A method for identifying gas abundance of a pressure-solution gas reservoir

Abstract

The present application relates to oil and gas exploration and development technical field, more particularly, it relates to a kind of gas abundance identification method of pressure solution gas reservoir, it includes the following steps: S1: obtaining multiple downhole fluid samples;S2: extract four gas logging sensitive parameters;S3: draw a triangular radar chart based on gas logging sensitive parameter;S4: the area ratio of two triangles in triangular radar chart is calculated.S5: with area ratio as ordinate, gas logging total hydrocarbon as abscissa, draw water gas layer qualitative identification chart;According to the identification of water gas layer, the gas abundance of reservoir is determined again.The present application overcomes the deficiency that single resistivity and gas logging are difficult to effectively identify gas-water layer and gas-bearing water layer in the prior art, leading to inaccurate gas abundance identification, the present application fully considers the difference in gas logging logging response characteristics of water gas layer, without fluid sample sampling and experiment, gas-water layer and gas-bearing water layer can be finely divided, and the accuracy of reservoir gas abundance identification is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration and development, and more particularly to a method for identifying gas abundance in a pressure-dissolved gas reservoir. Background Art

[0002] Pressure-dissolved gas refers to cap gas and its associated free and dissolved gas in high-temperature, high-pressure formations. Similar concepts include water-soluble gas and geogas. The reserves of pressure-dissolved gas depend on the adequacy of the natural gas solute and the formation water solvent (the size of the water body) and the solubility of natural gas in water. The former is primarily influenced by reservoir thickness, area, porosity, and water saturation, while water saturation, or the gas abundance, directly affects the size of pressure-dissolved gas reserves. Pressure-dissolved gas reservoirs have significantly higher gas abundance than conventional reservoirs and hold great potential for exploration and development. Classifying and identifying gas abundance levels is crucial for guiding development deployment.

[0003] The X gas field in the western South China Sea is a typical high-temperature, high-pressure gas field with poor reservoir properties and a complex pore structure. Single-resistivity fluid identification charts for medium-to-high porosity and permeability reservoirs have gradually demonstrated significant inadequacy. Due to the high pressure, the responses of single gas logging parameters for gas layers, gas-water layers, gas-water layers, and pure water layers are largely indistinguishable, making single parameters difficult to effectively identify gas-water layers. Methods for identifying high-pressure, low-permeability gas-water layers primarily include resistivity, dual saturation, and absolute value discrimination using gas logging. However, due to the complex porosity structure of the target area, high reservoir ash content, and high formation pressure coefficients, using single resistivity and gas logging is difficult to effectively identify gas-water layers. Identifying gas-water layers and gas-water layers is particularly challenging, making it difficult to accurately assess the gas abundance of pressure-solution gas reservoirs. At present, the most direct and effective method for classifying reservoir gas abundance is drill pipe formation testing. This method can best represent the actual gas abundance of the formation, but the testing cost is high and time-consuming. Its application conditions are limited and the number of times is small under special environmental conditions such as offshore. Therefore, there is an urgent need to develop new gas abundance identification methods. Summary of the Invention

[0004] In response to the problem in the above-mentioned prior art that it is difficult to effectively identify gas-water layers and gas-bearing water layers using a single resistivity and gas logging, resulting in inaccurate identification of gas abundance, the present invention provides a method for identifying gas abundance in pressure-dissolved gas reservoirs, which can finely divide gas-water layers and gas-bearing water layers, thereby improving the accuracy of reservoir gas abundance identification.

[0005] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0006] A method for identifying gas abundance in a pressure-solution gas reservoir comprises the following steps:

[0007] S1: Acquire multiple downhole fluid samples.

[0008] S2: Based on the gas logging data at the corresponding depth of the fluid sample, four gas logging sensitive parameters that are relatively sensitive to the water and gas layer are extracted.

[0009] S3: Drawing a triangular radar map of the water vapor layer of the fluid sample based on the gas measurement sensitive parameters; in the triangular radar map, the four gas measurement sensitive parameters are distributed in pairs on the left and right sides of the axis of the triangular radar map.

[0010] S4: Calculate the areas of the triangles on the left and right sides of the central axis of the triangular radar chart, and then calculate the area ratio of the two triangles. The total area enclosed by the sample data points in the triangular chart is divided into two parts with the central axis as the boundary: one part is the gas-bearing area. A larger gas-bearing area indicates a greater probability of gas, which is characteristic of a gas layer; the other part is the water-bearing area. A larger water-bearing area indicates a greater probability of water, which is characteristic of a water layer. This can amplify the impact of the water-bearing layer on gas measurement.

