Prediction method for SEC storage and production ratio peak value of tight sandstone gas reservoir gas well

Abstract

The invention relates to a method for predicting an SEC storage and production ratio peak value of a tight sandstone gas reservoir gas well, and belongs to the technical field of oil and gas field development. The prediction method comprises the following steps that the preset initial daily output, the preset stable production period and the preset annual declining rate of a target gas well are substituted into a prediction model, with the SEC storage and production ratio peak value as a dependent variable and the initial daily output, the stable production period and the annual declining rate as independent variables, of the tight sandstone gas reservoir, and the SEC storage and production ratio peak value of the target gas well is obtained; the prediction model is obtained by performing mathematical fitting on the initial daily output and the SEC storage and production ratio peak value of the plurality of virtual single wells in different preset stable production periods, preset annual declining rates and preset economic storable production quantities and corresponding preset stable production periods, preset annual declining rates and preset economic storable production quantities. According to the prediction method, the problem that the change rule of the storage and production ratio is difficult to analyze due to various reservoir types and multiple influence factors during overall analysis of the storage and production ratio of the gas reservoir is solved.

Description

Technical Field

[0001] The invention relates to a method for predicting a peak value of an SEC reserve-production ratio of a gas well in a tight sandstone gas reservoir, and belongs to the technical field of oil and gas field development. Background Art

[0002] According to the definition of BP Statistical Review of World Energy, the reserve-to-production ratio (R / P) refers to "the value obtained by dividing the remaining recoverable reserves at the end of any year by the production of that year, indicating the number of years these remaining recoverable reserves can be produced if the production continues to maintain the level of that year." For listed oil companies, it is the ratio of remaining economically recoverable reserves (SEC reserves) to the production of that year.

[0003] The reserve-to-production ratio is an important indicator that reflects reserve replacement capacity, production potential and material basis. A reserve-to-production ratio that is too high or too low is not conducive to the healthy development of an enterprise. A suitable reserve-to-production ratio can better guide oilfield exploration and development practices and make reasonable investments in oil and gas exploration, thereby ensuring the normal increase in natural gas production and the sustainable development of the enterprise.

[0004] Compared with conventional gas reservoirs, the production time of gas wells in tight sandstone gas reservoirs is longer during the low-pressure and low-production stages, the reservoir heterogeneity varies greatly, the development technology strategies and production allocation principles are different, the proportions of new and old wells are different, the overall reserve-production ratio of the gas reservoir can range from 2 to more than 10, and the reserve-production ratio of different blocks in the same gas reservoir is also different. Therefore, reserve-production ratio analysis based on gas reservoirs is not conducive to business prediction.

[0005] The existing analysis of the law of reserve-production ratio involves the statistics of reasonable reserve-production ratio, the analysis of its relationship with reservoir engineering parameters, and the law of change of reserve-production ratio at different development stages. The shortcomings are that, first, the differences in gas field reserve-production ratio caused by different reserve concepts and data statistical coverage are not taken into account, and the reserve-production ratio values ​​are simply compared or the reserve-production ratio is increased. Second, the reserve-production ratio calculated based on gas reservoirs is affected by factors such as the degree of reserve exploration and development, production system, contribution of new wells, decline of old wells, and enhanced recovery. It can only be used to perform statistics on historical data, and it is impossible to scientifically and reasonably predict the future changes in the reserve-production ratio. Third, the current research focuses more on oil reservoir analysis, less on natural gas, and even less on the analysis of the relationship between the reserve-production ratio of tight sandstone gas reservoirs and reservoir engineering parameters. Summary of the invention

[0006] The purpose of the present invention is to provide a method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir, which can make the predicted peak value measurement result of the SEC reserve-production ratio of a gas well in a tight sandstone gas reservoir more accurate.

