CN115266800A - Condensate oil saturation testing method based on two-dimensional nuclear magnetic resonance - Google Patents
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Abstract
The invention relates to a condensate saturation testing method based on two-dimensional nuclear magnetic resonance, which sequentially comprises the following steps of: (1) Cleaning, drying and weighing the core, and testing the porosity phi of the core to obtain the pore volume V of the core p (ii) a (2) Preparing condensate gas under the original formation pressure and the formation temperature; (3) Calibrating the relation between the core condensate oil saturation and the nuclear magnetic signal quantity under the formation condition; (4) recovering the original formation condition of the core; (5) Simulating the failure development process of the condensate gas reservoir, and performing two-dimensional nuclear magnetic resonance test on the rock core to obtain the T of the condensate gas of the rock core under different pressures in the failure process 1 ‑T 2 A two-dimensional spectrogram; (6) And (4) processing data, and determining the condensate oil saturation in the rock core under different pressures by combining with a calibration curve. The method is reliable in principle and simple and convenient to operate, and can provide a technical means for evaluating the condensate pollution degree of the gas reservoir near a well region, quantitatively determining the condensate loss and evaluating the gas well capacity by quantitatively determining the condensate saturation of the condensate gas reservoir.
Description
Technical Field
The invention relates to the field of petroleum and natural gas exploration and development, in particular to a condensate saturation testing method based on two-dimensional nuclear magnetic resonance.
Background
The condensate gas reservoir is different from the conventional black oil reservoir and pure dry gas reservoir, has the dual characteristics of an oil reservoir and a gas reservoir, and has relatively complex phase change in the production process. In the process of developing a condensate gas reservoir, when the local pressure is lower than the dew point pressure, condensate oil can be separated out from a gas phase and is accumulated in a near well area in a large quantity, so that the original seepage pore canal is blocked, the productivity of a gas well is reduced, and even the gas well stops spraying. Therefore, the condensate saturation in the stratum under different pressures in the failure process is determined, and the method has important guiding significance for evaluating the retrograde condensate pollution degree of the near well area, quantitatively determining the condensate loss and evaluating the gas well productivity.
At present, for testing the condensate saturation of a condensate gas reservoir, scholars at home and abroad develop a great deal of research, which mainly comprises the following steps: PVT experiment method, CT scanning method, phase balance theory method, numerical simulation method, experience model method, material balance method, state equation method, artificial neural network method, etc. The PVT experiment method mainly adopts a constant volume failure method in a PVT phase state experiment, intuitively determines the condensate oil saturation degree under each pressure through a PVT cylinder, and generally adopts an oil and gas reservoir fluid physical property analysis method (GB/T26981-2020), but the method does not consider the influence of the condition of a porous medium, and the condensate oil cannot flow. The CT scanning method mainly uses medical CT to perform gas condensate failure collaborative scanning, and can quantitatively determine the saturation of condensate oil under various pressures when dry cores fail, but when bound water exists in cores, it is difficult to effectively distinguish the change of the saturation of two phases of oil and water, and experimental quantification of the liquid phase precipitation amount cannot be performed, and only the liquid phase precipitation can be presumed by virtue of the change of the saturation of the gas phase (aou, lithua, zhen. The phase equilibrium theory method is mainly characterized in that a constant volume exhaustion theoretical model is established to predict condensate oil saturation by increasing the consideration of porous medium adsorption and pipe force factors (Du, J.F., li S.L., sun L., et al. Effect of porous medium adsorption on condensate-Gas phase equilibrium. Natural Gas industry.1998;18 (1): 33-36). The numerical simulation method mainly adopts oil reservoir numerical simulation software to perform constant volume failure experiment simulation, but needs to repeatedly fit well flow components, and has more complicated parameter adjusting work (Wanzhouhua, wang, yang Hongzi, and the like. Anyue low-permeability condensate gas reservoir single-well