Method and device for predicting gas-water properties of tight sandstone by using reservoir pore-throat volume ratio

Abstract

The invention relates to the technical field of oil-gas exploration and development, and discloses a method and a device for predicting gas-water properties of tight sandstone by utilizing a reservoir pore-throat volume ratio. The method comprises the following steps: firstly, establishing an irreducible water saturation model according to the reservoir pore-throat volume ratio, and calculating a movable water saturation parameter according to the irreducible water saturation model; and finally, comprehensively predicting and identifying the gas-water property of the tight sandstone based on the movable water saturation parameter and in combination with the nonlinear gas-water two-phase relative permeability curve. The method aims at the complex pore throat structure and heterogeneity of the tight reservoir, the result is accurate and effective, and a more scientific and objective prediction technology with higher applicability is provided for gas-water property recognition.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas exploration, and more particularly to a method and a device for predicting gas-water properties of tight sandstone by utilizing reservoir pore-throat volume ratio. Background Art

[0002] With the increasing demand for energy and the continuous decline in conventional oil and gas production, unconventional oil and gas has gradually become an important part of the oil and gas energy structure, among which tight sandstone gas is an important target for global unconventional natural gas exploration. At present, there are 70 basins in the world where tight sandstone gas has been discovered or speculated to develop, mainly distributed in North America, Europe and the Asia-Pacific region. In recent years, the exploration and development of tight sandstone gas in China has developed rapidly, and many large tight sandstone gas fields have been discovered and commercial exploitation of tight sandstone gas has been gradually realized. However, there are obvious differences between tight gas reservoirs and conventional gas reservoirs in the accumulation process, resulting in generally high water saturation in tight gas reservoirs and a more complex gas-water relationship. With the continuous deepening of gas reservoir development, test gas wells often produce water to varying degrees. The complex gas-water distribution seriously restricts the effective exploration and development of tight sandstone gas. This complex gas-water relationship limits the accuracy of tight sandstone gas reservoir reserve prediction, making it difficult to predict the sweet spot of tight sandstone gas reservoirs, and making production deployment and decision-making difficult during the rolling development of gas reservoirs, which directly affects the production and recovery rate of tight sandstone gas. Accurate fluid identification and prediction technology is the basis and difficulty of studying the gas-water distribution relationship in tight sandstone gas reservoirs. Accurately judging and identifying fluid properties is of great significance to determining gas well development plans, improving single well production capacity and input-output benefits.

[0003] The main reservoir properties of tight sandstone gas reservoirs are gas layers, gas-bearing layers, dry layers, gas-water layers, water layers, etc. Qualitative prediction of reservoir gas and water properties is a petroleum geological evaluation method that uses appropriate characterization parameters to qualitatively identify and predict reservoir fluid properties. In the early days, the method of qualitative prediction of gas and water properties first made an overall judgment on whether a single well was a gas well or a gas-water well based on the oil test results, and then interpreted the relative size of the water saturation value or calculated the movable water saturation with reference to the single well logging, and divided the samples of the gas layer in the gas well, and divided the samples of the gas-water layer or water layer in the gas-water well, so as to achieve the purpose of qualitatively predicting the gas and water properties of the reservoir. With the in-depth understanding of the identification of gas and water properties, some scholars have used the multi-curve combination method to comprehensively identify the fluid properties according to the corresponding logging characteristics of different fluid properties. First, various logging curves are used to superimpose the response differences of the gas layer, and the curves sensitive to gas-bearing response are amplified, and the insensitive curves are eliminated or suppressed; then, after the data formula is constructed, reorganized and optimized, the gas-bearing indicator curve is obtained, so as to achieve the purpose of identifying different fluid properties in the reservoir.

[0004] With the development of oil and gas exploration and development theory and the improvement of requirements, there are currently four methods for qualitative prediction of gas and water properties: ① porosity logging curve combination method; ② intersection method; ③ one- and two-dimensional nuclear magnetic resonance discrimination method; ④ longitudinal and transverse wave time difference ratio method, etc. Among them, using logging curves to identify gas and water properties and one- and two-dimensional nuclear magnetic resonance methods are the most commonly used prediction methods.

