Method and system for identifying fluid properties of tight sandstone fractured reservoir

Abstract

The invention discloses a method and system for identifying fluid properties of a tight sandstone fractured reservoir, and the method comprises the steps: calculating neutron difference ratio evaluation indexes at different depths in a fractured reservoir section in a current well according to a neutron logging curve of a to-be-evaluated well in a target region, the neutron difference ratio evaluation index is a ratio of a first difference value to a neutron value at a corresponding depth, and the first difference value is a difference value of the neutron value at the corresponding depth and a neutron standard value of a compact layer section in the well to be evaluated; and according to the neutron difference ratio evaluation indexes under different depths, utilizing a pre-constructed fracture section gas-water layer division standard to identify fracture reservoir fluid properties of different depth sections. The problems that the resistivity of a crack section is reduced and fluid identification is difficult due to mud invasion and leakage are solved, the geological requirement is met, and the actual application effect is good.

Description

Technical Field

[0001] The present invention relates to the technical field of tight oil and gas geophysical exploration and development, and in particular to a method and system for identifying fluid properties in tight sandstone fracture reservoirs. Background Art

[0002] Tight sandstone reservoirs, influenced by factors such as tectonic deformation, faulting, and rock facies association, are prone to the formation of fractures of varying types and occurrences. The presence of fractures results in significantly different logging response characteristics in tight reservoirs compared to unfractured reservoirs. Typical logging response characteristics compared to adjacent less fractured intervals include low or serrated resistivity, large acoustic transit times, relatively high neutron counts, and low density.

[0003] Resistivity is a key parameter for identifying reservoir fluid properties. Reservoir resistivity, in addition to being related to lithologic and physical parameters, primarily reflects reservoir fluid properties. Generally speaking, in reservoirs with identical lithologic and physical properties, the resistivity of pore spaces filled with oil and gas will be significantly higher than that of formations filled with water. However, when fractures are present, resistivity logging reveals low to medium resistivity anomalies within a high-resistivity background. Furthermore, drilling fluid intrusion and loss during drilling can further reduce resistivity, even dropping below the resistivity of the water layer. Therefore, using resistivity values ​​to identify fractured reservoir fluids is less reliable.

[0004] Theoretically, the three-porosity logging combination can effectively reflect the properties of gas reservoirs, and neutron logging data, in particular, is the most powerful means of identifying gas-water layers. The reason for this is that neutron logging has a mining effect in gas layers, where the neutron values ​​are significantly reduced. However, due to the high permeability of fractures, when fractures exist, large amounts of drilling fluid intrude into the fractured sections, resulting in high water content in the fractures. Near the wellbore, gas is displaced by mud, causing the neutron logging values ​​to significantly increase, even exceeding those of the adjacent water layers. Therefore, it is difficult to accurately identify the gas-water properties of fractured reservoirs.

[0005] In the existing technology, there are many methods for qualitatively identifying gas layers. The petroleum industry standard SY / T 6161 "Natural Gas Well Logging Data Processing and Interpretation Specification" involves 23 qualitative identification methods; however, there are few methods for identifying fractured gas layers, especially tight fractured gas layers.

[0006] Specifically, the articles "Technical Methods for Identifying Fluids in Fractured Reservoirs: A Case Study of the Meso-Neoproterozoic Buried Hill Reservoirs in the Daminhe Sag of the Liaohe Basin" and "Study on Methods for Identifying Fluid Types in Fractured Reservoirs Using Conventional Well Logging Data" propose three methods for identifying fluid properties: nuclear magnetic resonance, a comprehensive resistivity ratio index, and production logging. The article "Identifying Natural Gas Layers in Volcanic Fractured Formations Using the Structural Resistivity Ratio Method" proposes a method for identifying fluid properties in fractured formations using the resistivity ratio method. These fractured reservoir fluid identification methods all utilize the resistivity ratio method, which may be suitable for reservoirs such as carbonates and volcanic rocks, but less suitable for the continental tight sandstone fractured reservoirs in western Sichuan, China. This is primarily due to the low background resistivity and large-scale fractures in tight reservoirs, resulting in deeper drilling fluid invasion and a weaker gas impact on the logging response. In addition, the paper "Indirect Identification Method of Fluid Properties in Fractured Carbonate Reservoirs Using Logging Data" provides a method for indirectly dividing fracture fluids using the fluid properties of the reservoirs above and below the fracture development section. This technology is less effective in tight sandstone reservoirs with edge and bottom water and low-angle fractures. The article "Research on Fluid Property Identification Methods in Carbonate Reservoirs Under Drilling Fluid Loss Conditions" involves three methods, all of which use indirect means such as resistivity and loss volume, mud resistance changes, and loss volume to infer fracture fluid properties. The differences in mud properties used in different wells are not taken into account, so the universality of this method remains to be discussed.

