Drilling fluid, and additive for drilling fluid

Abstract

To provide a drilling fluid which is excellent in mud wall formability and lose water prevention property.SOLUTION: A drilling fluid contains water, and a water-absorbing silicate, and further contains poly(3-hydroxyalkanoate)-based resin particles, wherein an average value of an aspect ratio of the poly(3-hydroxyalkanoate)-based resin particles is 1 to 40.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to drilling fluids and additives for drilling fluids. [Background technology]

[0002] 2. Description of the Related Art Drilling fluid (also called "drilling mud" or simply "mud") is used in drilling for the purpose of extracting oil or the like. Specifically, the drilling fluid is pumped into the well through the inside of the drill string (a series of pipes consisting of the drill bit (corresponding to the drilling blade) and the drill pipe (a pipe that transmits rotational power to the drill bit)) by a suction tank that serves as a pump, and then returned to the surface through the annulus (the gap between the drill string and the well wall) for use. This allows the cuttings (also called "cuttings") from the bottom of the hole and around the drill bit to be transported to the surface (cuttings transport, hole cleaning). Drilling fluids also act as lubricants and coolants for the drill bit. Furthermore, the drilling fluid also plays a role in controlling the pressure in the wellbore, thereby preventing fluids in the formation from flowing into the wellbore or erupting above ground.

[0003] Used drilling fluid (drilling fluid that was transported to the surface with cuttings) is reused after removing the cuttings using a shale shaker (a large screening device) if necessary. In other words, the drilling fluid is circulated between the suction tank, the drill string, the annulus, and the shale shaker. When reusing drilling fluid, the components of the drilling fluid may be adjusted (also called "mud adjustment").

[0004] If the borehole wall is highly permeable to water (for example, if the soil particles that make up the strata on the borehole wall are coarse or if there are cracks in the borehole wall), the drilling fluid pumped into the borehole may seep into the strata, and some or all of the drilling fluid may not return to the surface (this is known as "lost circulation"). When lost circulation occurs, problems can arise, such as the formation becoming loose and the well wall becoming more susceptible to collapse, or a shortage of circulating drilling fluid, making it impossible to carry out sufficient drilling.

[0005] Conventionally, lost circulation prevention agents have been used to make lost circulation difficult or to stop it. By including the lost circulation prevention agent in the drilling fluid and circulating the drilling fluid containing the lost circulation prevention agent in the annulus, the above-mentioned cracks are blocked, or more microscopically, a mud wall is formed on the surface of the wellbore wall, thereby blocking the gaps between the soil particles, thereby suppressing lost circulation. As lost circulation prevention agents, fibrous materials (such as sugarcane fibers and mineral fibers), granular materials (such as limestone, marble and walnut shells), and flaky materials (such as mica flakes and resin film flakes) are used (for example, Patent Documents 1 and 2).

[0006] In order to further suppress lost circulation, a drilling fluid containing water, biodegradable fibers, and a thickener is used, in which the thickener contains a water-absorbent silicate and the fiber length of the biodegradable fibers is 5.0 mm or more and 50 mm or less (for example, Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2015 / 072317 [Patent Document 2] International Publication No. 2013 / 161755 [Patent Document 3] International Publication No. 2022 / 118964 Summary of the Invention [Problem to be solved by the invention]

[0008] However, if the mud wall becomes too thick, the gap between the mud wall and the drill string becomes narrower during drilling, making it more likely that the drill string will become trapped (in other words, will become unable to move), resulting in drilling problems. Therefore, in order to prevent the drill string from becoming trapped, it is desirable to reduce the thickness of the mud wall. For these reasons, there is a demand for a drilling fluid that can reduce the thickness of the mud wall while suppressing lost circulation, that is, that has excellent mud wall forming properties and lost circulation prevention properties. However, drilling fluids that are excellent in mud wall formation properties and loss of circulation prevention properties have not been sufficiently studied so far.

[0009] Therefore, an object of the present invention is to provide a drilling fluid and an additive for a drilling fluid that are excellent in mud wall formation property and lost circulation prevention property. [Means for solving the problem]

[0010] As a result of extensive research, the inventors discovered that a drilling fluid containing a water-absorbing silicate and poly(3-hydroxyalkanoate)-based resin particles having an average aspect ratio within a specified range has excellent mud wall formation properties and lost circulation prevention properties, and thus completed the present invention.

[0011] That is, the first aspect of the present invention is a drilling fluid comprising water and a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1 to 40.

[0012] The second aspect of the present invention is an additive for drilling fluids, comprising a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1-40. Effect of the Invention

[0013] According to the present invention, it is possible to provide a drilling fluid and an additive for a drilling fluid that are excellent in mud wall formation property and lost circulation prevention property. [Brief description of the drawings]

[0014] [Figure 1] Schematic diagram of low-temperature, low-pressure dehydration tester. [Diagram 2] Schematic diagram of high-temperature, high-pressure dehydration test apparatus. [Diagram 3] Images and spectrum charts of sepiolite particles and P3HA-based resin particles (P3HB3HH particles). [Figure 4] Images and spectrum charts of cross sections of mud walls of Example 2 and Comparative Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, one embodiment of the present invention will be described.

[0016] [Drilling fluids] The drilling fluid according to this embodiment includes water and a water-absorbing silicate. The drilling fluid according to this embodiment further contains poly(3-hydroxyalkanoate)-based resin particles. The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1-40.

[0017] (water) The drilling fluid according to this embodiment includes water. The water is not particularly limited. The water may be any water contained in a conventionally known water-based drilling fluid. Examples of the water include fresh water, brine (seawater, etc.), tap water, groundwater, and water (rainwater, etc.) that may enter a well during drilling in any environment, such as flat land, mountainous areas, rivers, canals, and oceans.

