Drilling fluid, drilling method, and additives for drilling fluid

Abstract

The present invention is a drilling fluid containing water, a biodegradable fiber, and a thickener, wherein the thickener contains water-absorbent silicate, and the fiber length of the biodegradable fiber is 5.0-50 mm.

Description

[Technical Field]

[0001] This invention relates to drilling fluids, drilling methods, and additives for drilling fluids. [Background technology]

[0002] In drilling operations, such as those for oil extraction, drilling fluid (also called "drilling slurry" or simply "slurry") is used. Specifically, the drilling fluid is pumped into the well via a suction tank (which acts as a pump) through the inside of the drill string (a series of pipes consisting of a drill bit (equivalent to a drilling blade) and a drill pipe (a pipe that transmits rotational power to the drill bit)), and then returned to the surface through the annulus (the gap between the drill string and the well wall) for use. This allows for the transport of excavated debris (also called "cuttings") from the bottom of the shaft and around the drill bit to the surface (cuttings transport, hole cleaning). Furthermore, the drilling fluid also serves as a lubricant and coolant for the drill bit. Furthermore, drilling fluids also play a role in controlling the pressure inside the well, thereby suppressing the inflow of fluids from within the geological formation into the well and the eruption of fluids to the surface.

[0003] Used drilling fluid (the drilling fluid carried to the surface along with the cuttings) is reused after the cuttings are removed as needed using a shale shaker (a large sieving device). In other words, the drilling fluid is circulated between the suction tank, drill string, annulus, and shale shaker. Furthermore, when reusing drilling fluid, adjustments to the composition of the drilling fluid (also known as "sludge adjustment") may be performed.

[0004] If the well wall has high water permeability (for example, if the soil particles that make up the well wall's geological layers are coarse, or if there are cracks in the well wall), the drilling fluid injected into the well may permeate into the geological layers, and some or all of the drilling fluid may not return to the surface (also known as "sludge loss"). When mud is lost, problems can arise such as the loosening of the geological layers making the well wall more prone to collapse, and a shortage of circulating drilling fluid, making it impossible to perform sufficient drilling.

[0005] Conventionally, mud loss inhibitors have been used to reduce or stop mud loss. By including the mud loss inhibitor in the drilling fluid and circulating the drilling fluid containing the mud loss inhibitor through the annulus, the gaps between soil particles are blocked, such as by sealing the cracks or, more microscopically, by forming a mud wall on the surface of the well wall, thereby suppressing mud loss. Examples of materials used as mud-removal inhibitors include fibrous materials (such as sugarcane fibers and mineral fibers), granular materials (such as limestone, marble, and walnut shells), and flake-like materials (such as mica flakes and resin film pieces) (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2015 / 072317 [Patent Document 2] International Publication No. 2013 / 161755 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Incidentally, further reduction of mud loss may be required in the future, but sufficient consideration has not been given to further reduction of mud loss so far.

[0008] Therefore, the object of the present invention is to provide a drilling fluid, a drilling method, and an additive for the drilling fluid that have high mud loss prevention properties. [Means for solving the problem]

[0009] The present invention relates to a drilling fluid containing water, biodegradable fibers, and a thickening agent, wherein the thickening agent contains a water-absorbing silicate, and the fiber length of the biodegradable fibers is 5.0 mm or more and 50 mm or less. Preferably, the thickener further comprises a biodegradable polysaccharide. More preferably, the biodegradable polysaccharide is present in the drilling fluid at a concentration of 2.0 g / L to 5.0 g / L. Even more preferably, the biodegradable polysaccharide comprises at least one selected from the group consisting of carboxymethylcellulose, polyanionic cellulose, xanthan gum, and guar gum. Preferably, the water-absorbing silicate is present in the drilling fluid at a concentration of 0.01 g / L to 100 g / L. Preferably, the water-absorbing silicate comprises at least one selected from the group consisting of bentonite and sepiolite. Preferably, the biodegradable fiber includes a fiber made of a polyhydroxyalkanoate resin. More preferably, the polyhydroxyalkanoate resin includes a 3-hydroxyalkanoic acid represented by the following general formula (1). [-CHR-CH2-CO-O-] (1) In the above general formula (1), R is C p H 2p+1 This represents an alkyl group represented by , where p is an integer from 1 to 15. More preferably, the polyhydroxyalkanoate resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). Preferably, the content of the biodegradable fibers is 0.50 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the thickener. The present invention also relates to a drilling method comprising the steps of drilling a well while supplying a drilling fluid to the well, and discharging the excavated material from the well to the outside, wherein the drilling fluid contains water, biodegradable fibers, and a thickener, the thickener contains a water-absorbing silicate, and the fiber length of the biodegradable fibers is 5.0 mm or more and 50 mm or less. Preferably, the excavation is riser excavation or riserless excavation in a marine environment. Preferably, the excavation is riserless excavation in a marine environment or excavation in a terrestrial environment. Furthermore, the present invention relates to an additive for a drilling fluid containing a biodegradable fiber and a thickener, wherein the thickener contains a water-absorbing silicate, and the fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide a drilling fluid, a drilling method, and an additive for a drilling fluid having high prevention of mud leakage.

