Engineering calculation prediction method for wellhead pressure of carbon dioxide injection well

Abstract

The invention discloses an engineering calculation prediction method for wellhead pressure of a carbon dioxide injection well. The engineering calculation prediction method comprises the steps that carbon dioxide injection displacement parameters, the vertical depth of the injection well, the size of an injection tubular column, the bottom hole temperature, the bottom hole pressure and the wellhead temperature are obtained; based on the bottom hole temperature and the bottom hole pressure, the bottom hole carbon dioxide density is obtained through calculation or query; according to the carbon dioxide injection displacement parameter, the vertical depth of the injection well, the size of the injection tubular column and the carbon dioxide density in the shaft, the friction resistance of the injection well tubular column is obtained through calculation or query; taking the vertical depth of the injection well, the bottom hole pressure, the friction resistance of the pipe string of the injection well and the carbon dioxide density in the shaft as input items, and taking the wellhead pressure as an output item to carry out iterative calculation; and when the wellhead pressure obtained by the first calculation is equal to the wellhead pressure obtained by the ith calculation, stopping the iterative calculation. The method can realize engineering calculation solution of rapid prediction of the wellhead pressure of the carbon dioxide injection well.

Description

Technical Field

[0001] The present invention relates to the field of engineering technology such as carbon dioxide oil / gas recovery, fracturing and storage, and in particular to an engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well. Background Art

[0002] Against the backdrop of increasing efforts in domestic oil and gas exploration and development and achieving the "dual carbon" goals, carbon dioxide injection to achieve oil / gas recovery, fracturing and other production increases and storage in unconventional oil and gas reservoirs is an effective "win-win" way to achieve efficient energy extraction and carbon storage. It has extremely high economic and social benefits and is also a hot topic in current domestic and foreign technical research and field trials.

[0003] Due to the physical properties of carbon dioxide itself, the phase state of the wellbore flow changes during its injection process, and the prediction of wellbore temperature and pressure is difficult. Most of the existing research is to establish a complex carbon dioxide wellbore flow temperature and pressure coupling model. After numerical simulation calculation, the wellbore temperature and pressure profile can be predicted. The settlement result is mainly an analytical value, which focuses on the derivation and coupling solution of theoretical formulas, but it needs to simplify many working conditions, and the calculation process is cumbersome, requiring a large amount of time and computing power. It is suitable for indoor theoretical and technical research, but it is not suitable for field engineering scheme design and rapid prediction. In the theoretical research process, the analytical solution of the wellhead pressure of carbon dioxide injection is cumbersome and time-consuming, which is in contradiction with the actual demand that the field working conditions are changeable and the calculation is convenient and fast but the accuracy requirement is not high. The design and field implementation of carbon dioxide injection engineering often pay more attention to the rapid prediction of wellhead pressure. Based on this, the present invention provides an engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide an engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well, which can realize the engineering calculation solution of the rapid prediction of the wellhead pressure of the carbon dioxide injection well and provide data support for the injection parameter design.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] An engineering calculation prediction method for wellhead pressure of a carbon dioxide injection well, characterized by comprising:

[0007] Obtain CO2 injection displacement parameters, vertical depth of the injection well, injection string size, bottom hole temperature, bottom hole pressure and wellhead temperature;

[0008] Based on the bottom hole temperature and bottom hole pressure, the bottom hole carbon dioxide density ρ is obtained by calculation or query 井底;According to the carbon dioxide injection displacement parameters, the vertical depth of the injection well, the injection string size and the carbon dioxide density in the wellbore, the injection well string friction resistance is obtained by calculation or query;

[0009] The vertical depth of the injection well, bottom hole pressure, pipe friction and carbon dioxide density in the wellbore are used as input items, and the wellhead pressure of the injection well is used as output item for iterative calculation. i≥2 and i is an integer to obtain the carbon dioxide density ρ in the wellbore at the i-th calculation, is the wellhead carbon dioxide density calculated for the i-1th time, which is based on the wellhead temperature and the wellhead pressure calculated for the i-1th time. Calculate or query to obtain;

[0010] When the wellhead pressure calculated for the i+1th time is equal to the wellhead pressure calculated for the ith time, the iterative calculation is stopped, and the wellhead pressure calculated for the i+1th time is the predicted value of the wellhead pressure of the carbon dioxide injection well.

