A method for judging reservoir categories based on residual oil and gas saturation of flushing

Abstract

The application discloses a kind of based on flushing zone residual oil and gas saturation reservoir category determination method, it is related to well logging interpretation technical field, steps are by conventional well logging to obtain neutron, density logging data;Residual oil and gas of flushing zone is obtained density;Calculate the hydrogen index of residual oil and gas of flushing zone;Residual oil and gas of flushing zone is obtained neutron apparent porosity and density apparent porosity;According to the logging response model of neutron and density in oil and gas reservoir, establish the mathematical model of residual oil and gas saturation of flushing zone, combine shale corrected neutron porosity and density porosity, calculate the residual oil and gas saturation of flushing zone, and when exceed specified index, define as gas layer.The application can obtain residual oil and gas saturation of flushing zone by using conventional neutron and density logging related data, which is less affected by geological factors, so that the calculation of residual oil and gas saturation of flushing zone is more accurate, the evaluation of reservoir gas content is more accurate, and the application range is more extensive.

Description

A method for determining reservoir category based on residual oil and gas saturation in the flushed zone Technical Field

[0001] This invention relates to the field of well logging interpretation technology, and more specifically to a method for determining reservoir type based on the residual oil and gas saturation of the flushed zone. Background Technology

[0002] The residual hydrocarbon saturation in the flushed zone is an important reservoir parameter for the comprehensive interpretation of well logging data, and its influencing factors are numerous and complex. Conventionally, the residual hydrocarbon saturation in the flushed zone is calculated using shallow directional resistivity via Archie's formula. However, this method requires extensive core experiments to obtain formation rock electrical parameters, and shallow directional resistivity is easily affected by wellbore fractures, caverns, induced fractures, special minerals, porosity, and other factors, making it difficult to accurately reflect the residual hydrocarbon content in the flushed zone.

[0003] The prior art includes a Chinese invention patent document with publication number CN109117505A and publication date of January 1, 2019. This patent document discloses a method for calculating the water saturation of the flushing zone of a porous reservoir based on dielectric experiments. The specific implementation steps are as follows: S1, Experimental core preparation: Select six core samples with different porosities and permeabilities, and perform oil washing and drying pretreatment on the cores;

[0004] S2. Multiple core samples are analyzed using an electromagnetic parameter analyzer at a frequency of 984MHz to obtain the dielectric parameters of each core sample under different water saturation conditions. S3. Porosity parameters of multiple core samples are measured using a porosity analyzer. S4. The dielectric experimental data of the core samples are analyzed. S5. Formation dielectric parameter data and formation porosity parameters are collected and recorded using a dielectric and porosity logging device. S6. The parameters are calculated according to the formula. S7. The calculation results are output. The advantage of this invention is that it solves the problem that conventional resistivity logging data for formations with complex pore structures cannot accurately evaluate the water saturation of the flushed zone and has low fluid identification accuracy.

[0005] However, while the aforementioned technology can evaluate the water saturation of the flushed zone in practical use, it requires extensive core sampling for dielectric measurements to obtain dielectric parameters under different water saturation conditions. Furthermore, it necessitates both dielectric logging and conventional logging to determine the residual hydrocarbon saturation of the flushed zone. This method incurs significant costs for core sampling and dielectric experiments, and the dielectric logging depth is extremely shallow, resulting in very low residual hydrocarbon content within its detection range. Consequently, its computational performance is unsatisfactory.

[0006] Further searching based on the above search results revealed a Chinese invention patent document with publication number CN108979629A and publication date of December 11, 2018, which discloses a method for calculating gas layer density based on density, neutron, and nuclear magnetic resonance logging. The specific steps are as follows: S1. Obtaining three logging curves: it is best to use the same measurement for neutron, density, and nuclear magnetic resonance logging during drilling, or to use the same measurement for neutron, density, and nuclear magnetic resonance logging via cable to ensure that the target formation is measured at a consistent time and with similar invasion depth; S2. Information from density logging measurements can be obtained using formulas; S3. Information from neutron logging measurements can be obtained using formulas; S4. Information from nuclear magnetic resonance logging measurements can be obtained using formulas; S5. By simultaneously solving the three equations for neutron, density, and nuclear magnetic resonance, three unknowns can be calculated: the true total porosity of the gas layer, gas saturation (1-Sxo), and gas layer density ρh; S6. Outputting the calculation results. This invention solves the problem of providing accurate and reliable total porosity, gas saturation in the flushed zone, and gas density for well logging evaluation of gas-bearing reservoirs, thereby improving the accuracy of geological evaluation. The model calculation results are accurate and have a wide range of applications.