Brief Description of the Drawings

[0011] [Figure 1] It is a diagram showing the relationship between the concentration of biodegradable fiber and the amount of water removed in the drilling fluid of the test example (concentration of biodegradable polysaccharide: 4.0 g / L, concentration of water-absorbing silicate (bentonite): 15.0 g / L). [Figure 2] It is a diagram showing the relationship between the concentration of biodegradable fiber and the thickness of the mud wall in the drilling fluid of the test example (concentration of biodegradable polysaccharide: 4.0 g / L, concentration of water-absorbing silicate (bentonite): 15.0 g / L). [Figure 3] It is a diagram showing the relationship between the concentration of biodegradable fiber and the amount of water removed in the drilling fluid of the test example (concentration of biodegradable polysaccharide: 1.0 g / L, concentration of water-absorbing silicate (bentonite): 15.0 g / L, fiber length of biodegradable fiber: 14.0 mm). [Figure 4] It is a diagram showing the relationship between the concentration of biodegradable fiber and the thickness of the mud wall in the drilling fluid of the test example (concentration of biodegradable polysaccharide: 1.0 g / L, concentration of water-absorbing silicate (bentonite): 15.0 g / L, fiber length of biodegradable fiber: 14.0 mm). [Figure 5] It is a diagram showing the relationship between the concentration of biodegradable fiber and the amount of water removed in the drilling fluid of the test example (biodegradable polysaccharide: none, concentration of water-absorbing silicate (bentonite): 80.0 g / L, fiber length of biodegradable fiber: 14.0 mm). [Figure 6] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of a test example and the thickness of the mud wall (biodegradable polysaccharides: none, concentration of water-absorbing silicate (bentonite): 80.0 g / L, fiber length of biodegradable fibers: 14.0 mm). [Figure 7] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of the test example and the amount of dewatering (concentration of biodegradable polysaccharides: 4.0 g / L, concentration of water-absorbing silicate (sepiolite): 15.0 g / L). [Figure 8] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of the test example and the thickness of the mud wall (concentration of biodegradable polysaccharides: 4.0 g / L, concentration of water-absorbing silicate (sepiolite): 15.0 g / L). [Figure 9] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of the test example and the amount of dewatering (concentration of biodegradable polysaccharides: 1.0 g / L, concentration of water-absorbing silicate (sepiolite): 15.0 g / L, fiber length of biodegradable fibers: 14.0 mm). [Figure 10] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of the test example and the thickness of the mud wall (concentration of biodegradable polysaccharides: 1.0 g / L, concentration of water-absorbing silicate (sepiolite): 15.0 g / L, fiber length of biodegradable fibers: 14.0 mm). [Figure 11] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of a test example and the amount of dewatering (biodegradable polysaccharides: none, concentration of water-absorbing silicate (sepiolite): 80.0 g / L, fiber length of biodegradable fibers: 14.0 mm). [Figure 12] This figure shows the relationship between the concentration of biodegradable fibers in the drilling fluid of a test example and the thickness of the mud wall (biodegradable polysaccharides: none, concentration of water-absorbing silicate (sepiolite): 80.0 g / L, fiber length of biodegradable fibers: 14.0 mm). [Modes for carrying out the invention]

[0012] The following describes one embodiment of the present invention.

[0013] [Drilling fluid] The drilling fluid according to this embodiment contains water, biodegradable fibers, and a thickening agent. The aforementioned thickening agent contains a water-absorbing silicate. The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less.

[0014] (water) The water contained in the drilling fluid according to this embodiment is not particularly limited. Conventional known water-based drilling fluids can be used as the water. Examples of such water include fresh water; brine (seawater, etc.); tap water; groundwater; and water that may enter a well during drilling in any environment, such as plains, mountains, rivers, canals, and oceans (rainwater, etc.).

[0015] (Thickening agent) The thickening agent is not particularly limited as long as it contains a water-absorbing silicate and increases the viscosity of the drilling fluid upon addition.

[0016] The thickening agent may be the water-absorbing silicate, and may also contain components other than the water-absorbing silicate. Other components besides the aforementioned water-absorbing silicates include biodegradable polysaccharides and organic colloids (polymers).

[0017] The aforementioned water-absorbing silicate is not particularly limited as long as it functions as a thickening agent. In other words, the water-absorbing silicate is not particularly limited as long as it increases the viscosity of water when added to it. Examples of water-absorbing silicates include bentonite and sepiolite. A commercially available bentonite product is "Tergel" manufactured by Ternite Co., Ltd. A commercially available sepiolite product is "Thermogel" manufactured by Ternite Co., Ltd.

[0018] In this embodiment, the drilling fluid contains a water-absorbing silicate as a thickening agent, which allows a mud wall to form on the surface of the well wall due to the water-absorbing material formed by the water-absorbing silicate absorbing water. As a result, the penetration of the drilling fluid into the well wall can be suppressed, that is, mud loss can be suppressed.

[0019] From the viewpoint of suppressing mud loss by forming a mud wall on the surface of the well wall, the concentration of water-absorbing silicate in the drilling fluid is preferably 0.01 g / L or more, more preferably 1.0 g / L or more, and even more preferably 10.0 g / L or more. On the other hand, if the mud wall becomes too thick, the gap between the mud wall and the drill string narrows, making it easier for drilling problems to occur, such as the drill string becoming stuck (in other words, unable to move). For this reason, the concentration of water-absorbing silicate in the drilling fluid is preferably 100 g / L or less, more preferably 80 g / L or less, and even more preferably 60 g / L or less.

[0020] The thickening agent preferably further contains the biodegradable polysaccharide as a component other than the water-absorbing silicate.

