RU2513216C1 - Oil deposit development method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: according to the method direction of reservoir-scale fractures is determined, development elements are formed by drilling of horizontal injection wells as per square grid pattern with parallel placement of boreholes and producing downhole splitters with rounded bottomhole ending which are placed around the borehole of each horizontal well. Pumping of working agent is done through injection wells and recovery of products through multi-hole producing wells. When the latter are water flooded water-flooding intervals are identified and isolated. According to the invention a downhole splitter is made in the semi-ellipse shape which major axis is directed at the angle of 30-60° towards direction of fractures while ratio of the minor semi-axis of the ellipse b/2 towards major semi-axis a/2 is equal to 0.1-0.8. At that boreholes of a downhole splitter have length of (0.6-0.8)·a each in productive part of the stratum and water-swellable packers are installed at them at each 50-250m. The boreholes are placed near the roof of the productive stratum at distance of 0.5 m at least and less than 2 m from the roof. The horizontal injection well is placed in plane along the ellipse major axis of a producing downhole splitter with length of (0,3-0,6)·a of its horizontal part in the productive stratum, at water-oil contact or the bottom of oil-filled formation in profile at distance of 0.2 m at least and less than 1m from it.

EFFECT: improving coverage of the productive stratum by development and increasing its production rate.

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Description

The invention relates to the oil industry and may find application in the development of oil deposits with a reservoir having a natural fracture.

A known method of developing deposits of a multilayer oil field with water-oil zones and / or massive type, including measurements of oil, water and water injection to clarify the current conditions of development and modeling of the development of the reservoir, determining the minimum distance from the open interval to the oil-water contact at which it does not occur premature flooding of well products. In the known method, it is proposed to drill branched horizontal and / or subhorizontal wells, the main horizontal and / or subhorizontal well being located above the oil-water contact at a minimum distance, ensuring an anhydrous period of operation of the wells, and horizontal and / or subhorizontal and / or vertical branches are drilled along an ascending profile with the same azimuth as that of the main horizontal and / or subhorizontal trunk, and / or with a departure from it towards the roof of the producing formation a or interlayers (RF patent No. 2282022, class E21B 43/20, publ. 08/20/2006).

The disadvantage of this method is the low oil recovery due to insufficient coverage of the reservoir by displacement over the area and high capital costs for the construction of wells in the element.

Closest to the proposed invention in technical essence is a method of developing an oil reservoir, comprising drilling a reservoir with horizontal and vertical wells on a square grid and forming elements by drilling in the center of an element of a vertical and / or directionally directed injection well, drilling multilateral wells producing horizontal wells on the sides of the elements, injecting working reagent through injection wells cyclically and product selection through production wells, production measurements n oil, water and injected fluid, conducting hydrodynamic studies and maintaining reservoir pressure in the selection zone at the initial level. In the known method, before drilling the deposits, areas with total oil-saturated thicknesses of more than 13 m in carbonate reservoirs and / or areas with effective oil-saturated thicknesses of at least 3 m in the oil zone and at least 5 m in the oil-water zone in terrigenous reservoirs are drilled, vertical and / or a directionally directed injection well in the center of each element, the sides of each element are closed with multilateral wells with a horizontal end in the form of semicircles, each of which covers half of the element, with about a bottom ascending branch in the middle of the semicircle, directed to the corner of the element for producing oil reserves in the underfloor part of the reservoir, replacing two horizontal or three vertical and / or directional wells in the element along the sides and corners of the elements, the displacing working reagent is injected through the injection well into the lower part of the productive interval cyclically, determine the optimal injection period at which the maximum pressure recovery in the selection zone and the expression of oil from the matrix (RF Patent No. 2439299, cl. E21B 43/20, publ. 01/10/2012 - prototype).

The known method allows to achieve enhanced oil recovery, however, 1/4 of the reservoir remains unreached by displacement over the area. Also, in fractured reservoirs, water breakthrough occurs, which reduces final oil recovery.

The proposed invention solves the problem of increasing the coverage of the formation by exposure and, accordingly, increasing the oil recovery of the productive formation.

