RU2462590C1 - Method for improvement of hydrodynamic connection of well with productive formation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method involves acid fracturing of formation by means of packer mounting above roof of perforated productive formation, pumping of hydraulic fracture liquid to underpacker zone, creation of hydraulic fracture pressure in underpacker zone and forcing-through of hydraulic fracture liquid to crack appeared. After acid fracturing of formation, repeated acid fracturing of formation is performed in two stages. At the first stage crack appeared due to acid fracturing of formation is strengthened by pumping of hydraulic fracture liquid with proppant in quantity enough for measurement of horizontal stresses in carbonate formation and provision of normal direction of the second crack appeared during the second stage of acid fracturing of formation in relation to the first crack. After the first stage of repeated hydraulic fracturing of formation, well is checked for drain through nozzles in increasing sequence of their diameters. At the first stage of hydraulic fracturing of formation jell is used as hydraulic fracturing liquid, at the second stage - acid composition.

EFFECT: simplifying the method and reducing labour intensity, improving efficiency of carbonate formation development due to enlargement of zone of productive formation drainage due to creation of two directed cracks.

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Description

The invention relates to the oil industry and can be used to improve the hydrodynamic connection of the well with the reservoir in carbonate rocks.

A known method of hydraulic fracturing and a device for its implementation (patent RU No.2007552, IPC 8 E21B 43/26, publ. 02/15/1994), including the descent into the well of a string of tubing with a perforator having perforations in one vertical the azimuthal orientation plane of the tubing, slotted perforation in a given direction, flushing the well, raising the tubing with a perforator, lowering the tubing with a packer and anchor, injecting fracturing fluid and sand carrier fluid under pressure.

The disadvantage of this method is the unwarranted propagation of cracks in the direction of a given slotted perforation.

Also known is a method of conducting directional hydraulic fracturing (patent RU No. 2177541, IPC E21B 43/26, publ. 12/27/2001), including the descent into the well of a device for cutting gaps in the casing, injection of abrasive fracturing fluid, suspension fluid carrier with fixing material and selling fluid. They are pumped at a rate that provides pressure at the bottom above the pressure of the fracturing. Carry out technological exposure and commissioning of the well. A slit is cut in the casing having an annular cross section and a conical profile to provide a hydro-monitor effect. When injecting liquids through a slit in the casing, a conical-shaped annular slot is cut through the liquid in the cement stone and rock in a plane perpendicular to the axis of the casing. Then this gap is deepened, after which they begin to pump the fracturing fluid.

The disadvantages of this method are the need for additional perforation by a device for cutting gaps in the casing, as well as the deepening of these gaps by injection of abrasive fluid, which worsens the permeability of the bottom-hole formation zone (PZP).

There is also known a method of conducting local directed hydraulic fracturing (patent RU No. 2355628, IPC E21B 43/26, published in Bulletin No. 28 of 10/10/2008), which includes determining the stress zones in the reservoir of an open hole borehole by seismic scattering using the dispersed method waves, drilling parallel lateral trunks of small diameter along the axis of the main compressive stresses of the rock mass. In this case, the distance between parallel horizontal shafts is selected from the condition of ensuring their stability and carrying out vertical hydraulic fracturing along the length of horizontal shafts with ensuring the movement of cracks towards each other and their merging with the involvement of oil pillars, its dead-end and stagnant zones in the formation with bottom water or in reservoir with higher - and underlying water. The disadvantages of this method are:

- the need to determine stress zones in the reservoir by seismic sounding by the method of scattered waves in an open hole;

- drilling parallel lateral shafts of small diameter along the axis of the main compression stresses of the rock mass.

The closest in technical essence is a method of improving the hydrodynamic connection of the well with the reservoir (patent RU No. 2351751, IPC E21B 43/16, 43/26, published in Bulletin No. 10 of 04/10/2009), including hydraulic fracturing by installing the packer over the roof of the perforated reservoir, injecting the fracturing fluid into the sub-packer zone, creating the fracturing pressure in the sub-packer zone and pushing the fracturing fluid into the crack, according to the invention, the annulus is sealed first kvazhiny and drilling of radial perforations in a predetermined range of the producing formation, whereupon hydraulic fracturing (frac) while drilling the radial perforations produce oriented in a predetermined direction, and as a fracturing fluid using acid composition.

