RU2618544C1 - Method for hydraulic fracturing of productive formation with clay layer and gas-bearing horizon - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention can be applied for the hydraulic fracturing treatment (HFT) of a formation containing a clay layer with a gas-bearing horizon. Method involves carrying out the perforation in the productive formation interval of the well oriented in the direction of the main maximum stress, lowering the tubing string (TS) with the packer to the well, seating the packer, performing the hydraulic fracturing treatment (HFT) by means of pumping the hydraulic fracture liquid via the tubing string with the packer through the perforation interval into the production formation with obtaining the fracture and its further fixation by a propping agent, relieving the pressure in the well, releasing the packer and its extracting with the TS from the well. The oriented perforation is carried out using a hydromechanical perforator with an orienting sub, the HFT process starts with pumping the hydraulic fracturing fluid, which is represented by a crosslinked gel, to create a fracture in the productive formation, after which the fracture formed is developed by pumping linear gel with the density of 1,150 kg/m³ with an ultralight proppant with the density of 1,050 kg/m³ of the 40/80 mesh fraction with the weight of 3 tons with the concentration of 200 kg/m³, then the fracture is fixed by pumping crosslinked gel with the proppant of 20/40 mesh fraction or 12/18 mesh fraction, depending on the permeability of the production formation, in batches with the stepwise increasing of the proppant concentration by 100 kg/m³, starting from 200 kg/m³ up to 900 kg/m³. Wherein the crosslinked gel with the proppant of 20/40 mesh fraction is pumped into the productive formation with the permeability from 0.01 to 100 mD during the fracture fixation, while in the productive formation with the permeability from 100 to 500 mD the crosslinked gel with a proppant of 12/18 mesh fraction is pumped during the fracture fixation.

EFFECT: improving the reliability of the fracture creation and development in the presence of a clay layer and a gas-bearing horizon above the production formation, increasing the method efficiency; reducing the hydraulic resistance in the perforation interval, reducing the length and complexity of the technological process of the method implementation.

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Description

The invention relates to the field of oil and gas industry, in particular, can be used for hydraulic fracturing (hydraulic fracturing) containing a layer of clay with a gas horizon.

The known method of hydraulic fracturing with clay interlayers and bottom water (patent RU No. 2544343, IPC ЕВВ 43/267, publ. March 20, 2015, bull. No. 8), including the descent of the tubing string with a packer into the well, packer planting, hydraulic fracturing by pumping through a tubing string with a packer through a well into a hydraulic fracturing reservoir followed by proppant injection through the perforation interval of a low-permeability formation, relieving pressure from the well. Additionally, temporary isolation of the perforation interval of the low-permeable formation is performed, the clay layer is perforated using alternating charges of large diameter and deep penetration, then the tubing string with the packer is lowered into the well so that the lower end of the tubing string is at the level of the clay layer roof, the packer is planted in the well , hydraulic fracturing is performed with the formation of cracks by injection of hydraulic fracturing fluid along the tubing string at intervals of perforation of the clay layer. The rim of the cross-linked gel on a hydrocarbon base is pumped into the cracks in a volume of 3-5 m ³ with a flow rate of 10 m ³ / min, and the proppant mixture is used as proppant, after which the cracks are fixed with a batch injection of hydraulic fracturing fluid and proppant mixture, starting from the concentration of the proppant mixture 400 kg / m ³ with a stepwise increase in its concentration by 200 kg / m ³ in hydraulic fracturing fluid in each portion and a flow rate of 5 m ³ / min, and the proppant mixture is prepared at the wellhead in the following ratio, wt. %: proppant 12/40 mesh - 30%; proppant 18/20 mesh - 30%; quartz flour - 40%. At the end of the hydraulic fracturing, the temporary isolation of the perforation interval of the low permeability formation is removed and the low permeability formation is perforated to form a hydraulic connection between the wellbore and the fracture.

The disadvantages of this method are:

- firstly, the low reliability of the creation and development of cracks in the presence of a clay layer and a gas-bearing or aquifer above the productive layer. This is due to the fact that in the process of hydraulic fracturing, a crack develops upward in width, and not in length, which leads to a breakthrough of the crack during its development into a gas-bearing or aquifer. As a result, water or gas from the upper gas-bearing or aquifer, respectively, breaks into the well during hydraulic fracturing;

- secondly, the low efficiency of the crack attachment, due to the low conductivity of the crack and, as a consequence, a weak influx of oil from the reservoir into the well. The fracture throughput depends on the size of the proppant fraction securing the fracture, and more precisely, on the distance between the proppant grains providing the fracture throughput, when the fracture throughput does not correspond to the volume of oil inflow from the reservoir depending on its permeability, the fracture conductivity decreases;

- thirdly, high hydraulic resistances in the interval of formation perforation increase the risk of a pressure surge during proppant pushing into the fracture, an emergency situation and failure to achieve the specified fracture parameters (width, length);

- fourthly, additional costs, since at the end of hydraulic fracturing, temporary isolation of the perforation interval of the low-permeability formation is removed and the low-permeability formation is perforated to form a hydraulic connection between the wellbore and the fracture.