[0007] Therefore, the prior art needs to provide a fluid property identification solution suitable for tight sandstone fracture reservoirs. Summary of the Invention

[0008] The purpose of the present invention is to provide a fluid property identification solution suitable for tight sandstone fracture reservoirs.

[0009] In order to solve the above technical problems, an embodiment of the present invention provides a method for identifying the fluid properties of tight sandstone fractured reservoirs, including: calculating a neutron difference ratio evaluation index at different depths in the fractured reservoir section of the current well based on the neutron logging curve of the well to be evaluated in the target area, wherein the neutron difference ratio evaluation index is the ratio of a first difference value to the neutron value at the corresponding depth, and the first difference value is the difference between the neutron value at the corresponding depth and the neutron standard value of the tight layer section in the well to be evaluated; according to the neutron difference ratio evaluation index at different depths, using a pre-constructed fracture section gas-water layer division standard, the fluid properties of the fractured reservoir at different depth sections are identified.

[0010] Preferably, the fracture section gas-water layer division standard is constructed by the following steps: selecting at least one test well in the target area, the test well should have a fracture gas layer, a fracture gas-water layer and a fracture water layer; selecting a tight layer section of each test well and determining the neutron standard value of the tight layer section; selecting at least one fracture representative section of each test well and determining the neutron standard value of the fracture representative section; calculating the difference ratio evaluation index of each fracture representative section based on the neutron standard value of the tight layer section and the neutron standard value of the fracture representative section; drawing an intersection diagram between the difference ratio evaluation index and the resistivity standard value of each fracture representative section; dividing the first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer and the second neutron difference ratio limit value for distinguishing the fracture gas-water layer from the fracture water layer according to the data point distribution characteristics of the intersection diagram, so as to form the fracture section gas-water layer division standard.

[0011] Preferably, the step of selecting at least one fracture representative section for each test well includes: selecting a well section in the test well with low resistivity, large acoustic wave value and large neutron value as the fracture representative section, wherein the neutron standard value of each fracture representative section is the average value or representative value of the neutron value of the corresponding well section.

[0012] Preferably, the step of selecting a tight layer section of the well to be evaluated or the test well includes: selecting a well section in the well to be evaluated or the test well with a regular borehole, a low natural gamma value, a high resistivity, and a small acoustic wave value as the tight layer section, wherein the neutron standard value of the tight layer section is the average value or representative value of the neutron value of the tight layer section.

[0013] Preferably, the difference ratio evaluation index of each fracture representative section is calculated by the following steps: calculating the difference between the neutron standard value of each fracture representative section and the neutron standard value of the tight layer section in the test well to which the current fracture representative section belongs; dividing the difference corresponding to each fracture representative section by the neutron standard value of the corresponding fracture representative section, thereby obtaining the difference ratio evaluation index of each fracture representative section.

[0014] Preferably, the fracture section gas-water layer division standard has a first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer in the same layer, and a second neutron difference ratio limit value for distinguishing the fracture gas-water layer in the same layer from the fracture water layer, wherein the fracture section gas-water layer division standard includes: when the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas layer; when the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas-water layer in the same layer; when the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a water layer.

[0015] Preferably, the first neutron difference ratio limit value is 0.4, and the second neutron difference ratio limit value is 0.53.

[0016] On the other hand, an embodiment of the present invention provides a computer-readable storage medium comprising a series of instructions for executing the method steps described above.

[0017] In addition, an embodiment of the present invention provides a system for identifying the fluid properties of tight sandstone fractured reservoirs, including: a depth point evaluation index generation module, which is configured to calculate the neutron difference ratio evaluation index at different depths in the fractured reservoir section of the current well based on the neutron logging curve of the well to be evaluated in the target area, wherein the neutron difference ratio evaluation index is the ratio of the first difference value to the neutron value at the corresponding depth, and the first difference value is the difference between the neutron value at the corresponding depth and the neutron standard value of the tight layer section in the well to be evaluated; a reservoir type evaluation module, which is configured to identify the fluid properties of the fractured reservoir at different depth sections based on the neutron difference ratio evaluation index at different depths and the constructed fracture section gas-water layer division standard.

[0018] Preferably, the fracture section gas-water layer division standard has a first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer in the same layer, and a second neutron difference ratio limit value for distinguishing the fracture gas-water layer in the same layer from the fracture water layer, wherein the reservoir type evaluation module is further configured as follows: when the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a gas layer; when the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a gas-water layer in the same layer; when the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a water layer.

