RU2783464C1 - Method for developing a low-permeability reservoir of an oil deposit - Google Patents

Abstract

FIELD: oil fields development.

SUBSTANCE: invention relates to the field of development of oil fields of complex geological structure with heterogeneous, including low-permeability reservoirs and improves the efficiency of oil production from productive deposits with hard-to-recover oil reserves. The method includes separating a low-permeability reservoir with the characteristics of reservoir oil with a gas content of at least 20 m³/t, a saturation pressure of at least 80% of the initial reservoir pressure, an oil viscosity of not more than 30 MPa*s; of the corresponding series of the design grid of production wells. The correction factor Fcor is determined for each circular zone, starting from the outermost circular zone towards the top of the oil deposit structure. In this case, the correction factor Fcor of the most remote circular zone from the arch of the reservoir structure is equal to one, then the minimum bottom hole pressure is calculated for production wells located in each circular zone. After comparing the absolute marks of the formation roof between adjacent production wells, if they do not match and the arch of the deposit structure is shifted relative to the design one, the location of the circular zones is corrected with the redistribution of the design production wells over the circular zones, the correction factor Fcor and the minimum bottom hole pressure Ph for each circular zone are corrected, production wells are commissioned into operation with drawdowns in the bottom hole zone reaching the calculated minimum bottom hole pressures Ph. Further, during the operation period, simultaneously once a year in each circular zone, the reservoir pressure is measured in production wells located along a straight line passing through the arch of the deposit and the bottom of the production well located in the most remote circular zone, at reservoir pressure greater than or equal to saturation pressure in the production well located in the outermost circular zone, the production wells are operated in the same set mode, and at reservoir pressure below the saturation pressure in the production well located in the outermost circular zone, all production wells located in the outermost circular zone are removed from operation, at the same time, the correction factor Fcor is equated to the unit of the circular zone next in distance from the arch of the structure of the oil deposit and the correction factors of the remaining circular zones and the minimum bottom hole pressures are recalculated.

EFFECT: improving the efficiency of development and maintaining high rates of oil reserves recovery in low-permeability reservoirs.

1 cl, 1 dwg

Description

The present invention relates to the development of oil fields of complex geological structure with heterogeneous, including low-permeability reservoirs and improves the efficiency of oil production from productive deposits with hard-to-recover oil reserves.

A known method for the development of low-permeability oil deposits (patent RU No. 1739697, IPC E21B 43/22, publ. 08/15/1994), by pumping gas or water-gas mixtures through injection wells and extracting oil, through production wells, and in production wells, preliminary work has been carried out to an increase in the permeability properties of the reservoir, characterized in that, in order to increase the development efficiency by using low gas viscosity during oil displacement during the entire period of reserves extraction, well productivity factors are determined before carrying out work to increase the permeability properties of the reservoir, and work to increase the permeability properties The formation is carried out around the well in the volumes of the deposit, which determine their productivity factors.

The disadvantage of this method is the low oil recovery of the development object due to the high probability of breakthrough of the injected agent through fractures and high-permeability interlayers with rapid watering of production wells or breakthrough of injected gas with blocking of oil-saturated interlayers in the bottomhole zone of production wells.

A known method for the development of an oil deposit with low-permeability reservoirs (patent RU No. 2162935, IPC E21V 43/20, publ. 02/10/2001), including the dependence of the gas factor on the magnitude of drawdown in the production wells at the reservoir pressure below saturation pressure and upon reaching the constancy in time of the gas factor corresponding to the initial reservoir pressure, the deposit is developed in the depletion mode with the pressure drawdown maintained in the production wells, ensuring this constancy.

The disadvantage of this method is the instantaneous decrease in reservoir pressure over the entire area of the reservoir without taking into account the structural plan, which creates the possibility of the formation of a gas cap in the arch of the structure with the shutdown of oil-saturated interlayers inside the deposit and a decrease in oil recovery of the development object.

The closest is the method of developing low-permeability reservoirs (patent RU No. 2738558, IPC E21V 43/20, 49/00, publ. December 14, 2020 in bull. No. 35), including sampling and core analysis, determining open porosity, effective permeability of an oil-saturated reservoir, taking deep oil samples and determining the content of dissolved gas, saturation pressure, oil viscosity, reservoir development, determination of the potential flow rate of the formation fluid and water cut of the produced product, identification of a low-permeability reservoir with certain characteristics of the formation oil, well pattern design, determination of the absolute elevation of the formation roof, area division deposits into zones relative to the arch of the deposit and distribution of project wells by zones, drilling of production production wells, performing geophysical surveys to identify the reservoir, obtaining updated data on the absolute elevation of the reservoir roof, comparing the absolute elevations of the reservoir roof between adjacent wells, in case of their discrepancy with respect to the design, adjustment of the location of zones with the redistribution of project wells by zones, lowering the downhole pumping equipment and putting the well into operation.

