Gas lift reverse circulation bottom hole pressure prediction method and system

Abstract

The present invention discloses a method for predicting bottomhole pressure in gas lift reverse circulation, comprising: regional grid division; unit parameter calculation; determination of iterative calculation position; and bottomhole pressure output. Gas lift reverse circulation drilling technology is one of the typical "bottomhole negative pressure" drilling technologies. This technology can significantly reduce wellbore circulation pressure consumption, reduce bottomhole pressure holding effect, and effectively reduce the probability of well leakage. The purpose of the present invention is to derive a calculation method for predicting gas injection point pressure and bottomhole pressure under gas lift reverse circulation, which provides an important reference for predicting bottomhole pressure and preventing well leakage, and is of great significance to the development of gas lift reverse circulation technology.

Description

Technical Field

[0001] The present invention relates to the technical field of oil and gas well control, and in particular to a method and system for predicting bottom hole pressure of a gas lift reverse circulation. Background Art

[0002] In oil and gas drilling projects, gas-lift reverse circulation drilling technology is widely used in the development of complex formations (such as shale gas blocks and karst landforms) because it can achieve a "negative bottomhole pressure" state. This technology injects gas into the drill pipe to form a gas-liquid two-phase flow, reducing circulation pressure loss, thereby reducing the bottomhole pressure holding effect and the risk of lost circulation. The purpose of this invention is to derive a calculation method for predicting the injection point pressure and bottomhole pressure under gas-lift reverse circulation. This provides an important reference for predicting bottomhole pressure and preventing lost circulation, and is of great significance to the development of gas-lift reverse circulation technology. Summary of the Invention

[0003] In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a gas lift reverse circulation bottom hole pressure prediction method and system, which has certain reference value for improving the bottom hole pressure control accuracy of gas lift reverse circulation drilling.

[0004] To achieve the above object, the present invention adopts a technical solution: a method for predicting bottom hole pressure in gas lift reverse circulation, comprising the following steps:

[0005] Step 1: Obtain the basic parameters of the experimental well, including the inner diameter of the drill pipe, wellhead temperature and bottom hole pressure;

[0006] Step 2: Divide the gas lift area of ​​the experimental wellbore into i grids, where i = 1, 2, 3, ..., k; the gas lift area is the gas-liquid two-phase flow area from the gas-water mixer to the wellhead;

[0007] Step 3: Calculate the top pressure and temperature of the jth segment in the grid, and thus calculate the compressibility, gas holdup, gas phase density, and miscible phase density of the jth segment;

[0008] Step 4: Calculate the liquid column pressure and flow pressure loss of the jth segment, and determine the flow type according to the flow pressure loss, including bubbly flow, slug flow, disturbed flow, and annular flow;

[0009] Step 5: Determine whether each iteration is completed according to the known gas injection point position: when j = k, the iteration is completed; when j ≠ k, it means that the iterative calculation process has not yet ended, and return to step 3 to continue the calculation cycle;

[0010] Step 6: Calculate the single-phase flow liquid column pressure and flow pressure loss in the bottom hole area and output the results; wherein the bottom hole area is the single-phase flow area of ​​the drilling fluid below the gas-water mixer.

[0011] As a further improvement of the present invention, the step 2 is specifically as follows:

[0012] The finite difference method is used to grid the spatial domain of the gas-liquid two-phase miscible layer in the gas lift area. Starting from the drill bit mouth and with the z axis pointing downward as positive, several segments of △L length are taken in sequence until the gas injection point is reached.

[0013] As a further improvement of the present invention, the step 3 is specifically as follows:

[0014] The top pressure and temperature of the divided micro-unit are calculated using the formula to obtain the compressibility coefficient, gas holdup, gas phase density, and mixed phase density, thereby solving the bottom temperature and pressure of the micro-unit; the solved temperature and pressure are used as the initial calculation conditions for the next micro-unit until the calculation reaches the gas injection point and ends.

