Gas-bearing abundance identification method for pressure-dissolved gas reservoir

Abstract

The invention relates to the technical field of oil-gas exploration and development, in particular to a gas-bearing abundance identification method for a pressure-dissolved gas reservoir, which comprises the following steps: S1, acquiring a plurality of underground fluid samples; s2, extracting four gas logging sensitive parameters; s3, drawing a triangular radar map based on the gas logging sensitive parameters; and S4, calculating the area ratio of two triangles in the triangular radar map. S5, drawing a water-gas layer qualitative identification chart by taking the area ratio as a vertical coordinate and the gas logging total hydrocarbon as a horizontal coordinate; and identifying a water-gas layer according to the chart, and then determining the gas-bearing abundance of the reservoir. The method overcomes the defect that in the prior art, the same gas-water layer and the gas-containing water layer are difficult to effectively recognize by using single resistivity and gas logging, so that the gas-containing abundance recognition is inaccurate, fully considers the difference of the gas logging response characteristics of the water-gas layer, and improves the gas-containing abundance recognition accuracy under the condition that fluid sample sampling and experiment are not carried out. Fine division of the same gas-water layer and the gas-containing water layer can be realized, and the recognition accuracy of the gas-containing abundance of the reservoir is improved.

Description

Technical Field

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

[0002] Pressure solution gas refers to the gas cap gas and its associated free gas and dissolved gas in high-temperature and high-pressure formations. Similar concepts are mainly water-soluble gas and geopressurized gas. The reserves of pressure solution gas depend on the adequacy of natural gas solutes and formation water solvents (water body scale) and the solubility of natural gas in water. The former is mainly affected by reservoir thickness, area, porosity, and water saturation, while water saturation, that is, gas abundance, directly affects the scale of pressure solution gas reserves. The gas abundance of pressure solution gas reservoirs is significantly higher than that of conventional reservoirs, and there is great potential for exploration and development. Classifying and identifying the high and low gas abundances in them is of great significance for guiding development deployment.

[0003] The X gas field in the western South China Sea is a typical high-temperature and high-pressure gas field with poor reservoir properties and complex pore structure. The single resistivity fluid identification chart for medium- and high-porosity and permeability reservoirs has gradually shown many inadaptabilities. Due to the influence of high pressure, the single gas logging parameter responses of gas layers, gas-water layers, gas-water layers and pure water layers are not much different, and it is difficult to effectively identify gas-water layers with a single parameter. The identification methods for high-pressure and low-permeability gas-water layers mainly include resistivity, dual saturation and gas logging absolute value discrimination methods. Due to the complex porosity structure of the target area, high ash content in the reservoir, and high formation pressure coefficient, it is difficult to effectively discriminate gas-water layers with a single resistivity and gas logging. It is particularly difficult to identify gas-water layers and gas-water layers, and it is difficult to accurately evaluate the gas abundance of pressure-solution gas reservoirs. At present, the most direct and effective method for classifying the gas abundance of reservoirs is the drill pipe formation test. This method can best represent the actual gas abundance of the formation, but the test 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 view of the problem that it is difficult to effectively identify gas-water layers and gas-containing water layers using a single resistivity and gas measurement in the above-mentioned prior art, resulting in inaccurate identification of gas abundance, the present invention provides a method for identifying gas abundance in pressure-solution gas reservoirs, which can finely divide gas-water layers and gas-containing water layers and improve 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 gas layer are extracted.

[0009] S3: Draw 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 area 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. The larger the gas-bearing area, the greater the probability of gas-bearing, which is a gas layer characteristic; the other part is the water-bearing area. The larger the water-bearing area, the greater the probability of water-bearing, which is a water layer characteristic. In this way, the influence of the water-gas layer on gas measurement can be magnified.

[0011] S5: According to 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 according to 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 scheme, the difference in gas logging response characteristics between water and gas layers is obvious. The natural gas content in pure gas layers 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. 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 scheme fully considers the difference 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 sampling method of the fluid sample includes 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 water-gas layers.

[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 step S1, a water vapor layer with a water vapor ratio less than 2 is a gas layer; a water vapor layer with a water vapor ratio in the range of [2, 10) is a gas-water layer; a water vapor layer with a water vapor ratio in the range of [10, 1000] is a gas-containing water layer; and a water vapor layer with a water vapor ratio greater than 1000 is a water layer.

[0017] Preferably, in step S2, four gas logging sensitive parameters that are more sensitive to the water vapor layer are 1 / C4, 1 / C5, TG*10, (C4+C5) / (C1+C2+C3)*1000; wherein 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, %.

[0018] Preferably, in step S4, the area ratio is calculated as follows:

[0019]

[0020] In the formula, 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, %.

[0021] Preferably, in step S5, in the triangular radar diagram, a larger area on the right side of the central axis represents a greater probability of containing gas, and a larger area on the left side of the central axis represents a greater probability of containing water.

[0022] Preferably, in step S5, a water vapor layer with an area ratio less than 0.01 is a water layer, a water vapor layer with an area ratio in the range of [0.01, 0.1) is a gas-containing water layer, a water vapor layer with an area ratio in the range of [0.1, 0.4) is a gas-water layer, and a water vapor layer with an area ratio greater than 0.4 is a gas layer.