[0005] The invention patent with the publication number CN101806215A and the publication date of August 18, 2010 discloses a method for distinguishing the type of reservoir fluid using irreducible water saturation data. The patent analyzes the irreducible water influencing factors such as reservoir rock particle size and pore structure, and uses core data calibration logging to accurately calculate reservoir parameters such as reservoir mud content, rock composition, porosity, and water saturation. The irreducible water saturation porosity data obtained from the core relative permeability experimental data is statistically regressed into the irreducible water saturation formula, and finally the irreducible water and movable water results calculated by the formula are used to distinguish the type of reservoir fluid. Although the patent considers many factors, the final prediction model is mainly judged by irreducible water saturation, movable water saturation and gas saturation, and the seepage effect is not considered as an influencing factor of the prediction standard. The analysis is relatively complicated and the irreducible water saturation is finally fitted only by porosity, which may lead to inaccurate results. Summary of the invention

[0006] In view of the problems and defects in the above-mentioned prior art, the present invention proposes a method and device for predicting the gas-water properties of tight sandstone using the reservoir pore throat volume ratio, and establishes a bound water saturation model using the pore throat volume ratio, thereby calculating the movable water saturation parameter and combining the gas-water two-phase permeability model to comprehensively predict and identify the gas-water properties. The present invention targets the complex pore throat structure and heterogeneity of tight reservoirs, and the results are accurate and effective, providing a more scientific, objective and more applicable prediction technology for the identification of gas-water properties.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution of the present invention is as follows: A method for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio mainly comprises the following steps: Step S1. Calculating the pore throat volume ratio of the reservoir based on mercury injection experimental data; Step S2. Establishing an irreducible water saturation model by combining the reservoir pore throat volume ratio and irreducible water saturation data; Step S3. Calculate the water saturation and calculate the movable water saturation by combining the irreducible water saturation model; Step S4. Based on the low permeability core gas and water two-phase permeability experiment, multivariate nonlinear regression fitting is performed to establish a gas-water phase permeability model; Step S5. Establish a prediction limit standard for gas-water properties in combination with movable water saturation and gas phase relative permeability, and predict the gas-water properties of tight sandstone based on the prediction limit standard.

[0008] Preferably, in the present invention, the method further comprises step S6. Using a new data set that does not belong to the above steps, the accuracy of the prediction limit standard is tested for reliability to verify its accuracy.

[0009] Preferably, in the present invention, the pore volume ratio is the ratio of the pore volume to the throat volume, and the specific calculation expression is as follows: ; Among them, S max is the total volume of pore throats, S R is the pore volume.

[0010] Preferably, in the present invention, the movable water saturation is the difference between the water saturation and the irreducible water saturation.

[0011] Based on the same inventive concept, the present invention also proposes a device for predicting the gas-water properties of tight sandstone using the reservoir pore-throat volume ratio, the device is used to implement the above-mentioned gas-water property prediction method, and the device mainly includes: The pore-throat volume ratio calculation module calculates the pore-throat volume ratio based on the pressure pump test data; Irreducible water saturation model building module, which builds the irreducible water saturation model based on the pore throat volume ratio and irreducible water saturation data; A movable water saturation calculation module is used to calculate the movable water saturation based on the water saturation; The gas-water relative permeability model establishment module is based on the multivariate nonlinear regression fitting of the gas-water two-phase permeability experiment of the low permeability core to establish the gas-water relative permeability model; The module for establishing the limit standards for gas and water property prediction combines movable water saturation and gas phase relative permeability to establish the limit standards for gas and water property prediction.

[0012] A computer device comprises a memory, a processor and a computer program stored in the memory and executable in the processor, wherein when the processor executes the computer program, the steps of the gas-water property prediction method are implemented.

[0013] A computer-readable storage medium stores a computer program, and when the computer program is executed in a computer processor, the steps of the gas-water property prediction method are implemented.

