JP6672911B2 - Well drilling method, drill pipe and tool joint used in the drilling method - Google Patents

Description

  The present invention relates to a well drilling method, a drill pipe and a tool joint used in the drilling method.

  In the drilling work of wells (hydrocarbon wells) typified by oil wells and gas wells, vertical or curved circular tunnels extending several thousand meters underground are formed. A drill string is used for drilling a well. The drill string includes a drill bit and a plurality of drill pipes connected by a tool joint.

  Excavation work will be carried out as follows. First, a drill pipe equipped with a drill bit at the tip is rotated. Then, digging is performed while pressing the drill bit against the bottom of the pit using the weight of the drill pipe to form a tunnel. At this time, muddy water is conveyed from the surface of the ground to the bottom of the tunnel through the inside of the drill pipe for the purpose of protecting the tunnel wall and transporting the excavated debris to the ground surface, and circulating again with the excavated debris to the ground surface.

  Deeper tunnels can increase formation pressure, encounter easily collapsed formations, and prevent the excavation of a bare pit. Therefore, in order to protect the tunnel from external pressure or collapse, a steel pipe called a casing smaller than the inner diameter of the tunnel is suspended from the ground surface to the bottom of the tunnel. After the tunnel is protected by the casing, the excavation work is resumed. This series of steps is repeated to dig up to the target position.

  The casing is formed by connecting a plurality of steel pipes in a row. Both ends of each steel pipe having a length of 10 to 13 mm are threaded. A steel pipe having a tool joint (screw joint) fastened to one of both ends is the minimum unit of the casing. When suspending a casing to a depth of 1000 m, about 100 casings are connected. Recently, since excavation work is performed in a highly corrosive environment, alloy steel having excellent corrosion resistance is used for the casing.

  Traditionally, wells have been drilled vertically. However, in recent years, “inclined excavation” for digging a well diagonally and “horizontal excavation” for digging a well horizontally have been implemented in order to improve production efficiency and the like. Of these, slope digging is performed when excavating multiple locations from one location, when digging cannot be performed vertically due to the presence of obstacles, or when extracting oil from the seashore from the coast, etc. .

  In inclined excavation, a portion where the connected casing and drill string are curved occurs. In this curved portion, the drill string may come into contact with the inner surface of the casing. In this case, friction between the rotating drill string and the inner surface of the stationary casing wears the inner surface of the casing.

  Heretofore, the angle of inclination of the curved portion of a well having a tunnel inclined with respect to the vertical direction with respect to the vertical direction is as small as about 3 to 6 ° / 100 feet, and the above-described friction is hardly generated. However, in recent years, in order to increase the recovery efficiency of oil or natural gas, the number of cases of performing inclined excavation with a large inclination angle of a curved portion and then performing horizontal excavation has been increasing. In this case, since the inclination angle of the curved portion increases, friction between the drill string and the inner surface of the casing increases, and the inner surface of the casing is easily worn.

  Casing friction is caused by the rotating drill string sliding against the inner surface of the stationary casing. Generally, a hard coating is formed on a drill pipe and / or a tool joint (hereinafter, referred to as a tool joint or the like) constituting a drill string, and wear resistance is enhanced. The hard coating is, for example, a hardfacing layer (hard band). The hard band is made of, for example, martensitic steel in which fine carbides are dispersed.

  Tool joints and the like on which such a hard coating is formed are disclosed in WO 2001/059249 (Patent Document 1) and WO 2012/116036 (Patent Document 2).

  The drill pipe described in Patent Document 1 has two coating layers on the outer surface of the drill pipe. Of the two coating layers, the inner coating layer is a hard layer such as ceramics, and the outer coating layer is a soft layer such as nylon. Patent Literature 1 describes that the friction between the drill pipe and the casing is thereby reduced and wear can be suppressed.

  The tool joint described in Patent Literature 2 has a hard band layer on an outer surface of the tool joint. The tool joint further has a low friction layer such as graphite on the hard band layer. Patent Document 2 describes that this can suppress friction, erosion, and the like between the tool joint and the casing.

International Publication No. 2001/059249 International Publication No. 2012/116036

  In Patent Documents 1 and 2, a hard coating is formed on an outer surface of a tool joint or the like. In this case, the tool joint and the like are protected. However, wear occurs on the inner surface of the casing made of alloy steel, which is softer than the hard coating.

  An object of the present invention is to provide a method for excavating a well, which suppresses wear of an inner surface of a casing.

  A method for excavating a well according to an embodiment of the present invention includes an insertion step and an excavation step. In the insertion step, a casing formed by connecting a plurality of steel pipes is inserted into a well. In the drilling process, a drill string including a plurality of drill pipes and a tool joint connected to pipe ends of the drill pipes is inserted into a casing to perform inclined drilling. The outer surface of the drill pipe and / or the tool joint is provided with a steel coating having a total content of Cr and Ni of 1% or less (including 0%) by mass%.

