A method for determining bedrock reservoir saturation model

Abstract

The invention discloses a method for determining a bedrock reservoir saturation model, comprising the following steps: step 1: selecting a core sample of a target layer; step 2: obtaining the resistance increase rate of all core samples and formation factors; step 3: calculating the average cementation index and saturation index of all fractured cores and the average cementation index and saturation index of all non-fractured cores by Archie's formula; step 4: establishing a saturation calculation model for a layer without fractures; step 5: obtaining additional conductivity of a fractured core, and using the additional conductivity to correct the resistance increase rate of the fractured core; and step 6: establishing a saturation calculation model for a fractured layer. This method solves the problem that the calculation results of the bedrock reservoir saturation by the previous logging saturation calculation method are low in accuracy, and the traditional saturation interpretation model is difficult to use.

Description

Technical Field

[0001] The invention relates to the technical field of well logging evaluation, in particular to a method for determining a bedrock reservoir saturation model. Background Art

[0002] Reservoir saturation is one of the most important parameters for reserve evaluation. Archie's formula is the core of electrical logging saturation calculation, but Archie's formula is mainly applicable to reservoirs with good reservoir properties and homogeneity, such as clastic rocks with good porosity and permeability. In reservoirs with complex pore structures and strong heterogeneity, the accuracy of saturation calculation results based on Archie's formula is very low. For this reason, a series of saturation calculation models have been developed based on Archie's formula, such as saturation models considering the influence of mud, saturation models considering the influence of skeletons and multiple pores, and general saturation models based on network conductivity. The above saturation models are mainly proposed for the influence of mud, skeleton conductivity, micropores and different pore structures, but the bedrock reservoir has a very low porosity (effective reservoir porosity is between 1.8% and 5%), fractures are widely developed, and the content of conductive minerals is high. Therefore, there are many factors affecting its electrical properties and the law of change is complex, so the traditional saturation interpretation model is difficult to apply. Summary of the invention

[0003] In view of this, in order to improve the calculation accuracy of oil and gas saturation in complex bedrock reservoirs, the present invention provides a bedrock reservoir saturation model determination method to solve the problem that the calculation results of bedrock reservoir saturation by previous well logging saturation calculation methods have low accuracy and traditional saturation interpretation models are difficult to use.

[0004] The present invention provides a method for determining a bedrock reservoir saturation model, comprising the steps of:

[0005] Step 1: Select core samples of the target layer, including cores with fractures and cores without fractures;

[0006] Step 2: Obtain the resistivity increase rate and formation factors of all core samples;

[0007] Step 3: According to the resistivity increase rate and formation factors, the average cementation index and saturation index of all cores with fractures, and the average cementation index and saturation index of all cores without fractures are calculated by Archie's formula;

[0008] Step 4: Establish a saturation calculation model for the fracture-free layer segment based on the resistivity increase rate of all the cores without fractures, formation factors, average cementation index and saturation index;

[0009] Step 5: obtaining additional conductivity of the core containing fractures, and using the additional conductivity to correct the resistance increase rate of the core containing fractures;

[0010] Step 6: A saturation calculation model for the fracture development layer section is established based on the corrected resistivity increase rate of the fractured core, formation factors, average cementation index and saturation index.

[0011] Preferably, the method for obtaining the resistivity increase rate of all core samples and formation factors in step 2 comprises the steps of:

[0012] Conducting multiple mineralization rock electrical experiments on all the core samples to obtain the water-saturated core resistivity of each core sample at different mineralizations and the core resistivity at different water saturations;

[0013] According to the resistivity of the water-saturated core under different mineralizations and the resistivity of the core under different water saturations, the resistivity increase rate and formation factors of each core sample are calculated by Archie's formula.

[0014] Preferably, the different mineralizations include:

[0015] The actual formation water mineralization of the target layer and the differential mineralization that is significantly different from the actual formation water mineralization.

[0016] Preferably, the method for obtaining additional conductivity of the fractured core in step 5 comprises:

[0017] According to the water-saturated core resistivity of the core sample at different salinities, a linear relationship between the core conductivity and the formation water conductivity at different salinities is established;

[0018] According to the linear relationship between the core conductivity and the formation water conductivity, the additional conductivity of the core is determined when the formation water conductivity is zero.

