A method for predicting the production potential of water-flooded oil fields

Abstract

The present invention provides a method for predicting the exploitation potential of a water-driven oilfield. The method mainly classifies all the wells in production according to the year of production for old oilfields that have been in production for a long time, uses water-driven characteristic curve-assisted automatic prediction technology to calculate the recoverable reserves of water-driven oilfields of all oilwells, and calculates the corresponding well-controlled reserves according to the order of single well production, so as to obtain the relationship between the average recoverable reserves of the wells in the old oilfields that are put into production year by year and the well-controlled reserves; then, based on the geological reserves planned to be used for all the oilfields in production in the oil field, the recoverable reserves of water-driven oilfields under different well-controlled conditions or under different single-well recoverable reserves limit conditions are predicted, so as to predict the exploitation trend and potential of new oilfields. The present invention can ignore the difference in reservoir types, and is suitable for the prediction of water-driven recovery rate of old oilfields / new oilfields, large and medium-sized oilfields, oilfield groups or oilfields, and provides a potential evaluation basis for the intensification adjustment in the middle and late stages of oilfield / oilfield group / oilfield development.

Description

Technical Field

[0001] The invention belongs to the technical field of oil field development, and in particular relates to a method for predicting the exploitation potential of a water-driven oil field. Background Art

[0002] Offshore oilfield development is difficult and has high investment costs, so the formulation of oilfield development planning is particularly important. When the oilfield development enters the middle and late stages, the planning of new adjustment wells and recovery rate targets plays a key role in controlling the decline rate and improving the recovery rate of the entire oilfield. The conventional recovery rate empirical formula prediction is only applicable to a single oilfield or block, and it is necessary to consider the conventional geological reservoir parameters and development parameters of the oilfield, such as the permeability of the reservoir, underground crude oil viscosity, porosity, well network density, etc., which are not easy to obtain accurately for oilfields in the early stages of development, and the prediction accuracy for oilfields of different types and sizes varies greatly, and the conventional empirical formula method cannot obtain the recoverable reserves of newly added single wells. For the development planning of the entire oilfield, in addition to focusing on the recovery rate target of a certain oilfield, it focuses more on the overall recovery rate planning of an oilfield or a certain type of oilfield, such as the number of new adjustment wells, the recoverable reserves that can be added by a single well, the scale of development investment, and the target recovery rate achieved. However, for oil fields put into production at different times in the oil region, there is no effective method to predict the production potential due to the differences in development stage, number of wells put into production, reservoir type, and the impact of newly put into production wells. Summary of the invention

[0003] In order to solve the above problems, the object of the present invention is to provide a method for predicting the production potential of water-driven oilfields.

[0004] The present invention provides a method for predicting the production potential of water-driven oilfields, which predicts the recoverable reserves of all oilfields under different well-controlled reserve conditions in the future through the relationship between the recoverable reserves of single wells of wells put into production year by year and the well-controlled reserves of old oilfields that have been put into production.

[0005] The method for predicting the production potential of a water-driven oil field of the present invention comprises the following steps:

[0006] 1) Based on the old oil fields in the oil region with a long production period, the geological reserves are N as of the end of the statistical year. R The total number of wells put into production is M, and the total number of wells put into production in the nth year in history is N n , the annual well-controlled reserves can be calculated as R no ;

[0007] 2) For all the wells in production, based on the historical production data of the wells in production, the predicted value of water-driven recoverable reserves of the i-th well put into production in the nth year is recorded as Then the average recoverable reserves of a single well in the production well in the nth year are calculated.

[0008] 3) Based on the average water-driven recoverable reserves of each well in each year The relationship between the recoverable reserves of a single well and the well-controlled reserves in the oil region is plotted, and the functional relationship expression between the average recoverable reserves of a single well and the well-controlled reserves of the wells put into production year by year is obtained by fitting:

[0009]

[0010] 4) For all producing oil fields in the oil region, based on the total number of wells put into production, geological reserves in use, and recoverable reserves by the end year, the relationship between the recoverable reserves of a single well and the well-controlled reserves in the above formula is combined to calculate the incremental recoverable reserves of water drive under different well-controlled reserve conditions:

[0011]