[0011] Furthermore, based on the calculation formula Perform iterative calculation, where P 井口 is the wellhead pressure, P 井底 is the bottom hole pressure, f is the friction resistance of the injection well string, g is the gravity coefficient, h is the vertical depth of the injection well, and ρ is the density of carbon dioxide in the wellbore.

[0012] The present invention has the following unexpected beneficial effects: the present invention continuously iterates and calculates the wellhead pressure of the carbon dioxide injection well based on the acquired parameters, namely, the vertical depth of the injection well, the bottom hole pressure, the pipe friction and the carbon dioxide density in the wellbore. The method has a simple and fast solution process, and is suitable for the reasonable optimization of injection parameter design, injection pump selection, reasonable injection equipment selection and initial evaluation of injection wellhead pressure level in different injection stages during the engineering scheme design stage. At the same time, during the injection process, the injection parameters can be quickly and real-time adjusted according to the real-time working conditions on site. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic flow chart showing the engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well according to the present invention;

[0014] Figure 2 The pipe string friction curves at different carbon dioxide injection rates and different pipe string sizes of injection wells are shown. DETAILED DESCRIPTION

[0015] The following will describe the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0016] In one embodiment, see Figure 1 As shown, the present invention provides an engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well, comprising:

[0017] An engineering calculation prediction method for wellhead pressure of a carbon dioxide injection well, comprising:

[0018] Obtain CO2 injection displacement parameters, vertical depth of the injection well, injection string size, bottom hole temperature, bottom hole pressure and wellhead temperature;

[0019] Based on the bottom hole temperature and bottom hole pressure, the bottom hole carbon dioxide density ρ is obtained by calculation or query 井底 ;According to the carbon dioxide injection displacement parameters, the vertical depth of the injection well, the injection string size and the carbon dioxide density in the wellbore, the injection well string friction resistance is obtained by calculation or query;

[0020] The vertical depth of the injection well, bottom hole pressure, pipe friction and carbon dioxide density in the wellbore are used as input items, and the wellhead pressure of the injection well is used as output item for iterative calculation. i≥2 and i is an integer to obtain the carbon dioxide density ρ in the wellbore at the i-th calculation, is the wellhead carbon dioxide density calculated for the i-1th time, which is based on the wellhead temperature and the wellhead pressure calculated for the i-1th time. Calculate or query to obtain;

[0021] When the wellhead pressure calculated for the i+1th time is equal to the wellhead pressure calculated for the ith time, the iterative calculation is stopped, and the wellhead pressure calculated for the i+1th time is the predicted value of the wellhead pressure of the carbon dioxide injection well.

[0022] The present invention continuously iterates and calculates the wellhead pressure of the carbon dioxide injection well based on the acquired parameters, namely, the vertical depth of the injection well, the bottom hole pressure, the pipe friction and the carbon dioxide density in the wellbore. The method has a simple and fast solution process and is suitable for the reasonable optimization of injection parameter design, injection pump selection, reasonable injection equipment selection and initial evaluation of injection wellhead pressure level in different injection stages during the engineering scheme design stage. At the same time, during the injection process, the injection parameters can be quickly and real-time adjusted according to the real-time working conditions on site.