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

[0024] Beneficial effects of the present invention:

[0025] 1. This method fully considers the differences in gas-water layers’ response characteristics in gas logging. Without fluid sampling and experiments, it realizes the fine division of gas-water layers and gas-water layers for the first time, which 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 layer in the X gas field in the western South China Sea. DETAILED DESCRIPTION

[0030] The drawings are only for illustrative purposes and cannot be construed as limiting the present invention. To better illustrate the present embodiment, some parts of the drawings may be omitted, enlarged, or reduced, and do not represent the size of the actual product. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are only for illustrative purposes and cannot be construed as limiting the present invention.

[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 the terms "upper", "lower", "left", "right", "long", "short" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limitations on 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 part of the South China Sea as an example to explain in detail a method for identifying the gas abundance of a pressure-dissolved gas reservoir, which includes the following steps:

[0035] S1: Collect formation fluid samples obtained from all on-site cable formation tests (pump sampling) and drill pipe formation tests in the X oil and gas field, clarify 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. 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 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 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-bearing water layer are closer to the water layer and are between the gas-water layer and the water layer.

[0037] S3: Draw the triangular radar map of the water and gas layer of the fluid sample based on the gas measurement sensitive parameters, including the triangular radar map of the water and gas layer of the typical gas layer, gas-water layer, gas-water layer, and water layer. 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, as shown in the following figure. Figure 2 shown.

[0038] S4: Calculate the area 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 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. The larger the gas-bearing area, the greater the probability of gas-bearing, which is a gas layer characteristic; the other part is the water-bearing area. The larger the water-bearing area, the greater the probability of water-bearing, which is a water layer characteristic. This can magnify the impact of the water-gas layer on gas measurement.

[0039] S5: According to the area ratio corresponding to the fluid sample, the area ratio is used as the ordinate and the total hydrocarbon measured by gas is used as the abscissa. 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 the water vapor layer are 1 / C4, 1 / C5, TG*10, (C4+C5) / (C1+C2+C3)*1000; wherein 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] In the formula, 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 diagram is divided into two parts with the central axis as the boundary. The right side of the central axis is the gas-bearing area SR1 composed of (C4+C5) / (C1+C2+C3)*1000, TG*10 and the center point. The larger the area, the greater the probability of gas-bearing, which is a gas layer characteristic. The left side of the central axis is the water-bearing area SL1 composed of 1 / C3, 1 / C4 and the center point. The larger the area, the greater the probability of water-bearing, which is a water layer characteristic. This can maximize the impact on gas measurement.

[0045] The working principle and effect verification of this embodiment: the difference in gas logging response characteristics between water and gas layers is obvious. The natural gas content in pure gas layers 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. 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 scheme fully considers the difference in gas logging response characteristics between water and gas layers, and can more accurately identify water and gas layers.

[0046] Taking the newly drilled X11 well in 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%. The resistivity is very similar. It is difficult to evaluate the fluid and gas abundance of the two layers using a single resistivity and gas logging. However, the right-to-left area ratio of the axis in the water-gas layer triangle diagram calculated for layer 1 is 0.9, which is identified as a gas layer; the right-to-left area ratio of the axis in the water-gas layer triangle diagram calculated for layer 2 is 0.08, which is identified as a gas-bearing water layer. The above method can be used to accurately evaluate the type and gas abundance of the two layers.

[0047] Beneficial effects of this embodiment:

[0048] 1. This method fully considers the differences in gas-water layers’ response characteristics in gas logging. Without fluid sampling and experiments, it realizes the fine division of gas-water layers and gas-water layers for the first time, which 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 a second embodiment of a method for identifying gas abundance of a pressure-solution gas reservoir, and this embodiment further explains step S1. 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-bearing water layer; and a water-gas layer with a water-gas ratio greater than 1000 is a water layer.

[0052] The 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-solution gas reservoir, and this embodiment further illustrates 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 containing gas, and a larger area to the left of the central axis represents a greater probability of containing water.

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

[0056] Further, 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] The other features, working principles and beneficial effects of this embodiment are consistent with those of Embodiment 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 clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description, and it is not necessary and impossible to list all the implementation methods here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for identifying gas abundance in a pressure-solution gas reservoir, characterized in that: The following steps are involved: S1: Obtain multiple downhole fluid samples; S2: based on the gas logging data at the corresponding depth of the fluid sample, extract four gas logging sensitive parameters that are more sensitive to the water gas layer; 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: According to 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 according to 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 of a pressure-solution gas reservoir according to claim 1, characterized in that: In the step S1, the fluid sample sampling method includes cable formation test sampling and drill pipe formation test sampling.

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

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

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

6. The method for identifying gas abundance of a pressure-solution gas reservoir according to claim 1, characterized in that: In step S2, 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; In the formula, 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 of a pressure-solution gas reservoir according to claim 6, characterized in that: In step S4, the area ratio is calculated as: In the formula, 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 the step S5, in the triangular radar diagram, a larger area on the right side of the central axis represents a greater probability of containing gas, and a larger area on the left side of the central axis represents a greater probability of containing water.

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

10. The method for identifying gas abundance of 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.

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