RU2351752C1 - Method of developing oil deposits in fractured reservoirs - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention refers to oil deposits developing , particularly to deposits presenting carbonate fractured reservoirs. The implementation of the method facilitates expanded process capabilities for deposit development and putting the sections of the deposit, not having produced oil before, into operation. Producing and pressure wells are set. Replacing fluid is pumped through pressure wells and production is withdrawn through producing wells. Development of deposit is performed by stages. Development is commenced at a natural mode till achieving reservoir pressure of 1% from the saturation pressure at the bottomhole of producing wells at a minimal yield. Further replacing fluid is pumped without the excessive pressure to the head of the pressure well at the level of 4.0% from the initial reservoir pressure up to reduction of intake capacity below the level, facilitating current compensation of withdrawal with pumping. Then replacing fluid is pumped with excessive head pressure facilitating reservoir initial pressure recovery. During recovery of initial reservoir pressure 0.05-0.1% of high molecular polymers are added into pumped fluid. At the final stage of deposit development either replacing fluid pumping is successively turned on and off in pressure wells in criss-cross manner by pairs or pumping is turned on and off successively around the circle in pairs of wells at pumping pressure facilitating reservoir pressure close to the initial one.

EFFECT: increased efficiency of oil deposit developing due to reduced watering of well production, to increased ratio of coverage of developing oil reserves stores, and to increased yield of wells and final oil extraction.

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Description

The proposed method relates to the field of development of oil fields, in particular deposits represented by carbonate fractured reservoirs.

A known method of developing a multilayer oil field, including the opening of high - and low permeability formations having impermeable sections between them. The seams have similar reservoir characteristics and are combined into production facilities (at least two), which cyclically inject the displacing agent and select the product. Cyclic injection is carried out to the limit of elastic deformation. At the same time, the pressure in the adjacent formation is reduced to saturation pressure. Increase and decrease in pressure lead in the opposite direction.

In order to increase oil recovery of zonal heterogeneous formations by changing the direction of the filtration flows, injection wells are placed on mutually intersecting profiles. In the first cycle, wells located on one of the profiles are stopped, and wells located on the other profile are put into operation, and the cycles of the injection wells are repeated (RF patent No. 1653403, ЕВВ 43/20, publ. 15.09.1994, Bull. No. 17).

The disadvantage of this method is that due to differences in reservoir properties, cracks in a highly permeable formation are first revealed. For this reason, the impermeable section, deformed, bends towards the low-permeability layer, worsening its capacitance-filtration properties, which leads to a decrease in oil production.

A known method of developing a water-cut oil reservoir, including cyclic water flooding through injection wells and oil extraction through production wells, and within the seven-point geometry of the location of the wells include the development of undeveloped sections of the oil reservoir between the injection wells. For this, the oil reservoir is divided into triangles so that their vertices are injection wells 1, 2, 3. Then, during one third of the cycle, water is flooded simultaneously through injection wells 1, 2, and in the next third of the cycle through injection wells 2, 3 and in the last third of the cycle - through injection wells 3, 1. After this, the waterflooding cycle is repeated in the selected direction (RF patent No. 2299318 C2, E 21B 43/20, publ. 05.20.2007, Bull. No. 14).

The disadvantage of this method is the low oil recovery coefficient and does not provide sufficient coverage of reservoirs with water flooding.

There is a method for developing high-viscosity oil deposits confined to fractured-pore carbonate reservoirs using an areal flooding system (in particular, cellular). During the development of such deposits, the reservoir in production wells behaves as a pore, and in injection, due to the opening of cracks under the influence of high bottomhole pressure, as a fracture-pore. The injectivity of injection wells increases sharply after the creation of artificial water-saturated zones near them. This leads to a multiple excess of injectivity of injection wells over the productivity coefficient of producing wells and, accordingly, high daily injectivity of the former at low flow rates of the latter. The use of conventional areal systems in such conditions results in a low production level with a large volume of water injected into the reservoir, which is much higher than the volume of fluid taken from the reservoir.