[0018] (Thickener: Water-absorbent silicate) The drilling fluid according to this embodiment includes a water-absorbing silicate. The water-absorbent silicate is not particularly limited as long as it functions as a thickener. In other words, the water-absorbent silicate is not particularly limited as long as it increases the viscosity of water by being added to water. Examples of the water-absorbent silicate include bentonite and sepiolite. In addition, from the viewpoints of excellent salt resistance and heat resistance, exhibiting the desired high viscosity characteristics and good mud wall formability with a small amount of addition, being less susceptible to the effects of electrolytes, and having wide applicability to deep wells, seawater with high salt concentrations, etc., it is preferable that the water-absorbent silicate includes at least one type selected from the group consisting of bentonite and sepiolite. Furthermore, since sepiolite has a stable crystal structure even at high temperatures (eg, 250° C. or higher), when the drilling fluid is used at high temperatures, sepiolite is preferred as the water-absorbing silicate. An example of a commercially available bentonite product is "Tergel" manufactured by Terunite Co., Ltd. An example of a commercially available sepiolite product is "Thermogel" manufactured by Terunite Co., Ltd.

[0019] The drilling fluid of this embodiment contains a water-absorbent silicate, and as a result, a mud wall can be formed on the surface of the well wall by the water-absorbent silicate absorbing water, thereby suppressing the penetration of the drilling fluid into the well wall, i.e., suppressing lost circulation.

[0020] From the viewpoint of suppressing lost circulation by forming a mud wall on the surface of the wellbore wall, the concentration of the water-absorbent 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 becomes narrow, and drilling failure such as the drill string being trapped (in other words, stuck) is likely to occur. 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.

[0021] (Thickeners other than water-absorbent silicates) The drilling fluid according to this embodiment may contain a thickening agent other than the water-absorbing silicate. Examples of thickeners other than water-absorbent silicates include at least one biodegradable polysaccharide selected from the group consisting of cellulose derivatives, xanthan gum, and guar gum; organic colloids (polymers); and the like.

[0022] The biodegradable polysaccharide is not particularly limited as long as it is a polysaccharide having biodegradability, water solubility, and increases the viscosity of the drilling fluid when added.

[0023] Here, in the present embodiment, "biodegradability" refers to a property that can be decomposed into low molecular weight compounds by microorganisms in nature. Specifically, the presence or absence of biodegradability can be determined based on tests suitable for 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. In addition, the decomposition by microorganisms in seawater can be evaluated by measuring biochemical oxygen demand. In addition, the "water-soluble polysaccharide" in this embodiment refers to a polysaccharide that dissolves in water without retaining its shape or leaving any residue under appropriate dissolution conditions (dissolution temperature, concentration, stirring time, etc.). It is sufficient that the polysaccharide dissolves in water partially or completely in the drilling fluid at least during drilling operations.

[0024] The drilling fluid according to this embodiment preferably further contains at least one biodegradable polysaccharide selected from the group consisting of cellulose derivatives, xanthan gum, and guar gum. The drilling fluid of this embodiment further contains the biodegradable polysaccharide, and therefore the water absorbent (water absorbent formed by water-absorbing silicate absorbing water) is coated with the biodegradable polysaccharide, maintaining the stable colloidal state of the drilling fluid and stabilizing the mud wall, thereby reducing the amount of drilling fluid penetrating the wellbore wall (dehydration amount), i.e., further suppressing the penetration of the drilling fluid into the wellbore wall. Moreover, by further containing the biodegradable polysaccharide, the drilling fluid according to the present embodiment can suppress the amount of water-absorbent silicate and enhance the prevention of lost circulation compared to a drilling fluid that does not contain the biodegradable polysaccharide. Since biodegradable polysaccharides are easily decomposed in the environment, the drilling fluid according to the present embodiment can suppress the load on the environment and enhance the prevention of lost circulation. Furthermore, the drilling fluid according to the present embodiment can suppress the amount of water-absorbent silicate to be stocked at the drilling site. Examples of the cellulose derivatives include carboxymethyl cellulose and polyanionic cellulose (PAC). The biodegradable polysaccharides include the cellulose derivatives, and the cellulose derivatives preferably include at least one selected from the group consisting of carboxymethyl cellulose and polyanionic cellulose (PAC). The carboxymethyl cellulose has excellent viscosity and is inexpensive. The polyanionic cellulose (PAC) has excellent viscosity and high salt tolerance. The xanthan gum exhibits high viscosity even in a small amount and has shear-thinning properties (the property of decreasing viscosity as the shear rate increases). The guar gum has the best viscosity and moisture retention at low temperatures. The above biodegradable polysaccharides can be appropriately selected depending on the environment of the well to be drilled, the drilling conditions, the market distribution situation, and the like.

[0025] The weight-average molecular weight of the biodegradable polysaccharide is preferably 200,000 or more, and may be 1,000,000 or less.

[0026] In the present embodiment, the weight average molecular weight is measured from the polystyrene equivalent molecular weight distribution by gel permeation chromatography (GPC) using chloroform as an eluent. As the column for the GPC, a column suitable for measuring the molecular weight may be used. For example, the weight average molecular weight (Mw) can be determined by setting the column temperature at 40°C, injecting 10 μl of 3 mg of the target substance dissolved in 2 ml of chloroform, and setting the flow rate of the chloroform eluent (mobile phase) to 1.0 ml / min. The GPC device used is an LC-10A system (manufactured by Shimadzu Corporation), and the column used is a GPCK-806M (manufactured by Showa Denko Corporation).

