RU2616016C1 - Recovery method for solid carbonate reservoirs - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: method includes drilling of horizontal wells, cementing of the annular space between the production casing and the reservoir in the horizontal shaft, the secondary penetration of the field with the orientation direction of perforation holes, conduction of multistage hydraulic fracturing, application of packers for separation of horizontal shaft to the sections, and product selection from the horizontal wells. According to the invention, the oil-saturated reservoir is selected with the average thickness H≥50 m and the average absolute permeability of less than 2 mD, the collector is drilled with parallel horizontal wells, the horizontal shafts of which are directed perpendicular to the main maximum collector voltage vector. Horizontal shafts are arranged vertically in three rows at the equal distances from one another h = (0.25-0.45) H. The horizontal shafts of the middle row are disposed in the plane between horizontal shafts of the upper and lower rows at the distance x = (1-5) h along the horizontal line. The length of each horizontal shaft is performed to be equal to 1 ≥ 8 h. In the wells of the upper row along the horizontal shaft the casing string and the cement stone lower half of the circumference is perforated, in the wells of the lower row - the upper, in the middle row wells the horizontal shafts are perforated along the whole area. All wells are subjected to the acid multistage hydraulic fracturing with the distance between the stages of not more than 50 m. Moreover, the location of each corresponding stage of the fracturing in the neighboring wells is performed in the staggered order. The rate and the volume of the pumped acid are determined according to the conditions, firstly, the formation of the carbonate dissolving structure, representing the branched hollows; secondly, the half-length of the fractures a = (0.5-1.0)·x and the half-height of the fractures c = (0.5-1.0)·h. After the multistage hydraulic fracturing, the wells of upper and lower rows - the production wells are completed and commissioned into production. At each reduction of the oil production rate of the production wells to the values lower than economically reasonable, such wells are stopped, and the middle row wells - injection wells are pumped by gas until the injection pressure increases at least in three times, and then the stopped production wells are allowed to work.

EFFECT: oil recovery of thick solid carbonate oil reservoirs increase.

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Description

The invention relates to the oil industry and may find application in the development of powerful dense carbonate oil reservoirs using multi-stage hydraulic fracturing (MHF).

A known method of hydraulic fracturing in a horizontal wellbore, including drilling a well, cementing a horizontal wellbore, perforating and forming cracks using hydraulic fracturing in a horizontal wellbore sequentially, starting from the end farthest from the axis of the vertical wellbore communicating the horizontal wellbore with the producing formation at the same time, during the next hydraulic fracturing, each perforated section through which hydraulic fracturing is performed is isolated from the rest of the column by packers. According to the invention, the drilling of a horizontal wellbore is carried out in the oil-saturated part of the reservoir with cementing the annular space between the casing and rock of the horizontal wellbore, and the perforation, azimuthally oriented by the intervals, is performed using a hydromechanical slotted perforator in one round-trip operation, after which the packers are lowered, cutting off each interval equal to the length of the formed gap from the rest of the column, and hydraulic fracturing in the horizon the entire part of the wellbore is performed sequentially, starting from the perforated section of the horizontal wellbore farthest from the axis of the vertical wellbore, and the hydromechanical slotted perforation is double-sided to form slots, which are 180 ° relative to each other in the vertical plane opposite each other, relative to the axis of the horizontal wellbore wells in one interval, or perform one-sided hydromechanical slotted perforation with a rotation of 180 ° in a vertical plane relative to the axis of the horizontal wellbore, alternately after each subsequent interval - in a checkerboard pattern equal to the length of the formed gap, or with a small thickness of the productive formation and in the presence of active bottom water, produce one-way hydromechanical slotted perforation in the direction of the formation roof. Additionally, waterproofing works are carried out at each of the intervals separately through the fracture gap (RF patent No. 2401942, class E21B 43/26, publ. 20.10 2010).

The disadvantage of this method is the uncontrolled development of a fracture in height, which during subsequent operation of the well leads to its rapid flooding. The development of oil deposits in this way is characterized by low oil recovery.

