CN115389387A - Experimental method for evaluating rock core damage - Google Patents
Experimental method for evaluating rock core damage Download PDFInfo
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- CN115389387A CN115389387A CN202110562320.6A CN202110562320A CN115389387A CN 115389387 A CN115389387 A CN 115389387A CN 202110562320 A CN202110562320 A CN 202110562320A CN 115389387 A CN115389387 A CN 115389387A
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- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume, or surface-area of porous materials
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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 provides an experimental method for evaluating core damage, and belongs to the technical field of development and research of oil and gas reservoirs. Based on the nuclear magnetic resonance technology, carrying out oil phase calibration, core physical property parameter testing, seepage experiments and test comparison after the experiments; the influence and damage degree of seepage damage fluid on the physical property of the rock core are evaluated by comparing the permeability and porosity of the dried rock core before and after the experiment, and the nuclear magnetic resonance T is used 2 And (4) intuitively evaluating the damage condition of the damage fluid to the pore structure of the rock core. The experimental method selects the gas logging permeability of the dried core as a data base of permeability damage, and is simpler in comparison with the traditional liquid logging permeability method, the core state is more stable in testing, and the result comparison is more visual.
Description
Technical Field
The invention belongs to the technical field of development and research of oil and gas reservoirs, and particularly relates to an experimental method for evaluating core damage.
Background
At present, exploration and development of unconventional oil and gas reservoirs become a key working direction in the oil and gas industry, and due to the particularity of physical properties of unconventional reservoirs, the unconventional oil and gas reservoirs are more easily damaged by fluid in the actual development process, so that difficulty is brought to effective development of oil and gas resources.
The core damage is a part of reservoir sensitivity evaluation, in the experimental process of evaluating the core damage of the reservoir, experiments are mostly carried out according to the industry standard SY/T5358-2010 reservoir sensitivity flow experiment evaluation method, the standard is better applied in the conventional high-permeability reservoir core testing process, but the core damage evaluation method has larger limitations in the low-pore and low-permeability unconventional reservoir core experiments, such as too high displacement pressure, very low flow, large measurement difficulty and the like, and how to more effectively carry out the core damage evaluation is also a problem which is always solved by laboratory workers for many years.
Chinese patent publication CN105527379B discloses a new core permeability test device, which can obtain the permeability before and after core contamination by monitoring the downstream pressure change of an instrument for damage degree evaluation; chinese patent publication CN111595756A discloses a core damage comprehensive evaluation device, which comprises a plurality of solution tanks, a core holder, a displacement unit and the like, and can switch test fluids in the displacement process and complete the damage test of different fluids to the core permeability on the same device; chinese patent publication CN106093299B discloses an experimental method for evaluating damage of drilling fluid in a tight gas reservoir, a nuclear magnetic resonance monitoring technology is introduced, and the invasion degree of the drilling fluid to a rock core is observed more visually through nuclear magnetic imaging on the basis of permeability comparison.
The main index for evaluating the damage of the rock core at present can be found to be the change degree of the liquid permeability before and after the experiment, the rock core before the experiment is often saturated with the test fluid, the test fluid is used for displacement to a stable state after different damage fluids are injected in the experiment process, the components of the fluid in the rock core are changed, and the effect among different fluids can possibly influence the permeability test result. Meanwhile, the change of the porosity of the rock core before and after the experiment is not considered, two indexes of the porosity and the permeability of the rock core of the reservoir are key parameters which can explain the characteristics of the reservoir, and the influence of the fluid on the physical properties of the reservoir can be better explained by increasing the damage evaluation of the porosity in the experimental process.
In the process of conducting reservoir core seepage experiments in a laboratory, different fluid types can cause damage influences to cores in different degrees, the currently common core damage evaluation method is better applied to conventional high-permeability cores, but more limitations are imposed on application to low-permeability unconventional reservoirs, and due to the fact that experiment operation is complex, measurement errors are large, and evaluation results are in certain dispute.
Disclosure of Invention
The invention aims to solve the problems in the prior art, provides an experimental method for evaluating core damage, optimizes the measurement methods of the permeability of the core before and after the experiment, facilitates the damage of the specific permeability, increases the evaluation of the porosity damage for analysis, can more comprehensively evaluate the damage degree of fluid to the core in the experiment process, and is beneficial to the further research of the sensitivity of the core of the reservoir.
The invention is realized by the following technical scheme:
an experimental method for evaluating core damage is based on a nuclear magnetic resonance technology, and is used for carrying out oil phase calibration, core physical property parameter testing, seepage experiments and test comparison after the experiments; the influence and damage degree of seepage damage fluid on the physical property of the rock core are evaluated by comparing the permeability and porosity of the dried rock core before and after the experiment by means of nuclear magnetic resonance T 2 And (4) intuitively evaluating the damage condition of the damage fluid to the pore structure of the rock core.
