CN112943167A

CN112943167A - Flushing fluid capable of quickly removing dead oil on pipe wall and flushing method thereof

Info

Publication number: CN112943167A
Application number: CN202110414049.1A
Authority: CN
Inventors: 马磊; 徐靖; 许发宾; 魏安超; 李祝军; 孟文波; 杨仲涵; 阳俊龙; 曹峰; 任松涛; 李大攀; 韩成; 邓文彪; 朱观进; 梅明阳; 杨志
Original assignee: CNOOC China Ltd Zhanjiang Branch
Current assignee: CNOOC China Ltd Zhanjiang Branch
Priority date: 2021-04-16
Filing date: 2021-04-16
Publication date: 2021-06-11
Anticipated expiration: 2041-04-16
Also published as: CN112943167B

Abstract

The invention discloses a well flushing fluid capable of quickly removing dead oil on a pipe wall and a well flushing method thereof, wherein the well flushing fluid comprises the following components in percentage by mass: 30-70% of dimethyl ether, 10-20% of mutual solvent, 3-5% of dispersing agent and the balance of water; the well flushing method comprises the steps of injecting well flushing liquid into the oil sleeve annulus for soaking in the normal production process; before the underground operation, the well is subjected to closed circulation, the original liquid in the air of the oil jacket ring is discharged, and a new well-flushing liquid is replaced. The invention provides a flushing fluid capable of quickly removing dead oil on a pipe wall and a flushing method thereof, which are used for solving the problems of low efficiency, long time consumption and high cost of a dead oil removing technology of an offshore oil field in the prior art and achieving the purposes of shortening the operation time of removing the dead oil in an oil jacket annulus of the offshore oil field, improving the downhole operation efficiency and reducing the operation cost.

Description

Flushing fluid capable of quickly removing dead oil on pipe wall and flushing method thereof

Technical Field

The invention relates to the field of oil and natural gas exploitation, in particular to a well flushing fluid capable of quickly removing dead oil on a pipe wall and a well flushing method thereof.

Background

In the oil well production process, the annular liquid level of the oil casing is relatively static, but gas in the well is often discharged through the annular space of the oil casing, the light component separated out in the crude oil can be taken away by the discharged gas, heavy components in the crude oil containing impurities such as silt and the like in the process, such as long-chain hydrocarbon, macromolecular asphaltene and injected chemical additives, such as polymer residues in tertiary oil recovery, can be adhered to the inner wall of the casing, and along with the lapse of production time, the heavy component substances form compact dead oil on the inner wall of the casing, thereby influencing the oil well production, particularly influencing the normal development of underground operation work such as pump inspection, packer entering and the like.

The dead oil is generally sensitive to temperature, namely the dead oil can be melted by heating, but the heat treatment efficiency of the dead oil on the casing is not high, and particularly for offshore oil fields, as the influence of seawater temperature on the riser is large, the efficiency of removing the dead oil by a heat treatment mode is lower, and the condition is particularly prominent on a semi-submersible oil production platform with deep seawater. In the prior art, a land oil field basically adopts a mechanical scraping method, namely dead oil on the inner wall of a casing is removed by using tools such as a milling cone or a drift size gauge after an oil pipe is pulled out, but the method can prolong the underground operation time and has low efficiency, and especially for the offshore oil field which is settled by daily fee, the mechanical scraping method is adopted to remove the dead oil, so that the underground operation cost is obviously increased, and the well is generally washed before underground operation in the offshore oil field. The well flushing is that the well flushing liquid is used for flushing dead oil on the pipe wall, generally, clean water or underground water at dozens of ℃ is pumped into a well, the principle of the well flushing operation is mainly that the dead oil in the annular space of an oil sleeve is flushed and removed through large-discharge high-flow-rate flushing, the removing efficiency is low, the required circulating well flushing time is also long, and the problems of low efficiency, long consumed time and high cost still exist. In conclusion, no oil sleeve annulus dead oil removing mode particularly suitable for the offshore oilfield development process exists in the prior art.