  The well excavation method according to the present invention suppresses wear of the inner surface of the casing.

FIG. 1 is an overall view of the excavator of the present embodiment. FIG. 2A is a diagram illustrating contact between a casing and a tool joint. FIG. 2B is a diagram showing a state where the casing adheres to the tool joint. FIG. 2C is a diagram showing contact between the transferred matter and the inner surface of the casing. FIG. 2D is a diagram showing growth of a transferred substance. FIG. 3 is a diagram schematically showing a wear tester. FIG. 4 is a cross-sectional view of the outer surface of the tool joint according to the present embodiment. FIG. 5A is a diagram showing contact between the inner surface of the casing and the steel coating. FIG. 5B is a diagram showing a transferred object on the inner surface of the casing. FIG. 5C is a diagram showing the contact between the transferred matter and the steel coating. FIG. 5D is a diagram showing suppression of growth of a transferred substance. FIG. 6 is a diagram schematically illustrating the wear tester used in this example.

  The well excavation method of the present embodiment includes an insertion step and an excavation step. In the insertion step, a casing formed by connecting a plurality of steel pipes is inserted into a well. In the drilling step, a drill string including a plurality of drill pipes and a tubular tool joint for connecting the ends of the drill pipes is inserted into a casing to perform inclined drilling. The drill pipe and / or the tool joint has on its outer surface a steel coating having a total content of Cr and Ni of 1% or less (including 0%) by mass%.

  In inclined excavation, a tool joint or the like contacts the casing. At this time, the casing causes adhesive wear. If a steel coating having a total content of Cr and Ni of 1% by mass or less (including 0%) is formed on the outer surface of a tool joint or the like, the steel coating is soft and easily oxidized, so that the casing has adhesive wear. Can be suppressed. Details will be described later.

  The drill pipe and / or tool joint may include a hardfacing layer between the outer surface and the steel coating.

  In this case, even if the steel coating is worn away due to long-term use, the tool joint and the like are protected by the hardfacing layer.

  Preferably, the hardness of the steel coating is no more than 1.2 times the hardness of the casing. The hardness here is a Vickers hardness specified in JIS Z 2244. In the following description, the ratio of the hardness of the steel coating to the hardness of the casing is also referred to as a hardness ratio. When the hardness ratio is 1.2 or less, adhesive wear of the casing is further suppressed.

  Preferably, the thickness of the steel coating is between 2 and 20 mm. When the thickness of the steel coating is less than 2 mm, the steel coating is easily worn. When the thickness of the steel coating is larger than 20 mm, the steel coating is easily cracked and the steel coating is easily worn away. When the thickness of the steel coating is 2 to 20 mm, more excellent durability can be obtained.

  The well drilling method described above is particularly effective when the casing is made of an alloy steel containing 10% by mass or more of Cr.

  Preferably, the steel coating consists of cast iron. More preferably, the cast iron is spheroidal graphite cast iron. Graphite crystals are precipitated in the matrix phase (mother phase) of cast iron. When the tool joint and the like wear due to contact with the casing, the precipitated graphite is exposed at the sliding interface. The graphite exposed at the sliding interface serves as a lubricant. Thereby, the cohesive wear of the casing is further suppressed.

  The tool joint and the drill pipe of the present embodiment are used for the above-described well drilling method.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts have the same reference characters allotted, and description thereof will not be repeated.

[Drilling equipment]
FIG. 1 is a schematic diagram of a well for explaining the excavation method of the present embodiment. Referring to FIG. 1, a drilling device 1 for drilling a well W includes a casing 2, a drill string 3, and a driving device 8.

  The casing 2 is formed by connecting a plurality of steel pipes. As a connection method, for example, a screw portion is provided at an end of the steel pipes to be connected, and the steel pipe ends are connected. The casing is made of, for example, an alloy steel. A slurry-like mud or the like exists on the inner surface of the casing 2 in the well W. Mud is drilling mud containing electrolyte material and solid powder.

  The drill string 3 includes a drill pipe 4, a tool joint 7, a drill collar 5, and a drill bit 6. The tool joint 7 is a steel pipe having both ends threaded, and connects the pipe ends of the plurality of drill pipes 4 to each other. The drill collar 5 is attached to the tip of the most downstream drill pipe 4. The drill collar 5 is a metal tube heavier than the drill pipe 4 and applies a load to the lower end of the drill string 3. The drill bit 6 is arranged at the most downstream (tip) of the drill string 3. The uppermost stream of the drill string 3 is attached to the driving device 8. The drill string 3 is rotatable around an axis by a driving device 8. Thereby, the drill string 3 excavates the well W.