The problem is solved in that in the method of developing an oil reservoir, including determining the direction of fracture of the reservoir, forming elements by drilling horizontal injection wells along a square grid with parallel arrangement of shafts and multilateral wells with rounded ends of shafts located around the trunk of each horizontal well, pumping the working agent through injection wells and product sampling through production wells; when watering the latter, determination of inter It is new that a multilateral well is made in the form of a semi-ellipse, the major axis of which is directed at an angle of 30-60 ° to the direction of fracture with respect to the minor semiaxis b / 2 to the major semiaxis a / 2 of the ellipse 0. 1-0.8, while the trunks of a multilateral well production well are performed in the productive part of the reservoir (0.6-0.8) long · and each, on which water swellable packers are installed every 50-250 m, and the trunks themselves are located at the roof of the productive layer at a distance of not less than 0.5 m and not more less than 2 m from it, the horizontal injection well is placed in the plan along the major axis a of the ellipse of the multilateral well, the length is (0.3-0.6) · and the horizontal part in the reservoir and placed at the water-oil contact or the sole of a purely oil-saturated formation in the profile at a distance of not less than 0.2 m and not more than 1 m from it. If the section of the productive formation is represented by a purely oil zone, then horizontal wells are drilled for oil after drilling until the reservoir pressure drops to 0.7 from the initial one, after which multilateral wells are drilled, and horizontal ones are transferred for injection of the working agent.

SUMMARY OF THE INVENTION

The oil recovery of an oil reservoir is significantly affected by the coverage of the reservoir by impact. Existing technical solutions do not fully allow the selection of oil from the reservoir. The proposed invention solves the problem of increasing oil recovery deposits. The problem is solved as follows.

Figure 1-3 shows, respectively, the layout of the wells in the reservoir with the allocation of development elements, the layout of the element in plan and the profile of the producing and horizontal wells. Accepted designations: 1-4 - horizontal injection wells capable of oil development, 5-8 - multilateral wells with trunks in the form of a semi-ellipse, h - oil saturated thickness, S - direction of fracture of the reservoir, a / 2 - semi-major axis, b / 2 - minor axis of the ellipse of the projection of the producing well in the plan, c - minimum distance from the shafts of the multilateral well production to the horizontal injection well, L - element dimensions or the distance between the entry points into the formation of the nearest injection horizons x, the distance from the multilateral well borehole in the lower part to the oil-water contact in the water-oil zone or the sole of the purely oil zone of the reservoir, y is the distance from the horizontal well bore in the upper part to the top of the reservoir, T is water swellable packers.

The method is implemented as follows.

On the site of a massive reservoir, the productive strata of which are represented by pore-fissure carbonate deposits of the Tournaisian stage, 3D seismic exploration is carried out, the direction of the cracks S is determined (Fig. 1). Geological and hydrodynamic modeling of the site is carried out taking into account the fracturing, the optimal parameters of the wells are calculated by the proposed method.

Then drill a rare square grid of horizontal injection wells 1-4 (figure 1) with a distance L between the points of entry of the shafts into the reservoir. Moreover, the trunks of horizontal wells are directed at an angle α = 30-60 ° to the directions of the cracks S (Fig. 2) and carried out at the water-oil contact or the sole of a purely oil-saturated formation at a distance x of not less than 0.2 m and not more than 1 m from it (figure 3). The values of x = 0.2-1 m are determined based on the accuracy of the well layout, the most effective displacement and the maximum well operating time until complete flooding. Horizontal wells are made in length (0.3-0.6) · and the horizontal part in the reservoir, determined by hydrodynamic modeling from the condition of maintaining reservoir pressure at the initial level for different operating modes of production wells and different lengths of their perforated sections. The angle α = 30-60 ° was also determined by calculation as the most effective from the point of view of moving the displacement front and longer working hours of production wells to complete flooding.