[0019] Preferably, the method for correcting the resistivity increase rate of the fractured core using the additional conductivity in step 5 comprises the steps of:

[0020] The additional conductivity is used to correct the core resistivity of the fractured core at different water saturations measured by the rock electrical experiment under the actual formation water salinity;

[0021] According to the corrected core resistivity of fractured core at different water saturations, the corrected resistivity increase rate of fractured core is calculated by Archie's formula.

[0022] Preferably, the method of correcting the core resistivity of a fractured core at different water saturations measured by a rock electrical experiment under real formation water salinity by using additional conductivity comprises the steps of:

[0023] The core resistivity of fractured cores at different water saturations is converted into conductivity;

[0024] The conductivity at each water saturation point is subtracted from the additional conductivity and converted into the core resistivity at that water saturation.

[0025] Preferably, it is characterized in that the step 1 further comprises:

[0026] The core samples are subjected to core processing and pretreatment.

[0027] Preferably, the saturation calculation model for the fracture-free layer in step 4 is:

[0028]

[0029] Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, a decimal; a1, b1, and n1 are unknown parameters, which are determined by fitting the experimental data of the resistivity increase rate I of the core without fractures and the water saturation Sw.

[0030] Preferably, the saturation calculation model of the fracture development layer in step 6 is:

[0031]

[0032] Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, a decimal; a2, b2, and n2 are unknown parameters, which are determined by fitting the experimental data of the resistivity increase rate I of the fractured core and the water saturation Sw.

[0033] Preferably, the Archie formula includes:

[0034]

[0035] Where: I is the resistivity increase rate, dimensionless; Rt is the core resistivity at different water saturations, ohm.m; R0 is the resistivity of the water-saturated core, ohm.m; Sw is the water saturation, a decimal; n is the saturation index, dimensionless; b is a constant.

[0036]

[0037] Where: F is the formation factor, dimensionless; R0 is the resistivity of the water-saturated core, ohm.m; Rw is the resistivity of the formation water, ohm.m; φ is the porosity, a decimal; m is the core cementation index, dimensionless, and a is a constant.

[0038] The present invention has the following beneficial effects:

[0039] The present invention provides a bedrock reservoir saturation model determination method, which classifies bedrock reservoir core samples and conducts systematic core experiments to clarify the bedrock reservoir formation factors, the influencing factors of the resistivity increase rate and the change law, and forms a bedrock reservoir (containing oil and gas) saturation model determination method through experimental data analysis, thereby improving the calculation accuracy of the oil and gas saturation of complex bedrock reservoirs. The problem that the calculation results of bedrock reservoir saturation by the previous logging saturation calculation method are low in accuracy and the traditional saturation interpretation model is difficult to use is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The above and other objects, features and advantages of the present invention will become more apparent through the following description of the embodiments of the present invention with reference to the accompanying drawings, in which:

[0041] Figure 1 It is a flow chart of a method for determining a bedrock reservoir saturation model according to an embodiment of the present invention.

[0042] Figure 2 It is a distribution diagram of the cementation index m of the target layer with and without fractures in the embodiment of the present invention.

[0043] Figure 3 3 is a diagram showing the relationship between the resistivity increase rate and water saturation of a layer section without fracture development in an embodiment of the present invention.

[0044] Figure 4 1 is a diagram showing the relationship between the resistivity increase rate and water saturation of the fracture development layer in the embodiment of the present invention.

[0045] Figure 5 It is a schematic diagram of the water saturation evaluation result of the target well in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The present invention is described below based on embodiment, but it is worth noting that the present invention is not limited to these embodiments. In the detailed description of the present invention below, some specific details are described in detail. However, for the part not described in detail, those skilled in the art can also fully understand the present invention.

[0047] In addition, those skilled in the art should understand that the drawings are only provided to illustrate the purpose, features and advantages of the present invention, and the drawings are not actually drawn to scale.

[0048] At the same time, unless the context clearly requires otherwise, the words "include", "comprises" and similar words throughout the specification and claims should be interpreted as inclusive rather than exclusive or exhaustive; that is, the meaning is "including but not limited to".