[0014] Beneficial effects of the present invention: (1) Considering that the pore throat volume ratio can well characterize the pore structure characteristics and permeability of tight reservoirs and that the data has a good correlation with irreducible water saturation, the present invention uses the pore throat volume ratio to establish an irreducible water saturation model, which is more accurate than physical property parameters. The movable water saturation parameters are calculated and combined with the nonlinear gas-water two-phase relative permeability curve and the logging interpretation results to comprehensively predict and identify the gas and water properties. The results are accurate and effective for the complex pore throat structure and heterogeneity of tight reservoirs, providing a more scientific, objective and more applicable prediction technology for the identification of gas and water properties.

[0015] (2) The present invention introduces multiple parameters that affect the identification of gas-water properties, such as pore throat volume ratio, movable water saturation, irreducible water saturation, gas phase relative permeability, etc., into the establishment of the prediction limit standard for gas-water properties, so that the prediction limit standard has wider applicability and high reliability.

[0016] (3) The discrimination standard is based on low-cost mercury injection experiments and gas-water phase permeability experiments. It can be constructed in a short time for the applicable study area, especially for the identification of gas and water properties in low-porosity, low-permeability reservoirs with high bound water saturation. The discrimination standard model has high accuracy, avoiding the multi-solution problem existing in conventional well logging and one-dimensional nuclear magnetic resonance prediction methods, and greatly improving the efficiency of gas and water property identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and following detailed description of the present invention will become more apparent when read in conjunction with the following drawings, in which: Figure 1 is a flow chart of the method of the present invention; Figure 2 It is a structural diagram of the device of the present invention; Figure 3 It is a schematic diagram of mercury injection curve; Figure 4 It is a schematic diagram of the fitting relationship between the average pore throat volume ratio and irreducible water saturation; Figure 5 It is a schematic diagram of gas-water relative permeability curve; Figure 6 Schematic diagram of pore fluid evolution profile; Figure 7 Establish a basis diagram for the prediction criteria; Figure 8 This is a profile diagram of gas-water prediction and evaluation based on pore throat volume ratio in region X in an embodiment of the present invention; DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions for achieving the purpose of the present invention will be further described below through several specific embodiments. It should be noted that the technical solutions claimed for protection in the present invention include but are not limited to the following embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0019] The technical solution for achieving the purpose of the present invention is further described below by means of specific embodiments. It should be noted that the technical solution claimed for protection by the present invention includes but is not limited to the following embodiments.

[0020] With the continuous deepening of gas reservoir development, test gas wells often produce water to varying degrees. The complex gas-water distribution seriously restricts the effective exploration and development of tight sandstone gas. This complex gas-water relationship limits the accuracy of tight sandstone gas reservoir reserve prediction, making it difficult to predict the sweet spot of tight sandstone gas reservoirs, and making production deployment and decision-making difficult during the rolling development of gas reservoirs, which directly affects the production and recovery rate of tight sandstone gas. Accurate fluid identification and prediction technology is the basis and difficulty of studying the gas-water distribution relationship in tight sandstone gas reservoirs. Accurately judging and identifying fluid properties is of great significance to determining gas well development plans, improving single well production capacity and input-output benefits.

[0021] With the development of oil and gas exploration and development theory and the improvement of requirements, there are currently four methods for qualitative prediction of gas and water properties: ① porosity logging curve combination method; ② intersection method; ③ one- and two-dimensional nuclear magnetic resonance discrimination method; ④ longitudinal and transverse wave time difference ratio method, etc. Among them, using logging curves to identify gas and water properties and one- and two-dimensional nuclear magnetic resonance methods are the most commonly used prediction methods.

[0022] However, the current qualitative prediction of gas and water properties still has the following shortcomings: (1) There are many multi-solution problems when using conventional logging and one-dimensional nuclear magnetic resonance logging methods to determine reservoir fluid properties. Under most conditions, low-porosity and low-permeability reservoirs are the product of the superposition of multiple genetic geological processes. Various logging curves superimpose and interfere with each other on the signals reflecting reservoir and fluid properties, which brings complexity to the identification of oil, gas and water layers; (2) Although two-dimensional nuclear magnetic resonance can directly identify fluids, its measurement cost is high, data processing is relatively complex, and there are often differences between lithology experimental data and logging data, which places more stringent conditions on the observation mode.