[0023] The present invention collects injection well parameters and carbon dioxide injection construction data, obtains carbon dioxide injection pipe string friction and carbon dioxide density under known conditions such as bottom hole temperature, pressure and wellhead temperature of the carbon dioxide injection well, takes the average value of carbon dioxide density at the wellhead and bottom hole as the calculation input value, and continuously iterates the calculation through the carbon dioxide injection wellhead pressure calculation formula until the wellhead pressure calculation iteration value no longer changes, and finally obtains the carbon dioxide injection wellhead pressure prediction engineering calculation value. The calculation method of the present invention is simple and convenient, does not need to establish a complex carbon dioxide wellbore flow model, saves a lot of time and computing power, can quickly predict the wellhead pressure of the carbon dioxide injection well, is suitable for the wellhead safety evaluation in the early stage of carbon dioxide injection well selection, the optimization design of carbon dioxide injection engineering program parameters, and the adjustment of injection parameters during the field implementation process, etc., and solves the contradiction between the complicated and time-consuming analytical solution process of the complex model of wellbore temperature and pressure of the carbon dioxide injection well and the actual demand of changeable field conditions and convenient and fast calculation but low precision requirements. The present invention can be widely used in engineering calculations for rapid prediction of carbon dioxide injection wellhead pressure in various reservoirs.

[0024] In a preferred embodiment, based on the calculation formula Perform iterative calculation, where P 井口 is the wellhead pressure, P 井底 is the bottom hole pressure, f is the friction resistance of the injection well string, g is the gravity coefficient, h is the vertical depth of the injection well, and ρ is the density of carbon dioxide in the wellbore.

[0025] The following is an analysis and explanation with specific examples.

[0026] Example 1: In order to achieve carbon dioxide flooding and storage, carbon dioxide is injected into a gas production well Y1. The injection depth of the well is 2727m. It is required that the reservoir does not rupture and fracture during the carbon dioxide injection process. The liquid carbon dioxide injection displacement is designed to be 10-100t / d. The maximum wellhead injection pressure is predicted. This value is the upper limit of the wellhead pressure when the reservoir does not rupture during the carbon dioxide injection process. When the injection wellhead pressure reaches the upper limit, the injection needs to be stopped and the construction parameters are adjusted. In the design of the injection scheme, the selection of the injection pump also refers to this value, that is, the maximum rated injection pressure of the injection pump is not lower than this value to meet the on-site injection requirements.

[0027] The maximum wellhead pressure calculation formula for carbon dioxide injection into the injection well is:

[0028] Where P 井口 The maximum wellhead pressure of the injection well into which carbon dioxide is injected, in MPa;

[0029] P 井底 is the carbon dioxide fracture pressure at the bottom of the injection well, in MPa;

[0030] f is the friction resistance of the injection well string, in MPa;

[0031] g is the gravity coefficient, which is 9.8N / kg;

[0032] h is the vertical depth of the injection well, in m;

[0033] ρ is the carbon dioxide density in the wellbore, in kg / m 3 .

[0034] It is known that the injection layer of the well is the mountain 2 layer. The well has been hydraulically fractured before. According to the fracturing construction data, the fracture pressure is 49MPa. It is known that the fracturing string is 2713m deep and the displacement is 3.3m 3 / min, guar gum concentration is 0.5%, the inner diameter of the injection well string is 62mm, and the friction resistance of the fracturing construction string is calculated to be 25.68MPa. The liquid column pressure is 27.12MPa, so the bottom hole fracture pressure converted to 50.44MPa. Considering that the carbon dioxide fracture pressure is lower than the hydraulic fracturing, the carbon dioxide bottom hole fracture pressure of the injection well is 85% of the hydraulic fracturing bottom hole fracture pressure of 50.44MPa, that is, 42.87MPa as the carbon dioxide injection bottom hole fracture pressure, and this value is used as the maximum bottom hole carbon dioxide injection pressure. The calculation depth is the middle depth of the perforation section of the mountain 2 layer, that is, 2727m. The formation temperature is based on the pressure recovery data, and the temperature of the middle of the perforation section of the mountain 2 layer is 89.7℃.

[0035] The designed carbon dioxide injection volume is 10-100t / d, i.e. the displacement is 0.0069-0.069m 3 / min, the carbon dioxide injection column is 2 7 / 8” Youtube and 3 1 / 2” There are two sizes, namely the inner diameter of the column is 62mm and 76mm respectively.