A further development of the invention consists in that the method comprises in particular the following steps:
step 2, nuclear magnetic signal scanning of a core dry sample;
step 3, saturating the kerosene in the rock core;
step 4, calibrating the nuclear magnetic signal quantity of the kerosene;
step 5, calculating the porosity of the rock core before the experiment;
step 6, carrying out a core seepage related experiment by using a saturated core;
step 7, secondary drying of the rock core after the experiment;
step 8, testing the permeability of the secondary dried rock core;
step 9, performing nuclear magnetic signal scanning on the secondary drying rock core;
step 11, scanning nuclear magnetic signals of the secondary saturated kerosene core;
step 12, calculating the porosity of the rock core after the experiment;
and step 13, evaluating core damage.
The invention has the further improvement that the permeability test of the core dry sample in the step 1 specifically comprises the following steps:
preparing the reservoir rock core by referring to a petroleum industry standard SY/T5336 conventional rock core analysis method to obtain a dry rock core sample after oil washing and drying, performing a gas logging permeability experiment on the dry rock core sample to obtain a gas logging permeability value K of the dry rock core sample 1 The unit is mD.
The invention has the further improvement that step 2 of nuclear magnetic signal scanning of the core dry sample specifically comprises the following steps:
step 2.1, weighing the dry core sample after gas permeability measurement, and recording the weight as m 1 In units of g;
step 2.2, placing the dry rock core sample in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the dry rock core sample 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of the dry core sample is S 1 In units of a.u.
The further improvement of the invention is that the core saturated kerosene in the step 3 is specifically as follows:
and placing the dry core sample in a core saturation device, and carrying out vacuumizing, saturation and kerosene pressurizing operation, wherein the vacuumizing time is more than 6 hours, the kerosene pressurizing and saturation time is more than 72 hours, and the pressurizing and saturation pressure is not less than 10MPa.
The invention has the further improvement that the step 4 of calibrating the nuclear magnetic signal quantity of the kerosene specifically comprises the following steps:
step 4.1, taking out the saturated kerosene core from the core saturation device, wiping the residual kerosene on the surface, weighing the saturated kerosene core, and recording the weight as m 2 In units of g;
step 4.2, placing the saturated kerosene core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of saturated kerosene rock core is recorded as S 2 In a.u.;
step 4.3, establishing a corresponding relation between the nuclear magnetic signal quantity and the kerosene volume by combining a weight loss method, and calibrating the nuclear magnetic signal quantity of the kerosene by using the formula (1):
in the formula:
a is the nuclear magnetic signal quantity corresponding to the unit volume of kerosene, and the unit is a.u./mL;
rho-kerosene density, unit is g/mL;
the formula (1) is a calculation formula for performing kerosene calibration by using a single core sample, if a plurality of core samples are calibrated at the same time, the kerosene calibration average value of a group of core samples is calculated by using the following formula (2), and the result is more accurate:
in the formula:
A i -calibration of kerosene nuclear magnetic signal quantities for different core samples in units of a.u./mL;
n is the number of core samples for carrying out a kerosene calibration experiment;
the more the number of the cores calibrated by the kerosene nuclear magnetic signal quantity is, the more accurate the measured kerosene calibration result is, and the calculation of subsequent experiments is facilitated.
The further improvement of the invention is that the calculation of the core porosity before the experiment in the step 5 specifically comprises the following steps:
according to the obtained nuclear magnetic signal quantity of the core dry sample and the saturated kerosene core, the porosity phi before the core experiment based on the nuclear magnetic resonance technology can be obtained by using the following formula (3) 1 ：
In the formula:
φ 1 core magnetic porosity measurement in units of core before experiment;
v is the volume of the core, the unit is mL, and the volume is calculated by the length and the diameter measured by the dry sample of the core.
The further improvement of the invention is that step 6, the saturated core is used for carrying out core seepage related experiments, and the method specifically comprises the following steps:
step 6.1, preparing the injury experiment fluid by using deuterium oxide;
step 6.2, carrying out seepage related experiments on the saturated kerosene core, and monitoring nuclear magnetic T of the core in the experiments 2 And (5) spectrum judging the oil-water distribution condition inside the rock core.
The invention has the further improvement that the secondary drying of the rock core after the experiment in the step 7 specifically comprises the following steps:
and taking out the rock core subjected to the seepage experiment from the experimental device, and placing the rock core in a constant-temperature drying box with a vacuumizing device for drying for not less than 120 hours to ensure that liquid-phase components in the rock core are completely dried.
The further improvement of the invention is that the step 8 of secondary drying core permeability test specifically comprises the following steps:
performing a gas logging permeability experiment on the secondary dried rock core to obtain a gas logging permeability value K of the secondary dried rock core 2 In mD.
The invention has the further improvement that in the step 9, nuclear magnetic signal scanning of the dried rock core is carried out for the second time, which specifically comprises the following steps:
placing the secondary dried rock core with measured gas permeability in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary dried rock core 2 Spectrum and nuclear magnetic signal quantity, recording the nuclear magnetic signal quantity of the secondary drying rock core as S 3 In units of a.u.
