A method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiments

Abstract

The present invention belongs to the field of tight gas reservoir evaluation research and discloses a method for calculating the permeability of tight sandstone based on a constant-rate mercury injection test. The method comprises the following steps: (1) performing a constant-rate mercury injection test and a permeability test on a tight sandstone sample to obtain a total mercury injection volume curve, a pore mercury injection curve, a throat mercury injection curve, and a permeability value K of the tight sandstone sample. m (2) According to the constant-rate mercury injection pore mercury injection curve, it is divided into the intergranular pore main control interval and the intragranular pore main control interval, and the proportion of the intergranular pore main control interval P is calculated. inter (3) Calculate the average throat radius r based on the constant-rate mercury injection throat mercury data t ; (4) P inter and r t As the independent variable, K m As the dependent variable, K is established through multivariate linear fitting m Calculation model. The pore parameters and throat parameters are simultaneously introduced into the permeability calculation model, that is, the main controlling interval ratio of intergranular pores related to pores P inter and the average throat radius r associated with the throat t , achieving accurate calculation of tight sandstone permeability.

Description

Technical Field

[0001] The present invention belongs to the field of tight gas reservoir evaluation research, and particularly relates to a method for calculating the permeability of tight sandstone based on a constant-rate mercury injection experiment. Background Art

[0002] Permeability is a key parameter for evaluating tight sandstone reservoirs. Accurate calculation of permeability is of great guiding significance for evaluating tight gas sweet spots and formulating scientific development policies.

[0003] Traditional methods for calculating tight sandstone permeability mainly rely on high-pressure mercury injection tests and nuclear magnetic resonance experiments, including the Coates model, the SDR (Schlumberger-Doll Laboratory) model, and the Pittman model, which can be expressed as follows:

[0004] Log(K)=A+B Log(φ)+C Log(f) (1)

[0005] Where K represents permeability, φ represents porosity, and f is a variable. The f in Coates model, SDR model, and Pittman model are FFI / BVI (ratio of free water saturation to bound water saturation by nuclear magnetic resonance), geometric mean of nuclear magnetic T2 spectrum, and r i (Pore throat radius corresponding to mercury saturation i%). A, B, and C are the parameters of the multivariate linear regression equation.

[0006] Traditional methods have the following shortcomings:

[0007] 1. The traditional method for calculating the permeability of tight sandstone has poor application effect. The pore structure of tight sandstone is very complex, and the strong heterogeneity leads to no obvious correlation between porosity φ and permeability K, resulting in low accuracy of the permeability calculation of tight sandstone using formula (1).

[0008] 2. Since porosity is not suitable for calculating the permeability of tight sandstone, the permeability calculation in formula (1) depends only on the variable f. However, there are many factors that affect the permeability of tight sandstone. Therefore, the application effect of using traditional methods to calculate the permeability of tight sandstone is very poor.

[0009] 3. The traditional method of calculating permeability does not fully consider the main controlling factors of tight sandstone permeability.

[0010] The research of Xiao Dianshi (Xiao Dianshi, Lu Shuangfang, Jiang Weiwei, et al. Classification of tight sandstone reservoirs based on the contribution of intergranular pores - taking the Xujiaweizi fault depression as an example [J]. Acta Petrolei Sinica, 2017, 38(10):12.) shows that the pores of tight sandstone can be divided into two categories, namely intergranular pores and intragranular pores, among which the intergranular pore content controls the permeability.

[0011] Wang (Characterization of the pore-throat size of tight oil reservoirs and its control on reservoir physical properties: A case study of the Triassic tight sandstone of the sediment gravity flow in the Ordos Basin, China [J]. Journal of Petroleum Science & Engineering, 2020, 186.) showed that the permeability of tight sandstone is highly correlated with the throat radius (correlation coefficient R 2 =0.9899), but has no obvious correlation with pore radius (R 2 =0.1889), which shows that the permeability of tight sandstone is not only related to the pore type, but also controlled by the throat radius.

