NO346845B1 - Oil/gas well structure and method for extracting a filter string from the well. - Google Patents

Description

OIL/GAS WELL STRUCTURE TO FACILITATE WITHDRAWAL OF A DOWNHOLE FILTER STRING AND METHOD FOR WITHDRAWING THE STRING

Technical area

The present invention relates to the oil extraction area, and in particular relates to an oil/gas well structure to facilitate the extraction of a downhole filter string and a method for extracting the downhole filter string from the oil/gas well. Here, oil/gas well refers to a production well in the broadest sense in the development of oil/gas fields and includes oil wells, gas wells, natural gas wells, injection wells, etc.

Background technology

The completion structure of most oil/gas wells with mechanical sand control comprises an oil/gas well and a downhole filter string inserted into the oil/gas well. The oil/gas well includes a vertical well, a deviation well, a high deviation well and a horizontal well. As shown in the figure, reference number 1 in figure 1 indicates a borehole wall in an oil/gas well, reference number 2 indicates a downhole filter string, reference number 3 indicates an annulus between the downhole filter string and the borehole wall, reference number 4 indicates a packer (eng. packer) to hang the downhole filter string. Here, the downhole filter string is a downhole filter string in the broadest sense and has several forms. In a first case, for example, there is a downhole filter string without a flow-limiting function, which serves only as a sand control filter and which is also called a sand control screen ("sand control screen"). In another case, there is a filter which has a flow-controlling function, i.e. a flow-control filter string which is also called a flow-control screen. The flow control filter has a flow control function, but at the same time also a filter function whose function is sometimes to prevent an anti-channeling particulate medium outside the flow control filter from entering a wellbore, and which also has the function of preventing formation sand from entering the wellbore when rotating about a sand production well. The flow-controlling function of the flow-control filter also implies a flow-limiting function.

Downhole filter string denotes a string formed by connecting one or more downhole filters in series. For example, a sand control screen with a total length of 300 meters, which is arranged in a horizontal well, is formed by connecting 30 sand control screens of approximately 10 meters in series.

In an oil/gas well containing the downhole filter string, the following two cases may exist on the outside of the downhole filter string: a case where artificially filled gravel, which includes quartz sand or ceramsite, is present around the downhole filter string; the other case where no fillers are present on the outside of the downhole filter string. When no fillers are present on the outside of the downhole filter string, the produced formation sand, after a certain production time at a sand production well, can also fill up the annulus between the downhole filter string and the borehole wall, as shown in Figure 1. Reference number 5 in Figure 1 indicates formation sand or artificially filled gravel that has accumulated on the outside of the downhole filter string. Both naturally filled formation sand and artificially filled gravel generate great resistance when a downhole filter string is pulled, so that it is difficult to pull out a downhole filter string in an oil/gas well. Especially for a well with a long downhole filter string, such as a high deviation well and a horizontal well, it is almost impossible to extract a downhole filter string.

In several cases, however, it is necessary to extract a downhole filter string, such as in the following cases:

1. When it is necessary to repair a damaged downhole filter string or to replace a downhole filter string;

2. When it is necessary to recycle extracted downhole filter strings to save large costs; and

3. When using a flow control filter string, the extraction of a flow control filter string in the production process can facilitate the regulation of the flow control filter string's flow control parameters, to achieve adaptation to the flow requirements of different recovery stages and to improve the production efficiency of an oil/gas well.

Currently, there is still no oil/gas well structure that facilitates the extraction of a downhole filter string, nor any particularly efficient method for extracting a downhole filter string from an oil/gas well.

Summary of the invention

The technical problem which the present invention is to solve is to provide an oil/gas well structure which facilitates the extraction of a downhole filter string and a method for extracting a downhole filter string from an oil/gas well.

To solve the above-mentioned problem, the invention uses the following technical solution:

The oil/gas well structure of the present invention to facilitate the extraction of a downhole filter string comprises a borehole wall and a downhole filter string installed in the oil/gas well. An end of the downhole filter string that is close to the wellhead is an upper end of the filter string and is firmly connected to the borehole wall. An annulus is formed between the downhole filter string and the borehole wall. The annulus between the downhole filter string and the borehole wall is filled with ultralight particles. A density of the ultralight particles approaches or corresponds to a density of a carrier fluid for carrying the ultralight particles. The carrier fluid for carrying the ultralight particles is a liquid for carrying and transporting the ultralight particles into the annulus, or for flushing back and transporting the ultralight particles out of the annulus. The ultralight particles are cross-linked styrene and divinylbenzene copolymer particles with an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm<3>.