[0021] The biodegradable polysaccharides are not particularly limited as long as they are biodegradable polysaccharides that are water-soluble and increase the viscosity of the drilling fluid when added.

[0022] In this embodiment, "biodegradability" refers to the property of being able to be broken down into low-molecular-weight compounds by microorganisms in nature. Specifically, the presence or absence of biodegradability can be determined based on tests appropriate to each environment, such as ISO 14855 (compost) and ISO 14851 (activated sludge) under aerobic conditions, and ISO 14853 (aqueous phase) and ISO 15985 (solid phase) under anaerobic conditions. Furthermore, the degradability by microorganisms in seawater can be evaluated by measuring the biochemical oxygen demand. Furthermore, in this embodiment, "water-soluble polysaccharides" refers to polysaccharides that dissolve in water without retaining their shape or leaving any residue, under appropriate dissolution conditions (dissolution temperature, concentration, or stirring time, etc.) for each polysaccharide. At a minimum, it is sufficient for them to be partially or completely dissolved in the drilling fluid during drilling operations.

[0023] Examples of biodegradable polysaccharides include cellulose derivatives such as carboxymethylcellulose and polyanionic cellulose; glucosamines such as chitosan; xanthan gum; and guar gum. Among these, at least one selected from the group consisting of carboxymethylcellulose, polyanionic cellulose, xanthan gum, and guar gum is preferred. For example, guar gum has the best viscosity and moisture retention under low temperature conditions, carboxymethylcellulose is inexpensive while having excellent viscosity, polyanionic cellulose has excellent viscosity and high salt resistance, and xanthan gum exhibits high viscosity in small amounts and has shear thinning properties (the property of viscosity decreasing as the shear rate increases). These polysaccharides can be appropriately selected depending on the environment of the well being drilled, drilling conditions, market availability, etc.

[0024] The weight-average molecular weight of the biodegradable polysaccharide is preferably 200,000 or more. It may also be 1,000,000 or less.

[0025] In this embodiment, the drilling fluid further contains biodegradable polysaccharides in addition to water-absorbing silicates as a thickening agent. As a result, the water-absorbing material (water-absorbing material formed when water-absorbing silicates absorb water) is coated with biodegradable polysaccharides, maintaining a stable colloidal state of the drilling fluid and improving mud wall formation. In other words, the mud wall is stabilized, which reduces the amount of drilling fluid (amount of dewatering) that permeates the well wall, and thus further suppresses the penetration of drilling fluid into the well wall.

[0026] From the viewpoint of stabilizing the mud wall by coating the aforementioned water-absorbing material (water-absorbing material formed when water-absorbing silicates absorb water) with biodegradable polysaccharides, the concentration of biodegradable polysaccharides in the drilling fluid is preferably 2.0 g / L or higher. Furthermore, from the viewpoint of suppressing excessive viscosity of the drilling fluid and maintaining good rheological properties and good drilling efficiency, the concentration of biodegradable polysaccharides in the drilling fluid is preferably 5.0 g / L or less, more preferably 4.5 g / L or less.

[0027] Examples of the aforementioned organic colloids (polymers) include PHPA (partially hydrolyzed polyacrylamide). PHPA may also include a copolymer of acrylamide and acrylic acid, and polyacrylamide. One commercially available PHPA product is "Telcoat" manufactured by Telnight Co., Ltd.

[0028] The concentration of organic colloids (polymers) in the drilling fluid may be 0.01 g / L or more, 0.5 g / L or more, or 1.0 g / L or more, and may be 10.0 g / L or less, 5.0 g / L or less, or 3.0 g / L or less.

[0029] (Biodegradable fiber) Biodegradable fibers contained in drilling fluid are fibers that are biodegradable. Furthermore, it is important that the fiber length of the biodegradable fiber is between 5.0 mm and 50 mm.

[0030] Furthermore, fibers are characterized by their thin and long form.

[0031] The fineness of biodegradable fibers is expressed in denier (D) or dtex. Denier (D) is expressed as a number representing the weight in grams per 9,000 m length, while dtex is expressed as a number representing the weight in grams per 10,000 m length. The fineness of biodegradable fibers is preferably 1 dtex or more, more preferably 3 dtex or more, and even more preferably 5 dtex or more. Furthermore, the fineness of biodegradable fibers is preferably 100 dtex or less, more preferably 50 dtex or less, and even more preferably 10 dtex or less.

[0032] One method for measuring the fineness and fiber length of biodegradable fibers involves measuring the diameter and length of 50 to 100 randomly selected fibers using a fineness meter, DENICON-DC21 (manufactured by Search Co., Ltd.), and then calculating the average value. Therefore, fineness can be rephrased as average fiber diameter, and fiber length as average fiber length.

[0033] Furthermore, it is preferable that the biodegradable fibers contained in the drilling fluid are water-insoluble. They must maintain their shape in the drilling fluid at least during the drilling operation.

[0034] Biodegradable fibers include those derived from biological resources (biomass) such as microorganisms, plants, and animals. Biomass-derived fibers include those extracted from the fibers present in the biological resources (biomass), and those chemically synthesized from the monomers present in the biological resources (biomass).

[0035] Examples of biodegradable fibers include monofilaments or composite fibers containing polyhydroxyalkanoate resins and aliphatic polyesters such as polylactic acid, or polysaccharides such as cellulose. Among these, fibers made of polyhydroxyalkanoate resins (including monofilaments or composite fibers) are preferred as biodegradable fibers. This is because polyhydroxyalkanoate resins have the most clearly understood biodegradation mechanism and possess an appropriate decomposition rate in the environment, making them useful as environmentally friendly materials.