  At the time of drilling, the drill string 3 is inserted into the casing 2 and the well W is drilled while rotating the drill string 3. At this time, the curved portion P is formed in the well W by performing the inclined excavation by the drill string 3. The curved portion P has a tunnel that is inclined with respect to the vertical direction. At the curved portion P, the drill pipe 4 or the tool joint 7 being drilled comes into contact with the casing 2. The outer diameter of the tool joint 7 is larger than the outer diameter of the drill pipe 4. Therefore, usually, the tool joint 7 is more likely to contact the inner surface of the casing 2 than the drill pipe 4.

  Conventionally, in order to suppress wear of the outer surface of the tool joint 7, a hardfacing layer or a hard protective film is formed on the outer surface of the steel pipe of the tool joint 7. The hardfacing layer is, for example, a high-hardness martensite steel or the like. The hard protective film is, for example, ceramics or cermet.

  Recently, development of deep wells in an environment containing high-pressure carbon dioxide gas and corrosive gas has been advanced. In such a deep well, since more excellent corrosion resistance is required, the casing 2 made of alloy steel having excellent corrosion resistance is used. However, when the alloy steel casing 2 comes into contact with the above-described tool joint 7 having a hard coating, the inner surface of the casing 2 is significantly worn.

  Wear on the inner surface of the casing 2 is caused by the rotating tool joint 7 sliding on the inner surface of the stationary casing 2. The present inventors have studied the wear of the alloy steel casing 2 and obtained the following knowledge. That is, when the alloy steel casing 2 slides on the tool joint 7, the transferred matter adheres to the outer surface of the tool joint 7. Due to this transfer, the wear mode of the casing 2 becomes adhesive wear. Here, the term "transferred matter" means that one member cut by sliding adheres to the other member. Hereinafter, the adhesive wear will be described.

  2A to 2D are views showing the process of generation of adhesive wear between the alloy steel casing 2 and the tool joint 7. The generation process of the adhesive wear proceeds in the order of FIGS. 2A to 2D.

  As shown in FIG. 2A, the inner surface of the casing 2 has roughness. Therefore, at the time of inclined excavation, the convex portion on the inner surface of the casing 2 comes into contact with the tool joint 7. Actually, the outer surface of the tool joint 7 also has the same roughness as the inner surface of the casing 2. Therefore, in FIGS. 2A to 2D, the tool joint 7 drawn on the upper side originally has a convex portion similarly to the casing 2 drawn on the lower side. 2A to 2D schematically illustrate the outer surface of the tool joint 7 as a flat surface and schematically show relative unevenness in order to make the following description easy to understand.

  When the casing 2 is made of an alloy steel, the inner surface of the casing 2 is hard. Therefore, on the inner surface of the casing 2, the surface pressure is locally increased while sliding with the tool joint 7. A portion of the inner surface having a high surface pressure generates heat. Since the alloy steel has a lower thermal conductivity in the surface layer than the carbon steel, the heat generated by the sliding hardly escapes to the inside. For this reason, a part of the inner surface of the casing 2 is easily welded due to heat generation, and a part is easily peeled off due to physical contact. Due to this welding and peeling, as shown in FIG. 2B, a part (transferred material) 9 of the inner surface of the casing 2 is transferred to the outer surface of the tool joint 7.

  The adhesion occurs when the materials of the sliding members (here, the casing 2 and the tool joint 7) have high mutual solubility. The metal-based hardfacing layer or the hard protective coating (tool joint) and the alloy steel (casing) have the same metal bond and therefore have high mutual solubility. Further, since the hardness of the hard protective film such as ceramics is harder than that of the alloy steel, the inner surface of the casing 2 is easily shaved. Therefore, when the tool joint 7 has a hardfacing layer or a hard protective coating on the outer surface, adhesion is particularly likely to occur.

  As shown in FIG. 2C, the transfer object 9 attached to the tool joint 7 comes into contact with a new convex portion on the inner surface of the casing 2 due to the rotation of the tool joint 7 as the excavation operation proceeds.

  As shown in FIG. 2D, when the projection 9 on the inner surface of the casing 2 comes into contact with the transferred object 9, a part of the inner surface of the casing 2 is scraped off by the transferred object 9, and a new transferred object 91 is generated. The new transfer material 91 adheres to the existing transfer material 9.

  2C and 2D are repeated by the rotation of the tool joint 7 with the progress of the excavation work, and the transfer material 9 grows gradually. Along with the growth of the transfer material 9, the inner surface of the casing 2 is also severely worn, and adhesive wear occurs.

  The present inventors assumed a friction between the casing 2 and the tool joint 7 and performed a wear test (pin-on-disk test). In the wear test, the hard coating of the tool joint 7 and the casing 2 of various materials were assumed.

  FIG. 3 is a diagram schematically showing the wear tester 20. Referring to FIG. 3, the abrasion tester 20 includes a container 21, a pin 22, and a disk 23. Assuming that the pin 22 was the coating of the tool joint 7 and the disc 23 was the casing 2, the wear depth of the pin 22 and the disc 23 in the test was examined.

