RU2597305C1 - Method for development of oil deposit in carbonate reservoirs - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: proposed method relates to oil industry, in particular to development of oil deposit in carbonate reservoirs without water-oil zones. Method for development of oil deposit in carbonate reservoirs, which involves construction of horizontal production and injection wells parallel to each other, arrangement of horizontal producing wells in lower part of productive formation, arrangement of injection horizontal wells in roof part of productive formation between production horizontal wells in horizontal projection, pumping displacement agent through injection wells and product extraction through production wells, before construction of wells, selecting section of deposit, which provides hydrodynamic connection between adjacent horizontal injection and production wells on entire thickness, during construction, selecting distance between adjacent horizontal shafts of producers and injectors directly proportional to permeability of rocks of section, wherein displacement agent is water with mineral content of not more than 4 g/l, which is pumped into productive formation with pressure higher than initial reservoir pressure of not more than 7 % of initial reservoir pressure, water pumping is stopped after reduction of intake capacity of horizontal injection wells to level, where low-mineralised water pumped into formation volume is higher than that of extracted formation fluid, then displacement agent used is 0.03-0.5 % aqueous solution of cellulose ester and 0.01-0.5 % aqueous solution of surfactant increasing in volume ratio of 1:1 to 1:5, and total volume of 30-50 % of initial oil content in formation, at pressure of pumping said aqueous solutions, 10-15 % higher than initial formation pressure, to recovery of initial reservoir pressure, after which cycles of injecting water with mineral content of not more than 4 g/l and aqueous solutions of polymers and surfactants is repeated.

EFFECT: high efficiency of processing.

1 cl, 1 ex, 2 dwg

Description

The proposed method relates to the oil industry, in particular to the field of development of oil deposits in carbonate reservoirs without water-oil zones.

A known method of implementing vertical flooding of an oil reservoir (RF patent No. 2342523, EV 43/20, publ. 12/27/2008, bull. No. 36), including drilling production and injection wells and the implementation of the displacement of oil by pumped water. Create an experimental site on the basis of two horizontal wells or horizontal lateral shafts. To do this, drill a producing horizontal well or producing a horizontal lateral well from an existing well, and a horizontal or horizontal lateral horizontal well is placed near the formation roof, and a horizontal horizontal well is located near the bottom of the formation; the trunks are parallel to each other and parallel to the long axis of the structure, their horizontal projections are located at a distance of no more than 150 m. In one of the trunks they carry out an exciting effect by pumping water or taking oil, in the other they observe the change in pressure over time. If there is a reaction to the stimulating effect, the permeability along the vertical coordinate is determined from the pressure change and experimental work is carried out by pumping water into the injection well and taking oil from the producing well. At the same time, the change in time of oil production and water cut in the producing well, water flow in the injection well, bottomhole and formation pressure in both shafts is observed. According to the results of experimental work, the vertical waterflooding process is designed and implemented on the basis of a single-row system for placing producing horizontal shafts near the top of the formation and injection shafts near the bottom of the formation with a displacement in terms of the bottom faces of producing and injection wells similar to placing vertical wells with a single-line system.

The disadvantage of this method is that it is not provided for the injection of aqueous solutions of polymers and surface-active substances (surfactants) into the formation, contributing to the uniform displacement of the formation fluid to the perforation intervals of the producing wells. The method does not use the injection of low-mineralized water at low pressures, as a result of which the formation is not uniformly covered by water flooding and the planned levels of oil recovery are not achieved.

The closest in technical essence is a method of producing highly viscous oil during thermal exposure of the formation, including drilling and placing horizontal wells in the reservoir, injecting the working agent through the upper horizontal wells, and oil is taken from the lower horizontal well (US patent US 5273111, Е21В 43 / 24, published on December 28, 1993). Each producing horizontal well is positioned vertically below and horizontally between two corresponding upper horizontal injection wells, and they are parallel to each other. The upper horizontal wells are located near the upper boundary of the reservoir, and the lower production wells are near the lower boundary of the reservoir. The vertical distance between them should be sufficient to maintain pressure differences in the fluid flow.

The disadvantage of this method is that mainly steam is used as the displacing agent, for the heating of which large energy inputs are required. Steam injection is carried out at high pressures, which leads to higher cost of work. When drilling a site, preliminary studies in wells are not carried out, allowing to determine the presence of a hydrodynamic connection between them, which reduces the effectiveness of the method. The method does not use the injection of low-mineralized water at low pressures, as a result of which uniform coverage of the formation by water flooding is not ensured. The lack of injection of polymers and surfactants to even out the front of the injected water and to avoid the breakthrough of the injected water into the reservoir prevents the increase in oil production rates.

