CN115807653A - Method for establishing a fluid barrier in a formation surrounding an oil well structure - Google Patents

Abstract

The invention relates to a method for establishing a fluid barrier in a formation surrounding an oil well structure, which enables precipitation and oil stimulation. The invention also relates to a method for building a well structure in a formation. The invention also relates to a well structure having such a fluid barrier. In accordance with the present invention, axial channeling of formation fluids in the formation may be prevented by a fluid barrier in the formation.

Description

Method for establishing a fluid barrier in a formation surrounding an oil well structure

Technical Field

The invention relates to a method for establishing a fluid barrier in a formation surrounding an oil well structure, which enables precipitation and oil stimulation. The invention also relates to a method for building a well structure in a formation. The invention also relates to an oil well structure having such a fluid barrier.

Background

At present, two water control technologies are applied more in the field of oil well water control. The first is a water control technique that utilizes a water control screen and a mechanical packer to control water. In the water control technology, a mechanical packer is used for sectionally packing the production section, and the water control sieve tube is used for balancing flow rate and controlling water, so that the place with large flow rate at the water outlet section of the horizontal well is intercepted by the water control sieve tube, and the water production is reduced.

The second is a water control technology using a water control screen and a continuous packing body to control water. The water control technology is the technology which is appeared in recent years and is used for packing by filling continuous packing body particles in an annular space between a water control screen pipe and a well wall. The method for filling the particles by controlling water of the continuous packer comprises the following steps: the water control screen pipe column is put in, the annular space between the water control screen pipe and the well wall is filled with packing particles, the particles are continuously accumulated in the annular space, and the sand-carrying fluid returns to the well mouth; after the filling is finished, the filling opening is closed.

The following problems exist in the application of the water control screen plus packer/continuous packer technique. When the water control sieve tube and the packer/continuous packer technology are applied to well completion, the high water outlet is limited due to the flow control effect of the added water control sieve tube, and the excessive water can flow to the sieve tubes on two sides along the well shaft annular space or the packer ring; because the axial resistance of the packer or the packer ring (equivalent to a subdivided packing unit) per se hinders the channeling of water in the shaft, the formation water in a high-permeability section cannot enter the shaft under the dual action of the water control screen pipe and the packer or the packer ring, and the formation water can generate axial channeling in the formation. If the sandstone, limestone and carbonate reservoir formations are not obstructed by the fluid barrier or the low-permeability barrier, the formation water finally has axial channeling inside the formations, so that the water control effect is weakened, as shown in fig. 1.

Accordingly, there is a need in the art to provide a method for establishing a fluid barrier in a formation surrounding a well structure and a well structure having such a fluid barrier that overcomes one or more of the above-mentioned drawbacks.

Disclosure of Invention

According to one aspect of the invention, there is provided a method for establishing a fluid barrier in a formation surrounding a well structure, the well structure comprising a wellhead and a well wall extending from the wellhead towards the formation, the well wall defining a well cavity. The method comprises the following steps: (i) Detecting whether the stratum around the well wall has natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall and/or a hypertonic layer with an included angle smaller than or equal to a preset angle with the normal line of the well wall, wherein the hypertonic layer is defined as a permeable layer with a permeability higher than the average permeability of the oil well structure; (ii) If the stratum around the well wall has natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall and/or a hypertonic layer with an included angle smaller than or equal to a preset angle with the normal line of the well wall, filling a filling medium into the natural fractures and/or the hypertonic layer to form one or more fluid barriers; (iii) If the stratum around the well wall does not have natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall and does not have hypertonic layers with an included angle smaller than or equal to a preset angle with the normal line of the well wall, performing a fracturing operation on the stratum around the well wall to form one or more artificial fractures in the stratum around the well wall, and injecting a filling medium into the one or more artificial fractures to form one or more fluid barriers, wherein the permeability of stratum fluid in the one or more fluid barriers is smaller than that of stratum fluid in the stratum.

In one embodiment, the predetermined angle is 60 degrees.

