JP2016148193A - Mining method using polylactic acid particle, and polylactic acid particle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable resource gas, particularly, shale gas to be efficiently extracted through cracks by providing a mining method using polylactic acid particles with hydrolyzability, circularity and a particle diameter, appropriate for a hydraulic fracture.SOLUTION: A polylactic acid particle with a weight average molecular weight (Mw) of 10,000 or more has an average particle diameter (D) set to be in the range of 300-800 μm, and has circularity with a minor axis/major axis ratio of 0.8 or more. A mining method includes a step of mixing the polylactic acid particles and proppant into an aqueous dispersion medium fluid and pressing the fluid into an ore chute that is formed underground.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a mining method using polylactic acid particles, and further relates to polylactic acid particles used in the mining method.

Hydrolyzable resins represented by polylactic acid are also excellent in biodegradability. From the viewpoint of environmental improvement, etc., they are currently being investigated as substitutes for various plastics in various applications, and some have been put to practical use. Has been.
Recently, the use as an additive to be added to the drilling fluid used when collecting underground resources has also been proposed (see Patent Documents 1 to 3).

  For example, a well drilling method called a hydraulic fracturing method is currently widely used for collecting underground resources. Such a drilling method pressurizes the drilling fluid filling the well at high pressure, thereby generating a crack (fracture) in the vicinity of the well, improving the permeability (ease of fluid flow) in the vicinity of the well, It expands the effective cross section of resources such as oil and gas into the well, and increases the productivity of the well. Such drilling fluids are also called fracturing fluids. In the past, viscous fluids such as gel-like gasoline were used, but recently, shale gas produced from a shale layer that exists in a relatively shallow place. With the development of the above, considering the influence on the environment, aqueous dispersions in which polymer particles are dissolved or dispersed in water have been used. As such polymers, hydrolyzable resins such as polyoxalate and polylactic acid have been proposed.

That is, when the drilling fluid in which the hydrolyzable particles as described above are dispersed in water is filled in the well and is pressurized, the particles penetrate into the vicinity of the well, and cracks (fractures) that have already formed are formed. ) As a sealing material (sealing material), and the passage of resources such as gas and oil can be effectively blocked temporarily.
In general, in order to generate a crack in a well, a preliminary blast called perporation is performed in a horizontal well. Such preliminary blasting produces a large number of small cracks along with relatively large cracks in the deep part of the well. After that, when a drilling fluid (fracturing fluid) is injected into the well, the fluid flows into these cracks, and a load is applied to these cracks, so that the cracks have a size suitable for collecting resources. Although it will grow, the crack formed at the beginning is temporarily clogged with the above-mentioned hydrolyzable resin particles, so that the subsequent fluid pressurization makes the crack more effective. It becomes possible to form. The additive added to the fluid in order to temporarily close the crack in this way is called a diverting agent.

  Since the hydrolyzable particles are hydrolyzed by underground water and enzymes and disappear, it is not necessary to remove the hydrolyzable particles in a subsequent process, and the well drilling is efficiently advanced.

By the way, the temperature of the well varies depending on the depth, the temperature in the well varies widely from 40 ° C. to 200 ° C., and the optimum hydrolyzable resin varies depending on the temperature in the well where a crack for resource collection is formed. Poly lactic acid that is collected from a relatively shallow stratum such as shale gas, etc., often has a well bore temperature of 100 degrees or less, is highly hydrolyzable, has high biodegradability, and does not cause environmental pollution. The use of is desired.
In particular, polylactic acid has an advantage that it is inexpensive, and there is a great expectation for its use as a mining liquid used in large quantities.

Further, when hydrolyzable particles are added to the dispersion for excavation, the particle shape and particle size become a problem. That is, such hydrolysable particles are introduced into cracks (fractures) formed in the ground, and serve to close the cracks or to suppress the collapse of the cracks. Therefore, it is required to have a particle shape close to a spherical shape and an appropriate particle size. For example, if the particle shape is indefinitely far from a sphere (ie, the roundness of the particle is low), there are many voids even if it is difficult to press-fit into the crack or it can be introduced into the crack. It becomes difficult to effectively suppress the outflow of gas from the crack. If the particles are too large, it is difficult to penetrate into the cracks. If the particles are too small, it is necessary to use a remarkably large amount of particles in order to close the cracks.
However, hydrolysable particles having a high sphericity and a particle size suitable for hydraulic fracturing have not been known so far.