[0012] Then the corresponding recovery factors of all oil fields in the oil region under different well-controlled reserve conditions in the future can be calculated as follows:

[0013]

[0014] Where:

[0015] a, b——both are constants;

[0016] E - the recovery factor predicted for all oil fields in the oil region in future years;

[0017] N RT ——The operating geological reserves of all oil fields in the oil region as of the end of the year for which statistical data are available;

[0018] M——the total number of wells put into production in the oil field statistical data ending year;

[0019] K j ——Plan the number of newly added wells to be put into production each year for all the oil fields that have been put into production in the oil region in the future years,

[0020] j——number of years in the future planning period, 1, 2, 3, etc.;

[0021] ΔR j ——The newly added recoverable reserves in the jth planning period in the future;

[0022] N e ——Recoverable reserves of all oil fields in the oil region as of the end of the year when statistical data are collected.

[0023] The historical production data of the production wells include monthly oil production, monthly water production and monthly production days.

[0024] Wherein, in step 2), water drive characteristic curve assisted automatic prediction technology is used to perform batch prediction of production wells, and the steps are as follows:

[0025] 21) For wells that have been shut down, side-drilled or transferred to injection, only the cumulative production is calculated as the recoverable reserves of single-well water drive;

[0026] 22) Wells that are in production and have produced for less than T months are not predicted;

[0027] 23) For wells that are in production and have produced for more than T months, if the current water cut is less than 30%, the decline method is used for prediction; if the current water cut is greater than 30%, the water drive characteristic curve is used for prediction;

[0028] 24) The predicted value of recoverable reserves of water drive of the i-th well is recorded as Where n is the year the production well was put into production.

[0029] In step 23, for the selection of the fitting segment during prediction: if the production time is greater than 10T months, the fitting segment selects the last 2T months; if the production time is between 5T months and 10T months, the fitting segment selects 0.2 times the production time; if the production time is less than 5T months, the fitting segment selects the last T months. T is an integer, which is determined according to actual production data.

[0030] The present invention applies water drive curve prediction technology to batch prediction technology. It does not need to use different curves. Only the type C water drive curve is used. When the above steps are used to select several months for prediction, more accurate prediction data can be obtained.

[0031] Among them, the steps for obtaining the relationship expression between the newly added recoverable reserves of a single well in the old oil field and the change of the well-controlled reserves in step 3) are as follows:

[0032] 31) All the wells put into production in this type of oil field are classified according to the year of production, and the average recoverable reserves of each well put into production each year are calculated as follows:

[0033]

[0034] in, is the recoverable reserves of the single well water flooding of the i-th well put into production in year n, N n is the total number of wells put into production in year n, It is the average recoverable reserves of a single well in the nth year.

[0035] 32) Obtain the geological reserves N of these old oil fields in the year when the statistical data is cut off. R , and then get the annual well-controlled reserves data R no ;

[0036]

[0037] 33) Data points are selected according to the year, and the relationship between the newly added single-well recoverable reserves and well-controlled reserves of this type of oil field is plotted. The functional relationship expression of the single-well recoverable reserves of the wells put into production year by year and the change of well-controlled reserves is obtained by fitting:

[0038]

[0039] Among them, a and b are constants.

[0040] Among them, the method for selecting old oil fields with a long production period is not unique. It is necessary to ensure that the oil fields have been in production for a long time, usually more than 8 years, and to ensure that the sample data is sufficient; the non-unique meaning is that old oil fields with production years of more than 8 years, more than 9 years or more than 10 years, etc. can be selected, with the purpose of ensuring sufficient data volume.

[0041] Among them, the expression of the relationship between the recoverable reserves of a single well in the old oil field and the change of well-controlled reserves is not unique: first, the prediction method of recoverable reserves of a single well is not unique; second, the trend function of the fitted data is not unique. It is necessary to select a high-precision and reasonable expression. If the years of the selected old oil fields are different, the calculated data points are also different, and the fitted trend line expression is also different. In principle, the fitted trend line is selected in the form of an exponential function or a power function to ensure that the fitted trend line does not intersect with the Y coordinate axis.