[0007] The patent document CN108979629A requires the combined use of neutron, density, and nuclear magnetic resonance (NMR) logging data to calculate the gas saturation of the flushed zone. NMR logging equipment and technology are relatively complex, requiring highly specialized operation and maintenance. This means that experienced technicians are needed to operate and interpret the data, increasing the cost and difficulty of using the technology. Furthermore, the application scope of NMR logging is relatively narrow. Due to equipment and technological limitations, NMR logging can only be effectively applied in specific geological environments, such as carbonate formations, limiting its applicability in certain regions and exploration projects. Finally, NMR logging is costly; the purchase and maintenance costs of equipment, as well as the training and usage expenses of technicians, represent significant investments in this technology. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention proposes a reservoir classification method based on the residual oil and gas saturation of the flushed zone. This invention utilizes conventional neutron and density logging data, and establishes a mathematical model of the residual oil and gas saturation in the flushed zone using well logging response models of neutron and density in oil and gas-bearing reservoirs and well logging response models of density in oil and gas-bearing reservoirs. This method is less affected by geological factors such as fractures, induced fractures, and special minerals, and has a wider range of applications, improving the accuracy of the residual oil and gas saturation in the flushed zone and making the evaluation of reservoir gas content more accurate.

[0009] This invention is achieved by adopting the following technical solution:

[0010] A method for determining reservoir type based on residual oil and gas saturation in the flushed zone comprises the following steps:

[0011] Step 1: Obtain reservoir neutron and density logging data through conventional logging;

[0012] Step 2: Obtain the density of residual oil and gas in the reservoir flushing zone;

[0013] Step 3: Calculate the hydrogen content index of the residual oil and gas in the reservoir flushing zone based on the density of the residual oil and gas obtained in Step 2.

[0014] Step 4: Calculate the neutron apparent porosity and density apparent porosity of residual oil and gas in the reservoir flushing zone based on the data obtained in Step 2 and Step 3;

[0015] Step 5: Based on the logging response model of neutrons in oil and gas reservoirs and the logging response model of density in oil and gas reservoirs, establish a mathematical model of residual oil and gas saturation in the flushing zone. Combine the neutron porosity corrected for clay and the density porosity corrected for clay to calculate the residual oil and gas saturation in the flushing zone.

[0016] The well logging response model of neutrons in oil and gas reservoirs is expressed by the following formula:

[0017] φ N =φ e +φ e S hr (φ Nhr -1) Equation 1

[0018] The logging response model of the density in oil and gas reservoirs is expressed by the following formula:

[0019] φ D =φ e +φ e S hr (φ Dhr -1) Equation 2

[0020] A mathematical model for the residual oil and gas saturation in the flushing zone can be established using equations 1 and 2:

[0021]

[0022] In equations 1, 2, and 3, φ N Density and porosity after clay correction; φ e Effective porosity; S hr To flush out residual oil and gas saturation; φ Nhr Neutron apparent porosity of residual oil and gas; φ D Density and porosity after clay correction; φ Dhr The density of residual oil and gas is relative to porosity;

[0023] Step 6: Determine the reservoir type based on the residual oil and gas saturation of the flushing zone obtained in Step 5.

[0024] The density and porosity after clay correction are calculated using the following formula:

[0025]

[0026] In Equation 4, φ D Density and porosity after clay correction; V Sh ρ represents the volume of the clay. Dma ρ b ρ sh ρ mf These represent the density of the pure rock skeleton, density logging value, clay density value, and mud filtrate density, respectively, in g / cm³. 3 ;

[0027] The neutron porosity after clay correction is calculated using the following formula:

[0028]

[0029] In Equation 5, φ N Density and porosity after clay correction; V Sh φ represents the volume of the clay. Nma φ CN φ Nsh φ Nmf These are, respectively, the neutron porosity of the pure rock skeleton, the neutron logging reading, the neutron porosity of the shale, and the neutron porosity of the mud filtrate.

