1. The purpose of wellbore cleaning
The wellbore is a "link container" that carries fluid from the formation to the wellhead, during the production cycle of the oil well, various impurities accumulate in the inner surface of the wellbore, resulting in smaller oil circulation diameter and poor storage environment，the operation of optimizing wellbore storage and circulation environment is called wellbore cleaning.
2. The wellbore cleaning technology solution
2.1 Clean the inner wall of the tubing
Main purpose3ARemove the surface accumulation, adhesion wax, heavy crude oil or other mechanical impurities in the upstream oil flow channel composed of pipe, rod and pump, optimize the flow path of oil and improve the efficiency of drilling system.
2.1.1 Hot oil flushing
Theory： Fluid into the annulus after heating, and then use the fluid pump lifting to the ground, fluid continuously circulation, gradually raise the temperature of wellbore, wax, heavy oil, mechanical impurities will gradually dissolve in wellbore fluid, discharge from the pipeline, and reach the wellbore paraffin, clear the purpose of impurity, improve the channel.
Features3A easy to operate, with compatible good output liquid to clean the well;It takes 8 ~ 14h to wash well.
Well selection conditions: the production fluid generally requires between 8 ~ 30m3 with water less than 40, and the sinking degree is suitable for pumping Wells between 100 and 300m.
2.1.2 Hollow rod cleaning
Theory3A Use a 36-mm hollow rod to replace the pumping rod of 1000m below the conventional pumping rod. The upper part is equipped with a special cleaning device, and the lowest part is a Check valve 。Through the hollow rod intermediate channel, the cleaning fluid enters the pipe through the check valve, under the pressure of pump，the cleaning fluid is discharged form tubing, to achieve the purpose of removing wax, purifying impurities and improving the diameter of wellbore.
Features3A high thermal energy efficiency, low water consumption, short cleaning time, no pollution oil layer, short recovery period, low vehicle volume and low cost of vehicle. However, the high cost of one-time input and high quality of hollow rod3B
The well selection condition3A it is suitable for heavy wax, shallow wax point, large shaft pump load, which leads to frequent test pump. It has higher producing ability; The road can ensure the smooth passage of boiler and water tanker.
2.1.3 Anti-pollution pipe cleaning
Theory3A26nbsp3BUsing the packer seal annulus, the side bypass compensator is adopted to form the annulus and the tubing channel after the packer is seated，it can isolate the flushing fluid from the formation contact, and the flushing fluid can be entered into the oil pipe by annulus.At the same time, the fluid in the well is returned to the annulus, which is also convenient for the pressure measurement of the well and the dynamic management of the well.
Features3A high degree of integration of pipe column, simple daily hot washing, and prevent reservoir damage, greatly improve the efficiency of wellbore pump, pipe and rod machine3B
The well selection condition3A It is suitable for well condition, and the pump cycle is long. The water supply is poor, the sink degree is low, and the wax is deep. The reservoir is sensitive and easy to be polluted; It can ensure the smooth passage of boiler and water tanker.
2.2 Annulus cleaning of tubing and casing.
Main purpose3A Remove impurities from wellbore, including casing wall and artificial pocket, improve the environment of annulus, ensure the operation and production of wellbore environment.
2.2.1. Well scraping and well cleaning
Theory3A using26nbsp;gauge check the wall of casing ，then using casing scraper scrape the inner wall of casing to remove the cement, hard wax, salt scale and burr on the inner wall of casing. After washing the well, remove the impurities from the wellbore and finally make sure the casing is smooth, so as to remove obstacles to other tools.
2.2.2 Foam fluid negative pressure flushing
Theory3A With the advantages of low density of foam fluid and strong ability to carry debris, it is effective to clean the bottom of the well；On the one hand, it reduces the leakage of the washing fluid to the layer, and on the other hand, it is more effective to carry the bottom debris or sand particles to the ground.
Features3A The well flushing fluid density is lowm forming negative pressure is not easy to leak； The viscosity of the fluid is high; Low return speed with strong portability；The fluid has good dispersibility and emulsibility, and it also has a good cleaning effect on other organic adhesives.
The well selection condition: ①The well is short of energy. ② Gas well, strongly sensitive formation well. ③ The layer is loose and easy to produce sand，conventional well cleaning is not complete.
2.2.3 Coiled tubing cleaning
Theory3A The coiled tubing operation equipment has the characteristics of pressure operation and continuous operationm and the equipment volume is small, the operation cycle is fast, the cost is low, and it is known as the 26quot3Buniversal operating machine26quot;. It is widely used in wellbore sand washing and well washing.
Features3A Coiled tubing can be carried out with pressure operation3B The construction is simple, the operation cycle is fast, can cooperate with a variety of well cleaning fluid to carry out the wellbore cleaning.
The well selection condition: ①High pressure，The well of gas well or oil and gas that is prone to overflow; ②he production of a well with a large impact on production;③The sensitivity of the reservoir is strong and the well is easily polluted.
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2.3 Wall cleaning
Main purpose3A Remove the skin pollution caused by mud cake and particle plugging near the perforation hole, reduce the skin coefficient and improve the conductivity of the near well zone.
2.3.1 Foam and fluid mix and unplug
Theory3A Through foam swallowing, negative pressure mixing, forming controllable well bottom negative pressure, The foam brings out the solid particles and organic precipitates in the near-well zone. ；At the same time, using the high speed return discharge fluid, it is used to wash the perforation of the perforation, dredge perforation hole, and achieve the purpose of relieving the reservoir blockage.
The well selection condition: ① Poor reservoir property and poor drainage capacity.; ② The mud and organic precipitation were mainly blocked.
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2.3.2 Use the coiled tubing water jet to remove the plug
Theory3A The continuous tubing has the characteristics of ductility and small outer diameter. The nozzle can be used to complete the flushing operation of the perforated sand plug, heavy oil plug and natural gas hydrate blockage through tubing or casing，The sprinkler head can be used to complete the flushing operation of the perforated sand plug, heavy oil plug and natural gas hydrate blockage through tubing or casing. Dredge the production channel and restore the capacity.
Features3A flexible construction, different fluid can be used according to the sensitivity of the reservoir. Different types of sprinkler head and changing joint can be provided according to the wellbore structure. Short construction period, high efficiency, good blocking effect.
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