[0011] S5: Based on the area ratio corresponding to the fluid sample, a water-gas layer qualitative identification chart is drawn with the area ratio as the ordinate and the total hydrocarbon measured by gas as the abscissa; then, the water-gas layer is identified based on the water-gas layer qualitative identification chart, and the gas abundance of the reservoir is determined based on the identified water-gas layer.

[0012] In the above technical solution, the difference in gas logging response characteristics between water and gas layers is obvious. The pure gas layer is rich in natural gas. During the gas logging process, the total hydrocarbon value usually increases significantly and can reach a high value. At the same time, the gas logging components are relatively complete and have certain heavy components. Pure water layers generally contain almost no hydrocarbon gas, and the total hydrocarbon value is low, close to or equal to the background value, and there are basically no heavy components. Since the gas content of the gas-water layer is better than that of the gas-bearing water layer, the gas logging characteristics of the gas-water layer are closer to the gas layer and are between the gas layer and the gas-bearing water layer. The gas logging characteristics of the gas-water layer are closer to the water layer and are between the gas-water layer and the water layer. The above technical solution fully considers the differences in gas logging response characteristics between water and gas layers and can more accurately identify water and gas layers.

[0013] Preferably, in step S1, the fluid sample is sampled by cable formation test sampling and drill pipe formation test sampling.

[0014] Preferably, in step S1, after obtaining a plurality of downhole fluid samples, the fluid properties are clarified and the water-gas layer is determined; in step S2, the gas logging data comes from the fluid samples that have been confirmed to be the water-gas layer.

[0015] Preferably, in step S1, whether the fluid sample comes from the water vapor layer is determined based on the water vapor ratio obtained by testing the fluid sample.

[0016] Preferably, in the step S1, the water-gas layer with a water-gas ratio less than 2 is a gas layer; the water-gas layer with a water-gas ratio ranging from 2 to 10 is a gas-water same layer; the water-gas layer with a water-gas ratio ranging from 10 to 1000 is a gas-bearing water layer; and the water-gas layer with a water-gas ratio greater than 1000 is a water layer.

[0017] Preferably, in the step S2, the four gas logging sensitive parameters sensitive to the water-gas layer are 1 / C4, 1 / C5, TG*10 and (C4+C5) / (C1+C2+C3)*1000 respectively; wherein C4=iC4+nC4; C5=iC5+nC5; wherein C1 is a gas logging methane component content, %; C2 is a gas logging ethane component content, %; C3 is a gas logging propane component content, %; iC4 is a gas logging isobutane component content, %; nC4 is a gas logging normal butane component content, %; iC5 is a gas logging isopentane component content, %; and nC5 is a gas logging normal pentane component content, %.

[0018] Preferably, in the step S4, the calculation formula of the area ratio is:

[0019]

[0020] wherein C1 is a gas logging methane component content, %; C2 is a gas logging ethane component content, %; C3 is a gas logging propane component content, %; iC4 is a gas logging isobutane component content, %; nC4 is a gas logging normal butane component content, %; iC5 is a gas logging isopentane component content, %; and nC5 is a gas logging normal pentane component content, %.

[0021] Preferably, in the step S5, in the triangular radar chart, the greater the area on the right side of the central axis, the greater the gas-bearing probability, and the greater the area on the left side of the central axis, the greater the water-bearing probability.

[0022] Preferably, in the step S5, the water-gas layer with an area ratio less than 0.01 is a water layer; the water-gas layer with an area ratio ranging from 0.01 to 0.1 is a gas-bearing water layer; the water-gas layer with an area ratio ranging from 0.1 to 0.4 is a gas-water same layer; and the water-gas layer with an area ratio greater than 0.4 is a gas layer.

[0023] Preferably, in the step S5, the gas abundance of the gas layer is defined as high, the gas abundance of the gas-water same layer is defined as relatively high, the gas abundance of the gas-bearing water layer is defined as relatively low, and the gas abundance of the water layer is defined as low.

[0024] The beneficial effects of the present application are as follows:

[0025] 1. This method fully considers the differences in gas logging response characteristics between water and gas layers. Without fluid sampling and experiments, it achieves the first fine division of gas-water layers and gas-water layers. This can improve the accuracy of reservoir gas abundance identification and provide a more reliable basis for reserve evaluation and development plans.

