JP2014134090A - Dispersion for drilling and drilling method using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion for drilling, which is produced by dispersing an inexpensive hydrolyzable resin material that shows high hydrolyzability in an aqueous medium, and is used when underground resources are collected by a well drilling method such as a hydrofracturing technique, a rotary drilling method and a riser-less drilling method.SOLUTION: In the dispersion for drilling, a hydrolyzable resin material containing a hydrolyzable resin that is hard to be hydrolyzed and a hydrolyzable resin that has ester decomposition promoting properties is dispersed in an aqueous medium.

Description

  The present invention relates to a dispersion for excavation used when collecting underground resources such as oil and natural gas by a well drilling method such as a hydraulic fracturing method, a rotary drilling method, and a riserless drilling method.

Currently, well drilling methods such as hydraulic fracturing, rotary drilling, and riserless drilling are widely used to collect underground resources.
In the rotary type drilling method, a well is formed by drilling with a drill while circulating mud water, and a finishing fluid is blended with a water loss prevention agent. A filter called mud wall is used on the wall of the well. A cake is formed. This cake keeps the well wall stable and prevents collapse, and reduces friction with the fluid flowing through the well.
In addition, the hydraulic fracturing method pressurizes the fluid filling the well at high pressure, thereby generating a crack (fracture) in the vicinity of the well, improving the permeability (fluidity 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.

By the way, as the water-dissipation inhibitor to be blended in the above-mentioned finishing fluid, calcium carbonate and various types of salt granules are mainly used. There are problems in that it requires processing, and that it is rooted in the formation where resources are to be mined, resulting in production failures.
The fluid used in the hydraulic fracturing method is also called a fracturing fluid. In the past, viscous fluid such as gel-like gasoline was used, but recently it has been produced from a shale layer that exists in a relatively shallow place. With the development of shale gas and the like, an aqueous dispersion in which a polymer is dissolved or dispersed in water has been used in consideration of the influence on the environment. Polylactic acid is known as such a polymer (see Patent Document 1).

That is, polylactic acid is a substance exhibiting hydrolyzability and biodegradability, and even if it remains in the ground, it does not adversely affect the environment because it is degraded by moisture and enzymes in the ground. In addition, it can be said that water used as a dispersion medium has little influence on the environment as compared with gasoline.
In addition, when such a polylactic acid water dispersion is filled in the well and pressurized, the polylactic acid penetrates into the vicinity of the well, but this polylactic acid is hydrolyzed and loses its resin form. As a result, a space (that is, a crack) is generated in a portion where the polylactic acid has permeated, and therefore, it is possible to increase a space for inflow of resources to the well.
In addition, polylactic acid also functions as a water loss prevention agent and suppresses excessive penetration of water used as a dispersion medium into the ground, thus minimizing environmental changes to the formation. Have. Moreover, since it decomposes in the ground, no acid treatment is required.
In addition, lactic acid, which is a degradation product of polylactic acid, is a kind of organic acid. After polylactic acid is decomposed, lactic acid is released, and it also has a function of promoting porosity of the shale layer by acid erosion of the shale layer. .

  However, polylactic acid hydrolyzes relatively quickly at high temperatures, but the temperature decreases and the hydrolysis rate is slow. Therefore, when applied to the collection of shale gas etc. produced from places with low underground temperatures. , Its efficiency is poor and improvement is required.

On the other hand, it has been proposed to use polyglycolic acid instead of polylactic acid (see Patent Document 2).
Polyglycolic acid is also known as a biodegradable resin, and is more hydrolyzable than polylactic acid. For example, the hydrolysis rate at a temperature of about 80 ° C. is considerably faster than polylactic acid. Effective as an alternative to lactic acid.
However, polyglycolic acid has a problem that it is considerably more expensive than polylactic acid, which is a fatal defect in the hydraulic fracturing method in which a large amount of fracturing fluid is used. Also, sufficiently satisfactory decomposability cannot be obtained under specific temperature conditions.

USP 7,833,950 WO2012-050187

  Accordingly, an object of the present invention is to provide a high-hydrolyzable and inexpensive hydrolyzable resin material dispersed in an aqueous medium, and a fracturing used in a finishing fluid or a hydraulic fracturing method when drilling a well. Disclosed is a drilling dispersion useful as a fluid.