The further improvement of the invention is that the rock core secondary saturated kerosene after the experiment of step 10 specifically comprises the following steps:
and placing the secondary dried rock core into a rock core saturation device, vacuumizing, and then carrying out secondary saturated kerosene operation, wherein the vacuumizing time is more than 6 hours, the pressurized saturated kerosene time is more than 72 hours, and the pressurized saturated pressure is not less than 10MPa.
The invention has the further improvement that in the step 11, the nuclear magnetic signal scanning of the secondary saturated kerosene core specifically comprises the following steps:
placing the secondary saturated kerosene core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, and recording the nuclear magnetic signal quantity of the secondary saturated kerosene rock core as S 4 In units of a.u.
The further improvement of the invention is that the calculation of the porosity of the rock core after the experiment in the step 12 specifically comprises the following steps:
obtaining the porosity phi after the core experiment based on the nuclear magnetic resonance technology by using the following formula (4) according to the nuclear magnetic signal quantity of the obtained secondary dried core and the secondary saturated kerosene core 2 ：
In the formula:
φ 2 nuclear magnetic porosity of cores after percolation experiments in%.
The invention has the further improvement that step 13 of evaluating core damage specifically comprises the following steps:
step 13.1, calculating a permeability reduction rate lambda through the following formula (5) by comparing the gas logging permeability of the dried rock core before and after the seepage experiment, and evaluating the damage degree of the fluid to the permeability of the rock core:
in the formula:
lambda is the core permeability reduction rate before and after the experiment, and the unit is percent;
K 2 greater than K 1 Lambda should be redefined as the permeability improvement;
step 13.2, calculating the porosity reduction rate eta of the rock core through the following formula (6) by comparing the porosity of the saturated kerosene rock core before and after the seepage experiment so as to evaluate the damage degree of the fluid to the rock core pore structure:
in the formula:
eta, the permeability reduction rate of the rock core before and after the experiment, and the unit is percent;
φ 2 when eta is larger than the predetermined value, the porosity increase rate is redefined;
step 13.3, saturating the core with kerosene state T 2 Spectrum deduction of core drying state T 2 Spectrum, dry core sample T 2 The spectrum is taken as a base signal, and the T of the signal completely coming from kerosene in the effective pore space of the rock core is obtained 2 Spectrum defined as core pore kerosene T 2 Spectrum, at this moment, the effective pore space in the rock core is filled with kerosene, so that the kerosene T in the pores of the rock core 2 The spectrum intuitively shows the effective pore distribution condition of the rock core;
step 13.4, saturating the core with kerosene T before and after the seepage experiment 2 Drying rock core T with corresponding states deducted from spectrum 2 Spectral bases, i.e. saturated kerosene cores T 2 Deduction core dry sample T 2 Second saturated kerosene core T 2 Deducting secondary drying rock core T 2 ObtainingCore pore kerosene T before and after core seepage experiment 2 And (4) comparing the two curves to visually evaluate the damage condition of the damage fluid to the pore structure of the rock core.
Compared with the prior art, the invention has the beneficial effects that:
according to the experimental method for evaluating the damage of the rock core, the gas logging permeability of the dried rock core is selected as a data base of the permeability damage, and compared with the traditional liquid logging permeability method, the experimental method is simpler, the state of the rock core is more stable during testing, and the comparison of results is more visual; porosity change parameters are added in the experiment to evaluate the porosity damage rate, the influence of seepage liquid on the pore space of the rock core is explained from another angle, the distribution characteristics of oil-containing pores in the rock core are analyzed by utilizing the characteristics of a low-field nuclear magnetic resonance technology, and the pore kerosene T of the nuclear magnetic rock core before and after the experiment is compared 2 The spectrum curve can be further analyzed to show the damage degree of the pore structure of the rock core, and is more convincing. The experimental method can have a good application effect in the aspect of reservoir core injury research.
Drawings
FIG. 1 is a flow chart of an experimental method of evaluating core damage according to the present invention;
FIG. 2 is a sample of core 6 before and after displacement experiment for pore kerosene T 2 A spectral curve;
FIG. 3 shows pore kerosene T before and after imbibition test of core sample 7 2 Spectral curves.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the core sample for the experiment is prepared according to SY/T5336 conventional core analysis method, the specification is a core plunger with the diameter of 2.5 +/-0.05 cm and the length of 4-7cm, the model of the nuclear magnetic resonance analyzer is MacroMR12-150H-G, the CPMG sequence (the scanning frequency NS =64, the echo time TE =0.1ms, the echo number NECH =6000 and the waiting time TW =5000 ms) is selected as the test sequence, the core sample is subjected to off-line test, and the gas logging permeability tester is a core overburden pressure hole permeability tester and the model CMS300.
One evaluation of the inventionThe experimental method of the core damage is divided into 13 experimental steps, and based on the nuclear magnetic resonance technology, contents such as oil phase calibration, core physical property parameter test, seepage experiment, test comparison after experiment and the like are developed; the influence and damage degree of seepage damage fluid on the physical property of the rock core can be evaluated by comparing the permeability and porosity of the dried rock core before and after the experiment, and the nuclear magnetic resonance T is used 2 The spectrum can visually evaluate the damage condition of the damage fluid to the pore structure of the rock core.