Disclosure of Invention

The invention provides a flushing fluid capable of quickly removing dead oil on a pipe wall and a flushing method thereof, which are used for solving the problems of low efficiency, long time consumption and high cost of a dead oil removing technology of an offshore oil field in the prior art and achieving the purposes of shortening the operation time of removing the dead oil in an oil jacket annulus of the offshore oil field, improving the downhole operation efficiency and reducing the operation cost.

The invention is realized by the following technical scheme:

a well flushing fluid capable of quickly removing dead oil on a pipe wall comprises the following components in percentage by mass: 30-70% of dimethyl ether, 10-20% of mutual solvent, 3-5% of dispersing agent and the balance of water.

For offshore oil fields, the mechanical scraping method and the traditional well flushing method for treating dead oil in an oil sleeve annulus in the prior art have the defects of low efficiency and long consumed time, so that the underground operation period is prolonged, and the cost is increased. Therefore, the invention firstly provides the well-flushing fluid capable of quickly removing dead oil on the pipe wall, wherein dimethyl ether is the substance with the minimum molecular weight in ether substances and has good dissolving capacity on long-chain hydrocarbon, colloid, asphaltene and the like. The application utilizes dimethyl ether as one of the main components of the flushing fluid, and utilizes the unique physicochemical properties: the saturated vapor pressure at normal temperature (20 ℃) is about 0.5MPa, the saturated vapor pressure is gaseous at normal temperature and normal pressure, the saturated vapor pressure is difficult to use as a solvent, however, the saturated vapor pressure is used in a well flushing fluid, and the saturated vapor pressure can naturally exist in a liquid state in a high-pressure environment in a well, so that the dissolution of the oil casing annulus, particularly the dead oil on the inner wall of the casing is fully realized. The mutual solvent helps to achieve sufficient dissolution of dimethyl ether with water. And because the density of the dimethyl ether is lower, the dimethyl ether can be dissolved with water at will after the mutual solvent is added, and the density of the flushing fluid can be flexibly adjusted by adjusting the component proportion, so that the flushing requirements of wells with different pressure coefficients are met, and the operation safety of oil jacket annular flushing is fully ensured. In addition, the adjustment of the components needs to meet the requirement that the mass percent of dimethyl ether is within a range of 30-70%, if the content of dimethyl ether is lower than the range, the dissolving effect of the flushing fluid on dead oil is weaker, and the flushing effect is not good, and if the content of dimethyl ether is higher than the range, the relative density of the dimethyl ether is only about 0.6, so that the overall density of the flushing fluid is lower no matter how the proportion of the other components is adjusted, and the safety of the oil jacket annulus in a static state cannot be ensured. The application also comprises a dispersing agent for dispersing the dead oil dissolved in the flushing fluid, and the dissolving capacity of the flushing fluid to the dead oil can be obviously improved. The principle of the flushing fluid for treating the dead oil on the inner wall of the oil sleeve ring air casing is that the dimethyl ether is used as a solvent to dissolve the dead oil on the inner wall of the casing, and the dimethyl ether is not used for achieving the effect of permeation and viscosity reduction. This application is except having the ability of the stagnant oil of washing away of ordinary flushing fluid, still can pour into the oil jacket annular space into, dissolve through soaking and clear away the stagnant oil, before needs carry out borehole operation, directly carry out airtight circulation, will soak this flushing fluid displacement in the oil jacket annular space out of the well can, later can directly play out oil pipe and carry out borehole operation such as pump replacement pump, consequently, use behind this application flushing fluid, need not to carry out pipe wall machinery before borehole operation and strike off, also need not long-time circulation to erode, the operating time that offshore oil field cleared away the oil jacket annular space stagnant oil has been showing, improve borehole operation efficiency, thereby the operating cost has been reduced, cost reduction increase is very showing.

Further, the mutual solvent is methanol and/or ethanol. The mutual solvent herein may be methanol alone, ethanol alone, or a mixture of methanol and ethanol.

Further, the dispersant is a surfactant. The surfactant is used as a dispersant in the scheme, and the surfactant in the scheme has a dispersing effect on the dead oil dissolved in the well-flushing fluid, so that the dissolved dead oil is prevented from being agglomerated again in the well-flushing fluid, and the surfactant is not mainly used for surface wetting reversal.