The closest in technical essence is the method of hydraulic fracturing with a clay layer and bottom water (patent RU No. 2566542, IPC ЕВВ 43/26, publ. 10/27/2015, bull. No. 30), including the descent of the tubing string with a packer into the well, landing the packer, hydraulic fracturing by pumping hydraulic fracturing fluid along the tubing string with the packer through the perforation interval into the reservoir with formation and subsequent fastening of the crack with proppant, relieving pressure from the well, unpacking the packer and removing it from the tubing string from the well. Before the tubing string with the packer is lowered into the well by geophysical methods, the orientation of the main maximum stress in the reservoir is determined, then perforation oriented in the direction of the main maximum stress is carried out in the upper half of the reservoir, then the lower half of the reservoir is cut off, the tubing string with the packer is lowered into the well so that the lower end of the tubing string is at the level of the roof of the reservoir, the packer is planted, hydraulic fracturing is carried out by injection along the string N T fracturing fluid, which is used as a linear gel with a flow rate of 0.3 ^m3 / min with creating cracks in the reservoir, then the fixing produce cracks in the reservoir in four cycles by alternating the injection tubing string at an interval of a producing formation perforations oriented equal portions linear gel with 20/40 mesh proppant facilitated equal portions and cross-linked gel with the addition of NaCl salt with a concentration of 400 kg / m ^3, wherein the crosslinked gel equal portions by volume less than twice the line n equal portions I, and the number of equal portions crosslinked gel at least one portion equal portions of a linear gel, and the concentration of lightweight proppant 20/40 mesh gel in a linear stepwise increased by 100 kg / m ^3, the first to third portions of each cycle, starting with a concentration of 100 kg / m ³ , in the last fourth cycle, one portion of a linear gel is injected containing a 16/20 mesh lightweight proppant with a concentration of 400 kg / m ³ , and then a 15% aqueous hydrochloric acid solution is injected and forced into the fracture of the reservoir in the volume equal to polo INE sum of the volumes of linear and cross-linked gel, injected into a crack in the process of fixing the crack.

The disadvantages of this method are:

- firstly, the low reliability of the creation and development of cracks, in the presence of a clay layer and a gas-bearing or aquifer above the productive layer. This is due to the fact that in the process of hydraulic fracturing, a crack develops upward in width, and not in length, which leads to a breakthrough of the crack during its development into a gas-bearing or aquifer. As a result, water or gas from the upper gas-bearing or aquifer, respectively, breaks into the well during hydraulic fracturing;

- secondly, the low efficiency of the crack attachment, due to the low conductivity of the crack and, as a consequence, a weak influx of oil from the reservoir into the well. The fracture throughput depends on the size of the proppant fraction securing the fracture, and more precisely, on the distance between the proppant grains providing the fracture throughput, when the fracture throughput does not correspond to the volume of oil inflow from the reservoir depending on its permeability, the fracture conductivity decreases;

- thirdly, high hydraulic resistances in the interval of formation perforation increase the risk of a pressure surge during proppant pushing into the fracture, an emergency situation and failure to achieve the specified fracture parameters (width, length);

- fourthly, a long and laborious technological process of implementing the method associated with multiple cycles of pumping portions of a linear gel with proppant, alternating with portions of a crosslinked gel with the addition of NaCl salt and pressing a 15% aqueous hydrochloric acid solution.

The technical objectives of the invention are to increase the reliability of the creation and development of cracks, the effectiveness of fastening cracks, as well as reducing hydraulic resistance in the perforation interval when pushing proppant into a crack, reducing the duration and complexity of the technological process of the method.

The stated technical problems are solved by the method of hydraulic fracturing of a productive formation with a clay layer and a gas-bearing horizon, including perforation in the interval of a productive formation of a well oriented in the direction of the main maximum stress, descent of a tubing string — tubing — with a packer into the well, planting the packer, hydraulic fracturing - hydraulic fracturing - pumping hydraulic fracturing fluid along the tubing string with a packer through the perforation interval into the reservoir with the image the formation and subsequent fastening of the crack with proppant, venting the well, unpacking the packer and removing it with the tubing string from the well.

