RU2222567C2 - Hydrogel drilling mud - Google Patents

Abstract

FIELD: drilling fluids. SUBSTANCE: drilling mud for use in oil and gas production and which can be in particular used when exposing productive deposits in the boring process, flushing-out wells during thorough repair operations, and when performing repeated perforation-mediated exposure of production formation, contains 0.025-0.5% aluminum chloride, 0.03-0.6% industrial-quality chalk, 3-4% stabilizer, and water. EFFECT: raised oil and gas recovery due to increased permeability of carbonate reservoir. 1 tbl

Description

The invention relates to the oil and gas industry, in particular to drilling fluids and drilling fluids, water-based, and can be used when opening productive deposits during drilling, flushing wells during overhauls, as well as in the secondary opening of the reservoir by perforation.

Known clay-free drilling fluid containing carboxymethyl cellulose-500 (CMC-500), polyacrylamide, oxyl and water, optionally containing potassium alum or aluminum sulfate and caustic magnesite, in the following ratio, wt. %:

Alum Potassium Alum

or aluminum sulfate 18.0-22.0

Caustic magnesite 4.5-5.5

Carboxymethyl cellulose - 500 0.3-0.5

Oxyl 0.3-0.5

Polyacrylamide 0.3-0.5

Water Else

(USSR AS No. 1384596, 5 IPC S 09 K 7/02, priority 07.04.86, publ. 30.03.87 in Bulletin No. 11).

A disadvantage of the known solution is that the presence of polyacrylamide and a high solids content reduce the permeability of the pores after the solution contacts the carbonate rock, which in turn reduces the oil and gas recovery of the formation.

The closest to the claimed purpose and combination of essential features is a hydrogel drilling fluid containing a polyvalent metal salt, a seed, sodium chloride, an alkaline reagent, a stabilizer and water, where it contains aluminum chloride as a polyvalent metal salt, and technical chalk as a seed, in the following ratio of components, wt.%:

Alumochloride 1.33-2.67

Technical chalk 1.5-4.0

Sodium Chloride 0.1-20.0

Alkaline reagent 0.1-0.5

Stabilizer 1.5-3.0

Water Else

while aluminum chloride and technical chalk are in a ratio of 1: 1.13-1.15, respectively (RF patent No. 2135542, IPC C 09 K 7/02, priority 1/16/97, publ. 08/27/99 in bull. No. 24).

In preparing the known hydrogel drilling fluid, hydrated aluminum cations (HCAs) are formed. When alkali is added (at pH 9), the equilibrium between the hydrated aluminum cation and the hydrolysis products is shifted to obtain a water-insoluble aluminum hydroxide compound Al (H ₂ O) ₃ (OH) ₃ . This leads to clogging of pores and excludes further reaction of HCA with rock calcium carbonate, which negatively affects the permeability of carbonate rock and reduces oil and gas recovery.

The claimed invention solves the problem of increasing oil and gas recovery by increasing the permeability of the carbonate reservoir.

To solve this problem in the inventive hydrogel drilling fluid containing aluminum chloride, technical chalk, stabilizer and water, the components are taken in the following ratios, wt.%:

Alumochloride 0.025-0.5

Technical chalk 0.03-0.6

3-4 stabilizer

Water Else

The difference of the proposed hydrogel drilling fluid is a new combination of components and their new ratio. The proposed solution has a pH of 5.5-7.0.

The authors experimentally established that HCA, formed during the preparation of the drilling fluid as a result of the interaction of aluminum chloride and technical chalk, at a given acidity of the drilling fluid penetrates the pores of the carbonate formation during drilling and enters into a chemical reaction with calcium carbonate of the formation, destroying it. In the region of the optimal concentration of hydrogen ions at pH 5.5-7.0, the maximum destruction of carbonate reservoirs is achieved in the HCA penetration zone. This allows you to increase the permeability of the reservoir.

Thus, a new set of components at their optimal ratio due to the manifestation of a new property of the drilling fluid, which consists in the ability to destroy carbonate rocks of the formation as a result of the occurrence of a substitution reaction between the calcium carbonate of the rock and the deeply penetrating HCA of the drilling fluid filtrate into the pores of the formation, provides a new technical result , which consists in increasing the permeability of the carbonate reservoir, which contributes to increased oil and gas recovery. This allows us to conclude that the claimed technical solution meets the criterion of "inventive step"

When preparing the proposed solution were used:

- aluminum chloride according to TU 38.3021-63-89;

- technical chalk in accordance with GOST 17498-72;

- as a stabilizer used various modifications of starch: modified starch (GOST 7698-93), food starch, as well as various modifications of carboxymethyl cellulose (CMC) - 85/700 (OST 6-05-386-80), KMTS-600, KMTS- 500;

- technical and mineralized water (0.05-26.5 wt.% NaCl).

Hydrogel drilling fluid is prepared as follows.

The calculated amount of aluminum chloride is introduced into a given amount of water and mixed for 5 minutes. Then a predetermined amount of technical chalk is introduced into the solution and mixed for 15-20 minutes. A stabilizer is introduced into the prepared hydrogel solution and mixed until the reagents are dissolved. Then, according to RD 39-2-645-81, the obtained technological parameters are measured on standard devices.

