CS263165B1 - Splitting liquid - Google Patents

Abstract

A fracturing fluid based on 0.6 to 1.0 weight percent starch carboxymethyl ether, 0.05 to 0.1 weight percent phosphoric oxychloride or sodium hexametaphosphate per amount of starch and 10 to 30 volume percent ethyl or methyl alcohol and water /up to 100 vol. %/. The fracturing fluid is used in the oil industry for hydraulic fracturing of low-permeability resin reservoirs sensitive to contact with water. It has good rheological properties. It can be used up to temperatures of approximately 100 °C, is easily pumped from the fractured horizon and does not clog the reservoir rock.

Description

263165 2

BACKGROUND OF THE INVENTION The present invention relates to a carboxymethyl ether starch cleavage fluid which is used for the hydraulic fracturing of a low-permeability borehole horizon from which natural gas is extracted.

Hydraulic fracturing as a method of stimulating deep probes is used to raise the feed resins to the well by creating a highly conductive crack that is made from bore to formation by the cleavage of the cleavage fluid to the pumped-up horizon higher than the rate of filtration of the liquid into the rock and at a pressure exceeding the strength of the rock. Fragmented liquids must have the appropriate physical and chemical properties required for this purpose. They must have sufficient viscosity, stability over time and temperature change, low filtration, low hydraulic losses, they must not collapse rock, they must be readily degradable and can be removed from the horizon after the hydraulic fracturing operation. Their preparation must be simple and economical to use. Cleavage fluids based on natural and synthetic polymers / polysaccharides, polyamides, polyacrylates, polyvinyl alcohols / prepared in the form of aqueous and aqueous alcoholic solutions are known. They differ in a wide range of rheological parameters, temperature and time stability. To increase the viscosity, these solutions are crosslinked with various agents.

The drawback of some polymeric cleavage fluids is the considerable collapse effect on low-permeability rocks and the strong decrease in viscosity at elevated temperature, even the destruction of the gel system, thereby rendering the liquid unable to carry the filler so-called proppant into the crack. For example, the carboxymethyl ether starch digestion fluid described in GDR Patent No. 683 640, Int. Cl. E 21 B 43/26 to have a good ability to carry proppantum must be used in high polymer concentrations, thereby increasing rock colmatization.

As an example of the destruction of the gel system at elevated temperatures, we mention a hydroalcoholic solution of polyvinyl alcohol flown by borax / CSSR AO No. 235 624, which can be used up to 60 ° C in the given concentration range of the individual components.

This problem is solved by the cleavage fluid of the invention, which comprises 0.6 to 1.0% by weight of carboxymethyl ether of starch, 0.05 to 0.1% by weight of sodium hexametaphosphate or phosphorus oxychloride for starch weighing and 10 to 30%. % by volume of ethyl or methyl alcohol, the remainder water. The cleavage fluid of the present invention has good rheological properties, by crosslinking the carboxymethyl ether of starch, higher solution viscosities are achieved over uncrosslinked starch (1% uncrosslinked). 1 is equal to about 0.75% flown - FIG. 1 /, thereby reducing the amount of starch polymer in solution / economic effect / with comparable rheological parameters thereby reducing the possibility of rock colmatization with a large amount of starch. It is usable up to 100 ° C, good proppant bears, has low hydraulic resistances and is very good to be pumped off the split horizon.

Crosslinking of the carboxymethyl ether of starch preferably takes place in an aqueous solution of 70 to 80% by volume of alcohol. At a lower alcohol content, the crosslinking reaction does not occur as a result of increased starch hydration. Therefore, the crosslinking is carried out in concentrated alcohol until aqueous solutions containing 10 to 30% by volume of alcohol are prepared from the reaction mixture to obtain the most suitable rheological parameters, high viscosity of the liquid. A higher alcohol content of the solution as 30% by volume causes a reduction in the cleavage liquid viscosity due to the lower swelling capacity of the starch. Alcohol as a dehydrating agent and a solution-surfactant enhancer serves in our case as a cross-linking reaction and at the same time slows down the starch hydration in the process of mixing the cleavage liquid into a 10-30% aqueous alcoholic solution, thereby ensuring uniform dispersion of the starch polymer in the liquid and achieving perfect homogeneity. gel. Table 1 shows the effect of alcohol concentration on the crosslinking process by comparing the apparent viscosity of a 1% aqueous solution of carboxymethyl ether of starch and 10% ethyl alcohol (measured after 1 hour of preparation at 25 ° C). 3 263165

Table 1

Ethyl alcohol concentration in the reaction mixture / vol. 1 /

Apparent viscosity 511 with "1 / mPa.s / 93 22280 / max crosslinking / 29870 27360 / min crosslinking / 160

At a proposed crosslinking agent concentration of 0.05 to 0.1% by weight on starch weighing, the highest solution viscosities are achieved.

A graphical representation of the apparent viscosity versus shear rate of 51 s -1 at different carboxymethyl ether starch concentrations at the temperature is shown in Figure 1. Increasing the temperature reduces the viscosity of the cleavage fluid, leaving the gel system complete. cleavage fluids with a carboxymethyl ether starch concentration of less than 0.6% by weight have a low viscosity and a reduced ability to carry the filler into the crack formed. On the contrary, liquids with a starch content above 1% by weight. they are very viscous, poorly pumped and have increased hydraulic resistances. In the concentration range of the carboxymethyl ether starch according to the invention, the speed of the paddle was 0.8 mm in diameter 0.15 to 0.01 m / min at 25 ° C.

The crosslinked gels based on carboxymethylether starch are readily degradable by mineral acid salt solutions, allowing easy removal of cleavage fluid from the rock. Fig. 2 shows a core damage test / reduction of rock core permeability / overpressure of a particular volume of cleavage liquid and its removal by sparging with a salt solution.

We can see that the core was almost completely clogged by the gel - minimal filtration of the liquid through the horn, which is a desirable property for the cleavage of the liquid, and when the rinse with the salt solution is poor, the rock permeability is restored to its original value. In the following examples, methods of preparing a cleavage fluid according to the invention (200 cm) are given. Example 1 Prepare a 1% solution of carboxymethyl ether of starch + 10% ethyl alcohol in water as follows: 3

The reaction mixture consists of 2 g of starch and 5 cm of 80% aqueous alcohol solution, pH 10 of sodium hydroxide solution. Add 0.05% by weight to the solution of phosphorous starch / oxychloride. The retention time is 3 h at 25 ° C with stirring. 3 3

After the reaction, the mixture is mixed with a solution composed of 180 cm of pure fresh water and 15 cm of ethanol. The apparent viscosity of the prepared solution at a shear rate of 511 s -1 and a temperature of 25 ° C is greater than 300 mPa.s, after 1 h 298 mPa.s.

Example2

The crosslinking is carried out under the same conditions as in Example 1, but a 0.6% solution of carbomethyl ether of starch and 1% of ethyl alcohol and water is prepared from the reaction mixture. The apparent viscosity (511 s-1) of the gel measured after 8 hours at 25 ° C is 64 mPa.s and the apparent viscosity at 170 µm -1 is 112 mPa.s. At 90 ° C, the apparent viscosity of 511 s is < 23 mPa.s and at 170 s -1, 35 mPa.s.

Claims (2)

Cleaving liquid, characterized in that it contains 0.6 to 1.0% by weight of carboxymethyl ether of starch, 0.05 to 0.1% by weight of phosphorus oxychloride or sodium hexametaphosphate per starch in 10 to 30% by volume of ethyl or methyl alcohol and water 100%.