[0049] Figure 1It is a flow chart of a method for determining a bedrock reservoir saturation model according to an embodiment of the present invention. Figure 2 It is a distribution diagram of the cementation index m of the target layer with and without fractures in the embodiment of the present invention. Figure 3 3 is a diagram showing the relationship between the resistivity increase rate and water saturation of a layer section without fracture development in an embodiment of the present invention. Figure 4 1 is a diagram showing the relationship between the resistivity increase rate and water saturation of the fracture development layer in the embodiment of the present invention. Figure 5 Schematic diagram of the water saturation evaluation result of the target well in the embodiment of the present invention. Figure 1 , 2 As shown in Figures 3, 4 and 5, a method for determining a bedrock reservoir saturation model comprises the following steps: 1: selecting core samples of a target layer, including cores with fractures and cores without fractures; 2: obtaining the resistivity increase rate and formation factors of all core samples; 3: calculating the average cementation index and saturation index of all cores with fractures and the average cementation index and saturation index of all cores without fractures by Archie's formula according to the resistivity increase rate and formation factors; 4: establishing a saturation calculation model for a layer without fractures according to the resistivity increase rate, formation factors, average cementation index and saturation index of all cores without fractures; 5: obtaining additional conductivity of cores with fractures, and using the additional conductivity to correct the resistivity increase rate of cores with fractures; 6: establishing a saturation calculation model for a layer with fractures according to the corrected resistivity increase rate, formation factors, average cementation index and saturation index of cores with fractures.

[0050] Compared with other saturation model determination methods, the present invention has the following significant advantages: 1. Due to the dense bedrock reservoir and the development of fractures, the influence of fractures on electrical properties is fully reflected by studying the rock-electrical relationship of fractured cores and non-fractured cores; 2. The additional conductivity of fractured cores is determined (the additional conductivity can be one or more of mud, conductive minerals, micropores, fractures, etc.; the dense bedrock reservoir is mainly manifested as additional conductivity of fractures, and the determination of additional conductivity of fractures is of great significance to the establishment of a quantitative relationship between bedrock saturation and resistivity); 3. In fracture-developed layers and fracture-undeveloped layers, the non-Archie formula is used to fit the relationship between the resistivity increase rate I and the water saturation Sw, which further improves the calculation accuracy of gas saturation, especially gas saturation in the low bound water saturation interval. The problem that the calculation results of bedrock reservoir saturation by the previous logging saturation calculation method are low in accuracy and the traditional saturation interpretation model is difficult to use is solved.

[0051] Step 1: Select core samples of the target layer, including cores with fractures and cores without fractures.

[0052] In the present invention, step 1 also includes the step of: performing core processing and pretreatment on the core sample.

[0053] In the embodiment of the present invention, the selected core samples are representative cores of the target layer section in the target well, and should include cores with cracks and cores without cracks. Core processing is to process the end face of the core to meet the needs of the rock electrical experiment holder, and pretreatment is to wash the core with salt, wash the oil and other pretreatments.

[0054] Step 2: Obtain the resistivity increase rate and formation factors of all core samples.

[0055] In the present invention, the method for obtaining the resistivity increase rate and formation factors of all core samples in step 2 includes the steps of: performing multi-mineralization rock electrical experiments on all core samples to obtain the water-saturated core resistivity and the core resistivity at different water saturations of each core sample; and calculating the resistivity increase rate and formation factors of each core sample by Archie's formula according to the water-saturated core resistivity and the core resistivity at different water saturations of each core sample.

[0056] In the present invention, different mineralizations include: the real formation water mineralization of the target layer and the differential mineralization that is significantly different from the real formation water mineralization.

[0057] In the present invention, Archie's formula includes:

[0058]

[0059] Where: I is the resistivity increase rate, dimensionless; Rt is the core resistivity at different water saturations, ohm.m; R0 is the resistivity of the water-saturated core, ohm.m; Sw is the water saturation, a decimal; n is the saturation index, dimensionless; b is a constant;

[0060]

[0061] Where: F is the formation factor, dimensionless; R0 is the resistivity of the water-saturated core, ohm.m; Rw is the resistivity of the formation water, ohm.m; φ is the porosity, a decimal; m is the core cementation index, dimensionless.

