A method and device for determining bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir

Abstract

The present invention relates to a method and device for determining the bottom hole flow pressure of a gas well in a tight sandstone gas reservoir, and belongs to the technical field of gas field development. Based on the distribution of pressure in the casing annulus during vertical well production, the present invention constructs a pressure relationship equation between two adjacent points in the casing annulus, and uses historical wellbore pressure test data to determine the relationship between the pressure gradient and the pressure; the wellhead casing pressure is used as the initial pressure, and according to the relationship between the pressure gradient and the pressure, iterative calculations are performed according to the pressure relationship equation until the pressure at the bottom hole position is calculated, and the pressure at the bottom hole is the bottom hole flow pressure. The present invention does not require too many parameters in the entire determination process, only the casing pressure at the wellhead and the historical wellbore pressure test data are required; at the same time, no complex calculations are required, only simple iterative calculations are required. The present invention can quickly and accurately calculate the bottom hole flow pressure of a vertical well in a tight gas reservoir, thereby improving the practicality and reliability of the calculation.

Description

Technical Field

[0001] The invention relates to a method and a device for determining the bottom flow pressure of a gas well in a tight sandstone gas reservoir, belonging to the technical field of gas field development. Background Art

[0002] In the production process of gas wells, the correct calculation of the bottom hole flowing pressure of gas wells is an important link in the development process of tight sandstone gas reservoirs and a prerequisite for stable and high production of gas wells. How to accurately calculate the bottom hole flowing pressure of gas wells based on production data is the basis for dynamic analysis, prediction and optimization of reasonable working systems of gas well production. At present, there are many methods for calculating the bottom hole flowing pressure of tight sandstone gas reservoirs in the journals published at home and abroad, such as the empirical formula method, the wellhead pressure calculation method (Cullender-smith, AZIZ, etc.), and the production instability analysis method. Some of these methods require shut-in measures for gas wells, which affects gas well production, and some have not been promoted because of the complex calculation process and too many parameters to be processed.

[0003] For example, the patent application document with application publication number CN108612525A discloses a method for calculating the dynamic reserves of gas reservoirs, and specifically gives a method for calculating the bottom hole flow pressure of gas wells using seepage theory, vertical pipe flow model, gas well production capacity equation and material balance equation. However, this method involves seepage mechanics, the calculation process is cumbersome, and it is difficult to apply in the field.

[0004] The patent document with authorization announcement number CN207245706U discloses a coalbed methane well bottom hole flow pressure test system, and specifically discloses the use of a temperature and humidity sensor to measure the humidity at the wellhead of the coalbed methane well annulus, and calculate the bottom hole flow pressure of the coalbed methane well based on the humidity. Although this method is simple and suitable for field application, it is only applicable to coalbed methane wells and cannot be used in tight sandstone gas reservoirs.

[0005] Therefore, the current methods for calculating the bottom hole flowing pressure of gas wells either require many parameters and are complex to calculate, or are only applicable to specific types of gas wells and cannot be applied to gas wells in tight sandstone gas reservoirs. Summary of the invention

[0006] The purpose of the present invention is to provide a method and device for determining the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir, so as to solve the problem of multiple required parameters and high complexity in the current bottom hole flowing pressure calculation process.

[0007] In order to solve the above technical problems, the present invention provides a method for determining the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir, and the determination method comprises the following steps:

[0008] 1) According to the distribution of pressure in the casing annulus during vertical well production, a pressure relationship equation between two adjacent points in the casing annulus is constructed. The pressure relationship equation reflects the relationship between the pressure at the current point and the pressure at the next point, the pressure gradient at the current point, and the depth difference between the current point and the next point;

[0009] 2) Determine the relationship between pressure gradient and pressure using historical wellbore pressure test data;

[0010] 3) Taking the casing pressure at the wellhead as the initial pressure, according to the relationship between the pressure gradient and the pressure, iterative calculation is performed according to the pressure relationship equation until the pressure at the bottom of the well is calculated, and the pressure at the bottom of the well is the bottom hole flowing pressure.

[0011] The present invention also provides a device for determining the bottom hole flow pressure of a gas well in a tight sandstone gas reservoir, the device comprising a processor and a memory, the processor executing a computer program stored in the memory to implement the method for determining the bottom hole flow pressure of a gas well in a tight sandstone gas reservoir as described above.

