A method for determining natural production of a low-permeability water-bearing gas well

Abstract

The present application relates to a kind of low permeability water-bearing gas reservoir gas well natural production determination method, belong to oil and gas field development technical field;Including the gas well of natural production in research area is screened, the deliverability of screened gas well is determined;Using well logging data and structure data determines the influence factor of gas well deliverability;Correlation analysis is carried out to gas well deliverability and influence factor, and main evaluation index is determined;The correlation degree between each main evaluation index and gas well deliverability is calculated using grey correlation analysis method, and the influence weight of each main evaluation index is determined;The relationship between main evaluation index and deliverability is established, and the standard value of main evaluation index is determined;The actual numerical value of each main evaluation index is obtained, and the discrimination parameter of gas well natural production in research area is determined;The relationship between deliverability and discrimination parameter is established, and the adaptability condition of gas well natural production is determined.The present application determines the adaptability condition of gas well natural production to determine whether gas well has the potential of natural production.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for determining natural production of a low-permeability water-bearing gas well, and belongs to the technical field of oil and gas field development. BACKGROUND

[0002] Low-permeability-dense gas reservoirs are a very important natural gas resource in China, with large reserves and mainly distributed in Ordos, Sichuan, Songliao and Tarim basins. With the continuous deepening of natural gas development process, the quality of the development target reservoirs gradually deteriorates. Influenced by the charging and preservation conditions of the reservoirs, the gas-bearing properties of the reservoirs differ greatly, and the gas-water relationship in local areas is complex. The reservoirs have no or low natural productivity. In order to achieve profitable development, fracturing is often used for production. However, for the upper-gas lower-water type reservoirs without stable interbeds between gas-bearing layers, the gas and water layers are easily connected after fracturing, and the development effect of the gas well with high water cut is poor. In addition, for the reservoirs with good physical properties and developed micro-faults in the middle and high positions, the gas and water are differentiated, and the gas well has the potential for natural production. By optimizing the production mode, the development investment is reduced, and the economic benefit is improved.

[0003] At present, there are few studies on the determination method of the natural production mode of low-permeability water-bearing gas reservoirs. For example, in December 2021, a document entitled "Gas-water distribution and development mode of litho-tectonic low-permeability water-bearing gas reservoirs in Shiguxiaohao gas area" was published in "Natural Gas Technology and Economy". It is pointed out that in terms of comprehensive geological conditions and economic benefits, the screening criteria for natural production are as follows: smooth box-shaped natural gamma ray, no interbed, acoustic time difference greater than 260 , porosity greater than 15%, and permeability greater than , but the influence of gas-bearing property and gas reservoir structure is not considered.

[0004] The patent application file with the publication number CN106761718A discloses a new method for determining the producing thickness limit of a middle-deep oil reservoir. According to the total investment of the oil well in the oil reservoir, the economic limit initial production under the natural production and the fracturing production is calculated, a relevant numerical model is established, the initial production of single-layer production and multi-layer superimposed production under different effective thicknesses under the two production modes is predicted, and the number of layers and the effective thickness corresponding to the initial production above the economic limit initial production are counted, which is the producing thickness limit of the middle-deep oil reservoir. The new method for determining the producing thickness limit of the middle-deep oil reservoir is simple to apply, and provides a reliable screening method for determining the effective thickness limit of the middle-deep oil reservoir and improving the reserve producing rate, but only considers the effective thickness of the oil reservoir, which has certain limitations. SUMMARY

[0005] The purpose of the present application is to provide a method for determining the natural production of a low-permeability water-bearing gas well, to solve the problem of how to provide a method for determining the natural production of a low-permeability water-bearing gas well.