[0023] The present invention takes into account that the pore throat volume ratio can well characterize the pore structure characteristics and permeability of tight reservoirs and that the data has a good correlation with irreducible water saturation. Based on this, an embodiment of the present invention proposes a method and device for predicting the gas-water properties of tight sandstones using the pore throat volume ratio of the reservoir. The present invention uses the pore throat volume ratio to establish an irreducible water saturation model, which has better accuracy than physical property parameters. The movable water saturation parameters are calculated and combined with the nonlinear gas-water two-phase relative permeability curve and the logging interpretation results to comprehensively predict and identify the gas-water properties. The results are accurate and effective for the complex pore throat structure and heterogeneity of tight reservoirs, providing a more scientific, objective and more applicable prediction technology for gas-water property identification.

[0024] This embodiment discloses a method and device for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio. Figure 1 , the method comprises the following steps: Step S1. Perform mercury injection experiments on samples from area X in the study area, and calculate the reservoir pore throat volume ratio of area X using the following formula (1) based on the mercury injection curve. The mercury injection curve is as follows: Figure 3 As shown; Formula (1); Among them, S max is the total volume of pore throats, S R is the pore volume. The pore volume and the total pore throat volume can be obtained from the injection and exit curves of the mercury injection curve, and the samples in the study area are selected based on existing oil testing data to prove their gas-water properties.

[0025] Step S2. Fit the reservoir pore throat volume ratio with the irreducible water saturation data to establish an irreducible water saturation model. The fitting results are shown in Figure 4 As shown, there is a linear correlation, and the correlation coefficient R 2 Higher.

[0026] In the present invention, it should be noted that the pore throat volume ratio reflects the pore structure characteristics of the reservoir. The higher the ratio, the lower the permeability; conversely, the lower the ratio, the stronger the permeability. Under very high pressure, the volume percentage of the part of the rock pore that mercury cannot enter is the irreducible water saturation. The irreducible water saturation is rarely affected by external factors during the evolution of the reservoir. A large amount of experimental data shows that the pore throat volume ratio has a certain positive correlation with the irreducible water saturation value. Therefore, a irreducible water saturation model based on the pore throat volume ratio can be established, and the irreducible water saturation can be quantitatively calculated by the irreducible water saturation model.

[0027] Furthermore, in the present invention, the irreducible water saturation can be obtained by adopting a relatively accurate nuclear magnetic resonance method. First, the core saturated with water is measured by nuclear magnetic resonance to obtain a transverse relaxation time T2 distribution spectrum (saturated T2 spectrum). Then, the free water in the core saturated with water is thrown out on a centrifuge, leaving only the irreducible water. Then, the core is measured by nuclear magnetic resonance to obtain a transverse relaxation time T2 distribution spectrum after centrifugation (centrifugal T2 spectrum). After the T2 cutoff value is obtained by combining the saturated T2 spectrum and the centrifugal T2 spectrum, the envelope area of ​​the immovable peak less than the T2 cutoff value in the saturated T2 spectrum is divided by the envelope area under the entire T2 spectrum to obtain the nuclear magnetic irreducible water saturation. The irreducible water saturation is rarely affected by external factors during the evolution of the reservoir. A large amount of experimental data shows that the pore throat volume ratio has a certain positive correlation with the irreducible water saturation value. Therefore, a irreducible water saturation model based on the pore throat volume ratio can be established. The irreducible water saturation is quantitatively calculated by the irreducible water saturation model, thereby eliminating the subsequent experimental process of obtaining the irreducible water saturation.

[0028] Step S3: Calculate the water saturation, and then calculate the movable water saturation of the reservoir in combination with the irreducible water saturation.