  Specifically, the container 21 was filled with environmental water 24. The environmental water 24 was a 3% by mass NaCl aqueous solution. The pin 22 was cylindrical, and the tip was spherical. The diameter of the spherical surface was 6 mm, and the axial length of the pin 22 was 6 mm. The disk 23 was a disk-shaped metal and was rotatable around a central axis. The diameter of the disk 23 was 20 mm and the thickness was 3 mm. The tip of the pin 22 and the disk 23 were mirror-finished by buffing.

  The wear test was performed as follows. The spherical surface of the pin 22 was pressed against the disk 23 with a load of 10N. The position where the pin 22 was pressed was 3 mm from the center of the disk 23. With the pin 22 pressed, the disk 23 was rotated, the circumferential speed of the disk 23 relative to the pin 22 was set to 1 cm / s, and the disk 23 was rotated for 20 minutes to perform a test.

  As the pin 22 (assuming a film formed on the outer surface of the tool joint 7), pure iron (Fe), S10C, S45C, S55C, SKD11, SUJ2, SUS304, and alumina according to JIS standards Was prepared. The S10C material contained, by mass%, 0.10% C, 0.20% Si, and 0.45% Mn, with the balance being Fe and impurities. The S45C material contained, by mass%, 0.45% of C, 0.23% of Si, and 0.45% of Mn, with the balance being Fe and impurities. The S55C material contained, by mass%, 0.55% of C, 0.23% of Si, and 0.75% of Mn, with the balance being Fe and impurities. The total content of Cr and Ni (Cr + Ni) in the S10C, S45C, and S55C materials described above is much less than 1%. The SKD11 material has, by mass%, C: 1.50%, Si: 0.20%, Mn: 0.45%, Cr: 12.0%, Mo: 1.0%, V: 0.35%. The balance was Fe and impurities. The SUJ2 material contained, by mass%, 1.0% C, 0.2% Si, 0.4% Mn, and 1.5% Cr, with the balance being Fe and impurities. SUS304 material is, by mass%, C: 0.50%, Si: 0.54%. Mn: 1.50%, Ni: 9.5%, Cr: 18.5%, the balance being Fe and impurities.

  As the disk 23 (assuming the casing 2), a carbon steel material, a 13% Cr steel material, a low carbon 13% Cr steel material, and a 25% Cr-30% Ni alloy material were prepared. The carbon steel material contained 0.2% by mass of C, 0.34% of Si, 0.48% of Mn, and 0.53% of Cr in mass%, with the balance being Fe and impurities. The 13% Cr steel material contains, by mass%, C: 0.20%, Si: 0.21%, Mn: 0.41%, Ni: 0.10%, Cr: 12.64%, and the balance is Fe and impurities. Low-carbon 13% Cr steel material is, in mass%, C: 0.04%, Si: 0.21%, Mn: 0.41%, Ni: 5.53%, Cr: 12.05%, Mo: 2 0.03%, with the balance being Fe and impurities. 25% Cr-30% Ni alloy material is, in mass%, C: 0.02%, Si: 0.32%, Mn: 0.64%, Ni: 29.7%, Cr: 25.2%, Mo: 2.85%, the balance being Fe and impurities.

  The unevenness profile of the surface of the disk 23 before and after the pin-on-disk test was measured, and the maximum depth was defined as the wear depth of the disk 23.

  Further, the hardness of each pin 22 and the disk 23 was measured by a Vickers hardness test method specified in JIS Z 2244. The test force of the Vickers hardness test was 0.98 N.

  Table 1 shows the amount of wear of the disk 23 obtained by the pin-on-disk test.

  The Vickers hardness (HV) of each material is described in parentheses of each pin material and disc material in Table 1. In each field in Table 1, the wear amount (μm) of the disk member 23 obtained by the test of the corresponding pin member 22 and the disk member 23 is described.

  Referring to Table 1, when pin 22 assumed to be tool joint 7 is made of Fe material, S10C material, S45C material, and S55C material, that is, the total content of Cr and Ni is 1% by mass or less (including 0%). ), The abrasion loss of the disk 23 was 18 μm or less, regardless of the material of the disk 2 assumed to be the casing 2. On the other hand, when the pin 22 is made of SKD11 material, SUJ2 material, SUS304 material and alumina material, that is, when the total content of Cr and Ni is metal or nonmetal (alumina) exceeding 1% by mass, the material of the disc 23 In any case, the abrasion amount was 30 μm or more.

  From the above results, the total content of Cr and Ni is smaller than that of the conventional case in which the hard coating (SKD11 material, SUJ2 material, SUS304 material, and alumina material) that is significantly harder than the casing 2 is formed on the outer surface of the tool joint 7. When a soft steel coating having an amount of 1% by mass or less (including 0%) is formed, adhesive wear is less likely to occur on the casing 2. As a result, wear of the casing can be suppressed.

