A method for testing bottom hole dryness of offshore steam injection wells

Abstract

This invention provides a method for testing the bottom-hole dryness of offshore steam injection wells, comprising: determining the bottom-hole inclination depth H and the volume V0 of the annular space between the tubing and casing based on the wellbore structure; injecting nitrogen at a fixed rate to ensure the annular space is filled with nitrogen, and then injecting nitrogen into the annular space at different rates, recording the corresponding wellhead casing pressure values; determining the corresponding bottom-hole pressure values ​​based on the wellhead casing pressure values ​​at different nitrogen injection rates, and calculating the bottom-hole temperature at the corresponding bottom-hole pressure value using the water vapor saturated steam pressure formula; and determining the overall heat transfer coefficient U of the well using a computer-programmed iterative method based on the determined bottom-hole temperature and pressure, thereby determining the bottom-hole dryness. The beneficial effect of this invention is that it establishes a method for testing the bottom-hole dryness of offshore steam injection wells, and by verifying the bottom-hole pressure at different nitrogen injection rates based on the bottom-hole pressure balance principle, it ensures the accuracy of the calculated steam dryness.

Description

Technical Field

[0001] This invention relates to the field of downhole dryness measurement, and more specifically to a method for testing the dryness at the bottom of a marine steam injection well. Background Technology

[0002] Steam injection is a common method for extracting heavy oil. Bottom hole dryness is a crucial indicator for evaluating the effectiveness of steam injection and development, and it is also of great significance for increasing the production of steam injection wells.

[0003] Currently, the commonly used methods for testing the dryness of well bottoms are mainly the oil wellbore sampling method, the multi-parameter testing instrument method, and the mathematical model method.

[0004] Wellbore sampling can only collect dryness data at a single point inside the wellbore during a single run, and cannot achieve continuous multi-point measurement. Furthermore, it is difficult to implement under special offshore operating conditions.

[0005] The multi-parameter testing method involves lowering the testing instrument into the wellbore during the heat injection process using a steel wire to test the dryness along the wellbore profile. This method carries risks such as high operational risk and steel wire breakage. Furthermore, offshore thermal recovery wells are generally highly deviated wells with a bottom inclination exceeding 60°, making it difficult to obtain the bottom dryness using a multi-parameter testing instrument.

[0006] The mathematical model method uses mathematical models for theoretical calculations. However, the thermal conductivity selected in the dryness calculation process cannot be directly measured and can only be estimated through the thermal conductivity of various materials downhole. This method has many uncertainties, which ultimately leads to a large deviation between the calculated results and the actual dryness at the bottom of the well.

[0007] In summary, currently used methods for testing steam dryness at the bottom of wells cannot meet the requirements of special offshore operating conditions under high temperature and high pressure. Therefore, it is urgent to solve the problems caused by existing technologies in downhole dryness measurement. Summary of the Invention

[0008] This invention overcomes the shortcomings of the prior art and provides a method for testing the dryness of the bottom of offshore steam injection wells.

[0009] The objective of this invention is achieved through the following technical solution.

[0010] A method for testing the bottom hole dryness of offshore steam injection wells, comprising: S1. Based on the wellbore structure of the offshore thermal recovery well, determine the bottom vertical depth H and the volume V0 of the annular space between the tubing and casing. S2. Based on the volume V0 of the annular space of the tubing and casing, nitrogen is injected into the annular space of the tubing and casing at a fixed injection rate. After the annular space is filled with nitrogen, nitrogen is injected into the annular space at different injection rates. The wellhead casing pressure values ​​corresponding to different injection rates are recorded. S3. Based on the wellhead casing pressure value under different nitrogen injection rates, determine the corresponding bottom hole pressure value, and use the water vapor saturated vapor pressure formula to calculate the bottom hole temperature under the corresponding bottom hole pressure value. S4. Based on the determined bottom hole temperature and pressure, use a computer programming iterative method to solve for the comprehensive heat transfer coefficient U of the well, and determine the bottom hole dryness based on the solved comprehensive heat transfer coefficient U. In step S3, the formula for calculating the bottom hole pressure value includes,