According to the present invention, a dispersion for excavation characterized in that a hydrolyzable resin material containing a hardly hydrolyzable hydrolyzable resin and an esterolysis-promoting hydrolyzable resin is dispersed in an aqueous medium. Liquid is provided.
Further, when mining natural resources from the underground, a mining method characterized by including a step of hydrolyzing the biodegradable resin material in hot water at 40 ° C. or higher by pressing the dispersion for excavation into the underground Provided.

In the drilling dispersion of the present invention,
(1) The ester decomposition-promoting hydrolyzable resin is acid-releasing.
(2) the acid released is glycolic acid and / or oxalic acid,
(3) The acid-releasing hydrolyzable resin is a polyoxalate,
(4) The hardly hydrolyzable hydrolyzable resin is polylactic acid,
(5) Containing 30 parts by weight or more of an esterolysis-promoting hydrolyzable resin with respect to 100 parts by weight of the hardly hydrolyzable hydrolyzable resin,
Is preferred.

  In the excavation dispersion liquid of the present invention, the hydrolyzable resin material dispersed in the aqueous medium is mainly composed of an inexpensive hardly hydrolyzable hydrolyzable resin typified by polylactic acid. Compared with the prior art using acid, the cost advantage is great.

  In addition, in the present invention, the hydrolysis of the hardly hydrolyzable hydrolyzable resin is carried out because the hydrolyzable resin that is not easily hydrolyzed and the hydrolyzable resin (for example, polyoxalate) that promotes ester decomposition are used in combination. For example, the hydrolysis rate at a low temperature of 80 ° C. or lower is remarkably increased. That is, hydrolysis of polylactic acid or the like is promoted by the acid or alkali released from the ester decomposition-promoting hydrolyzable resin as a catalyst. In this case, it may be possible to add acid or alkali directly in place of the ester decomposition-promoting hydrolyzable resin. In this case, however, the hydrolyzable resin before filling the well or pressurizing. Since the hydrolysis of the water proceeds, it cannot be put to practical use.

When mining underground resources, the temperature of the underground layer where the underground resources exist greatly affects the mining conditions. In a mining dispersion in which a hydrolyzable resin is dispersed in water, the hydrolyzable resin has a water loss of about 40% (or more) within 4 days in a temperature range of 45 ° C. to 200 ° C. Decomposition performance is demanded, and at present, resources are often collected from a stratum that exists in a shallow place like the shale layer. For example, the stratum temperature is 40 ° C to 80 ° C, In many cases, the sample is collected from a place of 40 ° C to 60 ° C.
Dispersion for excavation of the present invention using the above-mentioned hardly hydrolyzable hydrolyzable resin (for example, polylactic acid) and ester decomposition-promoting hydrolyzable resin (for example, polyoxalate) as a hydrolyzable resin material The liquid sufficiently satisfies the hydrolysis performance as described above. For example, the liquid is particularly preferably used as a finishing fluid used for drilling a well or a fracturing fluid used for a hydraulic fracturing method.

  That is, when the excavation dispersion liquid of the present invention is used as a finishing fluid, a filter cake of solid content (an anti-water agent) such as calcium carbonate formed on the wall surface of the well is made of the hydrolyzable resin material. Since it can be made to decompose with the acid produced | generated by hydrolysis, the subsequent acid treatment becomes unnecessary and a water loss prevention agent can be collect | recovered rapidly. In addition, since the hydrolyzable resin material (solid content) itself in this dispersion also has a function as a water loss preventing agent, the water drainage from the well (ground) is formed by the filter cake formed by this solid content. Infiltration of water into the inside can be prevented, and the cake hydrolyzes after a predetermined period of time, so that it can be recovered without any particular acid treatment.

In addition, when this drilling dispersion is used as a fracturing fluid, the hydrolyzable resin material penetrates into the vicinity of the well when the well is filled and pressurized. Even when the underground temperature is low, the hydrolyzable resin material hydrolyzes in a short time, so that a space (crack) with a pillar structure can be generated in the portion where the resin material has penetrated, for example, shale gas Etc. can increase the production efficiency of drilling. In addition, since the acid generated by hydrolysis of the hydrolyzable split resin material dissolves minerals such as shale, the generation of cracks can be promoted.
Furthermore, the hydrolyzable resin material in this dispersion can also function as a sealant that blocks the flow path in the well, but since it hydrolyzes later, problems such as clogging due to sedimentation of the sealant Can be avoided and the production efficiency can be increased.

  Furthermore, by adding a gelling agent such as chitosan that dissolves at low pH to this dispersion, gelation is caused in the well by the acid generated by hydrolysis of the hydrolyzable resin material. This makes it possible to effectively infiltrate the liquid near the well by press-fitting the fluid, and at the same time to decompose the gel (lower viscosity) by the acid generated by further hydrolysis. And the subsequent recovery of the fracturing fluid can be effectively performed.