  Table 2 shows the ratio of the hardness of the pin 22 to the hardness of the disk 23 (hardness ratio).

  Referring to Tables 1 and 2, when the hardness ratio is 1.2 or less, the amount of wear of the disk 23 is 16 μm or less and significantly reduced in any of the materials of the disk 23. Therefore, preferably, the ratio of the steel coating formed on the tool joint 7 to the casing 2 is 1.2 or less. In this case, regardless of the material of the casing 2, adhesive wear can be significantly suppressed.

  Based on the above findings, in the present embodiment, as shown in FIG. 4, the total content of Cr and Ni is 1% or less (including 0%) in mass% on the outer surface of the steel pipe constituting the tool joint 7. A steel coating 10 is formed. The steel coating 10 is soft because the total content of the alloy elements Cr and Ni is low. Therefore, when performing the inclined excavation, a part of the steel coating 10 is separated and transferred to the casing 2 instead of a part of the casing 2 being separated as in the related art.

  Further, the steel coating 10 is easily oxidized because the total content of Cr and Ni is 1% by mass or less (including 0%). In other words, the steel coating 10 (transferred matter) transferred to the casing 2 is easily oxidized. Therefore, the transferred matter on the inner surface of the casing 2 is unlikely to grow, and as a result, adhesive wear can be suppressed. Hereinafter, this point will be described in detail.

  FIG. 5A to FIG. 5D are views showing the wear process of the casing 2 made of alloy steel and the tool joint 7 having the steel coating 10 of the present embodiment. This wear process proceeds in the order of FIGS. 5A to 5D. In addition, actually, the inner surface of the casing 2 has roughness as shown in FIGS. 2A to 2D. Therefore, in FIGS. 5A to 5D, the casing 2 drawn on the upper side originally has a convex portion similarly to the steel coating 10 drawn on the lower side. FIGS. 5A to 5D schematically illustrate the outer surface of the casing 2 in a flat manner, and schematically illustrate relative unevenness, in order to facilitate the following description.

  When the casing 2 comes into contact with the steel coating 10 during the inclined excavation, a part of the steel coating 10 is shaved instead of the inner surface of the casing 2 unlike the related art. This is because the total content of Cr and Ni in the steel coating 10 is 1% by mass or less (including 0%), and the steel coating 10 is softer than the casing 2.

  As shown in FIG. 5B, a part of the steel coating 10 that has been shaved is transferred to the inner surface of the casing 2 as a transfer material 11. The transfer object 11 protrudes from the inner surface of the casing 2. Therefore, when the tool joint 7 further rotates during the inclined excavation, as shown in FIG. 5C, the transferred matter 11 comes into contact with the steel coating 10. At this time, the steel coating 10 is further shaved by the transferred material 11, and a fragment 12 of the steel coating 10 is newly generated as shown in FIG. 5D.

  However, since the transfer material 11 is easily oxidized, it is oxidized when it adheres to the inner surface of the casing 2. Therefore, the fragments 12 fall off from the transfer material 11 without adhering to the transfer material 11. Furthermore, since the transfer material 11 itself is oxidized, the adhesive force with the inner surface of the casing 2 is weak. Therefore, the transfer object 11 is also easily peeled off from the inner surface of the casing 2 by an impact due to the contact with the fragment 12.

  As described above, the fragments separated from the steel coating 10 are easily oxidized. Therefore, it is difficult for the deposits to grow. As a result, grinding wear (abrasive wear) occurs on the inner surface of the casing 2 instead of adhesive wear. Abrasive wear is unlikely to cause large local wear like adhesive wear. Therefore, the amount of abrasive wear is smaller than that of adhesive wear. Therefore, the amount of wear on the inner surface of the casing 2 is reduced.

  Preferably, steel coating 10 comprises cast iron. The chemical composition of the steel coating made of cast iron (hereinafter referred to as cast iron coating) contains, by mass%, C: 2.14 to 6.7% and Si: 1 to 3%, with the balance being Fe and impurities. The balance of the cast iron coating may be Fe, other elements and impurities. The total content of Cr and Ni in the cast iron coating is much less than 1% by mass. When a cast iron coating is used, not only the wear amount due to abrasive wear can be reduced as described above, but also the wear amount due to lubrication can be reduced. Specifically, cast iron contains a large amount of graphite (C) having high lubricity. Graphite crystals are precipitated in the matrix phase (Fe phase) of cast iron. When the cast iron coating slides on the inner surface of the casing, graphite precipitated in the matrix phase is exposed at the sliding interface. Graphite has a layered structure. Therefore, the graphite crystal is cleaved and slid by sliding with the inner surface of the casing. That is, the graphite exposed at the sliding interface serves as a lubricant. Thereby, wear of the cast iron coating and the casing is further suppressed. Further, since the cleaved graphite covers the sliding surface, seizure and wear of the cast iron coating and the casing due to the sliding are suppressed.

