Asphaltene deposition damage evaluation method based on nuclear magnetic resonance

Abstract

The invention discloses an asphaltene deposition damage evaluation method based on nuclear magnetic resonance, and belongs to the technical field of oilfield development. According to the nuclear magnetic resonance-based asphaltene deposition damage evaluation method provided by the invention, the distribution characteristics of the asphaltene in the rock core are accurately obtained by using a graphic technology, the deposition amount of the asphaltene in the rock core is intuitively obtained, and meanwhile, the deposition characteristics of the asphaltene and the damage characteristics of the asphaltene to the physical properties of the rock core are revealed from the microscopic scale; compared with a traditional method, the damage degree of asphaltene deposition generated by CO2 displacement of the rock core to the permeability and porosity of the reservoir rock sample is accurately and rapidly evaluated through a nuclear magnetic resonance method.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field development, in particular to an asphaltene deposition damage evaluation method based on nuclear magnetic resonance. Background Art

[0002] The currently accepted definition of asphaltene is a class of organic compounds in crude oil that are insoluble in low-order normal alkanes (nCs~nC7) but soluble in aromatic hydrocarbons (benzene, toluene, xylene, etc.). Asphaltene is a complex organic compound mainly composed of carbon and hydrogen elements, and also contains nitrogen, oxygen, sulfur and a small amount of metal elements such as nickel, vanadium, iron, etc. Its molecular structure and molecular weight are uncertain. Gel is a crude oil component that is soluble in normal alkanes, benzene and toluene at room temperature but insoluble in ethyl acetate. Its molecules are much smaller than asphaltene. Under normal reservoir conditions, colloid-asphaltene-crude oil is in a dynamic equilibrium state.

[0003] However, for reservoirs containing asphaltene, the injection of CO2 will break the initial equilibrium state of colloid-asphaltene-crude oil in the crude oil system, causing asphaltene flocculation and deposition, resulting in pore throat blockage, which has a great impact on the development effect. However, due to the limitations of experimental equipment and technology, most of the current experimental methods can only roughly evaluate the degree of core damage from a macroscopic perspective, and cannot observe the degree of damage to the core by asphaltene from a microscopic pore scale and permeability scale. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned shortcomings of the prior art and provide an asphaltene deposition damage evaluation method based on nuclear magnetic resonance.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for evaluating asphaltene deposition damage based on nuclear magnetic resonance comprises the following steps:

[0007] S1. extracting the oil from the reservoir core, drying the reservoir core and weighing it, and measuring the porosity and permeability of the reservoir core;

[0008] Using a predetermined mass of formation crude oil to perform nuclear magnetic resonance, obtain a T1-T2 spectrum curve, determine the distribution interval of asphaltene on the T1-T2 spectrum curve, and calculate the content of asphaltene in the crude oil bulk phase;

[0009] S2, saturating the reservoir core with crude oil once;

[0010] Then, the reservoir core was weighed, the T1-T2 spectrum curve of the reservoir core was measured, and the T2 spectrum curve of the core was extracted. The SDR model parameters were fitted to calculate the permeability K after primary saturation. oi ;

[0011] Using the T2 data after full saturation of crude oil, the following classification method is followed: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; large pores: 10ms<T2, and the small pore ratio coefficient P is established. 小 , Mesopore ratio coefficient P 中 and macropore ratio P 大 :

[0012] S3. Using CO2 to displace the crude oil in the reservoir core, when the displacement is completed, the reservoir core in this state is tested for a nuclear magnetic resonance T1-T2 spectrum curve and the T2 spectrum curve of the core is extracted;

[0013] Calculate the permeability and porosity of the core after CO2 displacement, and calculate the asphaltene content in the reservoir core and the asphaltene content in the driven crude oil when the displacement is completed;

[0014] S4, re-saturating the reservoir core with crude oil;

[0015] Then, NMR scanning is performed to obtain the NMR T1-T2 spectrum curve and extract the T2 spectrum curve of the core;

[0016] Calculate the permeability K after resaturation using SDR parameters oif , based on the permeability K after primary saturation oi and the permeability K after resaturation oif To evaluate the damage rate S of asphaltene deposition to the permeability of the reservoir K ;