To determine the permeability of the carbonate reservoir, capillary-type samples with a length of 560 mm and a diameter of 4 mm were used. The initial kerosene permeability of the carbonate reservoir samples and the permeability of the samples after their interaction with HCA after 5 days with the inventive composition was determined using the UIPK-4M installation.

The change in the permeability of the samples is determined by the coefficient of increase in permeability, which is calculated by the formula:

where M ₀ is the initial permeability of the sample, m ² · 10 ^-15 ;

M ₁ - the permeability of the sample after 5 days, m ² · 10 ^-15 .

Example. In 959.5 g of water, 2.5 g of dry aluminum chloride are added and mixed for 5 minutes. Then, with slow stirring, add 3 g of technical chalk. In the first minutes of mixing, foaming occurs due to carbon dioxide released during the reaction. A stabilizer, 35 g of modified starch, is introduced into the prepared hydrogel solution of aluminum hydroxide. The solution is stirred until the reagents are completely dissolved. Technological parameters of the solution (Run 6) are as follows: pH 6.4, filtration was 6.5 m ^3/30 minutes, increasing the permeability coefficient is 3.06.

All investigated compositions were prepared in a similar way, and the results of laboratory tests are shown in the table.

As can be seen from the table, the compositions of the prototype (experiments 18-20), the pH values are 8.3 and 8.4. This leads to the exclusion of further reaction of HCA with carbonate rock due to the formation of a water-insoluble aluminum hydroxide compound, which reduces the permeability of the carbonate reservoir.

It was found that the optimal content of aluminum chloride in the inventive drilling fluid is 0.025-0.5 wt.% (Experiments 2-13).

The lower limit of the content of aluminum chloride adopted 0,025 wt.% (Experiments 2-4), because with a decrease in its content to 0.02 wt.% (experiment 1), the pH increases to 7.5 and the activity of the reaction of interaction between HCA and carbonate rock decreases. The coefficient of increase in permeability is negligible and amounts to 1,036.

The upper limit of the content of aluminum chloride is 0.5 wt.% (Experiments 5, 8, 10), because with its further increase to 0.55 wt.% (experiment 14), deep pore colmatization of the carbonate rock occurs with an insoluble aluminum hydroxide compound and the coefficient of increase in permeability is only 1.2.

The chalk content is determined on the basis of the need to obtain the most active HCA valency of +3, (its chemical formula has the form [Al (H ₂ O) ₆ ] ⁺³ ). It was found that the ratio of aluminum chloride to chalk is 1: 1.2, while the content of technical chalk 0.03-0.6 wt.% In the inventive solution is optimal.

The upper limit of the content of technical chalk is 0.6 wt.% (Experiments 5, 8, 10, 11), and a further increase in the addition of chalk to 0.7 wt.% (Experiment 15) leads to a loss of valence of HCA and a decrease in the efficiency of the reaction of interaction with carbonate rock.

The lower limit of the content of technical chalk is 0.03 wt.% (Experiments 2-4), because its content of 0.025 wt.% (experiment 1) is already insufficient for the formation of HCA in full.

The stabilizer content of 3-4 wt.% Is optimal. The lower limit of the stabilizer content is 3 wt.% (Experiment 2), because while reducing its concentration to 2.5 wt.% (Test 1) filtering the drilling fluid is increased to 7,5 × 10 ^-6 m ^3/30 min, which leads to deterioration of drilling and increase the permeability coefficient is small and amounts to 1,036.

The upper limit of the stabilizer content in the solution is 4 wt.% (Experiments 4, 8), because a further increase in the flow rate of the stabilizer to 4.5 wt.% (experiment 16) is not advisable due to unreasonable overspending of the reagent, while there is no further significant improvement in filtration and increase in permeability.

As a stabilizer, you can use modified starch (experiments 2, 4, 6-10) or CMC domestic and imported (experiment 12) or together starch and CMC (experiments 3, 5, 11, 13).

If necessary, when drilling, the preparation of a hydrogel drilling mud is possible not only in fresh, but also in mineralized water (experiments 7, 9, 11, 13). The influence of the degree of mineralization of water on the change in the permeability of the carbonate reservoir was not noted.

To prepare a mineralized drilling fluid in fresh water, first the required amount of sodium chloride is dissolved (content 0.05-26.5 wt.%), And then the remaining components are introduced in the above manner.

The inventive hydrogel drilling fluid in comparison with the prototype has the following advantages:

- more effective destruction of carbonate rocks as a result of penetration of HCA into the depth of the reservoir by maintaining a pH of 5.5-7.0 drilling fluid, which ensures high activity of trivalent HCA;

- saving reagents due to the low content of the components of the solution.

Thus, the proposed drilling fluid due to the deep penetration of HCA into the pores of the formation and the effective destruction of the structure of carbonate rocks helps to increase the permeability of the carbonate reservoir, which increases the oil and gas recovery of the formation.

The inventive hydrogel drilling fluid was pilot-tested at ONGKM wells at Stimul CJSC. The oil production rate of the well increased 6 times. The estimated economic effect of the use of the proposed solution will be more than 4 million rubles. for 1 well.

Claims (1)

Hydrogel drilling fluid containing aluminum chloride, technical chalk, stabilizer and water, characterized in that the components are taken in the following proportions, wt.%: Alumochloride 0.025 - 0.5 Technical chalk 0.03 - 0.6 Stabilizer 3 - 4 Water Else