Compact sandstone permeability calculation method based on saturated nuclear magnetic resonance experiment

Abstract

The invention belongs to the technical field of oil and gas reservoir evaluation, development and research, and discloses a compact sandstone permeability calculation method based on a saturated nuclear magnetic resonance experiment, which comprises the following steps: carrying out a permeability determination experiment on a compact sandstone sample to obtain a sample permeability value, and recording the sample permeability value as KEm; carrying out a saturated nuclear magnetic resonance experiment on the compact sandstone sample to obtain a nuclear magnetic resonance T2 spectrum curve; logarithms of the nuclear magnetic resonance T2 spectrum and the porosity component # imgabs0 # are taken, a # imgabs1 # intersection curve is constructed, and inflection points of the curve are marked as T2-1 and T2-2 respectively; taking T2-1 and T2-2 as independent variables and KEm as a dependent variable, and establishing a compact sandstone permeability calculation model based on a saturated nuclear magnetic resonance experiment; recording a permeability value calculated by the permeability calculation model as KCal, establishing a KCal-KEm linear relation, and judging the effectiveness of the model according to the correlation coefficient of the KCal and the KEm. According to the method, accurate calculation of the permeability of the tight sandstone reservoir can be realized only by carrying out a saturated nuclear magnetic resonance experiment, and the method has the advantages of being economical, simple, efficient and high in practicability.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas reservoir evaluation and development research, and specifically relates to a method for calculating the permeability of dense sandstone based on a saturated nuclear magnetic resonance experiment. Background Art

[0002] Permeability controls the migration and accumulation of oil and gas in tight sandstone reservoirs and is a key parameter for reservoir evaluation. Accurately obtaining the permeability of tight sandstone reservoirs is of great significance for the formulation of oil and gas field development plans. However, due to the complex structure and diagenetic evolution during the formation of tight sandstone reservoirs, the microscopic pore structure of tight sandstone reservoirs is very complex, which greatly increases the difficulty of permeability calculation.

[0003] Domestic and foreign scholars have conducted a lot of research on reservoir permeability calculation. The porosity and permeability correlation analysis method is the most commonly used method for calculating permeability. This method calculates permeability by establishing a mathematical relationship between porosity and permeability. However, the method is mainly applicable to conventional sandstone reservoirs with high porosity and medium-high permeability, and has poor applicability to medium-low porosity and ultra-low permeability tight sandstone reservoirs.

[0004] The invention patent with the authorization announcement number CN 107917865 B provides a method for predicting the multi-parameter permeability of tight sandstone reservoirs. This invention patent establishes a multi-parameter permeability comprehensive prediction model based on seismic / well logging constraints by determining the main geological control factors of the permeability of various tight sandstone reservoirs. This method can accurately predict the permeability of tight sandstone reservoirs in single wells and planes, but lacks the accurate calculation of the micro-scale permeability of the reservoir.

[0005] The invention patent with the authorization announcement number CN 103279647 B provides a method for calculating the permeability of tight sandstone reservoirs based on pore characteristic parameters. The invention patent calibrates the high-pressure mercury injection capillary pressure curve through nuclear magnetic resonance logging data, and can obtain a pseudo capillary pressure curve to calculate the reservoir permeability. However, due to the complex microscopic pore structure and poor connectivity of tight sandstone reservoir samples, it is difficult to accurately determine the conversion coefficient between the nuclear magnetic resonance T2 spectrum curve and the high-pressure mercury injection capillary pressure curve, so the accuracy of the permeability calculation method provided by the invention patent is difficult to guarantee.

[0006] Nuclear magnetic resonance technology is widely used in the characterization of pore structure of unconventional oil and gas reservoirs due to its rapid, non-destructive, simple and convenient operation. Reservoir permeability can be calculated by nuclear magnetic resonance technology, among which the SDR model is the most commonly used permeability calculation model, which can be expressed by the following formula:

[0007] Log(K)=ALog(φ)+B Log(FFI / BVI)+C (1)

[0008] Where K is permeability, mD; φ is porosity, %; FFI / BVI is the ratio of free water to bound water saturation by nuclear magnetic resonance. A and B are the fitting parameters of the multivariate linear regression equation, dimensionless; C is a constant.