[0036] Knowing the temperature and pressure, the density of carbon dioxide can be obtained by querying the NIST database, and the physical properties of carbon dioxide in the NIST database can be called by the program. NIST (National Institute of Standards and Technology) is the National Institute of Standards and Technology of the United States, which provides a large amount of physical and chemical data and software tools, including the physical properties of carbon dioxide. In NIST, the physical properties of carbon dioxide are obtained through a combination of experimental data, theoretical calculations, and literature, with high accuracy and reliability, while saving computing time and cost.

[0037] The flow friction of the CO2 injection string is related to the physical parameters of CO2 such as density and viscosity, and is related to the CO2 injection string size and CO2 injection rate. Combined with the NIST database, the string friction under different CO2 injection rates and different string sizes is calculated. The specific process is as follows:

[0038] Through indoor carbon dioxide pipe flow experiments, the viscosity under different temperature and pressure conditions can be obtained, thereby forming an empirical formula for carbon dioxide viscosity for on-site engineering calculations. The calculation formula is:

[0039]

[0040] Where η is the viscosity of carbon dioxide, T cr , P cr are the critical temperature and pressure of carbon dioxide, which are 31.26℃ and 72.9atm respectively. T and P are the temperature and pressure of carbon dioxide respectively. Therefore, when the temperature and pressure of carbon dioxide are known, the corresponding viscosity of carbon dioxide can be calculated by the above formula.

[0041] Through indoor carbon dioxide pipe flow experiments, based on carbon dioxide viscosity, we can obtain the empirical formula of carbon dioxide friction under different working conditions for on-site engineering calculations. The calculation formula is:

[0042] ΔP=0.15808η 0.2501 ρ 0.7499 u 1.75 d -1.25

[0043] Among them, ΔP is the friction pressure drop of the carbon dioxide column flow / 1000m, η is the viscosity of carbon dioxide, ρ is the density of carbon dioxide, u is the carbon dioxide displacement, and d is the inner diameter of the carbon dioxide injection column. Therefore, the corresponding carbon dioxide column flow friction pressure drop can be calculated by the above formula.

[0044] When the temperature and pressure of carbon dioxide are known, the density of carbon dioxide can be obtained by querying the NIST database, and the viscosity of carbon dioxide can be obtained by substituting it into the empirical formula for viscosity. When the carbon dioxide injection displacement and pipe diameter are known, the friction resistance of different pipes under different displacement conditions can be calculated by substituting it into the empirical formula for friction resistance and pressure drop.

[0045] Assuming the wellhead injection temperature is 5°C and the wellhead injection pressure is 20 MPa, according to the NIST database, the density of carbon dioxide is 1001 kg / m 3 The carbon dioxide injection displacement is 0.0069~0.069m 3 / min, the inner diameters of the CO2 injection string are 62mm and 76mm respectively. Substituting them into the above two empirical formulas, we can obtain the string friction resistance (pressure drop / 1000m) chart under different CO2 injection rates and different string sizes, as shown in Figure 2 It can be found that the friction resistance is relatively small. Therefore, under the conditions of the carbon dioxide injection project in this embodiment, the friction resistance of the pipe string can be 1 MPa.

[0046] The injection depth is 2727m, the bottom hole temperature is 89.7℃ in the middle of layer 2, and when the bottom hole pressure is 42.87MPa, the bottom hole carbon dioxide density ρ 井底 =809.15kg / m 3 ; Assuming that the density of carbon dioxide at the wellhead is equal to that at the bottom of the well, then Substitute into the wellhead pressure calculation formula.

[0047] Right now

[0048] The wellhead temperature is 5°C, then T 井口 =5℃, but

[0049] Find the average of the wellhead density and the bottom hole density: Substitute into the wellhead pressure calculation formula;

[0050] but

[0051] That is T 井口 =5℃, but Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula;

[0052] but

[0053] That is T 井口 =5℃, but

[0054] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula;

[0055] That is T 井口 =5℃, but

[0056] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula;

[0057] That is T 井口 =5℃, but

[0058] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula;

[0059] at this time, Then the iterative calculation is stopped, and the predicted value of the maximum wellhead pressure is 19.704MPa. That is, when the wellhead injection pressure reaches 19.704MPa, the injection should be stopped. In addition, the rated pressure of the wellhead injection pump should not be less than 19.704MPa. Considering that the pump margin design is 15%, the rated pressure of the injection pump should not be less than 22.66MPa.