The closest in technical essence to the proposed method is a method of interval hydraulic fracturing of a carbonate formation in a horizontal wellbore with bottom water, comprising drilling a horizontal wellbore in a producing formation with cementing the annular space between the casing and rock, descent into the horizontal wellbore on a pipe string perforator and the implementation of perforations in the horizontal wellbore directed azimuthally upward, descent us tubing with a packer into the wellbore, the packer landing, injecting through the pipe string fracturing fluid and formation of cracks in hydraulic fracturing horizontal wellbore. In the known method, a horizontal wellbore in a producing formation is drilled parallel to the direction of maximum rock stress, then a perforator is lowered into a horizontal wellbore on a string of flexible pipes — GT — and holes are drilled in a horizontal wellbore in a row, a GT string with a perforator is removed from wells, dismantle the punch, then equip the bottom of the GT column with an inflatable packer, lower the GT column to the bottom by axial movement of the GT column from the mouth to the bottom at a distance of 50 m from with a speed of 0.5 m / min and simultaneous injection of a viscous gel with a density greater than the density of water, in a volume that ensures filling with the viscoelastic composition of the lower part of the horizontal borehole section by 2/3 of the horizontal bore diameter, an inflatable packer is planted, hydraulic fracturing is performed by injection of a thickened acid the composition, followed by filling with gelled liquid with a destructor of perforations and the upper part of the horizontal wellbore section by 1/3 of the horizontal wellbore diameter, unpack inflatable packer, then the hydraulic fracturing is carried out in the remaining part of the horizontal well; for this, the operations described above are repeated, starting from the axial displacement of the GT string from the mouth to the bottom to fill the treated interval with gelled liquid with a destructor; the gel liquefies upon contact with the formation fluids and releases the drained sections of the horizontal wellbore and is removed from the well (RF patent No. 2558058, cl. ЕВВ 43/27, publ. 07/27/2015 5 - prototype).

The known method allows you to control the direction of growth of the fracture, but does not take into account the location of neighboring wells, which can lead to a negative effect from hydraulic fracturing. Also, the energy state of the deposit is not taken into account when developing this method. Hydraulic fracturing leads to a sharp increase in flow rates, but reduces the ultimate oil recovery.

In the proposed invention solves the problem of increasing oil recovery powerful dense carbonate oil reservoirs.

The problem is solved in that in a method for developing dense carbonate reservoirs, including drilling horizontal wells, cementing an annular space between the casing and the reservoir in the horizontal wellbore, re-opening the deposit with the oriented direction of the perforations, conducting multi-stage hydraulic fracturing - hydraulic fracturing, the use of packers for separation horizontal trunks to sites, the selection of products from horizontal wells, according to the invention, choose oil-saturated to a collector with an average thickness of H ≥ 50 m and an average absolute permeability of not more than 2 mD, the collector is drilled by parallel horizontal wells, the horizontal trunks of which are directed perpendicular to the main maximum stress vector of the collector, horizontal trunks are placed vertically in three rows at an equal distance from each other h = (0.25-0.45) · N, horizontal trunks of the middle row are located in the plan between the horizontal trunks of the upper and lower rows at a distance x = (1-5) · h horizontally, the length of each horizon the borehole is equal to l ≥ 8 · h, the lower half of the circumference of the production string and cement stone is perforated along the horizontal well in the wells of the upper row, in the wells of the lower row - the upper half, in the wells of the middle row, horizontal bores are perforated over the entire area, in all wells acid multi-stage hydraulic fracturing with a distance between steps of no more than 50 m, moreover, in terms of the location of each multi-stage hydraulic fracturing in neighboring wells is staggered, the speed and volume of injected acid is determined from the conditions first, the formation of a carbonate dissolution structure, which is a branched cavity, and secondly, the half-length of cracks a = (0.5-1.0) · x and half-height of cracks c = (0.5-1.0) · h, after multi-stage hydraulic fracturing, the wells of the upper and lower rows — production wells — are mastered and put into production, with each decrease in the oil production rate of the production wells below an economically viable value, these wells are stopped, and the wells of the middle row — injection wells — pump gas until the pressure downloads will not grow at least three times after of stopped production wells allowed to work.