The ultralight particles and the carrier fluid for the ultralight particles have a density difference within a range of -0.35 to 0.35, which range contains these two endpoint values.

Preferably, the ultralight particles and the carrier fluid for the ultralight particles have a density difference within a range of -0.3 to 0.3, which range contains these two endpoint values.

ultralight particles can be macromolecular polymer particles.

Preferably, the ultralight particles are high density polyethylene particles with an average particle diameter of 0.05-0.8 mm and an actual density of 0.90-0.98 g/cm<3>.

Alternatively, the ultralight particles are cross-linked styrene and divinylbenzene copolymer particles with an average particle diameter of 0.05-0.8 mm and an actual density of 0.94-1.08 g/cm<3>.

The present invention also relates to a method for extracting a downhole filter string from an oil/gas structure to facilitate the extraction of a downhole filter string, which method includes the following steps:

1) Creating channels by opening an annulus between an upper end of a downhole filter string and a borehole wall;

2) removing ultralight particles using a backwash carrier fluid by injecting an ultralight particle carrier fluid into the downhole filter string to backwash and carry the ultralight particles away from the annulus;

3) Pull out the downhole filter string.

When the downhole filter string is a flow control filter string, the step of removing ultralight particles by means of a carrier fluid for backwashing takes place so that a fluid injection pipe is connected to the downhole filter string and the ultralight particle carrier fluid is injected directly into the downhole filter string. Due to a flow controlling action of the flow control filter string, the injection fluid is uniformly injected into the ultralight particles from different segments of the flow control filter string, and the ultralight particles that have accumulated on the outside of the downhole filter string are removed by means of an upper fluid flow passage of the downhole filter string.

When the downhole filter string is a flow control filter string, the step of removing ultralight particles by means of a carrier fluid for backwashing takes place so that a fluid injection pipe is introduced into the downhole filter string, in which the fluid injection pipe is used to perform fluid injection. A lower portion of the fluid injection tube has an opening, and an upper portion thereof is provided with a sealing ring having an outer diameter substantially identical to an inner diameter of the downhole filter string.

The fluid injection is carried out in sections, where the fluid injection pipe is gradually introduced into the bottom of the downhole filter string for sectionwise fluid injection and sectionwise removal of ultralight particles on the outside of the downhole filter string from the top of the downhole filter string. When the ultralight particles on the outside of a front segment up to the downhole filter string near the wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string of another segment, until the particles on the outside of the downhole filter string are completely removed. Alternatively, it is possible to move the fluid injection tube continuously to perform fluid injection until the ultralight particles on the outside of the downhole filter string are removed.

When the downhole filter string is a downhole filter string without a flow limiting function, then the step of removing ultralight particles by means of a carrier fluid for backwashing takes place so that a fluid injection pipe is inserted into the downhole filter string, in which the fluid injection pipe is used to perform fluid injection. A lower part of the fluid injection pipe has an opening, and an upper part thereof is provided with a sealing ring with an outer diameter which is substantially identical to an inner diameter of the downhole filter string, in which the fluid injection is carried out sectionwise.

The fluid injection tube is gradually fed into a bottom of the downhole filter string for sectionwise fluid injection and sectionwise removal of ultralight particles on the outside of the downhole filter string from the top of the downhole filter string. When the ultralight particles on the outside of a front segment of the downhole filter string near the wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string to another segment, until the particles on the outside of the downhole filter string are completely removed. The fluid injection pipe can be moved in a manner such that the fluid injection pipe is continuously moved to perform fluid injection until the ultralight particles on the outside of the downhole filter string are removed.

Preferably, the carrier fluid for ultralight particles as defined in the present invention is water or a water solution.

The present invention uses a carrier fluid for ultralight particles with a density of about 1 g/cm<3 >and uses ultralight particles with a real density very close to the density of the carrier fluid, so that the carrier fluid can easily carry the ultralight particles to fill them in an annulus between the downhole filter string and the borehole wall, as they are filled in and fill up the annulus between the downhole filter string and the borehole wall. A portion of the carrier fluid enters the downhole filter string and returns to the bottom surface, and a further portion of the carrier fluid penetrates into the formation through the borehole wall. Finally, a completion structure is formed in which ultralight particles fill up the annulus between the downhole filter string and the borehole wall.