[0012] The Coates model and the SDR (Schlumberger-Doll) model in the traditional method are based on nuclear magnetic resonance experiments, and the variables f are FFI / BVI and T 2g , these two parameters are related to the pore volume of tight sandstone. The Pittman model relies on high-pressure mercury injection experiments. The variable f is the pore throat radius corresponding to mercury injection saturation i%, and it does not distinguish between pore radius and throat radius. All three traditional methods consider only a single factor affecting the permeability of tight sandstone, failing to fully account for the primary controlling factors of tight sandstone permeability.

[0013] In order to overcome the shortcomings of traditional methods and improve the calculation accuracy of permeability of tight sandstone reservoirs, it is necessary to conduct in-depth research on the seepage laws of tight sandstone reservoirs, clarify the main controlling factors of tight sandstone permeability, and on this basis improve the traditional methods and propose a new method for calculating the permeability of tight sandstone reservoirs to meet the needs of fine characterization of tight reservoir permeability. Summary of the Invention

[0014] The purpose of the present invention is to provide a method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiments, so as to solve the problem of insufficient calculation accuracy of traditional methods.

[0015] To achieve the above object, the technical solution adopted by the present invention is:

[0016] A method for calculating the permeability of tight sandstone based on a constant-rate mercury injection experiment comprises the following steps:

[0017] (1) Constant-rate mercury injection experiments and permeability test experiments were conducted on tight sandstone samples to obtain the total mercury injection volume curve, pore mercury injection curve, throat mercury injection curve and permeability value K of tight sandstone samples. m ;

[0018] (2) According to the morphology of the mercury injection curve of constant-rate mercury injection, it is divided into the intergranular pore-dominated interval and the intragranular pore-dominated interval, and the proportion of the intergranular pore-dominated interval P is calculated. inter ;

[0019] (3) Calculate the average throat radius r based on the constant-rate mercury injection throat mercury data t ;

[0020] (4) P inter and r t As the independent variable, K m As the dependent variable, K is established through multivariate linear fitting m Computational model.

[0021] In step (1), the experimental sample is a core column with a length of 2-3 cm and a diameter of 2.5 cm.

[0022] In step (1), a permeability test experiment and a constant-rate mercury injection test are performed on the same sample in succession.

[0023] In step (1), the sample needs to be pretreated before the permeability test, including oil washing, salt washing and drying.

[0024] In step (1), the pretreatment is specifically performed according to the following process and method:

[0025] a. First, place the core column in a high-temperature and high-pressure oil washer and use an organic solvent to wash away the residual oil and mud in the core;

[0026] b. Then place the oil-washed core column into a crucible and repeatedly add distilled water to boil to wash away the residual salt in the core column;

[0027] c. Finally, place the washed core column into an oven and raise the temperature to 100°C to remove the water in the core column.

[0028] In step (1), the permeability test experiment is performed in accordance with the process specified in GB / T 29172-2012 "Core Analysis Method" standard.

[0029] In step (1), the constant rate mercury injection experiment is performed according to the process specified in the Q / SY DQ1526-2012 "Determination of rock capillary pressure curve - constant rate method" standard.

[0030] In step (2), the main control interval ratio P of the intergranular pores is determined based on the percentage of the mercury saturation corresponding to the inflection point of the constant-rate mercury injection curve to the total mercury saturation. inter .

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] Based on the analysis of the main controlling factors of tight sandstone permeability, the pore parameters and throat parameters are simultaneously introduced into the permeability calculation model, that is, the main controlling interval ratio of intergranular pores related to pores P inter and the average throat radius r associated with the throat t , achieving accurate calculation of tight sandstone permeability. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0034] Figure 1 This is a schematic diagram of the calculation of the main control space of intergranular pores;

[0035] Figure 2 Calculate the permeability K for tight sandstone permeability calculation method based on constant-rate mercury injection experiment c Compared with the measured permeability K m Comparison picture.