[0030] The neutron apparent porosity of the flushing zone with residual oil and gas is expressed by the formula:

[0031]

[0032] In Equation 6, φ Nhr To flush out neutron-perceived porosity containing residual oil and gas; φ Nma Neutron porosity of a pure rock framework; φ Nmf The porosity of the mud filtrate is neutron porosity.

[0033] The density of residual oil and gas in the flushing zone, depending on the porosity, is expressed by the formula:

[0034]

[0035] In Equation 7, φ Dhr The density of residual oil and gas in the flushing zone is determined by the apparent porosity; ρ ma This represents the density of the pure rock skeleton, in g / cm³.3 ;ρ mf Density of mud filtrate, in g / cm³ 3 ;ρ hr The density value of residual oil and gas in the flushing zone, in g / cm³. 3 .

[0036] The neutron porosity of the pure rock framework is expressed by the formula:

[0037]

[0038] In Equation 8, φ Nma For the neutron porosity of a pure rock framework, V i φ represents the volume of different minerals in the strata. e For effective porosity, V Sh φNmai represents the volume of the mud, φNmai represents the neutron value of different minerals, and n represents the number of minerals in the stratum.

[0039] The density value of the pure rock skeleton is expressed by the formula:

[0040]

[0041] In Equation 9, ρ ma This represents the density of the pure rock skeleton, in g / cm³. 3 V i φ represents the volume of different minerals in the strata. e For effective porosity, V Sh Let ρ be the volume of the clay. mai denoted by , where is the density of different mineral skeletons, and n is the number of minerals in the strata.

[0042] Step 2, obtaining the density of residual oil and gas in the flushing zone, includes the following steps:

[0043] First, calculate the relative pressure and relative temperature based on the reservoir pressure, reservoir temperature, critical pressure, and critical temperature. Then, obtain the compressibility factor from the natural gas compressibility factor chart based on the relative pressure and relative temperature. Obtain the volume factor based on the reservoir pressure, reservoir temperature, and compressibility factor. Calculate the density of residual oil and gas in the flushed zone under reservoir conditions based on the volume factor and relative density.

[0044] In step 3, the hydrogen content index of the flushing material containing residual oil and gas is expressed by the formula:

[0045]

[0046] In Equation 10, CNL hr To flush out the hydrogen content index of residual oil and gas, ρ hrThe density of residual oil and gas in the flushing zone.

[0047] In step 6, when the residual oil and gas saturation S in the flushing zone... hr When the residual oil and gas saturation is greater than 0.4, it is considered a gas layer. hr If the value is less than 0.4, it is considered a water layer.

[0048] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0049] 1. Compared with the prior art disclosed in CN109117505A, the present invention can calculate the residual gas saturation of the flushed zone using only conventional neutron and density logging data. It utilizes the different influence characteristics of residual gas in the flushed zone on neutron logging and density logging. It is less affected by geological factors such as fractures, induced fractures, and special minerals, and has advanced technology. At the same time, it is easier to implement and does not rely on resistivity logging to calculate gas saturation.

[0050] 2. Compared with the prior art disclosed in CN108979629A, this invention only requires conventional neutron and density logging data. Based on the acquisition of relevant parameters such as the density of residual oil and gas in the reservoir flushing zone, the hydrogen content index of residual oil and gas in the flushing zone, the neutron apparent porosity of residual oil and gas in the flushing zone, and the density apparent porosity, a mathematical model for the saturation of residual oil and gas in the flushing zone is jointly established using the logging response model of neutron and density in oil and gas-bearing reservoirs. After obtaining the saturation of residual oil and gas in the flushing zone, the reservoir type is determined. The method of obtaining the saturation of residual oil and gas in the flushing zone in this invention is completely different. This invention does not require nuclear magnetic resonance logging data, reducing the difficulty of data interpretation. Furthermore, this invention reduces the equipment and labor costs associated with nuclear magnetic resonance logging. At the same time, the model for obtaining the saturation of residual oil and gas in the flushing zone obtained by this invention has a wider range of applications and is not limited to specific regions or exploration projects. This invention is a method developed by the inventors through several experiments. The inventors finally obtained a mathematical model for the residual oil and gas saturation in the flushed zone, which is based on the well logging response model of neutrons and density in oil and gas reservoirs. This model accurately calculates the residual oil and gas saturation in the flushed zone and determines the reservoir type. Attached Figure Description