The disadvantages of this method are:

- firstly, the complexity and complexity of the process, as for hydraulic fracturing it is necessary to drill radial perforated channels, and this drilling is carried out oriented in a given direction;

- secondly, hydraulic fracturing is carried out with an acid composition without fixing the crack, which in the carbonate formation leads to a rapid decrease in productivity (injectivity) and requires repeated work to improve the permeability of the formation, and this generally reduces the effectiveness of this method.

The objectives of the invention are to simplify the implementation of the method and reduce the complexity of its implementation, as well as to increase the efficiency of developing a carbonate formation by increasing the drainage radius, the filtration surface and the drainage area of the productive formation by creating two directed hydraulic fractures, the first of which is fixed by pumping a fracture fluid with a crack fixer with subsequent development of the well at the spout.

The problem is solved by a method of improving the hydrodynamic connection of the well with the reservoir, including acid hydraulic fracturing (Fracturing), by installing a packer over the roof of the perforated reservoir, injecting fracturing fluid into the sub-packer zone, creating hydraulic fracturing pressure in the sub-packer zone and squeezing hydraulic fracture into the resulting fracture .

What is new is that after acid fracturing, repeated fracturing is carried out in two stages, and at the first stage, the crack formed as a result of acid fracturing is fixed by pumping hydraulic fracturing fluid with proppant in an estimated amount sufficient to change the horizontal stresses in the carbonate formation and the perpendicular direction of the second fracture formed when the second stage of acid hydraulic fracturing relative to the first fracture, and after the first stage of repeated hydraulic fracturing, the wells are drilled at the spill through fittings in an increasing sequence of their diameters, while in the first stage of hydraulic fracturing, gel is used as the hydraulic fracturing fluid, and in the second, the acid composition.

Figure 1 shows the plane of the crack, directed perpendicular to the minimum horizontal stress in the reservoir.

Figure 2 shows a diagram of the reorientation of the fracture in the second stage of hydraulic fracturing.

The essence of the method is as follows.

Figure 1 shows: 1 - well; 2 - hydraulic fracture plane; σ _min - the direction of the minimum horizontal stress in the reservoir.

During primary acid fracturing in carbonate rocks, an etching crack is created due to the dissolution of the carbonate formation rock in hydrochloric acid. As hydrochloric acid, for example, 25% hydrochloric inhibited acid manufactured by the company NIINEFTEPROMCHEM according to TU 2458-264-05765670-99 (Cheboksary, Russian Federation) is used.

Repeated acid fracturing will lead to even greater opening of the existing crack. This is because a hydraulic fracture always forms perpendicular to the direction of the minimum principal stress in the formation and dissolution of the rock in the existing fracture will lead to an even greater decrease in stress in this direction.

To increase the efficiency of repeated hydraulic fracturing and increase the coverage of the reservoir by depletion of reserves, the second fracture should be perpendicular to the first. To achieve this, repeated fracturing should be carried out in two stages.

In order to change the horizontal stresses in the carbonate formation and the azimuthal orientation of the second fracture perpendicular to the direction of the primary fracture, at the first stage hydraulic fracturing fluid (gel) with proppant is pumped to fill and push the walls of the first fracture formed due to acid fracturing.

The amount of proppant injected must be sufficient to deform and maximize the walls of the existing fracture so that the minimum horizontal stress in the formation perpendicular to the walls of the fracture increases more than the intermediate main stress.

For this purpose, the gel is injected (gelled hydraulic fracturing fluid) in portions: the first in an amount equal to 12 to 14 m ³ with a flow rate of 2 m ³ / min; the second is the injection of the fracture fluid together with the crack fixer in a volume of 30 to 35 m ³ with a flow rate of 2 m ³ / min, and the proppant of the 20/40 mesh fraction according to GOST R 51761-2005, the proppant concentration in the fracturing fluid, is used as the crack fixer gradually increase, after which the process fluid is squeezed in an amount equal to the internal volume of the lowered tubing, with a stepwise reduction in flow rate from 2 to 1 m ³ / min.