[0062] In an embodiment of the present invention, in order to conduct a rock electrical experiment on all core samples, it is necessary to determine the mineralization of at least two brines required for the rock electrical experiment based on the geological characteristics of the target layer, wherein one mineralization is the real formation water mineralization S1 of the target layer, and the other mineralization is the difference mineralization S2 that is significantly different from S1. If the real formation water mineralization S1 is low, the mineralization S2 can be selected to have a value larger than the real formation water mineralization S1; if the real formation water mineralization S1 is high, the mineralization S2 can be selected to have a value smaller than the real formation water mineralization S1. In addition to the above-mentioned two mineralizations S1 and S2, other different mineralizations can be selected as needed to conduct corresponding rock electrical experiments, but as the number of experimental mineralization types increases, the time required for the experiment increases. The difference between the two mineralizations has met the experimental needs and saved experimental time.

[0063] According to the geological characteristics and analysis data of the target layer section in the well, the formation water salinity of the study layer section in the embodiment of the present invention is 5000ppm, and the water type is sodium chloride, so the actual formation water salinity S1 in the experiment is 5000ppm. For formation fluid, the salinity of 5000ppm is relatively low, so another salinity S2 required for the experiment is selected as 50000ppm.

[0064] The processed core samples are subjected to multi-mineralization rock electrical experiments, that is, the selected core samples are subjected to the same temperature and pressure conditions, and the same experimental method is used to measure the water-saturated rock electrical core resistivity R0 at a mineralization of 5000ppm and 50000ppm, and the core resistivity Rt at different water saturations Sw. In the embodiment of the present invention, the rock electrical experiment temperature is 25 degrees, the confining pressure is 25Mpa, the displacement pressure is 2Mpa, and the experimental method is semi-permeable baffle gas drive.

[0065] Substitute the measured values ​​of the water-saturated core resistivity R0 and the core resistivity Rt at different water saturations Sw into Archie's formula to calculate the values ​​of the resistivity increase rate I and formation factor F of each core sample. At the same time, the porosity φ of the core sample will also be obtained through rock electrical experimental measurements.

[0066] Among them, saturated water means that the rock pores are completely filled with water, that is, Sw = 1; different water saturation Sw refers to the ratio of the volume of water to the pore volume when the rock pores contain different volumes of water, for example, Sw = 0.8 means that the rock pores contain 80% water, Sw = 0.6 means that the rock pores contain 60% water, and so on. The rock has different water saturation Sw, and the rock conductivity characteristics are different, and the rock resistivity Rt changes with the change of water saturation Sw.

[0067] Step 3: According to the resistivity increase rate and formation factors, the average cementation index and saturation index of all cores with fractures, as well as the average cementation index and saturation index of all cores without fractures, are calculated by Archie's formula.

[0068] In the embodiment of the present invention, it is required to obtain the average cementation index of the core containing fractures and the average cementation index of the core without fractures. It is necessary to first calculate the cementation index m of each core containing fractures and the cementation index m of each core without fractures. To obtain the value of the cementation index m of the core sample as the true cementation index m of the formation, it is necessary to obtain the value of the water-saturated core resistivity R0 of the core sample measured by the rock electrical experiment when the mineralization is S1, and the value of the core resistivity Rt under different water saturations Sw, and then combine the formation factor F, porosity φ and the value of the resistivity increase rate I, substitute into Archie's formula, and calculate the value of the cementation index m of each core sample, and the value of the saturation index n. Among them, according to the water analysis data of the study area, the value of the formation water resistivity Rw of the target layer can be obtained to be 0.3ohm.m.

[0069] After calculating the cementation index m of each core sample using Archie's first formula, the core samples were divided into two groups: cores with fractures and cores without fractures. The average values ​​of the cementation index m of all cores with fractures and the average values ​​of the cementation index m of all cores without fractures were calculated respectively.

[0070] like Figure 2 The figure shows the distribution of cementation index m of the target layer with and without fractures. Figure 2 It can be seen that the value of the cementation index m of the core with fractures is significantly lower than that of the core without fractures. Among them, the average value of the cementation index m of the core with fractures is 1.26, and the average value of the cementation index m of the core without fractures is 1.41.