[0036] The aforementioned poly(3-hydroxyalkanoate) resin is a polyester whose monomer is 3-hydroxyalkanoic acid. In other words, the poly(3-hydroxyalkanoate) resin is a resin that contains 3-hydroxyalkanoic acid as a constituent unit. The poly(3-hydroxyalkanoate) resin may be a homopolymer or a copolymer.

[0037] Polyhydroxyalkanoate resins more preferably contain 3-hydroxyalkanoic acid represented by the following general formula (1) as a constituent unit. This is because it is possible to achieve both appropriate moldability and good biodegradability. [-CHR-CH2-CO-O-] (1) In the above general formula (1), R is C p H 2p+1 This represents an alkyl group represented by , where p is an integer from 1 to 15.

[0038] The aforementioned poly(3-hydroxyalkanoate) resin preferably includes a poly(3-hydroxybutyrate) resin. Poly(3-hydroxybutyrate) resins are resins that contain 3-hydroxybutyrate as a constituent unit. Poly(3-hydroxybutyrate) resins may be homopolymers or copolymers.

[0039] Examples of poly(3-hydroxyalkanoate) resins containing 3-hydroxybutyrate as a constituent unit include P3HB, P3HB3HH, P3HB3HV, P3HB4HB, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Here, P3HB stands for poly(3-hydroxybutyrate). P3HB3HH stands for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). P3HB3HV stands for poly(3-hydroxybutyrate-co-3-hydroxyvalerate). P3HB4HB stands for poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0040] Furthermore, since P3HB has the function of promoting the crystallization of P3HB itself and poly(3-hydroxyalkanoate) resins other than P3HB, it is preferable that the poly(3-hydroxyalkanoate) resin contains P3HB.

[0041] As the poly(3-hydroxyalkanoate) resin, P3HB, P3HB3HH, P3HB3HV, P3HB4HB, etc., are preferred from the viewpoint of improving the biodegradability of the biodegradable fibers while also improving the moldability of the biodegradable fibers.

[0042] The aforementioned poly(3-hydroxyalkanoate) resin preferably contains 85.0 mol% or more of 3-hydroxybutyrate as a constituent unit. The poly(3-hydroxyalkanoate) resin contains 85.0 mol% or more of 3-hydroxybutyrate as a constituent unit, thereby increasing the rigidity of the biodegradable fiber.

[0043] Furthermore, the poly(3-hydroxyalkanoate) resin contains 3-hydroxybutyrate as a constituent unit, preferably 99.5 mol% or less, more preferably 97.0 mol% or less. The poly(3-hydroxyalkanoate) resin contains 99.5 mol% or less of 3-hydroxybutyrate as a constituent unit, which gives the biodegradable fiber excellent flexibility.

[0044] The biodegradable fiber may contain only one type of poly(3-hydroxyalkanoate) resin, or it may contain two or more types. If the poly(3-hydroxyalkanoate) resin contains a copolymer (such as P3HB3HH), it may contain two or more copolymers with different average composition ratios of constituent units.

[0045] The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is preferably 50,000 to 3,000,000, more preferably 50,000 to 1,500,000. The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is 3,000,000 or less, which facilitates the molding of biodegradable fibers. The weight-average molecular weight of the poly(3-hydroxyalkanoate) resin is 50,000 or more, which can increase the strength of the biodegradable fibers. In this embodiment, the weight-average molecular weight refers to the molecular weight measured from the polystyrene-reduced molecular weight distribution using gel permeation chromatography (GPC) with chloroform eluent. Any column suitable for measuring the molecular weight can be used in the GPC.

[0046] Furthermore, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is the most preferred polyhydroxyalkanoate resin. This is because it has excellent biodegradability, low environmental impact, and superior cutting, transport, and hole cleaning capabilities.

[0047] By incorporating fibers made of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) into the drilling fluid, it is possible to maintain low viscosity (in other words, maintain fluidity) in the drilling fluid in high shear rate regions such as around the drill bit, while increasing viscosity (and shear stress) in low shear rate regions. This significantly improves the cutting transport and hole cleaning capabilities.

[0048] Furthermore, fibers made of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) have particularly excellent biodegradability, resulting in a low environmental impact from disposal, dumping, and residual materials. Specifically, for example, they have excellent seawater decomposition properties, being broken down into water and carbon dioxide by microorganisms present in seawater and no longer remaining in seawater, thus resulting in a low environmental impact even when dumped into the ocean.

[0049] The drilling fluid according to this embodiment contains biodegradable fibers with a fiber length of 5.0 mm to 50 mm, which further suppresses the penetration of the drilling fluid into the well wall. The fact that the drilling fluid according to this embodiment contains biodegradable fibers can further suppress the penetration of the drilling fluid into the well wall is thought to be because biodegradable fibers with a predetermined fiber length are included in the mud wall, reducing the gaps in the mud wall.

[0050] The fiber length of the biodegradable fiber is preferably 5.0 mm or more, more preferably 7.0 mm or more, and even more preferably 10.0 mm or more. Furthermore, the fiber length of the biodegradable fiber is preferably 50 mm or less, more preferably 40 mm or less, and even more preferably 30 mm or less.

