A method and system for quantitatively evaluating gas saturation of a tight sandstone reservoir

Abstract

The application discloses a kind of compact sandstone reservoir gas saturation quantitative evaluation method, comprising the following steps: processing nuclear magnetic resonance logging original data, obtain nuclear magnetic resonance logging total porosity;Based on density porosity calculation formula, the apparent density porosity of compact sandstone gas reservoir is calculated;The difference between the apparent density porosity of compact sandstone gas reservoir and nuclear magnetic resonance logging total porosity is obtained;Establish compact sandstone reservoir gas saturation model based on the difference between apparent density porosity and nuclear magnetic resonance logging total porosity.The application can effectively avoid a series of problems such as rock rock-electricity parameter change, low-resistance gas layer is generally developed and the like faced by resistivity method for obtaining compact sandstone gas saturation, improve the calculation accuracy of compact sandstone reservoir gas saturation, and lay a foundation for compact gas reservoir reserves evaluation and efficient production.

Description

Technical Field

[0001] This invention relates to a method and system for quantitatively evaluating the gas saturation of tight sandstone reservoirs using coupled nuclear magnetic resonance and density logging, belonging to the field of oil and gas exploration. Background Technology

[0002] Tight sandstone gas, as an important component of my country's various natural gas reservoirs, boasts more reliable resources, more mature technology, and relatively lower costs compared to unconventional natural gas resources such as coalbed methane and shale gas. Furthermore, the widespread distribution of tight sandstone gas resources in my country can stably support the ever-increasing demand for natural gas production. Therefore, tight sandstone gas will remain a major growth driver for my country's natural gas energy in the foreseeable future.

[0003] Saturation assessment is the core of oil and gas reservoir evaluation, directly impacting oil and gas reserve assessment and development decisions. The most common method for saturation assessment is the classic Archie formula and its derivatives, based on experiments with medium-to-high porosity and permeability reservoirs. Compared to conventional gas reservoirs, tight sandstone reservoirs exhibit strong heterogeneity, complex pore structures, poorer physical properties, and complex rock conductivity, making it difficult to accurately determine rock electrical parameters. Furthermore, the conductive network formed by highly saturated bound water under the complex pore structure, along with the additional conductivity of thin-film clay minerals, results in the relatively well-developed low-resistivity gas layers in tight sandstone. Traditional methods such as the Archie or Indonesian formulas have low accuracy in saturation assessment and cannot meet the exploration and development needs of tight sandstone gas reservoirs.

[0004] Through a review of existing literature, the inventors found that current discussions on the saturation of tight sandstone reservoirs, both domestically and internationally, mainly focus on factors such as complex pore structures and strong reservoir heterogeneity leading to large variations in rock electrical parameters and deviations from the traditional Archie law in rock electrical relationships. These discussions often employ variable rock electrical parameters or modified Archie formulas to evaluate the saturation of tight sandstone reservoirs. Regarding low-resistivity gas-bearing layers, the focus is primarily on their formation and identification, with little attention paid to evaluating their saturation. Because of the low resistivity of low-resistivity gas-bearing layers, resistivity-based methods often underestimate gas saturation, potentially leading to underestimation of gas content or even overlooking gas-bearing layers altogether. Some scholars have used numerical simulations to correct the resistivity of low-resistivity gas-bearing layers before calculating gas saturation; however, this approach is practically difficult. Summary of the Invention

[0005] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention provides a method for quantitatively evaluating the gas saturation of tight sandstone reservoirs using coupled nuclear magnetic resonance (NMR) and density logging, aiming to effectively solve the problem of evaluating the gas saturation of tight sandstone reservoirs and improve the accuracy of gas saturation calculations.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, comprising the following steps: processing raw nuclear magnetic resonance logging data to obtain the total porosity of nuclear magnetic resonance logging; calculating the apparent density porosity of the tight sandstone gas reservoir based on the density porosity calculation formula; obtaining the difference between the apparent density porosity and the total porosity of nuclear magnetic resonance logging in the tight sandstone gas reservoir; and establishing a gas saturation model of the tight sandstone reservoir based on the difference between the apparent density porosity and the total porosity of nuclear magnetic resonance logging.

