RU2847728C1 - Method for cleaning a well - Google Patents

Abstract

FIELD: oil and gas production industry.

SUBSTANCE: invention relates to the oil and gas industry, namely to methods for cleaning and flushing wells from plugs of mechanical impurities and/or sand. The method includes lowering a column of pump-compressor pipes (PCP) with an oblique cut-off at the bottom into the wellbore to the blockage caused by mechanical impurities and/or sand, feeding a flushing fluid and extracting it with mechanical impurities and/or sand through the annular space with gradual lowering of the tubing string until the design depth is reached, stopping the supply of the flushing fluid, resumption of the supply of flushing fluid with backwashing through the inter-pipe space and its withdrawal with mechanical impurities and/or sand through the tubing string, followed by the removal of the tubing string. Before lowering, the tubing string above the feather is equipped with at least one hollow cylindrical body with a plugged top pipe, installed coaxially inside, hermetically connected to the lower part of the casing along the perimeter and equipped in the upper half with side channels directed from the inside to the outside and from the top down at an angle of 17-25° to the vertical to connect its internal space with the internal space of the casing. The total cross-sectional area of the side channels is equal to the cross-sectional area of the pipe or no more than 20% greater than the cross-sectional area of the pipe to reduce hydraulic resistance.

EFFECT: increased reliability of operations by eliminating moving parts inside the devices used, environmental protection by eliminating soil contamination when well fluid is spilled at the wellhead during tubing lift.

1 cl, 1 dwg

Description

The invention relates to the oil and gas production industry, namely to methods for cleaning and flushing wells from plugs of mechanical impurities and/or sand.

A method is known for flushing the bottom of a well (RU patent No. 2527433, IPC E21B 21/00, published on 27.08.2014, Bulletin No. 24), which includes lowering a tubing string with a feather at the end into the well until the feather rests against the bottomhole contamination, pumping flushing fluid through the tubing string and collecting it through the annular space of the well, the technological operations of lowering the tubing string until the weight changes and flushing until the weight is restored continue until the weight of the tubing string hanger is restored, and a ripper is made at the lower end of the feather, and a partition is installed inside the feather, in which holes of a smaller diameter are made eccentrically above the ripper, and opposite the holes of a smaller diameter, a hole of a larger diameter is made in the partition, into which a return a valve that passes from the bottom up, with a valve cage, lower the tubing string with a feather at the end into the well until the feather rests against the bottomhole contamination, simultaneously rotate the tubing string and pump flushing fluid through the tubing string through small diameter holes and lift the flushing fluid through the annular space of the well, while the feather check valve is closed, continue rotating the tubing string with pumping flushing fluid through the tubing string until the tubing string hanger weight is unloaded at the bottomhole by 10 kN, then stop rotating the tubing string and pumping flushing fluid through the tubing string, switch the direction of flushing and pump flushing fluid through the annular space under a pressure not exceeding the permissible pressure on the casing well column, loosened washed-out cuttings are lifted along the tubing string until the weight of the tubing string hanger is restored, then the process operations are repeated as described above, from the simultaneous rotation of the tubing string with pumping of washing fluid along the tubing string until the weight of the tubing string hanger is restored while pumping of washing fluid through the annular space, the number of process operations depends on the cessation of restoring the weight of the tubing string hanger after pumping of washing fluid through the annular space.