SUMMARY OF THE INVENTION

Dense here refers to heterogeneous low-permeable oil-saturated reservoirs with permeability varying from a few units to several hundred mcD (10 ^-6 μm ² ). Small interlayers or zones can also be several units of MD (10 ^-3 μm ² ). An example of such collectors is domanic deposits on the territory of the Republic of Tatarstan.

The oil recovery of powerful dense carbonate oil reservoirs is significantly affected by the efficiency of the development system being created. The main object of influence to increase oil recovery is the skeleton of the rock - increasing its permeability. For this, hydraulic fracturing (Fracturing) technologies have found widespread use; for carbonate rocks, acid hydraulic fracturing has been used. However, hydraulic fracturing in such reservoirs leads to a short-term effect due to a rather rapid drop in reservoir pressure. Moreover, due to the predominant hydrophobicity of the rock and its low permeability, it is rather difficult to pump water into it to maintain reservoir pressure. An increase in discharge pressure leads only to hydraulic fracturing. Thus, existing technical solutions do not fully allow the efficient development of these collectors. In the proposed invention solves the problem of increasing oil recovery powerful dense carbonate oil reservoirs. The problem is solved as follows.

In FIG. 1 is a schematic representation of a vertical section of a section of an oil reservoir in a face with staggered horizontal trunks. In FIG. 2 is a schematic plan view of an oil reservoir with horizontal wells. In FIG. 3 is a schematic representation of a section of an oil reservoir with a profile of horizontal wells. Designations: 1 - section of oil-saturated reservoir, 2 - horizontal production wells of the upper row, 3 - horizontal production wells of the lower row, 4 - horizontal injection wells of the middle row, 5 - perforation holes of production wells 2 of the upper row, 6 - perforation holes of production wells 3 of the upper rows, 7 - perforations of injection wells 4 of the middle row, 8 - pipe strings, 9 - filters, 10 - packers in horizontal shafts between the stages of hydraulic fracturing, 11 - packers at the junction of the column pipes 8 with a filter 9, H is the average thickness of the reservoir, h is the distance between the horizontal wells of adjacent wells in the vertical plane, x is the distance between the horizontal wells of neighboring wells in the horizontal plane, l is the length of the horizontal wells 2-4, b is the distance between by stages of hydraulic fracturing, w ^d - hydraulic fracturing in production wells 2, 3, w ⁿ - hydraulic fracturing in injection wells 4, c - half-height of hydraulic fracturing, a - half-length of hydraulic fracturing.

The method is implemented as follows.

Section 1 of a dense carbonate oil-saturated reservoir, the average absolute permeability of which is not more than 2 mD, and the average thickness H ≥ 50 m, are drilled by horizontal producing wells 2, 3 and horizontal injection wells 4 (Fig. 1, 2, 3). Horizontal wellbores 2, 3, and 4 are placed parallel to each other in a vertical plane, and are arranged vertically in three rows at an equal distance from each other h = (0.25-0.45) · N. Horizontal trunks of the middle row (injection wells 4) are placed in plan between the horizontal trunks of the upper and lower rows (production wells 2 and 3, respectively) at a distance x = (1-5) · h. Thus, the horizontal trunks are staggered when viewed in front (Fig. 1). Horizontal trunks are placed perpendicular to the vector of the main maximum stress σ _{max of the} reservoir, i.e. chosen for reasons of maximum coverage of subsequent multistage fracturing. The length of each horizontal wellbore 2-4 is equal to l ≥ 8 · h.

Next, wells 2, 3 and 4 are cased, the annulus between the casing and the reservoir is cemented. Horizontal trunks are re-opened with the oriented direction of the perforations. In the wells 2 of the upper row along the horizontal well, the lower half of the circumference of the production string and cement stone is perforated, obtaining perforations 5, in the wells 3 of the lower row - the upper, receiving perforations 6, which eliminates the development of cracks above and below the reservoir thickness. In wells 4 of the middle row, horizontal trunks are perforated over the entire area, receiving perforations 7. For conducting these operations, perforators are used that are lowered into horizontal trunks on strings of flexible pipes.