The cellular system provides a sharp increase in the ratio of the number of production and injection wells (up to 6: 1 or more), as well as the distance between injection and production wells at small distances between production wells. This helps to match the volumes of injected water and produced fluid, slows down the flooding of producing wells.

Flood-flooding development systems also have negative aspects. They practically do not allow regulating the speed of water movement to different producing wells of an element of the development system by redistributing the volumes of injected water. In this regard, the likelihood of premature flooding of a significant part of production wells increases. This process is exacerbated by the simultaneous commissioning of new production wells in the element, shutdowns of individual wells for underground and major repairs, shutdown of waterlogged wells, significant differences in well production rates, etc. (Muslim R.Kh. Modern methods of managing oil field development using water flooding: a Training manual. - Kazan: Publishing house of Kazan University, 2002. - 86 p.).

The closest in technical essence to the proposed one is a method of developing oil deposits folded by a porous-fractured type of reservoir, which includes maintaining an elastic mode of formation operation by applying cyclic injection of a displacing agent into injection wells and periodically operating groups of production wells with stopping them for a period of time, determined by data of hydrodynamic studies of wells. The direction of increased fracture of the reservoir is determined. Production wells are formed into cells with injection wells in the center and are divided into two groups. The first group includes production wells located at a distance of no more than half the distance between the wells from the injection axis passing through the injection well along the direction of increased fracture of the reservoir. The second group includes all other producing wells. The operation of production and injection wells in each cell is carried out in cycles. In the first period of each cycle, when production wells are stopped, a rim of viscoelastic composition is pumped into injection wells with a volume equal to the volume of cracks in the zone of injection wells. In the second period of the cycle, the first group of production wells is put into operation and at the same time the rim of the displacing agent is pumped into injection wells in an amount equal to the total volume of cracks in the zones of injection and all production wells. The production wells of the first group are operated for a time during which they take a volume of fluid equal to the volume of cracks in the drainage zones of the production wells of the first group. In the third period of the cycle, the injection of the displacing agent into the injection wells is stopped and the production wells of the first group are shut down. The second group of production wells is put into operation for a period of time during which the production wells of the second group take a volume of fluid equal to the total volume of fractures in the zones of injection wells and production wells of the second group. The cycles of periodic operation of production wells are repeated until the economic criteria for the termination of production are achieved (RF patent No. 2191255, ЕВВ 43/16, publ. 10.20.2002, Bull. No. 29).

The disadvantage of this method is that when the injection is stopped (with its subsequent resumption) in injection wells, the leveling of the displacement front in one cycle occurs in an insignificant part of the block. During this period, oil reserves in the displacement zone of injection wells are significantly developed, and with a large selection of associated water, which significantly reduces the efficiency of the method.

The technical task of the proposed method is to increase the efficiency of the development of oil deposits by reducing the water cut of the production of wells, increasing the coverage ratio by production of oil reserves, increasing the flow rate of wells, and the ultimate oil recovery. The application of the method allows you to expand the technological capabilities of the development of deposits, to include in the work areas of deposits that have not previously participated in oil production.

This problem is solved by the described method of developing an oil deposit, including the placement of production and injection wells, injection of displacing fluid through injection and selection of products through production wells.

The new fact is that the development of deposits is carried out in stages: they begin on a natural mode until the reservoir pressure is about 1% of the saturation pressure at the bottom of the producing wells with a minimum profitable flow rate, then the displacement fluid is pumped without excess pressure at the mouth of the injection well, which is no more than 4, 0% of the initial reservoir pressure until the injection rate drops below the level that provides current compensation for the selection by injection, then a displacement fluid with excess wellhead is pumped When the initial reservoir pressure is restored, when the initial reservoir pressure is restored, 0.05-0.1% of high molecular weight polymers are added to the injected fluid; at the final stage of reservoir development, the injection fluid is sequentially turned on and off in injection wells in pairs or turned on and off injection sequentially in a circle by pairs of wells at injection pressures that provide reservoir pressures close to the initial one.