In one embodiment, the permeability of formation fluids in the one or more fluid barriers is less than or equal to 50% of the permeability of formation fluids in the formation.

In one embodiment, in step (ii), the formation surrounding the wellbore wall is subjected to a fracturing operation prior to injection of the filling medium to further fracture the natural fractures and/or to form one or more man-made fractures.

In one embodiment, the packing medium comprises a plugging medium that is capable of solidifying in the formation.

In one embodiment, the packing medium comprises proppant and plugging medium that is capable of solidifying in the formation, and wherein injecting the packing medium comprises injecting the proppant first and then injecting the plugging medium.

In one embodiment, the plugging medium comprises at least one of glue, cement, clay.

In one embodiment, the plugging medium is capable of withstanding temperatures of 50-120 ℃.

In one embodiment, the proppant comprises at least one of quartz sand, gravel, ceramic particles, styrene, and divinylbenzene cross-linked copolymer particles.

In one embodiment, the method further comprises the steps of: (iv) The well structure is cleaned to remove residual fill medium in the well structure and around the well wall.

According to another aspect of the invention, there is provided a method for establishing a fluid barrier in a formation, comprising the steps of: (ii) (i) drilling from the surface into the formation to form a borehole wall; the well wall defining a well cavity; (ii) Performing a fracturing operation on the formation surrounding the wellbore wall to form one or more man-made fractures in the formation surrounding the wellbore wall; and (iii) injecting a packing medium from the well bore into the one or more artificial fractures to form one or more fluid barriers, wherein the permeability of formation fluids in the one or more fluid barriers is less than the permeability of formation fluids in the formation.

In one embodiment, the borehole wall extends in a direction substantially perpendicular to the direction of the earth stress in the formation.

According to another aspect of the present invention, there is provided an oil well structure comprising: a wellhead; a well wall extending from the wellhead to the formation; the well wall defining a well cavity; and one or more fluid barriers in the formation around the borehole wall, wherein the one or more fluid barriers are formed by at least one of: injecting a filling medium from the well cavity into a natural fracture and/or a hypertonic layer in the stratum around the well wall, wherein an included angle between the natural fracture and/or the hypertonic layer and a normal line of the well wall is smaller than or equal to a preset angle, and the hypertonic layer is defined as a permeable layer with a permeability higher than an average permeability of the oil well structure; and performing a fracturing operation on the formation surrounding the well wall to form one or more artificial fractures in the formation surrounding the well wall, and injecting a packing medium into the one or more artificial fractures, wherein the formation fluid has a permeability in the one or more fluid barriers that is less than the permeability of the formation fluid in the formation.

In one embodiment, the borehole wall extends in a direction substantially perpendicular to the direction of the earth stress in the formation.

Drawings

FIGS. 1A and 1B schematically illustrate the occurrence of axial cross-flow of formation fluids between formations during production of an oil well;

FIG. 2 schematically illustrates the positional relationship between natural fractures and/or hypertonic layers in the formation and the borehole wall;

fig. 3 schematically shows a well structure according to an embodiment of the invention.

Detailed Description

For a horizontal well, some production sections are low-permeability, some production sections are high-permeability, the high-permeability section corresponds to a water outlet section, and the low-permeability section corresponds to an oil production section. The viscosity of water is low, the permeability is high, so the water yield of the water outlet section is large, a large amount of water quickly reaches the position near the shaft, a water control system (a water control sieve pipe and packer particles) in the shaft can greatly control the water outlet, namely, a large amount of water is limited in the stratum. Supposing that the pressure in the middle of the oil layer is 10MPa, the pressure in the water control sieve tube is 0MPa, and when a large amount of formation water in the hypertonic section enters the water control sieve tube, the water control sieve tube has a large back pressure, for example, about 9MPa, so that the pressure outside the water control sieve tube is 9MPa; the oil layer pressure corresponding to the low-permeability section (oil outlet section) is also 10MPa, the pressure inside the water control sieve pipe is still 0MPa, and the pressure outside the oil outlet section water control sieve pipe is 1MPa because the flow rate of oil is low and the back pressure of the water control sieve pipe to the oil is small, for example, about 1MPa. Therefore, the stratum outside the water control sieve pipe at the water outlet section belongs to a high-pressure area (from 9MPa to 10 MPa), the stratum outside the water control sieve pipe at the oil outlet section belongs to a low-pressure area (from 1MPa to 10 MPa), and the high-pressure area has flow channeling to the low-pressure area and influences the water control effect of the water control system in the shaft, so that a fluid barrier needs to be established in the stratum outside the shaft, and the water control effect of the water control system in the shaft is improved.