[0015] As a further improvement of the present invention, the calculation method of the compression coefficient is as follows:

[0016]

[0017] In the formula: A1=0.3265; A2=-1.0700; A3=-0.5339; A4=0.01569; A5=-0.05165; A6=0.5475; A7=-0.7361; A8=0.1844; A9=0.1056; A 10 =0.6134; A 11 =0.7210;ρ pr is the pseudo relative density of the gas;

[0018] The calculation method of gas holdup is as follows:

[0019]

[0020] Where: Q is the drill pipe interface, Ω g is the cross-sectional area occupied by the gas phase at this node;

[0021] The gas phase density is calculated as follows:

[0022]

[0023] Where: P is the pressure at the current depth; M is the molar mass of air; Z is the compressibility; R is the gas constant; T is the temperature at the current depth.

[0024] As a further improvement of the present invention, in step 4, for the gas-liquid two-phase liquid column pressure, the density of the calculation point is selected as the mixed density of the gas-liquid two-phase: P qy =ρ m gΔh; the mixed density of gas and liquid phases is: ρ m =E g ρ g +(1-Eg )ρ l ; Among them: P qy is the pressure of the liquid column of the gas-liquid two-phase flow; g is the acceleration of gravity; Δh is the height of the gas-liquid two-phase flow in this section; ρ g is the gas density; ρ l is the drilling fluid density.

[0025] As a further improvement of the present invention, in step 4, judging the flow type according to the flow pressure loss specifically includes:

[0026] (1) The discriminant of bubbly flow is as follows:

[0027] ν sg <0.429ν sl +0.357ν 0∞

[0028] Where: v sg is the gas phase superficial velocity; v sl is the liquid phase superficial velocity; v 0∞ is the limiting rising velocity of a single bubble;

[0029] The pressure loss of bubbly flow is as follows:

[0030]

[0031] Where: f m is the Fanning friction coefficient; v m is the mixed velocity of gas-liquid two-phase flow; D is the inner diameter of the drill pipe;

[0032] (2) The discriminant of slug flow is as follows:

[0033] ν sg >0.429ν sl +0.357ν 0∞

[0034]

[0035] The slug flow pressure loss is as follows:

[0036]

[0037] (3) The discriminant of disturbed flow is as follows:

[0038]

[0039] Where: σ is the gas-liquid interfacial tension;

[0040] Disturbed flow pressure loss:

[0041]

[0042] (4) The discriminant of annular flow is as follows:

[0043]

[0044] The annular flow pressure loss is as follows:

[0045]

[0046] Where: ρ c is the liquid density in the center of the drill bit; f c is the friction coefficient of gas phase flowing along the liquid film surface.

[0047] As a further improvement of the present invention, in step 6, the method for calculating the flow pressure loss of the single-phase flow is specifically as follows:

[0048] The density of the fluid at the calculation point is taken as the density of the drilling fluid:

[0049] P d =ρ l gh2

[0050] Where: h2 is the height from the gas-water mixer to the bottom of the well;

[0051] The pressure loss of drilling fluid flow in the drill pipe can be calculated using Darcy's formula:

[0052]

[0053] Where: v l is the drilling fluid velocity; f l is the Fanning friction coefficient of the single-phase section of the drilling fluid.

[0054] The present invention also provides a gas lift reverse circulation bottom hole pressure prediction system, comprising:

[0055] Sensor module, used to collect real-time parameters such as wellhead temperature, gas injection volume, drilling fluid displacement and well depth;

[0056] A calculation module, used to execute the prediction method described above;

[0057] The execution module adjusts the gas injection volume and injection point location of the gas lift equipment according to the optimization results.

[0058] This study uses a fine-grained wellbore partitioning technique and iteratively solves wellbore parameters to establish a computational model for predicting bottomhole pressure. This model can estimate the impact of various parameters, such as injection point locations and injection volumes, on bottomhole pressure. The results offer valuable insights into improving the accuracy of bottomhole pressure control in gas-lift reverse circulation drilling.