The experimental method for evaluating core damage disclosed by the invention comprises the following steps of:
Preparing the reservoir rock core by referring to a petroleum industry standard SY/T5336 conventional rock core analysis method to obtain a dry rock core sample after oil washing and drying, performing a gas logging permeability experiment on the dry rock core sample to obtain a gas logging permeability value K of the dry rock core sample 1 In mD.
Step 2, nuclear magnetic signal scanning of core dry sample
Step 2.1, weighing the dry core sample after gas permeability measurement, and recording the weight as m 1 In units of g;
step 2.2, placing the dry rock core sample in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the dry rock core sample 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of the core dry sample is S 1 In units of a.u.
Step 3, saturating kerosene in rock core
And placing the dry core sample in a core saturation device, and carrying out vacuumizing, saturation and kerosene pressurizing operation, wherein the vacuumizing time is more than 6 hours, the kerosene pressurizing and saturation time is more than 72 hours, and the pressurizing and saturation pressure is not less than 10MPa.
Step 4, calibrating the nuclear magnetic signal quantity of the kerosene
Step 4.1, taking out the saturated kerosene core from the core saturation device, wiping the residual kerosene on the surface, weighing the saturated kerosene core, and recording the weight as m 2 In units of g;
step 4.2, placing the saturated kerosene core in nuclear magnetic resonancePerforming off-line nuclear magnetic signal test in the analyzer to obtain nuclear magnetic T of saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of saturated kerosene rock core is recorded as S 2 In a.u.;
step 4.3, establishing a corresponding relation between the nuclear magnetic signal quantity and the kerosene volume by combining a weight loss method, and calibrating the nuclear magnetic signal quantity of the kerosene by using the formula (1):
in the formula:
a is the nuclear magnetic signal quantity corresponding to the unit volume of kerosene, and the unit is a.u./mL;
rho-kerosene density in g/mL;
the formula (1) is a calculation formula for performing kerosene calibration by using a single core sample, if a plurality of core samples are calibrated simultaneously, the kerosene calibration average value of a group of core samples can be calculated by using the following formula (2), and the result is more accurate:
in the formula:
A i -calibration of kerosene nuclear magnetic signal quantities for different core samples in units of a.u./mL;
n-the number of core samples subjected to a kerosene calibration experiment.
The more the number of the cores calibrated by the kerosene nuclear magnetic signal quantity is, the more accurate the measured kerosene calibration result is, and the calculation of subsequent experiments is facilitated.
Step 5, calculating the porosity of the rock core before the experiment
Based on the core dried sample obtained andthe nuclear magnetic signal quantity of the saturated kerosene core can obtain the porosity phi before the core experiment based on the nuclear magnetic resonance technology by using the following formula (3) 1 ：
In the formula:
φ 1 core magnetic porosity in units of% before the experiment;
v is the volume of the core, the unit is mL, and the volume is calculated according to the measured length and diameter of the dry core sample.
Step 6, carrying out core seepage related experiment by using saturated core
6.1, the damage experiment fluid is prepared by deuterium (heavy water) which is selected because no signal is generated in the nuclear magnetic resonance detector, and the nuclear magnetic signals of the experiment fluid are all from kerosene in the rock core, so that the nuclear magnetic T of the rock core in the experiment can be monitored 2 Spectrum judgment is carried out on the oil-water distribution condition inside the rock core;
and 6.2, placing the saturated kerosene core in a displacement device or other experimental devices to perform seepage related experiments, wherein the experiments can be in displacement, seepage and absorption and other indoor experimental modes related to two-phase seepage.
Other experimental devices may be used as long as they can perform a percolation experiment.
Step 7, secondary drying of the rock core after the experiment
And taking out the rock core subjected to the seepage experiment from the experimental device, and drying the rock core in a constant-temperature drying box with a vacuumizing device for not less than 120 hours to ensure that liquid-phase components in the rock core are completely dried.
Step 8, testing permeability of the secondary drying rock core
Performing a gas logging permeability experiment on the secondary dried rock core to obtain a gas logging permeability value K of the secondary dried rock core 2 In mD.
Step 9, secondary drying core nuclear magnetic signal scanning
Secondary baking for testing gas and permeabilityPlacing the dry rock core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary dried rock core 2 Spectrum and nuclear magnetic signal quantity, recording the nuclear magnetic signal quantity of the secondary drying rock core as S 3 In units of a.u.
And placing the secondary dried rock core into a rock core saturation device, vacuumizing, and then carrying out secondary saturated kerosene operation, wherein the vacuumizing time is more than 6 hours, the pressurized saturated kerosene time is more than 72 hours, and the pressurized saturated pressure is not less than 10MPa.
Step 11, nuclear magnetic signal scanning of secondary saturated kerosene core
Placing the secondary saturated kerosene core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, and recording the nuclear magnetic signal quantity of the secondary saturated kerosene rock core as S 4 In units of a.u.