The disadvantage of this method is the low efficiency of the development of low-permeability reservoirs in the way that stimulation is created at a separate point of the development object, namely the production well, due to degassing and selection of free gas through the annulus. In this case, the dissolved gas is used to increase the well production rate, and not to maintain the energy state and displace oil in the reservoir of the development object, which leads to accelerated depletion of reservoir energy.

The technical objectives are to increase the efficiency of the development of low-permeability reservoirs, to maintain high rates of oil recovery from low-permeability reservoirs through an integrated approach, including the creation of an artificial free gas rim in the reservoir with the effect of gas-lift fluid withdrawal through production wells in natural development mode.

Technical problems are solved by the method of developing low-permeability reservoirs, including sampling and core analysis, determining open porosity, effective permeability of an oil-saturated reservoir, taking deep oil samples and determining the content of dissolved gas, saturation pressure, oil viscosity, reservoir development, determining the potential flow rate of the formation fluid and the water cut of the produced production, selection of a low-permeability reservoir with certain characteristics of reservoir oil, designing a grid of production wells, determining the absolute elevation of the top of the reservoir, dividing the reservoir area into zones relative to the arch of the deposit and distributing planned production wells by zones, drilling operational production wells, performing geophysical surveys to identify the reservoir, obtaining updated data on the absolute elevation of the reservoir top, comparing the absolute elevations of the reservoir roof between neighboring production wells, lowering downhole pumping equipment and commissioning of production wells.

What is new is that a low-permeability reservoir is isolated with the characteristics of formation oil with a gas content ^of at least 20 m the location in each circular zone of the corresponding row of the design grid of production wells, then the correction factor Kpopr is determined for each circular zone, starting from the most remote circular zone in the direction to the arch of the oil deposit structure, according to the formula: Kpopr=Nwell(n)/Nwell(n- 1), where

Kpopr - correction factor of the circular zone,

Nwell(n) - the number of planned production wells in the previous circular zone,

Nwell(n-1) - the number of planned production wells in the subsequent circular zone closer to the top of the reservoir structure,

at the same time, the correction factor Kpopr of the most remote circular zone from the arch of the reservoir structure is equal to one, then the minimum bottomhole pressure is calculated for production wells located in each circular zone, according to the formula:

where Рzab is the minimum bottom hole pressure in the production well, MPa;

Kpopr - correction factor for the circular zone on which the production well is located,

Rnas - saturation pressure of oil with gas, MPa,

after comparing the absolute elevations of the formation roof between neighboring production wells in case of their mismatch and displacement of the arch of the deposit structure relative to the design one, the location of the circular zones is corrected with the redistribution of the projected production wells in the circular zones, the correction factor Kpopr and the minimum bottom hole pressure Рzab for each circular zone are corrected, production wells are commissioned into operation with drawdowns in the bottomhole zone reaching the calculated minimum bottomhole pressures Рzab, then during the operation period, simultaneously once a year in each circular zone, the formation pressure is measured in production wells located along a straight line passing through the top of the deposit and the bottom of the production well located in the outermost circular zone, when the formation pressure is greater than or equal to the saturation pressure in the production well located in the outermost circular zone, the production wells are operated in the same set mode, and at reservoir pressure below saturation pressure in a production well located in the most remote circular zone, all production wells located in the most remote circular zone are decommissioned, while equating the correction factor Кprer to the unit of the circular zone next farthest from the arch of the oil reservoir structure and recalculate the correction factors for the remaining circular zones and minimum bottom hole pressures.

The figure shows a diagram of the location of wells in selected circular zones relative to the arch of the deposit.

The method of developing low-permeability reservoirs is carried out as follows.

Carry out the selection and analysis of the core on the site of the deposit in the exploration well 1. In the laboratory, the open porosity, the effective permeability of the oil-saturated reservoir are determined.

Next, deep oil samples are taken and the content of dissolved gas, saturation pressure, and oil viscosity are determined.

Reservoir development, determination of the potential reservoir fluid flow rate and water cut of the produced product are carried out.