[0071] Step 4: Based on the resistivity increase rate of all cores without fractures, formation factors, average cementation index and saturation index, a saturation calculation model for the fracture-free layer is established.

[0072] In the present invention, the saturation calculation model of the fracture-free layer section in step 4 is:

[0073]

[0074] Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, a decimal; a1, b1, and n1 are unknown parameters, which are determined by fitting the experimental data of the resistivity increase rate I of the core without fractures and the water saturation Sw.

[0075] In the embodiment of the present invention, by conducting rock electrical experiments on cores without fractures at different mineralizations and analyzing the experimental results, the influencing factors and changing laws between the resistivity increase rate I and the water saturation Sw are clarified, thereby establishing a non-Archie relationship between the resistivity increase rate I and the water saturation Sw of the fracture-free layer section as shown in formula (3).

[0076] For the experimental data of the core resistance increase rate I and water saturation Sw of the target layer without fractures obtained in the embodiment of the present invention, the non-Archie relationship, that is, formula (3), is used to fit the experimental data of the core resistance increase rate I and water saturation Sw of the target layer without fractures to obtain the values ​​of constants a1, b1, and n1, thereby obtaining a specific relationship formula between the resistance increase rate I and water saturation Sw of the layer without fractures, as shown in the following formula (4):

[0077]

[0078] Where: I is the resistance increase rate, dimensionless; Sw is the water saturation, a decimal; the undetermined parameters a1 is 0.50917, b1 is 0.5309, and n1 is 2.9652.

[0079] The experimental results of the core without fractures represent the reservoir characteristics of the layer without fractures. According to the relationship between the resistivity increase rate I and the water saturation Sw in the layer without fractures, and according to Archie formula (1), the resistivity increase rate so

[0080]

[0081] Combined with the formation factors F of the core without fractures measured by the rock electrical experiment, the resistivity R0 of the water-saturated core, and the porosity φ, according to Archie formula (2): The average value of the cementation index m1 of the core without fractures can be determined, so the relationship between R0, Rw and porosity φ of the core without fractures is as follows:

[0082]

[0083] Where: R0 is the resistivity of the water-saturated core, ohm.m; Rw is the resistivity of the formation water, ohm.m; φ is the porosity, a decimal; m1 is the average cementation index of the core without fractures.

[0084] According to formula (5) and formula (6), the calculation formula of water saturation Sw of reservoir without fracture development can be derived by elimination method:

[0085]

[0086] Where: Sw is water saturation, decimal; m1 is the average cementation index of cores without fractures, dimensionless; φ is porosity, decimal; Rw is the formation water resistivity of the target layer in the study area, ohm.m; Rt is the core resistivity at different water saturations, ohm.m.

[0087] Figure 3 This is the relationship between the resistivity increase rate I and the water saturation Sw in the fracture-free layer. The figure shows the fitting results of two different models, Archie and non-Archie. Figure 3 It can be seen that both Archie and non-Archie rock-electric relationship have very high fitting accuracy for experimental data, but when the reservoir water saturation Sw is lower than 0.6, the difference between the two models is very significant. When the water saturation Sw is lower than 0.6, it is generally a gas layer, so the rationality of the I-Sw relationship directly affects the identification of the gas layer. According to the analysis of mercury-injection bound water saturation, it is proved that the water saturation calculated by the saturation model established based on the non-Archie I-Sw relationship is more reasonable.

[0088] Step 5: Obtain additional conductivity of the core containing fractures, and use the additional conductivity to correct the resistivity increase rate of the core containing fractures.

[0089] In the present invention, the method for obtaining the additional conductivity of the fractured core in step 5 includes: establishing a linear relationship between the core conductivity and the formation water conductivity at different salinities based on the water-saturated core resistivity of the core sample at different salinities; and determining the additional conductivity of the core when the formation water conductivity is zero based on the linear relationship between the core conductivity and the formation water conductivity.

