Experimental device and method for evaluating influence of oil pipe impact load on integrity of cement sheath
Technical Field
The invention relates to an experimental device and method for influence of oil pipe impact load on integrity of a cement sheath in the field of petroleum engineering well cementation.
Background
The cementing cement sheath for the oil-gas well has the functions of protecting and supporting a casing in the oil-gas well, ensuring interlayer packing and preventing oil-gas water channeling. The cement sheath is not only required to bear the erosion of formation fluid in the underground environment, but also required to ensure the integrity of the cement sheath under the complex load of the construction pressure in formation rocks and a casing, and the safety exploitation of oil and gas is ensured.
At present, western gas fields in China generally face the problems of large depth of a producing zone, high pressure, high temperature and the like, and cement sheath often faces a severe service environment, which also provides challenges for various mechanical properties of the cement sheath and the integrity of the cement sheath. In the drilling process, the pressure in a shaft can be reduced or increased by circularly reducing the density, testing the pressure of the casing and other operations; during the oil testing and production testing, in the acidizing and fracturing stage, hundreds of low-density acid liquids or fracturing liquids are quickly squeezed into the stratum, so that the condition of low temperature and high pressure in a shaft is caused; in the production process, emergency shutdown and other accident handling procedures can also cause load impact on the cement sheath, even when in normal production, high-pressure high-temperature gas can cause thermal load to the annular space at the upper part of a production layer in an oil pipe, the oil pipe can randomly vibrate in a sleeve, and the continuous impact load can also bring influence and challenge to the integrity of the cement sheath.
In recent years, the loss of cement sheath integrity due to temperature and pressure changes within the casing has been widely studied. For example, the patent 'a dynamic test device and an experimental method for packing capacity of a well cementation cement sheath' (201611132395.6) can simulate temperature and pressure change, measure radial displacement of a sleeve and circumferential displacement of simulated surrounding rock, and research the packing capacity of the cement sheath under the condition of temperature and pressure cyclic loading; the cement sheath sealing integrity experimental device (SPE 168321) can simulate temperature and pressure changes, can simulate eccentricity and detect whether sealing failure occurs on a first interface, a second interface and a body of the cement sheath under the action of thermal load; the patent "a deep water well cementation cement sheath packing performance testing device" (CN 103174409A), adopts different types of materials to simulate different strata, and the instrument is provided with a strain gauge for measuring the strain of the cement sheath so as to calculate the stress, and the integrity of the cement sheath is tested by changing the internal pressure of the casing; a plurality of domestic research manufacturers also design own products aiming at the packing capacity of the cement sheath, and the main purposes are to simulate the underground temperature and pressure condition and detect whether the cement sheath is mechanically ineffective under the action of the internal pressure of the casing.
The currently developed device and experimental method are widely focused on the influence of temperature and pressure change in a shaft on the casing-cement sheath, and a research scheme that the impact load caused by continuous impact on the casing-cement sheath assembly due to vibration of an oil pipe in the production process influences the integrity of the cement sheath is not involved. For a high-temperature and high-pressure gas well, the integrity of a shaft can be ensured under the severe working condition of the drilling and oil testing process by the cement sheath, but in the normal production process, the pressure and temperature change of the shaft is more moderate than the drilling and oil testing, the cement sheath is damaged, so that the pressure of a well head is gradually pressed, and therefore, the influence rule and the damage mechanism of the continuous vibration of an oil pipe on the integrity of the cement sheath in the production process are researched, and the urgent affairs are made.
Disclosure of Invention
The invention aims to provide an experimental device for evaluating the influence of oil pipe impact load on the integrity of a cement sheath, which can simulate the actual temperature and pressure environment of the cement sheath in the underground, and can simulate the working condition that the oil pipe vibrates in a shaft to cause impact load on a casing-cement sheath, thereby providing a foundation for researching the influence of the oil pipe vibration on the integrity of the cement sheath and making up the defects of the current research and test means.