  The type of cast iron forming the cast iron coating is not particularly limited. The cast iron includes, for example, gray cast iron, spheroidal graphite cast iron and the like. Gray cast iron is specified in JIS G5501. Spheroidal graphite cast iron is specified in JIS G5502. Other cast irons include, for example, white cast iron, mottled cast iron, tough cast iron, malleable cast iron and the like. These cast irons have different components and different graphite precipitation states. The precipitation state of graphite depends on the heat treatment conditions of the cast iron.

  As the cast iron coating, spheroidal graphite cast iron in which graphite is spheroidized is particularly preferable. The lubricity of spheroidal graphite cast iron is comparable to that of general cast iron. However, the toughness of spheroidal graphite cast iron is superior to that of general cast iron. Therefore, when the steel coating is spheroidal graphite cast iron, even if friction occurs in the steel coating, the steel coating is difficult to peel off.

  In order to maintain the toughness of the cast iron coating, a preferable upper limit of the carbon (C) content is 5% by mass. In order to maintain the lubricity of the cast iron coating, a preferred lower limit of the C content is 3% by mass.

  Preferably, the tool joint or the like has a hardfacing layer between the steel coating 10 and the outer surface of the tool joint 7 or the like. The composition of the hardfacing layer is, for example, martensitic steel in which fine carbides are dispersed. Thus, when the steel coating 10 is worn by contact with the casing 2, the hardfacing layer protects the tool joint 7. In this case, the steel coating 10 is formed on the hardfacing layer. Therefore, the steel coating 10 has high adhesion due to metal bonding with the hardfacing layer. Therefore, the steel coating 10 does not easily come off due to the contact between the steel coating 10 and the casing 2. The hardfacing layer is formed by known overlay welding.

  As described above, in order to suppress adhesive wear, it is preferable that the steel coating 10 is soft. Specifically, the hardness of the steel coating 10 is 1.2 times or less the hardness of the casing 2. A more preferable hardness ratio (hardness of the steel coating 10 / hardness of the casing 2) is 0.7 or less.

  The thickness of the steel coating 10 is preferably 2 to 20 mm. When the thickness of the steel coating 10 is less than 2 mm, the steel coating 10 is easily worn out due to friction with the casing 2. When the thickness of the steel coating 10 is larger than 20 mm, the steel coating 10 is easily cracked. The steel coating 10 may be partially detached from the crack as a starting point. In this case, the steel coating 10 may be partially worn due to long-time contact between the casing 2 and the tool joint 7. More preferably, the thickness of the steel coating 10 is 5 to 12 mm.

  The well drilling method of the present embodiment is particularly effective when the casing 2 is an alloy steel containing 10% by mass or more of Cr. In this case, the steel coating 10 of the tool joint 7 is remarkably softer than the casing 2, so that abrasive wear occurs instead of adhesive wear.

  In the above-described embodiment, the case where the tool joint 7 and the inner surface of the casing 2 are in contact with each other has been described. However, in practice, the drill pipe 4 having a smaller outer diameter than the tool joint 7 may come into contact with the casing 2 depending on the inclination angle of the well, the length of the drill pipe 4, and the like. Therefore, the steel coating 10 may be formed on the outer surface of the drill pipe 4. In this case, the drill pipe 4 includes a steel pipe serving as a base material and a steel coating 10 formed on an outer surface of the steel pipe.

  The method of providing the steel coating 10 on the drill pipe 4 and the tool joint 7 includes, for example, plating, thermal spraying, and overlaying. The steel coating 10 can be formed again on the outer surface of the drill pipe 4 and the tool joint 7 already used. When the steel coating 10 is worn by use, a new steel coating 10 may be formed directly on the worn portion. Further, after the old steel coating 10 is mechanically or chemically removed, a new steel coating may be formed.

[Drilling method]
A method for excavating a well according to the present embodiment will be described.

  Referring to FIG. 1, after drilling a well to a predetermined depth using drill string 3, drill string 3 is once withdrawn from well W. Thereafter, to protect the excavated well W, the casing 2 is inserted into the well W. The casing 2 is fixed by, for example, cement poured between the casing 2 and the well W.

  After the casing 2 is inserted, the drill string 3 having the steel coating 10 formed on the outer surface of the tool joint 7 or the like is inserted into the casing 2. Then, the drill string 3 is rotated by the driving device 8, and the well is inclined and excavated. Thereby, an inclined well is formed. In this embodiment, the tool joint 7 and the like have the steel coating 10 having a total content of Cr and Ni of 1% by mass or less (including 0%). Therefore, even when the tool joint 7 or the drill pipe 4 comes into contact with or slides with the casing 2 at the curved portion P, adhesive wear is less likely to occur on the casing 2. Therefore, at the time of inclined excavation, wear of the casing can be suppressed.

