Method for measuring and correcting core porosity of argillaceous loose sandstone reservoir

Abstract

The invention discloses an argillaceous loose sandstone reservoir core porosity measurement and correction method. The method comprises the following steps: (1) measuring the porosity of an argillaceous loose sandstone sample at different drying temperatures; (2) obtaining the shale content of the shale-rich loose sandstone sample through a particle size analysis experiment; (3) establishing a percentage calculation relational expression of porosity increase caused by the increase of the drying temperature; and (IV) establishing a drying temperature correction formula for porosity measurement, and the like. According to the method, the measured value of the porosity of the argillaceous loose sandstone dried at the high temperature is corrected, and the problem that the measured value of the porosity experiment is too large due to the fact that the argillaceous loose sandstone is dried at the high temperature (116 DEG C) in order to pursue aging during porosity measurement is solved.

Description

Technical Field

[0001] The invention belongs to the field of petroleum exploration and development, and in particular relates to a method for measuring and correcting the core porosity of a mud-rich loose sandstone reservoir. Background Art

[0002] Shallow strata (typically less than 1500m deep) experience less diagenesis and compaction, resulting in loose, often argillaceous formations. The industry's standard drying temperature for porosity measurements in cores from these reservoirs is 60°C. However, to maximize experimental timeliness, many researchers use the standard drying temperature for consolidated sandstone (generally 116°C, the international standard). This high temperature, due to the high clay content and loose cementation within the cores, easily destroys the internal clay structure, resulting in an inflated porosity value. This, in turn, affects the accuracy of subsequent core calibration and reserve studies. Currently, a significant amount of porosity data for loose sandstones in laboratories was obtained using 116°C drying. Therefore, a method is needed to convert porosity measurements from high-temperature (116°C) drying experiments for argillaceous loose sandstone reservoirs to those obtained at the standard drying temperature (60°C).

[0003] Currently, when converting porosity values measured at high temperature (116°C) for such reservoirs to values measured at 60°C, a statistical approach is typically used. The average difference between porosity values measured at the two drying temperatures across multiple cores is used as the correction factor. This approach fails to account for potential differences in correction factors due to varying shale types or physical properties, and therefore has significant limitations and cannot effectively guide oil and gas field exploration and development. Summary of the Invention

[0004] The present invention is proposed to solve the problem in the prior art that when measuring the porosity of mud-rich loose sandstone reservoirs in the laboratory, high-temperature drying is used in pursuit of efficient measurement time, resulting in large measured values and reduced accuracy. Its purpose is to provide a core porosity measurement correction method for mud-rich loose sandstone reservoirs.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for measuring and correcting the core porosity of a muddy loose sandstone reservoir comprises the following steps:

[0007] (I) Measure the porosity of muddy loose sandstone samples at different drying temperatures;

[0008] (II) Obtaining the mud content of mud-rich loose sandstone samples through particle size analysis experiments;

[0009] (III) Establish a relationship to calculate the percentage increase in porosity due to an increase in drying temperature;

[0010] (IV) Establish a drying temperature correction formula for porosity measurement.

[0011] In the above technical solution, the specific operation of step (I) is as follows: washing the oil and salt from the mud-rich loose sandstone core sample in the study area, drying it at 60°C, and measuring the porosity using the helium method after drying. After the measurement, the core sample is further dried at 116°C, and the porosity is measured again using the helium method after drying.

[0012] In the above technical solution, the specific operation of step (II) is: performing particle size analysis on the mud-rich loose sandstone core samples in the study area to obtain the volume percentage of mud (here refers to the part with a particle size of less than 8 μm) in the total particle size, and obtaining the formation mud content data by introducing the porosity component.

[0013] In the above technical solution, the formula for calculating the mud content of the formation based on the mud ratio of particle size analysis is:

[0014] V sh =M sh ×(100-P or ) / 100

[0015] Where: V sh is the mud content, %; M sh P is the volume percentage of solid components with particle size less than 8 μm in all solid components, %; or is the porosity of parallel samples at corresponding depths measured by drying at 60°C, %.

[0016] In the above technical solution, the core samples in step (I) and step (II) are parallel samples.

[0017] In the above technical solution, the specific operation of step (III) is: first calculate the percentage increase in porosity due to the increase in drying temperature, then fit the percentage increase in porosity due to the increase in drying temperature with the mud content obtained in step (II), determine the coefficient of the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content, and thus establish the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content.