[0009] The invention patent with the authorization announcement number CN 109932297 B provides "A method for calculating the permeability of tight sandstone reservoirs", which establishes a permeability logging interpretation model based on the three pore components of the nuclear magnetic resonance T2 spectrum; the invention patent with the authorization announcement number CN 109932297 B provides "A method for calculating the permeability of tight sandstone based on nuclear magnetic resonance double cutoff values", which establishes a permeability model based on nuclear magnetic resonance double cutoff values ​​by studying the relationship between absolute movable water / absolute immovable water content and permeability. However, the above permeability calculation methods based on nuclear magnetic resonance experiments all rely on the calculation of the T2 cutoff value, and the T2 cutoff value cannot be accurately obtained at present, resulting in unavoidable permeability calculation errors. Summary of the invention

[0010] The purpose of the present invention is to provide a method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiments, so as to solve the problem of insufficient calculation accuracy of traditional methods.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is:

[0012] A method for calculating the permeability of tight sandstone based on saturated nuclear magnetic resonance experiments comprises the following steps:

[0013] (1) Perform a permeability test on a dense sandstone sample to obtain the sample permeability value, denoted as K Em ;

[0014] (2) Perform saturation NMR experiments on dense sandstone samples to obtain NMR T2 spectrum curves;

[0015] (3) NMR T2 spectrum and porosity component Take the logarithm and construct The intersection curve, the inflection point of the curve is denoted as T 2-1 and T 2-2 ;

[0016] (4) T 2-1 and T 2-2 As the independent variable, K Em As the dependent variable, a calculation model for the permeability of tight sandstone based on saturated NMR experiments was established;

[0017] (5) The permeability value calculated by the permeability calculation model is denoted as K Cal , establish K Cal -K EmThe linear relationship between the two is used to judge the effectiveness of the model.

[0018] Furthermore, for the same dense sandstone sample, the permeability measurement experiment in step (1) and the saturation nuclear magnetic resonance experiment in step (2) are carried out in sequence.

[0019] Furthermore, in step (1) and step (2), the dense sandstone sample is a core column with a length of 5 cm and a diameter of 2.5 cm.

[0020] Furthermore, in step (1), the dense sandstone sample needs to be pretreated, and the pretreatment items include washing oil, washing salt and drying the sample.

[0021] Furthermore, in step (1), the tight sandstone sample permeability determination experiment and the sample pretreatment before the experiment, the specific operation process is carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T5336-2006 "Core Analysis Method" of the People's Republic of China.

[0022] Furthermore, in step (2), a saturated nuclear magnetic resonance experiment is performed on the dense sandstone sample that has completed the permeability measurement experiment. The specific operation process is carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T6490-2014 "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples".

[0023] Furthermore, in step (3), the inflection point T is determined 2-1 and T 2-2 The specific operation method is: NMR T2 spectrum and porosity component Take the logarithm and record it as logT2 and Establish logT2 and The quadratic equation of two variables is expressed by formula (1):

[0024]

[0025] In formula (1), T2 is the saturation NMR T2 spectrum, ms; is the NMR pore volume component, %; A and B are the coefficients of the quadratic equation, dimensionless; C is a constant.

[0026] The T2 value corresponding to the inflection point of the intersection curve is T 2-1 and T 2-2 .

[0027] Furthermore, in step (3), logT2 and The method for determining the inflection point of the intersection curve is: taking the derivative of the quadratic equation described in formula (1), and the point where the derivative is equal to zero is the inflection point.

[0028] Furthermore, in step (4), the tight sandstone permeability calculation model based on saturation nuclear magnetic resonance experiment can be expressed by formula (2):

[0029] LogK Cal =ALogT 2-1 +BLogT 2-2 +C (2)

[0030] In formula (2), T 2-1 and T 2-2 They are T2 value corresponding to the two inflection points of the intersection curve, ms; K Cal is the permeability value calculated by the tight sandstone permeability calculation model, mD; A and B are coefficients, dimensionless; C is a constant.

[0031] Furthermore, in step (5), judging the validity of the model by the size of the correlation coefficient between the two specifically means that only when K Cal With K Em Correlation coefficient R 2 When ≥0.90, the tight sandstone permeability calculation model provided by formula (2) is considered to be valid.