[0027] From the viewpoint of stabilizing the mud wall by coating the absorbent material (water-absorbent material in which water-absorbent silicate has absorbed water) with the biodegradable polysaccharide, the concentration of the biodegradable polysaccharide in the drilling fluid is preferably 2.0 g / L or more, more preferably 2.5 g / L or more. In addition, from the viewpoint of suppressing excessive thickening of the drilling fluid and maintaining good rheological properties and good drilling efficiency, the concentration of the biodegradable polysaccharide in the drilling fluid is preferably 5.0 g / L or less, more preferably 4.5 g / L or less.

[0028] The organic colloids (polymers) include PHPA (Partially Hydrolyzed Polyacrylamide). PHPAs may include copolymers of acrylamide and acrylic acid, and polyacrylamides. An example of a commercially available PHPA product is "Telcoat" manufactured by Tellunite Corporation.

[0029] 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.

[0030] (Poly(3-hydroxyalkanoate) resin particles) The drilling fluid according to this embodiment contains the poly(3-hydroxyalkanoate)-based resin particles. The poly(3-hydroxyalkanoate)-based resin particles contain a poly(3-hydroxyalkanoate)-based resin.

[0031] The poly(3-hydroxyalkanoate) resin is a resin containing 3-hydroxyalkanoic acid as a constituent unit. The biodegradation mechanism of the poly(3-hydroxyalkanoate) resin has been elucidated, and the resin has an appropriate decomposition rate in the environment, making it useful as an environmentally friendly material. The poly(3-hydroxyalkanoate) resin may be a homopolymer or a copolymer.

[0032] The poly(3-hydroxyalkanoate) resin more preferably contains a 3-hydroxyalkanoic acid represented by the following formula (1), since this makes it possible to achieve both suitable moldability and good biodegradability. [-CHR-CH2-CO-O-] (1) In the formula (1), R is C p H 2p+1 and p represents an integer of 1 to 15.

[0033] The poly(3-hydroxyalkanoate) resin preferably includes a poly(3-hydroxybutyrate) resin. The poly(3-hydroxybutyrate)-based resin is a resin containing 3-hydroxybutyrate as a constituent unit. The poly(3-hydroxybutyrate)-based resin may be a homopolymer or a copolymer.

[0034] Examples of poly(3-hydroxyalkanoate) resins containing 3-hydroxybutyrate as a constituent unit include P3HB, P3HB3HH, P3HB3HV, P3HB4HB, poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate), and the like. Here, P3HB means poly(3-hydroxybutyrate). P3HB3HH means poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). P3HB3HV means poly(3-hydroxybutyrate-co-3-hydroxyvalerate). P3HB4HB means poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

[0035] Since P3HB has the function of promoting crystallization of P3HB itself and poly(3-hydroxyalkanoate) resins other than P3HB, it is preferable that the poly(3-hydroxyalkanoate) resin contains P3HB.

[0036] As the poly(3-hydroxyalkanoate)-based resin, from the viewpoint of enhancing the biodegradability of the poly(3-hydroxyalkanoate)-based resin particles, P3HB, P3HB3HH, P3HB3HV, P3HB4HB, and the like are preferred.

[0037] The poly(3-hydroxyalkanoate) resin preferably contains 85.0 mol % or more of 3-hydroxybutyrate as a constituent unit. The poly(3-hydroxyalkanoate) resin preferably contains 99.5 mol % or less, and more preferably 97.0 mol % or less, of 3-hydroxybutyrate as a constituent unit.

[0038] The poly(3-hydroxyalkanoate)-based resin particles may contain only one type of the poly(3-hydroxyalkanoate)-based resin, or may contain two or more types of the poly(3-hydroxyalkanoate)-based resin. When the poly(3-hydroxyalkanoate) resin contains a copolymer (such as P3HB3HH), it may contain two or more types of copolymers having different average composition ratios of structural units.

[0039] The poly(3-hydroxyalkanoate)-based resin particles preferably contain poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH). The shape of the poly(3-hydroxyalkanoate) resin particles is not particularly limited, but since the shape can be freely changed from the micron order to the millimeter order with various particle diameters and aspect ratios, it is possible to form a mud wall that can also accommodate the blocking of microcracks in a drilled well by adding it to the drilling fluid. In addition, when long fibers are added to the drilling fluid as in Patent Document 3 (International Publication No. 2022 / 118964), the fibers are entangled in the drilling fluid, but even if poly(3-hydroxyalkanoate) resin particles with an average aspect ratio of 1 to 40 are added to the drilling fluid, entanglement is unlikely to occur in the drilling fluid, so it is possible to increase the amount of poly(3-hydroxyalkanoate) resin particles added to the drilling fluid, and it is possible to form a sufficient mud wall with a small amount of drilling fluid. In addition, poly(3-hydroxyalkanoate)-based resin particles including poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) are particularly excellent in biodegradability, and therefore the environmental impact of being discarded or dumped and remaining in the sea is small. For example, the resin particles have excellent seawater decomposition properties, in that they are decomposed into water and carbon dioxide by microorganisms present in seawater and do not remain in seawater, so that even if they are dumped in the ocean, the environmental impact is small.

[0040] The weight average molecular weight of the poly(3-hydroxyalkanoate) resin is preferably 50,000 to 3,000,000, and more preferably 50,000 to 1,500,000.

[0041] The poly(3-hydroxyalkanoate) resin particles contain a poly(3-hydroxyalkanoate) resin in an amount of preferably 50 to 100% by mass, more preferably 70 to 98% by mass, and even more preferably 80 to 95%.