The figure which shows the molecular weight distribution of the sample after the hydrolysis test in Experimental example 14. FIG.

  The dispersion for excavation of the present invention is a dispersion in which a hydrolyzable resin material is dispersed in an aqueous medium, and this is blended to perform well drilling or hydraulic fracturing as necessary. These additives are appropriately blended.

<Hydrolyzable resin material>
In the present invention, the hydrolyzable resin material used includes a hardly hydrolyzable hydrolyzable resin and an ester decomposition-promoting hydrolyzable resin.

1. A hardly hydrolyzable hydrolyzable resin;
The hardly hydrolyzable hydrolyzable resin is the main component of this resin material. For example, a 1 mg / 1 ml aqueous dispersion is prepared with a sample obtained by freeze-pulverizing and pulverizing the hydrolyzable resin. In addition, after incubation at 45 ° C. for one week, the residual solution has a TOC (total organic carbon content) of 5 ppm or less. Further, it does not contain a water-soluble polymer. A water-soluble polymer (for example, solubility in water at 20 ° C. of 50 g / 100 g or more) is too high to penetrate into the ground, for example, has a large impact on the environment, and is suitable as a compounding agent used for a fracturing fluid. Absent.

  Examples of such hardly hydrolyzable hydrolyzable resins include polylactic acid, polyhydroxyalkanoate, polycaprolactone, polybutylene succinate, polybutylene succinate adipate, polybutylene terephthalate adipate, cellulose acetate, thermoplastic Starch and the like can be exemplified, and these can be used in the form of a copolymer or a blend, but polylactic acid is particularly optimal from the viewpoint of cost.

  The polylactic acid may be 100% poly-L-lactic acid or 100% poly-D-lactic acid, or a melt blend of poly-L-lactic acid and poly-D-lactic acid. It may be a random copolymer or block copolymer of lactic acid and D-lactic acid.

Furthermore, the hydrolyzable resin described above is a copolymer obtained by copolymerizing various aliphatic polyhydric alcohols, aliphatic polybasic acids, hydroxycarboxylic acids, lactones, etc., as long as the properties of the hydrolyzable resin are not impaired. It can also be used in the form of a coalescence.
Examples of such polyhydric alcohols include ethylene glycol, propylene glycol, butanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, and polyethylene glycol.
Examples of the polybasic acid include succinic acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, and terephthalic acid. Carboxylic acid diesters may be used.
Examples of the hydroxycarboxylic acid include glycolic acid, hydroxypropionic acid, hydroxyvaleric acid, hydroxycaproic acid, and mandelic acid.
Examples of the lactone include caprolactone, butyrolactone, valerolactone, poropiolactone, undecalactone, glycolide, and mandelide.
In addition, for such a hardly hydrolyzable resin, known plasticizers, heat stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, fillers, and the like are added as necessary. Additives such as agents, mold release agents, antistatic agents, fragrances, lubricants, foaming agents, antibacterial / antifungal agents, and nucleating agents may be blended.

  Moreover, the above-mentioned hardly hydrolyzable hydrolyzable resin should have an appropriate molecular weight in terms of function as a sealing material when used as a fracturing fluid and penetrability into the ground. In general, the weight average molecular weight should be in the range of 5,000 to 1,000,000, especially 10,000 to 500,000.

2. Ester decomposition-promoting hydrolyzable resin;
The above-mentioned hydrolyzable resin, such as polylactic acid, is hardly hydrolyzable, and requires a very long time for its decomposition at a temperature of 100 ° C. or lower, particularly at a low temperature of 80 ° C. or lower. For this reason, in the present invention, an ester decomposition-promoting hydrolyzable resin described below is blended.

  This ester decomposition-promoting hydrolyzable resin (hereinafter sometimes simply referred to as “ester-decomposable resin”) does not exhibit ester degradation by itself, but functions as a catalyst for ester decomposition when mixed with moisture. It releases acid or alkali.

  Such an ester-decomposable resin is usually uniformly dispersed inside the above-mentioned hardly hydrolyzable hydrolyzable resin, and the hydrolyzable resin is hydrolyzed by an acid or alkali released from the ester-decomposable resin. In order to accelerate the decomposition rapidly, for example, those having a weight average molecular weight of about 1,000 to 200,000 are used.

