RU2817834C1 - Method of increasing oil recovery in areas of non-stationary water flooding - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in the method of increasing oil recovery in sections of non-stationary water flooding, sections are selected for non-stationary water flooding with an compartmentalization factor of 1.5 and more, permeability of not less than 0.001 mcm², oil viscosity up to 300 mPa⋅with, as well as the average value of water cut for all production wells in the area of not more than 98% and exceeding the depletion index of the recoverable reserves in the area, with the section development system — intra-contour waterflooding, type of injected water — fresh, waste and mineralized water with density of up to 1.18 g/cm³, containing weighted average solid-weighted particles up to 50 mg/dm³, oil products up to 60 mg/dm³, wherein all wells of the area — injection and production — represent a single hydrodynamic system. Results of geophysical investigations are used to determine duration of decreasing injectivity of the least permeable formation by 40%. Then, duration of half-cycles of cyclic mode of water injection and shutdown of injection wells after each half-cycle for depression-repression action on formations is determined as follows: with reduction of formation injectivity by 40% for 1–5 days, performing a semi-cycle of cyclic water injection for 5 days with depression-repression effects between semi-cycles of cyclic water injection in amount of 6 pieces, with reduction of formation injectivity by 40% for 6–15 days — for 12 days with depression-repression effects between semi-cycles of cyclic water injection mode in amount of 5 pcs, with reduction of formation injectivity by 40% for 16–30 days — for 22 days with depression-repression effects between semi-cycles of cyclic water injection mode in amount of 3 pcs, at reduction of formation injectivity by 40% for 31 and more days — during 30 days with depression-repression effects between semi-cycles of cyclic mode of water injection in amount of 3 pcs. Depression-repression action on formations is carried out after a half-cycle of water injection into the well immediately after its shutdown.

EFFECT: increasing oil recovery of the developed section due to prevention of colmatation of low-permeability interlayers, maintaining the profile of injectivity and oil displacement.

1 cl, 1 tbl, 2 ex

Description

The invention relates to the oil and gas industry and can be used in the development of oil deposits at a late stage, characterized by heterogeneous reservoirs of various natures, in particular zonally heterogeneous reservoirs, reservoirs having layers of different permeability as a method of increasing oil recovery.

There is a known method for developing an oil deposit based on system-targeted action (patent RU No. 2418155, MPK E21 B 43/16, published on May 10, 2011), including cyclic changes in the injection modes of the displacing agent, analysis of geological and field data on well operation, targeted regulation development systems in designated areas. In the first cycle, a displacing agent is pumped into the rows of injection wells, and forced selection is made from the middle row of production wells with a volume 10-15% higher than during selection in other rows. Based on the results of the analysis of geological and field data from production wells, the quantity, rate and water cut and/or gasification of oil, a decision is made to move to the second cycle with a change in development zones, perpendicular and similar to the initial zones, while the modes of injection of the displacing agent into injection wells and selection oil from production wells is selected similarly to the first cycle; based on the results of the analysis, decisions are made to move to the first cycle, after which the cycles are alternated.

The disadvantage of this known method is the lack of measures for targeted changes in filtration flows and leveling of the injectivity profile, selection of optimal impact technologies in relation to the specific geological and physical conditions of the formation and the current state of development.

There is also a known method for systemic cyclic development of an oil deposit at a late stage (patent RU No. 2209947, IPC E21 B 43/16, publ. 08/10/2003), including injection of a displacing agent through one or more injection wells, oil extraction through one or more production wells , analysis of geological and field data on the operation of each well, taking into account the entire development history of a given deposit, identification from the development history of spontaneous - unplanned changes in the hydrodynamic operating regime of all wells and the response of the deposit to these spontaneous changes in the hydrodynamic regime by changes in the performance indicators of producing wells, identification by response deposits of zones of residual oil reserves, determination of the value of residual oil reserves based on the parameters of the received response and targeted regulation of the development system in the selected response zones, taking into account the received response results. In the selected zones, additional injection and/or production wells are drilled, and in the selected zones the preferential primary directions of the filtration flows of the displacing agent in the deposits are identified, after which the filtration flows are given new directions

The disadvantages of this method are the high cost of its implementation, due to the fact that additional injection and/or production wells are drilled in the selected zones, the low efficiency of the method due to the complexity of its implementation, and the lack of targeted alignment of injectivity profiles.