dry gas throughput parameter optimization. Special oil and gas reservoir, 2013,20 (6): 84-88). The empirical model method is mainly characterized in that a polynomial model is established by selecting specific independent variables and using a statistical regression method to predict condensate saturation (Cho S.J., civan, F.Starling KE.A. correlation to predict maximum saturation for controlling condensate saturation and uses in compression-prediction calculations. SPE annular Technical reference and inhibition. Las Vegas, nevada, september 1985), but the application range of the empirical model has certain limitation. The substance balance method is mainly based on an ideal storage tank thought under reservoir conditions, and is combined with actual produced quantity and residual quantity to establish a condensate failure idealized model to carry out condensate saturation backstepping, the method is simple and quick, but the calculation effect of condensate saturation under low formation pressure under the condensate failure conditions is poor (Zhang A.G., fan Z.F., zhao L, et al. New computing method for condensed oil saturation of gas condensation consistent resource, part A.2019, 24 (21): 2688-2697). The state equation method mainly carries out condensate oil saturation prediction through PR or SRK thermodynamic equations, and the method needs to carry out a large amount of fitting of binary interaction coefficients among all components, and has large and complicated workload. The artificial neural network method is mainly based on a large amount of PVT experimental data and adopts an artificial neural network or a support vector machine to predict the condensate oil saturation (Arabolo M, taghaki SR. SVM model of the Constant Volume Depletion (CVD) behavior of Gas consistency thresholds J Nat Gas Sci Eng.2014;21 1148-1155), but the method is more dependent on the roughness of a data sample and has the problem of overfitting at the same time.
In conclusion, although the PVT experimental method can intuitively and quantitatively determine the retrograde condensate volume, the influence of a real core porous medium is not considered, and other methods are mostly based on experimental data of a PVT experiment and have certain limitation on accurately evaluating the saturation change of condensate in a reservoir. Therefore, the method for directly testing the condensate oil saturation in the real stratum under the porous medium condition has important significance.
Disclosure of Invention
The invention aims to provide a condensate saturation testing method based on two-dimensional nuclear magnetic resonance, which has reliable principle and simple and convenient operation, can quantitatively determine condensate saturation in a real stratum of a condensate gas reservoir, and provides technical means for evaluating the condensate pollution degree of a near-well region of the gas reservoir, quantitatively determining condensate loss and evaluating the gas well productivity.
In order to achieve the technical purpose, the invention adopts the following technical scheme.
A condensate saturation testing method based on two-dimensional nuclear magnetic resonance sequentially comprises the following steps:
(1) Testing core porosity
Cleaning, drying and weighing the core, and testing the porosity phi of the core to obtain the pore volume V of the core p ；
(2) Preparation of gas condensate formation fluid sample
Obtaining dry gas and condensate oil required by the formation fluid sample preparation of a condensate gas reservoir, and preparing condensate gas under the original formation pressure and the formation temperature to ensure that the gas-oil ratio, the dew point pressure and the reverse condensate liquid amount of the condensate gas reservoir meet the experimental requirements;
(3) Calibrating relation between core condensate saturation and nuclear magnetic semaphore under stratum condition
Calculating the condensate oil densities of different pressures of condensate gas in a constant volume failure process under the stratum condition by adopting oil reservoir numerical simulation software; respectively preparing the degassing condensate oil with different densities, and then respectively saturating the core with the degassing condensate oil with different densities and stabilizing the core to the formation temperature; displacing the saturated rock core by adopting a gas flooding method to obtain condensate oil saturation under the condition of different densities of condensate oil, and testing the rock cores with different condensate oil saturations by adopting a two-dimensional nuclear magnetic resonance technologyT of 1 -T 2 Extracting and calculating a two-dimensional spectrogram to obtain nuclear magnetic semaphore, thereby establishing a relation curve between the saturation of the condensate oil of the rock core and the nuclear magnetic semaphore under different pressures under the formation condition;