[0059] The beneficial effects of the present invention are:

[0060] The present invention can estimate the impact of different parameters such as the location of different gas injection points and the size of gas injection volume on the bottom hole pressure; the present invention can provide construction parameters for gas lift reverse circulation drilling, which provides an important reference for determining the gas injection point and gas injection volume, thereby reducing the probability of well leakage during gas lift reverse circulation drilling. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 Schematic diagram of gas lift reverse circulation in an embodiment of the present invention;

[0062] Figure 2 Schematic diagram of grid division in an embodiment of the present invention;

[0063] Figure 3 is a calculation flow chart of an embodiment of the present invention;

[0064] Figure 4 This is a flow chart of a gas-liquid two-phase flow liquid column pressure and flow pressure loss calculation module in an embodiment of the present invention. DETAILED DESCRIPTION

[0065] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0066] Example 1

[0067] like Figure 3 As shown, a method for predicting bottom hole pressure of gas lift reverse circulation includes the following steps:

[0068] (1) The wellbore is divided into a bottom hole area, a gas lift area, and a wellhead area: the bottom hole area is the drilling fluid single-phase flow area below the gas-water mixer; the gas lift area is the gas-liquid two-phase flow area from the gas-water mixer to the wellhead; and the wellhead area is the drill pipe outlet area;

[0069] (2) Obtain basic parameters including drill pipe inner diameter, wellhead temperature, bottom hole pressure, etc.;

[0070] (3) Grid division of the gas-liquid two-phase flow in the gas lift area (i = 1, 2, 3 ... k); the finite difference method is used to grid the gas lift area, starting from the wellhead and dividing the grid into several micro-element segments of length △L along the drill pipe downward;

[0071] (4) Calculate the top pressure and temperature of the jth segment; the top pressure and temperature of the j+1th segment are calculated based on the top pressure and temperature of the jth segment;

[0072] (5) Calculate the parameters of the jth segment (compressibility, gas holdup, gas density, miscible density); in the iterative calculation, the gas density in each microelement will be corrected by combining the geothermal gradient and ignoring the effect of heat transfer;

[0073] (6) Determine the flow pattern (bubble flow, slug flow, turbulent flow, and annular flow); determine the flow pattern of the gas-liquid two-phase flow in each microelement based on the calculated parameters; and do not consider the effect of drill string rotation on the drilling fluid flow;

[0074] (7) Calculate the flow pressure loss and liquid column pressure of the jth section; the cuttings are evenly distributed in the drilling fluid, and the effect of the cuttings on the pressure is not considered;

[0075] (8) Determine whether each iteration is completed according to the known location of the gas injection point; each iteration is calculated starting from the wellhead, and the end of each iteration is marked by whether the gas injection point is calculated.

[0076] (9) Calculate the single-phase flow liquid column pressure and flow pressure loss in the bottom hole area; the output result is the bottom hole pressure under the combined action of the gas-liquid two-phase flow in the gas lift area and the single-phase flow of drilling fluid in the bottom hole area.

[0077] (10) Output the results.

[0078] like Figure 1 As shown, in the process of gas lift reverse circulation, the study of gas lift reverse circulation wellbore pressure can be divided into three parts. Since the solid phase has little effect on the wellbore pressure, the solid phase is ignored in this embodiment and only the fluid is considered. Bottom hole area (drilling fluid single phase), gas lift area (gas-liquid two-phase) and wellhead area. The drilling fluid is injected from the annulus until it flows into the drill pipe from the water hole at the drill bit at the bottom of the well. When the drilling fluid rises along the inner cavity of the drill pipe to the position of the gas-water mixer, the gas phase is injected into the drill pipe through the double-wall drill pipe. When the drilling fluid reaches the gas injection point of the drill pipe, it is mixed with the gas phase to form a gas-liquid two-phase flow. After mixing with the compressed air sprayed into the inner cavity of the drill pipe to form a gas-liquid two-phase flow, it continues to move upward and enters the ground circulation system to achieve the purpose of gas lift reverse circulation drilling.

