.2 porosity analysis
The signal intensity can be converted into the porosity by scaling the nuclear magnetic signal measured for the saturated sample with a standard scale sample, and the nuclear magnetic resonance sample calibration curve is shown in fig. 4. And substituting the measured signal quantity into a calibration curve to calculate the volume of water in the sample, wherein the volume ratio of the water to the sample is the porosity of the rock. The porosity of the carbonaceous mudstone under the effect of the dry-wet cycle is shown in figure 5. As can be seen from fig. 5: the porosity of the carbonaceous mudstone increases with the number of dry and wet cycles, but the rate of increase gradually decreases. This is because the surface of the pores is eroded by the erodible mass after the rock has undergone multiple wet and dry cycles, the chance of water contact with the erodible mass is reduced, the water action on the rock is reduced, and the rate of mineral erosion and crack propagation is reduced. The relationship between the porosity of the carbonaceous mudstone and the dry-wet cycle number is obtained by least square fitting:
φ＝A-Bexp(-C·n) (2.1)
wherein n is the dry-wet cycle number, phi is the porosity percent, and the A, B and C material parameters are respectively 16.03 percent, 9.20 percent and 0.038.
When n is 0, phi06.83% for a-B; when n → ∞, Φ ═ a ═ 16.03%. It shows that the porosity of the carbonaceous mudstone gradually increases with the increase of the dry-wet cycle, but does not always increase and finally stabilizes at 16.03％。
3. Chemical analysis of carbonaceous mudstone water-rock interaction
Through the test results of mineral composition (XRD), chemical composition content (XRF) and ion concentration of aqueous solution of the carbonaceous mudstone under the action of dry and wet circulation, the method is found that: the contents of calcite and feldspar in the carbonaceous mudstone are reduced, the content of montmorillonite is increased, and the contents of CaO and Na are increased under the action of dry-wet circulation2O and K2Reduced O content, Ca in aqueous solution2+、K+、Na+、Al3+And Fe2+The mass concentration of (a) increases. According to the chemical reaction principle, the following chemical reactions can be presumed to occur in the action process of the dry-wet cycle of the carbonaceous mudstone:
(1) calcite corrosion:
CaCO3+CO2+H2O＝Ca2++2HCO3 - (2.2)
the calcite reacts with carbon dioxide and water, the calcite is corroded, calcium ions are separated out, the content of the calcite is reduced, the content of a compound CaO is reduced, and Ca in an aqueous solution is contained2+The mass concentration increases.
(2) Hydrolysis of feldspar (potassium feldspar, albite):
KAlSi3O8+5.5H2O＝0.5Al2Si3O5(OH)4+K++OH-+2H4SiO4 (2.3)
NaAlSi3O8+5.5H2O＝0.5Al2Si3O5(OH)4+Na++OH-+2H4SiO4 (2.4)
after potassium feldspar and albite are hydrolyzed, kaolinite and Na are generated+And K+Precipitation, resulting in dry-wet cycle, reduced feldspar content, increased kaolinite content, and Na content in the compound2O and K2Reduced O content, Na in aqueous solution+And K+The mass concentration increases.
(3) And (3) hydrolyzing pyrite:
FeS2+3.5O2+H2O＝Fe2++2SO4 2-+2H+ (2.5)
the oxidation reaction of pyrite and oxygen in the dissolved water takes place, Fe2+The oxidation products are adsorbed on the surface of the pyrite to generate passivation, the oxidation reaction is inhibited to be carried out, the oxidation reaction strength of the pyrite is weakened, and the content of the pyrite and the compound Fe are reduced2O3And Fe2+The mass concentration of (a) does not vary significantly.
(4) Hydrolysis of mica (biotite):
KFe3AlSi3O10(OH)2+10H2O＝Al(OH)3+3Fe(OH)2+3H4SiO4+K++OH- (2.6)
hydrolysis of biotite to form colloidal Al (OH)3And Fe (OH)2Following loss of wet and dry cycle, K+Separating out ions to reduce the mica content in the carbonaceous mudstone, and reducing the content of the biotite in the carbonaceous mudstone so as to obtain K in the aqueous solution+、Al3+And Fe2+The mass concentration does not vary much.