[0042] The beneficial effects of the present invention are as follows: the well-controlled reserves and recovery rates of new and old oil fields in an oil region can be predicted based on the production laws of some old oil fields with a long production period, while ignoring the reservoir type and reservoir physical property parameters, and the prediction method has universal applicability; the method can obtain the changing laws of newly added single-well recoverable reserves and well-controlled reserves of all oil fields in the oil region, which is crucial to the planning of the number of newly added wells put into production. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a graph showing the relationship between recoverable reserves of a single well and well-controlled reserves. DETAILED DESCRIPTION

[0044] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the invention.

[0045] For old oil fields with a long production period in the oil region, based on historical production data, the water drive characteristic curve-assisted automatic prediction technology is used to batch predict the recoverable reserves of single well water drive for all production wells in the old oil fields. The specific steps are as follows:

[0046] (1) For wells that have been shut down, side-drilled or switched to injection, only the cumulative production shall be calculated as the recoverable reserves of single-well water drive;

[0047] (2) Wells that are in production and have produced for less than T months are not predicted;

[0048] (3) For wells that are in production and have produced for more than T months, if the current water cut is less than 30%, the decline method is used for prediction; if the current water cut is greater than 30%, the water drive characteristic curve is used for prediction. For the selection of fitting segments during prediction: if the production time is greater than 10T months, the fitting segment selects the last 2T months; if the production time is between 5T months and 10T months, the fitting segment selects 0.2 times the production time; if the production time is less than 5T months, the fitting segment selects the last T months. Wherein, T is an integer, which is determined based on actual production data.

[0049] (4) The predicted value of water-driven recoverable reserves of the i-th well is recorded as Where n is the year the production well was put into production.

[0050] 2. For the old oil fields selected in step 1, the steps for obtaining the relationship expression between the newly added single well recoverable reserves and the change of well controlled reserves are as follows:

[0051] (1) All the wells put into production in this type of oil field are classified according to the year of production, and the average recoverable reserves of each well put into production each year are calculated as follows:

[0052]

[0053] in, is the recoverable reserves of the single well water flooding of the i-th well put into production in year n, N n is the total number of wells put into production in the nth year, is the average recoverable reserves of a single well in the nth year.

[0054] (2) Obtain the geological reserves N of these old oil fields in the last year of statistical data R , and then the annual well-controlled reserves R no ;

[0055]

[0056] (3) Data points are selected according to the year, and the relationship between the newly added single-well recoverable reserves and well-controlled reserves of this type of oil field is plotted. The functional relationship expression of the change of single-well recoverable reserves and well-controlled reserves of wells put into production year by year is obtained by fitting:

[0057]

[0058] Among them, a and b are constants.

[0059] 3. Based on all the oil fields in production in the oil region, calculate the total number of production wells M and the geological reserves N in the year ending with the statistical data. RT , and recoverable reserves N e ;

[0060] 4. According to the plan of all the oil fields in the oil region that have been put into production in the future, the number of newly added wells is K1, K2...K j , the well-controlled reserves value in the future j year is calculated to be Substituting the well-controlled reserves value into the relationship between the recoverable reserves of a single well and the well-controlled reserves in step 2, the average recoverable reserves of a single well added by the newly put into production wells in the jth year during the planning period can be obtained as Then the total amount of newly added recoverable reserves in the jth year of the planning period is calculated as

[0061]

[0062] The predicted recovery factor for the jth year can be obtained by this calculation, as follows:

[0063]

[0064] Where:

[0065] a, b——both are constants;

[0066] E - the recovery factor to be achieved in future years for all oil fields in the oil region;

[0067] N RT ——The operating geological reserves of all oil fields in the oil region as of the end of the year for which statistical data are available;

[0068] M——the total number of wells put into production in the oil region in the closing year of the statistical data of all oil fields;

[0069] K j ——Plan the number of newly added wells to be put into production each year for all the oil fields that have been put into production in the oil region in the future years,

[0070] j——number of years in the future planning period, 1, 2, 3, etc.;

[0071] ΔR j ——The newly added recoverable reserves in the jth planning period in the future;

[0072] N e ——Recoverable reserves of all oil fields in the oil region as of the end of the year for which statistical data are available;

[0073] There is no unique method for selecting old oil fields with a long production period. It is necessary to ensure that the oil fields have been in production for a long time, usually more than 8 years, and to ensure that the sample data is sufficient.