JP2014-134090A JP2014-134091A JP2014-177618A

Accordingly, an object of the present invention is to provide a mining method using polylactic acid particles having hydrolyzability, roundness and particle size suitable for hydraulic fracturing.
Another object of the present invention is to provide polylactic acid particles having a particle form most suitable for the mining method.

According to the present invention, the average particle diameter (D ₅₀ ) is in the range of 300 to 1000 μm, the weight average molecular weight (Mw) having a roundness with a minor axis / major axis ratio of 0.8 or more is 10,000 or more. There is provided a mining method characterized by including a step of mixing polylactic acid particles and proppant into an aqueous dispersion medium fluid and press-fitting the fluid into a well formed underground.

According to the present invention, polylactic acid particles having an average particle diameter (D ₅₀ ) in the range of 300 to 1000 μm and a roundness with a minor axis / major axis ratio of 0.8 or more are provided. .

In the mining method of the present invention, polylactic acid particles and proppant are mixed with an aqueous dispersion medium fluid, and the fluid is pressed into a well formed in the ground. The polylactic acid added to the dispersion medium fluid These particles are introduced into the crack formed in the well and exhibit a function of temporarily closing the crack. That is, by introducing the polylactic acid particles into a crack formed by perforation (preliminary blasting) and temporarily closing the crack, a further crack is generated by a subsequent press-fitting of fluid or the like. It becomes possible to grow a crack. In cracks where polylactic acid particles are introduced, gas outflow is effectively suppressed from within the cracks, so fluid pressure is effective at other locations (for example, where fine cracks are generated). In addition, it promotes further growth of fine cracks.
The polylactic acid particles are hydrolyzed and disappear after a predetermined time, and as a result, the underground gas flows out into the crack and the gas flowing out from the crack is collected. This proppant has the function of maintaining this crack. That is, since a hollow channel structure is formed in the crack after the disappearance of the polylactic acid particles, it tends to collapse due to underground pressure. The proppant introduced into the crack effectively prevents the crack from collapsing, thereby efficiently collecting the resource gas through the crack.

  By the way, as the proppant, inorganic particles such as sand grains are generally used, and the shape of the particles is not limited as long as it has a size that can be introduced into the cracks. It is required to have a shape close to a true sphere in order to close and close the crack, and to have a size that can be introduced into the crack. It is also necessary to have particle strength.

However, polylactic acid particles satisfying such conditions have not been produced so far, but the present inventors have succeeded in producing such polylactic acid particles by adopting a specific method. It is.
That is, in the present invention, polylactic acid particles having a particle form that has not been produced so far, specifically, the average particle diameter (D ₅₀ ) is in the range of 300 to 1000 μm, and the ratio of minor axis / major axis is In addition to having a roundness of 0.8 or more and a weight average molecular weight (Mw) of 10,000 or more (especially 50000 or more), the introduction into the cracks can be performed quickly. (The particle size is in a certain range), and a predetermined particle shape is maintained for a certain period (weight average molecular weight is more than a certain range), and further, it is packed closely so that no voids are generated in the crack (Roundness is high), and temporary closure of cracks can be performed effectively.

  As described above, the mining method of the present invention including the step of mixing predetermined polylactic acid particles and proppant into an aqueous dispersion medium fluid and press-fitting it into a well effectively performs temporary clogging of cracks, Generation and growth operations can be performed effectively, and the retention of cracks after the disappearance of polylactic acid particles is also effectively performed, so that resource gas, particularly shale gas, can be efficiently collected through the cracks.

The electron micrograph which shows the polylactic acid particle | grains used by this invention. The figure which shows schematic structure of an example of the dripping type particle manufacturing apparatus used for manufacture of the polylactic acid particle | grains of this invention. The figure which shows schematic structure of the other example of the dripping type particle manufacturing apparatus used for manufacture of the polylactic acid particle | grains of this invention.

