RU2510456C2 - Formation method of vertically directed fracture at hydraulic fracturing of productive formation - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: two side horizontal shafts are drilled in a productive formation parallel to each other and arranged in one vertical plane. After perforation is completed, a well strainer is installed in the upper horizontal shaft and a perforated liner is installed in the lower one. Then, oilwell tubing with a packer is lowered to the main shaft of the well, and the above packer is installed between upper and lower horizontal shafts. Before hydraulic fracturing of the productive formation is performed, annular space of the well is equipped on the head with an adjustable throttle and sealed. Moment of fracture formation between upper and lower horizontal shafts is determined as per stepwise rise of pressure in the annular space of the well. After the fracture is formed, pressure in the annular space of the well is reduced by means of the adjustable throttle. Further pumping of carrying liquid with a propping agent and displacement fluid is performed at counter pressure created on the head. After the displacement fluid is pumped, the following is performed in series: unloading of the well, removal of the packer and flushing of the main shaft of the well. Size of cells of the well strainer shall be less than average diametre of particles of the propping agent used at hydraulic fracturing of the productive formation.

EFFECT: improving effectiveness of the hydraulic fracturing process of the productive formation and creating the conditions allowing to reduce carryover intensity of solid mechanical impurities from the productive formation to the well shaft.

6 cl, 1 dwg

Description

The invention relates to the mining industry and can be used in the development of oil, gas, gas condensate and methane fields.

A known method of conducting local directed hydraulic fracturing of the reservoir [1]. According to this method, stress zones are determined from an open hole in a well using seismic sounding using the scattered wave method in the reservoir. Drilling of two parallel, horizontal lateral shafts (GBS), located one below the other, in the reservoir is carried out along the axis of the main compressive stresses of the rock mass. In this case, the distance between the GWS is chosen from the condition of ensuring their stability, as well as the possibility of carrying out vertical hydraulic fracturing of the productive formation along the entire length of the GWS with the propagation direction of artificially created cracks towards each other.

The main disadvantages of this method include the significant investment of time on seismic sounding from an open hole and subsequent processing of the results.

A known method of locally directed fracturing of a reservoir [2]. The specified method involves drilling from a cased hole of a vertical well in the direction of the expected concentration of hydrocarbon reserves of two small-diameter GHS parallel to each other. Then, an elevator string is lowered into the well, the lower end of which is equipped with a packer, which is installed in the wellbore above the reservoir, i.e. above the location of the BGS. Next, hydraulic fracturing of the productive formation is carried out by pumping the process fluid under pressure simultaneously into both GHS through an elevator column, after which the crack created in the formation is fixed with proppant.

The main disadvantage of this method is the high probability of uncontrolled crack propagation in the vertical direction, which limits the possibility of using this method in productive formations with bottom water, as well as in the presence of water-saturated horizons close to the productive formation with small power jumpers.

The closest to the claimed method according to the technical nature (ie prototype) can be considered a method of forming a directed vertical or horizontal fracture during hydraulic fracturing [3]. According to the aforementioned method, from the main trunk of a vertical well in a predetermined direction, two GHSs parallel to each other are drilled, which are placed in the reservoir in the same vertical plane. Perforators are lowered into the main wellbore and, with their help, directional perforation of the GHS is carried out, as a result of which the perforation channels are located in the plane passing through both GHS and oriented towards each other. After that, a rupture fluid is pumped into both GHS under pressure, and then a proppant carrier fluid. As a result of this, an artificially created crack fixed by proppant is formed between the two CWGs in the reservoir.

The disadvantages of this method include the high probability of uncontrolled propagation of the created crack in the vertical direction, due to the need for simultaneous injection into both GBS under pressure of the fracture fluid, and then the carrier fluid with proppant. In addition, during the subsequent operation of the well, a significant amount of solid mechanical impurities (including rock particles, proppant, etc.) that will be carried out of the reservoir with the flow of the reservoir will begin to flow into both GHS and then into the main wellbore fluid.

The objective of the present invention is to increase the efficiency of the hydraulic fracturing process in order to form a vertical highly permeable crack that does not extend beyond its boundaries, as well as to create conditions that reduce the rate of removal of solid mechanical impurities from the reservoir into the wellbore.

The technical result is achieved due to the fact that in the proposed method for the formation of a vertically directed crack during hydraulic fracturing of a productive formation, including drilling from the main well of a vertical well of an upper and lower GHS, placed in a productive formation parallel to each other in the same vertical plane, installing perforators in both GHS, carrying out their perforation in the specified plane and in the direction towards each other, injection under pressure into the upper and lower GHS of the fracture fluid and the carrier fluid ty with proppant, and after the carrier fluid with proppant, injection fluid is injected under pressure, and after perforation, a downhole filter is installed in the upper GHS and a perforated liner in the bottom, after which they are lowered into the main well bore with an packer and the installation of the latter between the upper and lower GHS, and before the hydraulic fracturing of the reservoir, the annular space of the well is equipped at the mouth with an adjustable throttle and sealed, and m The moment of crack formation between the upper and lower GHS is determined by an abrupt increase in pressure in the annulus of the well, after which the indicated pressure is reduced by means of an adjustable throttle and further injection of the carrier fluid with proppant and squeezing fluid is carried out with backpressure created at the mouth, and after the squeezing fluid is injected in series carry out discharging of the well, disruption of the packer and flushing of the main wellbore, while the mesh size of the well filter should be less ednego diameter proppant particles used in the producing formation fracturing.