[0074] The present invention is further described in detail below through embodiments and drawings.

[0075] A method for predicting the production potential of a water-driven oil field according to the present invention comprises the following steps:

[0076] 1. Select old oil fields in oil region A that were put into production before 2010. Based on historical production data, water drive characteristic curve-assisted automatic prediction technology is used to batch predict the recoverable reserves of single-well water drive for all production wells in the old oil fields.

[0077] 2. For the old oil fields selected in oil region A in step 1, their geological reserves are N as of the end year of data statistics. R The total number of wells put into production each year, the cumulative number of wells put into production, and the annual well-controlled reserves R can be calculated. no , the average recoverable reserves of wells put into production each year As shown in Table 1. However, due to the small number of wells in the early stage of oil field development, the regularity was poor, and the production regularity of newly put into production wells in the past two years has not been stable, so the data points before 2007 and the past two years are discarded, and the statistical data only takes the data from 2007 to 2017. In 2017, the total number of wells put into production was 572.

[0078] Table 1 shows the overall overview of the producing wells in the old oil fields in Oil Region A that were put into production before 2010.

[0079]

[0080] 3. Select sample data from 2007 to 2017, with well-controlled reserves as the horizontal axis and average recoverable reserves of a single well as the vertical axis, and draw a relationship diagram between the average recoverable reserves of a single well and well-controlled reserves of old oil fields put into production before 2010 in Oil Region A, as shown in the figure below: Figure 1 As shown in the figure, the relationship between the average recoverable reserves of a single well and the change in well-controlled reserves of wells put into production year by year is obtained by exponential function fitting:

[0081]

[0082] Where:

[0083] ——The average recoverable reserves of wells put into production each year, ten thousand cubic meters;

[0084] R no ——is the annual well-controlled reserves, ten thousand cubic meters.

[0085] In this way, the relationship between the newly added recoverable reserves of a single well in the old oil field in Oil Region A and the change of well-controlled reserves is obtained.

[0086] 4. Screen all the oil fields in production in Oil Region A and calculate the total number of production wells M as of 2019, which is 720, and the geological reserves N RT 820 million cubic meters, recoverable reserves N e It is 360 million cubic meters. The current predicted recovery rate is 43.8% and the well-controlled reserves are 1.14 million cubic meters.

[0087] 5. According to the plan of adding new production wells K1 to K5 for all the oil fields in the oil region from 2020 to 2025, they are 23, 19, 21, 23, 25 and 27 respectively. Under the condition that the utilization rate of developed oil fields does not change, the well-controlled reserves in 2020 are calculated to be reduced to Average recoverable reserves per well New recoverable reserves Recoverable reserves are ΔR1+N e = 365.7 million cubic meters, the final predicted recovery rate The predicted recovery factors for the remaining years can be calculated in the same way, as shown in Table 2. As shown in Table 2, by 2025, the cumulative number of newly put into production wells will be 138, and the recovery factor will reach 46.9%, an increase of 3.1%.

[0088] Table 2 is the recovery factor forecast table for the A oilfield during the planning period of 2020-2025

[0089]

[0090] 6. In order to achieve the regional target recovery rate of 48%, without changing the reserve utilization level, the calculated well-controlled reserves need to be reduced to 890,000 cubic meters, and the calculated additional single-well recoverable reserves are reduced to 140,000 cubic meters. The total number of wells reaches 920, so it can be known that the area needs to add 200 new wells to be put into production.

[0091] It can be seen from this that the method for predicting the mining potential of water-driven oilfields can ignore the differences in reservoir types and predict the mining potential of the entire oilfield group or a certain oilfield. Conventional recovery rate prediction formulas, such as the empirical formula for the recovery rate of water-driven sandstone reservoirs of PetroChina, require physical parameters such as permeability, interlayer thickness, permeability variation coefficient, porosity, etc., which are difficult to obtain for new oilfields. This invention effectively avoids this problem. In addition, first, the method of the invention can intuitively predict the recovery rate of the area based on the new production wells drilled in the area each year, and can also well predict the future development and production rules of new oilfields; second, the method of the invention can present an intuitive change trend of the recoverable reserves and well-controlled reserves of the newly added production wells, which cannot be presented by the conventional empirical formula method; third, it is also easy for us to plan the number of new wells put into production year by year according to the planned target recovery rate, which is crucial to the entire oilfield operating company. These advantages are not available in conventional mining potential prediction methods.