What is new is that oriented perforation is carried out using a hydromechanical perforator with an orienting sub, the hydraulic fracturing process begins with the injection of hydraulic fracturing fluid, which uses a crosslinked gel to create a crack in the reservoir, after which the created fracture is developed by injecting a linear gel with a density of 1150 kg / m ³ with an ultralight proppant with a density of 1050 kg / m ³ fractions 40/80 mesh weighing 3 tons with a concentration of 200 kg / m ³ , then the crack is fixed by injection of a cross-linked gel with proppant fraction 20/40 mesh or 12/18 mesh, depending on the permeability of the reservoir, in portions with a stepwise increase in proppant concentration by 100 kg / m ³ , starting from 200 kg / m ³ to 900 kg / m ³ , while in the reservoir with permeability from 0.01 to A crosslinked gel with a proppant fraction of 20/40 mesh is pumped at 100 mD when a crack is attached, and a crosslinked gel with a proppant of a 12/18 mesh fraction is pumped into a reservoir with a permeability of 100 to 500 mD.

In FIG. 1-4 schematically and sequentially depicted the proposed hydraulic fracturing method with a clay layer and a gas-bearing horizon, where 1 is a producing well; 2 - productive layer with a height of H; 3 - clay layer (impermeable layer); 4 - upper gas-bearing horizon; 5 - tubing string; 6 - hydromechanical perforator; 7 - orienting sub; 8 - cutters hydromechanical perforator 6; 9 - oriented perforation made in the interval of the reservoir 2; 10 - packer; 11 - hydraulic fracture; 12 - ultralight proppant fraction 40/80 mesh; 13 - proppant fraction 20/40 mesh or 12/18 mesh, depending on the permeability of the reservoir 2.

Production well 1 (see Fig. 1) revealed a reservoir 2 with a height of H, for example, H = 3 m, with a clay layer 3 (impermeable layer) on top of a height of h = 1.5 m, above which there is a gas-bearing horizon 4.

Productive formation 2 of the producing well 1 through the existing perforation (not shown in Fig. 1-4) is operated, for example, by a sucker rod pump (not shown in Fig. 1-4). During operation, the flow rate in production well 1 (see Fig. 1) is rapidly reduced, and therefore it is necessary to intensify oil production from productive formation 2 of production well 1. To this end, hydraulic fracturing of production formation 2 is performed.

For this, production equipment is removed from the well (not shown in FIGS. 1, 2, 3 and 4) and the proposed method is implemented as follows.

Geophysical methods, for example, the method of cross-dipole acoustics, determine the orientation of the main maximum stress σ _max (see Fig. 1) in the reservoir 2.

Then in the interval of the reservoir 2 carry out hydromechanical perforation, oriented in the direction of the main maximum stress σ _max .

To do this, on the tubing string 5, lower the hydromechanical perforator 6 with the orienting sub 7 from above, having previously installed the guide of the spline sleeve (not shown in Fig. 1-4) of the orienting sub 7 and the cutters 8 of the hydromechanical perforator 6 in one direction with the direction of the main maximum formation stress σ _max , while on the wellhead flange (not shown in FIGS. 1-4) wells 1 (see FIG. 1) also carry out a mark in the direction of the main maximum stress σ _max (see FIG. 1).

Having reached the perforation interval by rotation of the tubing string 5, the guide of the spline sleeve of the orienting sub 7 (see Fig. 1) and the cutters 8 of the hydromechanical perforator 6 are aligned with the direction of the main maximum formation stress σ _max marked with a mark on the wellhead flange 1.

After the orientation of the cutters 8 of the hydromechanical perforator 6, the interval of the productive formation 2 is perforated with the formation of perforations (oriented perforations) 9, for example, in the form of two rows, two holes in each row and an angle between the holes of 180 °, the holes being made one under the other in the direction of the main maximum stress σ _max .

Work with the orienting sub 7 and the hydromechanical rotary hammer 6 is carried out according to their operating instructions.

A tubing string with a hydromechanical hammer drill 6 and an orienting sub 7 is removed from the well 1.

For hydraulic fracturing, a tubing string 5 with a packer 10 is lowered into the well 1. Any known packer is used as a packer. Packer 10 is planted in well 1 and the annular space of the tubing string 5 is sealed.