A low-permeability reservoir is isolated with reservoir oil characteristics, gas content of at least 20 m ³ /t, saturation pressure of at least 80% of the initial reservoir pressure, oil viscosity of not more than 30 MPa*s.

Designing a grid of production wells 2, determining the absolute elevation of the reservoir roof, dividing the area of the deposit into zones relative to the arch of the deposit.

Produce the distribution of design production wells 2 in zones with the location in each circular zone of the corresponding row of the design grid of wells. The first circular zone 3 is the design production wells 2 of the first row relative to the arch of the deposit (wells located around the highest hypsometric mark of the deposit). The second circular zone 4 - design production wells 2 of the second row relative to the arch of the deposit. The third circular zone 5 - design production wells 2 of the third row relative to the arch of the deposit. The fourth circular zone 6 - design production wells 2 of the fourth row and so on until the entire deposit is divided into circular zones with the distribution of design production wells 2 relative to the arch of the deposit structure. The division (ranking) of the design production wells 2 in circular zones is performed to determine the correction factor and calculate the minimum bottom hole pressure for each well within the zone.

Next, the correction factor Kpopr is determined for each circular zone, starting from the most remote circular zone 6 in the direction towards the arch of the reservoir structure, according to the formula: Kpopr=Nwell(n)/Nwell(n-1), where

Kpopr - correction factor of the circular zone,

Nwell(n) - the number of planned production wells 2 in the previous circular zone 5,

Nwell(n-1) - the number of design production wells 2 in the subsequent circular zone 4 closer to the top of the reservoir structure.

In this case, the correction factor Kpopr of the most remote circular zone 6 from the arch of the reservoir structure is always equal to one.

Next, the minimum bottomhole pressure is calculated for production wells 2 located in each circular zone 3, 4, 5, 6, according to the formula: Рzab=Kpopr*Рnas,

where Рzab - minimum bottomhole pressure in production well 2, MPa;

Kpopr - correction factor for the circular zone on which production well 2 is located,

Rnas - saturation pressure of oil with gas, MPa.

Production production wells 2 are drilled, geophysical surveys are performed to identify the reservoir, updated data are obtained on the absolute elevation of the reservoir roof, and the absolute elevations of the reservoir roof are compared between adjacent production wells 2.

After comparing the absolute marks of the formation roof between neighboring production wells in case of their mismatch and displacement of the arch of the structure of the deposit relative to the design one, the location of the circular zones is corrected with the redistribution of the design production wells over the circular zones, the correction factor Kpopr and the minimum bottom hole pressure Рzab for each circular zone are corrected.

Produce the descent of deep-pumping equipment.

Production wells are put into operation with drawdowns in the bottomhole zone reaching the calculated minimum bottomhole pressures Рzab for each circular zone.

Further, during the operation period, simultaneously once a year, in each circular zone, formation pressure is measured in production wells located along a straight line passing through the arch of the deposit and the bottom of the production well located in the most remote circular zone 6.

When the formation pressure is greater than or equal to the saturation pressure in the production well located in the outermost circular zone 6, the production wells are operated in the same set mode. Due to the higher pressure drawdown and, accordingly, greater fluid recovery, the reservoir pressure in the most remote zone 6 from the crest of the deposit structure decreases faster. When the reservoir pressure drops to saturation pressure in production wells located in the most remote zone 6, the dissolved gas is released in the reservoir and moves towards the top of the reservoir structure, the effect of energy of the dissolved gas in the reservoir is triggered.

When the reservoir pressure is below the saturation pressure in the production well located in the outermost circular zone 6, all production wells located in the outermost circular zone 6 are decommissioned. At the same time, the correction factor Kpopr is equated to unity in the circular zone 5 next farthest from the arch of the oil deposit structure and the correction factors Kpopr of the remaining circular zones 4, 3 and the minimum bottom hole pressure Pzab are recalculated.

The reservoir is exploited until the formation pressure in the closest circular zone 3 to the arch of the reservoir structure decreases to the gas saturation pressure.

An example of practical application.

Exploratory well 1 was drilled at the site of the deposit, an oil-saturated core was taken during the drilling process, which was used to determine the open porosity of 7%, the effective permeability of 0.025 μm ² , i.e. found out the low-permeability reservoir of the oil deposit.

In the process of developing a low-permeability reservoir, deep oil samples were taken, the initial reservoir pressure was determined to be 16 MPa, gas content - 50 m ³ /t, saturation pressure - 13 MPa, oil viscosity 25 MPa * s, initial flow rate equal to 10 m ³ / day, water cut 2 %.