In all wells 2-4, acid multistage fracturing is carried out according to any of the known technologies from the “toe” of the horizontal trunk to its “heel”. The distance b between the steps is set to not more than 50 m. Moreover, in terms of the location of each stage of multi-stage hydraulic fracturing in neighboring wells, they are staggered, i.e. the feet of the multistage hydraulic fracturing of production and injection wells 2-4 and 3-4 adjacent in terms of planes do not coincide, but they coincide in neighboring production 2 and 3, as well as in neighboring injection 4 (Fig. 2). The speed and volume of injected acid is determined from the conditions:

- the formation of the structure of the dissolution of carbonates, which is a branched cavity,

- half-length of cracks a = (0.5-1.0) · x,

- half-height of cracks with = (0.5-1.0) · h.

As a result of acid multistage fracturing, a system of branched fractures is obtained for producing wells — w ^d _n , for injection wells — w ⁿ _n , where n is the number of the multistage fracturing stage.

According to the Decree of the Government of the Russian Federation No. 700-R, with permeability values of 2 mD or less, reservoirs are classified as hard to recover reserves and they are subject to reduced mineral extraction tax (MET), which allows for horizontal drilling with multi-stage fracturing , in terms of economics. According to calculations, with a collector thickness H less than 50 m, the proposed QGD method significantly reduces oil recovery due to a decrease in reservoir coverage. The vertical distance h between the horizontal shafts is determined from the conditions of maximum coverage over the thickness by multi-fracturing fractures, taking into account the subsequent effective development. According to calculations, at a value of h <0.25 · N, sections of the formation above the injection well and below the production are not affected, and at h> 0.45 · N, there is a great risk of opening zones of the non-reservoir.

The distance x between the adjacent horizontal trunks of the upper and lower rows in the plan is determined from the conditions of maximum coverage of the reservoir over the area with multi-fracturing fractures, taking into account the subsequent effective development. According to the calculations, for x <1.0 · h, difficulties arise due to the fact that the length of the cracks of the subsequent multi-fracturing is less than the height, which significantly reduces the coverage over the area, and for x> 5.0 · h there is a danger of joining adjacent multi-fracture fractures production and injection wells due to the need to create them quite long in length. All this leads to a decrease in oil recovery.

Similarly, in order to achieve greater coverage, the lengths l of horizontal trunks are determined. Dense reservoirs are characterized by high zonal heterogeneity. According to calculations, for l <8 · h, due to the opening of a significant number of non-reservoir zones, the effective length of the well is greatly reduced, which leads to low coverage and low oil recovery.

According to studies, for reservoirs with a permeability of less than 2 mD, with a distance between hydraulic fracturing steps of more than 50 m, formation coverage is significantly reduced, which also reduces oil recovery. The fracture structure of acid multi-fracturing, which is a branched cavity, is most suitable for low-permeability carbonate reservoirs and is characterized by the maximum coverage of the reservoir.

Due to the fact that the location of each respective hydraulic fracturing stage in the production and injection wells adjacent in terms of planes does not coincide in the structural plan, it is estimated that the half-length and fractures of the hydraulic fracturing of each stage should not exceed the horizontal distance x between adjacent horizontal shafts, since at a> 1.0 · x, there is a danger of connecting fractures of the multi-fracturing of adjacent wells. When a <0.5 · x, coverage over area decreases, which leads to low oil recovery. According to the calculations, the optimal half-height from the fractures of the multi-stage fracturing steps was selected that should cover the vertical distance h between the wells, but not be greater than it, because at c> 1.0 · h, there is a danger of fractures leaving the formation, which can lead to watering the well. Moreover, if c <0.5 · h, then the thickness coverage decreases, which leads to low oil recovery.

After the multistage hydraulic fracturing, columns of pipes 8 with filters 9 in horizontal shafts and packers 10 installed on the filters 9 are lowered into wells 2-4 to seal the space between the production string and filter 9. Moreover, the packers 10 are installed at the points of horizontal trunks between the stages of the multistage fracturing. At the junction of the pipe string 8 with the filter 9, a packer 11 is also installed to seal the annulus. Thus, the horizontal trunks are divided into sections with the ability to disable certain sections of the barrel packers 10.