Around each horizontal injection well, multi-hole production wells 5–8 are drilled (Fig. 1), consisting of two shafts, a length in the productive part of the formation of (0.6-0.8) · and each, in the form of a semi-ellipse, determined by calculation as most effective in terms of coverage of elements. In these wells, the major axis a is directed at an angle α = 30-60 ° for the above reasons to the directions of the cracks S (Fig. 2) and coincides with the direction of the horizontal wells of injection wells 1-4, respectively, while the ratio of the minor axis b / 2 of the ellipse to its semi-major axis a / 2 is equal to b / a = 0.1-0.8, which is explained by different options for the configuration of wells depending on the configuration of the deposits and the directions of fracturing. The minimum distance from the trunks of a multilateral well production well to the horizontal injection is C. At the same time, water swellable packers 7 are installed on the trunks of the multilateral well production every 50-250 m (depending on the length of the horizontal trunks of the multilateral well production well), and the trunks themselves located at the top of the reservoir at a distance of not less than 0.5 m and not more than 2 m from it (figure 3). The values of x = 0.5-2 m are determined based on the maximum oil withdrawal and the maximum well operating time until complete watering. Specific parameter values are determined in advance by the results of hydrodynamic modeling.

Thus, the elements of the development system with the dimensions L × L are formed (Fig. 1). Oil is produced from producing wells 5-8 and the working agent is injected into injection wells 1-4.

In the process of operating a multilateral well, a water breakthrough occurs, primarily along vertical cracks from the aquifer of the reservoir into the lower part of horizontal shafts. When water cut more than 98% of the well is stopped, geophysical surveys are carried out, the intervals of well watering are determined. Then, the waterlogged intervals are cut off with water swellable packers T and the wells are put into operation again.

If the section of the reservoir is represented by a purely oil zone, then horizontal wells 1-4 are drilled after drilling for oil until the reservoir pressure drops to 0.7 from the initial one, after which multilateral wells are drilled 5-8 (Fig. 1), and horizontal 1- 4 transferred to the injection of water. The calculations showed that when the reservoir pressure decreases by more than 0.7 from the initial in the pore-fracture reservoir with the subsequent organization of the water flooding system, the productivity of production wells is lower.

The result of the implementation of this method is to increase the degree of oil recovery.

Examples of specific performance of the method.

Example 1. On the site of a massive reservoir, the productive strata of which are represented by pore-fissure carbonate deposits of the Tournaisian stage, 3D seismic exploration is carried out, and the direction of the cracks is determined. The predominant direction of fracturing S according to the research results was found north-west (figure 1). On the structural map allocate a plot with total oil-saturated thickness h = 6 m (Fig.3). Geological and hydrodynamic modeling of the site is carried out taking into account the fracturing, the optimal parameters of the wells are calculated by the proposed method. The values of the axes of the ellipse for an element of size 1200 × 1200 m were obtained a = 1000 m, b = 500 m (figure 2).

Then drill a rare square grid of horizontal injection wells 1-4 (figure 1) with a distance between the points of entry of the shafts into the reservoir L = 1200 m. Moreover, the trunks of horizontal wells are directed at an angle α = 45 ° to the directions of the cracks S (figure 2) and carried out at the water-oil contact at a distance x = 0.5 m from him (figure 3). Horizontal wells perform a length of 0.4 · a = 0.4 · 1000 = 400 m of the horizontal part in the reservoir, determined by hydrodynamic modeling.

Around each horizontal injection well, multi-hole production wells 5-8 are drilled (Fig. 1), consisting of two shafts, each in the productive part of the formation 0.75 · a = 0.75 · 1000 = 750 m each, in the form of a semi-ellipse, in of which the major axis a is directed at an angle α = 45 ° to the directions of the cracks S (Fig. 2) and coincides with the direction of the horizontal wells of injection wells 1-4, respectively, while the ratio of the minor axis b / 2 of the ellipse to its major axis a / 2 is b / a = 0.5. The minimum distance from the trunks of the multilateral well to the horizontal injection is C = 250 m. At the same time, water swellable packers T (for example, TAM) are installed on the trunks of the multilateral well (for example, TAM) (Fig. 2), and the trunks themselves are located at the formation at a distance y = 1 m from it (figure 3). These parameters are also determined in advance by the results of hydrodynamic modeling.

Thus, the elements of the development system with dimensions of 1200 × 1200 m are formed (Fig. 1). Oil is produced from producing wells 5-8 and formation water is injected into injection wells 1-4.

