RU2079644C1 - Method of increase of well productivity - Google Patents

Abstract

FIELD: oil producing industry; secondary methods of intensification of oil production. SUBSTANCE: the offered method includes injection of suspension of nonexplosive destructive means. It is displaced by displacing fluid to form round the wellbore the fissured zone free from fluid of hydraulic fracturing. Pressure of displacement is determined preliminarily. Nonexplosive destructive means is used with hydraulic pressure exceeding the pressure of displacement. Besides, nonexplosive destructive means is used in form of nonexplosive destructive means. EFFECT: provision of fixing the fractures of different sizes and reduced labor input. 2 cl

Description

 The invention relates to secondary methods of intensifying oil production.

 There is a method of increasing well productivity by hydraulic fracturing. Burst pressures are achieved by injecting high-pressure fluid into the well. In this case, existing cracks and microcracks open in the reservoir, or new ones are created that can significantly improve the hydrodynamic connection between the reservoir and the well. Proppants (quartz sand, walnut shells, glass balls, etc.) are introduced into the fracturing fluid, which penetrate the fracture, where they remain when the well is put into operation, keeping the fracture in the open state / 1 /.

 The method has disadvantages. Due to the variety of influencing factors, it is impossible to predict the magnitude of crack opening. Therefore, it is often not possible to select the type of proppant, the size of sand particles or glass balls. As a result, most of the cracks are closed after the fracturing pressure is removed. In addition, the great complexity of the proppant preparation, its manufacture and sorting.

 There is a method of increasing well productivity, in which the hydraulic fracturing increases the drainage zone and the resulting cracks are fixed by placing porous material in them, after which the well is mastered, and as a hydraulic fracturing fluid, cement mortar is pumped into the well, after the formation of cracks, the latter is pushed out with squeezing fluid to form near-trunk fractured zone, free from hydraulic fracturing fluid, and then the well is kept under pressure of displacement until the cement hardens about the solution in the cracks / 2 /.

 This method makes it possible to fix cracks of various sizes and is less time-consuming in comparison with the analogue.

 The disadvantage of the prototype is that the cement mortar under conditions of rock pressure (40 50 MPa) due to contraction is shrinkage. This leads to the fact that the cracks formed during the hardening of the cement mortar decrease their openness, and the cracks in the near-barrel zone, free from hydraulic fracturing, close. As a result of this, the expected effect of increasing the drainage zone and increasing the productivity of the well is not achieved.

 The task is to increase the efficiency of the method.

 This object is achieved by the fact that in a method comprising hydraulic fracturing with a fluid capable of hardening, it is forced out by squeezing fluid to form a near-barrel fractured zone free of hydraulic fracturing fluid, and the well is kept under pressure of displacement until the fracturing fluid solidifies in the cracks, the pressure of the fluid displacement is preliminarily determined fracturing, and as a fracturing fluid, a suspension of non-explosive destructive means (LRS) with hydration pressure is pumped into the well, pre yshayuschem pressure marginalization. Moreover, LDC-1 is used as an LDC.

 Non-explosive destructive substances (LDCs) are used mainly for the destruction of durable brittle materials, such as various rocks, concrete (reinforced concrete), masonry and other similar objects. Most often, LDCs are powdery, non-combustible and non-explosive materials that give an alkaline reaction with water (pH 12).

 When the LDC powder is mixed with water, a suspension (working mixture) is formed, which, being poured into a hole made in an object to be destroyed, hardens over time, hardens, while increasing in volume. The increase in volume due to hydration of the components that make up the LDCs leads to the development of hydration pressure in the hole (more than 50 MPa). Under the influence of hydration pressure, stresses develop in the body of the object, leading to its destruction.

NRS-1 (developed by the All-Russian Scientific Research Institute of Industrial Sciences named after P.P. Budnikov) is a milled product of firing marl rocks at a temperature of 1450 1500 ^o С. When grinding, plasticizing and hydration-inhibiting additives - sulfite-alcohol stillage and the product of condensation of naphthalene sulfonic acids with formaldehyde in the amount of 0.2 2.0 and 0.5 2.0% on dry matter by weight of the calcined product, respectively (TU 21-31-56-87).

 The proposed method for increasing well productivity is as follows.