[0042] From the viewpoint of sufficiently dispersing the poly(3-hydroxyalkanoate)-based resin particles in the drilling fluid, the poly(3-hydroxyalkanoate)-based resin particles preferably contain a dispersant.

[0043] From the viewpoints of excellent dispersibility in drilling fluids containing water and compatibility with other materials (e.g., water-absorbent silicates, biodegradable polysaccharides, etc.), it is preferable that the dispersant contains at least one selected from the group consisting of polyvinyl alcohol, modified cellulose, and polyalkylene oxide. The polyvinyl alcohol used may be a commercially available product. The modified cellulose and the polyalkylene oxide can be, for example, those described in International Publication No. 2021 / 075412.

[0044] From the viewpoints of productivity of the poly(3-hydroxyalkanoate)-based resin particles and maintaining good dispersibility of the poly(3-hydroxyalkanoate)-based resin particles in drilling fluid, the poly(3-hydroxyalkanoate)-based resin particles preferably contain 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and particularly preferably 0.75 to 5 parts by weight of the dispersant per 100 parts by mass of the poly(3-hydroxyalkanoate)-based resin particles.

[0045] The shape of the poly(3-hydroxyalkanoate) resin particles is not particularly limited as long as it is particulate, and may be any of granular, approximately spherical, spherical, fibrous, needle-like, columnar, rod-like, plate-like, similar shapes, amorphous, etc. Furthermore, particles having these shapes can be used in a suitable size after adjusting to a desired aspect ratio.

[0046] The poly(3-hydroxyalkanoate) resin particles are not particularly limited, and can be produced by a production method utilizing a known technique or a commonly used technique.

[0047] Methods for producing poly(3-hydroxyalkanoate)-based resin particles include, for example, a method comprising a step of decomposing, solubilizing and / or removing microbial components (particularly organic matter) other than P3HA from a microorganism (a microorganism capable of producing P3HAs) that has accumulated poly(3-hydroxyalkanoate)-based resin (P3HA) in its body, and then recovering poly(3-hydroxyalkanoate)-based resin particles A. The process of recovering poly(3-hydroxyalkanoate)-based resin particles A includes, for example, a process of preparing an aqueous suspension containing a poly(3-hydroxyalkanoate)-based resin and having a pH of 7 or less, and a process of spray-drying the aqueous suspension. The aqueous suspension may contain the dispersant.

[0048] Alternatively, the poly(3-hydroxyalkanoate) resin particles can be prepared as follows. First, the poly(3-hydroxyalkanoate)-based resin particles A obtained by the above-mentioned method are fed into a melt kneading extruder to obtain a melt. Next, the temperature and discharge rate are adjusted to obtain a molten strand from the melt. The strand is then crystallized and solidified in a cooling water tank. Thereafter, the strand is continuously subjected to a pelletizing process, during which the take-up speed and cutter rotation speed are adjusted to obtain poly(3-hydroxyalkanoate)-based resin particles B having a desired aspect ratio. In addition, when additives (e.g., lubricants, crystal nucleating agents, etc.) are to be incorporated into the poly(3-hydroxyalkanoate)-based resin particles, the additives can be supplied to the poly(3-hydroxyalkanoate)-based resin particles from a side feeder during melt extrusion and dry-blended in powder form, or the additives can be supplied to the poly(3-hydroxyalkanoate)-based resin particles using a liquid addition pump or the like, thereby allowing an appropriate amount of additive to be blended.

[0049] The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1-40, preferably 1-20, more preferably 1-10, further preferably 1-5, and particularly preferably 1-3. Since the average aspect ratio of the poly(3-hydroxyalkanoate) resin particles is 40 or less, the drilling fluid according to this embodiment has excellent mud wall forming properties and lost circulation prevention properties. The drilling fluid of this embodiment contains poly(3-hydroxyalkanoate)-based resin particles, and the poly(3-hydroxyalkanoate)-based resin particles have an average aspect ratio of 1 to 40, thereby providing excellent mud wall formation properties and prevention of lost circulation. This is thought to be because the poly(3-hydroxyalkanoate)-based resin particles, which have an average aspect ratio of 40 or less, are contained in the mud wall, thereby reducing the gaps in the mud wall. Furthermore, since the drilling fluid according to this embodiment contains the poly(3-hydroxyalkanoate)-based resin particles together with the water-absorbent silicate, it is possible to improve the prevention of lost circulation while suppressing the amount of water-absorbent silicate compared to a drilling fluid that does not contain the poly(3-hydroxyalkanoate)-based resin particles. In addition, since the poly(3-hydroxyalkanoate)-based resin particles are easily decomposed in the environment, the drilling fluid according to the present embodiment can enhance the prevention of lost circulation while suppressing the burden on the environment. In addition, the drilling fluid according to the present embodiment can suppress the amount of water-absorbent silicate stocked at the drilling site.

