RU2266396C2 - Method and device for oil pool development - Google Patents

Abstract

FIELD: oil industry, particularly oil field development.

SUBSTANCE: method involves recovering fluid through production wells and injecting water-and-gas mixture in injection wells. The water-and-gas mixture is obtained at well head by injecting gas in jet pump. Water-and-gas mixture is dispersed and homogenized. To perform dispersion and homogenization operations water-and-gas mixture is supplied by jet pump in hydrodynamic cavitation unit and then in jet disperser to convert jet energy into acoustic wave energy and to initiate pulsatory cavitation. Device comprises jet pump with conical nozzle installed on central water supply pipe, side gas inlet pipe and central gas-and-liquid mixture outlet. The device is provided with hydrodynamic cavitation unit and jet disperser serially arranged downstream the jet pump. The cavitation unit and jet disperser are located in common case. Hydrodynamic cavitation unit is formed as a chamber provided with cup arranged on end wall thereof. The cup has central cavity and tangential gas-water mixture inlet. Jet disperser is made as a chamber with cup connected to end wall thereof. The cup is provided with central cavity, radial inlet orifices and depressions made in cup bottom. Cavities of cavitation unit cup and jet disperser cup are communicated one with another through central channel. Dispersed gas-and-liquid mixture outlet is made as central pipe connected to the second end wall of jet disperser cup cavity.

EFFECT: increased oil recovery and oil producing ability of the well.

3 cl, 2 tbl, 3 ex, 1 dwg

Description

The invention relates to the oil industry and is intended to increase oil recovery and intensification of oil production in the development of oil and gas deposits.

A known method of developing an oil deposit, including the injection through the injection well of the fringes of the foaming agent, gas and water and the selection of oil through the producing well. As a foaming agent, oil with an oil-insoluble surfactant or polymer is used. The ratio of injected volumes of gas and water in reservoir conditions is determined by the formula, which takes into account the foaming ability of oil with the addition of an oil-soluble polymer or oil-soluble surfactant, the volumetric coefficient of oil, the solubility of the injected gas in oil and oil saturation (RF Patent No. 2039226, class E 21 B 43/22, publ. 1995.07.09).

The disadvantage of this method is the need for the injection of large quantities of oil and surfactants. In the experiments described in the patent, at least 0.1 pore volume of oil, which contained a surfactant in an amount of 0.5%, was pumped into the reservoir model. The oil displacement coefficient when injecting only water and gas was 0.525, and due to the use of oil rims, the displacement coefficient increased to 0.74. Therefore, with a reversed five-point well placement system with a distance between the wells of 500 m × 500 m, a volume factor of 1.1, a porosity of 0.2, a density of degassed oil of 0.850 kg / m ³ , an effective oil-saturated thickness of 10 m, an initial oil saturation of 0.65 and coverage of the formation with displacing agent 0.7, an additional 75,592 tons of oil will be produced. To produce this amount of oil, approximately 77,273 tons of oil must be pumped into the reservoir, as well as 386,365 tons of surfactant or polymer. Such a process cannot be considered effective.

A known method of developing oil deposits by injecting a mixture of gas and water in a pre-transition state with a volume ratio of components of 0.7 [(- 10 ^-3 (T _o -T _PL )] - 0.25 [1-10 ^-3 (T _o -T _pl ) (m ^{3 of} gas per 1 m ^{3 of} water at reservoir pressure in the reservoir, where T _pl and T _o are the initial and maximum temperature of the reservoir during the implementation of the method, ° C. Oil is displaced by a micro-germ solution of hydrocarbon gas in water that moistens its surface ( RF patent No. 1822219, class E 21 43/20, publ. 1998.06.27).

The disadvantage of this method is the need to use large amounts of displacing agent (water-carbon gas solution), since hydrocarbon gas is well soluble in residual oil, and the claims do not take this into account.

A device is known for developing an oil field, which describes the development of an oil deposit by taking oil-gas mixture through production wells, separating it, preparing a working agent in a liquid ejector from produced water and (or) associated petroleum gas, and injecting the working agent through injection wells. The possibility of using a gas-water mixture based on produced water and associated petroleum gas as a working agent is indicated. The working agent in the liquid ejector during the process of preparation is brought to a pressure sufficient for injection into the reservoir (RF Patent No. 2046931, CL E 21 B 43/00, publ. 27.10.95 - prototype).