  Assuming friction between the casing 2 and the tool joint 7, wear tests (cylindrical-plane contact-type wear tests) were performed on various combinations of materials.

  In this test, a wear tester 30 shown in FIG. 6 was used. The abrasion tester 30 was provided with a block 31, a disk 32, and a coating device 33. Block 31 assumed a casing. The disk 32 assumed a tool joint.

  The block 31 had a shape of 10 mm × 20 mm × 20 mm in height. The disk 32 had a cylindrical shape with a diameter of 110 mm and a height of 30 mm. The base material of the disk 32 (corresponding to the base material steel pipe of the tool joint) had a chemical composition in accordance with JIS standard SKD11. The surface roughness of the side surface 32A was Ra 0.01 μm. Various coatings assuming a steel coating were formed on the side surface 32A. Specifically, the material of the block 31 and the material of the coating of the disk 32 of each test number were as shown in Table 3.

  The film thickness of the coating on each disk 32 was as shown in Table 3. In Test Nos. 14 and 15, no film was formed on the side surface 32A of the disk 32. However, in Test No. 15, a hardfacing layer was formed on the side surface 32A as in Test Nos. 7 and 13. In Test Nos. 7 and 13, a hardfacing layer was formed between the coating and the side surface 32A. The method of forming each coating was as shown in Table 3. The coatings of Test Nos. 2 to 7, 9 and 10 had chemical compositions in accordance with JIS G 4051 (2009). The coating of Test No. 11 was cast iron according to JIS G5501 (1995). The coatings of Test Nos. 12 and 13 were cast iron based on JIS G 5502 (2001).

The materials of the coatings formed on the disks of each test number in Table 3 were as follows.
The coatings of Test Nos. 1 and 8 consisted of Fe, and the balance was impurities. Test Nos. 2, 4, 5, 7, 9 and 10 were made of S10C material.

  The S45C material was used for the coating of Test No. 3. S55C material was used for the coating of Test No. 6. The total content of Cr and Ni is less than 1% in each of the S10C, S45C, and S55C materials.

  The coating of Test No. 11 used FC100 material. The films of Test Nos. 12 and 13 used FCD350-22 material. The total content of Cr and Ni in the FC100 material and the FCD350-22 material was much less than 1%.

  Test No. 14 did not form a coating. Therefore, the disk surface was made of SKD11 as a base material, and the content of Cr was 12%.

  The surface of the disk of Test No. 15 was a hardfacing layer. The material of the surface contained 0.6% of C, 0.2% of Si, 5.0% of Cr, and 2.5% of Ti in mass%, and the balance was Fe and impurities.

The coating (cermet) of Test No. 16 contained, by mass%, 30% of TiC, 20% of TiN, 15% of WC, and 10% of Mo ₂ C, with the balance being Ni and impurities.

  The coating of Test No. 17 was a SUS304 material, with a Ni content of 9.50% and a Cr content of 18.5%. The coating of Test No. 18 was an acrylic resin.

The material of the block of each test number in Table 3 was as follows.
The blocks of Test Nos. 1 and 9 (low carbon 13% Cr steel) were, by mass%, C: 0.04%, Si: 0.21%, Mn: 0.41%, Ni: 5.53%, Cr : 12.05% and Mo: 2.03%, with the balance being Fe and impurities.

  The blocks (13% Cr steel) of Test Nos. 2 to 7 and 11 to 18 are represented by mass%, C: 0.20%, Si: 0.21%, Mn: 0.41%, Ni: 0.10% , Cr: 12.64%, with the balance being Fe and impurities.

  The block (carbon steel) of Test No. 8 contains 0.2% by mass of C, 0.34% of Si, 0.48% of Mn, and 0.53% of Cr in mass%, with the balance being Fe and impurities. there were.

  The block of Test No. 10 (25% Cr-30% Ni alloy) was, by mass%, C: 0.02%, Si: 0.32%, Mn: 0.64%, Ni: 29.7%, Cr: : 25.2%, Mo: 2.85%, and the balance was Fe and impurities.

  Using the disks 32 and the blocks 31 of the test numbers 1 to 18, a cylinder-plane contact abrasion test was performed by the following method. The 10 mm × 20 mm surface of the block 31 was pressed against the side surface 32A of the disk 32 with a load of 980N. While pressing the block 31, the disk 32 was rotated at 100 rpm for 3 hours. During the test, the saltwater-based drilling mud was continuously applied to the side surface 32A at 100 cc / min as environmental water. The temperatures of the block 31 and the disk 32 at the time of the test were room temperature.

  The wear depth of the block 31 and the disk 32 after the test was measured. Specifically, the profiles of the wear surfaces of the block 31 and the disk 32 after the test were measured with a confocal microscope, and the maximum wear depth was measured. The maximum wear depth was defined as the wear depth of the block 31 (μm) and the wear depth of the disk 32 (μm).