The technical objectives of the proposed method are to increase oil recovery and the development of oil deposits in carbonate reservoirs by conducting preliminary studies in vertical and directional wells drilled at the horizontal well location, allowing to determine the presence of hydrodynamic connection between them, ensuring uniform coverage of the waterflood at low pressures injection of weakly mineralized water and uniform displacement of reservoir fluid in the reservoir to shafts perforation wells extractive solutions of polymers and surfactants.

The technical result is achieved by the development method, including the construction of horizontal production and injection wells parallel to each other, the placement of horizontal production wells in the lower part of the reservoir, the placement of horizontal horizontal wells in the roof of the reservoir between the horizontal horizontal wells, injection of the displacing agent through the injection and selection of products through production wells.

What is new is that before the construction of the wells, a section of the reservoir is chosen that provides hydrodynamic connection between the nearby horizontal injection and production wells throughout the thickness, during construction, the distance between the nearby horizontal trunks of the production and injection wells is directly proportional to the rock permeability of the section, while as a displacing agent choose water with a salinity of not more than 4 g / l, which is pumped into the reservoir with a pressure higher than the start the reservoir pressure is not more than 7% of the initial reservoir pressure, water injection is stopped after the injection rate of horizontal injection wells is reduced to a level at which the volume of low-mineralized water injected into the reservoir exceeds the volume of the produced reservoir fluid, then 0.03-0 is used as the displacing agent 5% aqueous solution of cellulose ether and 0.01-0.5% aqueous solution of a surfactant - surfactant with their volume ratio increasing from 1: 1 to 1: 5 and the total volume of 30-50% from quantities initial content of oil in the formation, at a pressure of injection of said aqueous solutions, exceeding 10-15% initial reservoir pressure, to restore the initial reservoir pressure, after which water injection cycles with mineralization not more than 4 g / l and water solutions of polymers and surfactants is repeated.

In FIG. 1 shows a diagram of the implementation of the proposed method for the development of oil deposits in carbonate reservoirs (top view) on the site deposits. In FIG. 2 shows a section AA in FIG. one.

The inventive method is carried out in the following sequence.

Deposit 1 (Fig. 1) is drilled with wells on a rare grid. Clarify the geological structure of reservoir 1, build structural maps, maps of total and effective oil-saturated thicknesses, conduct core laboratory tests, determine the viscosity of oil, the permeability of the reservoir, the distribution of oil-saturated thicknesses over the area of the deposit (not shown in the figure). Determine the reservoir properties of rocks, conduct hydrodynamic studies with the obligatory determination of reservoir pressure.

Before the construction of horizontal wells, a section of reservoir 1 is selected that provides hydrodynamic connection between the nearby injection 2, 4, 6 and producing 3, 5 horizontal wells throughout the thickness h (Fig. 2) of the reservoir 7. Determine the residual recoverable oil reserves in the reservoir 1 ( Fig. 1).

Producing horizontal wells 3, 5 are placed in the lower part of the reservoir 7 (Fig. 2) parallel to each other. The effective oil-saturated thickness of the formation is 7 ≥25 m. The distance a from the trunk of producing horizontal wells 3, 5 to the bottom 8 of the formation is 7≥1.0 m. The absence of direct oil-water contact in the reservoir 7 increases the anhydrous period of operation of horizontal wells 2-6 ( Fig. 1, 2).

The horizontal injection wells 2, 4, 6 (Fig. 1) are placed in the roofing part of the reservoir 7 (Fig. 2) between the producing horizontal wells 3, 5 (Fig. 1) in a horizontal projection. The distance l and b (Fig. 2) between the horizontal trunks of producing 3 (Fig. 1, 2), 5 (Fig. 1) and injection 2 (Fig. 1, 2), 4, 6 wells is proportional to the permeability of the rocks composing the reservoir 7 (Fig. 2), is determined by geological and hydrodynamic modeling of the reservoir 1 (Fig. 1) laying production 3, 5 and injection 2, 4, 6 horizontal wells.

In the injection horizontal wells 2, 4, 6, a displacing agent is injected, in which water with a salinity of not more than 4 g / l is selected.

With an increase in the mineralization of water injected into the formation of ≥5 g / l, the formation of insoluble inorganic sediments increases, which, filling the pore space and cracks of carbonate rocks, clog them, thereby preventing the formation fluid from moving to the perforation intervals of production wells 3.5. When mixing produced water with fresh water, slightly mineralized water is obtained, as a result of which the formation of insoluble precipitates, such as, for example, calcium carbonate, calcium sulfate, is significantly reduced.

Horizontal injection wells 2, 4, 6 operate with a minimum pressure drop of not more than 7.0% of the initial reservoir pressure until injectivity drops below a level that provides current compensation for reservoir fluid selection by pumping low-saline water.