Further, the surfactant is a mixture of polyoxyethylene sorbitan monostearate and sorbitan tristearate. The polyoxyethylene sorbitan monostearate is obtained by reacting sorbitan monostearate with ethylene oxide, has excellent diffusion effect and can meet the use requirement of the dispersant in the application; in addition, the inventor of the present invention has found through a great deal of research and experiments that the polyoxyethylene sorbitan monostearate used as one of the dispersants has a good dissolution expansion effect in addition to a good dispersion effect, and can significantly increase the dissolving capacity for the dead oil. And sorbitan tristearate has a very good dispersing effect on dead oil. The scheme preferably selects two dispersants to be mixed for use, and experiments prove that the effect on the dispersion and the diffusion dissolution of the dead oil is excellent.

Further, the mass ratio of the polyoxyethylene sorbitan monostearate to the sorbitan tristearate is 3: 1. In the two dispersants, polyoxyethylene sorbitan monostearate is used as a main agent, and the optimal use effect is achieved when the proportion of the two dispersants is met.

A well washing method capable of quickly removing dead oil on a pipe wall comprises the following steps:

s1, pressurizing and preparing a well-flushing liquid in a closed container, and keeping the pressure higher than 0.5 MPa;

s2, injecting a well-flushing liquid into the oil sleeve annulus for soaking in the normal production process;

and S3, before the underground operation, performing closed circulation in the well, discharging the original liquid in the air of the oil jacket ring, and replacing with new well washing liquid.

The well flushing method is provided based on the well flushing liquid, and is different from the prior art in that the well flushing liquid can be injected into an annulus in the production process to soak, dissolve and remove dead oil on the pipe wall, the dead oil can play a role in the initial stage of dead oil forming to start dissolving, and the dead oil is prevented from being gradually accumulated to form a compact state; the well-flushing liquid dissolved with the dead oil is quickly discharged through closed circulation before the downhole operation (the closed circulation only needs one circulation period at least), then the oil pipe can be directly lifted out to carry out the downhole operation such as pump detection and pump replacement, the mechanical scraping of the pipe wall is not needed, the long-time circulating flushing is not needed, the operation time of removing the dead oil in the oil jacket annulus of the offshore oil field is obviously shortened, the downhole operation efficiency is improved, and the operation cost is reduced. In addition, the method adopts closed circulation to avoid gasification failure of dimethyl ether in the circulation process. Of course, if the operation time and cost are not considered, the closed circulation process in the application can also adopt an operation mode of large discharge and long-time flushing.

Further, the closed cycle is a positive cycle or a reverse cycle. So-called positive circulation, i.e. the circulation process of pumping fluid into the tubing through the christmas tree and displacing the well fluid from the annulus out of the well through the tubing head (tubing cross-over); reverse circulation is the process of pumping fluid into the annulus of the tubing string through the tubing head and displacing well fluid from the tubing out of the well through the christmas tree. Both of these two circulation modes are mature processes, and are not described herein. In the reverse circulation process, the oil pipe has smaller inner diameter, the upward return speed is higher, the carrying capacity is stronger, and the method is an optimal mode.

Furthermore, after the closed circulation is finished, the oil pipe is taken out, and the underground operation is directly carried out.

Furthermore, the density of the flushing fluid is adjusted by adjusting the mass percent of the dimethyl ether, so that the flushing requirements of wells with different pressure coefficients can be effectively met.

Further, in step S3, a closed circulation system is used to perform closed circulation, and the dimethyl ether in the discharged liquid is gasified and separated, so that the separated dimethyl ether is liquefied again for reuse, which is beneficial to reducing the use cost.

Compared with the prior art, the invention has the following advantages and beneficial effects:

1. the invention relates to a flushing fluid capable of quickly removing dead oil on a pipe wall and a flushing method thereof, which not only have the capability of flushing and removing the dead oil by using a common flushing fluid, but also can be injected into an oil sleeve annulus to remove the dead oil by soaking and dissolving, and directly carry out closed circulation before underground operation is required, so that the flushing fluid soaked in the oil sleeve annulus can be taken out of a well by displacing the flushing fluid out of the well, and then an oil pipe can be directly taken out to carry out underground operation such as pump detection and pump replacement.