[0051] From the viewpoint of reducing gaps in the mud wall, the drilling fluid according to this embodiment contains, preferably 0.50 parts by mass or more, more preferably 2.0 parts by mass, and even more preferably 5.0 parts by mass or more, of biodegradable fibers per 100 parts by mass of the thickener. Furthermore, the concentration of biodegradable fibers in the drilling fluid is preferably 0.050 g / L or more, more preferably 0.10 g / L or more. Furthermore, from the viewpoint of effectively suppressing mud loss through effective interaction with the thickening agent, the drilling fluid according to this embodiment contains biodegradable fibers in an amount of preferably 500 parts by mass or less, more preferably 200 parts by mass or less, per 100 parts by mass of the thickening agent. The concentration of biodegradable fibers in the drilling fluid is preferably 10.0 g / L or less, more preferably 5.0 g / L or less.

[0052] (optional ingredient) The drilling fluid according to this embodiment may contain, within the scope of the object of the present invention, any component other than water, biodegradable fibers, and a thickener, in addition to water, biodegradable fibers, and a thickener.

[0053] Examples of such optional components include weighting agents such as barite; dispersants such as lignosulfonic acid derivatives and humic acid; mudstone hydration swelling inhibitors such as KCl (potassium chloride); dehydration adjusting agents; mud wall strengthening agents; lubricants; surfactants; and pH adjusting agents such as caustic soda.

[0054] [Additives for drilling fluids] The drilling fluid additive according to this embodiment is used to produce a drilling fluid by mixing it with water. That is, the drilling fluid according to this embodiment can be obtained by mixing the drilling fluid additive according to this embodiment with water. The drilling fluid additive according to this embodiment contains biodegradable fibers and a thickening agent. The aforementioned thickening agent contains a water-absorbing silicate. The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less.

[0055] The drilling fluid and drilling fluid additive according to this embodiment are configured as described above. Next, the drilling method according to this embodiment will be described.

[0056] [Excavation Method] The drilling method according to this embodiment includes the steps of drilling a well while supplying drilling fluid to the well, and discharging the excavated material generated during the drilling to the outside of the well. The drilling fluid contains water, biodegradable fibers, and a thickening agent. The aforementioned thickening agent contains a water-absorbing silicate. The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less.

[0057] This section describes the process of excavating a well while supplying the drilling fluid according to this embodiment to the well, and discharging the excavated material to the outside of the well.

[0058] One specific method for drilling a well is to insert a drill string (a series of pipes consisting of a drill bit and a drill pipe) into the well and use the drill bit to break up or excavate the geological formation.

[0059] A specific method for discharging the excavated debris from the well is to transport it to the surface through an annulus together with the drilling fluid, thereby sending the excavated debris out of the well.

[0060] The drilling fluid sent outside the well and containing chips can be recovered, the chips removed from the drilling fluid using a shale shaker (a large sieving device), the composition of the drilling fluid adjusted as needed, and then the drilling fluid can be sent back into the well for reuse in drilling. In this case, the drilling fluid circulates through a suction tank (which acts as a pump), a drill string, an annulus, and a shale shaker.

[0061] Incidentally, in a marine environment, a pipe that connects the seabed to a drilling rig on the surface of the sea in order to form an annulus through which drilling fluid containing drilling debris flows is called a riser pipe, and drilling using a riser pipe is called riser drilling.

[0062] Riser drilling offers several advantages, including the ability to recover drilling fluid containing drilling debris in a marine environment, the ability to drill deeper due to the well's resistance to breakage, and the ease of adjusting pressure within the well. To prevent ejection of material from the well due to increased pressure, a blowout prevention device (BOP) may be installed at the top of the well, i.e., the wellhead.

[0063] Riserless drilling can be performed when drilling fluid containing drilling debris is not to be recovered after being sent outside the well. Riserless drilling is drilling without the use of riser pipes. In riserless drilling, drilling fluid is introduced into the well, allowing drilling debris to be discharged outside the well. The discharged debris is not recovered and is discarded into seawater. Compared to riser drilling, riserless drilling is suitable for shallow drilling and allows drilling in many locations in a short amount of time.

[0064] The drilling may be riser drilling or riserless drilling in a marine environment, or drilling in a land environment.

[0065] The environment in which the drilling method according to this embodiment is used is not particularly limited and can be used in any environment, such as plains, mountains, rivers, canals, and oceans. The drilling method according to this embodiment is particularly suitable for use in marine environments where reducing environmental impact is especially required. It can also be used for geothermal well drilling. In geothermal areas, the geological formations are much hotter than those of oil and natural gas, and the pressure of the formations is low, so it is desirable to use heat-resistant components as the components of the drilling fluid.

[0066] The drilling fluid according to this embodiment is configured as described above and has the following advantages.

