JP3243455B2 - How to repair a well using a pipe base screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for repairing a well using a pipe-based screen, and more particularly to a method which can be effectively achieved by applying a partial surging method.

[0002]

2. Description of the Related Art A pipe base screen is used as a well collecting pipe. The construction is such that a steel pipe is usually provided with a round hole having a diameter of about 16 to 20 mm and a water passage area of 10 to 15% based on the surface area of the steel pipe is provided as a pipe base. Iron square rods each having a side of about 5 to 6 mm are arranged at equal intervals in 8 to 24 rows (the number varies depending on the screen diameter to be manufactured) in the longitudinal direction of the pipe base and welded. Its outer diameter is 4-5mm on the upper side, 5mm in height, 3mm on the lower side.
An inverted trapezoidal wire formed to a degree is formed on the square bar as a pillow at a predetermined interval, for example, 1.5 mm, 2 mm, etc., at a width where water passes (this is referred to as a slot size). It is wound by spot welding.

[0003] The structure of the pipe base screen is as described above. However, in the wells using the pipe base screen, the gravel filled through the round hole of the pipe base is displaced because the wire of the screen is shifted or comes off. Fall into the well, and sand from the aquifer is mixed into the pumping water.

In the pipe base screen, the distance between the wire and the pipe base is large, so that the conventional finishing method is not sufficiently finished. In many cases, the sand is continuously lifted because the filled gravel does not function as a filter layer.

Conventionally, there has been no other way to prevent sand removal than to use a double casing or to reduce the amount of pumping extremely. However, even if a double casing is used, the sand is stopped by the conventional finishing method. It was difficult, and even if a triple casing was performed, the same result was obtained.

[0006] The reasons are the following two points. (1) In the case of a normal new well, a casing string is set in a borehole, and its annular gap is filled with gravel and finished.However, during the finishing, the filled gravel settles due to consolidation etc. Can be replenished from the ground. But,
Even after the completion of the well, the filling gravel outside the screen cannot be replenished even if the gravel falls into the well due to a defect in the screen and sand is raised. (2) In order to stop such sand lifting, fill the gravel into the aquifer around the screen, where the traces of sand erosion or hollowing out were found, and as much sand as possible was drawn into the well. Must be replaced to form a gravel filtration layer.

[0007]

The pipe base, which is the base of the screen, is durable and weaker than the blind steel pipe due to the holes, but the tensile strength and the strength against external pressure when used in a well are: There are few problems such as crushing and deformation.
However, since the wound wire is not welded to the steel bar serving as a pillow at all contact points, there is a serious drawback that the wound wire is easily detached by an external impact.

[0008] Further, the welding method performed at a key point is far from complete fusion bonding, and the accuracy of the screen slot size is inferior to that of the all-welded type screen. Particularly in the case of a corrosive water quality well, the spot joint is easily eroded and disappears, and the wire is displaced by the initial stress of the wound wire.

Each of a number of round holes formed in the peripheral wall of the pipe base has a sufficient cross-sectional area for water to pass therethrough, but becomes extremely large with respect to the particle size of the gravel filled on the outside of the screen. I have. Therefore, if the wire wound outside the round hole shifts or comes off for some reason and the round hole is exposed, the gravel and gravel of the outer layer flow into the well together with water, and sand is mixed into the pumped water. I do. And the pump breaks down due to repeated sand lifting, cavities are formed in the stratum, and finally the ground support is lost and the ground falls, so the well can not be used unless you take any action become.

[0010] If any trouble occurs in the well using the pipe base screen, an investigation into the well by an underwater television is performed. In the normal part of the screen part, keep the same distance from each other outside the round hole of the pipe base.
Three wires are observed, but in the abnormal part the wires are clearly displaced, and the wires are visible but clay-like and the gap is closed (this is also common in other types) Are often seen. In severe cases, there is no wire at all and the round hole is completely exposed. Further, in the case of a wire made of ordinary steel, there is a case that the wire is thinned or lost due to corrosion.

Usually, the inside of the pipe base or the screen portion is clearly illuminated by a strong light source. However, when there is no wire and there is some gravel, the round hole has a weak reflection of light rays and looks dark. Furthermore, when there is no gravel at all, the round hole looks black because there is no reflection of light rays, and the state of the cavity (container) can be easily visually recognized. In many cases, the image appears to be black.