The conducted patent research on the patent fund and the technical library of the TatNIPIneft Institute showed the absence of identical or equivalent technical solutions in comparison with the claimed method, which allows us to conclude that its criteria of "novelty" and "inventive step" are met.

The drawing shows the layout of wells in the deposits in fractured carbonate reservoirs.

The method is carried out in the following sequence.

To clarify the geological structure of the reservoirs, deposits in carbonate reservoirs are drilled with a rare grid of wells, and their arrangement is carried out. According to seismic data and the results of deep well drilling, the direction of fracture, the size of the reservoir, the thickness of oil-saturated formations, the reservoir properties of reservoirs (permeability, porosity, oil saturation of rocks) and the amount of oil reserves are determined. Unlike terrigenous, in carbonate reservoirs, the effectiveness of waterflooding methods is mainly influenced by the geological structure of the formations, rather than the viscosity of the oil. Obviously, this phenomenon is explained by the high zonal and layer-by-layer heterogeneity of carbonate reservoirs, due to which the nature of oil displacement from these formations differs significantly from the displacement from terrigenous reservoirs.

Given the available information, structural maps are built on the roof of reservoirs. Using a uniform triangular grid of wells, seven-point areal development elements are formed with six perimeter wells and one in the center of the triangle, and injection wells are placed at the vertices of the triangle, and the rest work as production wells.

The rows of wells are placed at an acute angle to the prevailing direction of fracture, which coincides with the major axis of the structure - No. 23 (see the drawing, and the distance between the injection wells is at least 400 m, and from the injection wells to the oil well no less than 200 m. Products are selected from producing wells (No. 1-22).

With a decrease in the oil flow rate below the maximum profitable, it is mastered for injection of well No. 19-22. Measure the selected oil and water. Displacement fluid is injected into injection wells in five stages.

The first stage - injection of injected fluid is carried out at a pressure not exceeding 1% of the initial reservoir pressure, that is, production wells practically operate in a natural mode. Downhole pressure reduction in producing wells is permissible for different deposits only by 10-20% of the saturation pressure. With a greater decrease, the degassing of oil in the reservoir can lead to a decrease in oil recovery due to the intensive development of the dissolved gas regime with weak cementation of reservoir rocks.

The second stage - injection wells operate with a minimum pressure at the wellhead - not more than 4.0% of the initial reservoir pressure until the injectivity drops below a level that provides current compensation for injection selection.

These two stages fulfill the task of stabilizing reservoir energy and contribute to a gradual increase in reservoir pressure in the reservoir. Throughout the stabilization period, research is carried out to monitor the operation of both production and injection wells. In production wells, the flow rate of oil and liquid is measured, and water cut is determined. In injection wells, formation and bottomhole pressure are measured.

As a result of the measures taken, the planned indicators for the increase in reservoir pressure are achieved.

With a decrease in the injectivity of the wells below the level that provides current compensation for the selection by injection of the displacing fluid, they proceed to the third stage. Injection wells operate in a mode with excess wellhead pressure exceeding the initial reservoir pressure by 10-20% until the initial reservoir pressure in the reservoir is restored.

The injection of displacing fluid significantly affects the performance of the well, especially the increase in reservoir and bottomhole pressures, as well as an increase in the proportion of water in the fluid and the flow rate of the fluid.

The fourth stage is a small addition of high molecular weight polymers to the injected fluid, which contributes to the alignment of the front of the progress of the injected fluid in the reservoir, 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 polymer consumption does not exceed 0.05-0.1% of the injected fluid. After injecting the rims of the aqueous polymer solution with a volume of 10-40% of the amount of oil originally contained in the reservoir, the well is turned off and a time delay is sufficient to redistribute the filtration flows, and they switch to normal flooding. The remainder of the polymer solution can be pumped at any stage of development, but the most effective injection at the initial stage of flooding. High oil viscosity (up to 100 mPa · s) and layer-by-layer heterogeneity of the formation are factors that increase the efficiency of the use of polymers. In this case, the data obtained during studies to monitor the operation of injection (flowmeter studies) and production wells (monitoring the position of the dynamic level, hydrodynamic studies, studies on the selection of deep samples in the reservoir in order to determine the saturation pressure) are taken into account.