[0018] In the above technical solution, the calculation formula for the percentage increase in porosity due to the increase in drying temperature is:

[0019] ΔP=100×(Por 116℃ -Por 60℃ ) / Por 60℃

[0020] Where: ΔP is the percentage increase in porosity due to the increase in drying temperature, %; Por 116℃ Porosity measured after drying at 116℃, %; 60℃ The porosity is measured after drying at 60°C, %.

[0021] In the above technical solution, the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content is:

[0022] ΔP=a×V sh b

[0023] Where ΔP is the percentage increase of porosity measured at two drying temperatures, %; V sh is the mud content, %; a and b are the coefficients obtained by fitting the percentage increase of porosity due to the increase of drying temperature with the mud content obtained in step (II).

[0024] In the above technical solution, the drying temperature correction formula for porosity measurement is:

[0025] Por 60℃ =Por 116℃ ×100 / (100+ΔP)

[0026] Where: Por 60℃ 、Por 116℃ The porosity values of the samples dried at 60℃ and 116℃ are measured, %; ΔP is the percentage increase of porosity measured at the two drying temperatures, %.

[0027] The beneficial effects of the present invention are:

[0028] The present invention provides a method for converting porosity experimental measurement values of mud-rich loose sandstone reservoirs using high-temperature (116°C) drying to values measured at a standard drying temperature (60°C). This method enables the porosity values measured in the laboratory using high-temperature drying to be corrected to obtain more realistic porosity values, plays an important role in exploration and development, and has strong versatility. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a flow chart of the method of the present invention;

[0030] Figure 2 1 is a fitted relationship curve diagram of the percentage increase in porosity and the shale content due to the increase in drying temperature in Example 1 of the present invention;

[0031] Figure 3 3 is a fitting relationship curve diagram of the porosity value after correction in Example 1 of the present invention and the porosity measurement value after drying at 60°C.

[0032] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific implementation methods.

[0034] Example 1

[0035] like Figure 1 As shown, a core porosity measurement and correction method for mud-rich loose sandstone reservoir includes the following steps:

[0036] (I) Measurement of the porosity of muddy loose sandstone samples at different drying temperatures

[0037] The core samples of muddy loose sandstone in the study area were washed for oil and salt, then dried at 60°C. After drying, the porosity was measured using the helium method. After the measurement, the core samples were dried at 116°C and the porosity was measured again using the helium method.

[0038] The oil washing, salt washing, drying time and porosity measurement methods of the sandstone cores are all carried out in accordance with the standard "GBT29172-2012-Core Analysis Method".

[0039] (II) Obtaining the mud content of mud-rich loose sandstone samples through particle size analysis experiments

[0040] Grain size analysis was performed on the core samples of mud-rich loose sandstone in the study area to obtain the mud volume percentage data, and the mud content data of the formation was obtained through the mud volume percentage data;

[0041] The particle size analysis method is performed in accordance with the specification "GBT 29172-2012-Core Analysis Method".

[0042] The core samples of step (I) and step (II) are parallel samples;

[0043] In the study area, the components with a particle size of less than 8 μm are considered as mud. Since particle size analysis can only obtain the volume percentage of different solid components, it is also necessary to introduce porosity components to obtain the mud content data of the formation. The formula for calculating the mud content of the formation based on the mud percentage of particle size analysis is:

[0044] V sh =M sh ×(100-P or ) / 100

[0045] Where: Vsh is the mud content, %; M sh P is the volume percentage of solid components with particle size less than 8 μm in all solid components, %; or is the porosity of parallel samples at corresponding depths measured by drying at 60°C, %.

[0046] (III) Establish a relationship to calculate the percentage increase in porosity due to an increase in drying temperature

[0047] First, calculate the percentage increase of porosity due to the increase of drying temperature, and then fit the percentage increase of porosity due to the increase of drying temperature with the mud content obtained in step (II) (e.g. Figure 2 As shown), determine the coefficient of the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content, thereby establishing the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content;

[0048] The calculation formula for the percentage increase in porosity due to the increase in drying temperature is:

[0049] ΔP=100×(Por 116℃ -Por 60℃ ) / Por 60℃

[0050] Where: ΔP is the percentage increase in porosity due to the increase in drying temperature, %; Por 116℃ Porosity measured after drying at 116℃, %; 60℃ is the porosity measured after drying at 60°C, %;

[0051] The relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content is calculated as follows:

[0052] ΔP=0.0046×V sh 2.3872

[0053] Where ΔP is the percentage increase of porosity measured at two drying temperatures, %; V sh is the mud content, %; 0.046 and 2.3872 are the coefficients obtained by fitting the percentage increase of porosity due to the increase of drying temperature with the mud content obtained in step (II).