[0050] The average aspect ratio of the poly(3-hydroxyalkanoate) resin particles can be determined using a caliper or a microscope as follows. When a microscope is used, 20 or more randomly selected poly(3-hydroxyalkanoate)-based resin particles or all poly(3-hydroxyalkanoate)-based resin particles are photographed at a magnification of 5,000 to 10,000 times using a microscope (e.g., a scanning electron microscope (SEM)) to obtain an image, and the long and short axes of each poly(3-hydroxyalkanoate)-based resin particle are visually determined from the image to determine the lengths of the long and short axes. In other words, the lengths of the long and short axes are determined when a three-dimensional shape is viewed on a two-dimensional plane (cross section, torus surface, etc.). For example, in the image, when the poly(3-hydroxyalkanoate)-based resin particles are rectangular, the long side is the long axis and the short side is the short axis. When the poly(3-hydroxyalkanoate)-based resin particles are rod-shaped, the length in the longitudinal direction is the long axis length and the diameter is the short axis length. Next, the average value (arithmetic mean value) of the long axis length is calculated from the long axis length of each poly(3-hydroxyalkanoate)-based resin particle, and the average value (arithmetic mean value) of the short axis length is calculated from the short axis length of each poly(3-hydroxyalkanoate)-based resin particle. Then, the average value of the long axis length / the short axis length is taken as the average aspect ratio. In addition, in the case where the poly(3-hydroxyalkanoate) resin particles are aggregated to form secondary particles, the aspect ratio means the aspect ratio of the primary particles. When using a caliper, the caliper is used to measure the length of each of the major axis and minor axis of at least 20 randomly selected poly(3-hydroxyalkanoate) resin particles or all poly(3-hydroxyalkanoate) resin particles. Then, the arithmetic mean value of each length is calculated in the same manner as in the above-mentioned method, and the aspect ratio can be calculated as an average value by dividing the average length of the major axis by the average length of the minor axis. A caliper (digital caliper) is a length measuring device. A commercially available caliper can be used as the caliper. When the particles are small, eg, the length of the particle's axes (eg, major and minor axes) is 10 μm or less, the average aspect ratio can be determined using a microscope. On the other hand, when the particles are large, for example when the particle has an axial length of 10 μm or more, the average aspect ratio can be determined using a caliper.

[0051] The average primary particle size of the poly(3-hydroxyalkanoate) resin particles is preferably 0.5 to 30 μm, and more preferably 0.8 to 10 μm. Since the average primary particle diameter of the poly(3-hydroxyalkanoate) resin particles is 30 μm or less, the drilling fluid of this embodiment can further reduce the gaps in the mud wall, resulting in even better mud wall formation properties and lost circulation prevention properties.

[0052] The average primary particle size of the poly(3-hydroxyalkanoate) resin particles can be determined as follows. First, 20 or more randomly selected poly(3-hydroxyalkanoate)-based resin particles or all of the poly(3-hydroxyalkanoate)-based resin particles are photographed at a magnification of 5,000 to 10,000 times using a scanning electron microscope (SEM) to obtain an image, and the diameter of each poly(3-hydroxyalkanoate)-based resin particle is visually determined from the image to determine the diameter. In addition, if each poly(3-hydroxyalkanoate) resin particle is not a perfect circle in the image, the area of ​​each poly(3-hydroxyalkanoate) resin particle in the image can be determined, and the diameter can be calculated from this area assuming that the particle is a perfect circle. Then, a calculated average value is determined from the value of the primary particle diameter of each poly(3-hydroxyalkanoate) resin particle, and this calculated average value is regarded as the average value of the primary particle diameter of the poly(3-hydroxyalkanoate) resin particles.

[0053] From the viewpoint of further improving the mud wall forming property and lost circulation prevention property of the drilling fluid, the average particle size of the poly(3-hydroxyalkanoate) resin particles is preferably 10 to 200 μm, and more preferably 100 to 150 μm.

[0054] The average particle size of the poly(3-hydroxyalkanoate) resin particles can be determined as follows. First, a spatula-sized amount of randomly selected poly(3-hydroxyalkanoate) resin particles, or the entire amount of poly(3-hydroxyalkanoate) resin particles, is placed into a 100 mL beaker, and 1 to 2 drops of household detergent (Kao: Kyukyutto) and approximately 20 to 30 mL of tap water are added to the beaker, and the mixture is dispersed with a spatula to prevent lumps from forming. Then, the median diameter (d50: particle size corresponding to 50% accumulation of all particles in normal distribution) is calculated using a particle size distribution measuring device MT3000II (Microtrack Bell, Inc., laser diffraction / scattering method), and the median diameter is taken as the average particle diameter.

[0055] The poly(3-hydroxyalkanoate) resin particles are contained in the drilling fluid in an amount of preferably 2.0 g / L to 100.0 g / L, more preferably 5.0 g / L to 70.0 g / L, and even more preferably 10.0 g / L to 50.0 g / L. When the poly(3-hydroxyalkanoate) resin particles are contained in the drilling fluid at 2.0 g / L or more, it becomes easier to effectively suppress lost circulation. When the poly(3-hydroxyalkanoate)-based resin particles are contained in the drilling fluid at 100.0 g / L or less, the poly(3-hydroxyalkanoate)-based resin particles tend to be sufficiently dispersed in the drilling fluid.

[0056] From the viewpoint of reducing gaps in the mud wall, the drilling fluid according to this embodiment contains poly(3-hydroxyalkanoate)-based resin particles in an amount of preferably 0.50 parts by mass or more, more preferably 2.0 parts by mass or more, and even more preferably 5.0 parts by mass or more per 100 parts by mass of water-absorbent silicate. In addition, from the viewpoint of effectively suppressing lost circulation through effective interaction with the thickener, the drilling fluid of this embodiment contains poly(3-hydroxyalkanoate)-based resin particles, preferably 500 parts by mass or less, more preferably 200 parts by mass or less, per 100 parts by mass of water-absorbing silicate.

[0057] (optional ingredient) The drilling fluid according to this embodiment may contain optional components within the scope of the present invention. Examples of the 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 adjusters; mud wall strengthening agents; lubricants; surfactants; and pH adjusters such as caustic soda.

[0058] [Drilling fluid additives] The drilling fluid according to this embodiment can be obtained by mixing the additive for a drilling fluid according to this embodiment with water. The drilling fluid additive according to this embodiment includes a water-absorbing silicate. The drilling fluid additive according to this embodiment further contains poly(3-hydroxyalkanoate)-based resin particles. The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1-40.

