CS237901B1 - Liquid for hydraulic forming of cracks - Google Patents

Abstract

The solution relates to a hydraulic fluid creating cracks, water-based, for intensification oil and gas probes. The essence of the solution is that the hydraulic fluid cracking is formed by the gel carboxyalkyl starch in aqueous solution. Taking the carboxyalkyl starch content is preferably it ranges from 0.3 to 5.0%.

Description

The invention relates to a water-based hydraulic cracking fluid for intensifying oil and gas probes.

As is known, a method of hydraulic cracking is used to intensify production, injection and UGS probes. In this case, cracks and fissures are used. Crack-forming liquids are known, such as gels and emulsions, the main components of which contain petroleum fractions. It is more common to use aqueous liquids to which considerable viscosity is added with the additives. This high viscosity imparts to liquids the ability to retain sand and other protective materials until they are suspended in the fissures. Only then is it desirable to reduce the viscosity to such an extent that they can easily be removed from the formations. The viscosity drop should occur after some time under given p, T conditions in the soil. This time is not essential to exceed the processing time.

At the same time, a small fluid loss is required at the fracture / matrix interface.

In addition to starches, other viscosity-increasing additives are known, such as gelatin, pectin, guar or alginates.

It is known that the water-based cracking fluids used hitherto have, due to their relatively high solids content, the drawback that they can lead to increased matrix damage. On the other hand, they do not have a sufficiently stable viscosity above 80 ° C, so it is necessary to take into account premature elimination of the protective material and increased initial loss of liquid. This means that a larger amount of cracking liquid must be used in advance to compensate for this loss.

The decomposition times at storage temperatures up to complete loss of viscosity are long, i.e. only after several hours or even days, the viscosity of the cracking liquid decreases to such an extent that it can be easily removed from the wells. In this way, the inflow of the carrier rock to the probe is blocked.

The purpose of the invention is to reduce the time lag between the action of the cracking liquid and the commencement of full extraction, while avoiding long-term blocking or reducing the coefficients of the cracking liquid to the extent that the additional amount of cracking liquid is lost. must be additionally available, can be reduced to a minimum.

The object of the invention is to provide a water-based cracking liquid with a low liquid coefficient and a small initial loss, the viscosity of which can be reduced after a relatively short time.

According to the invention, this problem is solved by forming a carboxyalkyl starch gel in water. A starch which is etherified with haloalkylcarboxylic acids, preferably monochloroacetic acid, is used as the starting product.

The carboxymethyl starch thus formed is cold water soluble and forms a highly viscous gel. It has been found that the required concentration of carboxymethyl starch in water is between 0.3 to 5.0%, preferably 0.4 to 2.4%.

Furthermore, it has been found that carboxymethyl starch is useful at a probe temperature of 60 ° C to 200 ° C. A temperature range of 80 to 150 ° C is preferred. During the day, there was no significant decrease in viscosity during 3 days of aging. Experiments have shown that the carboxymethyl starch gel is completely degradable in the aqueous solution within the recommended temperature range.

By using the carboxyalkyl starches in the water according to the invention, while keeping the salt content in the water, the viscosity, the load-bearing capacity of the sand and the gel blocking time under the action of the crack-forming liquid can be reduced or reduced as much as possible.

The invention will now be explained in more detail by way of examples.

Example 1

Carboxymethyl starch is cold water soluble. Stirring into the water increases the viscosity immediately. The product is completely agitated after 5 to 10 minutes.

After stirring for 15 minutes, a homogeneous highly viscous liquid is obtained, which swells additionally for 1 hour.

Table 1 shows the viscosity versus concentration at room temperature after aging for 1 h, 1 d, 2 d and 3 d.