[0067] In other words, the drilling fluid according to this embodiment contains water, biodegradable fibers, and a thickening agent. The thickening agent contains a water-absorbing silicate. The fiber length of the biodegradable fibers is 5.0 mm or more and 50 mm or less. In this embodiment, the drilling fluid contains a water-absorbing silicate as a thickening agent, which allows the water-absorbing silicate to absorb water and form a mud wall on the surface of the well wall. As a result, the penetration of the drilling fluid into the well wall can be suppressed, that is, mud loss can be suppressed. Furthermore, the drilling fluid according to this embodiment contains biodegradable fibers with a fiber length of 5.0 mm to 50 mm, which further suppresses the penetration of the drilling fluid into the well wall. The fact that the drilling fluid according to this embodiment contains biodegradable fibers can further suppress the penetration of the drilling fluid into the well wall is thought to be because biodegradable fibers with a predetermined fiber length are included in the mud wall, reducing the gaps in the mud wall. Therefore, according to this embodiment, it is possible to provide a drilling fluid, a drilling method, and an additive for the drilling fluid that have high mud loss prevention capabilities. The drilling fluid according to this embodiment contains biodegradable fibers along with water-absorbing silicates, thereby improving the prevention of mud loss while suppressing the amount of water-absorbing silicates compared to a drilling fluid that does not contain biodegradable fibers. Since biodegradable fibers are easily decomposed in the environment, the drilling fluid according to this embodiment can improve the prevention of mud loss while suppressing the burden on the environment. In addition, the drilling fluid according to this embodiment can suppress the amount of water-absorbing silicates that accumulate at the drilling site.

[0068] Furthermore, the drilling fluid according to this embodiment preferably further contains a biodegradable polysaccharide as a thickening agent. In this embodiment, the drilling fluid further contains biodegradable polysaccharides in addition to water-absorbing silicates as a thickening agent. As a result, the water-absorbing material (water-absorbing material formed when water-absorbing silicates absorb water) is coated with biodegradable polysaccharides, stabilizing the mud wall and further suppressing the penetration of the drilling fluid into the well wall. Furthermore, the drilling fluid according to this embodiment contains biodegradable polysaccharides along with water-absorbing silicates and biodegradable fibers, thereby improving the prevention of mud loss while suppressing the amount of water-absorbing silicates compared to a drilling fluid that does not contain biodegradable polysaccharides. Since biodegradable polysaccharides are easily decomposed in the environment, the drilling fluid according to this embodiment can improve the prevention of mud loss while suppressing the burden on the environment. In addition, the drilling fluid according to this embodiment can suppress the amount of water-absorbing silicates that accumulate at the drilling site.

[0069] Furthermore, the drilling fluid, drilling method, and drilling fluid additive according to the present invention are not limited to the embodiments described above. Also, the drilling fluid, drilling method, and drilling fluid additive according to the present invention are not limited by the effects described above. Moreover, the drilling fluid, drilling method, and drilling fluid additive according to the present invention can be modified in various ways without departing from the spirit of the present invention. [Examples]

[0070] Next, the present invention will be described in more detail with reference to test examples (examples and comparative examples). However, the present invention is not limited in any way to these examples.

[0071] (Drilling fluids for test examples 1-15, 26, and 27) The following materials were prepared. Specifically, as biodegradable fibers, we prepared fibers made of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH fibers) cut to average fiber lengths of 3.0 mm, 5.0 mm, 10.0 mm, and 14.0 mm. The P3HB3HH fiber has a fineness of 10.0 dtex, a tensile strength of 1.3 cN / dtex, an elongation of 70.0%, and a Young's modulus of 2.2 GPa. As a material containing biodegradable polysaccharides, we prepared Terpolymer H manufactured by Ternite Co., Ltd. (main component: polyanionic cellulose polymer (PAC) which is a biodegradable polysaccharide). As the water-absorbing silicate, we prepared Tergel (bentonite, from Wyoming, USA), manufactured by Ternite Co., Ltd. Tap water was prepared as the source of water. Then, using these materials and a household mixer, drilling fluids for Test Examples 1-15, 26, and 27 (Examples and Comparative Examples) were prepared with the mixing ratios shown in Table 1 below. In the table and figure below, the concentration of biodegradable fibers refers to the concentration of biodegradable fibers in the drilling fluid, the concentration of biodegradable polysaccharides refers to the concentration of biodegradable polysaccharides in the drilling fluid, the concentration of water-absorbing silicates refers to the concentration of water-absorbing silicates in the drilling fluid, and the fiber length refers to the fiber length of the biodegradable fibers.

[0072] [Table 1]

[0073] (Evaluation test) Using an LPLT filter press, a filtration testing device, the drilling fluid from each test example was filtered at a pressure of 7 MPa for 30 minutes (filtration test). Then, the amount of the liquid that passed through the filter (also referred to as the "dehydration amount"), the thickness of the mud wall formed on the surface of the filter of the filtration test apparatus, and the concentration of the solid content in the mud wall were determined.

[0074] Note that the concentration of the solid content in the mud wall was calculated using the following formula. C S = [{WL / (A × FC)} + 1] × M S [[ID=ll]]C S : Concentration of solid content in the mud wall (vol%) WL: Dehydration amount (cm 3 ) A: Filtration area (cm 2 ) FC: Thickness of the mud wall (cm) M S : Concentration of solid content in the drilling fluid (mud) (vol%) Here, the filtration area was 45.8 cm 2 at that time. In addition, when calculating the concentration of the solid content in the drilling fluid (mud), considering that the bentonite in the drilling fluid (mud) swells due to hydration, the density of the bentonite was set to 2.55 g / cm 3 at that time.

[0075] The results are shown in Tables 2 to 5 and Figures 1 to 6 below. Note that the above filtration test was carried out 3 times for each test example. As a result, the arithmetic mean value of the measured values for 3 times is shown.

[0076] Tables 2 and Figures 1 and 2 below show the results of the test example in which the concentration of the biodegradable polysaccharide in the drilling fluid is 4.0 g / L and the concentration of the water-absorbing silicate (bentonite) in the drilling fluid is 15.0 g / L.