[0017] Based on the small hole proportion coefficient P 小 , Mesopore ratio coefficient P 中 and macropore ratio P 大 The porosity damage rate S of asphaltene is evaluated by using the difference between the T2 spectra extracted from the first saturation and the second saturation. φ ;

[0018]

[0019]

[0020] Where, T 2o1 —Transverse relaxation time of the crude oil corresponding to the nuclear magnetic resonance T2 spectrum under the state of primary saturation, ms;

[0021] T 2o1,i —The i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum of crude oil under the state of primary oil saturation, ms;

[0022] m(T 2o1 ) i—The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil under the state of primary oil saturation;

[0023] T 2o2 —Transverse relaxation time of the crude oil corresponding to the NMR T2 spectrum under the re-saturated oil state, ms;

[0024] T 2o2,i —The i-th transverse relaxation time of the NMR T2 spectrum of crude oil under the re-saturated oil state, ms;

[0025] m(T 2o2 ) i —The corresponding amplitude value of the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil under the oil-saturated state again.

[0026] K oi —Oil phase permeability of rock sample, mD;

[0027] K oif —Permeability after resaturation, mD;

[0028] S φ —Porosity damage rate;

[0029] S K —Penetration damage rate;

[0030] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the small pores in the re-saturated oil state;

[0031] ∫1 10 m(T 2o2 ) i dT 2o2 —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the re-saturated oil state;

[0032] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores in the re-saturated oil state.

[0033] Furthermore, in S2, the permeability K after primary saturation is oi for:

[0034]

[0035]

[0036] C—coefficient related to rock mineral composition, fitted by experimental data, dimensionless;

[0037] m, n—coefficients related to the physical properties and microstructural coefficients of the rock sample, equal to 4 and 2 respectively, dimensionless;

[0038] T 2o1 —Transverse relaxation time of the crude oil corresponding to the nuclear magnetic resonance T2 spectrum under the state of primary saturation, ms;

[0039] T 2o1,i —The i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms;

[0040] T (2mi)1 —The logarithm-weighted average of the i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms;

[0041] m(T 2o1 ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve under the primary saturated oil state;

[0042] —core porosity, %;

[0043] S oi1 —Initial oil saturation of the core.

[0044] Furthermore, the permeability K after resaturation in S4 oif for:

[0045]

[0046] Where, C is a coefficient related to the mineral composition of rocks, which is fitted by experimental data and is dimensionless;

[0047] m, n—coefficients related to the physical properties and microstructural coefficients of the rock sample, equal to 4 and 2 respectively, dimensionless.

[0048] Furthermore, in S2, using the T2 data after full saturation of crude oil, the following classification method is followed: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; large pores: 10ms<T2, and the proportion coefficients of small, medium and large pores are established as follows:

[0049]

[0050]

[0051]

[0052] in, —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in small pores in the primary oil saturation state;

[0053] ∫110 m(T 2o1 ) i dT 2o1 —The sum of the amplitude values ​​corresponding to the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the primary oil saturation state;

[0054] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores of the primary oil saturation state;

[0055] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the core pores of the primary oil saturated state.

[0056] Furthermore, in S3, the permeability and porosity of the core after CO2 displacement are calculated, and the asphaltene content in the reservoir core and the asphaltene content in the driven crude oil are calculated at the completion of the displacement, as follows:

[0057]

[0058] R p —Asphaltene content in crude oil displaced by CO2, cm 3 ;

[0059] T 2pr —Transverse relaxation time of NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms;

[0060] T 2pr，i —The i-th transverse relaxation time of the NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms;

[0061] m(T 2pr ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve corresponding to asphaltene in crude oil displaced by CO2;

[0062] T 2or —Transverse relaxation time of T1-T2 spectrum of nuclear magnetic resonance of crude oil displaced by CO2, ms;

[0063] T 2or，i —The i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum of crude oil displaced by CO2, ms;

[0064] m(T 2or ) i —The amplitude value corresponding to the ith transverse relaxation time of the T1-T2 spectrum curve of the crude oil NMR displaced by CO2;

[0065] V o —Amount of crude oil displaced by CO2, cm3 ;

[0066] S p —Asphaltene content in initial crude oil, %.