[0006] To achieve the above object, the scheme of the present application comprises:

[0007] The method for determining the natural production of a low-permeability water-bearing gas well of the present application comprises the following steps:

[0008] 1) Screening the gas wells of the study area according to the specified conditions, and determining the deliverability of the screened gas wells;

[0009] 2) Determining a plurality of influence factors affecting the deliverability of the gas wells from the lithology, heterogeneity, physical property, gas-bearing property and structure by using the logging data and the structure data;

[0010] 3) Correlation analysis of the deliverability of the gas wells and the plurality of influence factors, and taking the plurality of influence factors having a high correlation rate with the deliverability of the gas wells as the main evaluation indexes;

[0011] 4) Calculating the correlation degree between each main evaluation index and the deliverability of the gas well by using the grey correlation analysis method, quantifying the influence weight of each main evaluation index on the deliverability of the gas well by the correlation degree, and determining the influence weight of the main evaluation index;

[0012] 5) Establishing the relationship between each main evaluation index and the deliverability, and determining the standard value of the main evaluation index under the constraint condition of the initial deliverability of the economic limit;

[0013] 6) Obtaining the actual value of each main evaluation index, and determining the discrimination parameter of the natural production of the gas well in the study area in combination with the influence weight of the main evaluation index and the ratio of the actual value of the main evaluation index to the standard value;

[0014] 7) Establishing the relationship between the deliverability and the discrimination parameter, and determining the adaptability condition of the natural production of the gas well.

[0015] The present application fully considers the influence of the lithology, heterogeneity, physical property, gas-bearing property and structure on the deliverability of the natural production of the gas well by using the logging data (conventional logging data) and the structure data, determines the discrimination parameter of the natural production of the gas well in the study area, and provides a basis for the selection of the production mode of the low-permeability water-bearing gas well. The method is easy to operate and practical, guides the economic and effective development of the low-permeability water-bearing gas reservoir, and improves the producing rate of the reserves. The method for determining the natural production of a low-permeability water-bearing gas well provided by the present application determines the adaptability condition of the natural production of the gas well to discriminate whether the gas well has the potential for the natural production, i.e., whether the gas well is suitable for the natural production mode, and further optimizes the production mode of the gas well.

[0016] Further, the specified conditions are the gas wells having the substandard deliverability caused by non-geological factors.

[0017] Further, the deliverability of the gas well is the average daily gas production of the gas well in the first year of production.

[0018] Further, the influencing factors affecting the productivity of the gas well include natural gamma, natural gamma tooth rate, acoustic time difference, compensated neutron, compensated density, porosity, permeability, induced resistivity, gas saturation, structural form and structural closure height.

[0019] Further, the discriminant parameter of the natural production of the gas well in the research area is , ; wherein, is the influence weight of the first main evaluation index, is the actual value of the first main evaluation index, is the standard value of the first main evaluation index.

[0020] Further, according to the relationship between the productivity and the discriminant parameter, the standard value of the discriminant parameter is determined as the constraint condition of the initial productivity of the economic limit.

[0021] Further, according to the actual calculation value of the discriminant parameter and the standard value of the discriminant parameter, the adaptability condition of the natural production of the gas well is determined as ; wherein, is the actual calculation value of the discriminant parameter, is the standard value of the discriminant parameter.

[0022] Further, the constraint condition is to reach or exceed the initial productivity of the economic limit. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the flow chart of the determination method of the natural production of the low-permeability water-bearing gas reservoir gas well of the present application;

[0024] Figure 2 is the schematic diagram of the relationship between the acoustic time difference as the main evaluation index and the productivity of the natural production gas well of the present application;

[0025] Figure 3 is the schematic diagram of the relationship between the deep induced resistivity as the main evaluation index and the productivity of the natural production gas well of the present application;

[0026] Figure 4 is the schematic diagram of the relationship between the structural height as the main evaluation index and the productivity of the natural production gas well of the present application;

[0027] Figure 5 is the schematic diagram of the relationship between the tooth rate as the main evaluation index and the productivity of the natural production gas well of the present application;

[0028] Figure 6 is the conventional comprehensive logging diagram of Well A in the embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application is further described in detail below with reference to the accompanying drawings and examples.