  Further, in such an ester-decomposable resin, as an alkali-releasing resin, an alkali metal salt of acrylic acid such as sodium acrylate or sodium alginate can be used. In particular, an acid releasing agent is preferably used.

As the acid released from the acid-releasing ester-decomposable resin, in particular, the pH (25 ° C.) in an aqueous solution or aqueous dispersion having a concentration of 0.005 g / ml is 4 or less, particularly 3 or less, Polymers that readily hydrolyze to release acid when mixed with water are preferably used. Examples of the acid to be released include oxalic acid and glycolic acid.
Examples of the polymer include polyoxalate and polyglycolic acid. These may be copolymers, used alone or in combination of two or more.
Examples of the component forming the copolymer include polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, octanediol, dodecanediol, neopentyl glycol, glycerin, pentaerythritol, sorbitan, bisphenol A, and polyethylene glycol; Acid, adipic acid, sebacic acid, glutaric acid, decanedicarboxylic acid, cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, anthracene dicarboxylic acid and other dicarboxylic acids and their diesters; glycolic acid, L-lactic acid, D-lactic acid, hydroxypropion Hydroxycarboxylic acids such as acid, hydroxybutyric acid, hydroxyvaleric acid, hydroxycaproic acid, mandelic acid, hydroxybenzoic acid; glycolide, caprolactone, Examples include lactones such as tyrolactone, valerolactone, poropiolactone, and undecalactone.
Also, for such ester-decomposable resins, known plasticizers, heat stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, flame retardants, colorants, pigments, fillers, fillers, if necessary. Additives such as mold release agents, antistatic agents, perfumes, lubricants, foaming agents, antibacterial / antifungal agents, and nucleating agents may be blended.

  In the present specification, a polymer obtained by polymerizing oxalic acid as at least one monomer in a homopolymer, copolymer, or blend is referred to as polyoxalate.

  In particular, the above-mentioned polyoxalate and polyglycolic acid are easily hydrolyzable hydrolyzable resins and rapidly hydrolyze, so that they are excellent in the ability to promote hydrolysis of hardly hydrolyzable resins. Among these, polyoxalates, particularly polyethylene oxalate, show remarkably high hydrolysis promoting ability compared to polyglycolic acid, and hydrolyze hardly hydrolyzable resins such as polylactic acid even at a temperature of 80 ° C. or lower. It can be remarkably accelerated, and is considerably cheaper than polyglycolic acid, and the merit of cost is extremely large.

  In addition, the ester-decomposable resin described above varies depending on the type, but in general, 1 part by weight or more per 100 parts by weight of the hardly hydrolyzable hydrolyzable resin is preferable in terms of promoting hydrolysis. In particular, from the viewpoint of hydrolysis promotion and cost, it is preferably used in an amount of 30 to 300 parts by weight, particularly 30 to 200 parts by weight. If the amount of the ester decomposing resin is too small, it becomes difficult to sufficiently promote the decomposition of the hardly hydrolyzable hydrolyzable resin. For example, it takes a considerable time for the hydrolysis at a temperature of about 80 ° C. Become. Further, if it is used in a larger amount than necessary, not only is it unsatisfactory in terms of cost, but the hydrolysis rate is too high, and there is a possibility that it may be difficult to handle as a fracturing fluid or a water loss adjusting agent.

3. Form of hydrolyzable resin material;
In the present invention, a biodegradable resin material containing the above-mentioned hardly hydrolyzable hydrolyzable resin (hardly hydrolyzable resin) and an ester decomposition promoting hydrolyzable resin (ester degradable resin) is known per se. By the above forming means, pellets, granules, crushed material obtained by breaking the film, fibers, capsules and the like are formed and dispersed in water.
That is, by causing a hardly hydrolyzable resin typified by polylactic acid and an ester decomposable resin to be in close contact with each other in a dispersion liquid, an acid etc. released from the ester decomposable resin causes a hardly hydrolyzable resin. It is possible to promote hydrolysis.

  Further, in the present invention, as long as the hardly hydrolyzable resin and the ester decomposable resin are present in close contact with each other and have an appropriate size, the form is limited to the above-described example. Although it is not a thing, it is particularly preferable to have a shell core structure in which a hardly hydrolyzable resin is a shell and an ester decomposable resin is a core. For example, in the above-described fiber, a core-sheath fiber having a non-hydrolyzable resin as a sheath and an ester-decomposable resin as a core is a preferred form. That is, by adopting such a form of the shell core structure, hydrolysis proceeds rapidly when water penetrates into the core portion, and the handleability as a fracturing fluid is enhanced.