After that, the design of a grid of production wells 2 was carried out.

The design production wells 2 of the first row were distributed from the arch of the deposit to the first circular zone 3 with the number of wells - 7 pcs. wells 2 from the arch of the deposit into the third circular zone 5 with the number of wells - 18 pcs., the last fourth row of projected production wells 2 from the arch into the fourth circular zone 6 with the number of wells - 22 pcs.

Next, we determined the correction factor Kcorr for each circular zone: Krefr for the fourth zone 6 is equal to one, Krefr for the third zone 5 is 22:18=1.22, Krefr for the second zone 4 is 18:12=1.5, Krefr for the first zone 3 is equal to 12:7=1.71.

The minimum bottomhole pressure Рzab was calculated for production wells 2 of the fourth circular zone 6 equal to 13 MPa, for production wells 2 of the third circular zone 5 equal to 13*1.22=15.86 MPa, for production wells 2 of the second circular zone 4 equal to 13*1, 5=19.5 MPa, for production wells 2 of the first circular zone 3 equal to 13*1.71=22.23 MPa.

After that, production production wells 2 were drilled. Geophysical studies were carried out to identify the reservoir, the actual data of the absolute elevation of the reservoir roof were determined, and the actual data were compared with the design data. Regarding the new location of the arch of the deposit, the location of the circular zones was adjusted with the redistribution of the design production wells 2 in the circular zones 3, 4, 5, 6 and the correction factor Kpopr was adjusted for the production wells 2, which were redistributed to other zones. The correction factor Kpopr was corrected for these production wells 2. Then, an updated calculation of the minimum bottomhole pressure Рzab for production wells 2 was carried out.

The results of practical tests are presented in table 1.

Table 1. Results of practical tests Example number circular zones Reservoir properties, physical and chemical properties of oil 1 zone 2 zone 3 zone 4 zone one 7 wells,
Rzab - 22.23 MPa 12 wells,
Rzab - 19.5 MPa 18 wells,
Rzab - 15.86 MPa 22 wells,
Rzab - 13 MPa Initial reservoir
pressure 16 MPa, gas content - 50 m ³ /t, saturation pressure - 13 MPa, oil viscosity -25 MPa * s 2 4 wells,
Rzab - 25.6 MPa 9 wells,
Rzab - 22.5 MPa 16 wells,
Rzab - 18.3 MPa 20 wells,
Rzab - 15 MPa Initial reservoir pressure 20 MPa, gas content - 65 m ³ /t, saturation pressure - 15 MPa, oil viscosity - 15 MPa * s 3 3 wells,
Rzab - 32.5 MPa 7 wells,
Rzab - 28.5 MPa 12 wells,
Rzab - 23.2 MPa 17 wells,
Rzab - 19 MPa Initial reservoir pressure 25 MPa, gas content - 75 m ³ /t, saturation pressure - 19 MPa, oil viscosity - 10 MPa * s

Downhole pumping equipment was lowered and production wells 2 were put into operation with drawdowns in the bottomhole zone reaching the calculated minimum bottomhole pressures Рzab. Further, during the operation period, simultaneously once a year in each circular zone, the reservoir pressure was measured in production wells 2 located along a straight line passing through the arch of the reservoir structure and the bottom of the production well 2 located in the most remote circular zone 6.

At reservoir pressure equal to the saturation pressure of 13 MPa in the production well 2, located in the outermost circular zone 6, the production wells 2 were operated in the same set mode.

Once in the production well 2 located in the circular zone 6, caught the value of the reservoir pressure below the saturation pressure, all production wells 2 in the circular zone 6 were simultaneously stopped and decommissioned.

Due to the higher drawdown and, accordingly, greater recovery, the formation pressure in production wells 2 in the most remote circular zone 6 from the arch of the deposit structure decreased faster than in the circular zone 5, in the circular zone 5 faster than in the circular zone 4, in circular zone 4 is faster than circular zone 3.

Further, the production wells 2 of the circular zone 5 were assigned the value of Kpopr equal to one. We recalculated the minimum bottomhole pressures Рzab for circular zones 5, 4 and 3. Changed the operating parameters of production wells 2, taking into account the recalculated minimum bottomhole pressures Рzab.

Then, at the same time, once a year in each circular zone, the formation pressure was measured in production wells 2 located along a straight line passing through the arch of the deposit structure and the bottom of the production well 2 located in the most remote circular zone 5.