[Hardness ratio measurement]
Before the abrasion test described above, the Vickers hardness of the coating of the disk 32 and the block 31 was measured according to JIS Z2244. The test force at the time of measurement was 0.98N. The hardness ratio (hardness of the coating of the disk 32 / hardness of the block 31) was determined based on the determined hardness. The Vickers hardness of SKD11 was 700 HV, and the Vickers hardness of the hardfacing layer was 710 HV.

[Test results]
Table 3 shows the test results. Referring to Table 3, in Test Nos. 1 to 13, the total content of Cr and Ni in the steel coating was 1% by mass or less. Therefore, the wear depth of the block was 1.2 mm or less. The wear depth of each disk was 2.0 mm or less.

  The hardness ratios of Test Nos. 1 to 5 and 7 to 13 were 1.2 or less. Therefore, the wear depth of the block was smaller than that of Test No. 6 in which the hardness ratio exceeded 1.2. Comparing Test Nos. 2, 4, 5 and 7 with the same material for the coating and the block, the film thickness of the coatings for Test Nos. 2 and 7 was 2 to 20 mm. Therefore, in Test No. 4 in which the film thickness of the coating was less than 2 mm, the disk base material itself was worn, and in Test No. 5 in which the film thickness of the coating exceeded 20 mm, cracks were formed in the coating. In Test Nos. 2 and 7, the disk preform itself did not wear and no cracks were formed in the coating.

  The coatings of Test Nos. 11 to 13 were cast iron coatings. Therefore, in Test Nos. 11 to 13, the wear depths of the block and the disk were all 0.5 mm or less as compared with Test Nos. 1 to 10.

  On the other hand, in Test No. 14, the Cr content on the disk surface exceeded 1% by mass. Therefore, the wear depth of the block 31 greatly exceeded 2.0 mm.

  In Test No. 15, the coating of the disk was a build-up layer, and the total content of Cr and Ni exceeded 1% by mass. Therefore, the wear depth of the block 31 greatly exceeded 1.2 mm.

  In Test No. 16, the disk coating was cermet, and the Ni content exceeded 1% by mass. Therefore, the wear depth of the block 31 greatly exceeded 1.2 mm.

  In Test No. 17, the disk coating was SUS304, and the total content of Cr and Ni exceeded 1% by mass. Therefore, the wear depth of the block 31 greatly exceeded 1.2 mm.

  In Test No. 18, the disk coating was not steel but a non-metallic acrylic resin. Therefore, the wear depth of the block 31 greatly exceeded 2.0 mm.

  The embodiment of the invention has been described. However, the above-described embodiment is merely an example for embodying the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.

2 Casing 4 Drill pipe 7 Tool joint 9, 11 Transferred material 10 Steel coating

Claims (11)

A step of inserting a casing formed by connecting a plurality of steel pipes into a well,
A plurality of drill pipes, a step of inserting a drill string including a tubular tool joint connecting the ends of the drill pipes into the casing to perform inclined drilling.
The drill pipe and / or the tool joint, iron is either of steel and cast iron, and less than 1% total content of Cr and Ni in mass% (including 0%) der Ru target film A method for drilling wells on the surface. The method of digging a well according to claim 1,
It said containing hardfacing layer between and / or between the outer surface of the tool joint and before Symbol the film of the outer surface of the drill pipe and the coating, drilling methods of the well. A well drilling method according to claim 1 or claim 2,
The hardness of prior Symbol the film is less 1.2 times the hardness of the casing, drilling methods of the well. The well drilling method according to any one of claims 1 to 3,
The thickness before Symbol the film is 2 to 20 mm, drilling methods of the well. The method for excavating a well according to any one of claims 1 to 4,
The method of digging a well, wherein the steel pipe constituting the casing is made of an alloy steel containing 10% by mass or more of Cr. A well drilling method according to any one of claims 1 to 5,
Before Symbol is the film made from cast iron, the drilling method of the wellbore. A method for drilling a well according to claim 6, wherein:
The method for drilling a well, wherein the cast iron is spheroidal graphite cast iron. A tool joint used for a drill string for well drilling,
Steel pipes,
Formed on the outer surface of the steel pipe, comprising iron, either steel and cast iron, and less than 1% total content of Cr and Ni in mass% and (including 0%) der Ru target membrane, Tool joint. The tool joint according to claim 8, wherein
Before Symbol the film is made of cast iron, tool joint. A drill pipe used for a drill string for well drilling,
Steel pipes,
Formed on the outer surface of the steel pipe, comprising iron, either steel and cast iron, and less than 1% total content of Cr and Ni in mass% and (including 0%) der Ru target membrane, Drill pipe. The drill pipe according to claim 10, wherein
Before Symbol the film is made of cast iron, drill pipe.

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