[0026] 2. Compared with traditional gas-water layer identification, this method only requires gas logging curves, has low data requirements, is simple to operate, has higher operating efficiency, and can reduce operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a flow chart of a method for identifying gas abundance in a pressure-solution gas reservoir;

[0028] Figure 2 This is a triangulated radar map of the water-gas layer in the X gas field in the western South China Sea;

[0029] Figure 3 This is a qualitative identification chart of the triangular area water and gas layers in the X gas field in the western South China Sea. DETAILED DESCRIPTION

[0030] The drawings are for illustrative purposes only and should not be construed as limiting this patent. To better illustrate the embodiments, some components in the drawings may be omitted, enlarged, or reduced in size, and do not represent actual product dimensions. Those skilled in the art will understand that some well-known structures and their descriptions may be omitted from the drawings. The positional relationships depicted in the drawings are for illustrative purposes only and should not be construed as limiting this patent.

[0031] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "long", "short", etc. indicating the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting this patent. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0032] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings:

[0033] Example 1

[0034] This embodiment takes the X oil and gas field in the western South China Sea as an example to describe in detail a method for identifying gas abundance in a pressure-dissolved gas reservoir, which includes the following steps:

[0035] S1: Collect formation fluid samples obtained from all on-site wireline formation tests (pump sampling) and drill pipe formation tests at the X oil and gas field, identify the fluid properties, and determine the water-gas layer and its gas abundance based on the water-gas ratio of the test fluid.

[0036] S2: Based on the gas logging data corresponding to the depth of the fluid samples in the confirmed water-gas layer, four gas logging sensitive parameters that are more sensitive to the water-gas layer are extracted. Pure gas layers are rich in natural gas. During the gas logging process, the total hydrocarbon value usually increases significantly, reaching a high value. At the same time, the gas logging components are relatively complete and contain a certain amount of heavy components. Pure water layers generally contain almost no hydrocarbon gas, with a low total hydrocarbon value close to or equal to the background value, and basically no heavy components. Because the gas content of the gas-water layer is higher than that of the gas-water layer, the gas logging characteristics of the gas-water layer are closer to the gas layer and are between the gas layer and the gas-water layer. The gas logging characteristics of the gas-water layer are closer to the water layer and are between the gas-water layer and the water layer.

[0037] S3: Draw triangular radar diagrams of water and gas layers of fluid samples based on gas measurement sensitive parameters, including triangular radar diagrams of water and gas layers of typical gas layers, gas-water layers, gas-water layers, and water layers. In the triangular radar diagram, the four gas measurement sensitive parameters are distributed in pairs on the left and right sides of the axis of the triangular radar diagram, as shown in the following example: Figure 2 shown.

[0038] S4: Calculate the areas of the triangles to the left and right of the central axis of the triangular radar chart, and then calculate the ratio of the areas of the right triangle to the left triangle. The total area enclosed by the sample data points in the triangular chart is divided into two parts, with the central axis as the boundary. One part is the gas-bearing area. A larger gas-bearing area indicates a greater probability of gas, which is characteristic of a gas layer. The other part is the water-bearing area. A larger water-bearing area indicates a greater probability of water, which is characteristic of a water layer. This can amplify the impact of the water-bearing layer on gas measurement.

[0039] S5: Based on the area ratio corresponding to the fluid sample, plot the area ratio as the vertical axis and the total hydrocarbon measured by gas as the horizontal axis. Figure 3 The water-gas layer qualitative identification plate is shown; the water-gas layer is then identified based on the water-gas layer qualitative identification plate, and the gas abundance of the reservoir is determined based on the identified water-gas layer.

[0040] Further, in step S2, four gas logging sensitive parameters that are more sensitive to water vapor layers are 1 / C4, 1 / C5, TG*10, and (C4+C5) / (C1+C2+C3)*1000; among which C4=iC4+nC4; C5=iC5+nC5; wherein, C1 is the methane component content of gas logging, %; C2 is the ethane component content of gas logging, %; C3 is the propane component content of gas logging, %; iC4 is the isobutane component content of gas logging, %; nC4 is the normal-butane component content of gas logging, %; iC5 is the isopentane component content of gas logging, %; nC5 is the normal-pentane component content of gas logging, %.