[0079] First, due to the complex fluid flow in the wellbore during the actual drilling process, the following assumptions are made:

[0080] 1. Assume that the drilling fluid is incompressible;

[0081] 2. The effect of drill string rotation on drilling fluid flow is not considered;

[0082] 3. The temperature is the geothermal gradient and heat transfer is ignored;

[0083] 4. The cuttings are evenly distributed in the drilling fluid, and the effect of the cuttings on the pressure is not considered. The pressure is calculated based on the gas-liquid two-phase flow in the gas lift area and the single-phase flow of the drilling fluid in the bottom hole area.

[0084] The calculation method for determining the optimal gas injection point for gas lift reverse circulation includes the following steps:

[0085] The pure drilling fluid section is a single-phase flow, and the pressure calculation is simple. However, the pressure drop gradient of the gas-liquid two-phase flow section changes with the flow pattern, and the pressure drop calculation is complicated. Therefore, in order to ensure the accuracy of the calculation results, the finite difference method will be used to mesh the gas-liquid two-phase mixture in the gas lift area. Figure 2 As shown in the figure, starting from the wellhead, several microelement segments of length △L are sequentially selected until the gas injection point is reached. The gas-liquid parameters within the cell are then calculated, iterating and looping from the wellhead until the gas injection point is reached. The single-phase flow of the drilling fluid in the bottomhole region is then calculated.

[0086] (1) Grid division:

[0087] The finite difference method is used to grid the spatial domain of the gas-liquid two-phase miscible layer in the gas lift area. Starting from the drill bit mouth and with the z axis pointing downward as positive, several segments of △L length are taken in sequence until the gas injection point is reached.

[0088] (2) Gas-liquid two-phase flow liquid column pressure and flow pressure loss calculation module:

[0089] For gas-liquid two-phase flow liquid column pressure and flow pressure loss calculation module, such as Figure 4 As shown in the figure, the top pressure and temperature of each microelement are calculated using formulas to determine parameters such as gas holdup, gas density, and miscible density, thereby solving for the bottom temperature and pressure of the microelement. This temperature and pressure are used as the initial calculation conditions for the next unit, and the calculation continues until the gas injection point is reached.

[0090] The gas-liquid two-phase flow liquid column pressure and flow pressure loss calculation module mainly calculates the following parameters.

[0091] Liquid column pressure of gas-liquid two-phase flow:

[0092] For the calculation of the gas-liquid two-phase liquid column pressure, the density of the calculation point should be the mixed density of the gas and liquid phases.

[0093] P qy =ρ m gΔh (1)

[0094] The mixed density of gas-liquid two phases is:

[0095] ρ m =E g ρ g +(1-E g )ρ l (2)

[0096] Gas-liquid two-phase flow pressure loss:

[0097] 1) Bubble flow:

[0098] Discriminant:

[0099] ν sg<0.429ν sl +0.357ν 0∞ (3)

[0100] Bubble flow pressure loss:

[0101]

[0102] 2) Slug flow:

[0103] Discriminant:

[0104] ν sg >0.429ν sl +0.357ν 0∞

[0105]

[0106] Slug flow pressure loss:

[0107]

[0108] 3) Disturbed flow:

[0109] Discriminant:

[0110]

[0111] Disturbed flow pressure loss:

[0112] In practice, the flow patterns between slug and slug flow are very similar, and the demarcation between them is also ambiguous. Therefore, in practical engineering applications, slug and slug flow are usually classified as the same and treated according to the same standards.

[0113] 4) Annular flow:

[0114] Discriminant:

[0115]

[0116] Annular flow pressure loss:

[0117]

[0118] (3) Calculation of drilling fluid single-phase flow column pressure and flow pressure loss:

[0119] In the gas lift reverse circulation condition, liquid-solid two-phase flow flows below the gas-water mixer. In this embodiment, the effect of cuttings on pressure is ignored, and the pressure in the cementing bottom zone is calculated based on pure liquid phase.

[0120] For the single-phase section of drilling fluid, the fluid density at the calculation point should be the drilling fluid density.

[0121] Pd =ρ l gh2 (10)

[0122] For the single-phase flow section of drilling fluid, the conventional Darcy formula can be used to calculate the pressure loss of drilling fluid flow in the drill pipe.