The following four points can be considered as causes of the wire displacement. 1. When the casing pipe and the screen are inserted into the excavated well hole while being connected to each other, the screen portion comes into contact with a boulder or the like that accidentally protrudes from the hole wall, and the wire is rolled up. 2. When the dug hole is bent and the screen portion is rubbed against the hole wall, the wire of the screen portion is rolled up as described above. If the suspended casing pipe and the screen part cannot enter at some point, raising or lowering will definitely destroy the screen part. 3. When the casing pipe and screen connected (called a casing string) reach a predetermined depth, the surrounding area is filled with gravel, but if a large amount is put in at once, a bridging phenomenon occurs in a narrow place and it is deposited there,
Next, when the gravel falls at a stroke with some momentum, the wire of the screen part is easily slipped down. F
In the case of a material having a low strength such as RP, the screen portion is crushed by the gravel falling in a mass shape, and there is no end to the case where the screen portion is literally squashed and excavated. 4. When the pipe base screen is inserted again inside the well where the round hole is exposed and sand is mixed in the pumping water, the screen breaks in the same way when the screen part contacts the old pipe, so the lifting sand is can not stop.

At the time of rehabilitation, a double casing was used to fill the annular gap with gravel, and it was attempted to stop the sand from being lifted by the gravel wall. There were many things that did not exist. Even temporarily
Even if the lifted sand stopped temporarily, the well's pumping capacity was significantly reduced due to the high resistance of the filled gravel wall to running water.

The present invention is an optimum rehabilitation method for solving the above-mentioned problems, and can prevent sand from being lifted in a well using a pipe base screen without impairing the pumping capacity of the well.

[0015]

According to the present invention, there is provided a method for repairing a well using a pipe base screen, wherein a well using a pipe base screen is mixed with sand of an aquifer during pumping. A new casing string having a V-slot screen is inserted into the existing casing string so that both screens face each other. Gravel is filled into the annular gaps of the existing and new casing strings to a position higher than the still water level. And finishing by partial surging in the V slot screen, the filled gravel flows into the aquifer from the round hole of the pipe base to thicken the gravel wall, preventing sand and increasing the pumping capacity Let it.

The method of the first invention will be described more specifically as follows. (1) Dredge the sediment deposited on the bottom of an existing well with sand using a pipe base screen using an air lift or a baler. (2) A new casing that is about twice smaller than the existing pipe base screen, such as a new casing string (connection between casing and screen) using a 250 A V-slot screen for an existing pipe base screen of 350 A. Insert a string. (3) Fill the annular gap between the existing and new casing strings with gravel to a sufficiently high position above the still water level. The slot size of the V-slot screen and the particle size of the gravel are selected in advance based on the formation. (4) See FIG. 7 for the state in which the gravel is filled. Assuming that the bulk density of the packed gravel is γ _b (usually around 1.6 to 1.7), the annular column of the filled gravel is h ₁ γ _{b with} respect to the aquifer at the depth z.
It has a potential of + h ₂ (γ _b −1), but when the water in the aquifer is at rest, the compressive stress of the aquifer gravel is balanced with the pressing force of the packed gravel. (5) Perform strong finishing by partial surging in the V-slot screen. The following description describes a case where a partial surging method using a partial surging block (Japanese Patent No. 2881125) is applied. In a cycle in which the surging block repeats vertical single pendulum motion, when it is lifted from the bottom dead center, a powerful shock wave propagates to the stationary water in the aquifer, and the water is transferred to the pipe base screen, filled gravel. Through the wall and the V-slot screen, it is strongly sucked into the well and flows. At this time, the pore water pressure of the aquifer gravel particles receiving the pressing force in the packed gravel increases, and the buoyancy acting on the sand particles becomes much larger than at rest. Thus, the sand particles and water are disturbed (that is, turbulent and liquefied), and the sand particles can easily flow even at a low flow velocity equal to or lower than the outflow limit flow velocity. This phenomenon is due to the smaller the particle size of the sand,
The higher the filling gravel column, the faster the flow velocity, and the greater the difference in the flow velocity, the more noticeable it is.
This is similar to the phenomenon in which a sand layer saturated with water is liquefied by a large earthquake. The sand particles pass through the round hole of the pipe base screen and the filled gravel wall and flow into the well, and after a large amount of sand particles flow, the filled gravel settles down due to potential energy in the space of the aerated and hollow aquifer. Replace and increase the effective diameter of the well by increasing the wall thickness of the gravel over the length of the partial surging stroke (the inside only extends outward due to the V-slot screen). (6) Next, in the early stage when the surging block begins to fall by its own weight from top dead center, the water around the well, which had been in a state of continuing the flow by inertia, instantaneously reversed the flow direction, Sometimes sand is liquefied by applying a shock wave to the aquifer, so that the mixed liquid of the filled gravel and water presses and retreats the sand particles to thicken the filled gravel wall. Then, as the surging block goes down, the water gradually stops. (7) The sand is sucked into the well during the process of raising the surging block, and the thickness of the gravel wall increases in both the upper and lower processes. (8) Repeat the partial surging cycle,
Continue until the aquifer is no longer sandy. (9) The amount by which the gravel expanded the wall thickness toward the aquifer was
Refill to maintain the potential of the packed gravel. (10) If the number of exposed round holes in the pipe base screen is small and it is predicted that the flow of the filled gravel will not be sufficient during partial surging, The required number of round holes can also be exposed using a special tool that staggers the wire covering the round holes. (11) As described above, in the existing well to which the method of the present invention is applied, the flow velocity in the aquifer generated at the time of the suction of the partial surging is much larger than the flow velocity of the catchment at the time of daily pumping. The thick filled gravel wall becomes a sand filter layer, and at the same time, increases the effectiveness of the well and increases the porosity of the filter layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference numeral 1 denotes a well using an existing pipe base screen which needs repair. 2 is this well 1
Reference numeral 3 denotes a pipe base, and 4 denotes a round hole formed in the pipe base 3. Reference numeral 5 denotes a rod which is provided on the outer periphery of the pipe base 3 at an interval from each other and in the axial direction thereof. Reference numeral 6 denotes a wire wound around the outer periphery of the pipe base 3 outside the rod 5 at a distance S from each other.