  In the present invention, such a hydrolyzable resin material is usually present in an aqueous dispersion in an amount of 0.01 to 20% by weight, particularly 0.01 to 10% by weight. It is suitable for carrying out crushing smoothly.

In the present invention, in addition to the above-mentioned hardly hydrolyzable resin and ester decomposable resin, a water-absorbing polymer such as polyvinyl alcohol or CMC can be blended. By blending such a water-soluble polymer, hydrolysis before hydraulic crushing can be suppressed, and handling as a fracturing fluid can be improved.
However, since the function of the ester-decomposable resin may be impaired if the water-absorbing polymer is used too much, the amount used is usually 50 parts by weight or less, especially 1 to 100 parts by weight per 100 parts by weight of the hardly hydrolyzable resin. A range of 10 parts by weight is preferred.

<Other additives>
In this invention, the well-known additive mix | blended with a well drilling method or a hydraulic crushing method can be mix | blended with the water dispersion liquid in which the hydrolyzable resin material mentioned above was disperse | distributed.
For example, in the case of hydraulic fracturing, cracks generated by hydraulic fracturing can be obtained by blending as a thickener proppant containing water-soluble polysaccharides (gelling agent) such as guar gum and chitosan and sand (supporting agent). It can be held so as not to be blocked.
In addition, a surfactant for dispersing the hydrolyzable resin material can be blended, and furthermore, an appropriate amount of acid or acid can be added to appropriately promote the hydrolysis of the hydrolyzable resin material. Alkaline and enzyme can be added.

  Any additive may be added in such an amount that the hydrolyzable resin material is dispersed in the aqueous dispersion in the amount described above and does not impair the function of the hydrolyzable resin.

The above-described dispersion for excavation of the present invention is extremely useful as a finishing fluid used for excavating a well, a fracturing fluid used for mining underground resources by a hydraulic fracturing method, and the like.
Hereinafter, these uses will be described.

<Finishing fluid>
When a well is excavated by a rotary excavation method or the like, it is necessary to fill the well with a finishing fluid in order to prevent the well from collapsing. In such a finishing fluid, calcium carbonate and various salt granules are blended as an anti-water loss agent. That is, by press-fitting this finishing fluid into the well, a filter cake of the antifouling agent is generated on the wall surface of the well, and the drainage of the finishing fluid from the well (the flow of fluid to the vicinity of the well) is generated by this cake. Penetration). However, such a water loss preventive agent (filter cake) needs to be collected in order to avoid a decrease in productivity due to clogging when mining resources, and for this purpose, an acid treatment is performed. There is a need.

When the excavation dispersion of the present invention is used as a finishing fluid, the solid content (that is, the hydrolyzable resin material) in the dispersion functions as a water loss preventing agent, and the solid cake is Although it will form on the wall surface of a well, this cake hydrolyzes and disintegrates after a predetermined time. Therefore, there is an advantage that the acid treatment for recovering the cake is not required. Of course, this drilling dispersion may contain a water-blocking agent such as calcium carbonate to increase the water-blocking prevention property by increasing the cake strength, etc. Even in the case, since the acid generated by hydrolysis of the hydrolyzable resin material dissolves the anti-water loss agent such as calcium carbonate, the merit that the subsequent acid treatment is unnecessary is not impaired.
In addition, when blending a water-dissipation inhibitor such as calcium carbonate into the dispersion for excavation of the present invention, the amount of the water-dissipation inhibitor is about 10 to 150 parts by weight per 100 parts by weight of the hydrolyzable resin material. is there.

<Drilling by hydraulic fracturing>
In the present invention, the excavation dispersion liquid in which the above-mentioned hydrolyzable resin material is dispersed is pressed into the basement, and the hydrolyzable resin in the dispersion liquid is hydrolyzed at a temperature of 40 ° C. or higher. Therefore, for example, the target underground resource can be excavated by hydraulic fracturing using as a fracturing fluid.

Specifically, a well is formed by excavating the formation where the target underground resource exists to form a pit, and then excavating in the horizontal direction to form a horizontal hole.
Fracturing is performed by filling the well formed in this way with the above-described drilling dispersion liquid containing proppant and pressurizing the well. That is, by this pressurization, the hydrolyzable resin material and the proppant penetrate into the vicinity of the horizontal hole, and the hydrolyzable resin material is hydrolyzed and disappears to form a pillar structure. After the remaining dispersion is sucked, recovery of underground resources such as gas and oil is started.