[0123]

[0124] (4) Determine whether the current calculated height is equal to the well depth:

[0125] If it is not equal, it means that the iterative calculation process has not yet ended, and return to step (2) to calculate the loop. If it is equal, go to the next step.

[0126] (5) Output calculation results:

[0127] Finally, the calculation results are output. The optimal position of the gas injection point is the position where the solid phase in the boundary layer reaches the settling velocity after gas injection, which can ensure the discharge of rock cuttings to the greatest extent.

[0128] Example 2

[0129] A method for predicting bottom hole pressure in gas lift reverse circulation comprises the following steps:

[0130] (1) Obtain basic parameter information of the experimental well;

[0131] (2) Transmitting the acquired basic parameters to the analysis system;

[0132] (3) Output the results through the analysis system;

[0133] Step (1) obtains basic parameters including the inner diameter of the drill pipe, wellhead temperature, bottom hole pressure, etc.

[0134] The new method for calculating the bottom hole pressure of gas lift reverse circulation in step (3) is divided into the following steps: 1) obtaining the basic parameters of the experimental well; 2) calculating the liquid column pressure and flow pressure loss calculation module of the gas-liquid two-phase flow; 3) calculating the pressure of the gas injection point; 4) calculating the liquid column pressure and flow pressure loss of the drilling fluid single-phase flow; 5) judging whether the calculation reaches the bottom hole; 6) calculating the bottom hole pressure, outputting the result and saving it.

[0135] The steps of the gas-liquid two-phase flow liquid column pressure and flow pressure loss calculation module in step (3) are as follows: 1) input the basic parameters of the known experimental well; 2) grid the gas-liquid two-phase flow (i = 1, 2, 3...k); 3) calculate the top pressure and temperature of the jth section; 4) calculate the parameters of the jth section (compressibility coefficient, gas holdup, gas phase density, mixed phase density); 5) determine the flow type; 6) calculate the flow pressure loss and liquid column pressure of the jth section; 7) determine whether the calculation process j is equal to k; 8) output the results.

[0136] Example 3

[0137] A gas lift reverse circulation bottom hole pressure prediction system, comprising:

[0138] Sensor module, used to collect real-time parameters such as wellhead temperature, gas injection volume, drilling fluid displacement and well depth;

[0139] A calculation module, configured to execute the prediction method described in Example 1 or Example 2;

[0140] The execution module adjusts the gas injection volume and injection point location of the gas lift equipment according to the optimization results.

[0141] The above-described embodiments merely represent specific implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, and all such variations and improvements fall within the scope of protection of the present invention.

Claims

1. A method for predicting bottom hole pressure in gas lift reverse circulation, characterized in that: The following steps are involved: Step 1: Obtain the basic parameters of the experimental well, including the inner diameter of the drill pipe, wellhead temperature and bottom hole pressure; Step 2: Divide the gas lift area of ​​the experimental wellbore into i grids, where i = 1, 2, 3, ..., k; the gas lift area is the gas-liquid two-phase flow area from the gas-water mixer to the wellhead; Step 3: Calculate the top pressure and temperature of the jth segment in the grid, and thus calculate the compressibility, gas holdup, gas phase density, and miscible phase density of the jth segment; Step 4: Calculate the liquid column pressure and flow pressure loss of the jth segment, and determine the flow type according to the flow pressure loss, including bubbly flow, slug flow, disturbed flow, and annular flow; Step 5: Determine whether each iteration is completed according to the known gas injection point position: when j = k, the iteration is completed; when j ≠ k, it means that the iterative calculation process has not yet ended, and return to step 3 to continue the calculation cycle; Step 6: Calculate the single-phase flow liquid column pressure and flow pressure loss in the bottom hole area and output the results; wherein the bottom hole area is the single-phase flow area of ​​the drilling fluid below the gas-water mixer.