[0008] The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, preferably, involves processing the raw nuclear magnetic resonance logging data to obtain the total nuclear magnetic resonance logging porosity (PMT). Specifically, this involves processing the raw nuclear magnetic resonance logging data using logging data processing software, including echo generation, time-depth conversion, T2 spectrum inversion, and reservoir parameter calculation, ultimately obtaining the total nuclear magnetic resonance logging porosity (PMT).

[0009] The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, preferably, involves calculating the apparent density porosity of the tight sandstone gas reservoir based on the density porosity calculation formula as follows: Through core experimental analysis, suitable rock skeleton density and fluid density values ​​are determined, and the apparent density porosity PHID of the tight sandstone gas reservoir is calculated using the following formula:

[0010]

[0011] In the formula, ρ is the density logging value; ρ ma ρ represents the density value of the rock skeleton. f This represents the fluid density value.

[0012] The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs preferably uses the following formula to calculate the difference ΔPOR between the apparent density porosity and the total porosity from nuclear magnetic resonance logging in tight sandstone gas reservoirs:

[0013] ΔPOR = PHID - PMT.

[0014] The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, preferably, involves establishing a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance (NMR) logging. Specifically, this involves coring tight gas-bearing layers by layer to analyze gas saturation, total porosity from NMR logging, apparent density porosity, and the average value of the difference between apparent density porosity and total porosity from NMR logging. The gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from NMR logging is then established through regression fitting, as follows:

[0015] S g = a × ΔPOR + b

[0016] In the formula, Sg denoted as σa, where σb represents the gas saturation of the tight sandstone reservoir; a and b are saturation model parameters, and the gas saturation S is analyzed using closed-loop core sampling. g The vertical axis is represented by ΔPOR, which is the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging. The slope of the curve fitted by linear regression is the value a, and the intercept is the value b.

[0017] Secondly, the present invention provides a quantitative evaluation system for gas saturation in tight sandstone reservoirs, comprising:

[0018] The first processing unit is used to process the raw nuclear magnetic resonance logging data to obtain the total porosity of the nuclear magnetic resonance logging.

[0019] The second processing unit is used to calculate the apparent density porosity of tight sandstone gas reservoirs based on the density porosity calculation formula.

[0020] The third processing unit is used to calculate the difference between the apparent density porosity and the total porosity of the tight sandstone gas reservoir through nuclear magnetic resonance logging.

[0021] The fourth processing unit is used to establish a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging.

[0022] Thirdly, the present invention provides a computer storage medium having a computer program stored thereon, characterized in that the computer program, when executed by a processor, implements the steps of the method described in the first aspect of the present invention.

[0023] Fourthly, the present invention provides a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the steps of the method described in the first aspect of the present invention.

[0024] The present invention has the following advantages due to the adoption of the above technical solutions:

[0025] 1. This invention fully utilizes the influence of reservoir gas content on nuclear magnetic resonance (NMR) and density logging porosity. Based on the rock physical volume model of gas-bearing reservoirs, it derives a positive correlation between gas saturation and the difference between density porosity and NMR porosity. Furthermore, based on closed coring analysis of tight gas layers to determine gas saturation, it establishes a relationship model between gas saturation and the difference between density porosity and NMR porosity, which can effectively solve the problem of evaluating tight gas saturation.

[0026] 2. This invention can effectively avoid a series of problems encountered in determining the gas saturation of tight sandstone using the resistivity method, such as large variations in rock electrical parameters and the widespread development of low-resistivity gas layers. It improves the accuracy of gas saturation calculation in tight sandstone reservoirs and lays the foundation for tight gas reservoir reserve assessment and efficient production. Attached Figure Description

[0027] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. In the drawings:

[0028] Figure 1 This is a correlation diagram showing the relationship between the difference between gas saturation and density porosity in closed-loop core sampling analysis and the total porosity in nuclear magnetic resonance logging.

[0029] Figure 2 This is a comparison chart of the gas saturation treatment results and the saturation results from closed-loop core sampling analysis in this invention.

[0030] Figure 3 This is a schematic diagram showing the result of the low-resistivity gas layer gas saturation treatment according to the present invention. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0032] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the system or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," etc., used to define components are merely for the convenience of distinguishing the aforementioned components. Unless otherwise stated, these terms have no special meaning and should not be construed as indicating or implying relative importance.