2. According to the flushing fluid capable of quickly removing dead oil on the pipe wall and the flushing method thereof, the density of the flushing fluid can be flexibly adjusted by adjusting the component proportion, the flushing requirements of wells with different pressure coefficients are met, and the operation safety of oil jacket annular flushing is fully ensured.

3. The flushing fluid capable of quickly removing the dead oil on the pipe wall comprises a dispersing agent used for dispersing the dead oil dissolved in the flushing fluid, and can obviously improve the dissolving capacity of the flushing fluid to the dead oil. The mixture of polyoxyethylene sorbitan monostearate and tristearyl sorbitan is used as the dispersing agent, so that the dispersing agent not only meets the excellent dispersing effect, but also has good solvent expansion effect, and can obviously increase the dissolving capacity for dead oil.

4. The well flushing liquid capable of quickly removing dead oil on the pipe wall and the well flushing method thereof can gasify and separate dimethyl ether in discharged liquid, reliquefies the separated dimethyl ether for reuse, and are favorable for reducing use cost.

Drawings

The accompanying drawings, which are included to provide a further understanding of the embodiments of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principles of the invention. In the drawings:

FIG. 1 is a schematic flow chart of an embodiment of the present invention;

FIG. 2 is a schematic diagram of the connection of a closed cycle system according to an embodiment of the present invention.

Reference numbers and corresponding part names in the drawings:

1-a first gas-liquid separation tank, 2-a second gas-liquid separation tank, 3-a storage tank, 4-a temporary storage tank, 5-a dosing tank, 6-a first valve, 7-a second valve, 8-a third valve, 9-a liquid pump, 10-a fourth valve, 11-an emptying valve, 12-a liquid discharge valve, 13-a pressure reducing valve, 14-a first pressurizing valve, 15-a second pressurizing valve, 16-a first tee joint, 17-a second tee joint, 18-a first reversing valve, 19-a second reversing valve, 20-a first bypass pipe, 21-a second bypass pipe and 22-a charging pipe.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples and accompanying drawings, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not meant to limit the present invention.

Example 1:

the pressure coefficient of a certain well stratum is 0.8, the flushing fluid adopts 60 mass percent of dimethyl ether, 10 mass percent of methanol as mutual solvent, 3 mass percent of surfactant as dispersant, and the balance of water. Pressurizing the above components in a closed container to above 0.5MPa, mixing with a pump, and stirring to obtain the flushing fluid with relative density of 0.78. During normal production, the annular space can be filled with the flushing fluid from a well head, and dead oil in the annular space of the oil sleeve is removed through soaking and dissolving; or the well can be washed circularly after being soaked for a certain time before being washed so as to further utilize the flushing capacity to clean the dead oil on the casing wall; the flushing fluid can be used for soaking an oil sleeve annulus at ordinary times, and can be directly replaced by new flushing fluid in a circulating mode when the underground operation requirement exists, and only one cycle is circulated at the lowest.

After the circulation well washing is finished, if dimethyl ether needs to be recovered, the dimethyl ether can be gasified and separated, and then the gaseous dimethyl ether is pressurized, liquefied and stored by a booster pump so as to be reused next time. If the dimethyl ether is not recovered, the dimethyl ether is gasified, emptied and combusted through a pressure reducing valve.

Example 2:

the pressure coefficient of a certain well stratum is 0.9, the flushing fluid adopts dimethyl ether with the mass percent of 30%, a mixture of methanol and ethanol with the mass percent of 20% as a mutual solvent, a surfactant with the mass percent of 5% as a dispersant, and the rest is water. Pressurizing the above components in a closed container to above 0.5MPa, mixing with a pump, and stirring to obtain the flushing fluid with relative density of 0.88.

Example 3:

a well flushing fluid capable of quickly removing dead oil on a pipe wall comprises the following components in percentage by mass: 30-70% of dimethyl ether, 10-20% of mutual solvent, 3-5% of dispersing agent and the balance of water, wherein the dispersing agent is a surfactant.