To optimize all parameters of the well’s operation, it is necessary to reduce the effect of the injected fluid; for this, unsteady (cyclic) flooding is provided with a change in the direction of fluid filtration flows in the formation.

The fifth stage - changing the filtration flows by sequentially turning on and off the injected fluid in opposite rows - a crosshair (19-22 and 20-21) or in a circle (19, 20, 21, 22) at injection pressures that provide reservoir pressures close to the initial . In heterogeneous carbonate reservoirs, the ratio of production wells to injection wells should be less than 5-6: 1, since with a small number of injection wells, sufficient coverage of oil reserves is not provided. With the introduction of the invariable technology of cyclic exposure, the process of oil displacement by liquid in a carbonate fractured reservoir eventually approaches a stationary one, which leads to a decrease in the effect.

With the cross cyclic waterflooding method, two injection wells (19-22) from opposite rows begin to work simultaneously, and the other two - wells 20-21 at this time. After 30 days of operation, the first two wells are stopped, and injection wells, which are idle, are launched for a month. Then the well cycle is repeated.

In a circular method of cyclic flooding, two injection wells 19-20 are started simultaneously, after a month of operation, injection well 19 is stopped, well 20 continues to work for another month, at the same time well 22 is put into operation, etc. The work of injection wells is carried out in pairs in a circle.

The effect of cyclic water flooding is to reduce the unevenness of oil displacement in a heterogeneous formation while creating an elastic fluid filtration regime in it. As a result, less water is taken from the reservoir and higher oil recovery is achieved.

Example 1 specific implementation.

The implementation of this method will be considered on the example of a site characteristic of reservoir deposits in carbonate fractured reservoirs of the middle Carboniferous of the Zlodarevskoye field (see drawing). The site is drilled with a rare grid of vertical wells, and their arrangement is carried out. According to seismic data and the results of deep well drilling, the size of the deposit and the direction of fracture are determined. Based on the results of geophysical and field studies conducted in the wells, the reservoir properties of the oil-saturated part of the formation are determined. The average effective oil saturated formation thickness is 5.4 m.

Drill along a triangular grid of 300 × 300 m and place production wells 1-18 at an acute angle to the prevailing southeastern direction of fracturing and drill wells 19, 20, 21, 22. Each injection well is located in the center of the seven-point element. Production and injection wells are placed within a four-meter isopach. The minimum distance from the injection wells to the oil-and-gas complex is 320 m. The production rates of oil and formation fluid, formation and bottomhole pressure are measured in the wells.

Water is injected into injection wells for two years, the pressure of the injected fluid is 0.3-0.8 MPa, that is, production wells operate in a natural mode. According to research, in 2-3 months there is a slight increase in the dynamic fluid level in many wells, especially in the central part of the reservoir.

Then, during the year, injection wells operate with a minimum wellhead pressure of 1.8-3.5 MPa until the injectivity drops below a level that provides current compensation for the selection of the injected fluid.

Both stages fulfill the task of stabilizing the situation in terms of reservoir energy and contribute to a gradual increase in reservoir pressure in the reservoir. Throughout the stabilization period, research was carried out to monitor the operation of both producing and injection wells. Reservoir pressure increased from 10.4 to 11.8 MPa, bottomhole pressure - from 7.6 to 9.0 MPa, while the amount of water in the fluid increased from 3.0 to 11.2%.