[0007] In order to achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir comprises the following steps: substituting a preset initial daily production, a preset stable production period, a preset annual decline rate and a preset economically recoverable reserves of a target gas well into a prediction model of a tight sandstone gas reservoir with the SEC reserve-production ratio peak value as a dependent variable and the initial daily production, the stable production period, the annual decline rate and the economically recoverable reserves as independent variables to obtain the SEC reserve-production ratio peak value of the target gas well; the prediction model is based on the initial daily production of multiple virtual single wells under different preset stable production periods, preset annual decline rates, preset economically recoverable reserves and the corresponding preset stable production periods, preset annual decline rates and preset economically recoverable reserves. The initial daily production and the SEC reserve-production ratio peak are obtained by mathematical fitting; the preset initial daily production of each single well in the multiple virtual single wells is distributed within the statistical range of the initial daily production of all single wells in the block where the target gas well is located; the preset stable production period of each single well in the multiple virtual single wells is distributed within the statistical range of the stable production period of all single wells in the block; the preset annual decline rate of each single well in the multiple virtual single wells is distributed within the statistical range of the annual decline rate of all single wells in the block; the preset economically recoverable reserves of each single well in the multiple virtual single wells are distributed within the statistical range of the economically recoverable reserves of all single wells in the block.

[0009] The method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir of the present invention solves the problem that the reservoir types are diverse, the influencing factors are many, and the change law of the reserve-production ratio is difficult to analyze when analyzing the reserve-production ratio of the gas reservoir as a whole. It is more applicable to the actual development and operation of the gas reservoir, and the reserve-production ratio prediction result is more accurate. In view of the strong heterogeneity of tight sandstone gas reservoirs, the mathematical model for predicting the SEC reserve-production ratio peak value of the gas well selects the key factors of stable production period, initial daily production and annual decline rate as factors, establishes a relationship, and can make scientific and reasonable predictions on the change law of the reserve-production ratio in the future, providing a reference for the reserve-production ratio analysis of similar gas fields.

[0010] In order to further improve the accuracy of the prediction, the statistical range of the preset stable production period of all the single wells in the multiple virtual single wells is the same as the statistical range of the stable production period of all the single wells in the block; the statistical range of the preset annual decline rate of all the single wells in the multiple virtual single wells is the same as the statistical range of the annual decline rate of all the single wells in the block; the statistical range of the preset economically recoverable reserves of all the single wells in the multiple virtual single wells is the same as the statistical range of the economically recoverable reserves of all the single wells in the block. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The stable production period, initial daily production, peak reserve-production ratio, decline rate, and economically recoverable reserves chart in Example 1 of the present invention;

[0012] Figure 2 It is a scatter plot of the predicted value and the measured value of the reserve-production ratio peak value in Example 1 of the present invention;

[0013] Figure 3 This is the production decline curve of the X1 well after reasonable production allocation in Example 1 of the present invention. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0015] The following Example 1 takes the A well area of ​​the D gas field in the northern margin of the Ordos Basin as an example to illustrate the prediction method of the SEC reserve-production ratio peak of the gas wells in the tight sandstone gas reservoir. The tight sandstone gas reservoir in the northern margin of the Ordos Basin has typical "low permeability, low pressure, and low abundance" characteristics, low saturation, high liquid-gas ratio, complex gas-water distribution, scattered sweet spots, and high difficulty in efficient development. The production of the A well area of ​​the D gas field was investigated. The well area was put into development in 2015 and showed an overall exponentially decreasing production characteristic.

[0016] Example 1

[0017] The method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir of this embodiment comprises the following steps:

[0018] 1) The economically recoverable reserves, stable production period, annual decline rate and daily gas production of a single well in the A well area of ​​the D gas field in the current tight sandstone gas reservoir are statistically analyzed. The results are shown in Table 1.

[0019] Table 1 Statistics of single well production data in well area A

[0020]

[0021] 2) Set a number of virtual single wells (i.e., hypothetical single wells) with economically recoverable reserves ranging from 10 million to 60 million cubic meters, and perform the following processing on each virtual single well with preset economically recoverable reserves: set the virtual single well to 10%, 20%, 30%, and 40% according to the annual decline rate range of the single wells in well area A as shown in Table 1, and then calculate the SEC reserves, SEC reserve-production ratio, and reserve-production ratio peak value of the virtual single well when the stable production period is 0 months, 3 months, 6 months, 9 months, 1 year, and 2 years respectively under each set annual decline rate according to the SEC reserve assessment rules, and obtain the data matrix. The preset economically recoverable reserves, stable production period, annual decline rate, and decline time of the virtual single well are shown in Table 2.

