RU2156356C1 - Method of oil formation hydraulic fracturing - Google Patents

Abstract

FIELD: oil producing industry. SUBSTANCE: method includes determination of oil-saturated parting in formation. Slow-reacting acid solution is injected selectively into oil-saturated parting at flow rate of 0.8-1.5 cu. m/min. Acid solution is pushed by water and well is closed to wait for pressure drop and acid reaction. EFFECT: higher efficiency of method. 3 ex

Description

 The invention relates to the oil industry and may find application in hydraulic fracturing of an oil reservoir.

 A known method of hydraulic fracturing, including injection into the reservoir at a pressure above the fracture pressure of acid agents and proppant [1].

 The known method allows along with the formation of cracks to conduct acid treatment of the formation at a great distance from the well. However, the known method does not allow to increase the productivity of injection wells and to develop for injection wells in clay reservoirs and low-power sandstones. The method has a long process time and high cost.

 A known method of softening rocks, including injection into the reservoir at a pressure above the fracture pressure of the hydrochloric acid solution without injection of proppant [2].

 The known method allows the formation of zones with high permeability in the reservoir. Moreover, the method is free from the disadvantages associated with the use of proppant. However, the method is suitable in carbonate reservoirs and not suitable in terrigenous. Well productivity decreases rapidly over time. The effectiveness of the method is small.

 Closest to the invention in technical essence is a method of hydraulic fracturing of an oil reservoir, which involves injecting slow acid into the reservoir at a pressure above the fracturing [3].

 The disadvantage of this method is the low efficiency, especially in terrigenous reservoirs.

 The invention solves the problem of increasing the efficiency of the method.

The problem is solved in that in the method of hydraulic fracturing of an oil reservoir, comprising injecting a slow-acting acid solution into the formation at a pressure above the fracturing pressure, according to the invention, an oil-saturated interlayer is released into the formation, into which a slow-acting acid solution is selectively pumped at a rate of 0.8-1 , 5 m ³ / min, push the solution of the acid of slow action with water and close the well to wait for the pressure drop and the reaction of the acid.

SUMMARY OF THE INVENTION
When developing an oil field, it is often necessary to carry out stimulation work in wells. Existing methods of stimulation by hydraulic fracturing do not always lead to the achievement of work goals. In addition, proppant fracturing is very expensive.

 The invention solves the problem of increasing the efficiency of stimulation by hydraulic fracturing. The problem is solved by the following set of operations.

An oil-saturated layer is emitted in the formation. A solution of an acid of slow action is injected into the oil-saturated interlayer at a pressure higher than the fracture pressure of the formation. The acid solution is selectively pumped into the oil-saturated interlayer at an injection rate of 0.8-1.5 m ³ / min. They push the acid solution with water and close the well to wait for the pressure drop and the acid to react.

 A slow-acting acid solution penetrates deeper into the formation and forms pore channels at great depths. Due to this, the permeability of the bottomhole zone increases. Estimate the depth of the contaminated bottomhole zone and determine the volume of injected acid solution. New pore channels reach an unpolluted formation.

 As a clay acid, mixtures of hydrochloric and hydrofluoric acid solutions are used, for example a mixture of a 12% aqueous hydrochloric acid solution and a 3% aqueous hydrofluoric acid solution.

A mixture of hydrochloric acid of 10-24% concentration or its mixture with hydrofluoric acid with an inhibitor of action, which is used as alkali metal lignosulfonates such as black liquor, sulphite-yeast mash, etc., is used as a slow-acting acid solution. Black monosulfate liquor is a waste of pulp and paper production and is produced according to TU 13-7308001-453-84. In appearance - a uniform dense liquid of dark brown color. Density - 1200 kg / m ³ , viscosity with a B3-4 viscometer not more than 80 s, pH - not less than 4. When the temperature decreases, it thickens and at 0 ^o C it becomes non-flowing.

The ratio between the hydrochloric acid solution and the black liquor is (40-60) :( 40-60) by volume. The volume of injected slow acid solution is 30-60 m ³ .

Case Studies
Example 1. Fracturing is performed in an oil well of the Mishkinsky field. A well with a water cut of produced products of more than 60% is selected. The reservoir has three layers in the carbonate reservoir. The upper and lower layers are waterlogged. The middle layer is oil saturated. The reservoir pressure at the level of the middle layer is 12 MPa.

The tubing string is lowered into the well with the perforated portion of the string located at a depth of the middle layer. The well is washed. Above and below the middle layer put a packer with anchors. A solution of slow acid is pumped into the interlayer under a pressure of 34 MPa at a flow rate of 1 m ³ / min in a volume of 50 m ³ — a mixture of 12% aqueous hydrochloric acid and a solution of sulfate liquor at a volume ratio of 50:50. The slow acid solution is pushed with water in the volume of the tubing string. Without reducing the pressure, the well is sealed at the wellhead and technological exposure is carried out until the pressure stabilizes over a period of about 12 hours. After that, the equipment in the well is changed to a deep-well pump and the well is put into operation.

As a result, the flow rate of the well increased from 2 m ³ / day to 14 m ³ / day.

Example 2. Fracturing is performed in an oil well of Listvynsky field. A well with a water cut of produced products of more than 60% is selected. The reservoir has three layers in the terrigenous reservoir. The upper and lower layers are waterlogged. The middle layer is oil saturated. The reservoir pressure at the level of the middle layer is 12 MPa. The tubing string is lowered into the well with the perforated portion of the string located at a depth of the middle layer. The well is washed. Above and below the middle layer put a packer with anchors. A solution of slow acid is injected into the interlayer under a pressure of 42 MPa at a flow rate of 0.8 m ³ / min in a volume of 48 m ³ - a mixture of clay acid consisting of a 12% aqueous hydrochloric acid solution and a 3% hydrofluoric acid solution and a solution sulfate liquor with a volume ratio of 60:40. The slow acid solution is pushed with water in the volume of the tubing string. Without reducing the pressure, the well is sealed at the wellhead and technological exposure is carried out until the pressure stabilizes over a period of about 12 hours. After that, the equipment in the well is changed to a deep-well pump and the well is put into operation.

As a result, the flow rate of the well increased from 2 m ³ / day to 12 m ³ / day.

Example 3. Perform, as example 1. In the interlayer injected under pressure 33 MPa with a flow rate of 1.5 m ³ / min in a volume of 47 m ^{3 a} solution of acid of slow action - a mixture of 12% aqueous hydrochloric acid and a solution of sulfate liquor when they volumetric ratio of 40:60.

As a result, the flow rate of the well increased from 2 m ³ / day to 13 m ³ / day.

 The application of the proposed method will improve the efficiency of stimulation work in the well.

Sources of information
1. RF patent N 2122633, cl. E 21 B 43/27, published. 1998.

 2. RF patent N 2012790, cl. E 21 B 43/26, published. 1994.

 3. Copyright certificate of the USSR N 953190, cl. E 21 B 43/26, published. 1982 - prototype.

Claims (1)

The method of hydraulic fracturing of an oil formation, comprising injecting a solution of an acid of slow action into the formation at a pressure above the pressure of the fracturing, characterized in that an oil-saturated interlayer is released into the formation, into which a solution of acid of slow action is selectively injected at a speed of 0.8-1.5 m ³ / min, push the solution of the acid of slow action with water and close the well to wait for the pressure drop and the reaction of the acid.