As a gel-like liquid, known compositions are used, for example, those developed by KhimekoGANG CJSC with the trade names Khimeko-N (TU 2481-053-17197708), Khimeko-T (TU2481-077-17197708-03), and Khimeko -B "(TU 2499-038-17197708-98). The procedure for the preparation of gelled liquid and its injection using the pump unit CA-320 is described in patent RU No. 2358100, IPC 8 E21B 43/26, publ. in bull. No. 16 dated 06/10/2009. As an additional example of the use of a gel-like fluid, there may be a structured hydrocarbon-like gel composition for hydraulic fracturing described in RU patent No. 2043491, IPC 8 E21B 43/26, publ. September 10, 1995

At the end of the first stage of repeated hydraulic fracturing, in order to fix the proppant pumped into the primary fracture and, accordingly, consolidate the achieved value of the minimum horizontal stress in the reservoir, which, due to the injection of the estimated amount of proppant to the first fracture, exceeds the value of the intermediate main stress in the reservoir, the well is drilled at the outflow through fittings in an increasing sequence of their diameters: 2, 4, 8, 16 mm and thereby provide a smooth increase in depression in the bottom hole it is accompanied by the removal of hydraulic fracturing fluid, strengthening of proppant rock pressure in the fracture, while during the entire hydraulic fracturing process, the aqueous phase does not enter the bottomhole reservoir from the outside, which favors the movement and recovery of the oil phase. For example, the fittings are installed inside a pipe made in the form of a pipe segment, which is screwed onto the upper end of the pipe string after the pipe valve is closed (after the first stage of hydraulic fracturing). After that, the pipe valve is opened and the well is launched into the spout, for example, into a container (not shown in Figs. 1 and 2). At the end of the spout (after time), turn off the pipe with fittings from the pipe string at the wellhead and begin the second stage of hydraulic fracturing.

The second stage of repeated hydraulic fracturing is carried out using an acid composition (acid hydraulic fracturing), but due to redistribution of stress directions, the second fracture develops perpendicular to the first and only away from the well will it turn and align according to the directions of the intermediate main stresses in the intact rock mass (see Fig. 2).

The second stage of acid fracturing is performed similarly to creating the first fracture with acid fracturing (see above), for example, using hydrochloric acid.

In order to change the direction of the minimum horizontal stress in the formation, it is necessary to increase the field of minimum stress by approximately 20% so that the condition is satisfied:

σ ' _min ▷ σ _min

where σ ' _min - the value by which it is necessary to increase the horizontal stress in the reservoir, MPa;

σ _min - the minimum horizontal stress in the reservoir, MPa.

The value by which it is necessary to increase the horizontal stress in the reservoir is determined by the formula:

σ ' _min ▷ σ _min · 0.2 MPa.

The minimum horizontal stress in the reservoir is determined by the formula:

where ν is the Poisson's ratio for carbonate rocks;

σ _ν - vertical rock pressure, MPa;

α is the constant of poroelasticity, taken equal to 0.9;

p - reservoir pressure, MPa.

The effective pressure that must be created in the fracture in order to push the walls of the existing fracture in the reservoir, we calculate by the formula:

p _eff = σ _min · 1.2 MPa.

Vertical rock pressure is determined by the formula:

σ _ν = ρ _g gH, MPa,

where ρ _g is the density of rocks (for carbonates taken equal to 2.5 t / m ³ );

g is the acceleration of gravity, m / s;

H - vertical depth of the reservoir, m

To ensure the condition σ ' _min ▷ σ _min , it is necessary to pump proppant into the fracture with a mass determined by the following formula:

where x _f is the half-length of the crack, m;

h _f - crack height, m;

- средняя ширина трещины, м;

- average crack width, m;

ρ _prop - the density of the proppant, taken equal to 3.08 t / m ³ .

The average crack width is determined by the formula:

where c is the ductility coefficient of the crack and is determined by the formula:

where: π - 3,141592653 ...;

h _f - crack height, m;

E '- the modulus of flat deformation, is determined by the formula:

where E is Young's modulus for carbonate rocks.

The proposed method for improving the hydrodynamic connection of the well with the reservoir is simple and has a low complexity, since it eliminates the drilling of radial perforated channels, which reduces the time and, therefore, saves material and financial resources.

In addition, when implementing this method, the development efficiency of the carbonate formation is increased by increasing the drainage radius, the filtration surface and the drainage area of the productive formation by creating two directed cracks during hydraulic fracturing in two stages, the first of which is fixed by pumping hydraulic fracturing fluid with a crack fixer followed by testing spout wells.

Concrete example

Hydraulic fracturing is performed, while an etching crack (first) is formed in the carbonate formation due to the dissolution of the carbonate formation in hydrochloric acid.