In this example, the surfactant is a mixture of polyoxyethylene sorbitan monostearate and sorbitan tristearate, and the mass ratio of the polyoxyethylene sorbitan monostearate to the sorbitan tristearate is 3: 1.

In the embodiment, the mixture of polyoxyethylene sorbitan monostearate and tristearyl sorbitan is used as the dispersing agent, so that the dispersing agent not only meets the excellent dispersing effect, but also has good solvent expansion effect, and can obviously increase the dissolving capacity for dead oil.

In order to verify the formula effect in the present embodiment, the inventor further performs a comparative experiment as follows, wherein the experimental pressure and temperature in the present embodiment are equal to those in each proportion, the pressure and temperature are both 20 ℃ and normal temperature and 0.6MPa, the mutual solvent is methanol, the dissolution object of the experiment is dead oil scraped from the well by a conventional mechanical scraping method, and the total amount of the well-flushing fluid and the quality of the dead oil used in each experiment are equal. The results of the verification are shown in the following table:

as can be seen from the above comparison, comparative examples 1 to 3 used several surfactants, which are common in the field of oilfield chemistry, as dispersants, and their dissolution rates or final dissolution rates for dead oil were inferior to those of the present example; comparative example 5 used only polyoxyethylene sorbitan monostearate, which has a dissolution rate for dead oil closer to that of the present example, but the dissolution rate is relatively low; comparative example 6, which uses sorbitan tristearate only, has a dissolution rate for dead oil closer to that of the present example, but the final dissolution rate is relatively low; the comparative example 4 is different from the present example only in the ratio of the two dispersants, and the effect is slightly different from the present example. As can be seen from the above experimental data, in the present embodiment, the dissolution rate of the dead oil can be improved by the polyoxyethylene sorbitan monostearate, because the polyoxyethylene sorbitan monostearate provides a significant dissolution expansion effect for the well flushing fluid; by means of sorbitan tristearate, the dissolution rate of the dead oil can be increased, because sorbitan tristearate has an excellent effect of dispersing the dead oil. In conclusion, the experimental effect and the theoretical analysis and cognition of the inventor can mutually prove.

Example 4:

a method of flushing a well comprising the steps of:

s1, maintaining the pressure in the closed container to be higher than 0.5MPa, and preparing a well-flushing liquid; the density of the flushing fluid is adjusted by adjusting the mass percentage of the dimethyl ether on the premise of meeting the requirement of the pressure coefficient of the current operation well;

The closed circulation preferably adopts reverse circulation, and after the closed circulation is finished, the oil pipe is taken out, so that conventional underground operation can be directly carried out.

Preferably, the sealed circulation is performed by a sealed circulation system, and the dimethyl ether in the discharged liquid is gasified and separated, and the separated dimethyl ether is liquefied again and reused.

Example 5:

on the basis of embodiment 4, the closed circulation system in this embodiment is shown in fig. 2, and includes a first gas-liquid separation tank 1, a second gas-liquid separation tank 2, a storage tank 3, a temporary storage tank 4, and a batching tank 5 communicated with the temporary storage tank 4; wherein a first valve 6 is arranged between the first gas-liquid separation tank 1 and the second gas-liquid separation tank 2, a second valve 7 is arranged between the second gas-liquid separation tank 2 and the storage tank 3, a third valve 8 is arranged between the storage tank 3 and the temporary storage tank 4, and a liquid pump 9 and a fourth valve 10 are arranged between the batching tank 5 and the temporary storage tank 4; an emptying valve 11 is arranged at the top of the first gas-liquid separation tank 1, a drain valve 12 is arranged at the bottom of the second gas-liquid separation tank 2, a pressure reducing valve 13 and a first pressurizing valve 14 are arranged at the top of the storage tank 3, and a second pressurizing valve 15 is arranged at the top of the temporary storage tank 4.