[0036] Figure 3 Calculate the permeability K for the Pittman model based on high-pressure mercury injection experiments c Compared with the measured permeability K m Comparison picture. Specific implementation methods

[0037] In order to make the technical means adopted by the present invention and the objectives achieved by the present invention easier to understand, the present invention is further described below in conjunction with specific implementation methods.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0039] Example 1

[0040] Reference Figure 1-3 This specific embodiment adopts the following technical solution: a method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment, comprising the following steps:

[0041] (1) Constant-rate mercury injection experiments and permeability test experiments were conducted on tight sandstone samples to obtain the total mercury injection volume curve, pore mercury injection curve, throat mercury injection curve and permeability value K of tight sandstone samples. m

[0042] Drilling cores with a deep hole drilling machine

[0043] The dense sandstone samples were made into core columns with a length of 3 cm and a diameter of 2.5 cm;

[0044] Use a core cutter to cut the cross section flat;

[0045] The tight sandstone samples were pretreated before the experiment;

[0046] Pretreatment before the experiment included oil washing, salt washing and drying;

[0047] The pretreatment before the experiment was carried out as follows:

[0048] 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;

[0049] Then put the oil-washed core column into a crucible and repeatedly add distilled water to boil to wash away the residual salt in the core column;

[0050] 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;

[0051] The treated experimental samples were subjected to permeability test and constant-rate mercury injection test;

[0052] The permeability test instrument model is KSY-overburden porosity tester, and the experiment is carried out in accordance with the process specified in GB / T29172-2012 "Core Analysis Method" standard.

[0053] The constant-rate mercury injection experiment was performed using the ASPE-730 constant-rate mercury injection instrument. The constant-rate mercury injection experiment was performed in accordance with the procedures specified in the Q / SY DQ1526-2012 “Determination of Rock Capillary Pressure Curve - Constant-Rate Method” standard.

[0054] (2) According to the morphology of the mercury injection curve of constant-rate mercury injection, it is divided into the intergranular pore-dominated interval and the intragranular pore-dominated interval, and the proportion of the intergranular pore-dominated interval P is calculated. inter ;

[0055] The total mercury injection curve, pore mercury injection curve and throat mercury injection curve of the constant rate mercury injection experiment of a typical sample are shown in the figure below: Figure 1 As shown;

[0056] According to the morphology of the total mercury intrusion curve, the samples can be divided into two categories, namely pore-dominated type and throat-dominated type;

[0057] The morphology of the total mercury injection curve of the pore-dominated sample is affected by the pore mercury injection curve, which shows that the pore mercury injection amount increases significantly at a lower mercury injection pressure. When the pressure rises to a certain value, the mercury injection in the pore stagnation throat increases significantly ( Figure 1 A);

[0058] The total mercury injection curve of the throat-dominated sample is affected by the throat mercury injection curve, which shows that the mercury injection amount in the throat increases significantly at a lower mercury injection pressure. When the pressure rises to a certain value, the mercury injection in the throat stagnates while the mercury injection in the pores increases significantly ( Figure 1 B);

[0059] Therefore, the pores of tight sandstone samples can be divided into the interval dominated by intergranular pores and the interval dominated by intragranular pores according to the inflection point of the pore mercury injection curve.

[0060] The ratio of the main control interval of intergranular pores to the total pore interval is the main control interval ratio of intergranular pores P. inter ;

[0061] (3) Calculate the average throat radius r based on the constant-rate mercury injection throat mercury data t ;

[0062] Permeability values ​​K and main controlling interval ratio of intergranular pores P of 7 tight sandstone samples inter and the average throat radius r t As shown in Table 1:

[0063]

[0064] (4) P inter and r t As the independent variable, K m As the dependent variable, K is established through multivariate linear fitting m Computational model.

[0065] Based on P inter and r t The permeability calculation model can be expressed as follows:

[0066] Log(K m )=ALog(P inter )+B Log(r t )+C (1)

[0067] Where: K m is the permeability, mD; P inter is the ratio of the main control interval of intergranular pores, %; r t is the average throat radius, um; A and B are dimensionless coefficients, and C is a constant;

[0068] The A, B, and C values ​​calculated by multivariate linear fitting were 1.01, 8.11, and 1.15, respectively;

[0069] The calculation model of tight sandstone permeability can be expressed as:

[0070] Log(K m )=1.01 Log(P inter )+8.11 Log(rt )+1.15 (2)

[0071] like Figure 2 As shown, the permeability k calculated by the new calculation model c and the measured value K m Very close, the correlation coefficient R 2 As high as 0.9755, it proves the accuracy of the new model.