FIGS. 1A and 1B schematically illustrate the occurrence of axial cross-flow of formation fluids between formations during production of an oil well. As shown in fig. 1A and 1B, the well includes a well structure 100. Well structure 100 includes a wellhead 102 and a wall 104 extending from wellhead 102 toward a formation. The well wall 104 defines a well bore 106. In FIG. 1A, the well structure 100 employs a water control screen 110 and a mechanical packer 120 for water control. In FIG. 1B, the well structure 100 employs a water control screen 110 and a continuous packer 130 for water control. As shown in fig. 1A and 1B, the dual action of the water control screen 110 and the mechanical packer 120/continuous packer 130 prevents formation fluids (e.g., formation water) from entering the wellbore from the hypertonic section from axial channeling inside the formation, which reduces the water control effectiveness of the overall water control system if there is no fluid barrier between the formations to prevent channeling.

According to one embodiment of the present invention, a method for creating a fluid barrier in a formation surrounding an oil well structure 100 as shown in FIG. 1A or FIG. 1B is presented. In the method, the formation surrounding the borehole wall is first tested for the presence of natural fractures and/or hypertonic layers suitable for forming a fluid barrier. In the present invention, a hypertonic layer is defined as a permeable layer having a permeability higher than the average permeability of the well structure.

Fig. 2 schematically illustrates the positional relationship between natural fractures S and/or hypertonic zones L in the formation and the borehole wall. As shown in fig. 2, the angle α between the natural fractures S and/or hypertonic layers L suitable for forming the fluid barrier and the normal N to the well wall 104 should not be too large, as if the angle α between the natural fractures S and/or hypertonic layers L and the normal N to the well wall 104 were too large, indicating that the natural fractures S and/or hypertonic layers L are close to being parallel to the well wall 104, the fluid barrier formed via such natural fractures S and/or hypertonic layers L would not provide a good inhibition of axial channeling of formation fluids. The natural fractures S and/or the hypertonic zones L may be at an angle α of less than or equal to a predetermined angle, such as 60 degrees, 50 degrees, 40 degrees, 30 degrees, 20 degrees, or 10 degrees, to the normal N to the borehole wall 104. The smaller the included angle between the natural fracture S and/or the high permeability layer L and the normal line of the well wall, the stronger the axial anti-channeling capacity of the formed fluid barrier.

If a natural fracture S and/or a hypertonic layer L suitable for forming a fluid barrier exists in the formation surrounding the well wall 104, a fill medium is injected into the natural fracture S and/or the hypertonic layer L to form one or more fluid barriers. If the formation surrounding the well wall 104 does not have a natural fracture S and/or a hypertonic layer L suitable for forming a fluid barrier (e.g., no natural fracture S and/or hypertonic layer L at all, or if there is a natural fracture S and/or hypertonic layer L but the natural fracture S and/or hypertonic layer L is at too small or too large an angle to the well wall), a fracturing operation may be performed on the formation surrounding the well wall 104 to form one or more artificial fractures in the formation surrounding the well wall 104 and a packing medium may be injected into the one or more artificial fractures to form one or more fluid barriers.

In the present invention, a fluid barrier refers to a structure that is capable of creating some resistance to the flow of formation fluids. That is, the formation fluid should have a permeability in the fluid barrier that is less than the permeability of the formation fluid in the formation. For example, the ratio of the permeability of the formation fluid in the fluid barrier to the permeability of the formation fluid in the formation may be less than or equal to 50%, or less than or equal to 40%, or less than or equal to 30%, or less than or equal to 20%, or less than or equal to 10%. The smaller the ratio of the permeability of the formation fluid in the fluid barrier to the permeability of the formation fluid in the formation, the greater the axial anti-channeling ability of the fluid barrier.