[0019] Compared with the prior art, one or more embodiments of the above solutions may have the following advantages or beneficial effects:

[0020] The present invention proposes a method and system for identifying fluid properties in tight sandstone fracture reservoirs. The method and system belong to the technical field of oil and gas geophysical tight gas exploration and development, and are used for identifying fluid properties in fracture-developed sections of tight reservoirs. The present invention utilizes the mining effect of gas layer neutron logging, and proposes using the difference ratio between the neutron value of the fracture section and the neutron value of the adjacent tight section as a parameter for fluid identification in the fracture section; through the analysis of the intersection diagram of known test wells, the identification standard of different fluids in the fracture section is obtained, and the standard value is used to further determine the fluid properties of different fracture sections. The present invention avoids the problems of reduced resistivity caused by mud intrusion and leakage, difficulty in fluid identification, etc., solves geological needs, and has good practical application effects.

[0021] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0023] Figure 1 Schematic diagram of the steps of a method for identifying fluid properties in a tight sandstone fracture reservoir according to an embodiment of the present application.

[0024] Figure 2 Schematic diagram of the construction process of the fracture section gas-water layer division standard in the method for identifying fluid properties of tight sandstone fracture reservoirs in an embodiment of the present application.

[0025] Figure 3 Schematic diagram comparing the construction effects of the fracture section gas-water layer differentiation plate in the method for identifying fluid properties in a tight sandstone fracture reservoir according to an embodiment of the present application.

[0026] Figure 4 This is an example diagram of the logging fluid identification results of the first well to be evaluated in the method for identifying fluid properties in a tight sandstone fracture reservoir according to an embodiment of the present application.

[0027] Figure 5 This is an example diagram of the logging fluid identification results of the second well to be evaluated in the method for identifying fluid properties in a tight sandstone fracture reservoir according to an embodiment of the present application.

[0028] Figure 6 This is a module block diagram of a system for identifying fluid properties in tight sandstone fracture reservoirs according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present invention in detail with reference to the accompanying drawings and examples, so that the present invention can fully understand how to apply technical means to solve technical problems and achieve technical effects, and thus implement the invention accordingly. It should be noted that, as long as no conflict exists, the various embodiments of the present invention and the various features of the embodiments can be combined with each other, and the resulting technical solutions are all within the scope of protection of the present invention.

[0030] In addition, the steps shown in the flowchart of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions. Also, although a logical order is shown in the flowchart, in some cases, the steps shown or described can be performed in a different order than here.

[0031] The terms used herein are intended only to describe specific embodiments and are not intended to limit exemplary embodiments. Unless the context clearly indicates otherwise, the singular forms "a", "an", "an item" used herein are also intended to include the plural. It should also be understood that the terms "comprise" and / or "include" used herein specify the presence of stated features, integers, steps, operations, units and / or components, and do not preclude the presence or addition of one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0032] In order to solve the technical problems in the above-mentioned background technology, the embodiment of the present application proposes a method and system for identifying the fluid properties of tight sandstone fracture reservoirs. Since the tight sandstone fracture reservoir section has good permeability, a large amount of drilling fluid often invades during the drilling process, causing the resistivity to decrease and the neutron to increase. Its response characteristics are similar to those of the adjacent water layer, and there is no obvious gas-bearing characteristics, which will cause the logging interpretation to be low and the favorable layer section to be missed. Therefore, the present invention determines the fluid properties of the fracture section by the size of the difference ratio between the neutron value of the fracture section and the neutron value of the adjacent tight section, thereby improving the reliability of the identification of the fluid properties of the fracture development section.

[0033] Example 1

[0034] Figure 1 This is a schematic diagram of the steps of the method for identifying the fluid properties of a tight sandstone fracture reservoir according to an embodiment of the present application. Figure 1 , the specific steps and processes of the reservoir fluid property identification method described in an embodiment of the present invention are described.

[0035] The present invention utilizes the mining effect of gas-layer neutron logging to propose using the difference ratio between the neutron values ​​of a fracture segment and the neutron values ​​of an adjacent tight segment as a fracture segment fluid identification parameter, thereby determining the properties of the fracture segment fluid. The theoretical basis for this is that during drilling, due to the influence of drilling fluid invasion, most gas is displaced by mud. However, since fractured gas layers often have high pressure, some gas can migrate back to the wellbore after pressure equilibrium and within a certain time interval, resulting in a certain decrease in the neutron value of the fracture segment, indicating that the fracture segment has high gas content. In contrast, for gas-water layers or water layers, the gas abundance is low and, theoretically, its pressure is lower than that of the gas layer. Therefore, the amount of gas migrating to the wellbore is reduced, and the impact on the neutron value is relatively small. Tight reservoir segments have low porosity, so even if they contain different fluids, the neutron effect is minimal. Furthermore, they have low permeability and are almost free of mud invasion. Therefore, the neutron value of such tight reservoir segments can be used as a background value, and the difference ratio between the neutron values ​​of the fracture segment and the tight segment can be used to qualitatively determine the fluid properties.

[0036] Step S110 calculates the neutron difference ratio evaluation index at different depths in the fracture reservoir section of the current well to be evaluated based on the neutron logging curves of the well to be evaluated in the target area.