Table 1 end-viscosity in cP at room temperature trace lh ld 2 d 3 d

% 480 s ¹ 160 s “ ¹ 480 s- ¹ 160 s “ ¹ 480 s ¹ 160 s ¹ 400 s “ ¹ 160 s ^-1 0.8 50 54 34 40 32 38 32 38 1.0 157 238 171 254 175 270 184 281 1,2 373 610 349 605 288 475 265 427 1.5 540 1026 540 1129 540 1048 540 1064 1,8 540 1399 540 1512 540 1139 502 923

Example 2 of methyl starch in water at a thermal load of more than 3 hours.

Table 2 shows the carboxy gel behavior of Table 2

conc. processing temperature % Noc: 2 ° C 0.8 25 80 120 1.0 25 80 120 1,2 25 80 120 1.5 25 80 120 1,8 25 80 120

temperature of measurement viscosity at ° C d = 480 s ¹ cP

25 50 80 40 25 12 25 157 80 110 25 13 25 373 80 288 25 14 25 > 540 80 243 25 16 25 > 540 80 301 25 24

Example 3

As the stress of the carboxymethyl starch gel in water carries sand, the stress is varied.

Attempts to measure the rate of fall of sand were conducted according to a standard test for cracking fluids (Recommend Practice Procedure the Evalution of Hydraulic Fracturing Fluids, API-Test RP 39, Juli 1960).

The results of measurements at room temperature, 80 ° C and 120 ° C are shown in Tables 3 and 4.

Tempering was performed at 120 ° C in a pressure vessel.

Table 3 concentration sand drop rate in cm / min at room temperature at 80 ° G%

0.8 19 Dec 8 1.0 <3 <3 1,2 <3 <3 1.5 <3 <3 1,8 <3 <3

Table 4 finished - sand drop rate at 120 ° G in cm / min trace 10 min 0.5 h 1 h 1.5 h 2 h 2.5 h 3 ih%

1.8 <3 <3 <3 9.4 20 75 300

Example 4

This example illustrates the dependence of carboxymethyl starch gel liquid loss properties in water under given β-T conditions (see Table 5).

The measurement method for determining the flow coefficients was carried out according to the standard method of testing the cracking fluid (Recommend Practice Procedure of the Hydraulic Fracturing Fluids, API-Test RP 39, Juli 1960).

A liquid consumption coefficient of about 1.10 " ³ m / Vmin is considered good, lower values are considered excellent.

S = initial loss (ml / cm ² ), p-pressure (MPa)

Q25 = accumulating amount of filtrate after 25 min (ml)

C = coefficient of liquid consumption (m / j / min)

Table 5 conc. temp. ΔΡ% ° C MPa

1,2 20 May 7.0 1.5 20 May 7.0 1,8 20 May 7.0 1,2 70 7.0 1.5 70 7.0 1,8 70 7.0 Example 5

S 'Q25 103 ml / cm ² ml m / Vmin

0.15 26 0.98

0.11 14 0.5

7 0,3

0.44 32 0.96

0.35 20 0.52

0.02 14 0.58

The effect on the permeability of the rock sample after destruction of the carboxymethyl starch gel in water was demonstrated as follows.

Sandstone core was used. The geometric dimensions of the core were 3 cm in diameter, 3.4 cm in length. A gel formed from 18 g / l of carboxymethyl starch in water was used. The test temperature was 120 ° C. After measuring the initial nitrogen permeability, the gel was pressed. The increasing volume of the extruded liquid was 22.7 ml in 36 minutes. Two hours of pressing time was followed by measurement of reversible nitrogen permeability. A 15% reduction was observed. Repeated measurement of reversible permeability after 10 hours showed that the reduction in permeability to baseline permeability is 0%.

Claims (2)

SUBJECT CLAIMS 1. Water-based hydraulic cracking fluid for intensifying oil and gas probes, including injection probes and UGS probes, characterized in that it is found on a carboxyalkyl starch gel in aqueous solution. 2. The fluid for hydraulic crack formation according to claim 1, characterized in that it contains 0.3 to 5.0% carboxyalkyl starch.