(4) Restoring the original formation conditions of the core
Putting a rock core into a rock core holder, gradually injecting dry gas into the rock core holder and pressurizing to the original formation pressure, then injecting the condensate gas into the rock core holder at a certain speed to replace the dry gas until the gas-oil ratio at the outlet end of the rock core is consistent with the gas-oil ratio at the inlet end;
(5) Simulating the exhaustion development process of the condensate gas reservoir to complete the acquisition of two-dimensional nuclear magnetic resonance data
Gradually reducing the back pressure at the outlet end of the rock core, gradually depleting the pore pressure of the rock core from the original formation pressure to the waste pressure, and performing two-dimensional nuclear magnetic resonance test on the rock core in the depletion process to obtain the T of the rock core condensate gas under different pressures in the depletion process 1 -T 2 A two-dimensional spectrogram;
(6) Data processing, and quantitatively determining the condensate oil saturation in the rock core under different pressures by combining with a calibration curve
Comparative core saturated condensate T 1 -T 2 Two-dimensional spectrogram and T of saturated condensate oil 1 -T 2 Two-dimensional spectrogram for respectively obtaining peak signals T of condensate gas and condensate oil 1 -T 2 Range, set T 1 /T 2 The ratio line distinguishes the nuclear magnetic signals of the condensate gas and the condensate oil so as to distinguish the T of the condensate gas 1 -T 2 And (3) acquiring a condensate nuclear magnetic signal area from the two-dimensional spectrogram, extracting and calculating the condensate nuclear magnetic signal quantity of the area, and substituting the condensate nuclear magnetic signal quantity into the relation curve between the core condensate saturation and the nuclear magnetic signal quantity established in the step (3), so that the condensate saturation in the core under different pressures in the failure process can be determined.
Further, the step (3) comprises the following steps:
(1) adopting oil reservoir numerical simulation software to calculate each pressure point P in the process of constant volume depletion to waste pressure of the condensate gas under the formation pressure and the formation temperature i Condensate density of rho oi Degassing condensate oil with different densities is prepared respectively and used for representing real condensate oil under different layer pressures;
(2) respectively taking the core saturation density as rho oi The mass of the saturated rock core is m i Then placing the core into a core holder and stabilizing the core holder to the formation temperature, injecting dry gas into the saturated core through a displacement pump for displacement, wherein the mass of the displaced condensate oil is m j Thereby obtaining the saturation degree S of the condensate oil in the rock core at different moments oi ＝(m i -m j )/(ρ oi ·V p )；
(3) Testing T of rock cores with different condensate oil saturation degrees by adopting two-dimensional nuclear magnetic resonance technology 1 -T 2 Extracting and calculating a two-dimensional spectrogram to obtain nuclear magnetic signal quantity, and calibrating the relation between condensate oil saturation and the nuclear magnetic signal quantity under different condensate oil densities, thereby establishing core condensate oil saturation S under different pressures oi And nuclear magnetic signal quantity M i The relationship of (1).
Further, the step (6) further comprises the following steps:
core pore size and T 2 The relaxation time has a direct proportion relation and is according to the one-dimensional T of the rock core saturated condensate oil 2 Setting corresponding T according to relaxation distribution characteristics reflected by spectrogram 2 Cutoff value, will T 2 Cutoff value applied to T 1 -T 2 The condensate oil nuclear magnetic signal area in the two-dimensional spectrogram is further divided, so that different T are represented 2 And (3) determining the condensate oil saturation under different pore scales (micropores, small pores, mesopores and macropores) by using the nuclear magnetic signal quantity of the condensate oil in the relaxation region.
Drawings
FIG. 1 is a schematic structural diagram of an experimental device for testing condensate saturation based on two-dimensional nuclear magnetic resonance.
In the figure: 1-displacement pump, 2-confining pressure pump, 3-back pressure pump, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13-valve, 14-dry gas intermediate container, 15-condensate gas intermediate container, 16, 17, 18, 19-pressure gauge, 20-core holder, 21, 22-permanent magnet, 23-industrial computer, 24-back pressure valve, 25-separator, 26-gas meter.
FIG. 2 shows a two-dimensional NMR T of saturated core condensate (ρ = 0.630) 1 -T 2 Spectra.