[0033] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "setting," and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0034] The present invention provides a method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, comprising the following steps: processing raw nuclear magnetic resonance (NMR) logging data to obtain the total porosity of NMR logging; calculating the apparent density porosity of the tight sandstone gas reservoir based on the density porosity calculation formula; calculating the difference between the apparent density porosity and the total porosity of NMR logging in the tight sandstone gas reservoir; and establishing a gas saturation model of the tight sandstone reservoir based on the difference between the apparent density porosity and the total porosity of NMR logging. This invention effectively avoids a series of problems encountered in determining the gas saturation of tight sandstone using the resistivity method, such as large variations in rock electrical parameters and the widespread development of low-resistivity gas layers, thereby improving the accuracy of gas saturation calculation in tight sandstone reservoirs and laying the foundation for tight gas reservoir reserve assessment and efficient production.

[0035] The following is a detailed description of the method and system for quantitative evaluation of gas saturation in tight sandstone reservoirs provided by the embodiments of the present invention, with reference to the accompanying drawings.

[0036] Example 1:

[0037] First, it should be noted that the quantitative evaluation method for gas saturation in tight sandstone reservoirs provided by this invention is based on the following principle:

[0038] Based on the principle of nuclear magnetic resonance logging, the nuclear magnetic resonance porosity of gas-bearing reservoirs can be expressed as:

[0039]

[0040]

[0041] In the above formula, PMT is the total porosity of nuclear magnetic resonance logging, a decimal. S represents the true porosity of the formation, a decimal. g HI represents gas saturation, a decimal. f HI is the hydrogen content index of pore fluids, dimensionless. g P is the hydrogen content index of natural gas, dimensionless; g T is the nuclear magnetic polarization factor for natural gas, which is dimensionless; w For nuclear magnetic polarization wait time, s; T 1g Let be the longitudinal relaxation time of natural gas, in seconds.

[0042] For tight sandstone gas reservoirs, the reservoir pore fluids are formation water and natural gas, therefore HI f =1.0, generally for natural gas reservoirs, the nuclear magnetic polarization waiting time T designed for nuclear magnetic resonance logging acquisition. w It is 12 seconds, which is more than 3 times T. 1g Furthermore, through on-site nuclear magnetic resonance logging point testing, T w =12s can guarantee that the natural gas in the tight gas reservoir is completely polarized, i.e., P g≈1, therefore equation (1) can be transformed into:

[0043]

[0044] According to the reservoir rock physical volume model, the density logging response equation for gas-bearing reservoirs is:

[0045]

[0046] In the above formula, ρ is the density logging value, in g / cm³. 3 ;ρ ma This represents the density of the rock skeleton, in g / cm³. 3 ;ρ f This represents the fluid density value, in g / cm³. 3 ;ρ g This represents the density of natural gas, in g / cm³. 3 .

[0047] According to the density porosity calculation formula, the apparent density porosity of tight sandstone gas reservoirs can be expressed as:

[0048]

[0049] In the above formula, PHID is the apparent density porosity of tight sandstone gas reservoirs, a decimal.

[0050] Substituting equation (4) into equation (5), we get:

[0051]

[0052] Combining equations (3) and (6) and subtracting the result, we get:

[0053]

[0054] Let: ΔPOR = PHID - PMT, then equation (7) can be further transformed into:

[0055]

[0056] From equation (8), it can be seen that the gas saturation S g The gas saturation of tight sandstone reservoirs is proportional to the difference between apparent density porosity and nuclear magnetic resonance porosity, ΔPOR. Therefore, gas saturation can be quantitatively evaluated by coupling nuclear magnetic resonance and density logging.

[0057] Based on the above principles, the quantitative evaluation method for gas saturation in tight sandstone reservoirs using coupled nuclear magnetic resonance and density logging provided in this embodiment includes the following steps:

[0058] S100. Process the raw nuclear magnetic resonance logging data to obtain the total porosity of the nuclear magnetic resonance logging, specifically as follows:

[0059] Nuclear magnetic resonance (NMR) logging primarily utilizes the nuclear magnetic resonance phenomenon of hydrogen nuclei in formation fluids within a known magnetic field to detect formation porosity and fluid characteristics. Its measurement signals are unaffected by the rock skeleton and formation water salinity, making it widely applicable in reservoir properties, pore structure, and fluid identification. Raw NMR logging data mainly consists of echo signals containing formation information. The raw data is processed using NMR logging processing modules in mainstream logging software, including echo generation, time-depth conversion, T2 spectrum inversion, and reservoir parameter calculation. The final result is the total porosity (PMT) obtained from the NMR logging data. However, it is crucial to avoid performing hydrogen content index correction for gas reservoirs when calculating reservoir parameters.