[0029] In the present invention, the movable water saturation is actually the difference between the water saturation and the bound water saturation. It should be noted that, depending on the actual physical properties of the reservoir, different water saturation calculation formulas can be used to specifically calculate the water saturation of the reservoir. The water saturation of a conventional sandstone reservoir can be calculated using the following formula (2), while the reservoir type is low porosity and low permeability, and the pore structure and mud distribution are complex. The following formula (3) with mud conductivity correction can be used to calculate it. In general, the choice of water saturation formula depends not only on the size of the physical properties, but also on the influence of mud content and formation water mineralization. ; (3); in, is the true resistivity of the formation (Ω·m), is the formation water resistivity (Ω·m), is the lithology index, is the cementation index, is a constant related to lithology, is the saturation index, is the effective porosity of the formation (%), is the formation mud volume fraction (%), is the resistivity of mud (Ω·m).

[0030] In this embodiment, since the reservoir mud content in the X area of ​​the study area is relatively low, the water saturation can be directly calculated using formula (2), and then the irreducible water saturation of the area is quantitatively calculated based on the fitted irreducible water saturation model. Finally, the movable water saturation is calculated based on the water saturation and the irreducible water saturation.

[0031] Step S4. Conduct core gas and water two-phase permeability experiments, and perform nonlinear multivariate regression fitting based on irreducible water saturation and water saturation data to establish a gas and water phase permeability model, thereby obtaining a calculation formula for gas-water phase relative permeability; Figure 5 This is the fitting result of the irreducible water saturation of 56%. The fitting formula is as follows: , R 2 =0.921; , R 2 =0.884; in, is the relative permeability of water phase; is the gas phase relative permeability; is the water saturation, is the bound water saturation.

[0032] Step S5. Establish the prediction limit standard of gas-water properties based on pore-throat volume ratio. The process first counts the pore-throat volume ratio data, and calculates the irreducible water saturation according to the irreducible water saturation model established in the previous step S2. Then, the gas phase relative permeability under different irreducible water saturations is calculated according to the gas-water phase permeability model established in step S4. Combined with the movable water saturation calculated in step S3, a gas phase relative permeability-movable water saturation scatter plot is made (refer to the attached manual). Figure 7 Finally, the movable water saturation and gas phase relative permeability value ranges are divided according to the existing oil test data to prove its gas-water properties, so as to establish the prediction limit standard of gas-water properties, as shown in Table 1 below. Based on this prediction limit standard, the gas-water properties of tight sandstone gas reservoirs are predicted.

[0033] Table 1 In this embodiment, it should be noted that the process of establishing the prediction limit standard requires existing oil test data to prove its gas-water properties. Under the constraints of theory (dry layer, bound water saturation ≈ water saturation, , Almost 0; air layer ≈0; air-water layer , Both reached the lower limit of mobility; water layer > ≈0. And as the movable water saturation increases, the irreducible water saturation decreases, and the pore throat volume ratio decreases) The prediction limit standard is established in combination with the actual calculation data.

[0034] Since the calculated movable water saturation alone is not sufficient to classify gas-water properties, the gas phase relative permeability combined with movable water saturation has a better effect on identifying gas-water properties. Figure 7 As shown in the figure, when there is only bound water in the gas layer, the relative permeability of gas is very high, while the relative permeability of water is close to 0. This type of reservoir only produces gas but not water. However, the presence of movable water in the reservoir does not mean that water will be produced during oil and gas production, because in the two-phase flow of gas and water, if the gas phase flow is absolutely dominant, the gas phase permeability is very high, and no water will be produced during production. In this study area, Figure 6 It can be seen that the 10% movable water saturation line can separate the gas layer and the gas-water layer, and only a very small number of gas layers and gas-water layers are mixed together.

[0035] Step S6. Using 6 wells in region X, the well-connected profile is as follows: Figure 8 As shown in Table 2, 18 new data were used to test the reliability of the model, and the results showed that the evaluation accuracy was 88.9% as shown in Table 2: Table 2 Further, based on the same inventive concept, an embodiment of the present invention also provides a device for predicting the gas-water properties of tight sandstone using the reservoir pore-throat volume ratio, and the device is used to implement the above-mentioned formation pressure prediction method, as described in the following embodiment. As used below, the term "unit" or "module" can be a combination of software and / or hardware that implements a predetermined function. Although the device described in the following embodiments is preferably implemented in software, the implementation of hardware, or a combination of software and hardware, is also possible and conceivable. Refer to the attached manual for details. Figure 2 Specifically, the device may include: a pore throat volume ratio calculation module 201, a bound water saturation model establishment module 202, a movable water saturation calculation module 203, a gas-water relative permeability model establishment module 204 and a gas-water property prediction limit standard establishment module 205. The structure will be specifically described below.