[0092] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for predicting the production potential of a water-flooded oil field, characterized in that: Through the relationship between the recoverable reserves of single wells put into production year by year and the well-controlled reserves in the old oil fields that have been put into production, the recoverable reserves of all oil fields under different well-controlled reserves conditions in the future are predicted; The following steps are involved: 1) Based on the old oil fields in the oil region with a long production period, the geological reserves are N as of the end of the statistical year. R The total number of wells put into production is M, and the total number of wells put into production in the nth year in history is N n , the annual well-controlled reserves can be calculated as R no ; 2) For all the wells in the old oil field in step 1, based on their historical production data, the predicted value of water-driven recoverable reserves of the i-th well put into production in the nth year is recorded as Then the average recoverable reserves of a single well in the production well in the nth year are calculated. 3) Based on the average water-driven recoverable reserves of each well in each year The relationship between the recoverable reserves of a single well and the well-controlled reserves in the oil region is plotted, and the functional relationship expression between the average recoverable reserves of a single well and the well-controlled reserves of the wells put into production year by year is obtained by fitting: 4) For all producing oil fields in the oil region, based on the total number of wells put into production, geological reserves in use, and recoverable reserves by the end year, the relationship between the recoverable reserves of a single well and the well-controlled reserves in the above formula is combined to calculate the incremental recoverable reserves of water drive under different well-controlled reserve conditions: Then the corresponding recovery factors of all oil fields in the oil region under different well-controlled reserve conditions in the future can be calculated as follows: Where: a, b——both are constants; E - the recovery factor predicted for all oil fields in the oil region in future years; N RT ——The operating geological reserves of all oil fields in the oil region as of the end of the year for which statistical data are available; M——the total number of wells put into production in the oil field statistical data ending year; K j ——Plan the number of newly added wells to be put into production each year for all the oil fields that have been put into production in the oil region in the future years, j——number of years in the future planning period, 1, 2, 3, etc.; ΔR j ——The newly added recoverable reserves in the jth planning period in the future; N e ——Recoverable reserves of all oil fields in the oil region as of the end of the year for which statistical data are available; In step 2), water drive characteristic curve-assisted automatic prediction technology is used to perform batch prediction of production wells, and the steps are as follows: 21) For wells that have been shut down, side-drilled or transferred to injection, only the cumulative production is calculated as the recoverable reserves of single-well water drive; 22) Wells that are in production and have produced for less than T months are not predicted; 23) For wells that are in production and have produced for more than T months, if the current water cut is less than 30%, the decline method is used for prediction; if the current water cut is greater than 30%, the water drive characteristic curve is used for prediction; 24) The predicted value of recoverable reserves of water drive of the i-th well is recorded as Where n is the year the production well was put into production; In the step 3), for the selection of the fitting segment during prediction: if the production time is longer than 10T months, the fitting segment selects the last 2T months; if the production time is between 5T months and 10T months, the fitting segment selects 0.2 times the production time; if the production time is less than 5T months, the fitting segment selects the last T months; wherein T is an integer, which is determined according to the actual production data; In step 3), the steps for obtaining the relationship expression between the newly added recoverable reserves of a single well in the old oil field and the change of the well-controlled reserves are as follows: 31) All the wells put into production in this type of oil field are classified according to the year of production, and the average recoverable reserves of each well put into production each year are calculated as follows: in, is the recoverable reserves of the single well water flooding of the i-th well put into production in year n, N n is the total number of wells put into production in year n, is the average recoverable reserves of a single well in the nth year; 32) Obtain the geological reserves N of these old oil fields in the year when the statistical data is cut off. R , and then get the annual well-controlled reserves data R no : 33) Data points are selected according to the year, and the relationship between the newly added single-well recoverable reserves and well-controlled reserves of this type of oil field is plotted. The functional relationship expression of the single-well recoverable reserves of the wells put into production year by year and the change of well-controlled reserves is obtained by fitting: Among them, a and b are constants.

2. The method for predicting the production potential of an oil field by water flooding development according to claim 1, characterized in that: The old oil field has been in production for more than 8 years.

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