A method for calculating the porosity of shale gas reservoirs based on the nickel element content

Abstract

The present invention provides a method for calculating the porosity of a shale gas reservoir based on the nickel element content. The porosity calculation method includes: calculating the total organic carbon content according to the nickel element analyzed by element logging; calculating the porosity of the shale gas reservoir according to the total organic carbon content. The calculation error of the porosity calculation method meets the production requirements, the trend is generally consistent, the error is reduced by about 10% compared with the prior art, and the calculation accuracy of the porosity of the Longyi-1 3 and Longyi-1 4 sub-layers is greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of oil and gas exploration and development, and relates to a method for calculating the porosity of shale gas reservoirs based on the nickel element content. Background Art

[0002] The porosity used in the mud logging industry mainly comes from three ways: core laboratory analysis, nuclear magnetic resonance mud logging, and logging porosity. Among them, core laboratory analysis and nuclear magnetic resonance mud logging for obtaining rock porosity require drilling to take cores. However, cores are not taken in shale gas development wells, so the shale gas reservoir development wells cannot obtain porosity through core laboratory analysis and nuclear magnetic resonance mud logging. In addition, due to factors such as cost and engineering complexity, shale gas development wells without logging in the horizontal section cannot obtain porosity data either. At present, there are no relevant cases in the mud logging industry for calculating the porosity of shale gas reservoirs using nickel elements. The present invention provides a method for calculating the porosity of shale gas reservoirs.

[0003] In the prior art, there are no relevant technical solutions for calculating reservoir porosity using nickel elements, but there are 4 technical solutions regarding element logging and porosity. One is a method, model establishment, device, and electronic equipment for evaluating reservoir while drilling in mud logging. Another is a method for calculating the porosity of dissolution reservoirs by mud logging. The third is a method for evaluating the pore permeability of rock formations while drilling in mud logging operations. The fourth is a method for calculating the porosity of shale gas reservoirs using element logging. The technical solution of the method, model establishment, device, and electronic equipment for evaluating reservoir while drilling in mud logging calculates reservoir porosity by fitting elements such as silicon, calcium, iron, and sulfur. This method lacks a theoretical basis and has poor applicability. The technical solution of a method for calculating the porosity of dissolution reservoirs by mud logging calculates the rock bulk density using elements such as Mg, Al, Ca, Si, K, Fe, S, and Ti, and then calculates the porosity according to the rock bulk density and the logging density porosity calculation model. The intermediate parameter, the rock bulk density, in this method is calculated by fitting the main elements, with low accuracy and poor applicability, greatly reducing the accuracy of rock porosity calculation. The technical solution of a method for evaluating the pore permeability of rock formations while drilling in mud logging operations calculates the pore permeability index of shale gas reservoirs using magnesium and sulfur elements. This index is a relative physical property evaluation parameter and cannot be directly compared with the quantitative evaluation parameter, porosity. The technical solution of a method for calculating the porosity of shale gas reservoirs using element logging calculates the porosity of shale reservoirs using minerals inverted by element logging. This method has good applicability in the Longyi 1 1 and Longyi 1 2 sub-layers of the Longmaxi Formation, but in the Longyi 1 3 and Longyi 1 4There is a large error between the sub-layer and the logging porosity, and the applicability is poor. At the same time, since there is no core data for shale gas horizontal wells, due to cost savings or engineering factors, some horizontal wells are not logged, and physical property parameters such as logging porosity cannot be obtained, and logging cannot accurately evaluate parameters such as "physical properties" and "rock mechanics" of shale gas reservoirs. Summary of the Invention

[0004] To solve the technical problems existing in the prior art, the present invention provides a method for calculating the porosity of a shale gas reservoir based on the nickel element content. The calculation error of the porosity calculation method meets the production requirements, the trend is generally consistent, and the error is reduced by about 10% compared with the prior art, and the calculation accuracy of the porosity of the Longyi-1 3 、 Longyi-1 4 sub-layer is greatly improved.

[0005] To achieve the above technical effects, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for calculating the porosity of a shale gas reservoir based on the nickel element content, and the porosity calculation method includes:

[0007] Calculating the total organic carbon content according to the nickel element analyzed by element logging;

[0008] Calculating the porosity of the shale gas reservoir according to the total organic carbon content.