[0077]

Table 2

[0078] As shown in Table 2 and Figure 1, in Test Examples 1 to 6 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 9 (Comparative Example) where the drilling fluid did not contain biodegradable fibers, and Test Examples 11 and 12 (Comparative Examples) where the fiber length of the biodegradable fibers was short at 3.0 mm. From this, it can be seen that the present invention can suppress mud loss.

[0079] Generally speaking, the thicker the mud wall, the less water is removed, so increasing the mud wall thickness is desirable to suppress mud loss. On the other hand, if the mud wall becomes too thick, the gap between the mud wall and the drill string narrows during excavation, making it easier for excavation problems to occur, such as the drill string becoming stuck (in other words, unable to move). Therefore, decreasing the mud wall thickness is desirable to suppress drill string stuckness. As shown in Table 2 and Figures 1 and 2, in Test Examples 1 to 6 (Examples) within the scope of the present invention, the amount of dewatering was less despite the smaller thickness of the mud wall, compared to Test Example 9 (Comparative Example) where the drilling fluid did not contain biodegradable fibers, and Test Examples 11 and 12 (Comparative Examples) where the fiber length of the biodegradable fibers was short at 3.0 mm. From this, it can be seen that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0080] Table 3 and Figures 3 and 4 below show the results of a test example where the concentration of biodegradable polysaccharides in the drilling fluid was 1.0 g / L, and the concentration of water-absorbing silicate (bentonite) in the drilling fluid was 15.0 g / L.

[0081] [Table 3]

[0082] As shown in Table 3 and Figure 3, in Test Examples 13 and 14 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 10 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that according to the present invention, mud loss can be suppressed.

[0083] Furthermore, as shown in Table 3 and Figures 3 and 4, in Test Examples 13 and 14 (Examples) within the scope of the present invention, the amount of dewatering was less than in Test Example 10 (Comparative Example) where the drilling fluid did not contain biodegradable fibers, despite the smaller thickness of the mud wall. This also shows that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0084] Table 4 and Figures 5 and 6 below show the results of a test example in which the drilling fluid did not contain biodegradable polysaccharides and the concentration of water-absorbing silicate (bentonite) in the drilling fluid was 80.0 g / L.

[0085] [Table 4]

[0086] As shown in Table 4 and Figure 5, in Test Examples 7, 8, 26, and 27 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 15 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that according to the present invention, mud loss can be suppressed.

[0087] Furthermore, as shown in Table 4 and Figures 5 and 6, in Test Examples 7, 8, 26, and 27 (Examples) within the scope of the present invention, the amount of dewatering was less, even though the mud wall thickness was smaller, compared to Test Example 15 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0088] Table 5 below shows the results of a test example where the fiber length of the biodegradable polysaccharide was 14.0 mm and the concentration of water-absorbing silicate (bentonite) in the drilling fluid was 15.0 g / L.

[0089] [Table 5]

[0090] As shown in Table 5, in Test Examples 5 and 6, where the concentration of biodegradable polysaccharides in the drilling fluid was 4.0 g / L, the mud wall thickness was greater and the amount of dewatering was less compared to Test Examples 13 and 14, where the concentration of biodegradable polysaccharides in the drilling fluid was 1.0 g / L. This indicates that by including biodegradable polysaccharides in the drilling fluid, the thickness of the mud wall can be increased, and as a result, the amount of dewatering can be reduced.

[0091] (Drilling fluids for test examples 16-25 and 28-32) Except for using Thermogel (sepiolite) manufactured by Ternite Co., Ltd. as the water-absorbing silicate and using the blending ratio shown in Table 6 below, the drilling fluids for Test Examples 1-15, 26, and 27 were prepared in the same manner as the drilling fluids for Test Examples 16-25 and 28-32 (Examples and Comparative Examples).

[0092] [Table 6]

[0093] Then, the above evaluation tests were conducted on test examples 16-25 and 28-32. The filtration area is 45.8 cm². 2 That was the case. Furthermore, when calculating the concentration of solids in the drilling fluid (mud), the density of sepiolite was set to 2.00 g / cm³, taking into account the swelling of sepiolite due to hydration in the drilling fluid (mud). 3 That's what I decided. The results are shown in Tables 7-10 and Figures 7-12 below.

[0094] Table 7 and Figures 7 and 8 below show the results of a test example in which the concentration of biodegradable polysaccharides in the drilling fluid was 4.0 g / L and the concentration of water-absorbing silicate (sepiolite) in the drilling fluid was 15.0 g / L.

[0095] [Table 7]

[0096] As shown in Table 7 and Figure 7, in Test Examples 16, 29, and 17 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 19 (Comparative Example), in which the drilling fluid did not contain biodegradable fibers, and Test Example 31, in which the amount of biodegradable fibers was the same and the fiber length of the biodegradable fibers was 3.0 mm. Furthermore, as shown in Table 7 and Figure 7, in Test Examples 28, 30, and 18 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 19 (Comparative Example), in which the drilling fluid did not contain biodegradable fibers, and Test Example 32, in which the amount of biodegradable fibers was the same and the fiber length of the biodegradable fibers was 3.0 mm. From this, it can be seen that the present invention can suppress mud loss.