[0032] The beneficial effects of the present invention are as follows: compared with the traditional method for calculating the permeability of tight sandstone based on nuclear magnetic resonance experiments, the present method does not require centrifugation experiments on samples, does not require obtaining T2 cutoff values, and only requires conducting saturated nuclear magnetic resonance experiments to achieve accurate calculation of the permeability of tight sandstone reservoirs. The method has the advantages of being economical, simple, efficient, and highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments:

[0034] Figure 1 :pass The inflection point of the intersection curve determines T 2-1 and T 2-2 ;

[0035] Figure 2 :K Em -T 2-1 Intersection diagram;

[0036] Figure 3 :K Em -T 2-2 Intersection diagram;

[0037] Figure 4 :K Cal -K Em Intersection diagram. DETAILED DESCRIPTION

[0038] In order to make the technical means and objectives adopted by the present invention easy to understand, the present invention is further described below in conjunction with specific implementation methods.

[0039] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0040] Reference Figure 1-Figure 4 , this specific implementation adopts the following technical solution: a method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment, comprising the following steps:

[0041] (1) Perform a permeability test on a dense sandstone sample to obtain the sample permeability value, denoted as K Em

[0042] The dense sandstone samples used in the examples of the present invention are natural cores taken from the Linan 6 well in the Lishu fault depression in the southern Songliao Basin, with a total of 20 samples;

[0043] The cores were drilled using a deep hole drilling machine and the dense sandstone samples were made into core columns;

[0044] The core column length is 5 cm and the diameter is 2.5 cm;

[0045] Use a core cutter to cut the cross section flat;

[0046] Before the permeability determination experiment, the dense sandstone samples need to be pretreated;

[0047] Pretreatment items include washing away residual oil and residual salt in the sample and drying the sample;

[0048] The specific operation process of the core pretreatment project shall be carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T5336-2006 "Core Analysis Method" of the People's Republic of China.

[0049] The pretreatment before the experiment was carried out as follows:

[0050] First, the core column is placed in a high-temperature and high-pressure oil washer, and the residual oil and mud in the core are washed away with an organic solvent;

[0051] Then put the oil-washed core column into a crucible, repeatedly add distilled water and boil it to wash away the residual salt in the core column;

[0052] Finally, the washed core column is placed in an oven and the temperature is raised to 100°C to remove the water in the core column;

[0053] The permeability test of tight sandstone samples and the pre-experimental sample pretreatment are carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T5336-2006 "Core Analysis Method" of the People's Republic of China.

[0054] (2) Perform saturated NMR experiments on dense sandstone samples to obtain NMR T2 spectrum curves

[0055] A saturated nuclear magnetic resonance experiment was carried out on the dense sandstone samples that had completed the permeability measurement experiment. The specific operation process was carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T6490-2014 "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples" of the People's Republic of China.

[0056] (3) NMR T2 spectrum and porosity component Take the logarithm and construct The intersection curve, the inflection point of the curve is denoted as T 2-1 and T 2-2

[0057] Take the sample No. 6-16 of Li Nan as an example. Figure 1 Shown The intersection curve has obvious segmented characteristics and can be divided into two segments. Each segment has an inflection point, which are recorded as inflection point 1 and inflection point 2.

[0058] Fitting the two curves with quadratic equations can be expressed by formula (3) and formula (4) respectively:

[0059]

[0060]

[0061] Derivatives of formula (3) and formula (4) are:

[0062]

[0063]

[0064] make and is zero, then: logT 2-1 =0.1128,logT 2-2 =1.7468;

[0065] Further: T 2-1 =10 0.1128 =1.30ms, T 2-2 =10 1.7468 =55.82ms

[0066] (4) T 2-1 and T 2-2 As the independent variable, K Em As the dependent variable, a tight sandstone permeability calculation model based on saturated NMR experiments was established.

[0067] As shown in Table 1, all 20 dense sandstone samples K Em , T 2-1 and T 2-2 Statistical results:

[0068] Table 1

[0069]

[0070]

[0071] like Figure 2 and Figure 3 As shown, T 2-1 and T 2-2 Both and K Em Has a good power function relationship, correlation coefficient R 2 They are 0.8976 and 0.8287 respectively, which indicates that T 2-1 and T 2-2 Establish a tight sandstone permeability model;

[0072] Therefore, T 2-1 and T 2-2 As the independent variable, K Em As the dependent variable, a calculation model for the permeability of tight sandstone is established, which can be expressed by formula (5):

[0073] LogK Cal =0.9239LogT 2-1 +3.8655LogT 2-2 -7.6350 (5)

[0074] (5) The permeability value calculated by the permeability calculation model is denoted as K Cal , establish K Cal -K Em The linear relationship between the two is used to judge the effectiveness of the model.