[0009] In the present invention, under normal compaction conditions, the shale porosity gradually decreases with the increase of the vertical depth, and the initial porosity of the shale surface is about 0.386%. Therefore, the shale porosity is very low. Due to the influence of the compaction effect, the porosity of the shale gas reservoir is mainly affected by the vertical depth, mineral composition, and total organic carbon content (TOC), among which the total organic carbon content (TOC) has the greatest influence, and the nickel element content has a strong positive correlation with the total organic carbon content (TOC). Therefore, the present invention uses the nickel element content analyzed by element logging to calculate the porosity of the shale gas reservoir.

[0010] As a preferred technical solution of the present invention, the formula for calculating the total organic carbon content is as follows:

[0011] TOC el = d×(a×ln(c×(ω Ni - ω Ni-B ))+b) Formula 1

[0012] Wherein, TOC el is the TOC calculated by element logging, with the unit of %; d is the TOC el adjustment coefficient, dimensionless; a is the fitting coefficient, dimensionless; c is the nickel element adjustment coefficient, dimensionless; b is a constant, dimensionless; ω Ni, ω Ni-B are the mass percentage of nickel element measured by element logging and the base value of the mass percentage of nickel element in this well, with the unit of %.

[0013] As a preferred technical solution of the present invention, when (d × (a × ln(c × (ω Ni - ω Ni-B )) + b)) < 0: TOC el = 0.

[0014] As a preferred technical solution of the present invention, the value of the fitting coefficient a includes 2.1228.

[0015] As a preferred technical solution of the present invention, the value of the constant b includes 14.4470.

[0016] As a preferred technical solution of the present invention, the formula for calculating the porosity of the shale gas reservoir is shown as follows:

[0017] φ el = a × POWER(TOC el , n) Formula 2

[0018] φ el = POWER(d × (a × ln(c × (ω N i - ω Ni-B )) + b), n) Formula 3

[0019] Among them, φ el is the porosity calculated by element logging, with the unit of %; n is the power exponent.

[0020] In the present invention, the main function of the POWER function is to return the power of a given number. The syntax of the POWER function is: POWER(number, power), where the parameter number represents the base number; the parameter power represents the exponent.

[0021] As a preferred technical solution of the present invention, when (d × (a × ln(c × (ω Ni - ω Ni-B )) + b)) < 0: φ el = 0.

[0022] As a preferred technical solution of the present invention, the value of the power exponent n includes 1.2.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects:

[0024] The present invention provides a method for calculating the porosity of a shale gas reservoir based on the nickel element content. The calculation error of the porosity calculation method meets the production requirements, and the overall trend is consistent. Compared with the existing technology, the error is reduced by about 10%, and the calculation accuracy of the porosity of the Longyi-1 3 、 Longyi-1 4 sub-layer in the Sichuan Basin is greatly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a porosity comparison chart of Well C in Example 1 of the present invention.

[0026] The present invention will be further described in detail below. However, the following examples are only simple examples of the present invention and do not represent or limit the scope of the protection of the present invention. The scope of protection of the present invention shall be subject to the claims. DETAILED DESCRIPTION OF THE INVENTION

[0027] To better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the typical but non-limiting embodiments of the present invention are as follows:

[0028] Embodiment

[0029] This embodiment provides a method for calculating the porosity of a shale gas reservoir based on the nickel element content. Taking a shale gas horizontal well in the Luzhou area of the Sichuan Basin as an example, the porosity calculation method includes:

[0030] (1) Calculate the total organic carbon content (TOC) according to the nickel element analyzed by elemental logging;

[0031] The formula for calculating the total organic carbon content is shown in Equation 1:

[0032] TOC el = d × (a × ln(c × (ω Ni - ω Ni-B )) + b) Equation 1

[0033] In the well section with a depth of 3850 - 5968 m in this well, 1067 samples were measured and analyzed by elemental logging. Among them, ω Ni-B is 0.006%, a = 2.1228, b = 14.4470, c = 1, d = 0.9. Taking the well depth points of 3950 m, 4420 m, and 4648 m as examples, at 3950 m: the nickel content is 0.0151%, at 4420 m: the nickel content is 0.0156%, and at 4648 m the nickel content is 0.0159%;

[0034] At 3950 m: TOC el = 0.9 × (2.1228 × ln(1 × (0.0151 - 0.006)) + 14.4470) = 4.02%;

[0035] 4420m: TOC el = 0.9×(2.1228×ln(1×(0.0156 - 0.006)) + 14.4470) = 4.13%;