[0051] Figure 1 shows the application results of this invention. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0053] Example 1

[0054] A method for determining reservoir type based on residual oil and gas saturation in the flushed zone comprises the following steps:

[0055] Step 1: Obtain reservoir neutron and density logging data through conventional logging;

[0056] Step 2: Obtain the density of residual oil and gas in the reservoir flushing zone;

[0057] Step 3: Calculate the hydrogen content index of the residual oil and gas in the reservoir flushing zone based on the density of the residual oil and gas obtained in Step 2.

[0058] Step 4: Calculate the neutron apparent porosity and density apparent porosity of residual oil and gas in the reservoir flushing zone based on the data obtained in Step 2 and Step 3;

[0059] Step 5: Based on the logging response model of neutrons in oil and gas reservoirs and the logging response model of density in oil and gas reservoirs, establish a mathematical model of residual oil and gas saturation in the flushing zone. Combine the neutron porosity corrected for clay and the density porosity corrected for clay to calculate the residual oil and gas saturation in the flushing zone.

[0060] The well logging response model of neutrons in oil and gas reservoirs is expressed by the following formula:

[0061] φ N =φ e +φ e S hr (φ Nhr -1) Equation 1

[0062] The logging response model of the density in oil and gas reservoirs is expressed by the following formula:

[0063] φ D =φ e +φ e S hr (φ Dhr -1) Equation 2

[0064] A mathematical model for the residual oil and gas saturation in the flushing zone can be established using equations 1 and 2:

[0065]

[0066] In equations 1, 2, and 3, φ N Density and porosity after clay correction; φ e Effective porosity; S hr To flush out residual oil and gas saturation; φ Nhr Neutron apparent porosity of residual oil and gas; φ D Density and porosity after clay correction; φ Dhr The density of residual oil and gas is relative to porosity;

[0067] Step 6: Determine the reservoir type based on the residual oil and gas saturation of the flushing zone obtained in Step 5.

[0068] This embodiment is the most basic implementation method. Compared with the prior art, the residual gas saturation of the flushed zone can be calculated using conventional neutron and density logging data, and the reservoir type can be determined.

[0069] Example 2

[0070] A method for determining reservoir type based on residual oil and gas saturation in the flushed zone comprises the following steps:

[0071] Step 1: Obtain reservoir neutron and density logging data through conventional logging;

[0072] Step 2: Obtain the density of residual oil and gas in the reservoir flushing zone;

[0073] Step 3: Calculate the hydrogen content index of the residual oil and gas in the reservoir flushing zone based on the density of the residual oil and gas obtained in Step 2.

[0074] Step 4: Calculate the neutron apparent porosity and density apparent porosity of residual oil and gas in the reservoir flushing zone based on the data obtained in Step 2 and Step 3;

[0075] Step 5: Based on the logging response model of neutrons in oil and gas reservoirs and the logging response model of density in oil and gas reservoirs, establish a mathematical model of residual oil and gas saturation in the flushing zone. Combine the neutron porosity corrected for clay and the density porosity corrected for clay to calculate the residual oil and gas saturation in the flushing zone.

[0076] The well logging response model of neutrons in oil and gas reservoirs is expressed by the following formula:

[0077] φ N =φ e +φ e S hr (φ Nhr -1) Equation 1

[0078] The logging response model of the density in oil and gas reservoirs is expressed by the following formula:

[0079] φ D =φ e +φ e S hr (φ Dhr -1) Equation 2

[0080] A mathematical model for the residual oil and gas saturation in the flushing zone can be established using equations 1 and 2:

[0081]

[0082] In equations 1, 2, and 3, φ N Density and porosity after clay correction; φ e Effective porosity; S hr To flush out residual oil and gas saturation; φ Nhr Neutron apparent porosity of residual oil and gas; φ D Density and porosity after clay correction; φ Dhr The density of residual oil and gas is relative to porosity;

[0083] Step 6: Determine the reservoir type based on the residual oil and gas saturation of the flushing zone obtained in Step 5.