[0011] In the formula, The density of nitrogen gas is kg / m³. 3 g is the acceleration due to gravity; H is the vertical depth of the well, in meters. This refers to the pressure loss when nitrogen is injected into the bottom of the well. The specific steps of step S4 include, S41, Input wellhead pressure P1, wellhead dryness x0, geothermal gradient α, bottom hole vertical depth H; S42. Determine the wellhead pressure P1 at the starting point, the comprehensive heat transfer coefficient U, the calculation depth increment ∆Z, and the number of segments N; S43. Preliminary setting of pressure drop in the calculation section Calculate the pressure at the lower end. Calculate the average pressure P in this calculation section. 1均 and average temperature T 1均 ; S44. Calculate the average pressure, and calculate the density, viscosity, and surface tension parameters of saturated steam and saturated water under the average temperature. S45. Determine the flow pattern of the computational section using the Brill-Beggs method, and calculate the pressure drop of that section. ; S46, Inspection If the test conditions are not met, the calculated pressure drop will be... Substitute the value into step S42 as the initial pressure drop value for the calculation section and solve iteratively. S47. If the test conditions in S46 are met, then the heat loss of this calculation section shall be calculated using the heat conduction equation. ; S48. Calculate the dryness value x at the end of this calculation segment based on the energy conservation equation. i ; S49. Substitute the calculated pressure and dryness values ​​at the end of the calculation section into step S44 to solve for the pressure P at the end of the next node. i计 and dryness x i计 , until the solution reaches the bottom of the well; S410, Inspection | Pn计 -P b If |≤0.001, and the test condition is not met, adjust the U value, return to step S41, and start the calculation again; P b The average pressure at the bottom of the well; S411. If the test conditions in S410 are met, the calculated bottom hole dryness is the bottom hole dryness value of the well.

[0012] A method for testing bottom hole dryness of a marine steam injection well according to claim 1, characterized in that: in step S2, there are more than 3 types of nitrogen injection rate values, and the difference between adjacent injection rates is 50Sm. 3 / d.

[0013] In step S2, there are more than three types of nitrogen injection rate values, and the difference between adjacent injection rates is 50 Sm. 3 / d.

[0014] The beneficial effects of this invention are as follows: This invention overcomes the problems existing in the current methods for measuring bottom hole dryness in offshore steam injection wells, and establishes a method for testing bottom hole dryness in offshore steam injection wells. By conducting nitrogen injection tests in the tubing-casing annulus, nitrogen fills the entire annular space, creating a pressure equilibrium point near the bottom of the well. Based on the bottom hole pressure equilibrium principle, the bottom hole pressure for steam injection is calculated. This pressure is then used to correct the comprehensive heat transfer coefficient of the mathematical model, thus determining the comprehensive heat transfer coefficient of the offshore steam injection well. The accuracy of the calculated steam dryness is ensured by verifying the bottom hole pressure at different nitrogen injection rates. Attached Figure Description

[0015] Figure 1 A schematic diagram of the wellbore structure of a marine steam injection well; Figure 2 This is a flowchart of the present invention; Figure 3 This is a flowchart for calculating the overall heat transfer coefficient of the wellbore according to the present invention.

[0016] In the diagram: 1. Waterproof conduit; 2. Cement ring; 3. 13-3 / 8" casing; 4. 9-5 / 8" casing; 5. Insulated oil pipe; 6. Vent valve; 7. High-temperature packer; 8. Top packer; 9. Sand screen pipe; 10. Nitrogen; 11. Steam; 12. Formation; 13. Pressure balance point. Detailed Implementation

[0017] Example like Figure 1As shown, in the process of offshore steam injection, the wellbore of the offshore steam injection well is set on the formation 12, and steam 11 is injected into the heat-insulated oil pipe 5. The annular space of the oil casing formed by the heat-insulated oil pipe 5, the 13-3 / 8" casing 3 and the 9-5 / 8" casing 4 is connected near the bottom of the well.