Fig. 3 is a calibration curve of the different saturations and corresponding nuclear magnetic signal intensities of the condensate oil (ρ = 0.630) in the core.
FIG. 4 is a two-dimensional NMR T of a core under the original formation pressure (29 MPa) 1 -T 2 Spectra.
FIG. 5 shows the two-dimensional NMR T of the core failure process (25 MPa) 1 -T 2 Spectra.
FIG. 6 shows one-dimensional NMR T of core saturated condensate (ρ = 0.630) 2 And (4) a spectrogram.
Fig. 7 is a graph of total condensate saturation change at different pressures during core failure.
FIG. 8 is microporosity (T) during core failure 2 <1ms，5ms<T 1 /T 2 <40 ms) condensate saturation profile.
Detailed Description
The invention is further illustrated below with reference to the figures and examples in order to facilitate the understanding of the invention by a person skilled in the art. It is to be understood that the invention is not limited in scope to the specific embodiments, but is intended to cover various modifications within the spirit and scope of the invention as defined and defined by the appended claims, as would be apparent to one of ordinary skill in the art.
See fig. 1.
Condensate oil saturation testing arrangement based on two-dimensional nuclear magnetic resonance, including displacement pump 1, confined pressure pump 2, back pressure pump 3, dry gas intermediate container 14, condensate gas intermediate container 15, rock core holder 20, permanent magnet (21, 22), industrial computer 23, back pressure valve 24, separator 25 and gas meter 26, the entry end of rock core holder 20 is connected displacement pump 1 through dry gas intermediate container 14, condensate gas intermediate container 15 respectively, and back pressure valve 24 and separator 25 are connected to the exit end, and back pressure valve connection back pressure pump 3, separator connection gas meter 26, and the rock core holder is located in the middle of permanent magnet 21, 22, connects confined pressure pump 2 simultaneously, and permanent magnet 21, 22 connect industrial computer 23.
Examples
The gas sample used for gas condensate formation fluid sample preparation is from field sampling of a certain gas well of a condensate gas reservoir, and the oil sample is prepared by adopting simulated oil under the original formation pressure and the formation temperature; the degassed condensate oil with different densities is prepared by adopting hydrocarbon liquid with different densities according to the condensate oil deposit numerical simulation constant volume failure process and the condensate oil density under each pressure correspondingly. Collecting T in core exhaustion process 1 -T 2 And (3) performing two-dimensional spectrum and extracting condensate nuclear magnetic signal quantity, and quantitatively determining the total condensate saturation change of the rock core in the failure process and the condensate saturation change under different pore scales.
A condensate saturation testing method based on two-dimensional nuclear magnetic resonance sequentially comprises the following steps:
(1) Core porosity test
A practical reservoir plunger core sample of a gas well of a condensate gas reservoir is obtained, after the core is cleaned and dried, the diameter D (cm), the length L (cm) and the dry weight m (g) of the core are measured, the porosity phi (%) of the core is tested according to a core analysis method (GB/T29172-2012), and the test result is shown in Table 1.