This mode of operation of the horizontal injection wells 2, 4, 6 stabilizes the reservoir energy, contributes to a gradual increase in reservoir pressure in the reservoir 1, increases the flow of reservoir fluid to the perforation intervals (not shown) of the producing horizontal wells 3, 5, thereby increasing oil production from the reservoir 7 (Fig. 2).

Throughout the stabilization period, research is carried out to monitor the operation of both producing 3, 5 (Fig. 1) and injection 2, 4, 6 horizontal wells. In producing horizontal wells 3, 5, the flow rates of oil and liquid are measured, and water cut is determined. In injection horizontal wells 2, 4, 6, formation pressure is measured.

After the injectivity of the horizontal injection wells 2, 4, 6 is reduced to a level at which the volume of low-mineralized water injected into the reservoir 7 (Fig. 2) exceeds the volume of the produced reservoir fluid, the water is stopped, the displacing agents are changed and they are continued to be pumped into the reservoir 7.

The injection of displacing agents significantly affects the performance of producing horizontal wells 3, 5, especially the increase in reservoir and bottomhole pressures, as well as an increase in the proportion of water in the fluid and oil production rates.

As a displacing agent, a 0.03-0.5% aqueous solution of cellulose ether and 0.01-0.5% aqueous solution of a surfactant — surfactant (neonol, bixol, etc.) are used.

A small addition of polymers to the injected low-mineralized water helps to level the front of the progress of the injected fluid over the formation 7 (Fig. 2), which occurs due to an increase in viscosity and a decrease in the mobility of water. As a result, the progress of water in high-permeability reservoirs slows down and low-permeability reservoirs are involved in the development. The above factors contribute to an increase in the coverage and displacement factors during flooding of reservoirs.

The injection of aqueous surfactant solutions improves the processes of oil displacement from carbonate reservoir rocks by increasing the hydrophilicity of the rock surface and reducing interfacial tension in the water-oil-rock system in areas of reservoir 7 that are not covered by the development. At low interfacial tension, oil droplets are easily deformed, so less force is required to push them through the narrowing of the pores, and the speed of movement in the formation increases. A more intense displacement of oil by water containing surfactants is also associated with a significant effect on the decrease in oil viscosity.

Aqueous solutions of cellulose ether and surfactant are pumped into the reservoir 7 (Fig. 2) in a volume of 30-50% of the amount of the initial oil content in the reservoir 7 at the site of reservoir 1 (Fig. 1) of oil.

The achievement of the technical result is achieved by increasing the volume ratio of the solution of cellulose ether and surfactant solution from 1: 1 to 1: 5. With an increase in water cut of produced products from producing horizontal wells, the ratio of injection volumes of an aqueous solution of a surfactant to an aqueous solution of cellulose ether is gradually increased to 1: 5, since pumping them into the formation allows waterlogged and low permeability sections to be introduced into development. When the ratio is below 1: 1, the production of oil from low-permeability areas is significantly reduced, when the ratio is above 1: 5, the aqueous solution of cellulose ether is washed out and there is a risk of breakthrough of the injected water to the perforation intervals of the producing horizontal wells.

The optimal injection pressure of the aqueous solution of cellulose ether and the aqueous surfactant solution should be 10-15% higher with respect to the initial reservoir pressure, and displacing agents are injected until the initial reservoir pressure is restored at reservoir 1 (Fig. 1).

After the process of injection of an aqueous solution of cellulose ether and an aqueous solution of a surfactant, the horizontal injection wells 2, 4, 6 (Fig. 1) are turned off and given an exposure time of up to eight days, sufficient to redistribute the filtration flows, with subsequent resumption of water injection from mineralization of not more than 4 g / l.

After the well reaches steady state, geophysical studies are carried out to determine the injectivity profile of formation 7 (Fig. 2) to decide on the need to change the volume ratio of polymer solutions and surfactants.

The cycles of water injection with a salinity of not more than 4 g / l and an aqueous solution of cellulose ether and an aqueous solution of a surfactant are repeated.

An example of a specific implementation.

The implementation of this method, we consider the example of the site of reservoir 1 (Fig. 1), characteristic of oil reservoir 1 in the Bashkir carbonate sediments without water-oil contact.

Deposit 1 was drilled with a rare grid of exploratory wells (not shown in the figure). The size of the allocated section 1 of the deposit amounted to 450 × 400 m, recoverable oil reserves - 140 thousand tons.

According to the results of geophysical studies of wells drilled in the area of reservoir 1, the following data were obtained: the effective oil-saturated thickness h (Fig. 2) of productive formation 7 was more than 26.0 m, permeability - 0.062 μm ² , porosity - 14.0%, oil saturation - 82.0%, reservoir pressure - 8.1 MPa, water cut of produced products does not exceed 12.7%.