[0018] During testing, nitrogen gas 10 is injected into the annular space of the oil casing to fill the entire annular space. The insulated oil pipe 5 and the annular space of the oil casing will have a pressure balance point 13 near the bottom of the well. Based on this pressure balance point 13, the bottom hole pressure of the oil pipe steam injection can be calculated. This pressure is used to correct the value of the comprehensive heat transfer coefficient of the mathematical model, thereby calculating the bottom hole dryness.

[0019] Furthermore, the water-proof conduit 1 and the cement ring 2 are outer sleeves, the high-temperature packer 7 is set between the heat-insulating oil pipe 5 and the 9-5 / 8" sleeve 4 for isolation, the high-temperature packer 7 is equipped with a vent valve 6 for gas conduction, and the top packer 8 is used to suspend the sand-proof screen pipe 9.

[0020] A method for testing the bottom hole dryness of offshore steam injection wells, comprising: S1. Based on the wellbore structure of the offshore thermal recovery well, determine the bottom vertical depth H and the volume V0 of the annular space between the tubing and casing. S2. Based on the volume V0 of the annular space of the tubing and casing, nitrogen is injected into the annular space of the tubing and casing at a fixed injection rate. After the annular space is filled with nitrogen, nitrogen is injected into the annular space at different injection rates. The wellhead casing pressure values ​​corresponding to different injection rates are recorded. S3. Determine the corresponding bottom hole pressure value based on the wellhead casing pressure value under different nitrogen injection rates; S3. Based on the wellhead casing pressure value under different nitrogen injection rates, determine the corresponding bottom hole pressure value, and use the water vapor saturated vapor pressure formula to calculate the bottom hole temperature under the corresponding bottom hole pressure value. S4. Based on the determined bottom hole temperature and pressure, use computer programming iterative method to solve for the overall heat transfer coefficient U of the well, and determine the bottom hole dryness based on the solved overall heat transfer coefficient U.

[0021] In this embodiment, step S2 involves injecting nitrogen 10 into the annular space between the insulated tubing 5 and the casing consisting of the 13-3 / 8" casing 3 and the 9-5 / 8" casing 4 using the platform's nitrogen equipment. Considering the compressibility of nitrogen 10, the injection volume of nitrogen 10 should be calculated based on the wellhead injection pressure, and the calculated injection volume should be equal to V0.

[0022] In step S3, using the platform's nitrogen equipment, nitrogen is applied at 150 Sm... 3 / h、200 Sm 3 / h, 250 Sm 3 / h and 300Sm 3 Nitrogen gas is injected into the annular space between the insulating oil pipe 5 and the casing at a rate of / h for 3-4 hours, and the casing pressure value P after stabilization is recorded. h1、 P h2、 P h3、 P h4 .

[0023] Based on the single-phase seepage theory of the annular space of the oil casing, the pressure P at the bottom of the nitrogen well is calculated. b1 P b2 P b3 P b4 Specifically, The formula for calculating bottom hole pressure is:

[0024] In the formula, Let g be the density of nitrogen gas and g be the acceleration due to gravity. Let i be the flow friction of nitrogen gas in the annular space, i = 1, 2, 3, 4.

[0025] In step S4, the average bottom hole pressure is calculated under different nitrogen injection rates. Using the formula for saturated steam pressure, the bottom-hole temperature at this pressure is calculated.

[0026] The average temperature under bottom hole pressure is calculated using the following formula:

[0027] like Figure 3 As shown, the bottom hole dryness fraction is solved iteratively using computer programming. The specific steps are as follows: S41, Input wellhead pressure P1, wellhead dryness x0, geothermal gradient α, bottom hole vertical depth H; S42. Determine the starting point pressure P1, the overall heat transfer coefficient U, and the calculation depth increment ∆Z and the number of segments N; S43, Pressure drop in the initial design section Calculate the pressure at the lower end: Calculate the average pressure P in this calculation section. 1均 and average temperature T 1均 .