In the design process of the closed circulation system, the special problems in the well washing method are considered: the reason why the method can be normally implemented is that when the well washing liquid is in the well, the dimethyl ether can naturally keep liquid state under the action of the liquid column pressure and the casing pressure in the well, and is fully dissolved with water under the action of the mutual solvent; in the circulating well washing process, as the fluid is continuously replaced and rises, the liquid column pressure is reduced, and the dimethyl ether is likely to be gasified, so that the function of the well washing liquid is interfered, and therefore, closed circulation is needed to ensure the pressure stability and avoid the gasification of the dimethyl ether; in addition, a core problem is that although most of gas in the well can be automatically discharged through the oil casing annulus, a small amount of small-scale bubbles still remain in the well, most of the bubbles are attached to the surface of dead oil, and after the dead oil is dissolved by the flushing fluid, the bubbles are suspended in the annulus and cannot rise automatically due to the fact that the bubbles are pressed by the pressure of a fluid column. However, in the circulating well washing process, the bubbles gradually return along with the well washing liquid, the liquid column pressure is continuously reduced and the bubbles gradually increase in the upward return process until the bubbles reach the ground and enter the closed container along with the dimethyl ether liquid to be destroyed, and at the moment, because the dimethyl ether needs to be recycled, the pressure needs to be applied to the closed container, so that the dimethyl ether is liquefied. However, most of the bubbles contain a large amount of light alkane components, wherein methane and ethane cannot be kept in a liquid state and still keep in a gaseous state, and butane and propane have large possibility of liquefaction, and are mixed with dimethyl ether after liquefaction, so that the subsequent recycling is not facilitated. Therefore, the embodiment is particularly provided with the closed circulating system, so that the dimethyl ether can be fully separated and recycled.

The use method of the closed circulating system comprises the following steps:

(a) the fluid returned from the well enters a first gas-liquid separation tank 1, the pressure in the first gas-liquid separation tank 1 is kept to be more than 0.5MPa and less than 2MPa, at the moment, dimethyl ether is kept in a liquid state and possibly mixed with propane and butane liquid, and methane, ethane or SO is mixed in the gas₂Gas-liquid separation is carried out on the gas in the well through a first gas-liquid separation tank 1, wherein the liquid enters a second gas-liquid separation tank 2 through a first valve 6, and the gas is discharged from an emptying valve 11 at the top and ignited;

(b) the liquid enters a second gas-liquid separation tank 2 for temporary storage, the pressure in the storage tank 3 is reduced to be below 0.5MPa through a pressure reducing valve 13, then a second valve 7 is opened, the pressure in the second gas-liquid separation tank 2 and the pressure in the storage tank 3 are automatically balanced to be 0.3-0.5 MPa, and at the moment, dimethyl ether in the second gas-liquid separation tank 2 is gasified and enters the storage tank 3 through the second valve 7; in the process, the impurity alkane mixed in the liquid still remains in a liquid state in the second gas-liquid separation tank 2 and is discharged through the liquid discharge valve 12 when appropriate, so that the purity of the dimethyl ether entering the storage tank 3 can be fully ensured;

(c) closing the second valve 7 to enable the storage tank 3 to form a closed space, pressurizing to above 0.5MPa through the first pressurizing valve 14 to enable the gaseous dimethyl ether to be liquefied again in the storage tank 3, and keeping the pressure higher than 0.5MPa to enable the liquid dimethyl ether to enter the temporary storage tank 4 for temporary storage;

(d) after the dosing tank 5 is matched with the mutual solvent, the dispersing agent and the water, the mixed solution is pumped into the temporary storage tank 4 through the liquid pump 9 and is fully and uniformly mixed with the recovered dimethyl ether again to form new well-flushing liquid, and then the mixed solution can enter the well again to participate in circulation.

The embodiment can realize uninterrupted recycling of dimethyl ether in the circulating process, and only needs to keep the normally closed state of the first gas-liquid separation tank 1, and then performs gas-liquid separation once after a period of time (according to the internal pressure or liquid level condition, the time interval is determined). The embodiment can realize the sufficient removal of a small amount of alkane impurities in the well-flushing liquid which is circulated out of the well, and obviously improves the purity of the recovered dimethyl ether. The embodiment shown in FIG. 2 is a reverse circulation process, i.e., flushing fluid is displaced from the tubing cross-section into the annulus and is discharged from the Christmas tree by-pass into the well.

