Dispersion solution for drilling and method of extraction using the dispersion solution

Abstract

A method of extracting underground natural resources through an ore chute located in a temperature region where temperature in the ground is not higher than 60 C., comprising introducing a dispersion solution obtained by dispersing polyoxaylate in water into the ore chute with pressure to hydrolyze the polyoxalate.

Claims

1. A method of extracting underground natural resources through an ore chute located in a temperature region where temperature in the region is not higher than 60 C., the method comprising introducing a dispersion solution into the ore chute with pressure, wherein the dispersion solution is obtained by dispersing, in water, a hydrolyzable resin pellet that contains a polyoxalate having a ratio of decomposition higher than 40% when the pellet is stored for 4 days at 45 C. in distilled water, in order to hydrolyze the hydrolyzable resin pellet to extract underground natural resources.

2. The method according to claim 1, wherein the hydrolyzable resin pellet contains a hydrolyzable resin other than the polyoxalate in amount of not more than 60 parts by weight per 100 parts by weight of the polyoxalate.

3. The method according to claim 2, wherein the hydrolyzable resin other than the polyoxalate is a polylactic acid, a polyhydroxyalkanoate, a polycaprolacone, a polybutylene succinate, a cellulose acetate or a thermoplastic starch.

Description

EXAMPLES

(1) The invention will now be described by way of the following Examples.

(2) In the Experiments, measurements were taken by the methods described below.

(3) <Measuring the Melting Points and Glass Transition Temperatures>

(4) Apparatus: DSC 6220 (differential scanning calorimeter) manufactured by Seiko Instruments Co. Preparation of samples: Amount of samples, 5 to 10 mg. Measuring conditions: Nitrogen atmosphere, elevating the temperature at a rate of 10 C./min. over a range of 0 C. to 250 C.
<Measuring the Molecular Weights> Apparatus: Gel permeation chromatograph GPC Detector: Differential refractive index detector RI (Model RI-2414 manufactured by Waters Co., sensitivity: 512) Column: Shodex HFIP-LG (one unit), HFIP-806M (2 units), manufactured by Showa Denko Co. Solvent: Hexafluoroisopropanol (5 mM sodium trifluoroacetate is added) Flow rate: 0.5 mL/min. Column temperature: 40 C. Preparation of samples: 5 milliliters of a solvent was added to about 1.5 mg of a sample and the mixture thereof was mildly stirred at room temperature (sample concentration of about 0.03%). After having confirmed with the naked eye that the sample had been dissolved, the solvent was filtered using a 0.45 m filter (repeated twice from the weighing). All samples were measured in about one hour from the start of preparation.

(5) Synthesis of the polyethylene oxalate (hereinafter abbreviated as PEOx).

(6) Into a 1 L separable flask equipped with a mantle heater, a stirrer, a nitrogen introduction tube and a cooling tube, there were introduced:

(7) dimethyl oxalate, 472 g (4 mols),

(8) ethylene glycol, 297 g (4.8 mols), and

(9) tetrabutyl titanate, 0.42 g,

(10) and the temperature in the flask was elevated in a nitrogen stream from 120 C. up to 180 C. while distilling the methanol off to conduct the reaction for 7 hours. Finally, 270 ml of methanol was distilled off.

(11) Thereafter, the temperature therein was elevated stepwise to 170 C. to 190 C. to conduct the reaction for 7 hours under a reduced pressure of 0.1 to 0.2 kPa. Since the viscosity has increased, the reaction product was taken out.

(12) The polymer that was taken out was granulated by using a crusher, and was dried in vacuum at 110 C. for 4 hours so as to be crystallized to thereby obtain PEOx pellets.

(13) The obtained polymer possessed a weight average molecular weight of 70,000, a melting point of 180 C. and a glass transition temperature of 35 C.

(14) <Preparation of Polylactic Acid (PLA) Pellets>

(15) For the purpose of comparison, the polylactic acid (PLA) was fed to a biaxial extruder (ULT Nano 05-20AG manufactured by Technovel Co.) and was melted at 205 C. to prepare pellets thereof so as to be used as a sample hydrolysable resin material. The polylactic acid was 4032D manufactured by Natureworks Co.

(16) <Hydrolyzing Test>

(17) A piece of pellet prepared above was added to 10 ml of a dispersant in a 25-ml vial which was then stored still at each of the temperatures. After stored for 4 days, the pellet was taken out, dried in a vacuum drier heated at 60 C. for 4 hours, measured for its weight and was measured for its ratio of decomposition. The ratio of decomposition was calculated according to the following formula,
Ratio of decomposition=(initial weightweight after decomposed)/initial weight100

(18) The samples having ratios of decomposition of not more than 40% were judged to be whereas the samples having ratios of decomposition exceeding 40% were judged to be .

(19) As the dispersants, there were used distilled water and guar gum aqueous solution (aqueous solution containing 0.7 wt % of guar gum) to evaluate the hydrolyzing capabilities.

Examples 1 to 6, Comparative Examples 1 to 5

(20) As pellets of the hydrolysable resin material, there were used the PEOx pellets prepared above. Namely, the PEOx pellets were dispersed in dispersion media of temperatures (decomposition temperatures) shown in Table 1, and the above hydrolysis test was conducted to measure their ratios of decomposition (Experiments 1 to 6). The results were as shown in Table 1.