TABLE 1
| Lithology | L(cm) | D(cm) | m(g) | Φ(％) |
| Sandstone | 5.00 | 2.50 | 46.48 | 25.95 |
Calculating to obtain the pore volume V of the rock core p ＝π·(D/2) 2 ·L·Φ＝6.37cm 3 。
(2) Sample preparation of gas condensate fluids
Obtaining a separator gas sample and a simulated oil sample of a certain production well of a condensate gas reservoir, preparing the condensate gas under the conditions of set original formation pressure of 29MPa and formation temperature of 25 ℃ according to a physical property analysis method of a fluid of the condensate gas reservoir (GB/T26981-2020), and enabling the gas-oil ratio GOR to be =2500m 3 /m 3 (GOR＝V g /V o ) Measuring the dew point pressure P of the condensate d ＝22.6MPa。
(3) Calibration of relation between core condensate saturation and nuclear magnetic semaphore under stratum condition
Adopting oil reservoir numerical simulation software to calculate and obtain each pressure P of the prepared sample condensate gas in the constant volume failure process under the original formation pressure of 29MPa and the formation temperature of 25 DEG C i Lower condensate density ρ oi The calculation results are shown in Table 2. Preparing corresponding different densities rho according to the calculation result oi The degassed condensate of (a) is used to characterize the true condensate at different formation pressures. The rock core is firstly put into a vacuumizing pressurizing saturation device to be saturated and prepared, and the relative density is rho oi The saturation time of the degassed condensate of (1) is 24 hours. Obtaining the mass m of the saturated rock core by a weighing method after the saturation is finished i Then, the rock core is put into a rock core holder 20 and stabilized to the formation temperature of 25 ℃, dry gas in a dry gas intermediate container 14 is injected into a saturated rock core for displacement at the speed of 0.125ml/min through an injection pump 1, and the mass m of the condensate oil displaced from a separator 25 is measured through a weighing method j Thereby obtaining the condensate oil saturation S in the rock core at different moments oi ＝(m i -m j )/(ρ oi ·V p ). Taking the prepared condensate oil with rho =0.630 as an example, the T of the rock core under different saturations is sequentially tested by adopting a two-dimensional nuclear magnetic resonance technology 1 -T 2 Two dimensional spectrum of which saturationT at degree of 100% 1 -T 2 The two-dimensional spectrum is shown in figure 2, and different condensate oil saturation degrees S are established oi Nuclear magnetic signal quantity M of rock core i See fig. 3. Repeating the steps to finish the rho with different densities oi Condensate saturation S oi And nuclear magnetic signal quantity M i The relationship is calibrated, the test result is shown in table 3, and the main test parameters of the two-dimensional nuclear magnetic resonance are shown in table 4.
TABLE 2
| pressure/MPa | Relative density of condensate in |
| 25 | 0.630 |
| 22 | 0.643 |
| 20 | 0.671 |
| 15 | 0.698 |
| 10 | 0.723 |
| 8 | 0.745 |
| 5 | 0.761 |
TABLE 3
TABLE 4
| Parameter(s) | Numerical value |
| |
10000 |
| Echo number NECH | 4096 |
| Echo spacing TE | 0.3 |
| Number of scans NS | 4 |
(4) Restoring original formation conditions of condensate gas reservoir
According to the connection experimental device of figure 1, the inlet end of a core holder 20 is connected with a dry gas intermediate container 14, a condensate gas intermediate container 15 and a displacement pump 1, the outlet end of the core holder 20 is respectively connected with a back pressure valve 24 and a separator 25, the back pressure valve 24 is connected with a back pressure pump 3, the separator 25 is connected with a gas meter 26, and the core holder 20 is located between permanent magnets 21 and 22 and is simultaneously connected with a confining pressure pump 2.
The holder temperature was maintained at 25 ℃. The back pressure of the back pressure valve 24 is set to be 29MPa through the back pressure pump 3, the dry gas in the dry gas intermediate container 14 is injected into the rock core through the injection pump 1, the pore pressure of the rock core is gradually increased to 29MPa, and the confining pressure is kept higher than the pore pressure by the confining pressure pump 2 all the time in the process. Then, the condensate gas in the condensate gas intermediate container 15 is injected into the rock core to replace the dry gas at the injection speed of 0.125ml/min under the constant speed mode through the injection pump 1 until the gas-oil ratio at the outlet end of the back pressure valve 24 reaches 2500m 3 /m 3 And ending the displacement, and recovering the rock core to the original stratum state of the condensate gas reservoir.
(5) Simulating the failure development process of condensate gas reservoir and completing two-dimensional nuclear magnetic resonance data acquisition
And closing the valve 9 at the inlet end of the core holder 20, and reducing the back pressure of the back pressure valve 24 by adjusting the back pressure pump 3 to ensure that the pore pressure of the core is exhausted from the original formation pressure of 29MPa to the waste pressure of 5MPa. Wherein the core is subjected to two-dimensional nuclear magnetic resonance test at 25MPa, 22MPa, 20MPa, 15MPa, 10MPa, 8MPa and 5MPa to obtain the T of the core under each pressure 1 -T 2 Two-dimensional spectra with a native formation pressure of 29MPa and a two-dimensional NMR T at depletion to 25MPa 1 -T 2 The results of the spectrum test are shown in fig. 4 and 5, respectively.