[0037] In this embodiment of the present invention, the target area is the tight sandstone gas reservoir region where the well to be evaluated is located. In step S110, one or more fractured reservoir (well) segments are first extracted from the well to be evaluated, and then the neutron difference ratio evaluation index at different depths within each fractured reservoir segment is calculated.

[0038] In one embodiment, based on the resistivity curve, sonic logging curve, and neutron logging curve of the well to be evaluated, a well section in the well to be evaluated with low resistivity, large sonic values, and large neutron values ​​is selected as the fractured reservoir section. Specifically, a layer section in the well to be evaluated with a resistivity less than a preset fractured section resistivity threshold, a sonic value greater than a preset fractured section sonic threshold, and a neutron value greater than a preset fractured section neutron threshold is selected as the fractured reservoir section.

[0039] In one embodiment, the neutron difference ratio evaluation index is the ratio of a first difference value to the neutron value at a corresponding depth, where the first difference value is the difference between the neutron value at the corresponding depth and the neutron standard value of the tight layer section in the well to be evaluated. For the well to be evaluated, to calculate the neutron difference ratio evaluation index at a corresponding depth in the well to be evaluated, it is necessary to first calculate the first difference value at the corresponding depth, that is, to use the difference between the neutron value at the corresponding depth and the neutron standard value of the tight layer section in the well to be evaluated as the first difference value at the current depth, and then calculate the ratio of the first difference value at the current depth to the neutron value at the current depth, thereby obtaining the neutron difference ratio evaluation index corresponding to the current depth.

[0040] In this embodiment of the present invention, based on the caliper curve, natural gamma ray log curve, resistivity curve, and sonic wave log curve of the well to be evaluated, a well section with a regular borehole, low natural gamma ray value, high resistivity, and low sonic wave value is selected as the tight layer section in the well to be evaluated. The neutron standard value for the tight layer section is the average or representative value of the neutron values ​​in that tight layer section. Specifically, a well section with a regular borehole, natural gamma ray value less than a preset tight layer gamma threshold, resistivity value greater than a preset tight layer resistivity threshold, and sonic wave value less than a preset tight layer sonic wave threshold is selected as the tight layer section.

[0041] After obtaining the neutron difference ratio evaluation index sequence at each depth in the fracture reservoir section, the process proceeds to step S120.

[0042] Step S120 identifies the fluid properties of the fracture reservoirs at different depths based on the neutron difference ratio evaluation index at different depths and using the pre-established fracture segment gas-water layer division standard.

[0043] Before executing step S120 , the embodiment of the present invention needs to first establish a standard for dividing gas and water layers in fracture sections. Figure 2 This is a schematic diagram of the construction process of the gas-water layer division standard in the fracture section of the method for identifying the fluid properties of the tight sandstone fracture reservoir in the embodiment of the present application. Figure 2 , the construction process of the gas-water layer division standard of the fracture section is explained.

[0044] Step S201: At least one test well is selected in the target area. In step S201: Multiple test wells are selected in the target area. In the embodiment of the present invention, the test wells should have fractured gas layers, fractured gas-water layers, and fractured water layers.

[0045] Step S202 selects the tight layer section of each test well and determines the neutron standard value for each tight layer section. In step S202, the tight layer section of each test well must be selected. Based on the caliper curve, natural gamma ray log curve, resistivity curve, and sonic log curve of the current test well, the section with a regular borehole, low natural gamma ray value, high resistivity, and low sonic value in the current test well is selected as the tight layer section of the corresponding well. The neutron standard value for each tight layer section is the average or representative value of the neutron values ​​of the corresponding tight layer section.

[0046] Step S203 selects at least one representative fracture segment for each test well and determines the neutron standard value for each fracture segment. In step S203, at least one representative fracture segment is first selected for each test well. Based on the resistivity curve, sonic logging curve, and neutron logging curve of each test well, segments with low resistivity, high sonic values, and high neutron values ​​are selected as one or more representative fracture segments for the current test well. The average or representative neutron value of each representative fracture segment (well) is then used as the neutron standard value for the corresponding fracture segment.

[0047] Step S204 calculates a difference ratio evaluation index for each fracture representative segment based on the neutron standard value of the tight layer segment and the neutron standard value of the fracture representative segment. In one embodiment, the difference between the neutron standard value of each fracture representative segment and the neutron standard value of the tight layer segment in the test well to which the current fracture representative segment belongs is first calculated. The difference corresponding to each fracture representative segment is then divided by the neutron standard value of the corresponding fracture representative segment to obtain the difference ratio evaluation index for each fracture representative segment.

[0048] Step S205 draws a cross-plot between the difference ratio evaluation index for each fracture representative segment and the resistivity standard value of the corresponding fracture representative segment.