The fracturing operation employed in the present invention may be any operation suitable for creating a fracture in a subterranean formation.

In a preferred embodiment, the packing medium may comprise a plugging medium that is capable of solidifying in the formation to form a fluid barrier. The plugging medium may comprise at least one of glue, cement, clay. In a preferred embodiment of the invention, the plugging medium is capable of withstanding temperatures of 50-120 ℃ to ensure that an effective barrier is provided throughout the production life of the well. The plugging medium may also include any material that may solidify in the formation to form a fluid barrier.

In a preferred embodiment, the packing media may include both proppant and plugging media. The role of the proppant includes: supporting the fracture after depositing and arranging in the fracture; the porosity is increased, the permeability is improved, and the crack has higher flow conductivity; the oil flow channel is enlarged, the flow resistance of the fluid is reduced, and the purpose of increasing the yield is achieved. Proppants may include, for example, quartz sand, gravel, ceramic particles, styrene and divinylbenzene cross-linked copolymer particles, and the like. In the filling process, the proppant is injected first and then the plugging medium, or alternatively, the proppant and the plugging medium may be injected simultaneously.

In a preferred embodiment, the fracturing operation may be performed on the formation surrounding the wellbore wall with natural fractures to further fracture the natural fractures and/or to form one or more man-made fractures. The natural and/or artificial fractures are then filled to form a fluid barrier. In this way, natural fractures may be made more suitable for forming a fluid barrier and/or to supplement natural fractures in quantity to further form more man-made fractures in addition to natural fractures.

In a preferred embodiment, the well structure may also be cleaned after the fluid barrier is formed to eliminate residual fill medium in the well structure and around the well wall, thereby preventing contamination of the producing formation. The cleaning mode comprises acidification blockage removal and the like. "contaminated producing zone" is also known as downhole damage and refers to the phenomenon of permeability reduction of the formation near the wellbore during drilling or workover of an oil well due to conditions such as loss of drilling fluid or leakage of filtrate from water-based drilling fluids into the formation.

According to one aspect of the invention, a method for constructing a well structure in a subterranean formation is provided. In the method, a borehole is first drilled from the surface to the formation to form a borehole wall that defines a borehole cavity. A fracturing operation is then performed on the formation surrounding the wellbore wall to form one or more man-made fractures in the formation surrounding the wellbore wall. A fill medium is then injected from the well bore into the one or more artificial fractures to form one or more fluid barriers, wherein the permeability of formation fluids in the one or more fluid barriers is less than the permeability of formation fluids in the formation.

When a fracturing operation is performed, the resulting man-made fracture will be generally along the direction of the earth stress of the formation. In a preferred embodiment, the earth stress direction of the formation can be detected before the well wall is formed, and the extension direction of the well wall is approximately vertical to the earth stress direction of the formation, so that the formed artificial fracture is ensured to be approximately vertical to the extension direction of the well wall, and the subsequently formed fluid barrier has better axial anti-channeling effect.

Fig. 3 schematically shows a well structure 200 according to an embodiment of the invention. As shown in fig. 3, the well structure 200 includes a wellhead 202 and a well wall 204. A borehole wall 204 extends from the wellhead 202 toward the formation. The well wall 204 defines a well cavity 206. The well structure 200 also includes one or more fluid barriers B in the formation surrounding the well wall 204. The fluid barrier B of the well structure 200 may be formed by injecting a packing medium from the well bore into natural fractures and/or hypertonic layers in the formation surrounding the well wall. The fluid barrier B of the well structure 200 may also be formed by injecting a filling medium from the well bore into artificial fractures in the formation surrounding the well wall, the artificial fractures being formed by performing a fracturing operation on the formation surrounding the well wall. The fluid barriers B of the well structure 200 may also include both the fluid barriers formed via natural fractures and/or hypertonic layers described above and the fluid barriers formed via man-made fractures. The well structure 200 of the present invention provides a fluid barrier in the formation around the well wall, thereby preventing axial channeling of formation fluids within the formation. The well structure 200 of the present invention may employ water control techniques for water control using water control screens and mechanical packers, or may employ water control techniques for water control using water control screens and continuous packers.