The ultralight particles occupy the annulus space between the downhole filter string and the borehole wall and at the same time block the accumulation of formation sand in the annulus space between the downhole filter string and the borehole wall.

The present invention uses particles with an average particle diameter of 0.05-1.2 mm and a real density of 0.7-1.3 g/cm<3> as ultralight particles to fill the annulus between the downhole filter string and the borehole wall. When it becomes necessary to pull out the downhole filter string, it is possible to easily remove the ultralight particles that have accumulated on the outside of the downhole filter string. Because the density of the ultralight particles is very close to the density of the carrier fluid, the carrier fluid circulating at a low speed can easily carry the ultralight particles down to the bottom and remove the ultralight particles in the annulus on the outside of the downhole filter string, so that the downhole filter string can easily extracted from the oil well. The requirements for the extraction of a downhole filter string are thereby fulfilled.

The method as defined in the invention, which is easy to carry out, overcomes the difficulties with the extraction of a downhole filter string in an oil well and thus simplifies production. In addition, the removed ultralight particles can be recycled and thereby greatly reduce production costs.

Description of the drawings

Figure 1 is an outline of a completion structure as defined in the background art.

Figure 2 is a drawing of a completion structure as defined in embodiment 1 of the present invention.

Figure 3 is a diagram of a flow path of a carrier fluid for backwashing and removal of ultralight particles on the outside of a filter string as defined in embodiment 2 of the present invention.

Figure 4 is a diagram of a flow path of a carrier fluid for backwashing and removal of ultralight particles on the outside of a filter string as defined in embodiment 3 of the present invention.

Figure 5 is a diagram of a flow path of a carrier fluid for backwashing and removal of ultralight particles on the outside of a filter string as defined in embodiment 4 of the present invention.

Figure 6 is a view of an oil/gas well structure after removal of ultralight particles as defined in the present invention.

Detailed description of preferred embodiments

Embodiment 1

As shown in Figure 2, an oil/gas well structure to simplify the extraction of a downhole filter string as defined in the present invention comprises a borehole wall 1 to an oil/gas well and a downhole filter string 2 introduced into the oil/gas well. A packer 4 for hanging the downhole filter string is provided between one end of the downhole filter string near the wellhead and the borehole wall. An annulus is formed between the downhole filter string and the borehole wall. The annulus between the downhole filter string and the borehole wall is filled with ultralight particles 6.

Embodiment 2 Method of extracting a flow control filter string

In the completion structure as shown in Figure 2 and as defined in Embodiment 1, the ultralight particles are macromolecular polypropylene and PVC polymer particles with an average particle diameter of 0.05-0.8 mm and a real density of 0.7-1.3 g/cm<3>.

As shown in Figure 3, the downhole filter string, which is a flow control filter string 2, is provided with a flow control filter 2-1.

The procedure for extracting the downhole filter string is as follows:

1) Open a packer to hang the downhole filter string: For a pull-release packer, the procedure for opening it is so that the packer is released automatically when the packer is pulled. For a packer that is released by rotation, the packer is automatically released when the packer is rotated. Between the loosened packer and the borehole wall there is a space, which becomes a fluid circulation passage.

2) Remove ultralight particulates using a backwash carrier fluid: Connect a fluid injection tube to the downhole filter string and inject the ultralight particulate carrier fluid directly into the flow control filter string. Due to a flow controlling action of the flow control filter string, the injection fluid is uniformly injected into the ultralight particles from different segments of the flow control filter string. In Figure 3, the arrow directions indicate how the carrier fluid flows.

3) Remove: Ultralight particles are removed from the well using the carrier fluid until the ultralight particles that have accumulated on the outside of the downhole filter string are removed. The structure of the oil/gas well after removal is as shown in Figure 6.

4) Pull out the downhole filter string.

Embodiment 3 Method of extracting a flow control filter string

In the completion structure as shown in Figure 2 and as defined in Embodiment 1, the ultralight particles are cross-linked styrene and divinylbenzene copolymer particles with an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm<3>.

As shown in Figure 4, the downhole filter string, which is a flow control filter string 2, is provided with a flow control filter 2-1.

The procedure for extracting the downhole filter string is as follows:

1) Open a packer to hang the downhole filter string: For a pull-release packer, the procedure for opening it is so that the packer is released automatically when the packer is pulled. For a packer that is released by rotation, the packer is automatically released when the packer is rotated. Between the loosened packer and the borehole wall there is a space, which becomes a fluid circulation passage.