[0059] The drilling fluid and the additive for the drilling fluid according to the present embodiment are configured as described above. Next, a drilling method using the drilling fluid according to the present embodiment will be described.

[0060] [Drilling method] The drilling method according to this embodiment includes the steps of drilling a well while pumping the drilling fluid according to this embodiment into the well, and discharging cuttings generated during the drilling to the outside of the well.

[0061] A process of drilling a well while pumping the drilling fluid according to this embodiment into the well and discharging cuttings generated during the drilling to the outside of the well will be described.

[0062] A method for drilling a well includes, for example, inserting a drill string (a series of pipes consisting of a drill bit and a drill pipe) into the well and fracturing or scraping the earth's formation with the drill bit.

[0063] As a method for discharging the cuttings generated during the drilling out of the well, for example, the cuttings may be transported to the surface through an annulus together with a drilling fluid, thereby sending the cuttings out of the well.

[0064] The drilling fluid can be pumped out of the well and collected with the drilling cuttings, the drilling fluid can be removed from the drilling fluid with a shale shaker (a large screening device), the composition of the drilling fluid can be adjusted if necessary, and the drilling fluid can be pumped back into the well to be used again for drilling. At this time, the drilling fluid circulates through the suction tank, the pump, the drill string, the annulus, and the shale shaker.

[0065] In a marine environment, a pipe that connects the seabed surface to a drilling rig on the sea surface to form an annulus through which drilling fluid containing drill cuttings flows is called a riser pipe, and drilling using a riser pipe is called riser drilling.

[0066] Riser drilling has the advantages of being able to recover drilling fluid with drill cuttings in a marine environment, being less susceptible to well fracturing, allowing for deeper drilling, and making it easier to regulate pressure in the well. A blowout preventer (BOP) may be installed at the top of the well, or at the wellhead, to prevent a blowout from occurring in the well due to an increase in pressure in the well.

[0067] When drilling fluid that is sent outside the well and contains cuttings is not collected, riserless drilling can be performed. Riserless drilling is drilling that does not use a riser pipe. In riserless drilling, drilling fluid is pumped into the well to discharge cuttings generated during drilling outside the well. The discharged cuttings are not collected but are discarded in seawater. Compared to riser drilling, riserless drilling is suitable for shallow drilling and can drill many places in a short time.

[0068] The drilling may be riser or riserless drilling in a marine environment or drilling in a land environment.

[0069] The environment in which the drilling method according to the present embodiment is used is not particularly limited, and the method can be used in any environment, such as flat land, mountainous areas, rivers, canals, and oceans. The drilling method according to the present embodiment is preferably used in marine environments where reduction of environmental load is particularly required. The method can also be used for drilling geothermal wells. Note that the strata in geothermal areas are much hotter and have lower pressures than those in oil and natural gas, so it is desirable to use heat-resistant components as components constituting the drilling fluid.

[0070] The present invention is not limited to the above-described embodiment. The present invention is also not limited to the above-described effects. Furthermore, the present invention can be modified in various ways without departing from the gist of the present invention.

[0071] [Disclosure items] Each of the following sections is a disclosure of a preferred embodiment.

[0072] [Item 1] A drilling fluid comprising water and a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The drilling fluid, wherein the poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1 to 40. [Item 2] 2. The drilling fluid according to item 1, wherein the poly(3-hydroxyalkanoate) resin particles have an average primary particle size of 0.5 to 30 μm. [Item 3] 3. The drilling fluid according to item 1 or 2, wherein the content of the poly(3-hydroxyalkanoate)-based resin particles is 0.50 parts by mass or more and 500 parts by mass or less per 100 parts by mass of the water-absorbing silicate. [Item 4] 4. The drilling fluid according to any one of items 1 to 3, wherein the poly(3-hydroxyalkanoate)-based resin particles are contained in the drilling fluid in an amount of 2.0 g / L or more and 100.0 g / L or less. [Item 5] 5. The drilling fluid according to any one of items 1 to 4, further comprising at least one biodegradable polysaccharide selected from the group consisting of cellulose derivatives, xanthan gum, and guar gum. [Item 6] 6. The drilling fluid according to item 5, wherein the biodegradable polysaccharide is present in the drilling fluid in an amount of 2.0 g / L or more and 5.0 g / L or less. [Item 7] the biodegradable polysaccharide comprises the cellulose derivative, 7. The drilling fluid according to item 5 or 6, wherein the cellulose derivative comprises at least one selected from the group consisting of carboxymethyl cellulose and polyanionic cellulose. [Item 8] 8. The drilling fluid according to any one of items 1 to 7, wherein the water-absorbing silicate is contained in the drilling fluid in an amount of 0.01 g / L or more and 100 g / L or less. [Item 9] 9. The drilling fluid according to any one of items 1 to 8, wherein the water-absorbing silicate comprises at least one selected from the group consisting of bentonite and sepiolite. [Item 10] The drilling fluid according to any one of items 1 to 9, wherein the poly(3-hydroxyalkanoate)-based resin particles have a poly(3-hydroxyalkanoate)-based resin containing a 3-hydroxyalkanoic acid represented by the following formula (1): [-CHR-CH2-CO-O-] (1) In the formula (1), R is C p H 2p+1 and p represents an integer of 1 to 15. [Item 11] 11. The drilling fluid according to item 10, wherein the poly(3-hydroxyalkanoate) based resin particles comprise poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). [Item 12] 1. An additive for a drilling fluid comprising a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1 to 40. EXAMPLES

[0073] The present invention will now be described in more detail with reference to examples and comparative examples, although the present invention is not limited to these examples in any way.