[0022] Table 2 Production data of virtual single well preset

[0023]

[0024] During the calculation process, the initial daily production in each combination of preset economic recoverable reserves, preset annual decline rate and preset stable production period is determined by the following method: According to formula 1, convert the daily production into the initial monthly production, convert the annual decline rate into the monthly decline rate according to formula 2, substitute the initial monthly production and monthly decline rate into formula 3 to calculate the monthly production, substitute into formula 4 to calculate the annual production, and sum up to get the economic recoverable reserves through formula 5. When the economic recoverable reserves are 10, 20, 30, 40, 50, and 60 million cubic meters, the daily gas production can be iteratively calculated through the single variable solution function of EXCEL. The initial daily production is calculated through this process.

[0025] The initial monthly output calculation formula is: q 1 =t·q 日产 Formula (1)

[0026] The formula for converting the annual decline rate to the monthly decline rate is: d = 1-(1-D) 1 / 12 Formula (2)

[0027] The monthly output calculation formula is: i =q i-1 ·(1-d) Formula (3)

[0028] The annual output calculation formula is:

[0029] The formula for calculating economically recoverable reserves is:

[0030] Among them, q 日产 is the daily gas production, t is the number of days in a month, d is the monthly decline rate, D is the annual decline rate; i is the monthly number from the current month and i is an integer ≥ 1, q i is the monthly output of the i-th month. When i=1, q is calculated according to Formula 1. 1 is the initial monthly output; Q T is the annual gas production and T is the number of years.

[0031] The final data matrix is ​​shown in Table 3.

[0032] Table 3 Data matrix

[0033]

[0034]

[0035]

[0036] Taking the economically recoverable reserves of 40 million cubic meters of wells A4-7 to A-12 as an example, the method of obtaining the data in Table 3 is explained:

[0037] For wells A4-7 to A4-12, when the annual decline rate is set to 20%, the monthly decline rate is converted to 1.84% according to formula (2); the stable production period is operated at 0 months, 3 months, 6 months, 9 months, 12 months, and 24 months respectively, and the monthly production is calculated according to formula (3). The annual production and economically recoverable reserves are calculated by combining formula (4) and formula (5). The daily gas production when the economically recoverable reserves are 40 million cubic meters is obtained by single variable solution. The reserve-production ratio is calculated according to formula (6).

[0038] The calculation formula of reserve-production ratio is:

[0039] Among them, N SEC is the remaining economically recoverable reserves, which is obtained by deducting the cumulative production from the economically recoverable reserves; Q T is the annual gas production and T is the number of years.

[0040] Taking the A4-7 well with a stable production period of 3 months as an example, the annual decline rate is 20%, and the daily production is calculated to be 23,800 cubic meters / day. The production of the A4-7 well in each month is calculated, and the production of the A4-7 well from the 1st to the 36th month is shown in Table 4. Based on the calculated production of each month, the annual production, cumulative production and reserve-production ratio of the A4-7 well are obtained, and the results are shown in Table 5.

[0041] Table 4 Production of Well A4-7 from 1st to 36th month

[0042]

[0043]

[0044] Table 5 Annual production, cumulative production and reserve-production ratio of Well A4-7

[0045] year Output (ten thousand cubic meters / year) Cumulative output (ten thousand cubic meters) Reserve-to-production ratio 1 820.20 820.20 3.88 2 665.22 1485.41 3.78 3 532.17 2017.59 3.73 4 425.74 2443.33 3.66 5 340.59 2783.92 3.57 6 272.47 3056.39 3.46 7 217.98 3274.37 3.33 8 174.38 3448.75 3.16 9 139.51 3588.26 2.95 10 111.60 3699.86 2.69 11 89.28 3789.15 2.36 12 71.43 3860.57 1.95 13 57.14 3917.72 1.44 14 45.71 3963.43 0.80 15 36.57 4000.00 0.00

[0046] When the annual decline rate is 20%, the reserve-production ratio and the peak value of the reserve-production ratio for wells A4-7 to A4-12 with economically recoverable reserves of 40 million cubic meters at various combinations of stable production time and initial daily production are shown in Table 6.

[0047] Table 6 Changes in peak reserve-production ratio of different production operation models of Wells A4-7 to A4-12

[0048]

[0049]

[0050] The data of other virtual single wells in Table 3 are obtained by referring to the above method.

[0051] Based on the data in Table 3, with the initial production as the horizontal axis and the peak value of the reserve-production ratio as the vertical axis, a chart of decline rate, stable production period, initial production, and peak value of the reserve-production ratio is formed, as shown in Figure 1 It shows that when the economically recoverable reserves remain unchanged, if the decline rate remains unchanged, extending the stable production period can effectively increase the reserve-production ratio, but the stable production period within one year has no significant impact on the reserve-production ratio; if the decline rate decreases, the reserve-production ratio can be greatly increased. When the decline rate remains unchanged, increasing the initial production can increase the economically recoverable reserves, but it has little effect on the reserve-production ratio. When the initial production remains unchanged, increasing the economically recoverable reserves can effectively improve the reserve-production ratio.