[0084] The density and porosity after clay correction are calculated using the following formula:

[0085]

[0086] In Equation 4, φ D Density and porosity after clay correction; V Sh ρ represents the volume of the clay. Dma ρ b ρ sh ρ mf These represent the density of the pure rock skeleton, density logging value, clay density value, and mud filtrate density, respectively, in g / cm³. 3 ;

[0087] The neutron porosity after clay correction is calculated using the following formula:

[0088]

[0089] In Equation 5, φ N Density and porosity after clay correction; V Sh φ represents the volume of the clay. Nma φ CN φ Nsh φ Nmf These are, respectively, the neutron porosity of the pure rock skeleton, the neutron logging reading, the neutron porosity of the shale, and the neutron porosity of the mud filtrate.

[0090] The neutron apparent porosity of the residual oil and gas is expressed by the formula:

[0091]

[0092] In Equation 6, φ Nhr Neutron apparent porosity of residual oil and gas; φ Nma Neutron porosity of a pure rock framework; φ NmfThe porosity of the mud filtrate is neutron porosity.

[0093] The density of the residual oil and gas, depending on the porosity, is expressed by the formula:

[0094]

[0095] In Equation 7, φ Dhr The density of residual oil and gas is relative to porosity; ρ ma This represents the density of the pure rock skeleton, in g / cm³. 3 ;ρ mf Density of mud filtrate, in g / cm³ 3 ;ρ hr The density value of the residual oil and gas, in g / cm³ 3 .

[0096] In step 6, when the residual oil and gas saturation S in the flushing zone... hr When the residual oil and gas saturation is greater than 0.4, it is considered a gas layer. hr If the value is less than 0.4, it is considered a water layer.

[0097] Example 3

[0098] A method for determining reservoir type based on residual oil and gas saturation in the flushed zone comprises the following steps:

[0099] Step 1: Obtain reservoir neutron and density logging data through conventional logging;

[0100] Step 2: Obtain the density of residual oil and gas in the reservoir flushing zone;

[0101] Step 3: Calculate the hydrogen content index of the residual oil and gas in the reservoir flushing zone based on the density of the residual oil and gas obtained in Step 2.

[0102] Step 4: Calculate the neutron apparent porosity and density apparent porosity of residual oil and gas in the reservoir flushing zone based on the data obtained in Step 2 and Step 3;

[0103] Step 5: Based on the logging response model of neutrons in oil and gas reservoirs and the logging response model of density in oil and gas reservoirs, establish a mathematical model of residual oil and gas saturation in the flushing zone. Combine the neutron porosity corrected for clay and the density porosity corrected for clay to calculate the residual oil and gas saturation in the flushing zone.

[0104] The well logging response model of neutrons in oil and gas reservoirs is expressed by the following formula:

[0105] φ N =φ e +φ e S hr (φ Nhr -1) Equation 1

[0106] The logging response model of the density in oil and gas reservoirs is expressed by the following formula:

[0107] φ D =φ e +φ e S hr (φ Dhr -1) Equation 2

[0108] A mathematical model for the residual oil and gas saturation in the flushing zone can be established using equations 1 and 2:

[0109]

[0110] In equations 1, 2, and 3, φ N Density and porosity after clay correction; φ e Effective porosity; S hr To flush out residual oil and gas saturation; φ Nhr Neutron apparent porosity of residual oil and gas; φ D Density and porosity after clay correction; φ Dhr The density of residual oil and gas is relative to porosity;

[0111] Step 6: Determine the reservoir type based on the residual oil and gas saturation of the flushing zone obtained in Step 5.

[0112] Step 2, obtaining the density of residual oil and gas in the flushing zone, includes the following steps:

[0113] First, calculate the relative pressure and relative temperature based on the reservoir pressure, reservoir temperature, critical pressure, and critical temperature. Then, obtain the compressibility factor from the natural gas compressibility factor chart based on the relative pressure and relative temperature. Obtain the volume factor based on the reservoir pressure, reservoir temperature, and compressibility factor. Calculate the density of residual oil and gas in the flushed zone under reservoir conditions based on the volume factor and relative density.