[0074] <Average primary particle size, average particle size, and average aspect ratio> The average primary particle size, average particle size, and average aspect ratio of the production examples were measured by the methods described above. The average aspect ratio of the poly(3-hydroxyalkanoate) resin fibers was calculated by measuring the diameter and length of each fiber using a fineness measuring device DENICON-DC21 (manufactured by Search Co., Ltd.).

[0075] <Production Example 1 (Production Method of Poly(3-hydroxyalkanoate)-Based Resin Particles A) (Used in Examples 1 and 2)> According to the method described in Example 1 of WO2021 / 085534, poly(3-hydroxyalkanoate)-based resin particles A (P3HA-based resin particles A) containing the P3HA-based resin poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH) were obtained in Production Example 1. The obtained P3HA-based resin particles A were approximately spherical, and the average primary particle diameter of the P3HA-based resin particles A was 2.0 μm, the average particle diameter (d50) was 148 μm, and the average aspect ratio was 1.0.

[0076] <Production Example 2 (Production Method of Poly(3-hydroxyalkanoate)-Based Resin Particles B) (Used in Examples 3 and 4)> The P3HA resin particles A obtained in Production Example 1 were melt-kneaded at 150°C using a twin-screw extruder (screw diameter: 40 mm) and cut to a length of 3 mm by pelletizing to obtain P3HA resin particles B. The obtained P3HA resin particles B were columnar, and the average aspect ratio of the P3HA resin particles B was 1.25.

[0077] <Production Example 3 (Production method of poly(3-hydroxyalkanoate)-based resin fiber (fiber length: 14.0 mm, diameter: 0.035 mm)) (used in Comparative Example 1)> The P3HA resin particles B obtained in Production Example 2 were melted in a kneading extruder (single-screw extruder, screw diameter 25 mm). The resulting melt was discharged from a spinning nozzle (temperature: 175°C, shape of nozzle hole: circular, diameter of nozzle hole: 0.3 mm, number of nozzle holes: 184) to obtain 184 spun filaments. The flow rate of the melt was adjusted to 5.2 kg / h by a gear pump. Next, in the spinning tube, air at 20°C was blown onto the spun filaments from the circumferential direction at a speed of 0.7 m / s to cool the spun filaments. The cooled spun filament was taken up by the first take-up roll section (speed: 448 m / min), transported in sequence by the second to fifth transport roll sections (speed: 517 m / min), and then wound up by the winding roll section (speed: 470 m / min) to obtain a multifilament. 20 of the multifilaments were combined to obtain a yarn with a total fiber size of about 100,000 dtex. The yarn was cut into a poly(3-hydroxyalkanoate)-based resin fiber (P3HA-based resin fiber) with a fiber length of 14 mm using a rotary cutter. The average aspect ratio of the obtained P3HA-based resin fiber was 395.

[0078] <Production Example 4 (Production method of poly(3-hydroxyalkanoate)-based resin fiber (fiber length: 14.0 mm, diameter: 0.016 mm)) (used in Comparative Examples 2 and 3)> P3HA resin fibers with a fiber length of 14 mm were obtained by the same method as in Production Example 3, except that the melt flow rate was 2.6 kg / h and the number of extrusion holes was 368. The average aspect ratio of the obtained P3HA resin fibers was 883.

[0079] (Drilling Fluids of Examples and Comparative Examples) In addition to the above materials, the following materials were prepared: That is, Thermogel (sepiolite) manufactured by Terunite Co., Ltd. was prepared as a water-absorbent silicate. As a material containing biodegradable polysaccharides (biodegradable thickener), Terpolymer H (main component: polyanionic cellulose polymer (PAC) which is a biodegradable polysaccharide) manufactured by Ternite Co., Ltd. was prepared. Tap water was prepared as water. Then, using the above-mentioned materials and a home mixer, drilling fluids of the examples and comparative examples were prepared in the blending ratios shown in Table 1 below.

[0080] (Low temperature and low pressure dehydration test) Using a low-temperature, low-pressure dehydration tester containing filter paper (Figure 1), the drilling fluid (mud) was dehydrated for 30 minutes under low-temperature, low-pressure conditions (room temperature, 100 psi) simulating the shallow part of the wellbore, and the thickness of the mud wall formed on the filter paper, the solid concentration in the mud wall, and the amount of dehydration were determined. The solid concentration in the mud wall was calculated using the following formula. C S = [{WL / (A×FC)}+1]×M S CS : Solid concentration in mud wall (vol%) WL: Dehydration amount (cm 3 ) A: Filtration area (cm 2 ) FC: Mud wall thickness (cm) M S : Solids concentration in drilling fluid (mud water) (vol%) Here, the filtration area is 45.8 cm 2 It was. In addition, when calculating the solid concentration in the drilling fluid (mud water), the density of sepiolite was set to 2.00 g / cm3, taking into consideration that sepiolite in the drilling fluid (mud water) swells due to hydration. 3 It was decided. The results are shown in Table 1 below.

[0081] (High-temperature, high-pressure dehydration test) Using a high-temperature, high-pressure dehydration tester containing filter paper (Figure 2), the drilling fluid (mud) was dehydrated for 30 minutes under high-temperature, high-pressure conditions (93°C, 500 psi) simulating those found deep in a wellbore, and the thickness of the mud wall formed on the filter paper, the solids concentration in the mud wall, and the amount of dehydration were determined. The results are shown in Table 1 below.