Next, the first stage of repeated hydraulic fracturing is performed. To do this, calculate the amount of proppant to fix the first fracture, sufficient for changes in horizontal stresses in the carbonate formation and the perpendicular direction of the second fracture formed during the second stage of hydraulic fracturing relative to the first fracture.

The initial data for the calculation

The density of rocks for carbonates (ρ _g ) is taken equal to 2.5 t / m ³ ; g - acceleration of gravity - 9.81 m ² / s; the depth of the vertical bed N - 1500 m; Poisson's ratio for carbonate rocks (ν) we take 0.30; poroelasticity constant (α) is taken equal to 0.9; reservoir pressure (p) is assumed to be 100 atm; the initial crack height of acid fracturing (h _f ) is determined using well logging methods, as an example we take 7 meters; Young's modulus for carbonate rocks (E) is assumed to be 10,000 MPa; averagely assume that the half-length of the crack (x _f ) was 50 m; the density of the proppant (ρ _prop ) is taken equal to 3.08 t / m ³ .

1. Calculate the vertical rock pressure:

σ _v = ρ _g gH = 2.5 · 9.81 · 1500 = 36.8 MPa

2. Determine the minimum horizontal stress in the reservoir:

3. The effective pressure in the crack is calculated by the formula:

p _eff = σ _min · 1.2 = 21 · 1.2 = 25.2 MPa

4. The value by which it is necessary to increase the horizontal stress is determined by the formula:

σ ' _min = σ _min · 0.2 = 21 · 0.2 = 4.2 MPa

5. Calculate the modulus of flat deformation:

6. The compliance coefficient of the crack is determined by the formula:

7. The average crack width is calculated by the formula:

8. Determine the amount (mass) of proppant that must be pumped into the first fracture during the first stage of repeated hydraulic fracturing:

Therefore, in order to change the direction of the minimum horizontal stresses in the formation and to perpendicularly direct the second fracture formed during the second stage of hydraulic fracturing relative to the first fracture, it is necessary to pump at least 9 tons of proppant into the first hydraulic fracture.

At the end of the first stage of repeated hydraulic fracturing, to fix the proppant injected into the first fracture of the reservoir, and, accordingly, fix the achieved value of the minimum horizontal stress in the reservoir, which, due to the injection of the estimated amount of proppant to the first fracture, exceeds the value of the intermediate main stress in the reservoir, spill wells through fittings in an increasing sequence of their diameters: 2, 4, 8, 16 mm. For example, the fittings (not shown in FIGS. 1 and 2) are installed inside a pipe made in the form of a pipe segment that is screwed onto the upper end of the pipe string after the pipe valve is closed (after the first hydraulic fracturing stage). After that, the pipe valve is opened and the well is poured into the spout, for example, in a tank. At the end of the spout (after time), turn off the pipe with fittings from the pipe string at the wellhead and begin the second stage of hydraulic fracturing.

The first fracture, formed as a result of acid fracturing, was filled with proppant in an amount of at least 9 tons, and the proppant was fixed in the first fracture of the productive formation by working out a well for spill. This allowed us to fix the achieved value of the minimum horizontal stress in the formation, which, due to the injection of the calculated amount of proppant into the first fracture, exceeds the value of the intermediate main stress in the reservoir, therefore, during the second stage of acid fracturing, the stress directions are redistributed and the second crack is formed perpendicular to the first crack.

Claims (1)

A method for improving the hydrodynamic connection of a well with a reservoir, including acid hydraulic fracturing (Fracturing), by installing a packer over the roof of a perforated reservoir, injecting frac fluid into the sub-packer zone, creating frac pressure in the sub-packer zone and pumping fracturing fluid into the resulting crack, characterized in that after acid hydraulic fracturing, repeated hydraulic fracturing is performed in two stages, and at the first stage, the crack formed as a result of acid fracturing is fixed by injection hydraulic fracturing fluid with proppant in an estimated amount sufficient to change the horizontal stresses in the carbonate formation and the perpendicular direction of the second fracture formed during the second stage of acid fracturing relative to the first fracture, and after the first stage of repeated fracturing, the well is poured through the nozzles in ascending order their diameters, while in the first stage of hydraulic fracturing, a gel is used as the hydraulic fracturing fluid, and in the second, the acid composition.

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