[0054] (IV) Establishing a drying temperature correction formula for porosity measurement

[0055] The drying temperature correction formula for porosity measurement is used to correct the porosity values measured by samples dried at 116°C, thereby realizing a method for converting the porosity experimental measurement values of mud-rich loose sandstone reservoirs dried at high temperature (116°C) to the measurement values at standard drying temperature (60°C).

[0056] The drying temperature correction formula for the porosity measurement is:

[0057] Por 60℃ =Por 116℃ ×100 / (100+ΔP)

[0058] Where: Por 60℃ 、Por 116℃ The porosity values of the samples dried at 60℃ and 116℃ are measured, %; ΔP is the percentage increase of porosity measured at the two drying temperatures, %.

[0059] Based on the present invention, Figure 3 As shown in the figure, the porosity values of 26 mud-rich loose sandstones in the study area after drying at 116℃ and the porosity values corrected by the method of the present invention are basically distributed on the 45° diagonal line with the values measured after drying at 60℃. The correlation R between the two fittings is 2 As high as 0.9938, it shows that the correction method has high accuracy and the correction amount is reliable.

[0060] This invention can quickly and effectively address the problem of inflated measured values caused by high-temperature drying during early porosity testing of muddy, loose sandstone. It also overcomes the problem of reduced accuracy in laboratory porosity measurements of muddy, loose sandstone reservoirs, often driven by the pursuit of time-efficiency. It plays a vital role in exploration and development, and possesses strong versatility.

[0061] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A method for measuring and correcting the core porosity of a muddy loose sandstone reservoir, characterized by: The following steps are involved: (I) Measure the porosity of muddy loose sandstone samples at different drying temperatures; (II) Obtaining the mud content of mud-rich loose sandstone samples through particle size analysis experiments; (III) Establish a relationship to calculate the percentage increase in porosity due to an increase in drying temperature; (IV) Establish a drying temperature correction formula for porosity measurement.

2. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1 is characterized by: The specific operation of step (I) is as follows: washing the oil and salt from the mud-rich loose sandstone core sample in the study area, drying it at 60°C, measuring the porosity using the helium method after drying, and continuing to dry the core sample at 116°C after measurement, and again measuring the porosity using the helium method after drying.

3. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1 is characterized by: The specific operation of step (II) is: performing particle size analysis on the mud-rich loose sandstone core samples in the study area to obtain the volume percentage of mud in all particle sizes, and obtaining formation mud content data by introducing porosity components.

4. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1, characterized in that: The formula for calculating the mud content of the formation based on the mud ratio of particle size analysis is: V sh =M sh ×(100-P or ) / 100 Where: V sh is the mud content, %; M sh P is the volume percentage of solid components with particle size less than 8 μm in all solid components, %; or is the porosity of parallel samples at corresponding depths measured by drying at 60°C, %.

5. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1, characterized in that: The core samples of step (I) and step (II) are parallel samples.

6. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1, characterized in that: The specific operation of step (III) is: first calculate the percentage increase in porosity due to the increase in drying temperature, then fit the percentage increase in porosity due to the increase in drying temperature with the mud content obtained in step (II), determine the coefficient of the calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content, and thus establish a calculation relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content.

7. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 6, characterized in that: The calculation formula for the percentage increase in porosity due to the increase in drying temperature is: ΔP=100×(By 116℃ -By 60℃ ) / By 60℃ Where: ΔP is the percentage increase in porosity due to the increase in drying temperature, %; Por 116℃ Porosity measured after drying at 116℃, %; 60℃ The porosity is measured after drying at 60°C, %.

8. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 6, characterized in that: The relationship between the percentage increase in porosity due to the increase in drying temperature and the mud content is calculated as follows: ΔP=a×V sh b Where ΔP is the percentage increase of porosity measured at two drying temperatures, %; V sh is the mud content, %; a and b are the coefficients obtained by fitting the percentage increase of porosity due to the increase of drying temperature with the mud content obtained in step (II).

9. The core porosity measurement and correction method for muddy loose sandstone reservoir according to claim 1, characterized in that: The drying temperature correction formula for the porosity measurement is: By 60℃ =By 116℃ ×100 / (100+ΔP) Where: Por 60℃ 、Por 116℃ The porosity values of the samples dried at 60℃ and 116℃ are measured, %; ΔP is the percentage increase of porosity measured at the two drying temperatures, %.

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