[0114] In step 3, the hydrogen content index of the flushing material containing residual oil and gas is expressed by the formula:

[0115]

[0116] In Equation 10, CNL hr To flush out the hydrogen content index of residual oil and gas, ρ hr The density of residual oil and gas in the flushing zone.

[0117] In step 6, when the residual oil and gas saturation Shr in the flushing zone is greater than 0.4, it is determined to be a gas layer; when the residual oil and gas saturation Shr is less than 0.4, it is determined to be a water layer.

[0118] Example 4

[0119] A method for determining reservoir category based on residual oil and gas saturation in the flushed zone includes the following steps:

[0120] Step 1: Obtain neutron and density logging data through conventional logging;

[0121] Step 2: Obtain the density of residual oil and gas in the flushing zone;

[0122] Based on the well test data, the reservoir pressure P and reservoir temperature T at the middle depth of the reservoir are obtained; based on the natural gas analysis data, the relative density r, critical pressure Ppc, and critical temperature Tpc of natural gas can be obtained; based on the above data, the comparative pressure Ppr and comparative temperature Tpr are first calculated, as shown in Table 1;

[0123] The compressibility factor Z was obtained from the natural gas compressibility factor chart based on the comparative pressure and temperature (see Table 1); the density ρ of the residual oil and gas in the flushed zone under reservoir conditions was calculated based on the volume factor Bg and relative density. hr See Table 1;

[0124]

[0125] Table 1

[0126] Step 3: Calculate the hydrogen content index of the residual oil and gas in the flushing zone based on the density of the residual oil and gas obtained in Step 2.

[0127]

[0128] Step 4: Obtain the neutron apparent porosity and density apparent porosity of the flushed area with residual oil and gas;

[0129] The neutron apparent porosity of the residual oil and gas is expressed by the formula:

[0130]

[0131] In the formula, φ Nhr Neutron apparent porosity of residual oil and gas; φ Nma Neutron porosity of a pure rock framework; φ Nmf The porosity of the mud filtrate is neutron porosity.

[0132] The neutron porosity of the pure rock framework is calculated based on the lithological profile obtained from conventional well logging:

[0133]

[0134] V1, V2, V3, V ShVolumes of the first, second, and third minerals and clay, respectively, in decimal form; φ Nma1 φ Nma2 φ Nma3 φ represents the neutron values ​​of the first, second, and third minerals, respectively, in decimal form. e The effective porosity is calculated from well logging.

[0135] The density of the residual oil and gas, depending on the porosity, is expressed by the formula:

[0136]

[0137] In the formula, φ Dhr The density of residual oil and gas is relative to porosity; ρ ma This represents the density of the pure rock skeleton, in g / cm³. 3 ;ρ mf Density of mud filtrate, in g / cm³ 3 ;ρ hr The density value of the residual oil and gas, in g / cm³ 3 .

[0138] The density value of the pure rock skeleton is calculated based on the lithological profile obtained from conventional well logging:

[0139]

[0140] V1, V2, V3, V Sh Volumes of the first, second, and third minerals and clay, respectively, as decimals; ρ ma1 ρ ma2 ρ mai These are the density values ​​of the first, second, and third minerals, respectively, in decimal form; φ e The effective porosity is calculated from well logging.

[0141] Step 5: Based on the two equations of the logging response model of neutrons in oil and gas reservoirs and the logging response model of density in oil and gas reservoirs, establish a mathematical model of residual oil and gas saturation in the flushing zone. Combine the neutron porosity corrected for clay and the density porosity corrected for clay to calculate the residual oil and gas saturation in the flushing zone.

[0142] The well logging response model of neutrons in oil and gas reservoirs is expressed by the following formula:

[0143] φ N =φ e +φ e S hr (φ Nhr -1) Equation 1

[0144] The logging response model of the density in oil and gas reservoirs is expressed by the following formula:

[0145] φ D =φ e +φ e S hr (φ Dhr -1) Equation 2

[0146] A mathematical model for the residual oil and gas saturation in the flushing zone can be established using equations 1 and 2:

[0147]

[0148] In equations 1, 2, and 3, φ N Density and porosity after clay correction; φ e Effective porosity; S hr To flush out residual oil and gas saturation; φ Nhr Neutron apparent porosity of residual oil and gas; φ D Density and porosity after clay correction; φ Dhr The density of residual oil and gas is relative to porosity;