Thus, the pipe base 3, the round hole 4, the rod 5, and the wire 6 form a pipe base screen 7, and the pipe base screen 7 and the casing 2 are appropriately connected to form an existing casing string 8. are doing.

The diameter D of the round hole 4 is sufficiently large with respect to the width W and the wire interval S of the wire 6, so that the opening surface of the round hole 4 is not closed by the wire 6. A portion where the wire interval S faces the opening surface of the round hole 4 forms a water flow gap 9.

When sand is mixed in the pumped water, the gravel G deposited on the bottom of the well 1 is dredged by an air lift or a baler (not shown).

When the dredging is completed, a new casing string 11 having a V-slot screen 10 is inserted into the existing casing string 8 so that the two screens 7 and 10 face each other. And both casing strings 8
In the annular gap A between the height h ₂ from the depth z to the still water level, and further up to a sufficiently high position h ₁ above the gravel 1
Fill 2

Further, partial surging is performed in the V-slot screen 10 to cause the gravel 12 to flow into the aquifer 13 from the round hole 4 of the pipe base 3 to thicken the filled gravel wall.

The well thus renovated has a thicker gravel wall facing the aquifer 13, so that sand is prevented from being pumped up and the pumping capacity is restored.

[0024]

According to the present invention, when sand from an aquifer is mixed during pumping in a well using a pipe base screen, a V-slot screen is inserted into the pipe base screen to face each other. Gravel is filled into the annular gap between the existing and new casing strings having a height higher than the still water level, and partial surging is performed in the V-slot screen, and the filled gravel is stripped from the round hole of the pipe base. Since the filling gravel wall is made thicker by flowing into the water layer, sand can be prevented from being lifted and the pumping ability can be restored.

[Brief description of the drawings]

FIG. 1 shows a specific example of a method for repairing a well using a pipe base screen according to the present invention, and is a partially cut-away side view of the well.

FIG. 2 is a cut-away side view of a portion of a screen.

FIG. 3 is an image obtained by observing a round hole of the screen from the inside with an underwater television camera, in which a wire is in a normal state.

FIG. 4 shows a state in which the wires are shifted.

FIG. 5 shows a case where a wire is largely displaced.

FIG. 6 shows a state in which the wire is completely removed from the round hole.

FIG. 7 is a cut-away side view of a well using a pipe base screen in a repaired state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Well 2 Casing 3 Pipe base 4 Round hole 5 Rod 6 Wire 7 Pipe base screen 8 Casing string 9 Water gap 10 V slot screen 11 New casing string 12 Gravel 13 Aquifer

Claims (1)

(57) [Claims] In a well (1) using a pipe base screen (7), when sand of an aquifer (13) is mixed during pumping, a V-slot is provided in an existing casing string (8). New casing string (11) with screen (10)
Into the annular gaps (A) of the existing and new casing strings (8, 11), and gravel (12) having an appropriate particle size up to a position higher than the hydrostatic level. Filling,
After finishing by the partial surging method in the V-slot screen (10), the filled gravel (12) flows into the aquifer (13) from the round hole (4) of the pipe base (3), and the filled gravel wall A method of repairing a well using a pipe base screen, characterized by thickening a pipe.