[0012] The present invention is based on the distribution of pressure in the casing annulus during vertical well production, constructs a pressure relationship equation between two adjacent points in the casing annulus, and uses historical wellbore pressure test data to determine the relationship between pressure gradient and pressure; the wellhead casing pressure is used as the initial pressure, and according to the relationship between pressure gradient and pressure, iterative calculations are performed according to the pressure relationship equation until the pressure at the bottom of the well is calculated, and the pressure at the bottom of the well is the bottom hole flow pressure. The present invention does not require too many parameters in the entire determination process, only the casing pressure at the wellhead and the historical wellbore pressure test data are required; at the same time, no complex calculations are required, only simple iterative calculations are required. The present invention can quickly and accurately calculate the bottom hole flow pressure of a vertical well in a tight gas reservoir, thereby improving the practicality and reliability of the calculation.

[0013] Furthermore, the present invention also provides a specific relationship equation, and the pressure relationship equation constructed in step 1) is:

[0014] P i+1 =P i +M i Δh i

[0015] Where P i is the pressure at the i-th point in the wellbore, P i+1 is the pressure at the i+1th point in the wellbore, M i is the pressure gradient at the i-th point in the wellbore, Δh i is the depth difference between the i+1th point and the ith point in the wellbore.

[0016] Furthermore, in order to quickly and accurately determine the relationship between the pressure gradient and the pressure, the relationship between the pressure gradient and the pressure in step 2) is obtained by linear fitting. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of pressure distribution in the casing annulus in the embodiment of the method of the present invention;

[0018] Figure 2 is a graph showing the relationship between pressure gradient and pressure in the tests performed over the years in the embodiments of the method of the present invention;

[0019] Figure 3 is a diagram of the tubular structure of the DX well during the verification process of the present invention;

[0020] Figure 4 It is a comparison diagram of the bottom hole flow pressure calculated by the present invention and the measured bottom hole flow pressure during the verification process of the present invention;

[0021] Figure 5 It is a flow chart of a method for determining bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir according to the present invention;

[0022] Figure 6 It is a structural schematic diagram of a device for determining bottom hole flow pressure of a gas well in a tight sandstone gas reservoir according to the present invention. DETAILED DESCRIPTION

[0023] Method Embodiment

[0024] Accurate calculation of the bottom hole flowing pressure of a gas well is the basis for dynamic analysis, prediction and optimization of a reasonable working system of gas well production. Aiming at the problems of complex calculation and too many parameters required in the current calculation process of the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir, the present invention proposes a method for determining the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir. The method determines the fitting relationship between the pressure gradient and the pressure based on historical pressure test data; establishes the relationship between the pressure of any point in the casing annulus and the pressure of the next point in the vertical well production process; takes the casing pressure at the wellhead as the pressure of the initial point, and uses the above fitting relationship to determine the bottom hole flowing pressure in an iterative manner. The process is as follows Figure 5 As shown, the specific implementation process of this method is as follows.

[0025] 1. Based on historical pressure test data, determine the fitting relationship between pressure gradient and pressure.

[0026] This embodiment takes the Daniudi gas field as an example, obtains the pressure test data of the gas field over the years, sorts out the pressure test data, and draws a scatter plot of the pressure gradient and test pressure obtained in the tests over the years in an EXCEl table. During the test, the pressure gradient M is recorded as a value every 100m, such as Figure 2For this embodiment, the pressure gradient and the pressure present a positive linear relationship, and the correlation coefficient is 0.93022, the correlation coefficient is high, and the fitting degree is very high.

[0027] The relationship between the pressure gradient and the pressure fitted in this embodiment is as follows:

[0028] M=0.00697*P+0.00174 (1)

[0029] Where M is the pressure gradient and P is the pressure.

[0030] 2. Construct the casing annulus pressure equation.

[0031] During the production process of a vertical well, a casing is installed, and a tubing is installed inside the casing. An annular space (referred to as the casing annulus) is formed between the casing and the tubing. The gas in the casing annulus is static, and the pressure distribution in the casing annulus is as follows: Figure 1 As shown, from top to bottom, P c , P1, P2...P n When using casing pressure to calculate bottom hole flowing pressure, the relationship between the pressure at any point in the casing annulus and the pressure at the next point is:

[0032] P i+1 =P i +M i Δh i (2)

[0033] Where P i is the pressure at the i-th point in the wellbore, P i+1 is the pressure at the i+1th point in the wellbore, M i is the pressure gradient at the i-th point in the wellbore, Δh i is the depth difference between the i+1th point and the ith point in the wellbore. When i=0, P0 represents the pressure at the wellhead, P0=P c , P c Indicates the casing pressure at the wellhead of the gas well. When i=n, ​​P n Indicates the pressure at the bottom of the well, P n =P wf , P wf Indicates the casing pressure at the wellhead of the gas well. Δh i Can be set as needed, Δh i The smaller it is, the higher the calculation accuracy is.