[0149] The density and porosity after clay correction can be calculated using the following formula:

[0150]

[0151] In Equation 4, φ D Density and porosity after clay correction; V Sh ρ represents the volume of the clay. Dma ρ b ρ sh ρ mf These represent the density of the pure rock skeleton, density logging value, clay density value, and mud filtrate density, respectively, in g / cm³. 3 ;

[0152] The neutron porosity after clay correction can be calculated using the following formula:

[0153]

[0154] In Equation 5, φ N Density and porosity after clay correction; V Sh φ represents the volume of the clay. Nma φ CN φ Nsh φ Nmf These are, respectively, the neutron porosity of the pure rock skeleton, the neutron logging reading, the neutron porosity of the shale, and the neutron porosity of the mud filtrate.

[0155] Substituting the above data into the mathematical model for residual oil and gas saturation in the flushing zone, the residual oil and gas saturation in the flushing zone is obtained, as shown in Table 2.

[0156] Depth Pure Framework Neutron Pure Framework Density Clay Corrected Neutron Porosity Clay Corrected Density Porosity Residual Gas Saturation (m) Decimal Decimal (%) (%) Decimal 59870.00902.869.14317.7710.6945987.1250.00902.8589.15817.7910.6945987.250.00902.8559.0917.57 10.6895987.3750.00902.8528.95617.1750.6815987.50.00902.8518.88517.0330.6815987.6250.00902.8518.86917.0090.6815987.750.00902.8518.89217.1960.68959 87.8750.00902.8488.88917.2120.6959880.00802.8428.75717.0220.6935988.1250.00802.8368.72416.9440.6925988.250.00802.8348.83617.0980.6885988.3750.008 02.8399.0917.760.6985988.50.00802.8419.38218.3790.75988.6250.00802.8399.58618.8120.7025988.750.00802.8379.8119.2940.7035988.8750.00802.83610.11219 9730.70759890.00802.8410.41720.8530.72。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。 。6003.8750.00302.761.0161.2910.25960040.00402.7751.6741.9570.1716004.1250.00502.7933.0123.4120.1376004.250.00602.8074.4434.8770.1036004.3750.00702. 8266.0276.8020.1346004.50.00802.8387.4348.230.1136004.6250.00902.8498.5639.3580.0996004.750.01002.8649.54310.4570.1026004.8750.01002.8710.50310.93 60.04560050.01002.8711.03210.99606005.1250.01002.8710.98810.82706005.250.01002.8710.43710.5360.0116005.3750.01002.879.46710.2090.0846005.50.01002. 8658.3739.480.1386005.6250.00902.8567.2468.2860.1496005.750.00902.8466.2616.90.1086005.8750.00802.8455.3195.8480.10560060.00802.8434.665.0460.089. surface

[0157] Table 2

[0158] Step 6: Evaluate the gas content of the reservoir based on the residual oil and gas saturation of the flushed zone obtained in Step 5. When the residual oil and gas saturation Shr of the flushed zone is greater than 0.4, it is determined to be a gas layer; when the residual oil and gas saturation Shr is less than 0.4, it is determined to be a water layer.

[0159] As the preferred embodiment of the present invention, this embodiment can calculate the residual oil and gas saturation of the flushed zone using conventional neutron and density logging data. It leverages the different influence characteristics of residual oil and gas in the flushed zone on neutron and density logging, and is less affected by geological factors such as fractures, induced fractures, and special minerals. This results in more accurate calculation of the residual oil and gas saturation of the flushed zone and a more accurate evaluation of reservoir gas content, demonstrating technological advancement and ease of implementation. It does not rely on resistivity logging for gas saturation calculation, exhibiting significant innovation. Furthermore, it eliminates the need for nuclear magnetic resonance (NMR) logging data, reducing the difficulty of data interpretation. Moreover, this invention reduces the equipment and labor costs associated with NMR logging. Additionally, the model for obtaining the residual oil and gas saturation of the flushed zone obtained by this invention has a wider range of applications, not limited to specific regions or exploration projects.