[0049] In step S205, first, based on the resistivity curve of each test well, the resistivity standard value of each fracture representative section is obtained (for example, the average resistivity value of each fracture representative section is used as the resistivity standard value of the corresponding representative section), and then the difference ratio evaluation index and the resistivity standard value of each fracture representative section are used as data points to draw an intersection diagram representing the difference ratio evaluation index and the resistivity standard value.

[0050] Next, step S206 uses the data point distribution characteristics of the crossplot constructed in step S205 to determine a first neutron difference ratio threshold for distinguishing fractured gas layers from gas-water layers, and a second neutron difference ratio threshold for distinguishing fractured gas-water layers from fractured water layers, thereby forming the fracture segment gas-water layer demarcation standard. Thus, the fracture segment gas-water layer demarcation standard formed in this embodiment of the present invention is marked with (has) a first neutron difference ratio threshold for distinguishing fractured gas layers from gas-water layers, and a second neutron difference ratio threshold for distinguishing fractured gas-water layers from fractured water layers.

[0051] The fracture section gas-water layer differentiation chart constructed by the present invention has a good effect in practical applications. Figure 3 Schematic diagram comparing the construction effects of the fracture section gas-water layer differentiation plate in the method for identifying fluid properties in a tight sandstone fracture reservoir according to an embodiment of the present application.

[0052] For example, 9 fracture test wells in a production block were selected for verification. The data showed that the resistivity of all data points was less than 50 ohmmm, the resistivity of the fracture gas layer was between 6-50 ohmmm, the neutron resistivity was between 2-10%, and the acoustic resistivity was between 190-350 us / m. Figure 3 As shown in the figure, the accuracy of identifying gas and water layers using conventional logging is low. Figure 3 In the left figure (resistivity-acoustic cross-plot), there is no clear boundary value; Figure 3 In the middle figure (resistivity and neutron cross-plot), the gas layer and the gas-water layer are difficult to separate; Figure 3 In the right figure (the intersection diagram of the difference ratio evaluation index and the resistivity standard value), the gas and water layers can be clearly identified.

[0053] In one embodiment, the first neutron difference ratio limit value is 0.4, and the second neutron difference ratio limit value is 0.53. For example, when the neutron difference ratio is less than or equal to 0.4, it is a fractured gas layer; when the neutron difference ratio is between 0.4 and 0.53, it is a fractured gas-water layer; and when the neutron difference ratio is greater than 0.53, it is a fractured water layer.

[0054] Therefore, the present invention utilizes the mining effect of gas formation neutron logging to propose using the difference ratio between the neutron values ​​in a fracture segment and those in the adjacent dense segment as a parameter for identifying fracture fluids. By analyzing crossplots of known test wells, a standard for identifying fracture fluids is derived, which is then used to further determine the fluid properties of different fracture segments. Using crossplot analysis of known test wells, this method achieves a consistency rate of over 95% for identifying fracture fluids.

[0055] After the fracture segment gas-water layer differentiation plate is completed and constructed based on the plate, step S120 will identify the fracture reservoir fluid properties at different depths according to the following fracture segment gas-water layer differentiation criteria based on the neutron difference ratio evaluation index at different depths in the well to be evaluated:

[0056] In the first embodiment, when the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a gas layer.

[0057] In the second embodiment, when the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a gas-water co-layer.

[0058] In a third embodiment, when the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, the fracture reservoir at the current depth is determined to be a water layer.

[0059] In this way, the embodiment of the present invention uses known test wells to establish identification standards according to steps S110 to S130, and combines them with relevant data such as resistivity to complete the fluid division of the fracture section.

[0060] Example 2

[0061] Based on the above reservoir fluid property identification method, the fluid in the fracture-developed section of the Xujiahe Formation in the Sichuan Basin is divided using the above reservoir fluid property identification method. The division results are shown in Figure 4 .

[0062] Figure 4 The following figure shows the processing and interpretation diagram of the logging data of the fracture gas layer of the well numbered XX11 in the block to be evaluated. Figure 4 As shown, from left to right:

[0063] The first channel is the depth channel, which displays the logging depth (DEPTH).

[0064] The second channel: lithology indicator channel, which lists the natural gamma ray curve (GR); the 5135-5136 meter well section was selected as the tight layer section (natural gamma is stable, neutron and sonic wave curves are stable, sonic wave values ​​are small, and resistivity is relatively high).

[0065] The third track is the porosity track, showing the neutron (CNL) and acoustic (AC) curves. The solid line is the acoustic curve, and the long-dashed line is the neutron curve. (Dense intervals: Neutron and acoustic curves are stable, acoustic values ​​are small, and neutron curve values ​​are relatively low.)

[0066] The fourth track is the resistivity track, which lists the resistivity curve, LLD is the deep lateral resistivity, and LLS is the shallow lateral resistivity.