[0067] Furthermore, the reservoir porosity in S1 is:

[0068]

[0069] Where: V T is the total volume of the rock sample, (cm 3 );

[0070] V P is the rock pore volume, (cm 3 );

[0071] V G is the rock skeleton volume, (cm 3 ).

[0072] Furthermore, in S1, according to Darcy's formula, the permeability of the reservoir is:

[0073]

[0074] Where: K is the permeability, Darcy (μm 2 ); Q is the volume flow rate of the liquid, cm 3 / s; ΔP is the pressure difference at both ends of the rock sample, 10 5 pa; μ is the viscosity of the liquid, centipoise (0.001Pa·s); A is the cross-sectional area of ​​the rock sample, cm 2 ; L is the length of the rock sample, cm.

[0075] Furthermore, when the crude oil was once saturated in S2, the reservoir core after vacuum was pressurized and saturated at a constant pressure of 20 MPa at the formation temperature for 48 h.

[0076] Furthermore, the displacement process in S3 is:

[0077] The reservoir core is placed in a holder, and when CO2 gas is injected, the outlet valve of the holder is opened to collect the outflowing crude oil, and the asphaltene content in the crude oil is analyzed. When the outlet end no longer produces oil, the displacement is completed.

[0078] Furthermore, the porosity was measured using the liquid saturation displacement method and the liquid saturation method in S1;

[0079] In case of plug rock samples, the porosity is measured by measuring the skeleton volume and pore volume respectively using the helium method.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] The present invention provides a method for evaluating asphaltene deposition damage based on nuclear magnetic resonance, which uses graphic technology to accurately obtain the distribution characteristics of asphaltene in the core, intuitively obtains the deposition amount of asphaltene in the core, and reveals the deposition characteristics of asphaltene and the damage characteristics to the physical properties of the core from a microscopic scale. Compared with traditional methods, the nuclear magnetic resonance method can accurately and quickly evaluate the degree of damage to the permeability and porosity of reservoir rock samples caused by asphaltene deposition generated by CO2 displacement in the core. BRIEF DESCRIPTION OF THE DRAWINGS

[0082] Figure 1 is a flow chart of the present invention;

[0083] Figure 2 The nuclear magnetic resonance T2 spectra of the core of the embodiment before displacement and after re-saturation;

[0084] Figure 3 The NMR T1-T2 results of the crude oil in the embodiment;

[0085] Figure 4 The NMR T1-T2 results before core flooding in the embodiment;

[0086] Figure 5 The corresponding NMR T1-T2 results before core flooding of the embodiment. DETAILED DESCRIPTION

[0087] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0088] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0089] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0090] See also Figure 1 , Figure 1 The flowchart of the present invention is a method for evaluating asphaltene deposition damage based on nuclear magnetic resonance, comprising the following steps:

[0091] S1. Core pre-processing:

[0092] Oil washing: Crude oil, especially heavy crude oil, is often dispersed in rock formations. There is a lot of oil inside the rock. Gas driving, solvent dissolution and other methods are used to extract the oil from the rock formation;

[0093] Drying: Dry the core after oil washing;

[0094] Weighing: Weigh the dried core;

[0095] Measurement: Measure the porosity and permeability of reservoir cores;

[0096] Reservoir porosity in oil and gas geology refers to the shape, size, connectivity and development of pore space in the reservoir. Oil and natural gas are stored in the pores of rocks underground. Therefore, the degree of pore development in rocks will directly affect the amount of oil and gas stored in the rocks.

[0097] The formula for porosity measurement is:

[0098]

[0099] Where: V T is the total volume of the rock sample, (cm 3 )

[0100] V P is the rock pore volume, (cm 3 )

[0101] V G is the rock skeleton volume, (cm 3 );

[0102] Porosity can be measured by liquid saturation displacement method and liquid saturation method. This method can also be used for block rock samples that only measure porosity. If plunger rock samples are used, it is recommended to use the helium method to measure the skeleton volume and pore volume to measure porosity.