[0097] As shown in Table 7 and Figures 7 and 8, in Test Examples 16, 29, and 17 (Examples) within the scope of the present invention, the amount of dewatering was less, despite the smaller thickness of the mud wall, compared to Test Example 19 (Comparative Example) where the drilling fluid did not contain biodegradable fibers, and Test Example 31 where the amount of biodegradable fibers was the same and the fiber length of the biodegradable fibers was 3.0 mm. Furthermore, as shown in Table 7 and Figure 7, in Test Examples 28, 30, and 18 (Examples) within the scope of the present invention, the amount of dewatering was less, despite the smaller thickness of the mud wall, compared to Test Example 19 (Comparative Example) where the drilling fluid did not contain biodegradable fibers, and Test Example 32 where the amount of biodegradable fibers was the same and the fiber length of the biodegradable fibers was 3.0 mm. From this, it can be seen that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0098] Table 8 and Figures 9 and 10 below show the results of a test example where the concentration of biodegradable polysaccharides in the drilling fluid was 1.0 g / L and the concentration of water-absorbing silicate (sepiolite) in the drilling fluid was 15.0 g / L.

[0099] [Table 8]

[0100] As shown in Table 8 and Figure 9, in Test Examples 20 and 21 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 22 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that according to the present invention, mud loss can be suppressed.

[0101] Furthermore, as shown in Table 8 and Figures 9 and 10, in Test Examples 20 and 21 (Examples) within the scope of the present invention, the amount of dewatering was less, even though the mud wall thickness was smaller, compared to Test Example 22 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0102] Table 9 and Figures 11 and 12 below show the results of a test example in which the drilling fluid did not contain biodegradable polysaccharides and the concentration of water-absorbing silicate (sepiolite) in the drilling fluid was 80.0 g / L.

[0103] [Table 9]

[0104] As shown in Table 9 and Figure 11, in Test Examples 23 and 24 (Examples) within the scope of the present invention, the amount of dewatering was less compared to Test Example 25 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that according to the present invention, mud loss can be suppressed.

[0105] Furthermore, as shown in Table 9 and Figures 11 and 12, in Test Examples 23 and 24 (Examples) within the scope of the present invention, the amount of dewatering was less, even though the mud wall thickness was smaller, compared to Test Example 25 (Comparative Example) in which the drilling fluid did not contain biodegradable fibers. This also shows that, according to this embodiment, it is possible to reduce the thickness of the mud wall while suppressing mud loss.

[0106] Table 10 below shows the results of a test example in which the fiber length of the biodegradable polysaccharide was 14.0 mm and the concentration of water-absorbing silicate (sepiolite) in the drilling fluid was 15.0 g / L.

[0107] [Table 10]

[0108] As shown in Table 10, in Test Examples 17 and 18, where the concentration of biodegradable polysaccharides in the drilling fluid was 4.0 g / L, the mud wall thickness was greater and the amount of dewatering was less compared to Test Examples 20 and 21, where the concentration of biodegradable polysaccharides in the drilling fluid was 1.0 g / L. This indicates that by including biodegradable polysaccharides in the drilling fluid, the thickness of the mud wall can be increased, and as a result, the amount of dewatering can be reduced.

Claims

1. A drilling fluid containing water, biodegradable fibers, and a thickening agent, The aforementioned thickening agent contains a water-absorbing silicate, The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less. The biodegradable fiber includes a fiber made of a polyhydroxyalkanoate resin, A drilling fluid comprising a polyhydroxyalkanoate resin that includes at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

2. The drilling fluid according to claim 1, wherein the thickening agent further comprises a biodegradable polysaccharide.

3. The drilling fluid according to claim 2, wherein the biodegradable polysaccharide is contained in the drilling fluid at a concentration of 2.0 g / L or more and 5.0 g / L or less.

4. The drilling fluid according to claim 2 or 3, wherein the biodegradable polysaccharide comprises at least one selected from the group consisting of carboxymethylcellulose, polyanionic cellulose, xanthan gum, and guar gum.

5. The drilling fluid according to any one of claims 1 to 4, wherein the water-absorbing silicate is contained in the drilling fluid at a concentration of 0.01 g / L or more and 100 g / L or less.

6. The drilling fluid according to any one of claims 1 to 5, wherein the water-absorbing silicate comprises at least one selected from the group consisting of bentonite and sepiolite.

7. The drilling fluid according to any one of claims 1 to 6, wherein the polyhydroxyalkanoate resin comprises poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

8. The drilling fluid according to any one of claims 1 to 7, wherein the content of the biodegradable fibers is 0.50 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the thickener.

9. The process includes the steps of supplying drilling fluid to the well while drilling the well, and discharging the excavated material from the well to the outside of the well. The drilling fluid contains water, biodegradable fibers, and a thickener. The aforementioned thickening agent contains a water-absorbing silicate, The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less. The biodegradable fiber includes a fiber made of a polyhydroxyalkanoate resin, A drilling method wherein the polyhydroxyalkanoate resin comprises at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

10. The drilling method according to claim 9, wherein the drilling is riser drilling or riserless drilling in a marine environment.

11. The drilling method according to claim 9, wherein the drilling is riserless drilling in a marine environment or drilling in a terrestrial environment.

12. An additive for drilling fluids containing biodegradable fibers and a thickening agent, The aforementioned thickening agent contains a water-absorbing silicate, The fiber length of the biodegradable fiber is 5.0 mm or more and 50 mm or less. The biodegradable fiber includes a fiber made of a polyhydroxyalkanoate resin, An additive for drilling fluids, wherein the polyhydroxyalkanoate resin comprises at least one selected from the group consisting of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate).

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