CN-121993128-A - Injection control device and control method for carbon dioxide injection well

CN121993128ACN 121993128 ACN121993128 ACN 121993128ACN-121993128-A

Abstract

The invention relates to the technical field of carbon dioxide injection wells, in particular to an injection control device and a control method of a carbon dioxide injection well, wherein the injection control device comprises an optical fiber composite cable, the inner side of an oil pipe is provided with the optical fiber composite cable capable of monitoring the temperature in real time from top to bottom, the optical fiber composite cable is connected with an optical fiber real-time monitoring system, the wellhead is provided with a wellhead pressure and temperature monitoring system, the wellhead is provided with a carbon dioxide injection system, the outlet end of the carbon dioxide injection system is provided with a pressure sensor and a temperature sensor in a carbon dioxide injection pipe, and a first pressure sensor and a first temperature sensor are arranged in the annulus of the casing pipe and the oil pipe close to the wellhead. The invention has reasonable and compact structure and convenient use, can monitor the temperature change in the shaft in real time by arranging the optical fiber composite cable, and the optical fiber composite cable is directly contacted with the carbon dioxide fluid, so that the instantaneous monitoring of the temperature in the shaft is realized, and the real-time performance and the accuracy of the monitoring are ensured.

Inventors

DING XINLU
CHEN JIANHUA
XIAN YUXI
WANG QIAN
WANG JINLI
ZHANG WENZHE
LIU HAILEI
JIANG JUNQIANG
CHEN FANG
LIU FEIYUE

Assignees

中国石油天然气集团有限公司
中国石油集团西部钻探工程有限公司

Dates

Publication Date: 20260508
Application Date: 20241108

Claims (6)

1. The utility model provides an injection controlling means of carbon dioxide injection well, its characterized in that includes the compound cable of optic fibre, the inboard optic fibre compound cable that can real-time supervision temperature that is equipped with down of oil pipe is connected with optic fibre real-time supervision system by last, the well head is equipped with well head pressure and temperature monitoring system, the well head is equipped with carbon dioxide injection system, carbon dioxide injection system exit end is equipped with pressure sensor and temperature sensor in the carbon dioxide injection pipe, be equipped with first pressure sensor and first temperature sensor in the annular space that is close to well head department sleeve pipe and oil pipe, be equipped with second pressure sensor and second temperature sensor in the oil pipe that is close to well head department, first pressure sensor and first temperature sensor, second pressure sensor and second temperature sensor are connected with well head pressure and temperature monitoring system.
2. The injection control device of a carbon dioxide injection well according to claim 1, wherein a roller is installed at the lower end of the oil pipe, the oil pipe is lowered, the cable passes through the annular space between the sleeve and the oil pipe, the coiled oil pipe is lowered in the oil pipe and connected with the cable, the coiled oil pipe is lifted to a wellhead after passing through the roller, the coiled oil pipe is removed, the optical fiber composite cable is connected with the cable positioned in the oil pipe, the cable positioned in the annular space is lifted, and the cable in the oil pipe pulls the optical fiber composite cable to move downwards so as to be positioned in the oil pipe.
3. The control method of the injection control device of the carbon dioxide injection well is characterized by comprising the steps of firstly determining the minimum miscible phase driving pressure of an underground injection layer, secondly setting the carbon dioxide injection speed to enable carbon dioxide in a shaft to be in a liquid phase in the whole injection process, determining the pressure and the temperature of a well head and the minimum miscible phase driving stratum pressure of a combined injection layer according to the set injection process, calculating a fluid motion equation in the shaft to obtain pressure distribution along the shaft, finally, carrying out initial injection, verifying the effectiveness of the whole system, and adjusting the injection process according to the injection pressure and the temperature.
4. A control method according to claim 3, wherein the minimum miscible flooding pressure of the subsurface injection layer is determined from formation properties, the pressure profile in the wellbore is calculated using the minimum miscible flooding pressure as a boundary condition downhole, and a wellhead pressure value is given.
5. A control method according to claim 3 or 4, characterized in that the pressure distribution in the wellbore is calculated according to the following formula: Wherein g is the gravity acceleration, 9.8m/s 2 is taken; P-the pressure at the point of the wellbore, pa; v-the flow rate of injected carbon dioxide in the tubing, m/s; z-vertical distance, m; The angle between the axis of the theta-shaft and the horizontal direction is theta=90° for a vertical injection well; ρ (T,P) —a function of density, temperature and pressure of carbon dioxide fluid, kg/m 3 ; lambda (T,P) -carbon dioxide fluid friction coefficient, function of temperature and pressure, dimensionless; r ti tubing radius; Assuming that the compressibility of the carbon dioxide fluid in the wellbore does not affect its velocity in the wellbore, i.e., is constant, the pressure gradient expression in the above equation may be reduced to: in a vertical well, where θ is 90 °, the above equation becomes: The expression for carbon dioxide fluid V is as follows: Wherein w is flow; from the gas state equation, the density of carbon dioxide can be obtained by considering the deviation coefficient of carbon dioxide, and the expression is as follows: m is the molar mass of carbon dioxide, and 0.04401kg/mol is taken; R-gas constant, 8.314472J/(K. Mol); Z (T,P) -the coefficient of deviation of carbon dioxide, a function of temperature and pressure, dimensionless; The deviation coefficient Z (T,P) of the carbon dioxide fluid injected into the well bore can be obtained through an RK state equation with wide temperature and pressure application; After considering the temperature dependence of fluid density and viscosity, simultaneous equation solution is required: a. temperature T (z) is first solved by the temperature distribution equation. B. Solving a pressure gradient equation to solve the pressure P (z) by using the obtained T (z) distribution; Discretizing and solving the equation by a numerical method to realize the coupling calculation of the fluid temperature distribution and the pressure gradient; And judging the phase change of the carbon dioxide in the shaft through the monitored temperature and the calculated pressure.
6. The control method according to claim 5, wherein the numerical method solving process is, First step, initializing Setting initial values according to the known boundary conditions of wellhead temperature T 0 and pressure P 0 , initializing the distribution of temperature T i and pressure P i and speed V i ; second step, iterative solving temperature distribution in time step Iteratively solving a temperature equation by using an explicit finite difference format to obtain a new temperature distribution T i n+1 ; Updating the fluid density ρ i n+1 and the viscosity μ i n+1 according to the new temperature T i n+1 ; And step three, updating the speed distribution: updating the velocity V i distribution among different nodes by combining a mass conservation equation or a flow velocity distribution hypothesis; fourth step, solving pressure distribution: Solving a new discrete momentum equation by utilizing a forward difference method, and gradually solving to obtain new pressure distribution P i n+1 ; Fifth step, checking convergence: comparing the current temperature and pressure distribution with the result of the previous time step, judging whether convergence is carried out, and if the difference value is smaller than a preset threshold value, considering that convergence is carried out; If not, returning to the second step to continue iteration.