[0103] The permeability of a reservoir refers to the permeability of a rock to a fluid when the rock is saturated with a single-phase fluid, there is no physical-chemical reaction between the rock and the fluid (no compression), and the fluid is in a horizontal linear stable flow state under a certain pressure difference.

[0104] According to Darcy's formula, the permeability can be written as:

[0105]

[0106] Where: K is the permeability, Darcy (μm 2 ); Q is the volume flow rate of the liquid, cm 3 / s; ΔP is the pressure difference at both ends of the rock sample, 10 5 pa; μ is the viscosity of the liquid, Repoise (0.001Pa·s); A is the cross-sectional area of ​​the rock sample, cm 2 ; L is the length of the rock sample, cm;

[0107] Measuring gas permeability K g for:

[0108]

[0109] Where, L is the length of the rock sample, cm; μ g is the viscosity of the gas, in ripoise (0.001 Pa·s); P0 is the atmospheric pressure, 10 5 pa; P1 is the core inlet pressure, 10 5 pa; P2 is the core outlet pressure, 10 5 pa;Q g is the gas flow rate, cm 3 / s.

[0110] S2. Preliminary treatment of crude oil:

[0111] A certain amount of formation crude oil is filled in a standard sample bottle and tested with the nuclear magnetic resonance T1-T2 spectrum curve to determine the distribution range of asphaltene on the T1-T2 spectrum and obtain the asphaltene content S in the crude oil bulk phase. p ;

[0112] Asphaltene content S p The calculation formula is:

[0113]

[0114] S p —Asphaltene content in crude oil, %;

[0115] T 2p —Transverse relaxation time of asphaltene corresponding to NMR T1-T2 spectrum, ms;

[0116] T 2p,i —The i-th transverse relaxation time of the NMR T1-T2 spectrum of asphaltene, ms;

[0117] m(T 2p ) i—The amplitude value corresponding to the i-th transverse relaxation time of the NMR T1-T2 spectrum curve of asphaltene.

[0118] T 2o —Transverse relaxation time of crude oil corresponding to NMR T1-T2 spectrum, ms;

[0119] T 2o,i —The i-th transverse relaxation time of crude oil NMR T1-T2 spectrum, ms;

[0120] m(T 2o ) i —The amplitude value corresponding to the i-th transverse relaxation time of the crude oil NMR T1-T2 spectrum curve;

[0121] —The sum of the amplitude values ​​corresponding to the transverse relaxation time of the NMR T1-T2 spectrum curve of asphaltene;

[0122] —The sum of the amplitude values ​​corresponding to the transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve of crude oil;

[0123] S3, saturated formation crude oil:

[0124] A vacuum pump is used to evacuate the sample in the holder;

[0125] The vacuumed samples were pressurized to be fully saturated at formation temperature and 20MPa pressure, the oil saturation of the core was calculated, the weight of the core and the T1-T2 spectrum curve were measured, and the T2 spectrum curve of the core was extracted. The following principles were used: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; large pores: 10ms<T2, and the proportion coefficients of small, medium and large pores were established;

[0126] Fit the SDR model parameters, the fitting formula is:

[0127]

[0128]

[0129] Using the T2 data after full saturation of crude oil, the following classification method is followed: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; large pores: 10ms<T2, and the proportion coefficients of small, medium and large pores are established:

[0130]

[0131]

[0132]

[0133] Koi —Oil phase permeability of rock sample, mD;

[0134] C—coefficient related to rock mineral composition, fitted by experimental data, dimensionless;

[0135] m, n—coefficients related to the physical properties and microstructural coefficients of the rock sample, equal to 4 and 2 respectively, dimensionless;

[0136] T 2o1 —Transverse relaxation time of the crude oil corresponding to the nuclear magnetic resonance T2 spectrum under the state of primary saturation, ms;

[0137] T 2o1,i —The i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms;

[0138] T (2mi)1 —The logarithm-weighted average of the i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms;

[0139] m(T 2o1 ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve under the primary saturated oil state;

[0140] —core porosity, %;

[0141] S oi1 —Initial oil saturation of the core;

[0142] P 大 — Macropore ratio coefficient;

[0143] P 中 —Mesopore ratio coefficient;

[0144] P 小 —Small pore ratio coefficient;