[0067] The fifth track is a typical layer selection track, showing the selected dense section and fracture section.

[0068] The sixth track is the fracture fluid identification track. The solid line is the fluid identification curve (i.e., the neutron difference ratio evaluation index at different depths), and its value indicates the fluid properties. The dotted line is the lower limit of the fracture gas layer (0.4), and the long dashed line is the upper limit of the fracture water layer (0.53).

[0069] The seventh question: Explain the conclusion. Figure 4 The middle shows the fluid properties of the fracture development section. This well is a fracture gas layer.

[0070] Track 8: Gas test conditions, showing the test conditions within the test section, which are mainly gas with a small amount of water.

[0071] ① Figure 4In the 5135-5136 meter well section, the natural gamma is around 80API, the neutron and acoustic wave curves are stable, the acoustic wave value is small, and the resistivity is high, which meets the conditions of a standard tight layer.

[0072] ② Figure 4 The lithology of the middle section (5139.50-5145.50m) is gray fine-grained lithic sandstone, with gas logging values ​​of ∑Cn: 0.095↗0.511%; drilling fluid: ρ: 1.61g / cm3, Fv: 49s, chloride: 2700-2808ppm, and mud logging evaluation indicates a fractured gas-bearing layer. This section has lost drilling fluid, with a total loss of 12.54m3 of drilling fluid. 3 The 5142-5142.5m well section is a typical fracture section, characterized by significantly lower resistivity compared to the background value, and significantly increased acoustic and neutron characteristics.

[0073] Section ③: 5147.00-5178.60 m; Lithology: Light gray, fine-grained, lithic quartz sandstone; Drilling time: 56-110 min / m. Gas logging values: ∑Cn: 0.037 ↗ 61.829%, C1: 0.035 ↗ 50.039%, C2: 0 ↗ 0.344%; Drilling fluid properties: ρ: 1.61 g / cm³, FV: 49 s, Chloride: 2700-2808 ppm. Mud logging indicates a fractured, gas-bearing zone. The section 5150.2-5150.9 m is a typical fractured zone, characterized by significantly lower resistivity compared to background values, and a significant increase in acoustic and neutron resistivity.

[0074] In the well section (4), the resistivity in the 5142-5142.5 meter section was as low as 30 ohmmm. Based on regional experience, this resistivity value indicates a gas-water layer or a gas-water layer. However, the maximum value of the calculated fluid identification curve is less than 0.4, which, as shown in the figure, is interpreted as a fractured gas layer. Test results show that this section has high pressure and gas production of up to 85,800 cubic meters per day, which is typical of a gas layer. This further demonstrates the reliability of the interpretation.

[0075] Figure 5 The following figure shows the processing and interpretation diagram of the logging data of the fractured gas-bearing water layer in the well numbered XX12 in the block to be evaluated. Figure 5 As shown, from left to right:

[0076] The first channel is the depth channel, which displays the logging depth (DEPTH).

[0077] The second channel: lithology indicator channel, which lists the natural gamma ray curve (GR); the 5007.4-5009.1 meter well section was selected as the tight layer section (natural gamma is stable, neutron and sonic wave curves are stable, sonic wave values ​​are small, and resistivity is relatively high).

[0078] The third track is the porosity track, showing the neutron (CNL) and acoustic (AC) curves. The solid line is the acoustic curve, and the long-dashed line is the neutron curve. (Dense intervals: neutron and acoustic curves are stable, acoustic values ​​are small, and neutron curve values ​​are picked up.)

[0079] The fourth track is the resistivity track, which lists the resistivity curve, LLD is the deep lateral resistivity, and LLS is the shallow lateral resistivity.

[0080] The fifth track is a typical layer selection track, showing the selected dense section and fracture section.

[0081] The sixth track is the fracture fluid identification track. The solid line is the fluid identification curve (i.e., the neutron difference ratio evaluation index at different depths), and its value indicates the fluid properties. The dotted line is the lower limit of the fracture gas layer (0.4), and the long dashed line is the upper limit of the fracture water layer (0.53).

[0082] The seventh question: Explain the conclusion. Figure 5 The middle shows the fluid properties of the fracture development section. This well is a fractured water-gas layer.

[0083] Track 8: Gas test conditions, showing the test conditions within the test section, which are mainly water with a small amount of gas.

[0084] ① Figure 5 In the 5007.4-5009.1 meter well section, the natural gamma is around 70API, the neutron and acoustic wave curves are stable, and the acoustic wave value is small and the resistivity is high, which meets the standard layer conditions and has a high resistivity.

[0085] ② Figure 5 Middle, 4985-4990.0m, drill thickness 5.00m; lithology: gray medium-grained lithic quartz sandstone, medium-grained lithic sandstone. Drilling time: 44↘20 min / m. No logging information, identified as a water layer.