A method for cleaning a well from a compacted sand plug is also known (RU patent No. 2756220, IPC E21B 37/00, published 09.28.2021 Bulletin No. 28), which includes lowering a tubing string into the well - tubing with a feather at the end until the feather rests against the bottomhole, with a ripper installed at the lower end of the feather, and a partition installed inside the feather, in which holes of a smaller diameter and a hole of a larger diameter are made eccentrically above the ripper, while above the partition opposite the hole of a large diameter, a check valve is installed that passes from the bottom up, pumping liquid through the tubing string through the holes of a small diameter with the rise of liquid through the annular space of the well, switching the direction of washing and lifting loosened washed-out cuttings along the tubing string until the weight of the tubing string hanger is restored by pumping liquid along annular space under a pressure not exceeding the permissible pressure on the well casing, characterized in that the tubing string, equipped at the bottom with a feather made in the form of a cylindrical nozzle with a peak at the end, is lowered into the well to the interval of the compacted sand plug, wherein the peak is made flat in the form of a rhombus with a transverse diagonal of a length equal to 0.9 of the internal diameter of the well, then a mechanical action is performed on the compacted sand plug until the upper layer of the compacted sand plug is loosened in 3-4 cycles, and in each cycle the weight of the tubing string is partially unloaded onto the compacted sand plug, the tubing string is lifted until the weight of the tubing string hanger is restored, and then the tubing string is turned from the wellhead, after the mechanical action on the compacted sand plug, a waste element is dropped from the wellhead into the tubing string, after the waste element is seated on the landing seat of the large hole In the partition, a hydromonitor effect is carried out on the compacted sand plug by pumping liquid through the tubing string through small-diameter holes located at different distances from the center of the cylindrical nozzle until the compacted sand plug is washed out, while during the hydromonitor effect, the tubing string is simultaneously lowered downwards with the possibility of partially unloading the weight of the tubing string onto the plug being washed out until the current bottomhole of the well is reached with the liquid rising through the annular space into the trough tank, after which the direction of washing is switched and by pumping the washing liquid through the annular space under a pressure not exceeding the permissible pressure on the casing string of the well, the washed-out sand is washed out along the tubing string into the trough tank.

The closest method is for flushing the well bottom (RU patent No. 2717167, IPC E21B 21/00, E21B 37/00, published 03/18/2020 Bulletin No. 8), characterized by lowering a tubing string with an oblique cut, equipped with a conical seat for replaceable nozzles, to the well bottom 2-2.5 meters above the current bottom, supplying flushing fluid and withdrawing it through the annular space of the well with a gradual lowering of the tubing string with an oblique cut, equipped with a conical seat for replaceable nozzles, until the oblique cut stops against the plug and the weight of the tubing string hanger changes, after which the supply of flushing fluid is stopped and the nozzle is discharged into the inner part The tubing string is then pumped with flushing fluid until the nozzle is seated in the conical seat for replaceable nozzles, which is determined by a sharp, sudden increase in pressure. The flushing fluid is then pumped through the tubing string through the nozzle and flushed with mechanical fractions are withdrawn through the annular space of the well until the design depth is reached. After this, the flushing fluid supply is stopped and the well is switched to reverse flushing, while the nozzle is removed along with the flushing fluid and mechanical impurities to the surface.

The disadvantages of all methods include the presence of moving elements inside, which, when interacting with mechanical particles, can jam in the closed or open position and prevent the possibility of filling the tubing string (TU) with liquid containing mechanical impurities or lifting liquid with mechanical impurities to the surface. When raising the TU, the drain holes become clogged (otherwise, the mechanical impurities are not retained inside the TU), and the well fluid located inside the TU spills out onto the wellhead, leading to contamination of the workplace and the surrounding soil, disrupting the environment.

The technical result is the creation of a method for cleaning a well, which makes it possible to increase the reliability of operations by eliminating moving elements inside the devices used and to protect the environment by eliminating soil contamination when well fluid is discharged onto the wellhead when the tubing string is raised.

The technical result is a method for cleaning a well, which includes lowering a tubing string with an oblique cut - a feather from below - into the well until a plug of mechanical impurities and/or sand is created, supplying flushing fluid and withdrawing it with mechanical impurities through the annular space of the well with gradual lowering of the tubing string until the design depth is reached, stopping the supply of flushing fluid, resuming the supply of flushing fluid with reverse flushing - through the annular space and withdrawing it with mechanical impurities and/or sand through the tubing string, followed by withdrawing the tubing string with flushing fluid and mechanical impurities and/or sand to the surface.

What is new is that before lowering the tubing string above the feather, it is equipped with at least one hollow cylindrical body with a branch pipe plugged at the top, installed coaxially inside, hermetically connected by the lower part along the perimeter with the body, and equipped in the upper half with lateral channels directed from the inside out and from the top down at an angle of 17-25º to the vertical to communicate its internal space with the internal space of the body, and the total cross-sectional area of the lateral channels is equal to the cross-sectional area of the branch pipe or no more than 20% greater than the cross-sectional area of the branch pipe to reduce hydraulic resistance.