<Polylactic acid particles>
The polylactic acid particles used in the present invention have a high sphericity, particularly as shown in the photomicrograph of FIG. 1, for example, a roundness represented by a minor axis / major axis ratio of 0. 8 or more, especially very close to 1.
Also, the particles have an average particle size based on volume measured by a laser diffraction scattering method _{(D 50)} is in the range of 300 to 1000.

That is, the polylactic acid particles of the present invention have high sphericity as described above, and at the same time, the size of the particles is suitable for introduction into cracks formed in a well during hydraulic fracturing. Have For this reason, it exhibits an excellent function as an agent called a diverting agent that is introduced into a crack formed in a well during hydraulic fracturing and temporarily closes the crack.
For example, if the sphericity is lower than the above range, even if it can be introduced into the crack, the function of closing the crack is poor, and the outflow of gas from the crack cannot be effectively suppressed. It will interfere with the work to be formed. If the particle size is larger than the above range, it is difficult to introduce particles into the crack, and if the particle size is smaller than the above range, it is difficult to effectively block the crack. In addition, problems such as dust scattering are likely to occur during handling.

  Thus, the polylactic acid particles of the present invention have a form suitable for use in addition to a dispersion for excavation for hydraulic fracturing at the time of hydraulic crushing. And the angle of repose is as very small as 50 degrees or less (for the measurement method, refer to Examples described later).

The polylactic acid forming the particles having the above-described form may be either 100% poly-L-lactic acid or 100% poly-D-lactic acid, or poly-L-lactic acid and poly-D-lactic acid. It may be a melt-blended product of L-lactic acid and a random copolymer or block copolymer of L-lactic acid and D-lactic acid.
Further, various copolymer components may be copolymerized in a small amount as long as the hydrolyzability of polylactic acid is not impaired. Examples of such copolymer components include ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol. Dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid, and diesters thereof; glycolic acid, Hydroxycarboxylic acids such as L-lactic acid, D-lactic acid, hydroxypropionic acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; And lactones such as caprolactone, butyrolactone, valerolactone, poropiolactone, and undecalactone.

  In addition, the above-mentioned polylactic acid has an appropriate particle strength, and at least during the excavation operation, the weight average molecular weight (Mw) is 10,000 or more, particularly 50,000 to 500,000, from the viewpoint that the particle morphology is stably maintained. Is in range.

  The polylactic acid particles used in the present invention can be hydrolyzed by mixing a small amount of other hydrolyzable resins (for example, polyoxalate or polyglycolic acid) as long as the excellent characteristics of polylactic acid are not impaired. May be adjusted, and if necessary, known plasticizers, heat stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, fillers, mold release Additives such as agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, and nucleating agents may be blended. Moreover, in order to control crystallinity, you may add the component compatibilized with polylactic acid, and a cellulose derivative, a polymethylmethacrylate, a polyvinyl acetate etc. are mentioned as a component to compatibilize.

<Manufacture of polylactic acid particles>
By the way, the polylactic acid particles having the above high sphericity and a moderately sized particle size are manufactured by a dropping method using a dropping nozzle having a single tube structure or a multiple tube structure. Difficult to manufacture.
For example, in the mechanical pulverization of a polylactic acid lump, the sphericity of the particles is naturally lowered.
In addition, as a method for producing spherical particles, a method using a poor solvent or a method such as spray spraying causes the particle size to become too fine, and even in strand cutting by resin extrusion, the particle size is too small. It becomes extremely coarse.
As described above, in the methods generally employed in the past, even if the particle diameter can be formed into a true sphere, the particle diameter cannot be adjusted to the above-described range (300 to 1000 μm).

  The polylactic acid particles of the present invention are manufactured using a dropping method using a dropping nozzle. The dropping type particle manufacturing apparatus used in such a dropping method has a single tube structure as shown in FIG. And a multi-tube structure as shown in FIG.