[0041] Furthermore, in step S4, the area ratio is calculated as follows:

[0042]

[0043] Wherein, C1 is the content of methane component in gas logging and well logging, %; C2 is the content of ethane component in gas logging and well logging, %; C3 is the content of propane component in gas logging and well logging, %; iC4 is the content of isobutane component in gas logging and well logging, %; nC4 is the content of normal butane component in gas logging and well logging, %; iC5 is the content of isopentane component in gas logging and well logging, %; nC5 is the content of normal pentane component in gas logging and well logging, %.

[0044] The total area enclosed by the sample data points in the triangle plot is divided into two parts by the central axis. The right side of the central axis is the gas-bearing area SR1, which is formed by (C4+C5) / (C1+C2+C3)*1000, TG*10, and the center point. A larger area indicates a greater probability of gas, indicating a gas layer. The left side of the central axis is the water-bearing area SL1, which is formed by 1 / C3, 1 / C4, and the center point. A larger area indicates a greater probability of water, indicating a water layer, thus maximizing the impact on gas logging.

[0045] The working principle and effect of this embodiment are verified: the difference in gas logging response characteristics between water and gas layers is obvious. The natural gas content in the pure gas layer is rich. During the gas logging process, the total hydrocarbon value usually increases significantly and can reach a higher value. At the same time, the gas logging components are relatively complete and have certain heavy components. The pure water layer generally contains almost no hydrocarbon gas, the total hydrocarbon value is low, close to or equal to the background value, and basically has no heavy components. Since the gas content of the gas-water layer is better than that of the gas-bearing water layer, the gas logging characteristics of the gas-water layer are closer to the gas layer and are between the gas layer and the gas-bearing water layer. The gas logging characteristics of the gas-water layer are closer to the water layer and are between the gas-water layer and the water layer. The above technical solution fully takes into account the difference in gas logging response characteristics between water and gas layers, and can more accurately identify water and gas layers.

[0046] Taking Well X11, a newly drilled well in the X gas field, as an example, the total hydrocarbon value of layer 1 is 6%, and the total hydrocarbon value of layer 2 is 5%. Their resistivities are very similar, making it difficult to assess the fluid and gas abundance of these two layers using only resistivity and gas logging. However, the right-to-left area ratio of the axis in the water-gas triangle plot calculated for layer 1 is 0.9, identifying it as a gas layer. The right-to-left area ratio of the axis in the water-gas triangle plot calculated for layer 2 is 0.08, identifying it as a gas-bearing water layer. Using this method, we can accurately assess the type and gas abundance of these two layers.

[0047] Beneficial effects of this embodiment:

[0048] 1. This method fully considers the differences in gas logging response characteristics between water and gas layers. Without fluid sampling and experiments, it achieves the first fine division of gas-water layers and gas-water layers. This can improve the accuracy of reservoir gas abundance identification and provide a more reliable basis for reserve evaluation and development plans.

[0049] 2. Compared with traditional gas-water layer identification, this method only requires gas logging curves, has low data requirements, is simple to operate, has higher operating efficiency, and can reduce operating costs.

[0050] Example 2

[0051] This embodiment is the second embodiment of a method for identifying gas abundance in a pressure-solution gas reservoir. This embodiment further explains step S1. In step S1, a water-gas layer with a water-gas ratio less than 2 is considered a gas layer; a water-gas layer with a water-gas ratio in the range of [2, 10] is considered a gas-water layer; a water-gas layer with a water-gas ratio in the range of [10, 1000] is considered a gas-water layer; and a water-gas layer with a water-gas ratio greater than 1000 is considered a water layer.

[0052] Other features, working principles and beneficial effects of this embodiment are consistent with those of embodiment 1.

[0053] Example 3

[0054] This embodiment is the third embodiment of a method for identifying the gas abundance of a pressure-dissolved gas reservoir. This embodiment further explains step S5. In step S5, in the triangular radar diagram, a larger area to the right of the central axis represents a greater probability of gas content, and a larger area to the left of the central axis represents a greater probability of water content.

[0055] Further, in step S5, the water-gas layer with an area ratio less than 0.01 is a water layer, the water-gas layer with an area ratio in the range of [0.01, 0.1) is a gas-water layer, the water-gas layer with an area ratio in the range of [0.1, 0.4) is a gas-water layer, and the water-gas layer with an area ratio greater than 0.4 is a gas layer.

[0056] Furthermore, in step S5, it is defined that the gas abundance of the gas layer is high, the gas abundance of the gas-water layer is relatively high, the gas abundance of the gas-water layer is relatively low, and the gas abundance of the water layer is low.