Example 1

The size of the well bore is 8-1/2', the horizontal section is 580 meters long, the well bore is a carbonate reservoir, and natural cracks exist around the well bore; the continuous packer technology is selected for well completion, a 5-1/2' water control sieve tube is put in, and 30-50 meshes of packer particles are filled; and carrying out liquid production 1210 m and oil production 169 m and water content 86% half year later. In contrast, a co-block on-stream is facing the well: fracturing natural fractures existing in the stratum; injecting a propping agent and a plugging medium in the fracturing process; circularly cleaning the shaft; a 5-1/2' water control sieve tube is put in, and particles with 30-50 meshes are filled after setting, and then filling is finished; and taking measures to carry out harvesting liquid 485 m/day and oil production 411 m/day half year later, wherein the water content is 15.2%. It can be seen that the water control and oil increasing effects of the horizontal well after the formation anti-channeling barrier is established are better.

Example 2

And the horizontal well, the size of the shaft is 6 inches, the horizontal section is 358 meters long, the horizontal well is a limestone oil reservoir, and the well is completed by adopting a water control sieve tube and a mechanical packer. Logging explains that the anti-channeling barrier in the stratum is insufficient, and the stratum anti-channeling barrier needs to be established manually, namely, plugging media are injected after manual fracturing. And carrying out measures for half a year, carrying out liquid yield 300 m and oil yield 268 m, and carrying out heavy planting and oil yield 268 m and carrying out water content of 10.6%. In contrast, a co-block of contemporaneous production faces the well: adopt water control screen pipe and mechanical packer completion, produce liquid volume 566 m/day after half a year, produce oil volume 62 m/day, moisture content is 89%. It can be seen that the water-controlling and oil-increasing effect of the horizontal well after the stratum anti-channeling barrier is established is better.

Example 3

Horizontal wells, horizontal section 730 meters long, wellbore size 6 inches, open hole completions. And (3) carrying out self-spraying production at the initial stage, carrying out liquid production 570 m/day and carrying out oil production 421 m/day, wherein the water content is 26%. And (3) carrying out water content breakthrough in 4 months of production, carrying out 1750 m liquid production and 16 m oil production in each year of production, and carrying out 99% water content. And (5) water plugging and oil increasing are urgently needed, and secondary well completion is planned to be carried out by using a continuous packer technology. The type of an oil reservoir of a block where the well is located is a marine sandstone oil reservoir, boundary water drives a heterogeneous oil reservoir, a mudstone interaction interlayer does not exist, a stratum anti-channeling barrier needs to be established manually, namely, a plugging medium is injected after manual fracturing is carried out, then the well is completed by using a continuous packer technology, the particle size of a filling packer is 40-70 meshes, and the size of a water control sieve tube is 4 inches. And performing half year later, performing ethanol production at 1000 m/day and oil production at 235 m/day, wherein the water content is 76.5%. Compared with the production situation before measures, the water control and oil increase of the horizontal well after the formation anti-channeling barrier is built are obvious, and the fact that the artificially built formation anti-channeling barrier plays a good anti-channeling role is shown.

While the present invention has been described with reference to exemplary embodiment(s), it will be understood by those skilled in the art that the invention is not limited to the precise construction and components described herein and that various modifications, changes, and variations may be apparent from the foregoing descriptions without departing from the spirit and scope of the invention as defined in the appended claims. The present invention is not limited by the illustrated ordering of steps, as some steps may occur in different orders and/or concurrently with other steps. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.

