Novel method for determining well opening instantaneous flow rate of low-yield well

Abstract

The invention relates to a novel method for determining the well opening instantaneous flow rate of a low-yield well. The novel method comprises the following steps that (1) a low-yield gas well shaft temperature distribution prediction model is established at first; 2) correcting the reliability and accuracy of the prediction model through actual testing; and 3) calculating the critical temperature of the hydrate generated by the low-yield and low-efficiency well by using the prediction model, and finally determining the critical anti-hydrate flow of the gas well, namely obtaining the critical anti-hydrate flow process by using the prediction model. According to the method, the critical hydrate prevention flow is adopted for well opening, on one hand, rapid carrying of terrestrial heat needs to be guaranteed, on the other hand, continuous production of the gas well needs to be guaranteed, the high-incidence stage of hydrate production of the gas well is effectively avoided, and the well opening time rate of the gas well is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas exploitation. In particular, it relates to a new method for determining the instantaneous flow rate of a low-yield well. BACKGROUND

[0002] From a geological perspective, a low-yield well is located at a low structural position, has poor reservoir properties, low open flow capacity, boundaries and limited energy. In terms of development dynamics, the single-well production of a low-yield well is low, and the wellhead temperature is low. From a production dynamic perspective, the node operating parameters of a low-yield gas well are in a high-risk zone for hydrate formation, and the wellbore is prone to throttling and freezing. Wellbore throttling is an important factor affecting the production rate of a low-yield well. At the initial stage of opening a low-yield gas well, if the well is opened with a large instantaneous flow rate, the instantaneous flow rate can quickly carry geothermal heat, but due to the limited energy of the low-yield well, the instantaneous flow rate quickly decreases in a very short period of time, and eventually fails to effectively carry geothermal heat. If the well is opened with a small instantaneous flow rate, the gas well can maintain production for a certain period of time, but hydrates are continuously produced during production, which can cause serious freezing and plugging of the wellbore. SUMMARY

[0003] The present application provides a new method for determining the instantaneous flow rate of a low-yield well. That is, the well is opened with a critical hydrate prevention flow rate, which can ensure the rapid carrying of geothermal heat and the continuous production of the gas well, effectively avoiding the high-occurrence period of hydrates during gas well production, and improving the opening rate of the gas well.

[0004] The technical solution provided by the present application is as follows: a new method for determining the instantaneous flow rate of a low-yield well includes the following steps: 1) First, establish a low-yield gas wellbore temperature distribution prediction model: when gas flows upward along the wellbore from the well bottom, there is a temperature difference between the gas and the surrounding formation, so heat is inevitably transferred to the surrounding formation through three heat transfer modes: conduction, convection and radiation. Assuming that the heat transfer from the wellbore to the second contact surface, which is the contact surface between the cement ring and the formation, is also called the wellbore / formation interface, is stable heat transfer, and the heat transfer from the second contact surface to the surrounding formation is non-steady heat transfer, the second contact surface temperature is used as a link between the wellbore and the surrounding formation, and a prediction model for the temperature distribution of the gas wellbore is established; 2) Correct the reliability and accuracy of the prediction model through actual testing: first, the gas well is produced in a fixed production mode, and the volume flow rate of the well and the wellbore engineering parameters are used as basic data to establish a prediction model as a tool to calculate the temperature distribution of each well section of the wellbore. Then, the gas well operating system is maintained unchanged, and flow temperature testing is carried out. Finally, the predicted wellbore temperature is compared with the measured wellbore temperature, and the relative error is controlled within 10%, meeting the engineering precision requirements; 3) Application of the prediction model to calculate the hydrate formation critical temperature of low-yield and low-efficiency wells, and finally determine the critical hydrate prevention flow rate of the gas well, that is, the process of applying the prediction model to obtain the critical hydrate prevention flow rate.

[0005] In step 1) above, when the gas flows upward along the wellbore from the bottom of the well, due to the temperature difference between the gas and the surrounding formation, heat transfer will inevitably occur through three heat transfer modes: conduction, convection and radiation. The formation temperature at any depth is: ; Through the assumption, the mathematical model for calculating the temperature distribution of the entire wellbore is obtained: ; Where: ; The boundary condition at the inlet of each section is: ; It is considered that the fluid temperature at the bottom of the well is equal to the formation temperature, and the boundary condition is as follows: ; c pm The constant-pressure heat capacity of the wellbore fluid is calculated as follows: ; The transient heat transfer function is calculated using an approximate formula that meets the engineering precision requirements: ; In the formula, g T —geothermal gradient, ℃ / m; T ebh —formation temperature at the bottom of the well, unit ℃; z—depth of a certain position in the formation from the bottom of the well, unit m; T ein , T eout —temperature at the inlet and outlet of each section of the formation, unit ℃; T fin , T fout —temperature at the inlet and outlet of each section of the wellbore, unit ℃; z in , z out —depth of the inlet and outlet of each section of the formation from the bottom of the well, unit m; θ—angle between the wellbore and the horizontal plane, unit degree; T f —temperature of the wellbore fluid, unit ℃; T e —formation temperature at any depth, unit ℃; w t —mass flow rate, unit kg / s; r to —outer diameter of the tubing, unit m; k e —thermal conductivity of the formation, unit W / (m·K); ɑ—thermal diffusivity of the formation, unit m2 t - production time, unit d; r h r - wellbore radius, unit m; U to U - overall heat transfer coefficient, need to be iterated; A - intermediate coefficient, unit 1 / m; Cp - constant pressure heat capacity of wellbore fluid, unit J / K.