There is also a known method for the non-stationary development of low-permeability reservoirs (patent RU No. 2716759, MPK E21 B 43/20, published on March 16, 2020), in which horizontal wells are drilled, with horizontal well bores located with an azimuth offset of more than 10 degrees. relative to the direction of the maximum horizontal stress in the formation. Multi-stage hydraulic fracturing is carried out in wells. Production is carried out in at least two wells; at least one of the above-mentioned wells is used as an injection well by injecting working fluid. The working fluid is injected into at least one injection well with the pressure exceeding the hydraulic fracturing pressure. When fluid breaks through from an injection well through auto-frac fractures into at least one well that is in production mode, the production well is shut down. The working fluid is pumped into the injection well until the volume of the working fluid pumped into the injection well exceeds the total volume of liquid extracted from the production well at the previous stages, the injection well is stopped, and production is carried out. The technical result is to increase the efficiency of developing low-permeability reservoirs and simplify the production process

The disadvantage of this method is the high cost of drilling horizontal wells and possible technological limitations on the possibility of increasing the injection pressure.

The closest is the method of developing an oil deposit (patent RU No. 2121060, MPK E21 V 43/22, published on October 27, 1998), including injection of a displacing agent - water through injection wells, oil extraction through production wells, determination of the parameters of the productive horizon layers and selection the duration of half-cycles of the cyclic mode of water injection through injection wells, at the beginning of the first half-cycle, reagents are pumped into the injection wells into highly permeable intervals of the productive horizon section, increasing the hydrodynamic resistance of the formations and maintaining these properties during the first half-cycle, and then water is pumped throughout the entire first half-cycle, During the second half-cycle, water is pumped into injection wells through the entire interval of the productive horizon section.

The disadvantages are the high cost of reagent injection when cycling a large number of wells, which at the last stage of development may not be repaid by the resulting effect, the existing risk of inconsistency of formation characteristics for reagent injection, which also reduces the scope of application of the proposed method, as well as insufficient involvement of those not previously covered by development zones

The technical objectives are to increase the oil recovery of the developed area by preventing clogging of low-permeability interlayers after cleaning the bottomhole formation zone between injection cycles, maintaining the injectivity profile and oil displacement.

Technical problems are solved by a method of increasing oil recovery in non-stationary flooding areas, including determining the parameters of the reservoirs of the productive horizon and the duration of half-cycles of the cyclic mode of water injection and shutdown of injection wells, subsequent cyclic injection of water and shutdown of injection wells, and oil extraction through production wells.

What is new is that the following parameters of the reservoirs of the productive horizon are determined: the coefficient of compartmentalization, permeability, oil viscosity, the average value of water cut for all production wells in the area and the depletion of recoverable reserves in the area; areas are selected for non-stationary flooding with a compartmentation coefficient of 1.5 and above , permeability of at least 0.001 µm², oil viscosity up to 300 mPa*s, as well as the average water cut for all production wells on the site is no more than 98% and exceeds the depletion rate of recoverable reserves for the site, with the site development system - intra-circuit flooding, type of injected water - fresh, waste and mineralized water with a density of up to 1.18 g/cm³, containing average suspended solids up to 50 mg/dm ³ , oil products up to 60 mg/dm ³ , all wells of the site - injection and production - represent a single hydrodynamic system, Based on the results of geophysical studies, the duration of the reduction in the injectivity of the least permeable formation is determined by 40%, then the duration of half-cycles of the cyclic mode of water injection and shutdown of injection wells after each half-cycle is determined for the depression-repression effect on the formations as follows: when the injectivity of the formation is reduced by 40% in 1- 5 days carry out a half-cycle of the cyclic mode of water injection for 5 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 6 pcs., with a decrease in reservoir injectivity by 40% for 6-15 days - for 12 days. depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 5 pcs., with a decrease in reservoir injectivity by 40% in 16-30 days - for 22 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 3 pcs., when the reservoir injectivity decreases by 40% for 31 or more days - for 30 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 3 pcs., depression-repression effects on the formations are carried out after a half-cycle of water injection into the well, immediately after eq stop, as follows: a pumping cementing unit with a piston diameter of at least 125 mm is connected to the well, a repressive effect is performed - water is pumped with an increase in wellhead pressure, not exceeding the maximum permissible pressure on the formations, at the maximum productivity of the cementing unit with wellhead pressure control , then the pressure in the wells is released to the initial wellhead pressure of the shut-in well, while the time of pressure change between the maximum value and the initial wellhead value should not exceed 10 s.