Step 12, calculating the porosity of the rock core after the experiment
According to the obtained nuclear magnetic signal quantity of the secondary dried rock core and the secondary saturated kerosene rock core, the porosity phi after the rock core experiment based on the nuclear magnetic resonance technology can be obtained by using the following formula (4) 2 ：
In the formula:
φ 2 nuclear magnetic porosity of cores after percolation experiments in%.
Step 13, evaluating core damage
Step 13.1, by comparing the gas logging permeability of the dried core before and after the seepage experiment, the permeability reduction rate lambda can be calculated through the following formula (5), and the damage degree of the fluid to the permeability of the core is evaluated:
in the formula:
lambda is the core permeability reduction rate before and after the experiment, and the unit is percent;
under normal conditions, the permeability, K, of the core is reduced by the seepage of multi-phase fluid 2 Values often less than K 1 However, it is not excluded that in some cases the permeability measured in the core after the percolation test is increased, i.e. K 2 Greater than K 1 At this point, λ should be redefined as the permeability increase.
Step 13.2, by comparing the porosity of the saturated kerosene core before and after the seepage experiment, calculating the porosity reduction rate eta of the core through the following formula (6), and evaluating the damage degree of the fluid to the pore structure of the core according to the method:
in the formula:
eta, the permeability reduction rate of the rock core before and after the experiment, and the unit is percent;
under normal conditions, the multi-phase fluid seepage can reduce the porosity of the core, phi 2 The value tends to be less than phi 1 However, the mutual communication of the core pores under the action of fluid even the generation of cracks under some conditions is not excluded, so that the measured porosity of the core after the experiment is improved, namely phi 2 Greater than phi 1 At this time, η should be redefined as porosity promotion;
and step 13.3, the nuclear magnetic resonance analyzer can visually represent the distribution of the hydrogen-containing fluid in different pore spaces of the rock core by analyzing the signal of hydrogen protons in the rock core sample, the hydrogen-containing fluid in the experiment is kerosene, and the hydrogen-containing fluid can be replaced by other hydrogen-containing light oil according to the specific experiment requirements, so that residual substances are left as little as possible in the drying process. Saturating the core with kerosene state T 2 Spectrum deduction of core drying state T 2 Spectrum (drying rock core T) 2 Spectrum as base signal) can obtain the T of the signal completely from kerosene in the effective pore space of the core 2 Spectrum defined as core pore kerosene T 2 Spectrum, at the moment, the effective pore space in the rock core is filled with kerosene,thus core pore kerosene T 2 The spectrum can intuitively show the effective pore distribution condition of the rock core;
step 13.4, saturating the core with kerosene T before and after the seepage experiment 2 Drying rock core T with corresponding states deducted from spectrum 2 Spectrum base (saturated kerosene core T) 2 Deduction core dry sample T 2 Second saturated kerosene core T 2 Deducting secondary drying rock core T 2 ) Obtaining core pore kerosene T before and after core seepage experiment 2 And the spectral curve is compared with the two curves, so that the damage condition of the damage fluid to the pore structure of the rock core can be visually evaluated.
The above are specific implementation steps of the experimental method of the present invention, and further detailed descriptions will be given in the examples with reference to specific cases.
[ example 1 ] kerosene Nuclear magnetic Signal calibration
No. 3 aviation kerosene is selected as experimental kerosene, the density is 0.83g/mL, 5 reservoir rock cores are used for carrying out kerosene calibration experiments according to experiment steps 2-4, the test results are calculated by a formula (1) to obtain the kerosene calibration value of the experiment, and the specific parameters are shown in Table 1.
TABLE 1 core kerosene calibration results
According to the test results in the table, the core kerosene calibration average value of the experiment can be obtained through the formula (2)
The test sample is 15810.9a.u./mL and is used as a data base of subsequent experiments.
[ example 2 ] evaluation of damage in core displacement experiment
The core sample 6 is a core plunger sample with the diameter of 2.46cm and the length of 4.07cm, and the experimental test is carried out according to the experimental steps of the content of the invention.
The relevant data of the rock core before the seepage experiment can be obtained through the steps 1 to 5, and the nuclear magnetism of kerosene with unit volume in the embodimentSignal magnitude Using test results of example 1
Dry nuclear magnetic scan signal S of core sample 6 1 7847a.u., gas permeability K 1 A value of 0.11mD; nuclear magnetic scanning signal quantity S of rock core after saturated kerosene 2 30934a.u., the core porosity phi before the percolation experiment can be obtained by the formula (3) 1 It was 7.55%.
The seepage experiment in the step 6 is a two-phase displacement experiment, the used instrument is an ACFS700 multifunctional displacement experiment system, the displacement liquid adopts a deuterium aqueous solution containing 3 mass percent of nano oil displacement agent, the displacement pressure is 10MPa, the confining pressure is 13MPa, and the displacement time is 7 days.
Taking out the core after the displacement experiment is finished, obtaining the relevant data of the core after the seepage experiment through the steps 7-12, and drying the gas logging permeability K of the core sample for the second time 2 A value of 0.14mD, nuclear magnetic scanning semaphore S 3 8364a.u. nuclear magnetic scanning signal S of a secondary saturated kerosene core sample 4 26031a.u., and calculating the core porosity phi after the seepage experiment by a formula (4) 2 It was 5.78%.