[0006] The beneficial effects of the present application are: the present application adopts critical hydrate flow rate to open the well, which on one hand ensures the rapid carrying of geothermal energy, and on the other hand ensures the continuous production of gas wells, effectively avoids the high incidence of hydrate production in gas wells, and improves the opening rate of gas wells. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a hydrate formation temperature and pressure curve diagram; Figure 1 Figure 2 is a temperature gradient calculation result diagram; Figure 3 is a gas and wellbore heat conduction, convection and radiation three heat transfer mode diagram. Figure 2 Figure 4 is a temperature distribution diagram of a low-yield well. Figure 5 is a temperature distribution diagram of a low-yield well. Figure 3 Figure 6 is a temperature distribution diagram of a low-yield well. DETAILED DESCRIPTION

[0008] The present application will be further described below with the accompanying drawings and examples: As shown in the drawings, the new method for determining the instantaneous flow rate of a low-yield well includes the following steps: Figures 1-2 1) First, establish a low-yield gas well wellbore temperature distribution prediction model: when the gas flows upward along the wellbore from the well bottom, there is a temperature difference between the gas and the surrounding formation, so it must be heat transfer to the surrounding formation through three heat transfer modes of heat conduction, convection and radiation. As shown in the drawings), assuming that the heat transfer from the wellbore to the second contact surface, that is, the contact surface between the cement ring and the formation, also known as the wellbore / formation interface, is steady-state heat transfer, and the heat transfer from the second contact surface to the surrounding formation is non-steady-state heat transfer, then the second contact surface temperature is used as the link between the wellbore and the surrounding formation to establish a prediction model for the temperature distribution of the gas well wellbore; when the gas flows upward along the wellbore from the well bottom, there is a temperature difference between the gas and the surrounding formation, so it must be heat transfer to the surrounding formation through three heat transfer modes of heat conduction, convection and radiation (as shown in the drawings); The temperature of the formation at any depth is: Figure 3 Through the assumption, the mathematical model for calculating the temperature distribution of the entire wellbore is obtained: ; The boundary condition at the inlet of each segment is: ; Wherein: ; The boundary condition at the inlet of each segment is: ;​ The boundary conditions are as follows if the fluid temperature at the bottom of the well is considered equal to the formation temperature: ; c pm The constant-pressure heat capacity of the wellbore fluid is calculated by the following formula: ; The transient heat transfer function is calculated by the approximate formula that meets the engineering precision requirements: ; In the formula, g T —geothermal gradient, ℃ / m; T ebh —formation temperature at the bottom of the well, unit: ℃; z—depth of a position in the formation from the bottom of the well, unit: m; T ein , T eout —inlet and outlet temperatures of each section of the formation, unit: ℃; T fin , T fout —inlet and outlet temperatures of each section of the wellbore, unit: ℃; z in , z out —depth of the inlet and outlet of each section of the formation from the bottom of the well, unit: m; θ—angle between the wellbore and the horizontal plane, unit: degree; T f —temperature of the wellbore fluid, unit: ℃; T e —formation temperature at an arbitrary depth, unit: ℃; w t —mass flow rate, unit: kg / s; r to —outer diameter of the tubing, unit: m; k e —thermal conductivity of the formation, unit: W / (m·K); ɑ—thermal diffusivity of the formation, unit: m 2 / h; t—production time, unit: d; r h —hole radius, unit: m; U to —total heat transfer coefficient, which needs to be iteratively calculated. A—intermediate coefficient, unit: 1 / m; Cp—constant-pressure heat capacity of the wellbore fluid, unit: J / K.

[0009] 2)The reliability and accuracy of the prediction model are corrected through actual testing: first, the gas well is produced in a constant production mode, such as 2×10 4 m 3 / d. Based on the volumetric flow rate and wellbore engineering parameters of the well, the temperature distribution of each section of the wellbore is calculated by using the prediction model as a tool. Then, the flow temperature test is carried out while keeping the working system of the gas well unchanged. Finally, the predicted wellbore temperature is compared with the measured wellbore temperature. The comparison results are shown in Table 2. The relative error is controlled within 10%, which meets the engineering precision requirements.