[0057] Other features, working principles and beneficial effects of this embodiment are consistent with those of Example 2.

[0058] In the specific contents of the above-mentioned specific implementation methods, the various technical features can be combined in any non-contradictory manner. In order to make the description concise, not all possible combinations of the above-mentioned technical features are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0059] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description, and it is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A method for identifying gas abundance in a pressure-dissolved gas reservoir, characterized in that: The following steps are involved: S1: Acquire multiple downhole fluid samples; S2: extracting four gas logging sensitive parameters that are more sensitive to water and gas layers based on the gas logging data at the corresponding depth of the fluid sample; S3: drawing a triangular radar map of the water vapor layer of the fluid sample based on the gas measurement sensitive parameters; in the triangular radar map, the four gas measurement sensitive parameters are distributed in pairs on the left and right sides of the axis of the triangular radar map; S4: Calculate the areas of the triangles on the left and right sides of the central axis of the triangular radar chart, and then calculate the area ratio of the two triangles; S5: Based on the area ratio corresponding to the fluid sample, a water-gas layer qualitative identification chart is drawn with the area ratio as the ordinate and the total hydrocarbon measured by gas as the abscissa; then, the water-gas layer is identified based on the water-gas layer qualitative identification chart, and the gas abundance of the reservoir is determined based on the identified water-gas layer.

2. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 1, wherein: In step S1, the fluid sample is sampled by cable formation test sampling and drill pipe formation test sampling.

3. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 1, wherein: In step S1, after obtaining multiple downhole fluid samples, the fluid properties are clarified and the water-gas layer is determined; in step S2, the gas logging data comes from the fluid samples that have been confirmed to be water-gas layers.

4. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 3, wherein: In step S1 , it is determined whether the fluid sample comes from a water vapor layer according to the water vapor ratio obtained by testing the fluid sample.

5. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 4, characterized in that: In step S1, a water-gas layer with a water-gas ratio less than 2 is a gas layer; a water-gas layer with a water-gas ratio in the range of [2, 10) is a gas-water layer; a water-gas layer with a water-gas ratio in the range of [10, 1000] is a gas-water layer; and a water-gas layer with a water-gas ratio greater than 1000 is a water layer.

6. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 1, wherein: In step S2, the four gas measurement sensitive parameters that are more sensitive to the water vapor layer are 1 / C4, 1 / C5, TG*10, (C4+C5) / (C1+C2+C3)*1000; where C4=iC4+nC4; C5=iC5+nC5; Wherein, C1 is the content of methane component in gas logging and well logging, %; C2 is the content of ethane component in gas logging and well logging, %; C3 is the content of propane component in gas logging and well logging, %; iC4 is the content of isobutane component in gas logging and well logging, %; nC4 is the content of normal butane component in gas logging and well logging, %; iC5 is the content of isopentane component in gas logging and well logging, %; nC5 is the content of normal pentane component in gas logging and well logging, %.

7. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 6, wherein: In step S4, the area ratio is calculated as follows: Wherein, C1 is the content of methane component in gas logging and well logging, %; C2 is the content of ethane component in gas logging and well logging, %; C3 is the content of propane component in gas logging and well logging, %; iC4 is the content of isobutane component in gas logging and well logging, %; nC4 is the content of normal butane component in gas logging and well logging, %; iC5 is the content of isopentane component in gas logging and well logging, %; nC5 is the content of normal pentane component in gas logging and well logging, %.

8. A method for identifying gas abundance in a pressure-solution gas reservoir according to any one of claims 1 to 7, characterized in that: In step S5, in the triangular radar diagram, a larger area to the right of the central axis represents a greater probability of gas content, and a larger area to the left of the central axis represents a greater probability of water content.

9. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 8, characterized in that: In step S5, the water-gas layer with an area ratio less than 0.01 is a water layer, the water-gas layer with an area ratio in the range of [0.01, 0.1) is a gas-water layer, the water-gas layer with an area ratio in the range of [0.1, 0.4) is a gas-water layer, and the water-gas layer with an area ratio greater than 0.4 is a gas layer.

10. The method for identifying gas abundance in a pressure-solution gas reservoir according to claim 9, characterized in that: In step S5, it is defined that the gas abundance of the gas layer is high, the gas abundance of the gas-water layer is relatively high, the gas abundance of the gas-water layer is relatively low, and the gas abundance of the water layer is low.

Images