2. The gas lift reverse circulation bottom hole pressure prediction method according to claim 1, characterized in that: The step 2 is specifically as follows: The finite difference method is used to grid the spatial domain of the gas-liquid two-phase miscible layer in the gas lift area. Starting from the drill bit mouth and with the z axis pointing downward as positive, several segments of △L length are taken in sequence until the gas injection point is reached.

3. The gas lift reverse circulation bottom hole pressure prediction method according to claim 2, characterized in that: The step 3 is specifically as follows: The top pressure and temperature of the divided micro-unit are calculated using the formula to obtain the compressibility coefficient, gas holdup, gas phase density, and mixed phase density, thereby solving the bottom temperature and pressure of the micro-unit; the solved temperature and pressure are used as the initial calculation conditions for the next micro-unit until the calculation reaches the gas injection point and ends.

4. The gas lift reverse circulation bottom hole pressure prediction method according to claim 3, characterized in that: The compression factor is calculated as follows: In the formula: A1=0.3265; A2=-1.0700; A3=-0.5339; A4=0.01569; A5=-0.05165; A6=0.5475; A7=-0.7361; A8=0.1844; A9=0.1056; A 10 =0.6134; A 11 =0.7210;ρ pr is the pseudo relative density of the gas; The calculation method of gas holdup is as follows: Where: Ω is the drill pipe interface, Ω g is the cross-sectional area occupied by the gas phase at the corresponding node; The gas phase density is calculated as follows: Where: P is the pressure at the current depth; M is the molar mass of air; Z is the compressibility; R is the gas constant; T is the temperature at the current depth.

5. The method for predicting bottom hole pressure in gas lift reverse circulation according to claim 3, characterized in that: In step 4, for the gas-liquid two-phase liquid column pressure, the density of the calculation point is the mixed density of the gas-liquid two-phase: P qy =ρ m gΔh; the mixed density of gas and liquid phases is: ρ m =E g ρ g +(1-E g )ρ l ; Where: P qy is the pressure of the liquid column of the gas-liquid two-phase flow; g is the acceleration of gravity; Δh is the height of the gas-liquid two-phase flow in this section; ρ g is the gas density; ρ l is the drilling fluid density.

6. The method for predicting bottom hole pressure in gas lift reverse circulation according to claim 3, characterized in that: In step 4, judging the flow type according to the flow pressure loss specifically includes: (1) The discriminant of bubbly flow is as follows: n sg <0.429v sl +0.357n 0∞ Where: v sg is the gas phase superficial velocity; v sl is the liquid phase superficial velocity; v 0∞ is the maximum rising velocity of a single bubble; The pressure loss of bubbly flow is as follows: Where: f m is the Fanning friction coefficient; v m is the mixed velocity of gas-liquid two-phase flow; D is the inner diameter of the drill pipe; (2) The discriminant of slug flow is as follows: n sg >0.429v sl +0.357n 0∞ The slug flow pressure loss is as follows: (3) The discriminant of disturbed flow is as follows: Where: σ is the gas-liquid interfacial tension; Disturbed flow pressure loss: (4) The discriminant of annular flow is as follows: The annular flow pressure loss is as follows: Where: ρ c is the liquid density in the center of the drill bit; f c is the friction coefficient of gas phase flowing along the liquid film surface.

7. The method for predicting bottom hole pressure in gas lift reverse circulation according to claim 6, characterized in that: In step 6, the calculation method of the flow pressure loss of the single-phase flow is as follows: The density of the fluid at the calculation point is taken as the density of the drilling fluid: P d =ρ l gh2 Where: h2 is the height from the gas-water mixer to the bottom of the well; The pressure loss of drilling fluid flow in the drill pipe can be calculated using Darcy's formula: Where: v l is the drilling fluid velocity; f l is the Fanning friction coefficient of the single-phase section of the drilling fluid.

8. A gas lift reverse circulation bottom hole pressure prediction system, characterized in that: include: Sensor module, used to collect real-time parameters such as wellhead temperature, gas injection volume, drilling fluid displacement and well depth; A calculation module, configured to execute the prediction method according to any one of claims 1 to 7; The execution module adjusts the gas injection volume and injection point location of the gas lift equipment according to the optimization results.

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