When the excavation dispersion liquid of the present invention is hydraulically crushed using a fracturing fluid, the hydrolyzable resin material is rapidly decomposed even at a temperature of about 80 ° C., so that it can be efficiently performed in a short time. . Other than fracturing fluid, it is also used as a plug or breakdown material.
Moreover, when excavating with a drill while recirculating muddy water, it can be used as a water loss adjusting agent in the finishing fluid, so that an acid treatment in a subsequent step is not necessary. In addition, there is no clogging and production trouble does not occur.
Even if the resin penetrates a wider area than necessary and remains without being hydrolyzed, the resin is biodegradable and has no risk of adversely affecting the environment.

  Also, when this drilling dispersion is used as a fracturing fluid, the hydrolyzable resin material hydrolyzes in a short time, so that a pillar-structured space (crack) is generated in the portion where the resin material has permeated. In addition, the acid generated by hydrolysis dissolves minerals such as shale and promotes the formation of cracks. As a result, the production efficiency of excavation of shale gas or the like can be increased.

  Furthermore, the hydrolyzable resin material in this dispersion can also function as a sealant that blocks the flow path in the well, but since it hydrolyzes later, problems such as clogging due to sedimentation of the sealant Can be avoided and the production efficiency can be increased.

In addition, the dispersion liquid can be mixed with a gelling agent such as chitosan that dissolves at a low pH to increase the viscosity of the fluid by gelation in the well. That is, the pH is lowered by the acid due to hydrolysis of the hydrolyzable material, and the gelling agent is dissolved in the dispersion, resulting in gelation and thickening. Therefore, it is possible to effectively infiltrate the liquid into the vicinity of the well by the press-fitting of the fluid, and also to efficiently transfer the proppant (support material).
Furthermore, since the above gel increases the acid amount due to subsequent hydrolysis and rapidly degrades (lower viscosity) due to further pH reduction, the fracturing fluid can also be collected effectively and productivity can be improved. Can be increased.

The invention is illustrated by the following examples.
The various measurements performed in the experimental examples are based on the following methods.

<Measurement of melting point and glass transition temperature>
Apparatus: DSC 6220 manufactured by Seiko Instruments Inc. (differential scanning calorimetry)
Sample preparation: Sample amount 5-10mg
Measurement conditions: Measured in a range of 0 ° C. to 250 ° C. at a rate of temperature increase of 10 ° C./min in a nitrogen atmosphere.

<Measurement of molecular weight>
Apparatus: Gel permeation chromatograph GPC
Detector: Differential refractive index detector RI (RI-2414 manufactured by Waters, sensitivity 512)
Column: Showa Denko Shodex HFIP-LG (1), HFIP-806M (2)
Solvent: hexafluoroisopropanol (5 mM sodium trifluoroacetate added)
Flow rate: 0.5 mL / min
Column temperature: 40 ° C
Sample preparation: 5 mL of a solvent was added to about 1.5 mg of a sample, and the mixture was gently stirred at room temperature (sample concentration: about 0.03%). After confirming that it was dissolved visually, it was filtered with a 0.45 μm filter (repeated twice from weighing). All samples were measured within about 1 hour from the start of preparation.

<Synthesis of polyethylene oxalate (hereinafter abbreviated as “PEOx”)>
To a 1 L separable flask equipped with a mantle heater, stirrer, nitrogen inlet tube, and cooling tube,
Dimethyl oxalate 472 g (4 mol)
297 g (4.8 mol) of ethylene glycol
Tetrabutyl titanate 0.42g
The flask was heated to 180 ° C. while distilling off methanol from 120 ° C. under a nitrogen stream, and reacted for 7 hours. Finally, 270 ml of methanol was distilled off.
Thereafter, the temperature was raised stepwise to an internal temperature of 170 ° C. to 190 ° C., and after a reaction for 7 hours at a reduced pressure of 0.1 kPa to 0.2 kPa, the viscosity increased and was taken out.
The taken-out polymer was granulated with a crusher, and crystallized by vacuum drying at 110 ° C. for 4 hours.
The obtained polymer had a weight average molecular weight of 70,000, a melting point of 180 ° C., and a glass transition temperature of 35 ° C.

<Ester-decomposed resin-containing PLA pellet (production of hydrolyzable resin material>
Polylactic acid (PLA) is dry blended with PEOx and melt mixed at 200 ° C. using a twin screw extruder (Technobel ULT Nano05-20AG) to produce a master pellet, which is a sample of hydrolyzable resin material. It was.