Additionally, the area reservoir 1 (Fig. 1) drilled producing two horizontal wells 3, 5, trunks trajectory which is arranged above the base 8 (Fig. 2) producing formation 7 in the region a = 3.0 m. Length extracting horizontal wells 3, 5 (Fig. 1) was 300 m.

Horizontal injection wells 2, 4, 6 300 m long were placed at a distance of c = 2.0 m below the roof 9 (Fig. 2) of the producing formation 7 between the producing horizontal wells 3, 5 (Fig. 1) in a horizontal projection. The optimal distances l and b (Fig. 2) between producing 3, 5 (Fig. 1) and injection 2, 4 (Fig. 1, 2), 6 (Fig. 2) horizontal wells were determined by the results of geological and hydrodynamic modeling of the reservoir area 1 (Fig. 1), and they amounted to 100 and 21 m, respectively.

In injection horizontal wells 2, 4, 6, water was injected with mineralization of 3.2 g / l for one year.

Over a given period of time, the horizontal injection wells 2, 4, 6 worked with a pressure of 8.5 MPa, research work was carried out to monitor the operation of both producing 3, 5 (Fig. 1) and injection 2, 4, 6 horizontal wells. The reservoir pressure decreased from 10.1 to 9.6 MPa, while the amount of water in the produced fluid increased from 4.0 to 15.2%.

A year later, the injectivity of horizontal injection wells 2, 4, 6 of water with a salinity of 3.2 g / l decreased from 130 to 75 m ³ / day.

In order to level the front of the progress of the injected low-saline water through the reservoir 7 (Fig. 2) and to involve low-permeability reservoirs in the development of reservoir 1 (Fig. 1) with low reservoir pressure into the injected low-saline water, a 0.03% aqueous solution of cellulose ether was added and 0 , 01% aqueous solution of neonol. The injection pressure of the solutions was increased to 9.0-9.3 MPa.

After the completion of the process of pumping an aqueous solution of cellulose ether and an aqueous solution of a surfactant in an amount of 21 m ³ / day, the composition was pressed into reservoir 7 (Fig. 2) with water in a volume of 16 m ³ . The horizontal injection wells 2, 4, 6 (Fig. 1) were stopped for 5 days for response. Then, in wells 2, 4, 6, geophysical studies were carried out to determine the injectivity profile of formation 7 (Fig. 2). The injectivity of wells 2, 4, 6 (Fig. 1) increased to 110 m ³ / day. The reservoir pressure was measured, which increased to 8.2 MPa, after which they decided on the need to increase the volume ratio of the aqueous solution of cellulose ether and the aqueous solution of neonol to 1: 2.

Water injection cycles with a mineralization of not more than 4 g / l and an aqueous solution of cellulose ether and an aqueous solution of a surfactant were repeated several times. After the sixth cycle, they decided to inject an aqueous solution of cellulose ether and an aqueous solution of neonol in a ratio of 1: 5. As a result of the application of the method of developing an oil reservoir in carbonate reservoirs, oil recovery has increased 1.1 times compared to conventional water flooding.

The proposed method improves oil recovery and the efficiency of the development of oil deposits in carbonate reservoirs by conducting preliminary studies in vertical and directional wells drilled at the horizontal well location to determine the presence of hydrodynamic connection between them, provides uniform coverage of the formation by flooding at low injection pressures of low-saline water and uniform displacement of formation fluid to the perforation intervals of production wells is low concentrated solutions of polymers and surfactants.

Claims (1)

A method for developing an oil reservoir in carbonate reservoirs, including the construction of horizontal production and injection wells parallel to each other, the placement of horizontal production wells in the lower part of the reservoir, the placement of horizontal horizontal wells in the roofing of the reservoir between horizontal production wells in a horizontal projection, injection of the displacing agent through injection and selection of products through production wells, characterized in that before the construction During the construction, the distance between the nearby horizontal trunks of the production and injection wells is directly proportional to the permeability of the rocks of the site, while water with a mineralization of not more than 4 g / l, which is pumped into the reservoir with a pressure exceeding the initial reservoir pressure of not more than 7% from the initial reservoir pressure, water injection is stopped after the injection rate of horizontal injection wells is reduced to a level at which the volume of weakly mineralized water injected into the reservoir exceeds the volume of the produced reservoir fluid, then a 0.03-0.5% ether solution is used as a displacing agent cellulose and a 0.01-0.5% aqueous solution of a surfactant - surfactant with their volume ratio increasing from 1: 1 to 1: 5, and a total volume of 30-50% of the initial oil content and in the reservoir, with the injection pressure of said aqueous solutions exceeding the initial reservoir pressure by 10-15%, until the initial reservoir pressure is restored, after which the cycles of water injection with mineralization of not more than 4 g / l and aqueous polymer and surfactant solutions are repeated.

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