(6) Data processing, and quantitatively determining the condensate oil saturation in the rock core under different pressures by combining with a calibration curve
By comparing T of rock core saturation condensate gas original formation pressure under 29MPa 1 -T 2 Two-dimensional spectra (see FIG. 4) and T of core saturated condensate 1 -T 2 Two-dimensional spectrum (see fig. 2), the condensate peak signal is mainly located at 40<T 1 /T 2 <100, condensate peak signal mainly located at 5<T 1 /T 2 <40, thus setting T 1 /T 2 =40 as boundary between condensate signal and condensate signal, 5<T 1 /T 2 <And 40 is a condensate signal region.
Extracting T under each pressure in the process of rock core exhaustion through special nuclear magnetic software 1 -T 2 Nuclear magnetic signal of condensate oil in two-dimensional spectrum, T at 25MPa of rock core 1 -T 2 The two-dimensional spectrum is taken as an example (see fig. 5), and the condensate signal quantity is calculated according to the following formula:
due to the pore size and T of the core 2 The relaxation time has a direct proportion relation and is determined according to the one-dimensional nuclear magnetic resonance T of the core saturated condensate oil 2 The spectral relaxation distribution characteristics show (see fig. 6) that the core pore distribution is relatively uniform without significant T 2 Cut-off value, hence T of the core 2 The whole relaxation range is gradient (0.1 ms-1ms, 1ms-10ms, 10ms-100ms, 100ms-1000 ms) in 10 times relation, and the region where the condensate oil signal is applied in the graph 5 passes through T 2 The relaxation range is further divided, and the total nuclear magnetic signal quantity of the condensate is further divided into the condensate signal quantities under different pore scales (region 1 2 <1ms，5<T 1 /T 2 <40. And (4) area 2:1ms<T 2 <10ms，5<T 1 /T 2 <40. And (4) area 3:10ms<T 2 <100ms，5<T 1 /T 2 <40. Region 4: t is a unit of 2 >100ms，5<T 1 /T 2 <40 To characterize the condensate signal volume in micro-, meso-, macro-pores.
T in the rock core of FIG. 5 at 25MPa 1 -T 2 Adding nuclear magnetic signal quantities of 4 areas of the two-dimensional spectrum to obtain a total signal quantity, and obtaining different saturation degrees S according to the established core condensate oil (rho = 0.630) oi And nuclear magnetic semaphores M i The obtained total nuclear magnetic signal quantity of the condensate oil is substituted into a corresponding empirical formula in the graph 3, so that the total condensate oil saturation in the rock core under 25MPa in the failure process can be quantitatively determined, then the total condensate oil saturation in the rock core under 25MPa is divided into condensate oil saturations under different pore scales according to the nuclear magnetic signal quantity ratio of each region, and the condensate oil saturations under other pressures in the rock core failure process are calculated and treated in a same way. All the calculations are shown in Table 5, the variation of total condensate saturation in the core at different pressures is shown in FIG. 7, and the condensate saturation in the core region (e.g., for example, in the core: microporosity, T 2 <1ms，5<T 1 /T 2 <40 Variation at different pressures is shown in fig. 8.