According to the obtained experimental data, the rock core damage evaluation before and after the displacement experiment can be completed through the step 13, and the permeability reduction rate is calculated through the formula (5), because K in the embodiment 2 Greater than K 1 Obtaining that the core permeability improvement rate lambda value of the experiment is 27.3%; calculating by a formula (6) to obtain a value of the rock core porosity eta of 23.4%; core pore kerosene T before and after the contrast displacement experiment 2 The spectral curve (as shown in fig. 2) can further illustrate the damage degree of the displacement experiment to the core.
Using nuclear magnetic T 2 The characteristic of the spectrum, the abscissa relaxation time and the core pore size are in positive correlation, namely the larger the relaxation time is, the larger the represented pore size is, the ordinate signal amplitude represents the signal quantity contained in the kerosene in the pore spaces with different sizes, and the higher the signal amplitude is, the more the oil quantity contained in the pore space is. Core pore kerosene T before and after comparative experiment 2 Spectral curveAnd the pore change of the rock core before and after the displacement experiment can be reflected.
The comparison shows that after the core sample 6 is damaged by the displacement experiment, the signal quantity of a small pore space (1 ms-10 ms) is obviously reduced, which indicates that the displacement experiment causes great damage to small pores of the core, the pores are blocked, kerosene cannot enter during secondary saturation, and the kerosene is a main reason for reducing the porosity of the core after the displacement experiment; and the small increase of the signal quantity of the larger pore space (100 ms-1000 ms) indicates that the pore space with the size is increased, more kerosene enters the pore space during the secondary oil saturation, namely, a small crack is caused in the core in the displacement experiment, or part of pores are communicated, and the change of the part may be the reason for improving the gas logging permeability of the core after the displacement experiment.
[ example 3 ] evaluation of damage in rock core imbibition test
The core sample 7 is a core plunger sample with the diameter of 2.48cm and the length of 4.19cm, and the experimental test is carried out according to the experimental steps of the content of the invention.
The core related data before the seepage experiment can be obtained through the steps 1 to 5, and the nuclear magnetic signal value of the kerosene with unit volume in the embodiment uses the test result of the embodiment 1
Dry nuclear magnetic scan signal S of core sample 7 1 5858a.u., gas permeability K 1 A value of 0.017mD; nuclear magnetic scanning signal quantity S of rock core after saturated kerosene 2 14306a.u., the core porosity Φ 1 before the percolation experiment was 2.64% as obtained by equation (3).
The seepage experiment in the step 6 is a spontaneous imbibition experiment at normal temperature and pressure, and the core sample 7 after being saturated with kerosene is placed in a deuterium aqueous solution containing 2% of potassium chloride by mass fraction, and the imbibition experiment time is 20 days.
Taking out the rock core after the spontaneous imbibition experiment is finished, obtaining the related data of the rock core after the imbibition experiment through the steps 7-12, and drying the gas logging permeability K of the rock sample for the second time 2 A value of 0.002mD and a nuclear magnetic scanning signal quantity S 3 6266a.u., nuclear magnetic scan of a secondary saturated kerosene coreNumber S 4 12587a.u., and calculating the core porosity phi after the imbibition experiment by the formula (4) 2 It was 1.98%.
According to the obtained experimental data, core damage evaluation before and after the imbibition experiment can be completed through the step 13, and the permeability reduction rate is calculated through the formula (5), so that the core permeability reduction rate lambda value of the experiment is 88.2%; calculating by a formula (6) to obtain a value of the rock core porosity reduction rate eta of 25.4%; core pore kerosene T before and after the contrast imbibition experiment 2 The spectral curve (shown in fig. 3) can further illustrate the damage degree of the imbibition experiment to the core.
Using nuclear magnetic T 2 The characteristic of the spectrum, the abscissa relaxation time and the core pore size are in positive correlation, namely the larger the relaxation time is, the larger the represented pore size is, the ordinate signal amplitude represents the signal quantity contained in the kerosene in the pore spaces with different sizes, and the higher the signal amplitude is, the more the oil quantity contained in the pore space is. Core pore kerosene T before and after comparative experiment 2 And the spectral curve can reflect the pore change of the rock core before and after the displacement experiment.
The data show that the core sample 7 has low permeability parameters and poor physical properties. The pore space of the core is single and is concentrated in the interval of 1ms-10 ms. By comparison of T 2 The spectrum finds that after the spontaneous imbibition experiment, the signal quantity of the pore space is obviously reduced, which shows that the imbibition experiment causes great damage to the pore of the rock core, the secondary saturated coal oil quantity is reduced, the pore space is blocked, and the reason that the porosity and the permeability of the rock core are greatly reduced after the imbibition experiment is intuitively explained.
Finally, it should be noted that the above-mentioned technical solution is only one embodiment of the present invention, and it will be apparent to those skilled in the art that various modifications and variations can be easily made based on the application method and principle of the present invention disclosed, and the method is not limited to the above-mentioned specific embodiment of the present invention, so that the above-mentioned embodiment is only preferred, and not restrictive.