Claims (14)

1. A method for establishing a fluid barrier in a formation surrounding an oil well structure, the oil well structure including a wellhead and a well wall extending from the wellhead toward the formation, the well wall defining a well cavity, the method comprising the steps of:

(i) Detecting whether natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall exist in the stratum around the well wall and/or a high-permeability layer with an included angle smaller than or equal to a preset angle with the normal line of the well wall, wherein the high-permeability layer is defined as a permeability layer with a permeability higher than the average permeability of the oil well structure;

(ii) If the stratum around the well wall has natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall and/or a hypertonic layer with an included angle smaller than or equal to a preset angle with the normal line of the well wall, filling a filling medium into the natural fractures and/or the hypertonic layer to form one or more fluid barriers;

(iii) If the stratum around the well wall does not have natural fractures with an included angle smaller than or equal to a preset angle with the normal line of the well wall and does not have hypertonic layers with an included angle smaller than or equal to a preset angle with the normal line of the well wall, performing a fracturing operation on the stratum around the well wall to form one or more artificial fractures in the stratum around the well wall, and injecting a filling medium into the one or more artificial fractures to form one or more fluid barriers;

wherein the permeability of formation fluid in the one or more fluid barriers is less than the permeability of formation fluid in the formation.

2. The method of claim 1, wherein the predetermined angle is 60 degrees.

3. The method of claim 1, wherein the formation fluid permeability in the one or more fluid barriers is less than or equal to 50% of the formation fluid permeability in the formation.

4. The method of claim 1 wherein in step (ii) the formation surrounding the borehole wall is subjected to a fracturing operation to further fracture the natural fractures and/or to form one or more man-made fractures prior to the injection of the filling medium.

5. The method of claim 1, wherein the packing medium comprises a plugging medium that is curable in the formation.

6. The method of claim 1, wherein the packing medium comprises proppant and plugging medium, the plugging medium being curable in the formation, and injecting the packing medium comprises injecting the proppant first and then the plugging medium.

7. The method of any of claims 5-6, wherein the plugging medium comprises at least one of a glue, a cement, a clay.

8. The method of any of claims 5-6, wherein the plugging medium is capable of withstanding a temperature of 50-120 ℃.

9. The method of claim 6, wherein the proppant comprises at least one of quartz sand, gravel, ceramic particles, styrene, and divinylbenzene cross-linked copolymer particles.

10. The method according to any one of claims 1-9, wherein the method further comprises the steps of:

(iv) The well structure is cleaned to remove residual fill medium in the well structure and around the well wall.

11. A method for constructing a well structure in a subterranean formation, comprising the steps of:

(i) Drilling from the surface into the formation to form a well bore wall, the well bore wall defining a well bore;

(ii) Performing a fracturing operation on the formation surrounding the wellbore wall to form one or more man-made fractures in the formation surrounding the wellbore wall;

(iii) Injecting a packing medium from the well bore into the one or more man-made fractures to form one or more fluid barriers,

wherein the permeability of formation fluid in the one or more fluid barriers is less than the permeability of formation fluid in the formation.

12. The method of claim 11, wherein the borehole wall extends in a direction substantially perpendicular to a direction of geostress of the formation.

13. An oil well structure comprising:

a wellhead;

a well wall extending from the wellhead to the formation, the well wall defining a well cavity; and

one or more fluid barriers in the formation surrounding the borehole wall,

wherein the one or more fluid barriers are formed by at least one of:

injecting a filling medium from the well cavity into a natural fracture and/or a hypertonic layer in the stratum around the well wall, wherein an included angle between the natural fracture and/or the hypertonic layer and a normal line of the well wall is smaller than or equal to a preset angle, and the hypertonic layer is defined as a permeable layer with a permeability higher than an average permeability of the oil well structure; and

performing a fracturing operation on the formation surrounding the wellbore wall to form one or more artificial fractures in the formation surrounding the wellbore wall, and injecting a packing medium into the one or more artificial fractures,

wherein the permeability of formation fluid in the one or more fluid barriers is less than the permeability of formation fluid in the formation.

14. The well structure of claim 13, wherein the well wall extends in a direction substantially perpendicular to the direction of the earth stress of the formation.

Images