Claims

1. A method for determining reservoir category based on residual oil and gas saturation in the flushed zone, characterized in that, The process includes the following steps: Step 1: Obtain reservoir neutron and density logging data through conventional logging; Step 2: Obtain the density of residual oil and gas in the reservoir flushing zone; Step 3: Calculate the hydrogen content index of residual oil and gas in the reservoir flushing zone based on the density obtained in Step 2; Step 4: Calculate the neutron apparent porosity and density apparent porosity of residual oil and gas in the reservoir flushing zone based on the data obtained in Steps 2 and 3; Step 5: Establish a mathematical model for the saturation of residual oil and gas in the flushing zone based on the logging response models of neutrons and density in oil and gas reservoirs, and calculate the saturation of residual oil and gas in the flushing zone by combining the neutron porosity corrected for clay and the density porosity corrected for clay; The logging response model of neutrons in oil and gas reservoirs is expressed by the following formula: The logging response model of density in oil and gas reservoirs described in Equation 1 is expressed by the following formula: Equation 2: A mathematical model for the residual oil and gas saturation in the flushing zone can be established from Equations 1 and 2. In Equations 3, 1, 2, and 3, Neutron porosity after clay correction; Effective porosity; To flush out residual oil and gas saturation; Neutron apparent porosity of residual oil and gas; Density and porosity after clay correction; The density of residual oil and gas is relative to porosity; Step 6: Determine the reservoir type based on the residual oil and gas saturation of the flushing zone obtained in Step 5.

2. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: The density and porosity after clay correction are calculated using the following formula: In Equation 4, Density and porosity after clay correction; The volume of the clay; 、 、 、 These are, respectively, the density of the pure rock skeleton, the density logging value, the clay density value, and the mud filtrate density. The neutron porosity after clay correction is calculated using the following formula: In Equation 5, Neutron porosity after clay correction; The volume of the clay; 、 、 、 These are, respectively, the neutron porosity of the pure rock skeleton, the neutron logging reading, the neutron porosity of the shale, and the neutron porosity of the mud filtrate.

3. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: The neutron apparent porosity of the flushing zone with residual oil and gas is expressed by the formula: In Equation 6, To flush out residual oil and gas and improve neutron porosity; Neutron porosity of a pure rock framework; The porosity of the mud filtrate is neutron porosity.

4. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: The density of residual oil and gas in the flushing zone, depending on the porosity, is expressed by the formula: In Equation 7, The density of residual oil and gas in the flushing zone depends on the porosity. This represents the density value of a pure rock skeleton. ； This is the density value of the mud filtrate. ； The density value of the residual oil and gas in the flushing zone. 。 5. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 3, characterized in that: The neutron porosity of the pure rock framework is expressed by the formula: In Formula 8, Neutron porosity of a pure rock framework The volume of different minerals in the strata. For effective porosity, For the volume of clay, denoted by neutron values ​​for different minerals, and n represents the number of minerals in the stratum.

6. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 4, characterized in that: The density value of the pure rock skeleton is expressed by the formula: In Equation 9, This represents the density value of a pure rock skeleton. ； The volume of different minerals in the strata. For effective porosity, For the volume of clay, denoted by , where is the density of different mineral skeletons, and n is the number of minerals in the strata.

7. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: In step 2, obtaining the density of residual oil and gas in the flushed zone includes the following steps: First, calculate the comparative pressure and comparative temperature based on the reservoir pressure, reservoir temperature, critical pressure, and critical temperature; then, obtain the compressibility factor by referring to the natural gas compressibility factor chart based on the comparative pressure and comparative temperature; obtain the volume factor based on the reservoir pressure, reservoir temperature, and compressibility factor; and calculate the density of residual oil and gas in the flushed zone under the reservoir conditions based on the volume factor and relative density.

8. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 7, characterized in that: The reservoir pressure and reservoir temperature are obtained from oil testing data, while the critical pressure, critical temperature, and relative density are obtained from natural gas analysis data.

9. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: In step 3, the hydrogen content index of the flushing material containing residual oil and gas is expressed by the formula: In Equation 10, To flush out the hydrogen content index containing residual oil and gas, The density of residual oil and gas in the flushing zone.

10. The reservoir category determination method based on residual oil and gas saturation in the flushed zone according to claim 1, characterized in that: The specified index is 0.4, when the residual oil and gas saturation S in the reservoir flushing zone is... hr A value greater than 0.4 indicates an air layer.

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