[0036] 4648m: TOC el = 0.9×(2.1228×ln(1×(0.0159 - 0.006)) + 14.4470) = 4.18%;

[0037] (2) Calculate the porosity of the shale gas reservoir according to the total organic carbon content:

[0038] The formulas for calculating the porosity of the shale gas reservoir are shown in Formulas 2 and 3:

[0039] φ el = a×POWER(TOC el , n) Formula 2

[0040] φ el = POWER(d×(a×ln(c×(ω N i - ω Ni-B )), n) Formula 3

[0041] 3950m: φ el = POWER(4.02, 1.2) = 5.32%;

[0042] 4420m: φ el = POWER(4.13, 1.2) = 5.48%;

[0043] 4648m: φ el = POWER(4.18, 1.2) = 5.57%.

[0044] In this embodiment, at the well depths of 3950m, 4420m, and 4648m, the logging porosities (see Table 1) are 5.80%, 5.23%, and 5.30% respectively, and the errors between the porosities calculated by element logging and the logging porosities are -8.26%, 4.70%, and 5.03% respectively.

[0045] Comparative Example

[0046] Adopt the method for calculating the porosity of the shale gas reservoir using element logging disclosed in CN116066064A to calculate the porosity in the well section of Well C with a depth of 3850 - 5968m.

[0047] Some calculation results of the embodiment and the comparative example are as Figure 1 shown in Table 1.

[0048] From Figure 1 As can be seen from Table 1, taking Well C, a horizontal shale gas well in the Luzhou area of the Sichuan Basin, as an example, within the well section of 3850m to 5968m, there are 1067 elemental analysis samples. The minimum value of the elemental calculated porosity is 0.14%, the maximum value is 7.86%, and the average value is 5.52%. The minimum value of the logging porosity corresponding to the well depth of the elemental analysis is 2.97%, the maximum value is 7.19%, and the average value is 5.14%. Comparing the elemental logging calculated porosity with the logging porosity, the maximum positive error is 144.49%, the average is 18.89%, the minimum negative error is -96.80%, the average is -17.02%, and the overall error is basically within the range of ±19%. Compared with the comparative example, the error of the example is reduced by about 10%, greatly improving the porosity calculation accuracy of the Longyi 1 3 、 Longyi 1 4 sub-layer in the Sichuan Basin.

[0049] Table 1

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[0055]

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[0058]

[0059] The applicant declares that the present invention illustrates the detailed structural features of the present invention through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of the components selected by the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0060] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0061] In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without conflict. To avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0062] Furthermore, any combinations can be made among the various different embodiments of the present invention, as long as they do not violate the idea of the present invention, and they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for calculating the porosity of a shale gas reservoir based on the nickel element content, characterized in that The porosity calculation method includes: Calculating the total organic carbon content based on the nickel element analyzed by elemental logging; The formula for calculating the total organic carbon content is shown as follows: TOC el = d×(a×ln(c×(ω Ni - ω Ni-B ))+b) Equation 1 Among them, TOC el is the TOC calculated by elemental logging, with the unit of %; d is the TOC el adjustment coefficient, dimensionless; a is the fitting coefficient, dimensionless; c is the nickel element adjustment coefficient, dimensionless; b is a constant, dimensionless; ω Ni and ω Ni-B are the mass percentages of nickel element content measured by elemental logging and the base value of nickel element mass percentage content in this well, respectively, with the unit of %. Calculating the porosity of the shale gas reservoir based on the total organic carbon content; The formula for calculating the porosity of the shale gas reservoir is shown as follows: φ el = POWER(d × (a × ln(c × (ω N i - ω Ni-B )) + b), n) Equation 3 Among them, φ el is the porosity calculated by element logging, with the unit of %; n is the power exponent, and n = 1.2; The function of the POWER function is to return the power of a given number. The syntax of the POWER function is: POWER(number, power), where the parameter number represents the base number; the parameter power represents the exponent.

2. The porosity calculation method according to claim 1, characterized in that, When (d × (a × ln(c × (ω Ni - ω Ni-B )) + b)) < 0: TOC el = 0。 3. The porosity calculation method according to claim 1, characterized in that, The value of the fitting coefficient a includes 2.1228.

4. The porosity calculation method according to claim 1, characterized in that, The value of the constant b includes 14.4470.

5. The porosity calculation method according to claim 1, characterized in that When (d × (a × ln(c × (ω Ni - ω Ni-B )) + b)) < 0: φ el = 0.

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