[0060] S200. Based on the density porosity calculation formula, calculate the apparent density porosity of tight sandstone gas reservoirs, specifically:

[0061] Using the above formula (5), the appropriate rock skeleton density value and fluid density value are determined through core experiment analysis, and the apparent density porosity PHID of the tight sandstone gas reservoir is calculated.

[0062] S300. Calculate the difference between the apparent density porosity and the total porosity from nuclear magnetic resonance logging in a tight sandstone gas reservoir. Specifically:

[0063] The difference between apparent density porosity and nuclear magnetic resonance porosity ΔPOR can be obtained by subtracting the total porosity PMT obtained from the nuclear magnetic resonance logging in step S100 from the apparent density porosity PHID of the tight sandstone gas reservoir calculated in step S200.

[0064] S400. Establish a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging. Specifically:

[0065] Compared with core experimental analysis, nuclear magnetic resonance (NMR) logging has a lower vertical resolution. To match the scale of the two, closed coring was performed on tight gas reservoirs by layer to analyze gas saturation, total porosity from NMR logging, apparent density porosity, and the average value of the difference between apparent density porosity and total porosity from NMR logging. A gas saturation model for tight sandstone reservoirs based on the difference between density porosity and total porosity from NMR logging was established through regression fitting, as follows:

[0066] S g = a × ΔPOR + b

[0067] In the formula, S g denoted as σa, where σb represents the gas saturation of the tight sandstone reservoir; a and b are saturation model parameters, and the gas saturation S is analyzed using closed-loop core sampling. gThe vertical axis is represented by ΔPOR, which is the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging. The slope of the curve fitted by linear regression is the value a, and the intercept is the value b.

[0068] Due to the hydrogen content index (HI) of natural gas g The porosity varies with formation pressure and temperature, making it difficult to determine accurately; furthermore, for gas-bearing reservoirs, the true porosity is affected by natural gas. It is also difficult to obtain the gas saturation accurately. Therefore, it is difficult to calculate the gas saturation directly using Equation (8). However, by using closed core sampling to analyze the gas saturation and the difference between apparent density porosity and NMR porosity to directly establish a relationship model, the problem of needing to obtain the actual porosity and hydrogen index of the reservoir first when directly using Equation (8) to calculate the gas saturation can be effectively avoided.

[0069] The following example, using a tight sandstone reservoir in a domestic gas field, further illustrates the quantitative evaluation method for gas saturation in tight sandstone reservoirs according to the present invention.

[0070] 1) Process the raw nuclear magnetic resonance logging data to obtain the total nuclear magnetic resonance logging porosity (PMT).

[0071] The raw nuclear magnetic resonance logging data was processed using the nuclear magnetic resonance logging processing module of mainstream logging data processing software. This process mainly included echo generation, time-depth conversion, T2 spectrum inversion, and reservoir parameter calculation. The final result was the total nuclear magnetic resonance logging porosity (PMT), which was then converted into a percentage.

[0072] 2) Calculate the apparent density porosity (PHID) of tight sandstone gas reservoirs based on the following density porosity calculation formula:

[0073]

[0074] Core experiments were conducted to determine the rock skeleton density value ρ of the gas field. ma It is 2.68 g / cm³ 3 Fluid density value ρ f 1.0 g / cm 3 Input the density logging value ρ, calculate the apparent density porosity PHID of the tight sandstone gas reservoir, and convert it to a percentage.

[0075] 3) Calculate the difference ΔPOR between apparent density porosity and total nuclear magnetic resonance porosity using the following formula:

[0076] ΔPOR = PHID - PMT.

[0077] 4) Establish a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total nuclear magnetic resonance porosity:

[0078] Compared with core experimental analysis, nuclear magnetic resonance logging has a lower vertical resolution. In order to match the scale of the two, the average values ​​of gas saturation, total porosity, apparent density porosity, and the difference between apparent density porosity and total porosity were calculated by closed coring analysis of tight gas layers according to the layer. Table 1 shows the average values ​​of gas saturation and the difference between apparent density porosity and total porosity of nuclear magnetic resonance analysis of 10 layers in 5 wells.