Next, production wells 2 and 3 are washed, mastered and put into production. With each decrease in the oil production rate of one of the producing wells 2 and / or 3 below an economically viable value, the middle row injects gas (CO ₂ , N ₂ or hydrocarbon) into the corresponding injection wells 4 (simultaneously into two injection wells located on both sides of the production well) gas). At the same time, these production wells are stopped. The injection is carried out until the injection pressure rises at least three times, because at a lower value, according to studies, the restoration of reservoir pressure in dense reservoirs is not enough. After that, stopped production wells are put into operation. According to studies, the use of gas is most effective for predominantly hydrophobic reservoirs, in addition, the gas is much more mobile than water, which allows it to penetrate deep into the reservoir, restoring the reservoir pressure and partially dissolving in oil.

Development is carried out until the full economically viable development of a dense carbonate reservoir section.

The result of the implementation of this method is to increase oil recovery powerful dense carbonate oil reservoirs.

Examples of specific performance of the method.

Example 1. Section 1 of a dense carbonate oil-saturated reservoir, the average absolute permeability of which is 2 mD and the average thickness H = 50 m, are drilled with four horizontal producing wells 2, 3 and three horizontal injection wells 4 (Fig. 1, 2, 3). Horizontal boreholes 2, 3 and 4 are placed parallel to each other in a vertical plane, and vertically arranged in three rows at an equal distance from each other h = 0.45 · N = 0.45 · 50 = 22.5 m. Horizontal boreholes the middle row (injection wells 4) is placed in plan between the horizontal trunks of the upper and lower rows (respectively, production wells 2 and 3) at a distance of x = 5 · h = 5 · 22.5 = 112.5 m. Horizontal trunks are placed perpendicular to the main vector maximum stress σ _{max of the} collector. The length of each horizontal wellbore 2-4 is equal to l = 8 · h = 8 · 22.5 = 180 m.

Next, wells 2, 3 and 4 are cased, the annulus between the casing and the reservoir is cemented. Horizontal trunks are re-opened with the oriented direction of the perforations. In the wells 2 of the upper row, the lower half of the circumference of the production string and cement stone is perforated along the horizontal well, receiving perforations 5, in the wells 3 of the lower row, the upper one, receiving perforations 6, in the wells 4 of the middle row, horizontal shafts are perforated over the entire area, obtaining perforations 7. For carrying out these operations, perforators are used that are lowered into horizontal trunks on the columns of flexible pipes. The perforating system PK114KL ORION is used as a perforator (CJSC Vzryvgeoservis, Republic of Bashkortostan, Neftekamsk, 19 Magistralnaya St.).

Acid multi-stage hydraulic fracturing is designed in all wells 2-4 according to the technology with twin packers launched on flexible pipes, with breaks from the “toe” of the horizontal trunk to its “heel”. The distance b between the hydraulic fracturing steps is determined by calculating the optimal coverage on the hydrodynamic model, b = 45 m. Moreover, in terms of location, each hydraulic fracturing step in neighboring wells is performed in a checkerboard pattern, i.e. the feet of the multistage hydraulic fracturing of production and injection wells 2-4 and 3-4 adjacent in terms of planes do not coincide, but they coincide in neighboring production 2 and 3, as well as in neighboring injection 4 (Fig. 2). Thus, four stages of multi-stage fracturing in each well 2-4 are obtained.

Laboratory studies determine the optimal pressure (speed) of acid injection for the formation of branched cavities. As the acid using 22% hydrochloric acid. Modeling determines the optimal half-length a = 0.5 · x = 0.5 · 112.5 ≈ 56 m and half-height of cracks with = 1.0 · h = 1.0 · 22.5 = 22.5 m.

Next, acid multistage fracturing is carried out, as a result of which a branched crack system is obtained for producing wells — w ^d _n , for injection wells — w ⁿ _n , where n is the number of the multistage fracturing stage.

After the multistage hydraulic fracturing, columns of pipes 8 with filters 9 in horizontal shafts and packers 10 installed on the filters 9 are lowered into wells 2-4 to seal the space between the production string and filter 9. Moreover, the packers 10 are installed at the points of horizontal trunks between the stages of the multistage fracturing. At the junction of the pipe string 8 with the filter 9, a mechanical packer 11 is also installed to seal the annulus. Thus, the horizontal trunks are divided into sections with the ability to disable certain sections of the barrel packers 10.