2) Removing ultralight particles with a carrier fluid for backwashing: Insert a fluid injection pipe 7 into the downhole filter string, in which fluid injection pipe 7 is used to perform fluid injection. A lower part of the fluid injection pipe has an opening, and an upper part thereof is provided with a sealing ring 8 with an outer diameter which is substantially identical to an inner diameter of the downhole filter string.

The fluid injection is carried out section by section. The fluid injection pipe is gradually penetrated into the bottom of the downhole filter string for sectional fluid injection and sectional removal of ultralight particles on the outside of the downhole filter string from a top of the downhole filter string. Due to an effect of the sealing ring, the sealing ring can block the carrier fluid injected into the downhole filter string by means of the fluid injection pipe, at a lower side of the sealing ring and thus concentrate the carrier fluid to act on parts with deposited ultralight particles. When ultralight particles on the outside of a front segment of the downhole filter string near a wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string to another segment, until the particles on the outside of the downhole filter string are completely removed. This prevents the carrier fluid from affecting the deposited ultralight particles and saves a lot of carrier fluid. The arrow direction in Figure 4 indicates a flow direction of the carrier fluid. The dashed line in Figure 4 shows that the fluid injection pipe is gradually penetrated into the downhole filter string for sectional fluid injection.

The fluid injection pipe can be penetrated into the downhole filter string in a continuously penetrating manner at a uniform rate. As the injection pipe, which moves continuously and at a constant speed, gradually injects fluid, the depth gradually increases after ultralight particles are removed, until the ultralight particles on the outside of the downhole filter string are completely removed. The arrow direction in Figure 4 indicates a flow method of the carrier fluid.

3) Remove: The ultralight particles are taken out of the well using the carrier fluid until the ultralight particles that have accumulated on the outside of the downhole filter string are removed. The structure of the oil/gas well after removal is as shown in Figure 6.

4) Pull out the downhole filter string.

Embodiment 4 Method for extracting a downhole filter string without a flow controlling function

In the completion structure as shown in Figure 2 and as defined in Embodiment 1, the ultralight particles are high density polyethylene particles with an average particle diameter of 0.1-0.5 mm and a real density of 0.94 g/cm<3>.

As shown in Figure 5, the downhole filter string is a downhole filter string 2 without a flow controlling function. The procedure for extracting the downhole filter string is as follows:

1) Open the annulus between one end of the downhole filter string close to the wellhead and the wellbore wall and create a fluid circulation passage at an upper part of the annulus between one end of the downhole filter string close to the wellhead and the wellbore wall: For a packer loosened by pulling, is the procedure for opening it so that the packer is released automatically when the packer is pulled. For a packer that is released by rotation, the packer is automatically released when the packer is rotated. Between the loosened packer and the borehole wall there is a space, which becomes a fluid circulation passage.

2) Removing ultralight particles using a carrier fluid for backwashing: Insert a fluid injection pipe 7 into the downhole filter string, in which the fluid injection pipe 7 is used to perform fluid injection. A sealing ring 8 with an outer diameter which is substantially identical to an inner diameter of the downhole filter string is provided on the end of the fluid injection tube. A fluid outlet 9 on the fluid injection tube is located in a slightly lower position than the fluid injection tube's sealing ring. The fluid injection is carried out sectionwise, in which the fluid injection tube gradually penetrates into the bottom of the downhole filter string for partial fluid injection and sectionwise removal of ultralight particles on the outside of the downhole filter string from the top of the downhole filter string. Due to an effect of the sealing ring, the sealing ring can block the carrier fluid injected into the downhole filter string by means of the fluid injection pipe on a lower side of the sealing ring inside the downhole filter string so that it becomes difficult for the carrier fluid to enter the upper side of the sealing ring. In places where the ultralight particles have been removed on an upper side, no carrier fluid enters from the filter string, so that the carrier fluid is concentrated to remove ultralight particles that are required to be removed. When ultralight particles on the outside of a front segment of the downhole filter string near the wellhead are removed, the fluid injection pipe is penetrated into the downhole filter string to another segment, until the particles on the outside of the downhole filter string are completely removed. This prevents the carrier fluid from rising and thus saves a lot of carrier fluid and maintains a higher flow rate that affects ultralight particles. The arrow direction in figure 5 indicates a flow direction of the carrier fluid. The dashed line in the figure shows that the fluid injection pipe is gradually penetrated into the downhole filter string for sectional fluid injection. The fluid injection pipe can be penetrated into the downhole filter string in an intermittent penetrating manner. The injection pipe, which moves intermittently, gradually injects fluid until the ultralight particles on the outside of the downhole filter string are completely removed.