[0079] Table 1. Layer average values ​​of the difference between gas saturation and apparent density porosity and total porosity from closed core samples of a gas field.

[0080]

[0081] Using the data in Table 1, the correlation between gas saturation and apparent density porosity and the difference between total nuclear magnetic resonance porosity was established (see Table 1). Figure 1 The following gas saturation calculation model was obtained:

[0082] S g = 4.6796 × ΔPOR + 28.753

[0083] This invention can use software such as Geolog, Techlog, and EGPS to calculate the gas saturation S of a tight sandstone reservoir in a domestic gas field. g .

[0084] Please see Figure 2 The gas saturation S is plotted using Geolog software. g As can be seen from the image:

[0085] The 9th solid line represents the calculated apparent density porosity, the dashed line represents the total porosity from nuclear magnetic resonance (NMR) logging, and the bar line represents the core analysis porosity, i.e., the true formation porosity. The 10th solid line represents the difference between the calculated apparent density porosity and the NMR porosity; the better the gas content, the larger the value. The 11th solid line represents the gas saturation calculated based on the difference between density and NMR porosity, and the bar line represents the gas saturation analyzed from closed core samples; the two agree very well.

[0086] Figure 3This is an example of processing gas saturation in a low-resistivity gas reservoir. The graph shows a high and clearly abnormal total hydrocarbon content in the gas layer, with density-neutron porosity intersection. Fracturing tests showed a natural gas flow rate of 46,000 cubic meters per day without water production, confirming it as a low-resistivity gas reservoir. The third-to-last solid line represents the gas saturation calculated based on the difference between apparent density porosity and NMR porosity. The dashed line represents the gas saturation calculated using the Indonesian formula, and the dotted dashed line represents the lower limit of gas saturation (greater than 40%). It can be seen that the gas saturation calculated using the Indonesian formula is lower than the lower limit, while the calculation results of the method described in this invention are more consistent with actual test results, thus demonstrating that this invention has higher accuracy in calculating the gas saturation of low-resistivity gas reservoirs.

[0087] Therefore, the quantitative evaluation method for gas saturation in tight sandstone reservoirs provided by this invention can effectively solve the problem of evaluating gas saturation in tight sandstone reservoirs and improve the calculation accuracy of gas saturation in tight sandstone reservoirs.

[0088] Example 2:

[0089] The above-described embodiment 1 provides a method for quantitatively evaluating the gas saturation of tight sandstone reservoirs. Correspondingly, this embodiment provides a system for quantitatively evaluating the gas saturation of tight sandstone reservoirs. The system provided in this embodiment can implement the method described in embodiment 1. This system can be implemented through software, hardware, or a combination of both. For example, the system may include integrated or separate functional modules or units to execute the corresponding steps in the methods of embodiment 1. Since the system in this embodiment is basically similar to the method embodiment, the description process is relatively simple. Relevant details can be found in the description of embodiment 1. This system is merely illustrative.

[0090] The tight sandstone reservoir gas saturation quantitative evaluation system provided in this embodiment includes:

[0091] The first processing unit is used to process the raw nuclear magnetic resonance logging data to obtain the total porosity of the nuclear magnetic resonance logging.

[0092] The second processing unit is used to calculate the apparent density porosity of tight sandstone gas reservoirs based on the density porosity calculation formula.

[0093] The third processing unit is used to calculate the difference between the apparent density porosity and the total porosity of the tight sandstone gas reservoir through nuclear magnetic resonance logging.

[0094] The fourth processing unit is used to establish a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging.

[0095] Example 3:

[0096] This embodiment provides a processing device for implementing the quantitative evaluation method for gas saturation in tight sandstone reservoirs provided in Embodiment 1. The processing device can be a client-side processing device, such as a mobile phone, laptop, tablet computer, or desktop computer, to execute the method of Embodiment 1.

[0097] The processing device includes a processor, a memory, a communication interface, and a bus. The processor, memory, and communication interface are connected via the bus to enable communication between them. The memory stores a computer program that can run on the processor. When the processor runs the computer program, it executes the quantitative evaluation method for gas saturation in tight sandstone reservoirs provided in Embodiment 1.

[0098] Preferably, the memory may be high-speed random access memory (RAM), and may also include non-volatile memory, such as at least one disk storage device.