Next, production wells 2 and 3 are washed, mastered and put into production. If after 10 months the oil production rate of one of the producing wells decreases 3 to 0.5 t / day, i.e. below an economically viable value, this production well is stopped in the corresponding injection wells 4 (at the same time into two injection wells located on both sides of the production well 3) mid-range carbon dioxide is pumped with CO ₂ flow rate of 400 m ³ / day. The injection is carried out until the injection pressure increases three times. Then the injection of CO _{2 is} stopped, and the production well 3 is put into production.

The re-injection of CO _{2 is} repeated 10 more times during the entire period of development of section 1 of the dense carbonate reservoir at each of the production wells 2 and 3 with a decrease in oil production to 0.5 t / day.

Development is carried out until the full economically viable development of section 1 of the dense carbonate reservoir.

Example 2. Perform as example 1. The average thickness of the reservoir H = 200 m, horizontal boreholes 2 and 3 are placed at a vertical distance h = 0.25 · N = 0.25 · 200 = 50 m, horizontal x = 1, 0 · Н = 1,0 · 200 = 200 m. The length of each horizontal wellbore 2-4 is equal to l = 10 · h = 10 · 50 = 500 m. The distance between the hydraulic fracturing steps is b = 50 m. Thus, 10 stages of multi-stage fracturing at each well. By modeling, the optimal half-length a = 1.0 · x = 1.0 · 200 = 200 m and half-height of the cracks with = 0.5 · h = 0.5 · 50 = 25 m are determined. Associated petroleum gas from overlying traditional gas is used collectors.

As a result of the development of section 1, which was limited by a decrease in the oil production rate of producing wells 2 and 3 to less than 0.5 t / day, while it was impossible to increase it by gas injection into injection wells 2, 289.7 thousand tons of oil were produced, the oil recovery factor (CIN) was 0.259 units According to the prototype, ceteris paribus, 165.5 thousand tons of oil were produced, oil recovery factor amounted to 0.148 units. The increase in recovery factor by the proposed method is 0.111 units

The proposed method allows to increase the coverage and oil recovery coefficient of powerful dense carbonate oil reservoirs through the use of acid multistage fracturing and subsequent periodic gas injection.

The application of the proposed method will solve the problem of increasing oil recovery powerful dense carbonate oil reservoirs.

Claims (1)

A method of developing dense carbonate reservoirs, including drilling horizontal wells, cementing an annular space between the casing and the reservoir in the horizontal borehole, re-opening the reservoir with the oriented direction of the perforations, conducting multi-stage hydraulic fracturing — hydraulic fracturing, using packers to divide horizontal trunks into sections, selecting products from horizontal wells, characterized in that an oil-saturated reservoir with an average thickness is selected H ≥ 50 m and average absolute permeability of not more than 2 mD, the collector is drilled by parallel horizontal wells, the horizontal shafts of which are directed perpendicular to the main maximum stress vector of the collector, horizontal shafts are placed vertically in three rows at an equal distance from each other h = (0.25 -0.45) · N, horizontal trunks of the middle row are arranged horizontally between the horizontal trunks of the upper and lower rows at a distance x = (1-5) · h horizontally, the length of each horizontal trunk is performed by l ≥ 8 · h, in the wells of the upper row, the lower half of the circumference of the production string and cement stone is perforated along the horizontal wellbore, in the wells of the lower row, the upper half, in the wells of the middle row, horizontal bores are perforated over the entire area, acid fracturing is performed in all wells with the distance between the steps is not more than 50 m, and in terms of the location of each stage of multi-stage hydraulic fracturing in neighboring wells is performed in a checkerboard pattern, the speed and volume of injected acid is determined from the conditions, firstly, the formation of the dissolution of carbonates, which is a branched cavity, and secondly, the half-length of the cracks a = (0.5-1.0) · x and half-height of the cracks c = (0.5-1.0) · h, after the multi-fracturing of the upper well and the lower rows — production wells — are mastered and put into production, with each decrease in the oil production rate of production wells below an economically viable value, these wells are stopped, and middle wells — injection wells — pump gas until the injection pressure rises at least three times, after which they stopped mining e wells allowed to work.

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