Calculate the pressure of the displacement fluid fracturing, which is associated with rock pressure in the reservoir by the following ratio
P _o = P _g + G, (1)
where P _{about the} pressure of the displacement fluid fracturing, MPa;
G crack expansion pressure, MPa;
P _g rock pressure, MPa.

P _g 0.02 • H, (2)
where H is the depth of the reservoir productivity, m

 The LDCs are selected, during the expansion of which hydration pressure arises above the displacement pressure calculated by the formula (1).

A tubing string with a packer is lowered into the well to the roof of the reservoir. A portion of the LDC suspension is pumped into the tubing and forced into the interval of occurrence of the reservoir. The packer is brought into working condition (the annulus is packaged), squeezing fluid is pumped into the tubing, the pressure necessary for hydraulic fracturing is created at the mouth / 6 /
P _ug P _g 0.01 • Y _p • H + Q, (3)
where P _yr pressure at the mouth during fracturing, MPa;
Y _{p the} density of the displacement fluid, g / cm;
Q is the excess pressure necessary to open existing and the formation of new cracks, MPa.

 After the formation of hydraulic fractures, the LDC suspension is forced into the near-trunk zone.

The volume of opened fractures can be estimated by the formula of the theory of elasticity
V = 8 • G • (1-μ ² ) ³ R / 3 • E, (4)
where V is the volume of cracks, m;
μ Poisson's ratio for rocks, MPa;
R is the radius of the cracks, m;
E modulus of elasticity for rocks, MPa.

 For the formation of a zone free of LDCs, the volume of squeezing fluid should be greater than the volume of the suspension of LDCs. In this case, it is necessary to be guided by the volume of hydraulic fractures (4).

 At the end of the injection fluid injection, the well is kept under pressure for the time of solidification of the suspension of the LDCs in the cracks. Then the excess pressure in the tubing is removed, causing fluid flow from the well.

Example. In a well drilled in one of the fields in Western Siberia, the productive formation lies at a depth of 2000 m. According to formula (2), at this depth, the rock pressure is P _g 40 MPa.

By the formula (3) we calculate the pressure at the mouth during hydraulic fracturing (if Y 1 g / cm ³ , Q 5 MPa), P _at 25 MPa.

For the rock mass of Western Siberia, you can take E 10 ⁴ MPa, m 0.3, then at R 15 m, at G 5 MPa according to the formula (5)
V 8 • 5 • (1 0,3 ²⁾ • ¹⁵ March / April ¹⁰ • 3 4 m ^3.

The volume of the suspension of LDCs can be taken 4 m ³ .

A tubing string with a packer is lowered into the well. LDC-1 powder is mixed with water in a ratio of 1: 1.5. With an open annulus, 4 m ^{3 of} LDC suspension is pumped into the tubing string. They close the annulus and, increasing the pressure at the mouth to 25 MPa, provide hydraulic fracturing. 4 m ^{3 of the} suspension of LDCs from the tubing are pressed into the crack with a squeezing liquid, the volume of which is 2 3 m ³ more than the volume of the suspension of LDCs.

 After the sale of the LDC suspension is completed, the well is left under pressure until the solidification of the LDC suspension is complete. Then the overpressure at the mouth is reduced to zero. Master the well.

 In the presented example, during the push, the fluid pressure in the crack was 45 MPa. The same pressure was maintained during the solidification of the LDC suspension. After solidification, the suspension of LDCs, as mentioned above, the hydration pressure in the solidified LDCs rises above 50 MPa, i.e. at least 5 MPa more. This leads to the appearance of additional hydraulic fractures or additional disclosure of existing ones. In this case, the resulting cracks are not filled with solid material, but remain empty or are filled with formation fluid. Thus, the permeability of the near-trunk zone is increased, and due to this, the productivity of the well is increased.

Claims (2)

 1. A method of increasing the productivity of a well, including hydraulic fracturing with a fluid capable of hardening, displacement by squeezing fluid to form a near-barrel fractured zone, free of hydraulic fracturing fluid, and maintaining the well under pressure of displacement until the fracture solidifies in the cracks, characterized in that the pressure is preliminarily determined displacement of the fracturing fluid, and as a fracturing fluid, a suspension of non-explosive destructive means with hydration is pumped into the well pressure in excess of the displacement pressure.  2. The method according to claim 1, characterized in that the NRS-1 is used as an non-explosive destructive agent.