[0086] In the well section (3), the resistivity in the 4985-4990.0-meter section was below 3 ohms, indicating a gas-water layer or a gas-water layer. The minimum value of the calculated fluid identification curve was greater than 0.53, indicating a fractured gas-water layer, as shown in the diagram. The test results showed a daily water production of 360 cubic meters in this section, typical of a water layer. This further demonstrates the reliability of the interpretation.

[0087] Example 3

[0088] Based on the above-described reservoir fluid property identification method, embodiments of the present invention also provide a computer-readable storage medium storing a computer program. The computer program is executed to implement a method for identifying fluid properties in tight sandstone fractured reservoirs. The computer program is capable of executing computer instructions, which include computer program code. The computer program code may be in source code form, object code form, an executable file, or some intermediate form.

[0089] Computer-readable storage media may include: any entity or device that can carry computer program code, recording media, USB flash drives, mobile hard drives, magnetic disks, optical disks, computer memory, read-only memory (ROM), random access memory (RAM), electrical carrier signals, telecommunication signals, and software distribution media, etc.

[0090] It should be noted that the content contained in computer-readable storage media can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, the content contained in computer-readable storage media does not include electric carrier signals and telecommunication signals.

[0091] Example 4

[0092] Based on the above reservoir fluid property identification method, an embodiment of the present invention further provides a system for identifying fluid properties in tight sandstone fracture reservoirs (also referred to as a "reservoir fluid property identification system"). The reservoir fluid property identification system is used to implement the above reservoir fluid property identification method.

[0093] Figure 6 Module block diagram of the system for identifying fluid properties of tight sandstone fracture reservoirs according to an embodiment of the present application. Figure 6 As shown, the reservoir fluid property identification system according to the embodiment of the present invention includes: a depth point evaluation index generation module 61 and a reservoir type evaluation module 62 .

[0094] Specifically, the depth point evaluation index generation module 61 is implemented according to the method described in step S110 above, and is configured to calculate the neutron difference ratio evaluation index at different depths in the fracture reservoir section of the current well based on the neutron logging curve of the well to be evaluated in the target area. The neutron difference ratio evaluation index is the ratio of the first difference value to the neutron value at the corresponding depth, and the first difference value is the difference between the neutron value at the corresponding depth and the neutron standard value of the tight layer section in the well to be evaluated; the reservoir type evaluation module 62 is implemented according to the method described in step S120 above, and is configured to identify the fracture reservoir fluid properties of different depth sections based on the neutron difference ratio evaluation index at different depths using a pre-constructed fracture section gas-water layer division standard.

[0095] In one embodiment, the fracture section gas-water layer division standard has a first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer, and a second neutron difference ratio limit value for distinguishing the fracture gas-water layer from the fracture water layer.

[0096] Furthermore, the reservoir type evaluation module 62 is further configured to:

[0097] When the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas layer;

[0098] When the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas-water co-layer;

[0099] When the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, it is determined that the fracture reservoir at the current depth is a water layer.

[0100] The present invention discloses a method and system for identifying fluid properties in tight sandstone fracture reservoirs. The method and system belong to the technical field of oil and gas geophysical tight gas exploration and development, and are used for identifying fluid properties in fracture development sections of tight reservoirs. The present invention utilizes the mining effect of gas layer neutron logging, and proposes using the difference ratio between the neutron value of the fracture section and the neutron value of the adjacent tight section as a parameter for fluid identification in the fracture section; through the analysis of the intersection diagram of known test wells, different fluid identification standards in the fracture section are obtained, and the standard value is used to further determine the fluid properties of different fracture sections. The present invention avoids the problems of reduced resistivity caused by mud intrusion and leakage, difficulty in fluid identification, etc., solves geological needs, and has good practical application effects.

[0101] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by anyone skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

[0102] In the description of the present invention, unless otherwise specified, "plurality" means two or more; terms such as "upper," "lower," "left," "right," "inner," "outer," "front end," "rear end," "head," and "tail" indicate positions or relationships based on those shown in the accompanying drawings. These terms are intended solely to facilitate the description of the present invention and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, terms such as "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0103] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "connected" and "connection" should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integral connection; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0104] It should be understood that the embodiments disclosed herein are not limited to the specific structures, processing steps, or materials disclosed herein, but should extend to equivalent substitutions of these features understood by those skilled in the relevant art. It should also be understood that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting.

[0105] References in this specification to "one embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Therefore, appearances of the phrases "one embodiment" or "an embodiment" in various places throughout this specification do not necessarily refer to the same embodiment.