3) Remove: The ultralight particles are taken out of the well using the carrier fluid until the ultralight particles that have accumulated on the outside of the downhole filter string are removed. The structure of the oil/gas well after removal is as shown in Figure 6.

4) Pull out the downhole filter string.

The carrier fluid as defined in embodiments 2-4 can be water or a water solution with additives that are common for an oil field.

The method as defined in the present invention, which is easy to implement, overcomes the difficulties with the extraction of a downhole filter string in an oil well and thus simplifies production. In addition, the removed ultralight particles can be recycled and thereby greatly reduce production costs.

The density of the particles in the present patent refers to a real density for the particles.

The present invention also covers a case where a thinner downhole filter string is secondarily introduced into an original filter string to a well which is already equipped with a downhole filter string. It covers cases where a filter string is inserted into a well with perforated casing, a well with pore tube and an open hole well.

Claims (1)

Patent claims 1. Oil/gas well structure to facilitate the withdrawal of a downhole filter string, where the structure comprises: a borehole wall (1) in an oil/gas well; and a downhole filter string (2) installed in the oil/gas well, where an upper end of the downhole filter string (2) near the wellhead is firmly connected to the borehole wall (1), and where an annulus (3) is formed between the downhole filter string (2) ) and the borehole wall (1), characterized by: the annulus (3) between the downhole filter string (2) and the borehole wall (1) is filled with ultralight particles (6) with a density approaching or equal to a density of a carrier fluid to carry the ultralight particles (6) in that carrier fluid is a liquid to carry and transport the ultralight particles (6) into the annulus (3), or to backwash and transport the ultralight particles (6) out of the annulus (3), and the ultralight particles (6) are cross-linked styrene - and divinylbenzene copolymer particles with an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm<3>.. .2. Method for extracting a downhole filter string (2) from an oil/gas well structure to facilitate the extraction of a downhole filter string (2), wherein the structure includes: a borehole wall (1) in an oil/gas well and a downhole filter string (2 ) installed in the oil/gas well, in which an upper end of the downhole filter string (2) near a wellhead is fixedly connected to the wellbore wall (1), in which an annulus (3) is formed between the downhole filter string (2) and the wellbore wall (1) ), c a r a c t e r i s e r t w e e d that: the annulus (3) between the downhole filter string (2) and the borehole wall (2) is filled with ultralight particles (6) with a density approaching or equal to a density of a carrier fluid to carry the ultralight particles (6), and wherein the carrier fluid is a liquid to carry and transport the ultralight particles (6) into the annulus, or to backwash and transport the ultralight particles (6) out of the annulus (3), and the ultralight particles (6) are cross-linked styrene and divinylbenzene copolymer particles with an average particle diameter of 0.05-0.8 mm and a real density of 0.94-1.08 g/cm<3>, and wherein the method comprises the steps to: creating channels by opening an annulus (3) between an upper end of a downhole filter string (2) and a borehole wall (1); removing ultralight particles (6) from the annulus (3) using a carrier fluid for backwashing, in which carrier fluid is injected into the downhole filter string (2) to backwash and carry the ultralight particles (6) away from the annulus (3); and pull out the downhole filter string (2). 3. The method of extracting a downhole filter string according to claim 2, wherein the downhole filter string (2) is a flow control filter string, and wherein the step of removing the ultralight particles (6) includes connecting a fluid injection pipe to the downhole filter string (2) and injecting the carrier fluid directly into the downhole filter string (2). 4. The method of extracting a downhole filter string according to claim 2, wherein the step of removing the ultralight particles (6) includes installing a fluid injection pipe in the downhole filter string (2) to perform fluid injection, in which a lower portion of the fluid injection pipe has an opening , where an upper part of the fluid injection pipe above the opening is provided with a sealing ring with an outer diameter which is essentially identical to an inner diameter of the downhole filter string (2), and where the fluid injection is carried out in sections. 5. The method for extracting a downhole filter string (2) according to claim 2, wherein the carrier fluid is water or an aqueous solution.