[0030] An embodiment of a method for determining natural production of a gas well in a low-permeability water-bearing gas reservoir:

[0031] A method for determining natural production of a gas well in a low-permeability water-bearing gas reservoir, as shown in the figure, includes the following steps: Figure 1

[0032] 1) Screening the natural production gas wells in the study area according to the specified conditions to determine the deliverability of the screened gas wells; wherein the specified conditions are to remove the gas wells with substandard deliverability caused by non-geological factors. The natural production gas wells in the study area are screened to remove the wells with substandard deliverability caused by non-geological factors (remove the gas wells with substandard deliverability caused by non-geological factors), i.e. from all the natural production gas wells in the study area, the gas wells with substandard deliverability caused by non-geological factors are screened out, and the deliverability of the remaining gas wells after screening is determined.

[0033] 2) Using conventional logging data and structural data to determine the influencing factors affecting the deliverability of the natural production gas wells from the aspects of lithology, heterogeneity, physical property, gas-bearing property and structure; through correlation analysis, the main evaluation indexes of the natural production wells (natural production gas wells) are determined, the correlation degree between each main evaluation index and the deliverability (the deliverability of the gas well) is calculated by using the grey correlation analysis method, the influence weight of each main evaluation index on the deliverability of the natural production well is quantitatively quantified by the correlation degree, and the influence weight of the main evaluation indexes is determined.

[0034] ​The established research area natural production well productivity is the average daily gas production of the first year of gas well production, and the natural production well evaluation index system is determined by comprehensively considering the lithology, heterogeneity, physical property, gas content and structure of the gas well reservoir, and specifically includes natural gamma, natural gamma tooth rate, acoustic time difference, compensated neutron, compensated density, porosity, permeability, induced resistivity, gas saturation, structure shape and structure closure height; correlation analysis is performed on the gas well productivity and a plurality of influencing factors, and a plurality of influencing factors with a large correlation rate with the gas well productivity are taken as main evaluation indexes, that is, the correlation data of each factor and the gas well productivity data are obtained through the conventional logging curve and the gas well production, the correlation analysis of each factor and the natural production well productivity is performed, and the factors with a large correlation rate are selected as the main evaluation indexes of the natural production well; the correlation analysis is a scatter plot of the gas well productivity and each productivity influencing factor, if the points on the scatter plot are regularly distributed, such as positive correlation or negative correlation, the factor is determined as the main evaluation index, and if the points on the scatter plot are very scattered and have no rules, that is, not correlated, the factor is not determined as the main evaluation index. The present application selects four main evaluation indexes, which are natural gamma tooth rate, acoustic time difference, induced resistivity and structure height.

[0035] 3) The relationship between each main evaluation index and the productivity is established, the standard value of the main evaluation index of the natural production well in the research area is determined by taking the economic limit initial productivity as a constraint condition.

[0036] The relationship chart between each main evaluation index and the natural production well productivity is drawn, and the standard value of the main evaluation index of the natural production well in the research area is determined by taking the economic limit initial productivity as a constraint condition; wherein the economic limit initial productivity is the minimum productivity with economic benefits, and the gas well has economic benefits only when the productivity exceeds the economic limit initial productivity. The economic limit initial productivity means that the gas well productivity reaches or exceeds the economic limit initial productivity.

[0037] 4) The actual values of the main evaluation indexes of the natural production gas well are obtained, and the discrimination parameter of the natural production of the gas well in the research area is established by combining the weight (influence weight) of the main evaluation index of the natural production well, and the ratio of the actual value of the main evaluation index to the standard value.

[0038] The discrimination parameter of the natural production of the gas well in the research area is represented as

[0039]

[0040] wherein, is the weight proportion (influence weight) of the first main evaluation index, which is dimensionless (i.e. is dimensionless); is the actual value of the first main evaluation index, which corresponds to the national standard unit; To meet the economic limit initial production of the first The standard value of the first main evaluation index of the economic limit initial production corresponds to the unit of the national standard.

[0041] 5) According to the relationship chart between the deliverability of the natural production gas well in the research area and the discrimination parameter of the natural production of the gas well, the adaptability condition of the natural production of the gas well is determined.

[0042] According to the relationship chart between the deliverability of the natural production gas well in the research area and the discrimination parameter of the natural production of the gas well, the standard value of the discrimination parameter corresponding to the discrimination parameter of the natural production of the gas well when the deliverability meets the economic limit initial production (the standard value of the discrimination parameter) is determined, and the adaptability condition of the natural production of the gas well is further determined.

