RU2141029C1 - Method of isolation of lost circulation zones in well - Google Patents

Abstract

FIELD: drilling of oil and gas wells, particularly, isolation of lost circulation zones. SUBSTANCE: method includes injection of grouting mix into well in form of aqueous solution of water-swelling polymer. The latter is injected to formation to be isolated in form of first portion of powdery water-swelling polymer AK-639 in water with concentration equalling 10-20%, then it is held in well for 0.5-4 h, and second portion of said polymer in water is injected, whose concentration is less than that in the first portion and portions of injected grouting mix are forced into formation to be isolated. EFFECT: higher efficiency of isolation jobs due to filling of finely fissured and moderately fissured rocks, and reduced consumption of water-swelling polymers.

Description

 The invention relates to the drilling of oil and gas wells, in particular to the isolation of the absorption zones of drilling fluid during drilling.

 A known method of isolating absorption zones, including the injection into the well of a cement slurry based on acrylic polymers and their derivatives / 1 /. These water-soluble polymers are used in water-insulating compositions in combination with electrolytes, forming either sediments (gels) or viscoelastic clogging masses that are stable in the environment of mineralized and fresh waters. However, the method has disadvantages. A “fused" polymer during pumping into an insulated formation passes through the pores in trickles and acquires their cross-sectional shape, which subsequently does not increase the resistance to water effects.

 The closest technical solution chosen by the authors for the prototype is a method of isolating absorption zones, including the injection of grouting mixture in the form of an aqueous solution of a water-swelling polymer / 2 /.

 In the known solution, a cavelast-composite obtained from bentonite clay and polyacrylamide is used as a water-swelling polymer. Cavelast-composite is a granular powder that swells in water 30-40 times. The components of the cavelast composite are hydrophilic. It is prepared according to the following scheme: the cavelast-composite is shut up in water to such a “density" that the pump can pump it through the pipes into the well. When squeezed into the reservoir, caeplast is mixed with water, and since it is hydrophilic, it is diluted to the state of a clay-polymer solution. It is impossible to withstand this composition in the well (so that it thickens) before being forced into the formation, since the water from it can be filtered out and then the solution cannot be moved “from the spot”. The grouting composition based on cavelast (in the form of a thick mixture) is advisable to use mainly when isolating absorption zones with large channels. The bulk of the grouting mixture goes deep into the reservoir along these channels. The passage of a thick mixture into medium and small channels requires very high excess pressure on the reservoir, which sometimes leads to hydraulic fracturing of the rock. In addition, passing through large cracks, the mixture displaces the formation fluid deep into the trunk, while the formation fluid dilutes the mixture forced into large cracks. The process becomes inefficient and you have to take a large amount of grouting material.

 The objective of the invention is to increase the efficiency of insulation work by ensuring the filling of finely cracked, medium cracked and coarse-grained rocks and to reduce the consumption of water-swelling polymer.

 The problem is achieved due to the fact that in the method of isolating the absorption zones in the well, which includes injecting the grouting mixture in the form of an aqueous solution of a water-swellable polymer, a portion of powdered AK-639 water-swellable polymer in water with a concentration of 10 is pumped to the insulated formation as a water swellable polymer -20%, withstand it in the well for 0.5 to 4 hours, after which a second portion of the aforementioned polymer is pumped in water, the concentration of which is less than the concentration of the polymer of the first portion, and then sell the taste of the portions of the grout mixture pumped into the well into an isolated formation.

Table 1 shows the results of experiments to determine the resistance to dilution of samples of cavelast composite and GNP. For this, two large beakers were taken with a height of 480 mm, a diameter of 55 mm and a volume of 1000 cm ³ .

A sample of cavelast composite was taken after 3 hours for swelling in a volume of 50 cm ³ . GNP during the tests is presented in the form of 2 samples: 1 - a sample with a concentration of 15% in water (sample weight - 50 g), 2nd sample - 5% in water (sample weight - 50 g). GNP samples were also taken after 3 hours in water. The first GNP sample adopted a state of monolithic plastic mass; the second is scattered across swollen particles.

 For testing, the samples were lowered into beakers with water. After 1 hour of exposure, water was poured from the beaker and the state of the test samples was determined. As can be seen from table 1, the sample cavelast-composite took the state of a viscous fluid, GNP - did not change in shape.

Water-swelling acrylic polymer AK-639 is a white powder with a particle size of not more than 2 mm, density 1150 - 1200 kg / m ³ , bulk density 600 - 700 kg / m ³ capable of absorbing water or aqueous solutions, depending on the brand, in quantity , from 100 to 1000 times exceeding its own mass, and to keep them in its structure even when exposed to certain pressures.

 The first portion is prepared as follows.

 The required volume of fresh water is collected in Central Asia and, in accordance with it, a certain amount of water-swelling polymer (GNP) is introduced into it. Water should be enough to absorb its GNP in order to ensure the transfer of disparate particles into a viscoplastic substance. The use of GNP powder allows one to achieve a high concentration in water, which cannot be done using particles from the gel for technological reasons - the pump becomes clogged.

 Table 2 shows the data on the transition of an aqueous dispersion of GNP into a viscoplastic monolithic state.

 The first portion: a mixture of water and GNP is pumped into the well, time is given for swelling and the transition of an aqueous dispersed system based on GNP powder to a viscoplastic state.

 After that, the second portion is pumped - the dispersion from GNP in fresh water and the process continues until the second portion is completely pushed into the reservoir.

 The advantage of the proposed method over the known one is that it provides high-quality insulating work due to the penetration of the grouting mixture into the finely cracked, medium cracked and coarse-grained rocks, with the claimed method the consumption of grouting material is significantly reduced.

 Sources of information.

 1. USSR author's certificate N 1559114, cl. E 21 B 33/138, 1990

 2. Copyright certificate of the USSR N 1745123, C 09 K 7/02, 1990 / prototype /.

Claims (1)

 A method of isolating absorption zones in a well, including injecting a grouting mixture in the form of an aqueous solution of a water-swellable polymer, characterized in that a portion of powdered water-swellable acrylic polymer AK-639 is pumped into the well in water with a concentration of 10-20%, it is kept in the well for 0.5 to 4 hours, after which a second portion of the aforementioned polymer is pumped in water, the concentration of which is less than the concentration of the polymer of the first portion, and then we pump the portions of the grouted mixture pumped into the well into isolate th layer.

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