The invention also aims to provide a method for evaluating the influence of the impact load of the oil pipe on the integrity of the cement sheath by using the device, which has reliable principle and simple and convenient operation, can simulate the vibration process of the oil pipe, test and evaluate the influence of the oil pipe on the casing cement sheath assembly, and has wide market prospect.
In order to achieve the technical purpose, the invention adopts the following technical scheme.
The device can simulate that the continuous vibration of the oil pipe causes impact load to the sleeve pipe under the high-temperature and high-pressure conditions, detect and evaluate the influence of mechanical vibration on the integrity of the cement sheath, test the sealing failure of the cement sheath under any working condition, and judge the influence of the vibration of the oil pipe in actual operation on the cement sheath of the sleeve pipe.
The invention more truly simulates the influence of oil pipe vibration on the casing cement sheath, the upper limit of the temperature is 200 ℃, and simultaneously the pressure and the temperature can be changed in the experimental process. The upper limit of the pressure of the surrounding rock is simulated to be 100MPa, and the upper limit of the internal pressure of the sleeve is simulated to be 120 MPa.
An experimental device for evaluating the influence of oil pipe impact load on the integrity of a cement sheath mainly comprises a kettle body, a heating cover, a simulation surrounding rock, a sleeve, a vibrator, a filter screen, an eccentric seat and a gas inlet and outlet pipeline.
The kettle body is a hollow steel cylinder, the device is heated through a heating cover outside the kettle body, simulated surrounding rocks and a casing pipe are arranged in the kettle body, cement slurry is placed into an annular space between the simulated surrounding rocks and the casing pipe, after the cement slurry is cured to form a cement sheath, a simulated surrounding rocks-cement sheath-casing pipe combination body is formed in the kettle body, a vibrator is arranged in the casing pipe, and the kettle body can randomly vibrate in the casing pipe after being opened and mechanically impact the casing pipe wall.
The kettle body is provided with an upper kettle cover and a lower kettle cover; the contact parts of the upper kettle cover and the lower kettle cover and the end surfaces of the simulated surrounding rock-cement sheath-sleeve assembly are a filter screen, a sealing washer and an eccentric seat; the lower kettle cover is provided with a confining pressure boosting and reducing valve, and the upper kettle cover is provided with an internal pressure boosting and reducing valve; the upper kettle cover and the lower kettle cover are also provided with gas inlet and outlet pipelines which are communicated with the upper end surface and the lower end surface of the cement sheath; the gas inlet and outlet pipeline is provided with a gas inlet and a gas outlet, the gas inlet on the lower end surface of the cement sheath is connected with a nitrogen cylinder, and the gas outlet on the upper end surface of the cement sheath is connected with a gas flowmeter.
The jar is arranged in the sleeve, can realize stepless speed change, and can normally work in a high-temperature and high-pressure environment.
The upper kettle cover and the lower kettle cover are made of stainless steel materials, and the size of the upper kettle cover and the size of the lower kettle cover are matched with that of the kettle body, so that the purpose of sealing a 'simulated surrounding rock-cement sheath-casing' assembly is achieved.
The simulated surrounding rock is made of copper alloy, and experiments can be performed on the basis of reducing actual stratum geological parameters.
All pressure manifolds of the device are stainless steel pipelines capable of bearing 140 MPa.
The device is provided with a connecting component and a sealing element, wherein the connecting component is a thread, a nut and a pressing ring; the sealing element is a gasket and an O-shaped ring, and is made of polytetrafluoroethylene.
The invention can simulate the influence of the impact load of the oil pipe on the integrity of the cement sheath under the conditions of high temperature and high pressure when the casing is centered, can perform experiments under the simulation conditions of a large-belly well, an elliptical well, eccentricity, slurry mixing, uneven filling and the like, can adjust the internal structure of the device according to the actual condition, enriches the test structure and has wider research conditions.