The technical result is also achieved due to the fact that:

- punching is performed using a hydro-jet punch, which forms a longitudinal felling slot in each of the CBC;

- on the outer surface of the downhole filter and perforated liner set the centering elements;

- casing packers are installed at the ends of the downhole filter and perforated liner facing the main wellbore;

- after installing the packer in the main shaft, the density of the fluid in the annulus of the well is reduced, and the density of the fluid in the annulus of the well is reduced by organizing reverse circulation using a bypass valve installed in the elevator string above the packer.

The drawing (Fig. 1) shows a flow chart of a method for the formation of a vertically directed crack during hydraulic fracturing of a reservoir.

The proposed method is implemented as follows.

From the cased and cemented main wellbore 1 of a vertical well, two in parallel and located in the same vertical plane BGS are constructed in the reservoir 2 (upper 3 and lower 4). Before starting drilling, determine the azimuthal direction of the BGS wiring, as well as the optimal values of their length and distance (vertical) between them.

Perforators (for example, cumulative type) are lowered into the drilled BGS and with their help create perforation channels 5, which are located in the aforementioned vertical plane and are directed towards each other. In the case of using a sandblasting perforator, instead of the indicated perforation channels 5, a rather deep, longitudinally located felling slot (not shown) in each GBS can be formed.

After perforation, a downhole filter 6, which, as a rule, consists of several sections interconnected, is placed in the upper GHS 3. Each section is a pipe with through radial channels (or axial grooves), on the outside of which there is a single or multilayer filter element. The specified filter element must not pass particles of proppant used in hydraulic fracturing of reservoir 2, i.e. the cell size of the filter element must be less than the average proppant particle diameter.

In the lower GHS 4, drilled in the reservoir 2, a perforated shank 7 is placed. In the case where there is no probability of collapse of the walls of the lower GHS 4, the latter can be left uncased.

When choosing the optimal diameter of the through holes in the perforated shank 7, it should be taken into account that it should be at least six average diameters of the proppant particles used in the hydraulic fracturing of the productive formation 2. Practical experience confirms that in this case the proppant concentration in the carrier fluid can be increased without fearing clogging of through holes in the perforated shank 7.

On the outer surface of the downhole filter 6 and the perforated liner 7, which are located respectively in the upper 3 and lower 4 GHS, set the centering elements 8. In addition, at the ends of the downhole filter 6 and the perforated liner 7 facing the main barrel 1 of the well, it is advisable to place casing packers 9.

If the section of the main wellbore 1, located below the bottom of the productive formation 2, has a considerable length, then it is usually cut off before the hydraulic fracturing by installing a cement bridge 10 (or bridge plug, etc.).

An elevator string 11 is lowered into the main wellbore 1, the lower end of which is equipped with a packer 12. The packer 12 is placed in the main wellbore 1 between the upper 3 and lower 4 GHS, due to which their reliable isolation is achieved. In this case, the upper BGS 3 is hydraulically connected to the annulus 13 of the well, and the lower BGS 4 is connected to the internal cavity of the elevator column 11.

On the lateral branch of the wellhead equipment 14 connected with the annular space 13 of the well, an adjustable choke 15 is installed, which is connected to the flow line (not shown in the drawing).

In practical conditions, when performing hydraulic fracturing of a productive formation 2, quite often, in order to facilitate the working conditions of the packer 12, they try to increase the pressure above it in the annulus 13 of the well. This is achieved either by increasing the density of the fluid in the annulus 13 of the well, or by creating excess pressure in the latter. However, in the present invention (in the case when the conditions for hydraulic fracturing of the reservoir 2 allow), the opposite should be done, i.e. as much as possible reduce the density of the fluid in the annulus 13 of the well. For this, after installing the packer 12 in the main wellbore 1, it is necessary, by reverse circulation, to replace the liquid filling the annulus 13 with a liquid of lower density. To this end, the composition of the elevator column 11 should provide for the installation of an overflow valve 16, designed to communicate the annular space 13 of the well with the internal cavity of the elevator column 11.

The bypass valve 16 is placed above the packer 12. The bypass valve 16 is opened by creating an excess pressure in the annulus 13 of the well that exceeds the pressure in the inner cavity of the elevator column 11.