4. Analysis of porosity evolution
After the solid mineral is chemically reacted, the solid volume difference between the reactant and the product causes the formation of pores, and if the product is a soluble substance, that is, the volume of the reactant which is reacted is the pores, the following are:
in the formula, V(A,i)And V(C,i)The solid volumes, V, of the i-th reactant A and product C, respectivelysIs the total volume of the solid minerals.
The rate of change of mass of product ions with dry-wet cycles was:
in the formula, dm(B,i)And d ρ(B,i)Respectively the mass change and the mass concentration change of the ith ion of the product B, dN is the number of times of increase of dry and wet cycles, VLIs the volume of the soaking solution.
The rate of change of the amount of the resultant substance was:
dn(B,i)the amount of change in the amount of substance of the i-th ion of the product B, M(B,i)The molar mass of the i-th ion of product B.
According to the principle of conservation of ions, the rate of change of the amount of species from which the reactants can be derived is:
γ(B,i)the stoichiometric number of the product B was determined.
The rate of change of mass of the reactants under the action of the dry-wet cycle is given by the formula (2.10):
in the formula, dm(B,i)And M(A,i)The mass change amount and the molar mass of the ith mineral of the reactant A are respectively.
The volume change of the reactants under the action of the dry-wet cycle is as follows:
ρ(A,i)mass density of the i-th mineral of reactant a.
Similarly, the volume of the solid product can be obtained:
in the formula, gamma(C,i)And ρ(C,i)The stoichiometric number and the mass density of the ith mineral of the product C are respectively shown.
From formulae (2.12), (2.13) and (2.7):
the molar masses and densities of the individual minerals are shown in Table 4.
TABLE 4
The volume of the soaking solution in the dry-wet cycle of the carbonaceous mudstone is 2500ml, and the reaction and generation volumes of the minerals are calculated by substituting formulas (2.12) and (2.13) and are shown in Table 5.
TABLE 5
The average volume of the carbonaceous mudstone sample is 185.25cm3And the mineral reaction volume calculated in table 5 is substituted into formula (2.14), and the change rule of the porosity increment of the carbonaceous mudstone under the action of dry-wet circulation is calculated and shown in fig. 6. From fig. 6, it can be seen that: under the action of dry-wet circulation, the carbonaceous mudstone minerals are corroded and hydrolyzed to form pores, the porosity is gradually increased along with the increase of the dry-wet circulation times, but the soluble minerals on the surfaces of the pores are gradually corroded along with the increase of the dry-wet circulation times, the probability of contact between water and the soluble minerals is reduced, the mineral corrosion and hydrolysis rates are reduced, and the porosity increase rate is reduced.
The porosity of 0, 5, 10, 15, 20 and 25 dry-wet cycles measured by low-field nmr test is compared with the calculation of formula (2.14) in fig. 7. As can be seen in fig. 7: the result calculated by the formula (2.14) can reflect the change rule of the porosity along with the increase of the dry and wet cycle number, but the test value is slightly larger than the calculated value. It is possible that part of the mineral components and the reaction between the mineral components and water are not clear, and the chemical reaction process does not consider the pores generated by the erosion of the mineral components; in addition, mineral erosion causes closed pores originally closed by the rock to be gradually opened to form open pores, and the closed pores cannot be measured by using ion calculation of mineral erosion, so that the calculation result is smaller. The porosity of the rock is calculated by utilizing the mass concentration of ions corroded by minerals, the porosity of the carbonaceous mudstone under the action of dry-wet circulation is calculated quantitatively, and a new idea is provided for researching the microscopic damage of the soft rock.
It should be noted that: like reference numbers and letters refer to like items in the following figures, and thus once an item is defined in one figure, it need not be further defined and explained in subsequent figures, and moreover, the terms "first", "second", "third", etc. are used merely to distinguish one description from another and are not to be construed as indicating or implying relative importance.
Finally, it should be noted that: the above-mentioned embodiments are only specific embodiments of the present invention, which are used for illustrating the technical solutions of the present invention and not for limiting the same, and the protection scope of the present invention is not limited thereto, although the present invention is described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art can modify or easily conceive the technical solutions described in the foregoing embodiments or equivalent substitutes for some technical features within the technical scope of the present disclosure; such modifications, changes or substitutions do not depart from the spirit and scope of the present invention in its spirit and scope. Are intended to be covered by the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