The invention can also analyze the influence of the impact load of the oil pipe on the integrity of the cement sheath under the corrosion condition by changing the injection fluid at the end surface of the cement sheath.
The experimental method for testing the influence of the impact load of the oil pipe on the integrity of the cement sheath by using the device sequentially comprises the following steps:
(1) preparing required cement paste according to API specification, pouring the cement paste into an annular space of simulated surrounding rock and a casing, sealing an upper kettle cover, converting the temperature pressure into the temperature pressure in an experimental device through a corresponding equivalent model according to the temperature pressure during underground well cementation construction operation, and determining a maintenance condition and a series of experimental working conditions;
(2) connecting a gas inlet and outlet pipeline with a pressure pump, adjusting the temperature in the kettle body, the internal pressure of the sleeve, the ambient pressure outside the simulated surrounding rock and the pressure of the end face of the cement sheath to the maintenance condition, waiting for setting within a specified time according to the requirements of site construction, maintaining and hardening to form a ring, and forming a simulated surrounding rock-cement sheath-sleeve assembly;
(3) connecting a gas inlet on the lower end face of the cement sheath with a nitrogen cylinder, connecting a gas outlet on the upper end face of the cement sheath with a gas flowmeter, keeping the confining pressure constant, starting an experiment according to the experimental working condition, simultaneously starting a vibrator, simulating the vibration of an oil pipe in a sleeve, adjusting the temperature and pressure in the sleeve, adjusting the temperature and pressure to continue the experiment after stabilizing for a certain time, and monitoring the sealing failure condition of the cement sheath through the gas flowmeter;
(4) and taking out the simulated surrounding rock-cement sheath-casing assembly, carrying out microscopic detection, detecting micro cracks generated in the cement sheath and micro annular gaps generated at a first interface and a second interface, and analyzing the sealing failure mode of the cement sheath.
Compared with the prior art, the invention has the following beneficial effects:
the invention can simulate the impact load of the oil pipe on the integrity of the cement sheath, the former testing device simulates the deformation and damage conditions of the casing and the cement sheath under the temperature and pressure load, but in the actual production, the oil pipe vibrates in the casing and continuously impacts the casing, which can cause the impact load on the casing and the cement sheath and influence the integrity of the cement sheath.
Drawings
FIG. 1 is a schematic structural diagram of an experimental device for evaluating the influence of oil pipe impact load on the integrity of a cement sheath.
In the figure: 1-kettle body; 2-heating a cover; 3-simulating surrounding rock; 4-cement sheath; 5-sleeving a pipe; 6-a jar knocker; 7-putting on a kettle cover; 8-lower kettle cover; 9-a sealing gasket; 10-filtering the screen; 11-an eccentric seat; 12-internal pressure increasing and decreasing valve; 13-gas inlet and outlet pipes; 14-confining pressure increasing and reducing valve.
Detailed Description
The invention is further illustrated by the following figures and examples.
It should be noted that: without departing from the principle of the invention, a person skilled in the art can also make several modifications and refinements, which fall within the scope of protection of the claims of the present invention.
See fig. 1.
An experimental device for evaluating the influence of oil pipe impact load on the integrity of a cement sheath mainly comprises a kettle body 1, a heating cover 2, a simulated surrounding rock 3, a sleeve 5, a vibrator 6, a filter screen 10, a sealing washer 9, an eccentric seat 11 and a gas inlet and outlet pipeline 13.
The reactor body 1 is a hollow steel cylinder, a heating cover 2 is arranged outside the reactor body, a simulated surrounding rock 3 and a casing 5 are arranged in the reactor body, cement slurry is placed into an annular space between the simulated surrounding rock and the casing, after the cement slurry is cured to form a cement sheath 4, a simulated surrounding rock-cement sheath-casing assembly is formed in the reactor body, a vibrator 6 is arranged in the casing 5, and the reactor body can randomly vibrate in the casing after being opened and mechanically impact the casing wall.