[0072] For comparison, the permeability of seven samples was calculated using the Pittman model based on high-pressure mercury injection experiments.

[0073] Porosity values ​​φ and permeability values ​​K of 7 tight sandstone samples m 、30% mercury saturation corresponds to pore radius r 30 As shown in Table 2:

[0074]

[0075] With Φ and r 30 As the independent variable, K m As the dependent variable, K is established through multivariate linear fitting m Computational model.

[0076] Based on P inter and r t The permeability calculation model can be expressed as follows:

[0077] Log(K m )=ALog(Φ)+B Log(r 30 )+C (1)

[0078] Where: K m is the permeability, mD; Φ is the porosity of the sample, %; r 30 is the pore radius corresponding to 30% mercury saturation in high-pressure mercury injection experiment, μm; A and B are dimensionless coefficients, and C is a constant;

[0079] The A, B, and C values ​​calculated by multivariate linear fitting were -0.1639, 6.45311, and -7.0716, respectively;

[0080] The calculation model of tight sandstone permeability can be expressed as:

[0081] Log(K m )=-0.1639 Log(Φ)+6.45311 Log(r 30 )-7.0716 (2)

[0082] like Figure 3 As shown, the permeability k calculated by the Pittman model cand the measured value K m Correlation coefficient R 2 It is only 0.7316, which further proves the effectiveness of the new model.

[0083] Although some embodiments of the present invention have been described herein, those skilled in the art will appreciate that modifications may be made to the embodiments herein without departing from the spirit of the present invention. The above embodiments are merely exemplary and should not be used as limitations on the scope of the present invention.

Claims

1. A method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment, characterized in that: The following steps are involved: (1) Conduct constant-rate mercury injection experiments and permeability test experiments on tight sandstone samples to obtain the total mercury injection volume curve, pore mercury injection curve, throat mercury injection curve and permeability value K of tight sandstone samples. m ; (2) According to the shape of the mercury injection curve of constant-rate mercury injection, it is divided into the main control interval of intergranular pores and the main control interval of intragranular pores, and the proportion of the main control interval of intergranular pores P is calculated. inter ; (3) Calculate the average throat radius r based on the constant-rate mercury injection throat mercury data t ; (4) P inter and r t As the independent variable, K m As the dependent variable, K is established through multivariate linear fitting m Computational model.

2. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 1, characterized in that: In step (1), the dense sandstone sample is a core column with a length of 2-3 cm and a diameter of 2.5 cm.

3. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 1, characterized in that: In step (1), a permeability test experiment and a constant-rate mercury injection test are performed on the same dense sandstone sample.

4. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 2, characterized in that: In step (1), the dense sandstone sample needs to be pretreated before the permeability test, including washing oil, washing salt and drying.

5. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 4, characterized in that: In step (1), the pretreatment is specifically carried out according to the following process and method: a. First, place the core column in a high-temperature and high-pressure oil washer and use an organic solvent to wash away the residual oil and mud in the core column; b. Then, the core column after oil washing is placed in a crucible and distilled water is repeatedly added to boil to wash away the residual salt in the core column; c. Finally, place the washed core column into an oven and raise the temperature to 100°C to remove the water in the core column.

6. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 1, characterized in that: In step (1), the permeability test experiment is performed in accordance with the process specified in GB / T 29172-2012 "Core Analysis Method" standard.

7. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 1, characterized in that: In step (1), the constant-rate mercury injection experiment is performed according to the process specified in the Q / SY DQ1526-2012 "Determination of rock capillary pressure curve - constant-rate method".

8. The method for calculating the permeability of tight sandstone based on constant-rate mercury injection experiment according to claim 1, characterized in that: In step (2), the main control interval ratio P of the intergranular pores is determined based on the percentage of the mercury saturation corresponding to the inflection point of the constant-rate mercury injection curve to the total mercury saturation. inter .

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