[0060] In Example 2, the carbon dioxide injection well is still the well in Example 1. Since the carbon dioxide injection is to be carried out for a long time, it is necessary to pay attention to the corresponding wellhead pressure when the bottom hole pressure reaches different values ​​during the injection process. According to the numerical simulation of the gas reservoir, when the pressure value reaches 30MPa, the injection parameters need to be adjusted and the injection rate needs to be changed. Therefore, it is necessary to predict the corresponding wellhead pressure value, that is, when the wellhead pressure reaches the predicted value, the injection parameters are adjusted.

[0061] The basic data are as shown in Example 1. The friction resistance of the carbon dioxide pipe flow is still 1MPa, the wellhead temperature is 5°C, the injection depth is 2727m, the bottom hole temperature is 89.7°C in the middle of the second layer, and when the bottom hole pressure is 30MPa, the bottom hole carbon dioxide density ρ 井底 =712.12kg / m 3 Assuming that the CO2 density at the wellhead is equal to that at the bottom of the well, the CO2 density in the wellbore is 712.12 kg / m 3 , substituted into the wellhead pressure calculation formula,

[0062] but

[0063] That is T 井口 =5℃, but

[0064] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula,

[0065] but

[0066] That is T 井口 =5℃, but

[0067] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula,

[0068] but

[0069] That is T 井口 =5℃, but

[0070] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula, then

[0071] That is T 井口 =5℃, but

[0072] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula,

[0073] but

[0074] That is T 井口 =5℃, but

[0075] Find the average of the wellhead density and the bottom hole density Substitute into the wellhead pressure calculation formula, then

[0076] at this time, When the bottom hole pressure is 30MPa, the predicted value of the wellhead pressure is 8.914MPa. Therefore, when the wellhead pressure reaches 8.914MPa during the injection process, the injection parameters are adjusted.

[0077] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or change made by a person skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. An engineering calculation and prediction method for the wellhead pressure of a carbon dioxide injection well, characterized in that: include: Obtain CO2 injection displacement parameters, vertical depth of the injection well, injection string size, bottom hole temperature, bottom hole pressure and wellhead temperature; Based on the bottom hole temperature and bottom hole pressure, the bottom hole carbon dioxide density ρ is obtained by calculation or query 井底 ;According to the carbon dioxide injection displacement parameters, the vertical depth of the injection well, the injection string size and the carbon dioxide density in the wellbore, the injection well string friction resistance is obtained by calculation or query; The vertical depth of the injection well, the bottom hole pressure, the friction resistance of the injection well pipe and the carbon dioxide density in the wellbore are used as input items, and the wellhead pressure of the injection well is used as the output item for iterative calculation. The carbon dioxide density ρ in the wellbore at the i-th calculation is obtained, is the wellhead carbon dioxide density calculated for the i-1th time, which is based on the wellhead temperature and the wellhead pressure calculated for the i-1th time. Calculate or query to obtain; When the wellhead pressure calculated for the i+1th time is equal to the wellhead pressure calculated for the ith time, the iterative calculation is stopped, and the wellhead pressure calculated for the i+1th time is the predicted value of the wellhead pressure of the carbon dioxide injection well.

2. The engineering calculation prediction method for the wellhead pressure of a carbon dioxide injection well according to claim 1, characterized in that: Based on calculation Perform iterative calculation, where P 井口 is the wellhead pressure, P 井底 is the bottom hole pressure, f is the friction resistance of the injection well string, g is the gravity coefficient, h is the vertical depth of the injection well, and ρ is the density of carbon dioxide in the wellbore.

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