<Hydrolysis test>
In a 25 ml vial, one pellet produced as described above was added to 10 ml of the dispersion medium and stored at each temperature. Four days later, the pellets were taken out, dried in a vacuum dryer at 60 ° C. for 4 hours, the weight was measured, and the decomposition rate was measured. The decomposition rate was calculated by the following formula.
Decomposition rate = (initial weight−post-decomposition weight) × 100 / initial weight A decomposition rate of 40% or less was evaluated as “x”, and a sample exceeding 40% was evaluated as “good”.
As the dispersion medium, hydrolyzability was evaluated using distilled water, a guar gum aqueous solution (a guar gum 0.7 wt% aqueous solution), and an alkali aqueous solution (a 1 wt% sodium hydroxide aqueous solution).

<Experimental Examples 1-13, Comparative Examples 1-5>
As the hydrolyzable resin material pellets, polyethylene oxalate (PEOx) content (% by weight) per polylactic acid (PLA) was prepared as shown in Table 1, and a dispersion having the temperature (decomposition temperature) shown in Table 1 was prepared. The pellets were dispersed in and the hydrolyzability was evaluated. The results are shown in Table 1.

<Experimental Example 14>
As hydrolyzable resin materials, pellets of polylactic acid (PLA) and pellets of mixed resin (PEOx 40% PLA) with a content of polyethylene oxalate (PEOx) per PLA of 40% by weight were prepared.
Each of these hydrolyzable resin material pellets was vacuum-dried at 120 ° C. for 3 hours for crystallization.
14 mg of the above pellets and 10 ml of distilled water were added to a 25 ml vial. The vial was placed in a 70 ° C. oven and stored in a stationary state. After 4 days, the pellets were collected, and after drying, the weight was measured and the decomposition rate was calculated. The results are shown in Table 2 below.

Furthermore, the molecular weight (Mw) of each pellet before and after the hydrolysis test was measured. The results are shown in Table 3.
Moreover, molecular weight distribution was shown in FIG. 1 by the GPC measurement about the pellet before a hydrolysis test and after a hydrolysis test (after 4 days). For sample preparation, chloroform was used as a solvent to a concentration of 3 mg / ml, and filtered.
GPC measurement using chloroform solvent;
For GPC, HLC-8120 manufactured by Tosoh Corporation was used, TSKgel SuperHM-H × 2 was used as a column, and TSKguard column SuperH-H was used as a guard column. The temperature of the column oven was 40 ° C., chloroform was used as the eluent, and the flow rate was 0.5 ml / min. The sample injection volume was 20 μl. The standard used was chloroform dissolved in chloroform.

Furthermore, when each pellet after the hydrolysis hydrolysis test was subjected to acupressure, PLA did not collapse, but PEOx 40% PLA easily collapsed due to porosity and molecular weight reduction by hydrolysis.
From this, it can be seen that PEOx-containing PLA effectively functions as a sealing material, and after it has been sealed in the well, it hydrolyzes with time and easily collapses due to the pressure in the well.
The collapsed PEOx-containing PLA decomposition residue is easily recovered along with the well water.

<Experimental Example 15>
As hydrolyzable resin materials, pellets of polylactic acid (PLA), pellets of mixed resin (PEOx 5% PLA) with a content of polyethylene oxalate (PEOx) per PLA of 5% by weight, and a content of PEOx of 40% by weight And a mixed resin (PEOx40% PLA) pellet.
Each of these hydrolyzable resin material pellets was vacuum-dried at 120 ° C. for 3 hours for crystallization.
To a 25 ml vial, 450 mg of the above crystallized pellets, 250 mg of calcium carbonate and 50 μl of water were added and allowed to stand at 120 ° C. for 3 hours. Thereafter, 10 ml of water was added and the solution was collected after 3 hours, and the amounts of calcium lactate and oxalic acid were measured by HPLC. The results are shown in Table 4.

As understood from the above results, the amount of calcium lactate produced from PEOx-containing PLA is 20 times or more compared to PLA. From this, it can be seen that PEOx-containing PLA has a high dissolution rate of minerals containing calcium components such as shale, and is highly applicable as so-called acid fracture.
By the way, in the above results, oxalic acid is hardly eluted. For this reason, possibility that it newly precipitated as calcium oxalate is considered. Thus, an elution amount of oxalic acid was measured by combining an experimental system excluding calcium carbonate.