[0090] In the embodiment of the present invention, when the formation water salinity Cw of the target layer is zero, it represents the additional conductivity of the fracture, which is recorded as C0. To obtain the additional conductivity C0 of the fractured core, it is necessary to first establish a linear relationship between the core conductivity C when saturated with water and the formation water conductivity Cw at different salinities. The water-saturated core resistivity R0 of the fractured core was measured by rock electrical experiments at two salinities of 5000PPM and 50000PPM. According to the conversion chart of mineralization and resistivity, the formation water resistivity Rw when the mineralization is 5000PPM and 50000PPM is obtained; according to the reciprocal relationship between resistivity and conductivity, the resistivity R0 of the water-saturated core is converted to the conductivity C of the water-saturated core, and the formation water resistivity Rw is converted to the formation water conductivity Cw; based on the two sets of C and Cw data after conversion, the linear relationship between the conductivity C of the water-saturated core and the formation water conductivity Cw is established by the data fitting method:

[0091] C=0.0015Cw+0.0027; (8)

[0092] Where: C is the conductivity of the water-saturated core, S / m; Cw is the conductivity of the formation water, S / m.

[0093] According to the linear relationship between the conductivity C of the water-saturated core and the formation water conductivity Cw, the additional conductivity C0 is determined. According to the linear relationship, when the formation water conductivity Cw is zero, the additional conductivity C0 value of the water-saturated core is 0.0027. The cause of the additional conductivity may be one or more of mud, conductive minerals, micropores, cracks, etc.

[0094] In the present invention, the method for correcting the resistance increase rate of the fractured core by using additional conductivity in step 5 includes the steps of: correcting the core resistivity of the fractured core at different water saturations measured by the rock electrical experiment under the actual formation water salinity by using additional conductivity; and calculating the corrected resistance increase rate of the fractured core by using the Archie formula according to the corrected core resistivity of the fractured core at different water saturations.

[0095] In the present invention, a method for correcting the core resistivity of a fractured core at different water saturations measured in a rock electrical experiment under real formation water salinity by using additional conductivity comprises the steps of: converting the core resistivity of the fractured core at different water saturations into electrical conductivity; subtracting the additional conductivity from the electrical conductivity at each water saturation point, and converting the resultant into the core resistivity at the water saturation.

[0096] In the embodiment of the present invention, it is necessary to correct the core resistivity Rt of the fractured core at different water saturations under the actual formation water salinity, that is, when the salinity is 5000 ppm, according to the additional conductivity, so that the core resistivity value obtained by the experiment is more consistent with the core resistivity of the actual reservoir.

[0097] First, the core resistivity Rt of fractured cores at different water saturations needs to be converted into conductivity Ct. The conversion formula is:

[0098]

[0099] Where: Rt is the core resistivity at different water saturations, ohm.m; Ct is the core conductivity at different water saturations, S / m.

[0100] According to the conversion formula of core resistivity Rt at different water saturations and conductivity Ct at different water saturations, the conductivity Ct at different water saturations is obtained, and then the converted conductivity Ct at different water saturations is subtracted from the additional conductivity C0 to obtain the corrected conductivity Ct' at different water saturations, which is as follows:

[0101] Ct'=Ct-C0; (10)

[0102] Where: Ct is the conductivity at different water saturations; Ct' is the corrected conductivity at different water saturations; C0 is the additional conductivity.

[0103] According to the above formula, the corrected conductivity Ct' at different water saturations is obtained and then converted into the resistivity Rt' at the water saturation. The conversion formula is:

[0104]

[0105] Where: Rt' is the corrected core resistivity at different water saturations; Ct' is the corrected conductivity at different water saturations.

[0106] The converted core resistivity Rt' at different water saturations is the corrected core resistivity Rt' at different water saturations of the fractured core when the mineralization is S1.

[0107] According to the corrected core resistivity Rt' at different water saturations of the fractured core, the corrected resistivity increase rate I of the fractured core is calculated by Archie's formula.

[0108] Step 6: Based on the corrected fracture core resistivity increase rate, formation factors, average cementation index and saturation index, a saturation calculation model for fracture development layers is established.

[0109] In the present invention, the saturation calculation model of the fracture development layer in step 6 is:

[0110]

[0111] Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, a decimal; a2, b2, and n2 are unknown parameters, which are determined by fitting the experimental data of the resistivity increase rate I of the fractured core and the water saturation Sw.