[0052] 3) Perform multiple regression on the data points in Table 3 above to obtain the reserve-production ratio prediction model.

[0053] The above data matrix is ​​subjected to multiple regression calculation with the dependent variable being the peak value of the reserve-production ratio and the independent variables being the stable production period, initial daily production, economically recoverable reserves, and annual decline rate, and the relationship is as follows:

[0054] (R / P) max =

[0055] 0.24(T / 10) 1.882 -18.196q 0.022 +8.957*(N e / 1000) 0.044 +10.059(10D) -0.489 +5.694

[0056] Formula (7)

[0057] R 2 =0.999

[0058] Among them, (R / P) max is the peak value of the reserve-production ratio, T is the stable production period (month), q is the daily gas production of a single well (10,000 cubic meters / day), Ne is the economically recoverable reserves (10,000 cubic meters), and D is the annual decline rate (f).

[0059] Substitute the stable production time, initial production, economically recoverable reserves and decline rate of each well in Table 3 into Formula 7 to obtain the predicted value of the peak value of the reserve-production ratio. The actual value of the peak value of the reserve-production ratio of each well in Table 3 is the horizontal axis, and the predicted value calculated by the formula is the horizontal axis. Draw a correlation diagram between the actual reserve-production ratio and the predicted reserve-production ratio, as shown in the figure below: Figure 2 As shown. Figure 2 It can be seen that the formula has high accuracy.

[0060] Well X1 in well area A was put into production in 2020. The economically recoverable reserves are calculated to be 67 million cubic meters. The initial daily production is 60,000 cubic meters / day, the decline rate is more than 40%, and the reserve-production ratio is 1.61. It is planned to carry out a reasonable production allocation test. If June 2022 is taken as the starting point, the daily output of 41,000 cubic meters is the initial daily output, the decline rate is 33.6% of the current decline rate, and the stable production period is 0. According to the formula established in step 3), the peak reserve-production ratio is predicted to be 2.22. If the initial daily output is reduced to 20,000 cubic meters / day, the decline rate needs to be slowed down to 15% for the reserve-production ratio to reach more than 5. According to the formula established in step 3), the peak reserve-production ratio is predicted to be 5.2. Therefore, the production allocation is adjusted to 20,000 cubic meters / day, and the decline rate is controlled to 15% (such as Figure 3 shown).

Claims

1. A method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir, characterized in that: The following steps are involved: Substituting the preset initial daily production, preset stable production period, preset annual decline rate and preset economically recoverable reserves of the target gas well into a prediction model of a tight sandstone gas reservoir with the SEC reserve-production ratio peak as the dependent variable and the initial daily production, stable production period, annual decline rate and economically recoverable reserves as the independent variables, the SEC reserve-production ratio peak of the target gas well is obtained; the prediction model is obtained by mathematically fitting the initial daily production and SEC reserve-production ratio peak of multiple virtual single wells under different preset stable production periods, preset annual decline rates, preset economically recoverable reserves and corresponding preset stable production periods, preset annual decline rates and preset economically recoverable reserves; The preset stable production period of each of the multiple virtual single wells is distributed within the statistical range of the stable production period of all single wells in the block where the target gas well is located; the preset annual decline rate of each of the multiple virtual single wells is distributed within the statistical range of the annual decline rate of all single wells in the block; the preset economically recoverable reserves of each of the multiple virtual single wells are distributed within the statistical range of the economically recoverable reserves of all single wells in the block.

2. The method for predicting the SEC reserve-production ratio peak value of a gas well in a tight sandstone gas reservoir according to claim 1, characterized in that: The statistical range of the preset stable production period of all the single wells in the multiple virtual single wells is the same as the statistical range of the stable production period of all the single wells in the block; the statistical range of the preset annual decline rate of all the single wells in the multiple virtual single wells is the same as the statistical range of the annual decline rate of all the single wells in the block; the statistical range of the preset economically recoverable reserves of all the single wells in the multiple virtual single wells is the same as the statistical range of the economically recoverable reserves of all the single wells in the block.

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