[0043]

[0044] Among them, The discrimination parameter of the natural production of the gas well in the research area (the actual calculation value of the discrimination parameter) is dimensionless. The discrimination parameter of the natural production of the gas well in the research area (the actual calculation value of the discrimination parameter) is dimensionless.

[0045] The present application determines the influencing factors of the deliverability of the natural production gas well from the lithology, heterogeneity, physical property, gas content and structure by using the conventional logging data and structure data, determines the main evaluation index of the natural production well through correlation analysis, adopts the grey correlation analysis method to determine the influence weight of the main evaluation index, determines the standard value of the main evaluation index of the natural production well in the research area by taking the economic limit initial production as a constraint condition, and establishes the discrimination parameter of the natural production of the gas well in the research area by combining the weight of the main evaluation index of the natural production well and the ratio of the actual value and the standard value of the main evaluation index. The present application fully considers the influence of the lithology, physical property, gas content and structure on the natural production of the gas well by using the conventional logging data and structure data, establishes the discrimination parameter of the natural production of the gas well, and provides a basis for the selection of the production mode of the gas well in the low-permeability water-bearing gas reservoir. The method is easy to operate and practical, can guide the economic and effective development of the low-permeability water-bearing gas reservoir, and improves the producing rate of the reserves.

[0046] Specific implementation method

[0047] This embodiment takes a certain well area low-permeability tight water-bearing gas reservoir as an example. The productivity of 25 natural production gas wells in the main layer of the well area He 2+3 layer is 0-32,000 m3 / d, and the productivity difference is large. From the analysis of conventional logging data and structure data, the influencing factors of productivity include natural gamma, natural gamma tooth rate (tooth rate), deep induction resistivity, acoustic time difference, compensated neutron, compensated density, structural height, porosity, permeability, and gas saturation. The correlation analysis between these factors and the productivity of the gas well is performed. It is known from the correlation analysis that the acoustic time difference, deep induction resistivity, natural gamma tooth rate, and structural height have a larger correlation with the productivity, as shown in Figures 2 to 5 . Among them, the acoustic time difference, deep induction resistivity, and structural height are positively correlated with the productivity, and the natural gamma tooth rate is negatively correlated with the productivity. The weights (influence weights) of the acoustic time difference, deep induction resistivity, natural gamma tooth rate, and structural height are 0.25, 0.32, 0.12, and 0.31 respectively determined by the grey correlation.

[0048] Under the condition that the internal rate of return of single well investment is 8%, the economic limit initial productivity of the natural production well is . Taking the economic limit initial productivity as the minimum standard, when the productivity meets the economic limit initial productivity, the acoustic time difference is greater than , the deep induction resistivity is greater than , the natural gamma tooth rate is less than 0.2, and the structural height is greater than . That is, the standard values of the main evaluation indexes of the natural production well in the study area, namely the acoustic time difference, deep induction resistivity, tooth rate, and structural height, are , , 0.2, and .

[0049] After determining the standard values of the four main evaluation indexes, the discrimination parameter Z value of the natural production gas well in the study area is calculated,

[0050]

[0051] Among them, is the weight proportion of the first main evaluation index, and is dimensionless; is the actual value of the first main evaluation index, corresponding to the national standard unit; is the standard value of the first main evaluation index meeting the economic limit initial production (productivity), corresponding to the national standard unit; AC is the acoustic time difference, and the unit is ; ILD is the deep induction resistivity, and the unit is ; C is the natural gamma tooth rate, and is dimensionless;H The height is the structural height, in meters (m).

[0052] The Z-value of currently naturally producing gas wells is calculated using the formula for the discrimination parameter of naturally producing gas wells. A scatter plot of the relationship between Z-value and production capacity shows that Z > 1 when the production capacity meets the initial economic limit. Therefore, the adaptability condition for natural production of gas wells is:

[0053]

[0054] Well A in the well area, such as Figure 6 As shown, the primary production target layer is Box 2. The average natural gamma curve value of the production layer is 61 API, the natural gamma ray densification rate is 0.15, and the average acoustic transit time is [missing value]. The average deep induced resistivity is The structure has a height of 32m. The Z-value of the discrimination parameter for naturally producing gas wells is 1.46. The initial production capacity of the well after natural production is 23,000 cubic meters, and the production stability is good.