[0036] A pore throat volume ratio calculation module 201 is used to calculate the pore throat volume ratio based on the pump pressure test data; The irreducible water saturation model building module 202 builds the irreducible water saturation model based on the pore throat volume ratio and the irreducible water saturation data; A movable water saturation calculation module 203 is used to calculate the movable water saturation based on the water saturation; The gas-water relative permeability model building module 204 is used to build a gas-water relative permeability model by performing multivariate nonlinear regression fitting based on the gas-water two-phase permeability experiment of the low permeability core; The gas-water property prediction limit standard establishment module 205 establishes the gas-water prediction limit standard in combination with the movable water saturation and the gas phase relative permeability.

[0037] It should be noted that the systems, devices, models or units described in the above embodiments can be implemented by computer chips or entities, or by products with certain functions. For the convenience of description, in this specification, the above devices are described in various units according to their functions. Of course, when implementing the present invention, the functions of each unit can be implemented in the same or multiple software and / or hardware.

[0038] Furthermore, in the present specification, adjectives such as first and second may be used merely to distinguish one element or action from another, without necessarily or implying any actual such relationship or order.

[0039] Furthermore, an embodiment of the present invention also provides a computer device, which includes a memory, a processor, and a computer program stored in the memory and executable in the processor. When the processor executes the computer program, the steps of any of the above-mentioned gas-water property prediction methods are implemented.

[0040] Furthermore, an embodiment of the present invention also provides a computer-readable storage medium, which stores a computer program. When the computer program is executed in a computer processor, it implements the steps of any of the above-mentioned gas-water property prediction methods.

[0041] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Any simple modification or equivalent change made to the above embodiment based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio, characterized in that: The following steps are involved: Calculate the pore throat volume ratio based on mercury injection experimental data; Combining the pore-throat volume ratio with irreducible water saturation data, an irreducible water saturation model is established. Calculate water saturation and find movable water saturation; Based on the gas-water two-phase permeability experiment of low permeability core, a multivariate nonlinear regression fitting was performed to establish a gas-water phase permeability model. The prediction limit standard of gas-water properties is established by combining movable water saturation and gas relative permeability.

2. The method for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio according to claim 1, characterized in that: The method further includes: using a new data set that does not belong to the above steps to perform a reliability test on the accuracy of the prediction limit standard to verify its accuracy.

3. The method for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio according to claim 1, characterized in that: The pore volume ratio is the ratio of the pore volume to the throat volume, and the calculation expression is as follows: ； Among them, S max is the total volume of pore throats, S R is the pore volume.

4. The method for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio according to claim 1, characterized in that: The movable water saturation is the difference between the water saturation and the irreducible water saturation.

5. A device for predicting gas-water properties of tight sandstone using reservoir pore-throat volume ratio, characterized in that: The device is used to implement the prediction method described in any one of claims 1 to 4, including: The pore-throat volume ratio calculation module calculates the pore-throat volume ratio based on the pressure pump test data; Irreducible water saturation model building module, which builds the irreducible water saturation model based on the pore throat volume ratio and irreducible water saturation data; A movable water saturation calculation module is used to calculate the movable water saturation based on the water saturation; The gas-water relative permeability model establishment module is based on the multivariate nonlinear regression fitting of the gas-water two-phase permeability experiment of the low permeability core to establish the gas-water relative permeability model; The module for establishing the limit standards for gas and water property prediction combines movable water saturation and gas phase relative permeability to establish the limit standards for gas and water property prediction.

6. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable in the processor, characterized in that: When the processor executes the computer program, the method steps described in any one of claims 1 to 4 are implemented.

7. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed in a computer processor, the method steps described in any one of claims 1 to 4 are implemented.

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