The drawing shows a diagram of the implementation of the method with one housing.

The well cleaning method is implemented in the following sequence.

Initially, geophysical surveys (the author makes no claims) are used to determine the depth (h1) of plug 2 of mechanical impurities and/or sand in well 1, and to what depth (h2 – not shown) this plug 2 extends in well 1 (h2 – taken as the design depth), for example, to the physical bottom of the well or packer (not shown). Based on this, the thickness (Δh) of plug 2 is determined:

, [1]

where Δh is the thickness of the plug 2, m;

h1 – depth of plug 2, m;

h2 – design depth of plug 2, m.

The volume (V1) of plug 2 is determined using the formula:

, [2]

where V1 is the volume of plug 2, ^m3 ;

π ≈3.14 – constant;

D – internal diameter of well 1, m;

Δh – thickness of plug 2, m.

After which the internal diameter (D1) and length (L) of body 3 are determined based on the following conditions: the internal diameter (D1) of body 3 must be no less than the internal diameter (D2) of tubing string 4, but no more than 20% of this diameter (D2) (D1=(1-1.2)•D2), and the length (L) of body 3 must ensure an internal volume (V2) of body 3 that is 1.3–2 times greater than the volume (V1) of plug 2 (V2=(1.3-2)•V1).

The internal volume (V3) of body 3 is determined by the formula:

, [3]

where V2 is the internal volume of body 3, ^m3 ;

π ≈3.14 – constant;

D1 – internal diameter of the housing 3, m;

L – body length 3, m.

All conditions for casing 3 are selected empirically: firstly, if its internal diameter (D1) is less than the internal diameter (D2) of tubing string 4, then the hydraulic resistance for the liquid flow during direct or reverse flushing increases sharply, and if it is more – by 20% of the internal diameter (D2) of tubing string 4, then the external diameter of casing 3 will also increase, which will make it difficult to lower into well 1; secondly, if the internal volume (V2) of the housing 3 is less than 1.3 times greater than the volume (V1) of the plug 2, then a portion of the mechanical impurities and/or sand in the housing 3 from the plug 2 destroyed by direct flushing will accumulate above the lower level of the side channels 5 of the internal pipe 6 with their blocking and an increase in the resistance to the flow of liquid during backwashing, and more than 2 times - there will be excess internal space not used to collect mechanical impurities and/or sand from the destroyed plug 2, which increases the dimensions and, as a consequence, the metal content of the housing 3.

In this case, it is recommended that the length (L) of casing 3 should not exceed the length of the pipes (not shown) of tubing string 4, in order to avoid the use of longer-stroke and more expensive wellhead equipment (not shown) for tripping operations. If it is impossible to achieve an internal volume (V2) of casing 3 at least 1.3 times greater than the volume (V1) of plug 2 with an internal diameter (D1) of casing 3 and its length (L) not greater than the length of the pipes of tubing string 4, it is recommended to use two or more identical casings 3 (to simplify manufacturing) with a total length (ΣL) providing a total internal volume (ΣV2) of casing 3 1.3 - 2 times greater than the volume (V1) of plug 2 (ΣV2=(1.3-2)•V1).

The total internal volume (ΣV3) of body 3 is determined by the formula:

, [4]

where ΣV2 is the total internal volume of body 3, ^m3 ;

π ≈3.14 – constant;

D1 – internal diameter of the housing 3, m;

ΣL – total length of hull 3, m.

For each housing 3, identical nozzles 6, plugged at the top, are made, in the upper half of which lateral channels 5 are made, directed from the inside out and from top to bottom at an angle of α = 17-25º to the vertical for communicating their internal space with the internal space of the housing 3. Such an angle α = 17-25º to the vertical is selected empirically, since it ensures maximum collection in the housing 3 of mechanical impurities and / or sand from the destroyed plug 2. Moreover, in order to reduce the hydraulic resistance to the flow of liquid during direct and reverse flushing and not to make unnecessary inclined lateral channels 5 in the nozzle 6, the total cross-sectional area of the lateral channels 5 should be equal to or greater than 20% of the area of the internal diameter (D3) of the nozzle 6:

, [5]

where ΣS _k is the total area of channels 5, m ² ;

π ≈3.14 – constant;

D3 – internal diameter of pipe 6, m.