[0112] In the embodiment of the present invention, by conducting rock electrical experiments on fractured cores at different mineralizations and analyzing the experimental results, the influencing factors and changing laws of the relationship between the resistivity increase rate I and the water saturation Sw are clarified, thereby establishing a non-Archie relationship between the resistivity increase rate I and the water saturation Sw of the fracture development layer segment as shown in formula (12).

[0113] For the experimental data of the resistivity increase rate I and water saturation Sw of the target layer section containing fractures obtained in the embodiment of the present invention, the non-Archie relationship, i.e., formula (12), is used to fit the corrected experimental data of the resistivity increase rate I and water saturation Sw of the core containing fractures to obtain the values ​​of constants a2, b2, and n2, thereby obtaining the relationship formula between the resistivity increase rate I and water saturation Sw of the specific fracture development layer section, as shown in the following formula (13):

[0114]

[0115] Where: I is the resistance increase rate, dimensionless; Sw is the water saturation, a decimal; the undetermined parameters a2 is 0.2126; b2 is 0.8346; n2 is 4.7751.

[0116] The experimental results of fractured cores represent the reservoir characteristics of fracture-developed layers. According to the relationship between the resistivity increase rate I and water saturation Sw in fracture-developed layers, and according to Archie formula (1), the resistivity increase rate so

[0117]

[0118] Combined with the formation factors F, water-saturated core resistivity R0, and porosity φ of the fractured core measured by rock electrical experiments, according to Archie formula (2): The average cementation index m2 of the fractured core can be determined, and the relationship between R0, Rw and porosity φ of the fractured core is as follows:

[0119]

[0120] Where: R0 is the resistivity of the water-saturated core, ohm.m; Rw is the resistivity of the formation water, ohm.m; φ is the porosity, a decimal; m2 is the average cementation index of the fractured core.

[0121] According to formula (14) and formula (15), the calculation formula of water saturation Sw of fractured reservoir can be derived by elimination method:

[0122]

[0123] Where: Sw is water saturation, decimal; m2 is the average cementation index of fractured cores; φ is porosity, decimal; Rw is formation water resistivity, ohm.m; Rt is core resistivity at different water saturations, ohm.m.

[0124] Figure 4is the relationship between the resistivity increase rate I and the water saturation Sw of the fractured layer. The figure shows the fitting results of two different models, Archie and non-Archie. Figure 4 It can be seen that both Archie and non-Archie rock-electric relationship have very high fitting accuracy for experimental data, but when the water saturation of the reservoir is lower than 0.6, the difference between the two models is very significant. When the water saturation Sw is lower than 0.6, it is generally a gas layer, so the rationality of the I-Sw relationship directly affects the identification of the gas layer. According to the analysis of mercury-injection bound water saturation, it is proved that the water saturation calculated by the saturation model established based on the non-Archie I-Sw relationship is more reasonable.

[0125] In the embodiment of the present invention, the saturation of the target layer is calculated using the established fracture development and non-development reservoir saturation model, and the results are as follows: Figure 5 Schematic diagram of water saturation evaluation results of the target well shown. Figure 5 The first track is the lithology curve, the second track is the depth, the third track is the resistivity curve, the fourth track is the three-porosity curve, the fifth track is the calculated porosity, the sixth track is the water saturation calculated by the method proposed by the present invention, and the seventh track is the gas test result. The average water saturation of this section is 0.42, that is, the gas saturation is 0.58. The lithology of this layer is metamorphic andesite. Mercury injection analysis shows that the bound water saturation is relatively high. The gas test result is 2110.7 cubic meters of gas per day, which is consistent with the saturation calculation result of the embodiment of the present invention.

[0126] The method proposed in the present invention studies the rock-electricity relationship of fractured reservoirs and non-fractured reservoirs respectively, fully reflecting the influence of fractures on electrical properties; through multi-mineralization experiments, the additional conductivity of fractured cores is accurately determined, and the resistance increase rate I is corrected by the additional conductivity of fractures; the relationship between I and Sw of the non-Archie formula is adopted for both fracture-developed and fracture-undeveloped layers, reflecting the non-Archie characteristics of the electrical properties of the bedrock reservoir, and greatly improving the calculation accuracy of the bedrock reservoir saturation.