Description

Injection control device and control method for carbon dioxide injection well Technical Field The invention relates to the technical field of carbon dioxide injection wells, in particular to an injection control device and an injection control method for a carbon dioxide injection well. Background Carbon dioxide capture, utilization and sequestration (CCUS) is one of the important means to cope with global climate change, and can greatly reduce the carbon dioxide gas emissions in the atmosphere. Carbon dioxide is injected into a reservoir of the oil and gas reservoir to drive the oil and gas, so that the oil and gas recovery ratio is improved, long-term sealing is realized, and the dual purposes of economy and carbon reduction are achieved. However, in the process of injecting carbon dioxide liquid fluid through a shaft, the liquid carbon dioxide in the shaft may be converted into a gaseous state or a critical state due to the increase of the temperature of the formation, so that the gas is difficult to be pressed into the formation, and higher requirements are set for surface equipment, so that huge potential safety hazards are caused. Thus, no phase transition occurs during the injection of liquid carbon dioxide throughout the wellbore. However, carbon dioxide enters the stratum at the bottom of the well in a supercritical state to form mixed phase flooding, so that the oil displacement effect can be improved to the greatest benefit. Therefore, the phase state of carbon dioxide injected into the section of the oil and gas reservoir keeps the best supercritical state oil displacement effect. There may also be local hyperthermia due to the pressure and temperature of the formation at the formation depth increasing with increasing wellbore depth. During carbon dioxide injection, the temperature in the wellbore decreases, and the formation conducts heat into the wellbore, possibly resulting in an increase in the temperature in the wellbore and a change in the phase of carbon dioxide gas to the wellbore. However, increasing the injection rate may effect a temperature drop in the wellbore, and the carbon dioxide phase may change from a gaseous or critical state to a liquid state, but increasing the injection pressure. Thus, monitoring the temperature in the wellbore in real time and maintaining the injection state where the carbon dioxide phase of the injection layer is critical is the optimal injection state. Monitoring the temperature in the wellbore in real time is a critical control parameter for carbon dioxide injection. Because of the relatively high speed of carbon dioxide injection in the well bore, the carbon dioxide phase change occurs instantaneously, and therefore, the sensitivity requirement for temperature monitoring in the well bore is high. The conventional temperature monitoring mode can not be directly applied to transient temperature in a shaft, so that local transient temperature can not be obtained in real time, and inaccuracy exists in control of a carbon dioxide injection well, so that the phase state of the carbon dioxide injection well is not easy to control, and the oil displacement effect is affected. Disclosure of Invention The invention provides an injection control device and an injection control method for a carbon dioxide injection well, which overcome the defects of the prior art, and can effectively solve the problem that the phase state of the carbon dioxide injection well is not easy to control and the oil displacement effect is affected because the traditional temperature monitoring mode cannot be directly applied to transient temperature monitoring in a shaft. The injection control device of the carbon dioxide injection well comprises an optical fiber composite cable, wherein the optical fiber composite cable capable of monitoring temperature in real time is arranged on the inner side of an oil pipe from top to bottom, the optical fiber composite cable is connected with an optical fiber real-time monitoring system, a wellhead is provided with a wellhead pressure and temperature monitoring system, the wellhead is provided with a carbon dioxide injection system, an outlet end of the carbon dioxide injection system is provided with a pressure sensor and a temperature sensor in a carbon dioxide injection pipe, a first pressure sensor and a first temperature sensor are arranged in an annular space between a sleeve pipe and the oil pipe close to the wellhead, a second pressure sensor and a second temperature sensor are arranged in the oil pipe close to the wellhead, and the first pressure sensor and the first temperature sensor, the second pressure sensor and the second temperature sensor are connected with the wellhead pressure and temperature monitoring system. The following are further optimizations and/or improvements to the above-described inventive solution: Preferably, the roller is arranged at the lower end of the oil pipe, the oil pipe is lowered, the cable passes throug