[0028] S44. Calculate the density, viscosity, and surface tension parameters of saturated steam and saturated water under average pressure and average temperature. S45. Determine the flow pattern of the computational section using the Brill-Beggs method, and calculate the pressure drop of that section. ; S46, Inspection If the test conditions are not met, the calculated pressure drop will be... Substitute the value into step S42 as the initial pressure drop value for the calculation section and solve iteratively. S47. If the test conditions in S46 are met, then the heat loss of this calculation section shall be calculated using the heat conduction equation. ; S48. Calculate the dryness value x at the end of the calculation terminal according to the energy conservation equation. i ; S49. Substitute the calculated pressure and dryness values ​​at the end of the calculation section into step S44 to solve for the pressure P at the end of the next node. i计 and dryness x i计 , until the solution reaches the bottom of the well; S410, Inspection | P n计 -P b If |≤0.001, and the test condition is not met, adjust the U value, return to step S41, and start the calculation again; S411. If the test conditions in S410 are met, the calculated well bottom dryness is the well bottom dryness value. The embodiments of the present invention have been described in detail above, but the content described is only a preferred embodiment of the present invention and should not be considered as limiting the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A method for testing the bottom-hole dryness of offshore steam injection wells, characterized in that, include: S1. Based on the wellbore structure of the offshore thermal recovery well, determine the bottom vertical depth H and the volume V0 of the annular space between the tubing and casing. S2. Based on the volume V0 of the annular space of the tubing and casing, nitrogen is injected into the annular space of the tubing and casing at a fixed injection rate. After the annular space is filled with nitrogen, nitrogen is injected into the annular space at different injection rates. The wellhead casing pressure values ​​corresponding to different injection rates are recorded. S3. Based on the wellhead casing pressure value under different nitrogen injection rates, determine the corresponding bottom hole pressure value, and use the water vapor saturated vapor pressure formula to calculate the bottom hole temperature under the corresponding bottom hole pressure value. S4. Based on the determined bottom hole temperature and pressure, use a computer programming iterative method to solve for the comprehensive heat transfer coefficient U of the well, and determine the bottom hole dryness based on the solved comprehensive heat transfer coefficient U. In step S3, the formula for calculating the bottom hole pressure value includes, In the formula, The density of nitrogen gas is kg / m³. 3 g is the acceleration due to gravity; H is the vertical depth of the well, in meters. This refers to the pressure loss when nitrogen is injected into the bottom of the well. The specific steps of step S4 include, S41, Input wellhead pressure P1, wellhead dryness x0, geothermal gradient α, bottom hole vertical depth H; S42. Determine the wellhead pressure P1 at the starting point, the comprehensive heat transfer coefficient U, the calculation depth increment ∆Z, and the number of segments N; S43. Preliminary setting of pressure drop in the calculation section Calculate the pressure at the lower end. Calculate the average pressure P in this calculation section. 1均 and average temperature T 1均 ; S44. Calculate the average pressure, and calculate the density, viscosity, and surface tension parameters of saturated steam and saturated water under the average temperature. S45. Determine the flow pattern of the computational section using the Brill-Beggs method, and calculate the pressure drop of that section. ; S46, Inspection If the test conditions are not met, the calculated pressure drop will be... Substitute the value into step S42 as the initial pressure drop value for the calculation section and solve iteratively. S47. If the test conditions in S46 are met, then the heat loss of this calculation section shall be calculated using the heat conduction equation. ; S48. Calculate the dryness value x at the end of this calculation segment based on the energy conservation equation. i ; S49. Substitute the calculated pressure and dryness values ​​at the end of the calculation section into step S44 to solve for the pressure P at the end of the next node. i计 and dryness x i计 , until the solution reaches the bottom of the well; S410, Inspection | Pn 计 -P b If |≤0.001, and the test condition is not met, adjust the U value, return to step S41, and start the calculation again; P b The average pressure at the bottom of the well; S411. If the test conditions in S410 are met, the calculated bottom hole dryness is the bottom hole dryness value of the well.

2. The method for testing the bottom dryness of a marine steam injection well according to claim 1, characterized in that, include: In step S2, there are more than three types of nitrogen injection rate values, and the difference between adjacent injection rates is 50 Sm. 3 / d.

Images