Once in the production well 2 located in the circular zone 5, caught the value of the reservoir pressure below the saturation pressure, all production wells 2 in the circular zone 5 were simultaneously stopped and decommissioned.

Further, the production wells 2 of the circular zone 4 were assigned the value of Kpopr equal to one. We recalculated the minimum bottomhole pressures Рzab for production wells of circular zones 4 and 3. Changed the operating parameters of production wells 2, taking into account the recalculated minimum bottomhole pressures Рzab.

Further, at the same time, once a year in each circular zone 4, 3, the formation pressure was measured in production wells 2 located along a straight line passing through the arch of the deposit structure and the bottom of the production well 2 located in the most remote circular zone 4.

Once in the production well 2 located in the circular zone 4, caught the value of the formation pressure below the saturation pressure, all production wells 2 in the circular zone 4 were simultaneously stopped and decommissioned.

Further, the production wells 2 of the circular zone 3 were assigned the value of Kpopr equal to one. Recalculated the minimum bottomhole pressures Рzab for the circular zone 3. Changed the operating parameters of production wells 2, taking into account the recalculated minimum bottomhole pressures Рzab.

After the production wells 2 in the circular zone 3 reached reservoir pressure below saturation pressure, the reservoir was withdrawn from development due to the depletion of reservoir energy.

The proposed method increases the efficiency of development of low-permeability reservoirs, maintains high rates of oil recovery from low-permeability reservoirs due to an integrated approach, including the creation of an artificial free gas rim in the reservoir with the effect of gas-lift fluid withdrawal through production wells in a natural development mode.

Claims (9)

A method for developing a low-permeability reservoir of an oil deposit, including sampling and core analysis, determining open porosity, effective permeability of an oil-saturated reservoir, taking deep oil samples and determining the content of dissolved gas, saturation pressure, oil viscosity, reservoir development, determining the potential production fluid flow rate and water cut of the produced product , identification of a low-permeability reservoir with certain characteristics of reservoir oil, designing a grid of production wells, determining the absolute elevation of the top of the reservoir, dividing the area of the deposit into zones relative to the arch of the deposit and distributing projected production wells by zones, drilling operational production wells, performing geophysical surveys to identify the reservoir, obtaining updated data on the absolute elevation of the reservoir roof, comparison of the absolute elevations of the reservoir roof between neighboring production wells, lowering downhole pumping equipment and putting in production wells into operation, characterized in that they extract a low-permeability reservoir with the characteristics of reservoir oil with a gas content of at least 20 m ³ /t, a saturation pressure of at least 80% of the initial reservoir pressure, an oil viscosity of not more than 30 MPa * s wells by zones with the location in each circular zone of the corresponding row of the design grid of production wells, then the correction factor Kpopr is determined for each circular zone, starting from the most remote circular zone in the direction to the arch of the oil deposit structure, according to the formula: Kpopr=Nwell(n)/ Nwell(n-1), where Kpopr - correction factor of the circular zone, Nwell(n) - the number of planned production wells in the previous circular zone, Nwell(n-1) - the number of planned production wells in the subsequent circular zone closer to the top of the reservoir structure, at the same time, the correction factor Kpopr of the most remote circular zone from the arch of the reservoir structure is equal to one, then the minimum bottomhole pressure is calculated for production wells located in each circular zone, according to the formula: where Рzab is the minimum bottomhole pressure in the production well, MPa; Kpopr - correction factor for the circular zone on which the production well is located, Rnas - saturation pressure of oil with gas, MPa, after comparing the absolute elevations of the formation roof between neighboring production wells in case of their mismatch and displacement of the arch of the deposit structure relative to the design one, the location of the circular zones is corrected with the redistribution of the projected production wells in the circular zones, the correction factor Kpopr and the minimum bottom hole pressure Рzab for each circular zone are corrected, production wells are commissioned into operation with drawdowns in the bottomhole zone reaching the calculated minimum bottomhole pressures Рzab, then during the operation period, simultaneously once a year in each circular zone, the formation pressure is measured in production wells located along a straight line passing through the top of the deposit and the bottom of the production well located in the outermost circular zone, when the formation pressure is greater than or equal to the saturation pressure in the production well located in the outermost circular zone, the production wells are operated in the same set mode, and at reservoir pressure below saturation pressure in a production well located in the most remote circular zone, all production wells located in the most remote circular zone are decommissioned, while equating the correction factor Кprer to the unit of the circular zone next farthest from the arch of the oil reservoir structure and recalculate the correction factors for the remaining circular zones and minimum bottom hole pressures.

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