The lower end of the tubing string 5 is placed above the oriented perforation 9, for example at a distance of 2 m

Next, determine the volume of hydraulic fracturing fluid to create a crack according to the following formula:

V _g = k⋅H,

where V _g - the volume of hydraulic fracturing fluid to create a crack, m ³ ;

k = 2-3 - conversion factor, m ³ / m;

N - the height of the reservoir, m

In this formula, the conversion coefficient k is obtained experimentally and depends on the physicochemical properties of formation 2 (see Fig. 1), in which hydraulic fracturing is performed.

The height of the reservoir 2 is 3.0 m (see above).

Substituting V _g = k⋅Н in the formula, we obtain the volume of hydraulic fracturing fluid:

V _g = (2-3) (m ³ / m) ⋅3.0 (m) = (6.0-9.0) m ³ .

Take V _g = 8.0 m ³ . As a fracturing fluid, any known crosslinked gel is used.

The hydraulic fracturing process begins with the injection of a cross-linked gel until a crack is created (see Fig. 2) in the reservoir 2. To do this, using pumping units along the injection line (not shown in Fig. 1-4) into well 1 (see Fig. 2 ) through the tubing string 5 through the holes of oriented perforation 9 of the reservoir 2, the crosslinked gel is pumped in a volume of V _g = 8.0 m ³ and a crack 11 'is created.

After that, the created crack 11 'is developed to 11ʺ (see Figs. 1 and 2) by injection of a linear gel with a density of 1150 kg / m ³ with an ultralight proppant of 12 fractions 40/80 mesh weighing 3 t = 3000 kg with a concentration of 200 kg / m ³ . Therefore, without interrupting the download, i.e. the process of creating and developing a crack, a linear gel is injected in a volume of: V _l = 3000 kg / 200 kg / m ³ = 15 m ^{3 with a} density of 1150 kg / m ³ with ultralight proppant 12 fractions 40/80 mesh with a concentration of 200 kg / m ³ .

When implementing the proposed method, a linear gel density of 1150 kg / m ^{3 is} provided, for example, waste water with a density of 1180 kg / m ³ with the addition of any known gelatinizing agent is used and the linear gel density is adjusted to 1150 kg / m ³ , while in the process injections using a hydrometer control the density of 1150 kg / m ³ linear gel.

Due to the difference in the densities of the linear gel (ρ _lg = 1150 kg / m ³ ) and ultralight proppant (ρ _p = 1050 kg / m ³ ) 1150 kg / m ³ > 1050 kg / m ³ , having fallen into an 11ʺ crack (see Fig. 3 ), the ultralight proppant 12 of the 40/80 mesh fraction pops up in a linear gel and rushes to the upper part of the 11 трещ crack and the interval of the impermeable layer (clay layer), and the linear gel is filtered at the bottom, widening the 11 трещ crack. A dense pack of ultralight proppant 12 with minimal conductivity is formed in the upper part of the 11ʺ crack, since the ultralight proppant 12 of one of the smallest 40/80 mesh fractions is selected, which ensures a minimum throughput between grains, which prevents the crack 11'ʺ from developing (see Fig. 4) up through the clay layer 3 into the gas-bearing horizon 4.

The injection of ultralight proppant 12 (see Fig. 3) during the development of the crack 11ʺ prevents its expansion upward. This is due to the fact that the ultralight proppant 12 has a lower density compared to the density of the linear gel, therefore, having got into the 11 трещ fracture, the lightweight proppant 12 floats in the linear gel and rushes to the top of the 11ʺ fracture in the bottomhole formation zone (PPP), preventing its development upward, while a linear gel freed from ultralight proppant acts as a fracturing fluid and develops a crack in length (see Fig. 4).

Creating a crack 11 'and developing a crack up to 11ʺ, 11'ʺ according to the proposed method allows to exclude a breakthrough of a crack in the gas-bearing horizon 4, located above the productive formation 2, through clay interlayer 3 with a height of h = 1.5 m, which means to increase the reliability of creation and crack development.

The cracks are fixed by injection of a crosslinked gel with proppant 13 fractions of 20/40 mesh or 12/18 mesh, depending on the permeability of the reservoir by portions with a stepwise increase in proppant concentration by 100 kg / m ³ , starting from 200 kg / m ³ to 900 kg / m ³ .

A crosslinked gel with a proppant of 20/40 mesh fraction is pumped in a producing formation with a permeability of 0.01 to 100 mD when a crack is attached, and a crosslinked gel with a proppant of a 12/18 mesh fraction is pumped in a reservoir with a permeability of 100 to 500 mD. .