[0075] like Figure 4 As shown, K Cal and K Em Has a good linear relationship, the correlation coefficient R 2 The error analysis statistical results show that the average absolute error is only 6.09%, which proves the effectiveness of the method.

[0076] Although some embodiments of the present invention have been given herein, those skilled in the art should understand that the embodiments of the present invention may be modified without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as a limitation on the scope of the present invention.

Claims

1. A method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiments, characterized in that: The following steps are involved: (1) Perform a permeability test on a dense sandstone sample to obtain the sample permeability value, denoted as K Em ; (2) Perform saturation NMR experiments on dense sandstone samples to obtain NMR T2 spectrum curves; (3) Take the logarithm of the NMR T2 spectrum and the porosity component φ to construct the LogT2-Logφ intersection curve. The inflection points of the curve are denoted as T 2-1 and T 2-2 ; (4) T 2-1 and T 2-2 As the independent variable, K Em As the dependent variable, a calculation model for the permeability of tight sandstone based on saturated NMR experiments was established; (5) The permeability value calculated by the permeability calculation model is denoted as K Cal , establish K Cal -K Em The linear relationship between the two is used to judge the effectiveness of the model.

2. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1 is characterized in that: For the same dense sandstone sample, the permeability measurement experiment in step (1) and the saturation nuclear magnetic resonance experiment in step (2) are carried out in sequence.

3. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1 is characterized in that: In step (1) and step (2), the dense sandstone sample is a core column with a length of 5 cm and a diameter of 2.5 cm.

4. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1 is characterized in that: In step (1), the dense sandstone sample needs to be pretreated, and the pretreatment includes washing the oil, washing the salt and drying the sample.

5. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 4 is characterized in that: In step (1), the permeability measurement of the dense sandstone sample and the pretreatment of the dense sandstone sample are carried out in accordance with the provisions of the petroleum and natural gas industry standard SY / T5336-2006 "Core Analysis Method" of the People's Republic of China.

6. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1, characterized in that: In step (2), the specific operation process of the saturation nuclear magnetic resonance experiment is carried out in accordance with the provisions of the Petroleum and Natural Gas Industry Standard SY / T6490-2014 "Laboratory Measurement Specifications for Nuclear Magnetic Resonance Parameters of Rock Samples".

7. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1, characterized in that: In step (3), determine the inflection point T 2-1 and T 2-2 The specific operation method is: take the logarithm of the nuclear magnetic resonance T2 spectrum and the porosity component φ, record them as logT2 and logφ respectively, and establish a two-variable first-order equation of logT2 and logφ, which is expressed by formula (1): logφ=A(logT2) 2 +B(logT2)+C (1) In formula (1), T2 is the saturated NMR T2 spectrum, ms; φ is the NMR pore volume component, %; A and B are the coefficients of a quadratic equation, dimensionless; and C is a constant. The T2 value corresponding to the inflection point of the logT2-logφ intersection curve is T 2-1 and T 2-2 .

8. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1, characterized in that: In step (3), the method for determining the inflection point of the intersection curve of logT2 and logφ is: taking the derivative of the quadratic equation described in formula (1), and the point where the derivative is equal to zero is the inflection point.

9. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1, characterized in that: In step (4), the tight sandstone permeability calculation model based on saturation nuclear magnetic resonance experiment can be expressed by formula (2): LogK Cal =ALogT 2-1 +BLogT 2-2 +C (2) In formula (2), T 2-1 and T 2-2 are the T2 values ​​corresponding to the two inflection points of the logT2-logφ intersection curve, ms; K Cal is the permeability value calculated by the tight sandstone permeability calculation model, mD; A and B are coefficients, dimensionless; C is a constant.

10. The method for calculating the permeability of dense sandstone based on saturation nuclear magnetic resonance experiment according to claim 1, characterized in that: In step (5), judging the validity of the model by the correlation coefficient between the two specifically means that only when K Cal With K Em Correlation coefficient R 2 When ≥0.90, the tight sandstone permeability calculation model provided by formula (2) is considered to be valid.

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