[0145] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in small pores in the primary oil saturation state;

[0146] ∫1 10 m(T 2o1 ) i dT 2o1 —The sum of the amplitude values ​​corresponding to the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the primary oil saturation state;

[0147] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores of the primary oil saturation state;

[0148] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the core pores of the primary oil saturated state;

[0149] The vacuum pump uses a high-speed rotating rotor to transfer momentum to the gas, so that it obtains a directional speed, and is compressed and driven to the exhaust port. The vacuum pump that is drawn away by the previous stage draws the gas molecules of the molecular pump to collide with the high-speed moving rotor to obtain momentum and be driven to the outlet of the pump.

[0150] S4, CO2 displacement:

[0151] The sample in the holder is heated to a certain temperature and placed under a constant pressure environment;

[0152] Then a certain amount of CO2 is injected into the gripper;

[0153] Record the pressure difference between the inlet and outlet of the holder during displacement, as well as the liquid and gas production at the outlet;

[0154] After the CO2 injection experiment is completed, the core weight is weighed, the T1-T2 spectrum curve is measured, and the T2 spectrum curve of the core is extracted;

[0155] When CO2 gas is injected, the outlet valve of the holder is opened to collect the produced crude oil sample. When the outlet end no longer produces oil, the displacement is stopped, and the asphaltene content in the crude oil is obtained through nuclear magnetic resonance T1-T2 experiment and four-component experimental analysis;

[0156] CO2 gas is injected into S4 until the outlet end stops producing oil. Nuclear magnetic resonance is performed on the core in this state to calculate the permeability and porosity of the core after CO2 displacement, and the asphaltene content in the core and the asphaltene content in the driven crude oil are determined at the same time;

[0157] The calculation formula is:

[0158]

[0159] R p —Asphaltene content in crude oil displaced by CO2, cm 3 ;

[0160] T 2pr —Transverse relaxation time of NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms;

[0161] T 2pr，i —The i-th transverse relaxation time of the NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms;

[0162] m(T 2pr ) i—The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve corresponding to asphaltene in crude oil displaced by CO2;

[0163] T 2or —Transverse relaxation time of T1-T2 spectrum of nuclear magnetic resonance of crude oil displaced by CO2, ms;

[0164] T 2or，i —The i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum of crude oil displaced by CO2, ms;

[0165] m(T 2or ) i —The amplitude value corresponding to the ith transverse relaxation time of the T1-T2 spectrum curve of the crude oil NMR displaced by CO2;

[0166] V o —Amount of crude oil displaced by CO2, cm 3 ;

[0167] S p —Asphaltene content in initial crude oil, %;

[0168] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve corresponding to asphaltene in crude oil displaced by CO2;

[0169] —The sum of the amplitude values ​​corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve of crude oil displaced by CO2;

[0170] S5, re-saturation of crude oil:

[0171] The re-saturated crude oil is subjected to nuclear magnetic resonance scanning, the nuclear magnetic resonance T1-T2 spectrum curve is measured and the T2 spectrum curve of the core is extracted; the permeability after re-saturation is obtained using the obtained SDR parameters to evaluate the damage rate of asphaltene deposition to the reservoir, and the difference between the T2 spectra of the first saturation and the re-saturation is used to evaluate the damage rate of asphaltene to the porosity.

[0172] Evaluate the damage rate of asphaltene to porosity and permeability;

[0173] The calculation formula is as follows:

[0174]

[0175]

[0176]

[0177]

[0178] T (2mi)2—The logarithm-weighted average of the i-th transverse relaxation time of the NMR T2 spectrum under the re-saturated oil state, ms;

[0179] T 2o2 —Transverse relaxation time of the crude oil corresponding to the NMR T2 spectrum under the re-saturated oil state, ms;

[0180] T 2o2,i —The i-th transverse relaxation time of the NMR T2 spectrum of crude oil under the re-saturated oil state, ms;

[0181] m(T 2o2 ) i —The corresponding amplitude value of the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil under the re-saturated oil state;

[0182] S oi2 —Oil saturation after core is resaturated;

[0183] K oif —Permeability after resaturation, mD;

[0184] S φ —Porosity damage rate;

[0185] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the small pores in the re-saturated oil state;

[0186] ∫1 10 m(T 2o2 ) i dT 2o2 —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the re-saturated oil state;

[0187] —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores in the re-saturated oil state;

[0188] S K —Penetration damage rate;

[0189] S6. Complete the experiment.