[0127] The above embodiments are only for expressing the implementation mode of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present invention, several modifications, equivalent substitutions, improvements, etc. can be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for determining a bedrock reservoir saturation model, characterized in that: Includes steps: Step 1: Select core samples of the target layer, including cores with fractures and cores without fractures; Step 2: Obtain the resistivity increase rate and formation factors of all core samples; Step 3: According to the resistivity increase rate and formation factors, the average cementation index and saturation index of all cores with fractures, and the average cementation index and saturation index of all cores without fractures are calculated by Archie's formula; Step 4: Establish a saturation calculation model for the fracture-free layer segment based on the resistivity increase rate of all the cores without fractures, formation factors, average cementation index and saturation index; The saturation calculation model of the fracture-free layer in step 4 is: Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, decimal; a1, b1, n1 are unknown parameters, which are determined by fitting the resistivity increase rate I of the core without fractures and the experimental data of water saturation Sw; Step 5: obtaining additional conductivity of the core containing fractures, and using the additional conductivity to correct the resistance increase rate of the core containing fractures; Step 6: Establishing a saturation calculation model for the fracture development layer segment according to the corrected resistivity increase rate of the fractured core, formation factors, average cementation index and saturation index; The saturation calculation model of the fracture development layer in step 6 is: Where: I is the resistivity increase rate, dimensionless; Sw is the water saturation, a decimal; a2, b2, and n2 are unknown parameters, which are determined by fitting the experimental data of the resistivity increase rate I of the fractured core and the water saturation Sw.

2. The method for determining a bedrock reservoir saturation model according to claim 1, characterized in that: The method for obtaining the resistivity increase rate and formation factors of all core samples in step 2 comprises the steps of: Conducting multiple mineralization rock electrical experiments on all the core samples to obtain the water-saturated core resistivity of each core sample at different mineralizations and the core resistivity at different water saturations; According to the resistivity of the water-saturated core under different mineralizations and the resistivity of the core under different water saturations, the resistivity increase rate and formation factors of each core sample are calculated by Archie's formula.

3. The method for determining a bedrock reservoir saturation model according to claim 2, characterized in that: The different mineralizations include: The actual formation water mineralization of the target layer and the differential mineralization that is significantly different from the actual formation water mineralization.

4. The method for determining a bedrock reservoir saturation model according to claim 3, characterized in that: The method for obtaining additional conductivity of the fractured core in step 5 comprises: According to the water-saturated core resistivity of the core sample at different salinities, a linear relationship between the core conductivity and the formation water conductivity at different salinities is established; According to the linear relationship between the core conductivity and the formation water conductivity, the additional conductivity of the core is determined when the formation water conductivity is zero.

5. The method for determining a bedrock reservoir saturation model according to claim 4, characterized in that: The method for correcting the resistance increase rate of the fractured core using the additional conductivity in step 5 comprises the following steps: The additional conductivity is used to correct the core resistivity of the fractured core at different water saturations measured by the rock electrical experiment under the actual formation water salinity; According to the corrected core resistivity of fractured core at different water saturations, the corrected resistivity increase rate of fractured core is calculated by Archie's formula.

6. The method for determining a bedrock reservoir saturation model according to claim 5, characterized in that: The method for correcting the core resistivity of a fractured core at different water saturations measured by a rock electrical experiment under real formation water salinity by using additional conductivity comprises the following steps: The core resistivity of fractured cores at different water saturations is converted into conductivity; The conductivity at each water saturation point is subtracted from the additional conductivity and converted into the core resistivity at that water saturation.

7. The method for determining a bedrock reservoir saturation model according to claim 1, characterized in that: The step 1 also includes: The core samples are subjected to core processing and pretreatment.

8. The method for determining a bedrock reservoir saturation model according to any one of claims 1 to 7, characterized in that: The Archie formula includes: Where: I is the resistivity increase rate, dimensionless; Rt is the core resistivity at different water saturations, ohm.m; R0 is the resistivity of the water-saturated core, ohm.m; Sw is the water saturation, a decimal; n is the saturation index, dimensionless; b is a constant; Where: F is the formation factor, dimensionless; R0 is the resistivity of the water-saturated core, ohm.m; Rw is the resistivity of the formation water, ohm.m; φ is the porosity, a decimal; m is the core cementation index, dimensionless, and a is a constant.

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