The selection of the proppant fraction 13 when fixing the crack in the reservoir, depending on the permeability of the reservoir allows you to select the optimal conductivity of the fracture and ensure maximum oil flow through the grains of the proppant that secures the crack 11'ʺ, which allows to increase the conductivity of the crack, and therefore, increase the efficiency of crack fixing.

Example 1. The permeability of the formation is 40 mD, using proppant 13 fractions of 20/40 mesh, without interrupting the process of pumping units along the injection line along the tubing string 5 through oriented perforation 9, the crack 11'ʺ is fixed (see Fig. 4) by injection of a cross-linked gel with proppant fraction 20/40 mesh in portions: 200 kg / m ³ , 300 kg / m ³ , 400 kg / m ³ , 500 kg / m ³ , 600 kg / m ³ , 700 kg / m ³ , 800 kg / m ³ , 900 kg / m ³ .

Example 2. The permeability of the formation is 200 mD, using proppant 13 fractions 12/18 mesh, without interrupting the process of pumping the pump units along the injection line along the tubing string 5 through the oriented perforation 9, the crack 11'ʺ is fixed (see Fig. 4) by injection of the cross-linked gel with proppant fraction 12/18 mesh portions: 200 kg / m ³ , 300 kg / m ³ , 400 kg / m ³ , 500 kg / m ³ , 600 kg / m ³ , 700 kg / m ³ , 800 kg / m ³ , 900 kg / m ³ .

Any known crosslinked gel formulation is used. The crosslinked gel has low pressure loss due to friction in the pipes and high viscosity in the reservoir, which ensures uniform filling of the 11'ʺ crack with proppant (proppant 13). Upon destruction, it does not form a precipitate, does not damage the formation and packing, which also contributes to the preservation of the highly conductive 11'ʺ crack.

The hydraulic resistance in the perforation interval is reduced by a factor of 2–3 when implementing the proposed method using a hydromechanical perforator that performs rectangular holes with a minimum side size of 10 by 20 mm, which completely eliminates the pressure jump in the tubing string, emergency shutdown of the hydraulic fracturing process and failure to achieve design fracture parameters and provides less crushing pressure compared to the prototype with comparable injection volumes.

Thus, the crack 11' 11 is fixed with proppant 13. At the end of the crack attachment, the pressure is released from the well, the packer 10 is unpacked and it is removed from the well with the tubing string. The fracturing process is completed.

The duration and complexity of the technological process of implementing the method are reduced, since the crack is fixed with a proppant of one fraction of 20/40 mesh or 12/18 mesh, depending on the permeability of the reservoir 2.

The proposed method of hydraulic fracturing allows you to:

- to increase the reliability of the creation and development of cracks in the presence of a clay layer and gas-bearing horizon above the productive layer;

- to increase the efficiency of the method by selecting a proppant fraction depending on the permeability of the reservoir;

- reduce hydraulic resistance in the perforation interval by making perforations with a hydromechanical perforator and, as a result, reduce the proppant delivery pressure;

- reduce the duration and complexity of the technological process of implementing the method.

Claims (1)

A method of hydraulic fracturing of a productive formation with a clay layer and a gas-bearing horizon, including perforating in the interval of the productive formation of a well oriented in the direction of the main maximum stress, lowering the tubing string with a packer into the well, planting the packer, and carrying out hydraulic fracturing ( Hydraulic fracturing) by pumping hydraulic fracturing fluid along the tubing string with a packer through the perforation interval into the reservoir with the formation and subsequent fastening of the proppa crack volume, pressure relief from the well, unpacking the packer and removing it with the tubing string from the well, characterized in that the oriented perforation is performed using a hydromechanical perforator with an orienting sub, the hydraulic fracturing process is started by pumping a hydraulic fracturing fluid, using a crosslinked gel to create a crack in the reservoir, after which the created fracture develop gel injection linear density 1150 kg / m ³ with ultralight proppant density 1050 kg / m ³ 40/80 mesh fraction weighing 3 tons with conc ntratsiey 200 kg / m ³ and then producing attachment crack pumping crosslinked gel fraction 20/40 mesh proppant or 12/18 mesh, depending on the permeability of producing formation with stepped portions increasing proppant concentrations to 100 kg / m ^3, starting from 200 kg / m ³ up to 900 kg / m ³ , while in the reservoir with permeability from 0.01 to 100 mD when fixing the crack, a cross-linked gel with proppant fraction of 20/40 mesh is pumped, and in the reservoir with permeability from 100 to 500 mD when attached cracks pump cross-linked gel with proppant fraction 12/18 mesh.

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