Claims (15)
1. Evaluation rock core damageThe experimental method is characterized in that based on the nuclear magnetic resonance technology, oil phase calibration, core physical property parameter testing, seepage experiments and test comparison after the experiments are carried out; the influence and damage degree of seepage damage fluid on the physical property of the rock core are evaluated by comparing the permeability and porosity of the dried rock core before and after the experiment, and the nuclear magnetic resonance T is used 2 And (4) intuitively evaluating the damage condition of the damage fluid to the pore structure of the rock core.
2. The experimental method for evaluating core damage according to claim 1, characterized in that the method specifically comprises the following steps:
step 1, testing permeability of a dry core sample;
step 2, nuclear magnetic signal scanning of a core dry sample;
step 3, saturating the kerosene in the rock core;
step 4, calibrating kerosene nuclear magnetic signal quantity;
step 5, calculating the porosity of the rock core before the experiment;
step 6, carrying out core seepage related experiments on the saturated core;
step 7, drying the rock core for the second time after the experiment;
step 8, testing the permeability of the secondary drying rock core;
step 9, performing nuclear magnetic signal scanning on the secondary drying rock core;
step 10, performing secondary saturated kerosene on the rock core after the experiment;
step 11, scanning nuclear magnetic signals of a secondary saturated kerosene core;
step 12, calculating the porosity of the rock core after the experiment;
and step 13, evaluating core damage.
3. The experimental method for evaluating core damage according to claim 2, wherein the step 1 core dry sample permeability test specifically comprises:
preparing the reservoir rock core by referring to petroleum industry standard SY/T5336 conventional rock core analysis method to obtain a dry rock core sample after oil washing and drying, performing a gas logging permeability experiment on the dry rock core sample to obtain a gas logging of the dry rock core samplePermeability value of K 1 In mD.
4. The experimental method for evaluating core damage according to claim 3, wherein the step 2 of core dry sample nuclear magnetic signal scanning specifically comprises:
step 2.1, weighing the dry core sample after gas permeability measurement, and recording the weight as m 1 In units of g;
step 2.2, placing the dry rock core sample in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the dry rock core sample 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of the core dry sample is S 1 In units of a.u.
5. The experimental method for evaluating core damage according to claim 4, wherein the step 3 core saturated kerosene specifically comprises:
and placing the dry core sample in a core saturation device, and carrying out vacuumizing, saturation and kerosene pressurizing operation, wherein the vacuumizing time is more than 6 hours, the kerosene pressurizing and saturation time is more than 72 hours, and the pressurizing and saturation pressure is not less than 10MPa.
6. The experimental method for evaluating core damage according to claim 5, wherein the step 4 of calibrating kerosene nuclear magnetic signal quantity specifically comprises:
step 4.1, taking out the saturated kerosene core from the core saturation device, wiping the residual kerosene on the surface, weighing the saturated kerosene core, and recording the weight as m 2 In units of g;
step 4.2, placing the saturated kerosene core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, the nuclear magnetic signal quantity of saturated kerosene rock core is recorded as S 2 In a.u. units;
step 4.3, establishing a corresponding relation between the nuclear magnetic signal quantity and the kerosene volume by combining a weight loss method, and calibrating the nuclear magnetic signal quantity of the kerosene by using the formula (1):
in the formula:
a is the nuclear magnetic signal quantity corresponding to the unit volume of kerosene, and the unit is a.u./mL;
rho-kerosene density in g/mL;
the formula (1) is a calculation formula for performing kerosene calibration by using a single core sample, and if a plurality of core samples are calibrated at the same time, the kerosene calibration average value of a group of core samples is calculated by using the following formula (2):
in the formula:
A i -calibration of kerosene nuclear magnetic signal quantities for different core samples in units of a.u./mL;
n is the number of core samples for carrying out a kerosene calibration experiment;
the more the number of the cores calibrated by the kerosene nuclear magnetic signal quantity is, the more accurate the measured kerosene calibration result is, and the calculation of subsequent experiments is facilitated.
7. The experimental method for evaluating core damage according to claim 6, wherein the calculation of core porosity before the experiment of step 5 specifically comprises:
according to the obtained nuclear magnetic signal quantity of the dry core sample and the saturated kerosene core, the porosity phi before the core experiment based on the nuclear magnetic resonance technology can be obtained by using the following formula (3) 1 ：
In the formula:
φ 1 core magnetic porosity in units of% before the experiment;
v is the volume of the core, the unit is mL, and the volume is calculated by the length and the diameter measured by the dry sample of the core.
8. The experimental method for evaluating core damage according to claim 7, wherein the step 6 of conducting core seepage related experiments by using saturated cores specifically comprises:
step 6.1, preparing the injury experiment fluid by using deuterium oxide;
step 6.2, carrying out seepage related experiments on the saturated kerosene core, and monitoring nuclear magnetic T of the core in the experiments 2 And (5) spectrum judging the oil-water distribution condition inside the rock core.