For final assembly, a corresponding branch pipe 6 is coaxially inserted into each housing 3, which is connected to the housing 3 at the bottom along the perimeter in a hermetically sealed manner (by welding, gluing, threading, etc.).

After which the assembled casings 3 are delivered to the well 1 for cleaning from the plug 2. Into the well 1, a feather 7, at least one casing 3, are successively lowered, which on the tubing string 2 are lowered into the well 1 up to the plug 2 (to a depth of h1), which is recorded by a decrease in the weight of the tubing string 2, registered by the wellhead weight indicator (UIN - not shown). After which, the wellhead pumping equipment (not shown) initiates the supply of drilling fluid along the tubing string 2 through at least one casing 3 channels 6 and feather 7, the collection of this fluid with very small particles of mechanical impurities (the settling velocity of which is greater than the flow velocity of the liquid in the annular space 8) through the annular space 8 of the well 1 with a gradual lowering of the tubing string 2 until the destruction of the entire plug 2, that is, until the design depth (h2) is reached. The supply of drilling fluid is stopped and then resumed with reverse flushing - through the annular space 8 and its collection with mechanical fractions and/or sand remaining in the well 1 after direct flushing, through the feather 7, casings 3 and the tubing string 2. In this case, the liquid from the branch pipe 6 through the channels 5 is directed from top to bottom into the corresponding casing 3, mechanical impurities and/or sand collide with each other and with the wall of the corresponding casing 3, sticking together, increasing in size and weight, and settle at the bottom of the corresponding casing 3. If the internal volume of this casing 3 is not enough to collect all the mechanical impurities and/or sand and their sediment level in the corresponding casing 3 reaches the level of the channels 5, then the remaining mechanical impurities and/or sand are washed into the next casing 3 located above, where they are collected in a similar manner, etc., until almost all the mechanical impurities are collected impurities and/or sand in casings 3. After pumping drilling fluid in a volume equal to at least one and a half times the internal volume of well 1, the fluid supply is stopped and tubing strings 2, casings 3 with drilling fluid and mechanical impurities and/or sand, and blade 7 are removed from well 1 to the surface. During lifting, the fluid from tubing string 2 flows under its own weight through the channels and blade 7 into well 1, thereby preventing the discharge of fluid from tubing string 2 at the wellhead. Casings 3 are disassembled and flushed of accumulated mechanical impurities and/or sand, after which casings 3 are again ready for operation.

As practice has shown, the absence of moving parts inside the 3-unit housing, compared to similar units, increases its service life by at least 2.5 times, and the period between repairs by at least 7 times.

The proposed well cleaning method allows for increased reliability of operations by eliminating moving elements within the devices used and for environmental protection by eliminating soil contamination when well fluid spills onto the wellhead when the tubing string is lifted.

Claims (1)

A method for cleaning a well, which includes lowering a tubing string (TUB) with an oblique feather cut from below into the well until a plug of mechanical impurities and/or sand is created, supplying flushing fluid and withdrawing it with mechanical impurities and/or sand through the annular space of the well with gradual lowering of the TUB string until the design depth is reached, stopping the supply of flushing fluid, resuming the supply of flushing fluid with reverse flushing through the annular space and withdrawing it with mechanical impurities and/or sand through the TUB string, followed by retrieving the TUB string with flushing fluid and mechanical impurities and/or sand to the daylight surface, characterized in that before lowering the TUB string above the feather, it is equipped with at least one hollow cylindrical body with a branch pipe plugged at the top, installed coaxially inside, hermetically connected by the lower part along the perimeter with the body and equipped in the upper half with side channels directed from the inside out and from top to bottom at an angle of 17-25° to the vertical to communicate their internal space with the internal space of the housing, and the total cross-sectional area of the side channels is equal to the cross-sectional area of the branch pipe or no more than 20% greater than the cross-sectional area of the branch pipe to reduce hydraulic resistance.