Example 6:

on the basis of example 5, this example further optimizes dosing tank 5. As shown in fig. 2, a feed pipe 22 is arranged at the top of the batching tank 5, a first three-way joint 16 and a second three-way joint 17 which are distributed up and down are arranged on the feed pipe 22, and a first reversing valve 18 and a second reversing valve 19 are respectively arranged in the first three-way joint 16 and the second three-way joint 17 and respectively correspond to the first bypass pipe 20 and the second bypass pipe 21.

When the dimethyl ether quality of retrieving in the jar 4 of keeping in is enough, need not to increase when dimethyl ether, this embodiment only needs first switching-over valve 18 of adjustment, second switching-over valve 19 all to communicate filling tube 22, closes first bypass pipe 20, second bypass pipe 21 promptly, directly adds mutual solvent, dispersant and water to batching jar 5 in through filling tube 22 and premix can.

When the quality of the dimethyl ether recovered in the temporary storage tank 4 is not enough, when the dimethyl ether needs to be increased, adjust the first reversing valve 18 and the communication direction of the second reversing valve 19, so that the first bypass pipe 20 is closed and the second bypass pipe 21 is opened, at the moment, the nitrogen gas is introduced into the feeding pipe 22 firstly, until the nitrogen gas can be detected at the outlet end of the second bypass pipe 21, at the moment, the first bypass pipe 20 is communicated with the dimethyl ether adding equipment, the direction of the first reversing valve 18 is switched, the first bypass pipe 20 is opened, the dimethyl ether is introduced at the moment, the dimethyl ether enters the feeding pipe from the first bypass pipe 20, and then enters the temporary storage tank 4 through the second reversing valve 19. The embodiment can guarantee the safety in the process of adding dimethyl ether, discharges air in the feeding pipe in advance, obviously reduces the operation hidden danger, improves the security performance of circulation batching.

Preferably, a needle valve can be arranged at the top of the temporary storage tank 4, and nitrogen is introduced into the temporary storage tank 4 before the ingredients are mixed until the nitrogen is discharged from the needle valve; alternatively, the entire pipeline is purged with nitrogen prior to operation.

It is noted that, herein, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Further, the term "connected" used herein may be directly connected or indirectly connected via other components without being particularly described.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are merely exemplary embodiments of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. The well-flushing fluid capable of quickly removing dead oil on the pipe wall is characterized by comprising the following components in percentage by mass: 30-70% of dimethyl ether, 10-20% of mutual solvent, 3-5% of dispersing agent and the balance of water.

2. The well-flushing fluid capable of rapidly removing dead oil from pipe wall of claim 1, wherein the mutual solvent is methanol and/or ethanol.

3. The well-flushing fluid capable of rapidly removing dead oil from pipe wall as claimed in claim 1, wherein said dispersant is a surfactant.

4. The well-flushing fluid capable of rapidly removing dead oil from pipe wall according to claim 3, wherein the surfactant is a mixture of polyoxyethylene sorbitan monostearate and sorbitan tristearate.

5. The well-flushing fluid capable of rapidly removing dead oil from pipe walls as claimed in claim 4, wherein the mass ratio of polyoxyethylene sorbitan monostearate to sorbitan tristearate is 3: 1.

6. A well washing method of well washing liquid capable of rapidly removing dead oil on the wall of a pipe based on any one of claims 1 to 5, characterized by comprising the following steps:

7. A method of well flushing according to claim 6 wherein the closed cycle is a forward cycle or a reverse cycle.

8. A method according to claim 6, wherein after completion of the closed circuit, the tubing is pulled out and the downhole operation is carried out directly.

9. A method of well flushing according to claim 6 wherein the flushing fluid density is adjusted by adjusting the mass percentage of dimethyl ether.

10. The well washing method according to claim 6, wherein in step S3, the sealed circulation is performed by a sealed circulation system, and the dimethyl ether in the discharged liquid is gasified and separated, and the separated dimethyl ether is liquefied again for reuse.