The kettle body is provided with an upper kettle cover 7 and a lower kettle cover 8; the contact parts of the upper kettle cover 7, the lower kettle cover 8 and the end surfaces of the simulated surrounding rock-cement sheath-sleeve assembly are a filter screen 10, a sealing washer 9 and an eccentric seat 11; the upper kettle cover is provided with an internal pressure increasing and reducing valve 12, and the lower kettle cover is provided with a confining pressure increasing and reducing valve 14; the upper kettle cover and the lower kettle cover are also provided with gas inlet and outlet pipelines 13 which are communicated with the upper end surface and the lower end surface of the cement sheath; the gas inlet and outlet pipeline 13 is provided with a gas inlet and a gas outlet, the gas inlet on the lower end surface of the cement sheath is connected with a nitrogen cylinder, and the gas outlet on the upper end surface of the cement sheath is connected with a gas flowmeter.
(1) The test of the influence of the impact load of the oil pipe on the integrity of the cement sheath under the condition of casing centering comprises the following steps:
the method comprises the steps of researching the stratum temperature of a cement ring to be located at 120 ℃, researching the stratum pressure of the cement ring to be located at 50MPa, reducing the actual pipe column size to the device size according to a geometric model in an equal proportion, assembling an instrument, preparing to be poured with cement slurry, preparing the slurry by using a field application cement formula according to an API standard, placing the slurry into an annular space, sealing the instrument, converting the liquid column pressure in a shaft into the experimental casing internal pressure through a model according to the well cementation moment, setting the casing internal pressure, the confining pressure, the cement ring end face pressure and the maintenance temperature, and forming. According to subsequent actual working conditions, the experimental working conditions are converted through the model, namely the stratum pressure is kept constant, the internal pressure of the casing is changed, the experiment is started, the temperature and the pressure are adjusted, the vibrator is started, and meanwhile, whether the gas channeling occurs in the cement sheath is detected. And after the experiment is finished, taking out the 'simulated surrounding rock-cement sheath-casing' assembly, carrying out microscopic detection, detecting 1 and 2 interface cementation and cement sheath body damage conditions, and carrying out next analysis.
(2) The test of the influence of the impact load of the oil pipe on the integrity of the cement sheath under the eccentric condition of the casing pipe comprises the following steps:
adjusting the eccentric seats of the upper and lower kettle covers, approximately selecting 66.7%, 50% and 33.3% of eccentricity according to actual conditions, carrying out experiments, wherein the subsequent experimental process is similar to that under the centering condition of the sleeve, and is not repeated herein.
(3) The experiment of the influence of the impact load of the oil pipe on the integrity of the cement sheath under the condition of a big belly well hole:
the method is characterized in that the simulated surrounding rock is manufactured according to the actual underground well structure, the method is that the contact wall surface of the simulated surrounding rock and the cement sheath is made into a mode with a narrow upper part and a narrow middle part, and then the test is carried out according to the normal procedure.
(4) Testing the influence of the impact load of the oil pipe on the integrity of the cement sheath under the condition of uneven filling:
according to the actual underground cement sheath filling condition, blocky foam is unevenly placed in the annular space for cement injection, and then cement slurry is injected for testing.
(5) The test of the influence of the impact load of the oil pipe on the integrity of the cement sheath under the corrosion condition comprises the following steps:
after the device is assembled according to the method (1), injecting corrosive gas into the gas injection hole on the end surface of the cement sheath to continue the experiment, adjusting the pressure and the temperature, starting a vibrator, simulating the working condition on site, and detecting whether the cement sheath is in sealing failure; and then, repeating the experiment, wherein the difference is that the end face gas injection hole injects non-corrosive gas to detect whether the cement sheath is in sealing failure or not, and the influence of the corrosion of different fluids on the sealing capability of the cement sheath can be judged by comparing the time when the cement sheath is damaged.