  In the single tube structure of FIG. 2, A liquid is supplied to the nozzle of the single tube shown by 5 and a droplet 7 of A liquid is dripped from the tip of the A tube. It is dripped.

As the above-mentioned liquid A, the liquid material of polylactic acid described above (including a compounding agent appropriately blended) is used. Although it is possible to supply a polylactic acid melt directly to the single tube nozzle 5 as such a liquid material (liquid A), a droplet 7 having a high viscosity and adjusted to a predetermined particle diameter is dropped. Therefore, it is preferable to adjust the viscosity to about 10 to 10000 mPa · sec (25 ° C.) using a predetermined organic solvent, and supply the organic solvent solution of polylactic acid as A liquid. .
Examples of the organic solvent used here include dichloromethane, chloroform, dimethyl sulfoxide, dimethylformamide, acetone, toluene, ethyl acetate, and the like. The concentration of the organic solvent solution is preferably in the range of 10% to 70% by weight.

  The liquid droplets dropped from the tip of the single tube nozzle 5 as described above are dropped into the receiving tank 9. The receiving tank 9 is filled with a poor polyoxalate solvent such as water or methanol, and can be precipitated and solidified on the spot to obtain polyoxalate particles 11 having a target particle size.

  Further, in the multi-tube structure of FIG. 3, the dropping nozzle 5 is formed of the core tube 1 and the outer tube 3, and the droplet 7 dropped from the nozzle 5 is received in the receiving tank 9 as described above. It is dripped.

  That is, in this apparatus, the liquid A is supplied to the core tube 1 of the dropping nozzle 5 and the liquid B is supplied to the outer tube 3, so that the droplet 7 dropped from the nozzle 5 has the liquid A as a core. The capsule structure has the B liquid as a shell.

  In the present invention, the liquid material of polylactic acid described above is used as the liquid A forming the core of the liquid droplet 7 as in FIG. 2, and the liquid B forming the shell of the liquid droplet 7 is sodium alginate. An aqueous solution is used. That is, this B liquid functions as a particle size adjusting agent that prevents the fusion of the polylactic acid particles and maintains a constant particle size.

By supplying such A liquid to the core tube 1 and supplying and dropping the above-mentioned sodium alginate aqueous solution as B liquid, droplets 7 encapsulated with A liquid as the core and B liquid as the shell are formed. However, in this case, in order to effectively perform the encapsulation, the viscosity of the sodium alginate aqueous solution used as the liquid B is preferably adjusted to be about 10 to 1000 mPa · sec (25 ° C.). For example, the concentration of the aqueous solution is preferably in the range of about 1 to 5% by mass.
The inner diameter of the tip of the nozzle 5 as described above (the inner diameter of the core tube 1 and the outer tube 3) is set to such a range that the diameter of the finally obtained particles is within the aforementioned range, and the A liquid and The supply speed of the B liquid is also set to be in an appropriate range, but it is usually desirable that the flow ratio of the A liquid and the B liquid is appropriately set.

The droplet 7 dropped from the tip of the nozzle 5 as described above is dropped into the receiving tank 9.
The receiving tank 9 is filled with an aqueous calcium chloride solution, whereby polylactic acid particles 10 covered with calcium alginate are deposited. By soaking the droplet 10 thus deposited in a sodium citrate aqueous solution stretched in the receiving tank 9 ', polylactic acid particles 11 in which the shell of the B liquid is removed from the particles 10 are obtained.

The polylactic acid particles 11 obtained using the dripping nozzles of FIGS. 2 and 3 are all recovered immediately from the receiving tank 9 or 9 ′, and when containing a solvent, are appropriately put into water to remove the solvent. To do. This operation may be performed before removing the coated sodium alginate when encapsulation is performed using the apparatus of FIG.
In general, the obtained particles are appropriately sieved to collect particles having a predetermined particle size, and further appropriately dried with hot air to be used as target polylactic acid particles.

  In the above description, an example in which an aqueous sodium alginate solution is used as the liquid B forming the shell is not limited to this, but the liquid A is stably coated around the liquid droplets. Any aqueous solution of a salt or the like having an appropriate viscosity capable of preventing fusion between the A liquids can be used as the B liquid. Moreover, according to the kind of B liquid, the kind of aqueous solution stretched to the receiving tank 9 can also be selected suitably.