A method for increasing oil recovery in non-stationary flooding areas is carried out as follows.

At the late stage of development, effective waterflooding plays an important role in order to displace residual oil reserves. As a result of pumping a large volume of water, flushed zones are formed in more permeable layers, while less permeable zones that contain a larger volume of oil remain uncovered. When developing layer-by-layer formations with heterogeneous permeability, the technology of non-stationary reservoir flooding has found widespread use, the effect of which is expressed in the redistribution of reservoir pressure between layers and increased production of oil reserves from low-permeability layers. Moreover, the more pronounced the heterogeneity of the formation, the greater the effect of the non-stationary waterflooding technology. Due to the fact that the water prepared for injection still has a certain amount of solid suspended particles, less permeable reservoirs become clogged and stop accepting injected water. This leads to a decrease in oil displacement coverage and a decrease in the efficiency of non-stationary waterflooding.

The essence of the proposed method is to select a non-stationary flooding site for cyclic injection and stop injection into injection wells with the presence of perforated formations with different reservoir properties and to carry out a depression-repression effect on the bottom-hole zone of the formation after each half-cycle of injection, immediately after closing the injection well. The development object is watered terrigenous and carbonate reservoirs of the pore or fractured-pore type, which have permeability heterogeneity in the section of the productive horizon.

The following parameters of the reservoirs of the productive horizon are determined: coefficient of compartmentalization, permeability, oil viscosity, average water cut for all production wells in the area and depletion of recoverable reserves in the area. Select areas for non-stationary flooding with a compartmentalization coefficient of 1.5 and higher, a permeability of at least 0.001 µm², an oil viscosity of up to 300 mPa*s, as well as an average water cut for all production wells that exceeds the depletion rate of recoverable reserves for the area, but not more 98% (i.e. the average water cut must exceed the depletion of recoverable reserves in the area). The least permeable layer is identified. With an average water cut of 98% or more, advanced water flooding develops; non-stationary waterflooding under such conditions is impractical. When selecting areas for non-stationary flooding, the following indicators are also taken into account:

- development system - in-circuit flooding;

- type of injected water - fresh, waste and mineralized water with a density of up to 1.18 g/cm³;

- injectivity of injection wells - without restrictions;

- all wells of the site (injection and reactive production) must represent a single hydrodynamic system;

- the ratio of injection and production wells in the impact area - without restrictions;

- ensuring the quality of treated water - weighted average solid suspended particles - up to 50 mg/dm ³ , oil products - up to 60 mg/dm ³ .

Based on the results of geophysical research, the duration is determined

reducing the injectivity of the least permeable formation by 40%, then determine the duration (expressed in the number of days) of half-cycles of the cyclic mode of water injection and stopping injection wells after each half-cycle for depression-repression effects on the formations.

The choice of this limit value is due to a significant reduction in the displacement front in the target formation when the above indicator of injectivity reduction is achieved. In this case, after each half-cycle of water injection, immediately after stopping the well, a depression-repression effect is carried out on the formations.