[0106] Although the embodiments disclosed above are for facilitating understanding of the present invention, the contents described are merely embodiments adopted for facilitating understanding of the present invention and are not intended to limit the present invention. Any person skilled in the art of the present invention may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope of the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A method for identifying fluid properties in tight sandstone fracture reservoirs, characterized in that: include: Calculating a neutron difference ratio evaluation index at different depths within the fractured reservoir section of the current well based on the neutron logging curve of the well to be evaluated in the target area, wherein the neutron difference ratio evaluation index is a ratio of a first difference value to the neutron value at the corresponding depth, wherein the first difference value is a difference between the neutron value at the corresponding depth and a neutron standard value of the tight layer section in the well to be evaluated; According to the neutron difference ratio evaluation index at different depths, the pre-established fracture section gas-water layer division standard is used to identify the fluid properties of fracture reservoirs at different depths.

2. The method according to claim 1, characterized in that The fracture section gas-water layer division standard is constructed through the following steps: Select at least one test well in the target area, which should have fractured gas layers, fractured gas-water layers, and fractured water layers; Selecting a tight layer section of each test well and determining a neutron standard value of the tight layer section; selecting at least one representative fracture section of each test well and determining a neutron standard value of the representative fracture section; Calculating a difference ratio evaluation index of each fracture representative segment according to the neutron standard value of the dense layer segment and the neutron standard value of the fracture representative segment; Draw a cross-plot between the difference ratio evaluation index and the resistivity standard value for each representative fracture segment; According to the data point distribution characteristics of the intersection diagram, a first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer and a second neutron difference ratio limit value for distinguishing the fracture gas-water layer from the fracture water layer are divided to form the fracture section gas-water layer division standard.

3. The method according to claim 2, characterized in that The step of selecting at least one representative fracture section of each test well includes: A well section in the test well with low resistivity, large acoustic wave value and large neutron value is selected as the fracture representative section, wherein the neutron standard value of each fracture representative section is the average value or representative value of the neutron value of the corresponding well section.

4. The method according to claim 2 or 3, characterized in that The steps of selecting a tight zone interval for a well to be evaluated or tested include: A well section in the well to be evaluated or the test well with a regular borehole, a low natural gamma value, a high resistivity, and a small acoustic wave value is selected as the tight layer section, wherein the neutron standard value of the tight layer section is the average value or representative value of the neutron value of the tight layer section.

5. The method according to any one of claims 2 to 4, characterized in that The difference ratio evaluation index of each crack representative segment is calculated through the following steps: Calculate the difference between the neutron standard value of each fracture representative section and the neutron standard value of the tight layer section in the test well to which the current fracture representative section belongs; The difference value corresponding to each fracture representative section is divided by the neutron standard value of the corresponding fracture representative section, thereby obtaining the difference ratio evaluation index of each fracture representative section.

6. The method according to any one of claims 1 to 5, characterized in that The fracture section gas-water layer division standard includes a first neutron difference ratio limit value for distinguishing the fracture gas layer from the gas-water layer, and a second neutron difference ratio limit value for distinguishing the fracture gas-water layer from the fracture water layer, wherein the fracture section gas-water layer division standard includes: When the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas layer; When the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas-water co-layer; When the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, it is determined that the fracture reservoir at the current depth is a water layer.

7. The method according to claim 6, characterized in that The first neutron difference ratio limit value is 0.4, and the second neutron difference ratio limit value is 0.

53.

8. A computer-readable storage medium, characterized in that It contains a series of instructions for executing the method steps according to any one of claims 1 to 7.

9. A system for identifying fluid properties in tight sandstone fracture reservoirs, characterized in that: include: a depth point evaluation index generation module configured to calculate a neutron difference ratio evaluation index at different depths within the fracture reservoir section of the current well based on the neutron logging curve of the well to be evaluated in the target area, wherein the neutron difference ratio evaluation index is a ratio of a first difference value to the neutron value at the corresponding depth, wherein the first difference value is a difference between the neutron value at the corresponding depth and a neutron standard value of the tight layer section in the well to be evaluated; The reservoir type evaluation module is configured to identify the fluid properties of fracture reservoirs at different depths based on the neutron difference ratio evaluation index at different depths and the constructed fracture segment gas-water layer division standard.

10. The system according to claim 9, characterized in that The fracture segment gas-water layer classification standard includes a first neutron difference ratio limit value for distinguishing a fracture gas layer from a gas-water layer, and a second neutron difference ratio limit value for distinguishing a fracture gas-water layer from a fracture water layer, wherein the reservoir type evaluation module is further configured to: When the neutron difference ratio evaluation index at the current depth is less than or equal to the first neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas layer; When the neutron difference ratio evaluation index at the current depth is greater than the first neutron difference ratio limit value and less than or equal to the second neutron difference ratio limit value, determining that the fracture reservoir at the current depth is a gas-water co-layer; When the neutron difference ratio evaluation index at the current depth is greater than the second neutron difference ratio limit value, it is determined that the fracture reservoir at the current depth is a water layer.

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