<Drilling method>
The above-mentioned polylactic acid particles can effectively avoid inconveniences such as dust scattering and are effectively prevented from being fused on the ground. And has a function of temporarily closing the crack, and hydrolyzes and disappears after a certain period of time.
Therefore, it is suitably used for the preparation of a drilling dispersion such as a fracturing fluid used in underground resource mining sites, and this polylactic acid particle and proppant are used as an aqueous dispersion medium fluid (specifically for mining shale gas). In other words, the fluid is mixed with water and used by injecting the fluid into a well formed underground.

  As described above, the proppant used together with the polylactic acid particles is for maintaining the channel structure of cracks formed by the disappearance of the polylactic acid particles. Usually, sand grains and other hard inorganic particles are used. (For example, clay) is used, and the particle size thereof may be a size that can be quickly introduced into the crack, and specifically, it may be in the range of 800 μm or less, like the polylactic acid particles. More preferably, it has a size of 300 μm or more. This is because, when the particles are extremely fine, the effect of retaining cracks is reduced.

  In addition, guar gum or xanthone is added as a thickener to impart moderate viscosity to the water of the aqueous dispersion medium fluid to which the polylactic acid particles and proppant are added, and to promote the formation of cracks due to press-fitting. You can also keep it. Prior to the injection of polylactic acid particles and proppant, a salt such as calcium carbonate is dispersed as a water-dissipating agent, and a fluid is injected in this state to form a cake on the wall surface of the well. You can also. By forming such a cake, water can be prevented from penetrating into the ground from the wall surface of the well, and the collapse of the well can be effectively avoided.

  After the above-described polylactic acid particles and proppant are injected, many cracks are generated, and the disappearance of polylactic acid particles forms the channel structure of cracks maintained in proppant. For example, shale gas is collected. Of course, polylactic acid particles and proppant can be repeatedly press-fitted to promote the generation of more cracks.

  The invention is illustrated by the following experimental example.

<Measurement of roundness>
For 10 particles randomly selected by SEM observation, the average value of the minor axis / major axis was calculated and used as the roundness.

Production of polylactic acid (PLA) particles;
A dichloromethane solution (concentration: 10% by weight) of PLA (Revode 101) was prepared and used as solution A. Moreover, 1.5% sodium alginate aqueous solution was used as B liquid.
As a dripping type particle manufacturing apparatus, an encapsulating apparatus with a concentric nozzle (Encapsulator B-390 manufactured by Nihon Büch, core nozzle tip diameter 450 μm, shell nozzle tip diameter 900 μm) having a structure shown in FIG. 3 was prepared.
The liquid A (10% PLA solution) is introduced into the core flow path (1), and the liquid B (1.5% sodium alginate aqueous solution) is introduced into the shell flow path (3) to obtain a 10% calcium chloride aqueous solution. Was dropped into a receiving tank (9) stretched with a sodium alginate-coated PLA capsule (10).

The sodium alginate-coated PLA capsule (10) obtained above was once immersed in water to remove the solvent (dichloromethane) in the capsule, then immersed in a 55 mM aqueous sodium citrate solution for one day, and then an opening of 150 μm After collecting through a sieve, the particles were washed with water to obtain PLA particles.
The roundness of the particles was 0.95, and the SEM photograph was as shown in FIG.

1: Core tube 3: Outer tube 5: Multiple tube nozzle for dropping 7: Droplet 9: Receiving tank

Claims (2)

Polylactic acid particles having an average particle diameter (D ₅₀ ) in the range of 300 to 1000 μm, a short diameter / long diameter ratio of 0.8 or more, and a weight average molecular weight (Mw) of 10,000 or more; A mining method comprising the steps of mixing proppant with an aqueous dispersion medium fluid and press-fitting the fluid into a well formed underground. Polylactic acid particles having an average particle diameter (D ₅₀ ) in the range of 300 to 1000 μm and a roundness with a minor axis / major axis ratio of 0.8 or more.