At the third stage, injection wells operate with an injection pressure of 8–9 MPa until the initial reservoir pressure in the reservoir is restored. After three years of operation of the injection wells, it was found that the effect of the injected liquid on almost the entire reservoir is too large and the question arose of its optimization. The reservoir pressure in the reservoir reached 12.3 MPa, bottomhole pressure - 0.1 MPa, the amount of water in the produced fluid increased on average to 45.5%.

In order to level the front of the advancement of the injected fluid through the reservoir and to involve low-permeability reservoirs in the development of the reservoir with reduced reservoir pressure, 0.05% polyacrylamide (PAA) was added to the injected fluid. The volume of the rim of the aqueous PAA solution was 20% of the amount of oil originally contained in the formation. Then the injection wells were turned off, they were held in a sufficient time for the redistribution of the filtration flows. We measured reservoir pressure. Further work of the injection wells was carried out in pairs by the cross cyclic flooding method. Injection wells worked with bottomhole pressure from 8 to 9 MPa.

An analysis of the technological performance of the wells showed that the sequential shutdown of the injection fluid in the cross pairs of injection wells during the month compensates for the selection of production of wells by the injection fluid, therefore the injection wells 19 and 22, 20 and 21 worked in the sequential mode of switching on and off the injection of fluid in opposite rows cross at injection pressures that provide reservoir pressure close to the initial.

Example 2

The implementation of this method will be considered on the example of a site characteristic of reservoir deposits in carbonate fractured reservoirs of the middle Carboniferous of the Zlodarevskoye field (see drawing). The site is drilled with a rare grid of vertical wells, and their arrangement is carried out. According to seismic data and the results of deep well drilling, the size of the deposit and the direction of fracture are determined. Based on the results of geophysical and field studies conducted in the wells, the reservoir properties of the oil-saturated part of the formation are determined. The average effective oil saturated formation thickness is 6.2 m.

Drill along a triangular grid of 300 × 300 m and place production wells 1-18 at an acute angle to the prevailing southeastern direction of fracturing and develop wells 19, 20, 21, 22 for injection. In the wells, oil and formation fluid, reservoir and bottomhole pressure.

The process of developing deposits from the first to fourth stages is carried out analogously to example 1.

Further work of injection wells was carried out by pairs of neighboring wells using a circular method of cyclic flooding. Injection wells worked with bottomhole pressure from 8 to 9 MPa.

An analysis of the technological performance of the wells showed that the sequential stop of the injection of displacing fluid into neighboring pairs of injection wells during the month compensates for the selection of production of wells by the injected fluid, therefore the injection wells 19 and 22, 20 and 21 worked in the mode of sequentially turning on and off the injection of displacing fluid into neighboring pairs of wells in a circle at injection pressures providing reservoir pressure close to the initial one.

The proposed method provides an increase in the efficiency of the development of oil deposits by reducing the water cut in the production of wells, increasing the coverage factor by production of oil reserves, increasing the flow rate of wells, and the ultimate oil recovery. The application of the method allows you to expand the technological capabilities of the development of deposits, to include in the work areas of deposits that have not previously participated in oil production.

Claims (1)

A method for developing oil deposits in fractured reservoirs, including placement of production and injection wells, injection of displacing fluid through injection wells and selection of products through production wells, characterized in that the development of deposits is carried out in stages: they begin on a natural mode until formation pressure of about 1% of saturation pressure is reached at the bottom of production wells with a minimum flow rate, then displacing fluid is pumped without excessive pressure at the mouth of the injection well, it is not more than 4.0% of the initial reservoir pressure until the injectivity drops below the level that provides current compensation for injection selection, then a displacement fluid is pumped with excess wellhead pressure to restore the initial reservoir pressure, while restoring the initial reservoir pressure, 0.05 is added to the injected fluid -0.1% of high molecular weight polymers, at the final stage of the development of the deposits, sequentially turn on and off the injection of the displacing fluid into the injection x wells in pairs or turning on and off the injection sequentially in a circle in pairs of wells at injection pressures that provide reservoir pressures close to the initial one.