[0034] 3. Starting from the wellhead, perform iterative solution to determine the bottom hole flowing pressure.

[0035] The casing pressure at the wellhead can be directly measured, and the casing pressure at the wellhead is taken as the pressure P0 at the wellhead. The pressure gradient M0 at this point can be calculated using formula (1). P0 and M0 are substituted into formula (2) for iterative calculation to calculate the pressure P1 at the next point. Similarly, the pressure at any point can be iteratively calculated. For this embodiment, the pressure P at the middle depth of the gas layer at depth H is n The pressure P can be calculated according to the above iterative method. n It is the required bottom hole flowing pressure.

[0036] The effect of the present invention is verified by taking the DX well in the Daniu gas field as an example. The pipe string structure of the DX well in this example is as follows: Figure 3 As shown, the depth of the middle layer is 2663m. It was put into production in March 2012. The production has been stable since then. A total of 8 bottom hole pressure tests have been carried out since it was put into production.

[0037] According to the calculation method of the present invention, iterative calculation is performed on the DX well, and the calculated values ​​are compared with the measured values. The results are shown in Table 1.

[0038] Table 1

[0039]

[0040] The comparison results of the two are Figure 4 To show, from Table 1 and Figure 4 It can be seen that the relative errors of the calculation results of the present invention compared with the measured values ​​are within 10%, indicating that the accuracy of the bottom hole flowing pressure obtained by the present invention using the wellhead casing pressure through the pressure gradient iteration method is guaranteed.

[0041] Device Embodiment

[0042] The device proposed in this embodiment, such as Figure 6 As shown, it includes a processor and a memory, and a computer program that can be run on the processor is stored in the memory. The processor implements the method of the above method embodiment when executing the computer program. That is to say, the method in the above method embodiment should be understood as a flow chart of a method for determining the bottom hole flow pressure of a gas well in a tight sandstone gas reservoir that can be implemented by computer program instructions. These computer program instructions can be provided to the processor so that the processor executes these instructions to generate functions specified by the above method flow chart, and VBA can be used to compile the corresponding program.

[0043] The processor referred to in this embodiment refers to a processing device such as a microprocessor MCU or a programmable logic device FPGA; the memory referred to in this embodiment includes a physical device for storing information, which usually digitizes the information and then stores it in a medium using electrical, magnetic or optical methods. For example: various memories that use electrical energy to store information, such as RAM, ROM, etc.; various memories that use magnetic energy to store information, such as hard disks, floppy disks, magnetic tapes, magnetic core memories, magnetic bubble memories, and U disks; various memories that use optical methods to store information, such as CDs or DVDs. Of course, there are other types of memories, such as quantum memories, graphene memories, and so on.

[0044] The device is composed of the above-mentioned memory, processor and computer program, and is implemented by the processor executing corresponding program instructions in the computer. The processor can be equipped with various operating systems, such as Windows operating system, Linux system, Android, iOS system, etc. As another embodiment, the device can also include a display, which is used to display the diagnosis results for reference by the staff.

Claims

1. A method for determining the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir, characterized in that: The determination method comprises the following steps: 1) According to the distribution of pressure in the casing annulus during vertical well production, a pressure relationship equation between two adjacent points in the casing annulus is constructed. The pressure relationship equation reflects the relationship between the pressure at the current point and the pressure at the next point, the pressure gradient at the current point, and the depth difference between the current point and the next point. The pressure relationship equation is constructed as follows: P i+1 =P i +M i Δh i Where P i is the pressure at the i-th point in the wellbore, P i+1 is the pressure at the i+1th point in the wellbore, M i is the pressure gradient at the i-th point in the wellbore, Δh i is the depth difference between the i+1th point and the ith point in the wellbore; 2) Determine the relationship between pressure gradient and pressure using historical wellbore pressure test data; the relationship between pressure gradient and pressure is obtained by linear fitting; 3) Taking the casing pressure at the wellhead as the initial pressure, according to the relationship between the pressure gradient and the pressure, iterative calculation is performed according to the pressure relationship equation until the pressure at the bottom of the well is calculated, and the pressure at the bottom of the well is the bottom hole flowing pressure.

2. A device for determining the bottom hole flow pressure of a gas well in a tight sandstone gas reservoir, characterized in that: The determination device comprises a processor and a memory, wherein the processor executes a computer program stored in the memory to implement the method for determining the bottom hole flowing pressure of a gas well in a tight sandstone gas reservoir as described in claim 1 above.

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