In the process of operating a multilateral well, a water breakthrough occurs, primarily along vertical cracks from the aquifer of the reservoir into the lower part of horizontal shafts. When water cut more than 98% of the well is stopped, geophysical surveys are carried out, the intervals of well watering are determined. Then, the waterlogged intervals are cut off with water swellable packers T and the wells are put into operation again.

Example 2. Perform, as example 1. A multilateral well is made in the form of a semi-ellipse, the major axis a = 1500 m of which is directed at an angle α = 30 ° to the direction of natural fracturing with the ratio of the minor axis b / 2 to the major axis a / 2 of the ellipse 0, one. The trunks of a multilateral well production well are 0.6 · a = 0.6 · 1500 = 900 m long each in the productive part of the formation, on which water swellable packers are installed every 250 m, and the trunks themselves are located at the roof of the productive formation at a distance of 2 m from it . The horizontal injection well is placed in the plan along the major axis a of the ellipse of the multilateral well, the length is 0.3 · a = 0.3 · 1500 = 450 m of the horizontal part in the reservoir and placed at the water-oil contact at a distance of 1 m from it.

Example 3. Perform, as example 1. A multilateral well is made in the form of a semi-ellipse, the major axis a = 400 m of which is directed at an angle α = 60 ° to the direction of natural fracturing with the ratio of the minor axis b / 2 to the major axis a / 2 of the ellipse 0, 8. The trunks of a multilateral well production well are 0.8 · a = 0.8 · 400 = 320 m each in length in the productive part of the formation, on which water swellable packers are installed every 50 m, and the trunks themselves are placed at the top of the productive formation at a distance of 0.5 m from her. The horizontal injection well is placed in the plan along the major axis a of the ellipse of the multilateral well, the length is 0.6 · a = 0.6 · 1500 = 240 m of the horizontal part in the reservoir and placed at the water-oil contact at a distance of 0.2 m from him.

Example 4. The area of the reservoir is represented by a pure oil zone. Perform as examples 1-3. After drilling, horizontal wells 1-4 are drilled for oil until the reservoir pressure drops to 0.7 from the initial one, after which multi-hole production wells 5-8 are drilled (Fig. 1), and horizontal 1-4 are transferred for water injection.

As a result, according to examples 1-4 with 1 element, consisting of 1 horizontal injection and 1 production multilateral well in the form of a semi-ellipse, during the development period, which was limited to 98% by watering the production well or achieving a minimum profitable oil production rate of 0.5 t / day, 149.1 thousand tons of oil were produced, the oil recovery ratio was 0.184. According to the prototype, ceteris paribus, 97.3 thousand tons of oil was produced, oil recovery factor 0.120. The increase in oil recovery by the proposed method amounted to 0.064.

Thus, the proposed method provides an increase in oil recovery.

The application of the proposed method will solve the problem of increasing the coverage of the formation by exposure and, accordingly, increasing oil recovery of the productive formation.

Claims (2)

1. A method of developing an oil reservoir, including determining the direction of fracture of the reservoir, forming elements by drilling horizontal injection wells along a square grid with parallel arrangement of shafts and multilateral wells with rounded shaft ends located around the bore of each horizontal well, pumping a working agent through injection wells and selecting production through production wells, when watering the latter, determination of the intervals of watering and isolation w waterlogged intervals, characterized in that the multilateral well is made in the form of a semi-ellipse, the major axis a of which is directed at an angle of 30-60 ° to the direction of fracture with a ratio of the minor axis b / 2 to the major axis a / 2 of the ellipse 0.1-0.8 , while the trunks of a multilateral well production well are performed in the productive part of the formation (0.6-0.8) · a each long, on which water swellable packers are installed every 50-250 m, and the trunks themselves are placed at the roof of the productive formation at a distance of at least 0.5 m and not more than 2 m from it, horizontally The injection well is placed in the plan along the major axis a of the ellipse of the multilateral well, performed (0.3-0.6) · in the horizontal part in the reservoir and placed at the water-oil contact or the sole of a purely oil-saturated formation in the profile at a distance of less than 0.2 m and not more than 1 m from it. 2. The method according to claim 1, characterized in that the horizontal wells are drilled after drilling for oil until the reservoir pressure drops to 0.7 from the initial one, after which multilateral wells are drilled, and the horizontal ones are transferred for injection of the working agent.

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