  To the 25 ml vial, 450 mg of the above-mentioned crystallization pellet and 50 μl of water were added, and the mixture was allowed to stand at 120 ° C. for 3 hours. Thereafter, 10 ml of water was added and the solution was collected after 3 hours, and the amount of oxalic acid was measured by HPLC. The results are shown in Table 5.

  From the above results, elution of oxalic acid was observed even in PLA containing 5% PEOx. In other words, in the system in which calcium carbonate is mixed, most of the PEOx 40% PLA is precipitated as calcium oxalate. From this, it can be seen that the performance as Acid fracture is preferably such that the blending amount of PEOx is less than 40%.

<Experimental Example 16>
PLA pellets and PLA pellets containing 5% PEOx were each crystallized by vacuum drying at 120 ° C. for 3 hours, and crystallized powder samples were prepared by freeze pulverization.

  To a 25 ml vial, 450 mg of the above crystallized powder and 50 μl of water were added and allowed to stand at 120 ° C. for 3 hours. Thereafter, 10 ml of water was added and the solution was collected after 3 hours, and the amount of lactic acid was measured by HPLC. The results are shown in Table 6.

  As can be seen from the above results, the PLA crystallized powder containing 5% PEOx had 20 times the dissolution amount of lactic acid (20 times degradation rate) compared to PLA, that is, mixed with calcium carbonate. It can be seen that the excavation dispersion of the present invention can be suitably used as a finishing fluid because it is excellent in suitability for an easily self-degradable filter cake (that is, characteristics as a water escape inhibitor).

<Experimental Example 17>
In exactly the same manner as in Experimental Example 14, a crystallization pellet of PLA and a crystallization pellet of PEOx 40% PLA were prepared.
To a 25 ml vial, 5 ml of water, 0.2 g of chitosan (gelling agent) and 1 g of the above crystallization pellets were added, and placed in an oven at 70 ° C. and stored still. The change in fluidity with time was observed.
The results are shown in Table 7, where the liquid that gelled and lost its fluidity was indicated by ◯, the liquid that exhibited fluidity but a viscosity higher than water was indicated by Δ, and the liquid equivalent to water was indicated by x.

PLA does not exhibit hydrolyzability at 70 ° C, so lactic acid is not released. As a result, gelation does not occur because the pH of the solution does not decrease and chitosan does not dissolve.
On the other hand, PLA containing 40% PEOx hydrolyzes at 70 ° C., releasing oxalic acid, lowering the pH and dissolving chitosan into a gel.
Furthermore, it has been found that when the amount of oxalic acid is large, the fluidity of the solution increases again after gelation.By increasing the PEOx content or increasing the amount of PEOx-containing PLA, A fracturing fluid can be obtained that can gel in the region and eliminates the need for a gel breaker.

Claims (11)

  A dispersion for excavation, characterized in that a hydrolyzable resin material containing a hardly hydrolyzable hydrolyzable resin and an esterolysis-promoting hydrolyzable resin is dispersed in an aqueous medium.   The dispersion for excavation according to claim 1, wherein the ester decomposition-promoting hydrolyzable resin is acid-releasing.   The dispersion for excavation according to claim 2, wherein the acid released is glycolic acid and / or oxalic acid.   The dispersion for excavation according to claim 1, wherein the acid-releasing hydrolyzable resin is polyoxalate.   The dispersion for excavation according to claim 1, wherein the hardly hydrolyzable hydrolyzable resin is polylactic acid.   2. The mining dispersion liquid according to claim 1, comprising 30 parts by weight or more of an ester decomposition-promoting hydrolyzable resin with respect to 100 parts by weight of the hardly hydrolyzable hydrolyzable resin.   In a method of mining natural resources underground from a well formed by excavation, the dispersion liquid for mining according to claim 1 is injected into the well and the hydrolyzable resin material is hydrolyzed in hot water at 40 ° C or higher. A mining method including a step of performing decomposition.   By press-fitting the mining dispersion into the well, a filter cake of solid content contained in the dispersion is formed on the wall surface of the well, and the filter is released by the acid released by hydrolysis of the hydrolyzable resin material. The mining method according to claim 7, wherein the cake is decomposed.   The mining method according to claim 7, wherein a mineral around the well is dissolved by an acid generated by hydrolysis of the hydrolyzable resin material, and a crack is generated around the well.   The mining method according to claim 7, wherein the well is sealed with the hydrolyzable resin material.   The gelling agent is blended in the mining dispersion, a gel is generated in the well by the acid released by hydrolysis of the hydrolyzable resin material, and the gel is further decomposed. Mining method.

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