[0010]

[0011] 3) Applying a predictive model to calculate the critical temperature for hydrate formation in low-yield, inefficient wells, and ultimately determining the critical hydrate flow rate for gas wells, is the process of obtaining the critical hydrate flow rate using the predictive model. Through prediction by the model, it can be known that well XY-6A has a daily gas production of 2.5 × 10⁻⁶. 4 m 3 ,like Figure 2 As shown, the instantaneous value is equivalent to 1042m. 3 Under the condition of / h, the wellhead temperature is 10℃, which is 8℃ higher than the hydrate formation temperature (the gas well production pressure is controlled at 4.5MPa; according to the hydrate production curve, under this condition, the wellhead hydrate formation temperature is 8℃). This temperature can reach above the hydrate formation temperature. Considering a safety factor of 1.2, in actual production, an instantaneous 1200m... 3 The production rate is calculated at / h, which we call the critical hydrate flow rate for that well. This significantly improves the well-opening rate during the winter production period for low-yield wells after the treatment. The application results are shown in Table 3.

[0012] The formation of hydrates requires specific thermodynamic conditions, namely, a certain temperature and pressure. The temperature at which hydrates form is called the hydrate formation temperature. In a high-pressure sealed reactor containing natural gas and liquid water, under a constant pressure (2 MPa), the mixture of natural gas and liquid water is cooled. When the temperature drops to 0°C, a snow-like solid substance begins to appear in the reactor; this substance is the formed hydrate. 0°C is the temperature at which natural gas forms hydrates at 2 MPa. By changing the gas pressure in the sealed reactor and using the same experimental method, the hydrate formation temperature under different pressure conditions can be obtained. Ultimately, a hydrate formation temperature-pressure curve can be obtained, as shown below. Figure 1 As shown.

[0013] Table 3 Comparison of freezing and blockage in low-yield gas wells before and after treatment.

Claims

1. A new method for determining the instantaneous flow rate upon opening a low-production well, comprising the following steps: 1) First, establish a prediction model for the temperature distribution of the wellbore in low-yield gas wells: When gas flows upward from the bottom of the well along the wellbore, due to the temperature difference between the gas and the surrounding formation, it will inevitably transfer heat to the surrounding formation through three heat transfer methods: conduction, convection and radiation. Assuming that the heat transfer from the wellbore to the second contact surface, which is the contact surface between the cement sheath and the formation, also known as the wellbore / bottom interface, is steady-state heat transfer, and the heat transfer from the second contact surface to the surrounding formation is unsteady-state heat transfer, then the temperature of the second contact surface is taken as the link between the wellbore and the surrounding formation, and a prediction model for the temperature distribution of the gas wellbore is established. 2) Improve the reliability and accuracy of the prediction model through actual testing: First, the gas well is produced in a fixed production mode. Based on the volumetric flow rate and wellbore engineering parameters of the well, the prediction model is established as a tool to calculate the temperature distribution of each section of the wellbore. Then, while keeping the gas well operating system unchanged, flow temperature testing is carried out. Finally, the predicted wellbore temperature is compared with the measured wellbore temperature. The relative error is controlled within 10% to meet the engineering accuracy requirements. 3) Applying a predictive model to calculate the critical temperature at which low-yield and inefficient wells produce hydrates, and finally determining the critical hydrate flow rate of the gas well, is the process of obtaining the critical hydrate flow rate by applying a predictive model.

2. The new method for determining the instantaneous flow rate at the start of a low-production well according to claim 1, characterized in that: In step 1), when the gas flows upward from the bottom of the well along the wellbore, due to the temperature difference between the gas and the surrounding formation, it will inevitably transfer heat to the surrounding formation through three heat transfer methods: conduction, convection and radiation. The formation temperature at any depth is: ； Based on the assumptions, a mathematical model for calculating the temperature distribution throughout the wellbore is derived: ； in: ； The boundary conditions at the entry point of each segment are: ； Assuming the fluid temperature at the bottom of the well is equal to the formation temperature, the boundary conditions are as follows: ； c pm The isobaric heat capacity of well fluids is calculated using the following formula: ； The transient heat transfer function is calculated using an approximate formula that meets engineering accuracy requirements: ； In the formula g T —Geothermal gradient, °C / m; T ebh — Formation temperature at the bottom of the well, in °C; z — Depth of a specific location in the formation from the bottom of the well, in meters; T ein T eout —Inlet and outlet temperatures of each section of the formation, in °C; T fin T fout —Inlet and outlet temperatures of each section of the wellbore, in °C; in , z out — Depth of the wellbore from the inlet and outlet of each formation segment, in meters; θ — Angle between the wellbore and the horizontal plane, in degrees; T f —Wellbore fluid temperature, in °C; T e —The formation temperature at any depth, in °C; w t —Mass flow rate, in kg / s; r to —Outer diameter of the oil pipe, in meters; k e — Formation thermal conductivity, in W / (m·K); α— Formation thermal diffusivity, in m 2 / h; t—production time, in days; r h —Well radius, in meters; U to —Overall heat transfer coefficient, requires iterative calculation; A—Intermediate coefficient, unit 1 / m; C p —Isobaric heat capacity of fluid in wellbore, in J / K.

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