9. The experimental method for evaluating the damage of the rock core according to claim 8, wherein the secondary drying of the rock core after the experiment of the step 7 is specifically as follows:
and taking out the rock core subjected to the seepage experiment from the experimental device, and drying the rock core in a constant-temperature drying box with a vacuumizing device for not less than 120 hours to ensure that liquid-phase components in the rock core are completely dried.
10. The experimental method for evaluating core damage according to claim 9, wherein the step 8 of secondary drying core permeability test specifically comprises:
performing a gas logging permeability experiment on the secondary dried rock core to obtain a gas logging permeability value K of the secondary dried rock core 2 In mD.
11. The experimental method for evaluating core damage according to claim 10, wherein the step 9 of secondary drying core nuclear magnetic signal scanning specifically comprises:
secondary drying rock for measuring gas and permeabilityPlacing the core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary dried core 2 Spectrum and nuclear magnetic signal quantity, recording the nuclear magnetic signal quantity of the secondary drying rock core as S 3 In units of a.u.
12. The experimental method for evaluating the core damage according to claim 11, wherein the secondary saturated kerosene of the core after the experiment of step 10 is specifically:
and placing the secondary dried rock core into a rock core saturation device, vacuumizing, and then carrying out secondary saturated kerosene operation, wherein the vacuumizing time is more than 6 hours, the pressurized saturated kerosene time is more than 72 hours, and the pressurized saturated pressure is not less than 10MPa.
13. The experimental method for evaluating core damage according to claim 12, wherein the step 11 of secondary saturated kerosene core nuclear magnetic signal scanning specifically comprises:
placing the secondary saturated kerosene core in a nuclear magnetic resonance analyzer for off-line nuclear magnetic signal test to obtain nuclear magnetic T of the secondary saturated kerosene core 2 Spectrum and nuclear magnetic signal quantity, recording the nuclear magnetic signal quantity of secondary saturated kerosene rock core as S 4 In units of a.u.
14. The experimental method for evaluating core damage according to claim 13, wherein the calculation of the porosity of the core after the experiment in the step 12 is specifically as follows:
obtaining the porosity phi after the core experiment based on the nuclear magnetic resonance technology by using the following formula (4) according to the obtained nuclear magnetic signal quantity of the secondary dried core and the secondary saturated kerosene core 2 ：
In the formula:
φ 2 nuclear magnetic porosity of cores after percolation experiments in%.
15. The experimental method for evaluating core damage according to claim 14, wherein the step 13 of evaluating core damage specifically comprises:
step 13.1, calculating a permeability reduction rate lambda through the following formula (5) by comparing the gas logging permeability of the dried rock core before and after the seepage experiment, and evaluating the damage degree of the fluid to the permeability of the rock core:
in the formula:
lambda is the core permeability reduction rate before and after the experiment, and the unit is percent;
K 2 greater than K 1 Lambda is the permeability increase rate;
step 13.2, calculating the porosity reduction rate eta of the rock core through the following formula (6) by comparing the porosity of the saturated kerosene rock core before and after the seepage experiment so as to evaluate the damage degree of the fluid to the rock core pore structure:
in the formula:
eta, the permeability reduction rate of the rock core before and after the experiment, and the unit is percent;
φ 2 greater than phi 1 Time η is porosity promotion rate;
step 13.3, saturating the core with kerosene state T 2 Spectrum deduction of core drying state T 2 Spectrum, dry sample of rock core T 2 The spectrum is taken as a base signal, and the T of the signal completely coming from kerosene in the effective pore space of the rock core is obtained 2 Spectrum defined as core pore kerosene T 2 And (4) spectrum, wherein the effective pore space in the rock core is filled with kerosene, so that the kerosene T in the pores of the rock core 2 The spectrum intuitively shows the effective pore distribution condition of the rock core;
step 13.4, rock before and after seepage experimentCore saturated kerosene T 2 Drying rock core T with corresponding states deducted from spectrum 2 Spectral bases, i.e. saturated kerosene cores T 2 Deduction core dry sample T 2 Second saturated kerosene core T 2 Deducting secondary drying rock core T 2 Obtaining core pore kerosene T before and after core seepage experiment 2 And (4) comparing the two curves to visually evaluate the damage condition of the damage fluid to the pore structure of the rock core.
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| US11846623B1 (en) * | 2022-08-29 | 2023-12-19 | Southwest Petroleum University | Core holder and prediction method for starting pressure gradient of shale oil based on core holder |
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| US11846623B1 (en) * | 2022-08-29 | 2023-12-19 | Southwest Petroleum University | Core holder and prediction method for starting pressure gradient of shale oil based on core holder |
| CN116539815A (en) * | 2023-06-07 | 2023-08-04 | 四川省科源工程技术测试中心有限责任公司 | Device and method suitable for evaluating and optimizing working fluid of oil and gas reservoir |
| CN116539815B (en) * | 2023-06-07 | 2024-03-19 | 四川省科源工程技术测试中心有限责任公司 | Device and method suitable for evaluating and optimizing working fluid of oil and gas reservoir |
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