[0055] Through case studies, the method for determining the natural production of gas wells in low-permeability water-bearing gas reservoirs can be used to quickly and easily determine whether gas wells in low-permeability water-bearing gas reservoirs can be put into production naturally. This provides a basis for screening the production mode of gas wells in low-permeability water-bearing gas reservoirs. The method is easy to operate and practical, guiding the economical and effective development of low-permeability water-bearing gas reservoirs and improving the utilization rate of reserves.

[0056] This invention employs a quantitative method to determine whether a gas well in a low-permeability water-bearing gas reservoir can naturally commence production, overcoming the blind nature of relying solely on natural well production. It provides a basis for selecting production methods for gas wells in low-permeability water-bearing gas reservoirs, guiding their economical and effective development and improving reserve utilization. Furthermore, the method is simple in principle, easy to operate, and effective, having already been practically applied in gas fields. It is easily promoted and has high application prospects.

Claims

1. A method for determining the natural flow of a low permeability water- bearing gas well, characterized in that, The method comprises the following steps: 1) screening the natural production gas wells in the research area according to specified conditions, and determining the deliverability of the screened gas wells; 2) determining a plurality of influence factors affecting the deliverability of the gas wells from lithology, heterogeneity, physical property, gas-bearing property and structure by using logging data and structure data; 3) performing correlation analysis on the deliverability of the gas wells and the plurality of influence factors, and taking the plurality of influence factors having a high correlation rate with the deliverability of the gas wells as main evaluation indexes; 4) calculating the correlation degree between each main evaluation index and the deliverability of the gas wells by using the grey correlation analysis method, quantifying the influence weight of each main evaluation index on the deliverability of the gas wells by the correlation degree, and determining the influence weight of the main evaluation indexes; 5) establishing the relationship between each main evaluation index and the deliverability, and determining the standard value of the main evaluation indexes under the constraint condition of the initial deliverability of the economic limit; 6) obtaining actual values of each main evaluation index, combining the influence weight of the main evaluation index and the ratio of the actual value of the main evaluation index to the standard value, determining the discrimination parameter of the natural production of the gas well in the study area; according to the relationship between the productivity and the discrimination parameter, taking the initial productivity of the economic limit as the constraint condition, determining the standard value of the discrimination parameter; according to the actual calculation value of the discrimination parameter and the standard value of the discrimination parameter, determining the adaptability condition of the natural production of the gas well as ; wherein, is the actual calculation value of the discrimination parameter, is the standard value of the discrimination parameter; 7) establishing the relationship between the deliverability and the discrimination parameters, and determining the adaptability condition of the natural production of the gas wells.

2. The method of determining a low permeability water-bearing gas well natural flow according to claim 1, characterized in that, The specified conditions are the removal of the gas wells with substandard deliverability caused by non-geological factors.

3. The method of determining a low permeability water-bearing gas well natural flow according to claim 1, characterized in that, The deliverability of the gas well is the average daily gas production of the gas well in the first year of production.

4. The method of determining a low permeability water-bearing gas well natural flow according to claim 1, characterized in that, The influence factors affecting the deliverability of the gas well include natural gamma, natural gamma tooth rate, acoustic time difference, compensated neutron, compensated density, porosity, permeability, induced resistivity, gas saturation, structure form and structure closure height.

5. The method of determining a low permeability water-bearing gas well natural flow according to claim 1, wherein, The actual calculation value of the discrimination parameter of the natural production of the gas well in the research area is , ; wherein, is the influence weight of the first main evaluation index, is the actual value of the first main evaluation index, is the standard value of the first main evaluation index.

6. The method of determining a low permeability water-bearing gas well natural flow according to claim 1, wherein, The constraint condition is to reach or exceed the initial deliverability of the economic limit.

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