TABLE 5
Claims (3)
1. A condensate saturation testing method based on two-dimensional nuclear magnetic resonance sequentially comprises the following steps:
(1) Cleaning, drying and weighing the core, and testing the porosity phi of the core to obtain the pore volume V of the core p ；
(2) Preparing condensate gas under the original formation pressure and the formation temperature;
(3) Calculating the condensate oil densities of different pressures of the condensate gas in the constant volume depletion process under the stratum condition; respectively preparing degassing condensate oil with different densities, and then respectively saturating the core with the degassing condensate oil with different densities and stabilizing the core to the formation temperature; the saturated rock core is displaced by adopting a gas flooding method, condensate oil saturation under the condition of different densities of condensate oil is obtained, and the T of the rock core with different condensate oil saturations is tested by adopting a two-dimensional nuclear magnetic resonance technology 1 -T 2 Extracting and calculating a two-dimensional spectrogram to obtain nuclear magnetic semaphore, thereby establishing a relation curve between the saturation of the condensate oil of the rock core and the nuclear magnetic semaphore under different pressures under the formation condition;
(4) Putting a rock core into a rock core holder, gradually injecting dry gas into the rock core holder and pressurizing to the original formation pressure, then injecting the condensate gas into the rock core holder at a certain speed to replace the dry gas until the gas-oil ratio at the outlet end of the rock core is consistent with the gas-oil ratio at the inlet end;
(5) Gradually reducing the back pressure at the outlet end of the rock core, gradually depleting the pore pressure of the rock core from the original formation pressure to the waste pressure, and carrying out two-dimensional nuclear magnetic resonance test on the rock core in the depletion process to obtain the T of the gas condensate of the rock core under different pressures in the depletion process 1 -T 2 A two-dimensional spectrogram;
(6) T by core saturation condensate 1 -T 2 Two-dimensional spectrogram and T of saturated condensate oil 1 -T 2 Two-dimensional spectrogram for respectively obtaining peak signals T of condensate gas and condensate oil 1 -T 2 Range, set T 1 /T 2 The ratio line distinguishes the nuclear magnetic signals of the condensate gas and the condensate oil so as to distinguish the T of the condensate gas 1 -T 2 And (3) acquiring a condensate nuclear magnetic signal area from the two-dimensional spectrogram, extracting and calculating the condensate nuclear magnetic signal quantity of the area, and substituting the condensate nuclear magnetic signal quantity into the relation curve between the core condensate saturation and the nuclear magnetic signal quantity established in the step (3), so that the condensate saturation in the core under different pressures in the failure process can be determined.
2. The condensate saturation degree test method based on two-dimensional nuclear magnetic resonance as claimed in claim 1, wherein the step (3) comprises the following steps:
(1) adopting oil reservoir numerical simulation software to calculate each pressure point P in the process of constant volume depletion to waste pressure of the condensate gas under the formation pressure and the formation temperature i Condensate density ρ oi Degassing condensate oil with different densities is prepared respectively and used for representing real condensate oil under different layer pressures;
(2) respectively taking the core saturation density as rho oi The saturated core mass of the degassed condensate oil is m i Then placing the core into a core holder and stabilizing the core holder to the formation temperature, injecting dry gas into the saturated core through a displacement pump for displacement, wherein the mass of the displaced condensate oil is m j Thereby obtaining the saturation degree S of the condensate oil in the rock core at different moments oi ＝(m i -m j )/(ρ oi ·V p )；
(3) Testing T of rock cores with different condensate oil saturation degrees by adopting two-dimensional nuclear magnetic resonance technology 1 -T 2 Extracting and calculating a two-dimensional spectrogram to obtain nuclear magnetic signal quantity, and calibrating the relation between the condensate saturation and the nuclear magnetic signal quantity under different condensate densities so as to establish the core condensate saturation S under different pressures oi And nuclear magnetic signal quantity M i The relationship of (1).
3. The two-dimensional nuclear magnetic resonance-based condensate saturation test method according to claim 1, wherein the step (6) further comprises the following steps:
core pore size and T 2 The relaxation time has a direct proportion relation and is according to the one-dimensional T of the rock core saturated condensate oil 2 Setting corresponding T according to relaxation distribution characteristics reflected by spectrogram 2 Cutoff value, will T 2 Application of a cutoff value to T 1 -T 2 The nuclear magnetic signal area of the condensate oil in the two-dimensional spectrogram is further divided, so that different T are represented 2 And (4) determining the condensate oil saturation under different pore scales by using the nuclear magnetic signal quantity of the condensate oil in the relaxation interval.
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