[0082] [Table 1]

[0083] As shown in Table 1 above, in Examples 1, 2, and 4 within the scope of the present invention, the mud wall thickness was smaller and the dewatering amount was smaller than those of Comparative Examples 1 to 3, which had a large aspect ratio, and Comparative Example 4, which did not contain P3HA-based resin particles. Furthermore, in Example 3 within the scope of the present invention, the mud wall thickness was smaller and the amount of dewatering was smaller than those of Comparative Examples 1, 2, and 4 and Comparative Example 4 which did not contain P3HA-based resin particles. Furthermore, in Example 3 within the scope of the present invention, the thickness of the mud wall was comparable to that of Comparative Example 3, but the amount of dewatering was smaller than that of Comparative Example 3. Therefore, it is seen that the present invention can provide a drilling fluid that is excellent in mud wall formation property and lost circulation prevention property.

[0084] In Example 1, in which the average primary particle diameter of the P3HA-based resin particles was within the range of 0.5 to 30 μm, the amount of P3HA-based resin particles was similar, but the mud wall thickness was smaller and the amount of dewatering was smaller than in Example 3, in which the average primary particle diameter of the P3HA-based resin particles was larger (2.4 mm or more). In addition, in Example 2, in which the primary particle diameter of the P3HA-based resin particles was in the range of 0.5 to 30 μm, the amount of P3HA-based resin particles was similar, but the mud wall thickness was smaller and the dewatering amount was smaller than in Example 4, in which the average primary particle diameter of the P3HA-based resin particles was larger (2.4 mm or more). Therefore, it can be seen that by containing P3HA resin particles having an average primary particle diameter in the range of 0.5 to 30 μm in a drilling fluid, a drilling fluid with even better mud wall formation properties and lost circulation prevention properties can be provided.

[0085] (The shape and composition of water-absorbent silicate and P3HA-based resin particles) Using a scanning electron microscope (SEM), images of sepiolite, a water-absorbent silicate, and P3HA-based resin particles A (P3HB3HH particles) were taken, and elemental analysis was also performed. The image and a spectrum chart are shown in FIG.

[0086] As shown in Figure 3, sepiolite was observed to be in the form of needle-like crystals, and it was also confirmed that the main component of sepiolite was silica. Furthermore, as shown in Figure 3, single particles (primary particles) (2 μm) and aggregate particles (secondary particles) (40 μm) of P3HA-based resin particles (P3HB3HH particles) were observed. It was also confirmed that the main component of the P3HA-based resin particles was carbon.

[0087] (Evaluation of sealing ability of P3HA resin particles in mud walls) Using the same high-temperature, high-pressure dehydration tester as in FIG. 2 except that it contained a 20μ ceramic disk instead of filter paper, the drilling fluid of Example 2 and the drilling fluid of Comparative Example 4 were each dehydrated under high-temperature, high-pressure conditions (93°C, 300 psi) for 30 minutes, and the thickness of the mud wall formed on the ceramic disk and the amount of dehydration were determined. The results are shown in Table 2. The mud wall formed on the ceramic disk was then vacuum dried at 60°C. Then, a scanning electron microscope (SEM) was used to obtain images of the cross sections of the dried mud walls and perform elemental analysis. The image and a spectrum chart are shown in FIG.

[0088] [Table 2]

[0089] As shown in Table 2, in Example 2, compared to Comparative Example 4, the amount of dewatering was reduced by 20% and the thickness of the mud wall was reduced by 2.8%. Furthermore, from FIG. 4, it can be seen that in Example 2, the pores in the mud wall are blocked by individual particles and aggregated particles of about 2 μm. Thus, it is believed that in the present invention, the P3HA resin particles block the pores in the mud wall, thereby improving the prevention of lost circulation.

Claims

1. A drilling fluid comprising water and a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1 to 40.

2. The drilling fluid according to claim 1, wherein the poly(3-hydroxyalkanoate)-based resin particles have an average primary particle size of 0.5 to 30 μm.

3. The drilling fluid according to claim 1 or 2, wherein the content of the poly(3-hydroxyalkanoate)-based resin particles is 0.50 parts by mass or more and 500 parts by mass or less with respect to 100 parts by mass of the water-absorbing silicate.

4. The drilling fluid according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin particles are contained in the drilling fluid in an amount of 2.0 g / L or more and 100.0 g / L or less.

5. 3. The drilling fluid of claim 1 or 2, further comprising at least one biodegradable polysaccharide selected from the group consisting of cellulose derivatives, xanthan gum, and guar gum.

6. 6. The drilling fluid of claim 5, wherein the biodegradable polysaccharide is present in the drilling fluid in an amount of 2.0 g / L or more and 5.0 g / L or less.

7. the biodegradable polysaccharide comprises the cellulose derivative, 6. The drilling fluid of claim 5, wherein the cellulose derivative comprises at least one selected from the group consisting of carboxymethyl cellulose and polyanionic cellulose.

8. The drilling fluid according to claim 1 or 2, wherein the water-absorbing silicate is contained in the drilling fluid in an amount of 0.01 g / L or more and 100 g / L or less.

9. The drilling fluid according to claim 1 or 2, wherein the water-absorbing silicate comprises at least one selected from the group consisting of bentonite and sepiolite.

10. The drilling fluid according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin particles have a poly(3-hydroxyalkanoate)-based resin containing a 3-hydroxyalkanoic acid represented by the following formula (1): [-CHR-CH ２ -CO-O-] (1) In the formula (1), R is C ｐ H ２ｐ＋１ and p is an integer of 1 to 15.

11. The drilling fluid of claim 10, wherein the poly(3-hydroxyalkanoate) based resin particles comprise poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

12. 1. An additive for a drilling fluid comprising a water-absorbing silicate, Further comprising poly(3-hydroxyalkanoate)-based resin particles, The poly(3-hydroxyalkanoate) resin particles have an average aspect ratio of 1 to 40.

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