[0190] Example

[0191] See also Figure 2 , Figure 2 The NMR T2 spectra of the core of the embodiment before displacement and after re-saturation are shown. The porosity damage rate and permeability damage rate of the core can be determined by combining the curve with steps 5 and 2.

[0192] See also Figure 3 , Figure 3The NMR T1-T2 results of the crude oil in the embodiment are obtained. The distribution position, content and T in formula 10 of asphaltene can be determined by the spectrum. 2pr,min and T 2pr,max .

[0193] See also Figure 4 , Figure 4 This is the nuclear magnetic resonance T1-T2 result before the core flooding of the embodiment. The amount of asphaltene dissolved in the core can be determined by combining this spectrum with step 4.

[0194] See also Figure 5 , Figure 5 The corresponding NMR T1-T2 results before core flooding of the embodiment.

[0195] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for evaluating asphaltene deposition damage based on nuclear magnetic resonance, characterized in that: The following steps are involved: S1. extracting the oil from the reservoir core, drying the reservoir core and weighing it, and measuring the porosity and permeability of the reservoir core; Using a predetermined mass of formation crude oil to perform nuclear magnetic resonance, obtain a T1-T2 spectrum curve, determine the distribution interval of asphaltene on the T1-T2 spectrum curve, and calculate the content of asphaltene in the crude oil bulk phase; S2, saturating the reservoir core with crude oil once; Then, the reservoir core was weighed, the T1-T2 spectrum curve of the reservoir core was measured, and the T2 spectrum curve of the core was extracted. The SDR model parameters were fitted to calculate the permeability K after primary saturation. oi ; Using the T2 data after full saturation of crude oil, the following classification method is followed: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; Large hole: 10ms<T2, establish small hole ratio coefficient P 小 , Mesopore ratio coefficient P 中 and macropore ratio P 大 : S3. Using CO2 to displace the crude oil in the reservoir core, when the displacement is completed, the reservoir core in this state is tested for a nuclear magnetic resonance T1-T2 spectrum curve and the T2 spectrum curve of the core is extracted; Calculate the permeability and porosity of the core after CO2 displacement, and calculate the asphaltene content in the reservoir core and the asphaltene content in the driven crude oil when the displacement is completed; S4, re-saturating the reservoir core with crude oil; Then, NMR scanning is performed to obtain the NMR T1-T2 spectrum curve and extract the T2 spectrum curve of the core; Calculate the permeability K after resaturation using SDR parameters oif , based on the permeability K after primary saturation oi and the permeability K after resaturation oif To evaluate the damage rate S of asphaltene deposition to the permeability of the reservoir K ; Based on the small hole proportion coefficient P 小 , Mesopore ratio coefficient P 中 and macropore ratio P 大 The porosity damage rate S of asphaltene is evaluated by using the difference between the T2 spectra extracted from the first saturation and the second saturation. φ ; Where, T 2o1 —Transverse relaxation time of the crude oil corresponding to the nuclear magnetic resonance T2 spectrum under the state of primary saturation, ms; T 2o1,i —The i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum of crude oil under the state of primary oil saturation, ms; m(T 2o1 ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil under the state of primary oil saturation; T 2o2 —Transverse relaxation time of the crude oil corresponding to the NMR T2 spectrum under the re-saturated oil state, ms; T 2o2,i —The i-th transverse relaxation time of the NMR T2 spectrum of crude oil under the re-saturated oil state, ms; m(T 2o2 ) i —The corresponding amplitude value of the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil under the re-saturated oil state; K oi —Oil phase permeability of rock sample, mD; K oif —Permeability after resaturation, mD; S φ —Porosity damage rate; S K —Penetration damage rate; —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the small pores in the re-saturated oil state; ——The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the re-saturated oil state; —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores in the re-saturated oil state.

2. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: In S2, the permeability K after primary saturation oi for: C—coefficient related to rock mineral composition, fitted by experimental data, dimensionless; m, n—coefficients related to the physical properties and microstructural coefficients of the rock sample, equal to 4 and 2 respectively, dimensionless; T 2o1 —Transverse relaxation time of the crude oil corresponding to the nuclear magnetic resonance T2 spectrum under the state of primary saturation, ms; T 2o1,i —The i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms; T (2mi)1 —The logarithm-weighted average of the i-th transverse relaxation time of the NMR T2 spectrum under the primary saturated oil state, ms; m(T 2o1 ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve under the primary saturated oil state; —core porosity, %; S oi1 —Initial oil saturation of the core.

3. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: The permeability K after resaturation in S4 oif for: Where, C is a coefficient related to the mineral composition of rocks, which is fitted by experimental data and is dimensionless; m, n—coefficients related to the physical properties and microstructural coefficients of the rock sample, equal to 4 and 2 respectively, dimensionless.

4. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: In S2, using the T2 data after full saturation of crude oil, the following classification method is followed: small pores: 0ms<T2<1ms; medium pores: 1ms<T2<10ms; Large hole: 10ms<T2, the proportion coefficients of small, medium and large holes are established as follows: in, —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in small pores in the primary oil saturation state; —The sum of the amplitude values ​​corresponding to the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the pores in the primary oil saturation state; —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of crude oil in the macropores of the primary oil saturation state; —The sum of the corresponding amplitude values ​​of the transverse relaxation time of the nuclear magnetic resonance T2 spectrum curve of the crude oil in the core pores of the primary oil saturated state.

5. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: In S3, the permeability and porosity of the core after CO2 displacement are calculated, and the asphaltene content in the reservoir core and the asphaltene content in the driven crude oil are calculated at the completion of the displacement, as follows: R p —Asphaltene content in crude oil displaced by CO2, cm 3 ; T 2pr —Transverse relaxation time of the NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms; T 2pr，i —The i-th transverse relaxation time of the NMR T1-T2 spectrum corresponding to asphaltene in crude oil displaced by CO2, ms; m(T 2pr ) i —The amplitude value corresponding to the i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum curve corresponding to asphaltene in crude oil displaced by CO2; T 2or —Transverse relaxation time of T1-T2 spectrum of nuclear magnetic resonance of crude oil displaced by CO2, ms; T 2or，i —The i-th transverse relaxation time of the nuclear magnetic resonance T1-T2 spectrum of crude oil displaced by CO2, ms; m(T 2or ) i —The amplitude value corresponding to the ith transverse relaxation time of the T1-T2 spectrum curve of the crude oil NMR displaced by CO2; V o —Amount of crude oil displaced by CO2, cm 3 ; S p —Asphaltene content in initial crude oil, %.

6. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: The reservoir porosity in S1 is: Where: V T is the total volume of the rock sample, (cm 3 ); V P is the rock pore volume, (cm 3 ); V G is the rock skeleton volume, (cm 3 ).

7. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: In S1, according to Darcy's formula, the permeability of the reservoir is: Where: K is the permeability, Darcy (μm 2 ); Q is the volume flow rate of the liquid, cm 3 / s; ΔP is the pressure difference at both ends of the rock sample, 10 5 pa; μ is the viscosity of the liquid, centipoise (0.001Pa·s); A is the cross-sectional area of ​​the rock sample, cm 2 ; L is the length of the rock sample, cm.

8. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: When the crude oil was saturated once in S2, the reservoir core after vacuum was pressurized and saturated at a constant pressure of 20 MPa at the formation temperature for 48 h.

9. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: The displacement process in S3 is: The reservoir core is placed in a holder, and when CO2 gas is injected, the outlet valve of the holder is opened to collect the outflowing crude oil, and the asphaltene content in the crude oil is analyzed. When the outlet end no longer produces oil, the displacement is completed.

10. The asphaltene deposition damage evaluation method based on nuclear magnetic resonance according to claim 1, characterized in that: In S1, the porosity was measured using the liquid saturation displacement method and the liquid saturation method; In case of plug rock samples, the porosity is measured by measuring the skeleton volume and pore volume respectively using the helium method.

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