(21) Instead of using the PEOx pellets, further, the PLA pellets prepared above were dispersed in dispersion media of temperatures shown in Table 1 like in the above Experiments. The results were as shown in Table 1.

(22) TABLE-US-00001 TABLE 1 Decomposition Ratio of temperature decom- Pellets Dispersion medium ( C.) position Experiment 1 PEOx distilled water 45 Experiment 2 PEOx distilled water 55 Experiment 3 PEOx distilled water 70 Experiment 4 PEOx distilled water 80 Experiment 5 PEOx guar gum al. sol. 55 Experiment 6 PEOx quar gum aq. sol. 70 Comp. Ex. 1 PLA Distilled water 55 X Comp. Ex. 2 PLA Distilled water 70 X Comp. Ex. 3 PLA distilled water 80 X Comp. Ex. 4 PLA guar gum aq. sol. 55 X Comp. Ex. 5 PLA guar gum aq. sol. 70 X
<Experiment 7>

(23) As the hydrolysable resin materials, there were used crystallized powders obtained by freeze-pulverizing the PEOx pellets and the PLA pellets prepared above.

(24) 18 Milligrams of the above PEOx crystallized powder or the PLA crystallized powder and 10 ml of distilled water were put into the 25-ml vial. The vial was then put into an oven maintained at 50 C. or 70 C. and was stored still. After stored for 3 days, the solution was filtered to recover the powder. After drying, the powder was measured for its weight to calculate the ratio of decomposition. The results were as shown in Table 2 below.

(25) TABLE-US-00002 TABLE 2 Ratio of decomposition (%) 0 day After 3 days 50 C. PEOx 0 85 PLA 0 0 70 C. PEOx 0 100 PLA 0 0

(26) In the case of the PLA, a reduction in the weight due to the hydrolysis could not be confirmed at either 50 C. or 70 C. The PEOx, on the other hand, had been hydrolyzed. At 70 C., specifically, the PEOx had been completely decomposed.

(27) It will, therefore, be learned that the PEOx contained in the dispersion solution for drilling of the present invention effectively works as a filler, undergoes the hydrolysis with the passage of time after having been filled in the well and easily collapses therein due to the pressure in the well. Besides, the PEOx can be used as a support for holding cracks formed in the vicinities of the well. After having extracted the resources, the PEOx quickly undergoes the hydrolysis and can be easily recovered together with water in the well.

Example 8

(28) Gelation Test Using an Acid-Containing Aqueous Solution:

(29) There were prepared aqueous solutions each containing 5% of oxalic acid (Ox), glycolic acid (Gly) or lactic acid (LA).

(30) 5 Milliliters of the above acid-containing aqueous solution and 0.2 g of chitosan (gelling agent) were put into the 25-ml vial which was stored still in an oven heated at 70 C. The fluidity was judged after one hour, 12 hours and 24 hours have passed.

(31) The liquids that were gelled and lost fluidity were evaluated to be , the liquids that exhibited fluidity but possessed viscosity larger than that water were evaluated to be , and the liquids having viscosity equivalent to water were evaluated to be . The results were as shown in Table 3.

(32) TABLE-US-00003 TABLE 3 After After After 1 hour 12 hours 24 hours 5% Ox aq. sol. X 5% Gly aq. sol. 5% LA aq. sol.

(33) From the above results, the aqueous solutions of glycolic acid and lactic acid were both gelled and lost fluidity irrespective of the time.

(34) On the other hand, the aqueous solution of oxalic acid was once gelled at 70 C. and lost fluidity but, after 24 hours have passed, has resumed fluidity showing a specific change in the properties. It was, therefore, learned that if there is used, as a fracturing fluid, a dispersion solution containing a gelling agent and a hydrolysable resin that releases oxalic acid upon the hydrolysis, then cracks can be formed due to the fracturing in the stage where the solution undergoes the gelling. Thereafter, the dispersion solution resumes the fluidity with the passage of time; i.e., the fracturing fluid can be recovered without using a gel breaker.

(35) Gelling Test Using a Polymer:

(36) By taking the above experimental results into consideration, a gelling test was conducted using a polymer.

(37) That is, 1 g of the crystallized PEOx pellet or the PLA pellet prepared above was put into the 25-ml vial together with 5 ml of water and 0.2 g of chitosan. The vial was then stored still in an oven maintained at 70 C., and the fluidity was judged after the passage of one hour, 6 hours and 12 hours in the same manner as described above. The results were as show in Table 4.

(38) TABLE-US-00004 TABLE 4 After After After 1 hour 6 hours 12 hours PLA X X X PEOx X

(39) From the above results, the PLA is not hydrolyzed at 70 C., no lactic acid is released therefrom, the pH of the solution does not decrease and, as a result, chitosan that is a gelling agent does not dissolve, and the liquid is not gelled.

(40) The PEOx, on the other hand, hydrolyses at 70 C., releases the oxalic acid and, therefore, behaves like an oxalic acid-containing aqueous solution. It will, therefore, be understood that the dispersion solution for drilling of the present invention that contains the PEOx, can be gelled in a low-temperature range and can be used as a fracturing fluid that necessitates no gel breaker.