Hydraulic fracturing of the productive formation 2 is carried out using an elevator string 11, equipped with a packer 12, lowered into the main bore 1 of the well, with a sealed annular space 13. The calculated volume of the fracture fluid is pumped under the elevator string 11 into the lower BSS 4 under pressure. The moment of formation of a crack in the reservoir 2 between the lower 4 and upper 3 GHS is fixed at the mouth by a sharp (spasmodic) increase in pressure in the annular space 13 of the well. After that, the adjustable throttle 15 is smoothly slightly opened, thereby providing the possibility of liquid exit from the annulus 13 of the well into the flow line. The required amount of backpressure at the wellhead, necessary to create an artificial fracture of a given width in the reservoir 2, is maintained by changing the area of the passage section of the adjustable throttle 15.

Following the rupture fluid, the calculated volume of the carrier fluid with proppant is pumped into the elevator column 11. The carrier fluid first enters the lower GHS 4, then through the crack into the upper GHS 3 and then rises to the mouth along the annular space 13 of the well. After passing through the adjustable throttle 15, the carrier fluid is sent to the flow line. At the final stage of hydraulic fracturing, an estimated portion of the squeezing liquid is pumped into the elevator column 11, which displaces the remaining proppant carrier fluid from its internal cavity.

Since the cell size of the filter element does not allow proppant particles to pass through it, only liquid enters the internal cavity of the downhole filter 6, and the proppant is distributed outside it. The main volume of proppant, after completion of the injection of squeezing fluid into the lift column 11, is located: in the lower GHS 4; in the crack created in the reservoir 2; in the annular space between the outer surface of the downhole filter 6 and the inner surface of the upper BGS 3.

It is quite obvious that around the downhole filter 6, installed in the upper BGS 3, after the completion of hydraulic fracturing of the reservoir 2, an additional, sufficiently homogeneous and compacted, proppant filter is formed, which in the future will perform the same functions as the gravel filter widely used in the operation of oil, gas and water wells.

After the injection of the squeezing fluid into the elevator column 11 is completed, a small portion of the proppant remains in the main wellbore 1 and eventually settles on the cement bridge 10.

Following the controlled discharge of the well, the packer 12 is disrupted, then the elevator column 11 is removed to the surface. If a cement bridge 10 (or bridge plug, etc.) was installed in the main shaft 1 before hydraulic fracturing of the reservoir 2, then it is drilled, and finally the main shaft 1 of the well is thoroughly washed.

As a result of a set of works, the upper 3 and lower 4 GHS turn out to be connected by a highly permeable vertical crack, which is artificially created in the reservoir 2 by hydraulic fracturing.

At the final stage, the selected layout of the underground equipment is lowered into the main wellbore 1 and placed at the calculated depth. Further development and operation of the well is carried out in accordance with the work plan.

Information sources

1. RF patent №2335628, Е21В 43/26 and ЕВВ 43/17, publ. 10/10/2008

2. Yu.A. Ikonnikov and R. G. Ramazanov “New oil recovery enhancement technologies that have been developed in the fields of OAO“ Lukoil. ”- Interval Magazine, No. 7 (114), 2008, p.50.

3. RF patent No. 2176021, ЕВВ 43/26 and ЕВВ 43/17, publ. November 20, 2001

Claims (6)

1. The method of formation of a vertically directed crack during hydraulic fracturing of the reservoir, including drilling from the main well of a vertical well of the upper and lower lateral horizontal shafts placed in the reservoir parallel to each other in the same vertical plane, installing perforators in both side horizontal shafts, perforating them in the specified plane and in the direction towards each other, injection under pressure into the upper and lower lateral horizontal trunks of the fracture fluid and carrier fluid with proppant, characterized in that after the carrier fluid with proppant pumping is performed under the pressure of the squeezing fluid, and after perforation, a downhole filter is installed in the upper horizontal lateral barrel, and a perforated liner is placed in the lower one, and after their placement, they are lowered into the main a borehole of the elevator string with a packer and installation of the latter between the upper and lower lateral horizontal trunks, moreover, before hydraulic fracturing of the productive formation of the annulus The borehole space is equipped at the wellhead with an adjustable throttle and sealed, and the moment of crack formation between the upper and lower lateral horizontal boreholes is determined by an abrupt increase in pressure in the annulus of the well, after which the indicated pressure is reduced by means of an adjustable throttle and further pumping of carrier fluid with proppant and squeezing liquids are carried out with backpressure created at the mouth, and after pumping the squeezing liquid, the discharge of Azhinov, the failure of the packer and washing the main wellbore, the well screen size of cells to be smaller than the average diameter of the proppant particulate used in the producing formation fracturing. 2. The method according to claim 1, characterized in that the perforation is performed using a waterjet perforator, which forms in each of the lateral horizontal trunks a longitudinal cutting slot. 3. The method according to claim 1, characterized in that on the outer surface of the downhole filter and the perforated liner set the centering elements. 4. The method according to PP.1 and 3, characterized in that at the ends of the downhole filter and perforated liner facing the main wellbore, annular packers are installed. 5. The method according to claim 1, characterized in that after installing the packer in the main trunk, the fluid density in the annulus of the well is reduced. 6. The method according to claim 5, characterized in that the decrease in the density of the fluid in the annulus of the well is carried out by organizing the reverse circulation using the bypass valve installed in the elevator column above the packer.

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