When the reservoir injectivity decreases by 40% in 1-5 days, a half-cycle of the cyclic mode of water injection is carried out for 5 days with depression-repression effects between the half-cycles of the cyclic mode of water injection in the amount of 6 pcs., with a decrease in the reservoir injectivity by 40% in 6- 15 days carry out a half-cycle of the cyclic mode of water injection for 12 days with depression-repression effects between the half-cycles of the cyclic mode of water injection in the amount of 5 pcs., with a decrease in reservoir injectivity by 40% for 16-30 days, carry out a half-cycle of the cyclic mode of water injection in for 22 days with depression-repression effects between half-cycles of the cyclic mode of water injection in an amount of 3 pcs., with a decrease in reservoir injectivity by 40% for 31 or more days, a half-cycle of the cyclic mode of water injection is carried out for 30 days with depression-repression influences between half-cycles of cyclic water injection in an amount of 3 pcs. (see table).

Table. Duration of the half-cycle of injection and shutdown, the number of depression-repressive effects

Duration of time (days) during which the reservoir injectivity decreases by 40% Half-cycle period of injection and shutdown, days Number of depression-repression effects between half-cycles of injection, pcs. 1-5 5 6 6 -15 12 5 16-30 22 3 from 31 or more thirty 3

Thus, the period of the half-cycle of the cyclic mode of water injection (the continuous period of operation of the injection well) and the shutdown of the injection well can vary from 5 to 30 days and is selected depending on the duration (in days) of reducing the injectivity of the least permeable formation by 40%.

After a half-cycle of pumping water into the well, immediately after stopping it, a depression-repression effect is performed, due to which the bridging agent will be removed from the bottom-hole zone of the formation and its extraction into a tanker or sedimentation into a sump. To do this, use a pump cementing unit (CA) with a piston diameter of at least 125 mm, which is connected to the well. Water is injected (repressive action) with an increase in wellhead pressure that does not exceed the maximum permissible pressure on the formations. In this case, the repressive effect is carried out at the maximum productivity of the central pump with control of wellhead pressure. The wellhead pressure for Devonian objects can reach 21.0 MPa, for the Lower and Middle Carboniferous - 14.0 MPa.

Next, the pressure in the wells is released to the wellhead pressure of the shut-in well, while the time of pressure change between the maximum value and the initial wellhead value should not exceed 10 seconds, thus a pulse effect on the formations occurs. Due to the depression-repression effect, the formation is “shaken” (removal of the bridging agent) from the bottomhole zone of the formation. This allows you to maintain the injectivity of the well, where less permeable areas continue to participate in development, and the oil recovery factor from the area increases. The use of this method also allows you to increase the overhaul period by 1.5 times.

This depression-repression effect is proposed to be repeated depending on the duration of the reduction in the injectivity of the least permeable formation according to Table.

Examples of practical application.

Example 1

The section of injection well No. 666 (injectivity 150 m ³ /day at a pressure of 120 atm) has a depletion of recoverable reserves of 86% with an average water cut of reacting production wells of 92%, a compartmentation coefficient of 1.5, permeability of 0.02 µm², oil viscosity of up to 300 mPa*s. At the same time, at the injection well, according to the injectivity profile, after development for injection, water was distributed as follows: formation “a” (sandstone) - 80%, formation 6 (siltstone) - 20%. It was experimentally determined that the reduction in injectivity of the least permeable formation “b” by 40% was 35 days.

After the first half-cycle of work, pressure was pumped using a central pressure pump up to 160 atm (the maximum permissible for the formations) and then the valve was opened and excess pressure was released from the well into the receiving tank (depression-repression effect). In this case, the volume of bleed was 4.7 m³. We repeated the process of creating an impulse two more times. The total volume of water released was 12.4 m³. Then the well was left for a shutdown period of 30 days. After putting the well into production, the injectivity profile was re-tested, as a result of which the fluid loss into formation “a” was 80%, into formation “b” - 20%. As a result of the proposed method, it was possible to return the original injectivity profile, ensure oil recovery from the less permeable formation "b" and obtain additional production in the area of 1.3 tons/day.