[0099] Preferably, the processor can be any type of general-purpose processor such as a central processing unit (CPU) or a digital signal processor (DSP), and there is no limitation herein.

[0100] Example 4:

[0101] The quantitative evaluation method for gas saturation in tight sandstone reservoirs in Embodiment 1 can be specifically implemented as a computer program product. The computer program product may include a computer-readable storage medium on which computer-readable program instructions for executing the method described in Embodiment 1 are loaded.

[0102] A computer-readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any combination thereof.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for quantitatively evaluating the gas saturation of tight sandstone reservoirs, characterized in that, Includes the following steps: The raw nuclear magnetic resonance logging data is processed to obtain the total porosity of the nuclear magnetic resonance logging data. Based on the density porosity calculation formula, the apparent density porosity of tight sandstone gas reservoirs is calculated. Calculate the difference between the apparent density porosity and the total porosity from nuclear magnetic resonance logging in tight sandstone gas reservoirs; A gas saturation model for tight sandstone reservoirs is established based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging. Specifically: By analyzing closed coring data from tight gas reservoirs within each stratigraphic segment, gas saturation, total porosity from nuclear magnetic resonance (NMR) logging, apparent density porosity of tight sandstone gas reservoirs, and the average value of the difference between apparent density porosity and total porosity from NMR logging, a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from NMR logging was established through regression fitting, as follows: In the formula, S g denoted as ρ, where ρ is the gas saturation of the tight sandstone reservoir; a and b are the saturation model parameters. The gas saturation from closed coring analysis is used as the ordinate, and the difference between the apparent density porosity and the total porosity from nuclear magnetic resonance logging (ΔPOR) of the tight sandstone gas reservoir is used as the abscissa. The slope of the curve fitted by linear regression is the value of a, and the intercept is the value of b.

2. The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs according to claim 1, characterized in that, The specific steps for processing the raw nuclear magnetic resonance logging data to obtain the total porosity are as follows: The raw nuclear magnetic resonance logging data was processed using logging data processing software, including echo generation, time-depth conversion, T2 spectrum inversion, and reservoir parameter calculation, and finally the total porosity (PMT) of the nuclear magnetic resonance logging was obtained.

3. The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs according to claim 2, characterized in that, The calculation of the apparent density porosity of tight sandstone gas reservoirs based on the density porosity calculation formula is as follows: Core experiments were conducted to determine suitable rock skeleton density and fluid density values. The apparent density porosity (PHID) of the tight sandstone gas reservoir was then calculated using the following formula: In the formula, ρ is the density logging value; This represents the density value of the rock skeleton. This represents the fluid density value.

4. The method for quantitatively evaluating the gas saturation of tight sandstone reservoirs according to claim 3, characterized in that, The difference ΔPOR between the apparent density porosity and the total porosity from nuclear magnetic resonance logging in tight sandstone gas reservoirs is calculated using the following formula: ΔPOR = PHID - PMT.

5. A quantitative evaluation system for gas saturation in tight sandstone reservoirs, characterized in that, include: The first processing unit is used to process the raw nuclear magnetic resonance logging data to obtain the total porosity of the nuclear magnetic resonance logging. The second processing unit is used to calculate the apparent density porosity of tight sandstone gas reservoirs based on the density porosity calculation formula. The third processing unit is used to calculate the difference between the apparent density porosity and the total porosity of the tight sandstone gas reservoir through nuclear magnetic resonance logging. The fourth processing unit is used to establish a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from nuclear magnetic resonance logging. Specifically: By analyzing closed coring data from tight gas reservoirs within each stratigraphic segment, gas saturation, total porosity from nuclear magnetic resonance (NMR) logging, apparent density porosity of tight sandstone gas reservoirs, and the average value of the difference between apparent density porosity and total porosity from NMR logging, a gas saturation model for tight sandstone reservoirs based on the difference between apparent density porosity and total porosity from NMR logging was established through regression fitting, as follows: In the formula, S g denoted as ρ, where ρ is the gas saturation of the tight sandstone reservoir; a and b are the saturation model parameters. The gas saturation from closed coring analysis is used as the ordinate, and the difference between the apparent density porosity and the total porosity from nuclear magnetic resonance logging (ΔPOR) of the tight sandstone gas reservoir is used as the abscissa. The slope of the curve fitted by linear regression is the value of a, and the intercept is the value of b.

6. A computer storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1-4.

7. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1-4.

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