Example 2

The section of injection well No. 777 (injectivity 100 m ³ /day at a pressure of 130 atm) has a depletion of recoverable reserves of 85% with an average water cut of reacting production wells of 90%, a compartmentation coefficient of 2.1, permeability of 0.015 µm², oil viscosity of up to 300 mPa* c. At the same time, at the injection well, according to the injectivity profile, after development for injection, water was distributed as follows: formation “a” (sandstone) - 40%, formation “b” (siltstone) - 20%, formation “c” (sandstone) - 45%. It was experimentally determined that the reduction in injectivity of the least permeable formation “b” by 40% was 5 days.

After the first half-cycle of work, the well was shut down and pressure was pumped up with the help of a central pressure pump to 175 atm (the maximum permissible for the formations) and then the valve was opened and excess pressure was released from the well into the receiving tank (depression-repression effect). In this case, the volume of bleed was 5.1 m³. We repeated the process of creating an impulse 5 times. The total volume of water released was 29.1 m³. Then the well was left for a shutdown period of 5 days.

After the well was put into operation, the injectivity profile was re-investigated, as a result of which the fluid loss into the formation, formation “a” (sandstone) - 40%, formation “b” (siltstone) - 20%, formation “c” (sandstone) - 45% . As a result of the proposed method, it was possible to maintain the original injectivity profile, ensure oil recovery from the less permeable formation “b” and obtain additional production of 1.9 tons/day.

The proposed method allows you to maintain the displacement front, increase the efficiency of non-stationary waterflooding and increase the overhaul period of wells by 1.5 times (carrying out repairs to restore injectivity).

Claims (1)

A method for increasing oil recovery in areas of non-stationary flooding, including determining the parameters of the reservoirs of the productive horizon and the duration of half-cycles of the cyclic mode of water injection and shutdown of injection wells, subsequent cyclic injection of water and shutdown of injection wells, oil extraction through production wells, characterized in that the following parameters of productive reservoirs are determined horizon: compartmentation coefficient, permeability, oil viscosity, average water cut for all production wells in the area and depletion of recoverable reserves in the area, select areas for non-stationary flooding with a compartmentation coefficient of 1.5 and higher, permeability of at least 0.001 µm ² , oil viscosity up to 300 mPa⋅s, as well as the average water cut for all production wells on the site is no more than 98% and exceeds the depletion rate of recoverable reserves on the site, with the site development system - intra-circuit flooding, type of injected water - fresh, waste and mineralized water with a density of up to 1.18 g/cm ³ , containing average suspended solid particles up to 50 mg/dm ³ , petroleum products up to 60 mg/dm ³ , all wells of the site - injection and production - represent a single hydrodynamic system; based on the results of geophysical studies, the duration of the reduction in injectivity of the least permeable reservoir by 40%, then determine the duration of half-cycles of the cyclic mode of water injection and stopping injection wells after each half-cycle for depression-repression effects on the formations as follows: when the reservoir injectivity decreases by 40% in 1-5 days, a half-cycle of the cyclic mode of water injection is carried out for 5 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 6 pcs., with a decrease in reservoir injectivity by 40% in 6-15 days - for 12 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 5 pcs. , when the reservoir injectivity decreases by 40% in 16-30 days - for 22 days with depression-repression effects between half-cycles of the cyclic mode of water injection in the amount of 3 pcs., when the reservoir injectivity decreases by 40% in 31 or more days - for 30 days with depression-repression effects between half-cycles of the cyclic mode of water injection in an amount of 3 pcs., depression-repression effects on the formations are carried out after a half-cycle of water injection into the well immediately after it is stopped as follows: a pump cementing unit with a piston diameter of at least 125 mm is connected to well, perform a repressive effect - water injection with an increase in wellhead pressure, not exceeding the maximum permissible pressure on the formations, at the maximum productivity of the cementing unit with control of the wellhead pressure, then the pressure is released into the wells to the initial wellhead pressure of the shut-in well, while the time of pressure change between the maximum value to the initial wellhead should not exceed 10 s.