The disadvantage of this method is its unrealizability in real conditions, because to create sufficient pressure for water injection at the entrance to the ejector should be huge. Such pressure cannot be provided using conventional fishing equipment. So for the conditions of the deposit, lying at a depth of 2500 m with a reservoir pressure of 25 MPa, the water pressure at the wellhead should be about 65 MPa at a working pressure at the inlet of the jet apparatus of about 90 MPa. For the conditions of the White Tiger field (Vietnam), pumps must develop a pressure of more than 250 MPa. / The use of inkjet apparatus in the oil and gas industry. Author: Mishchenko I.T., Sakharov V.A., Mokhov M.A. et al. M., Oil and Gas Publishing House. 1999 59 p. /

Closest to the proposed invention in technical essence is a method of displacing oil from a formation, in which, when a gas-gas treatment is applied to the formation, water and gas are simultaneously pumped separately and mixed in the wellbore by ejection. The depth of mixing water and gas is determined from the ratio

where N _Op - the estimated depth of the discharge column, m;

P _{v / g} - pressure of the gas-water mixture, MPa;

ρ _in - the density of water, kg / m ³ ;

t _kpi - critical temperature of hydrate formation of each component, ° C;

n _i is the mass fraction of each component in the mixture;

G - geothermal gradient, ° C / m;

t ₀ - ambient temperature, ° С.

The aim of this invention is to increase the efficiency of oil displacement from the reservoir by increasing the coverage of the oil by exposure while increasing the stability of the formed gas hydrate system and eliminating the risk of hydrate formation in the wellbore (RF Patent No. 1810505, CL. E 21 B 43/22, publ. 1993.23. 04).

The disadvantage of this technical solution is its practical impossibility. The patent proposes to pump water through tubing, and gas through the annulus, so the water injected will be heated by the rocks surrounding the well very slowly under normal reservoir pressure maintenance modes (normal injection wells injections from several tens of cubic meters of water per day to several hundred cubic meters per day) it is necessary to mix water with gas at much greater depths. To draw in low-pressure gas, very high water pressures of dozens of megapascals will be required.

The problem to which the invention is directed in terms of a method for developing an oil reservoir is to increase oil recovery and increase the productivity of oil wells.

The problem is solved due to the fact that in the method of developing an oil deposit, including the selection of liquids through production wells and pumping aerated by ejecting a water-gas mixture into injection wells, the water-gas mixture is subjected to cavitation dispersion during ejection to form gas bubbles with sizes from 1 to 100 microns.

In addition, the problem is solved due to the fact that the injection of water-gas mixture into the injection wells is carried out periodically, while in between the periods of the injection of the gas-water mixture, periodic water injection is performed.

It is advisable that the volumetric gas content in the water ranged from 1% to 80%.

When a finely dispersed water-gas mixture (MVGS) is injected into the formation, the filtration resistance should increase to the greatest extent in the most permeable parts of the reservoir. On the contrary, in low-permeability zones with small pore sizes, resistances should not differ from resistances during water filtration.

The minimum sizes of gas bubbles (1 μm) are used in cases where the mixture is pumped into a low-permeability reservoir with small pore sizes of the filtration channels. The largest sizes of gas bubbles in a water-gas mixture (100 μm) are created when the effect is on a highly permeable pore or fractured (fractured-pore) reservoir.

If regulation of the filtering of the displacing agent in zones with different permeabilities is not achieved in a particular formation, then alternate injection of water and the gas mixture can be used. With alternate injection, the water-gas mixture will play the role of a plugging composition, which increases the filtration resistance in highly permeable zones. Due to the increase in pressure gradients in the reservoir, ordinary water will be able to filter in areas with reduced permeability.

The gas content of the water-gas mixture can vary from 1% to 80%. The lowest gas content (1%) must be used in fields with a low permeability reservoir, which contains oil with a high pressure of oil saturation with gas. The highest values of gas content (80%) of the injected mixture should be used on deposits with a highly permeable reservoir, which is saturated with oil with a small gas factor and has low permeability in the bedside. Under such conditions, part of the gas contained in the injected water-gas mixture will dissolve in oil, and part of the gas will segregate into the bedside of the formation and displace oil from the low-permeability reservoir.

Due to the proposed development method for oil deposits, the displacement coefficient will increase, since the water-gas mixture, as was recorded by laboratory studies, has less mobility, and the gas dissolved in oil reduces its viscosity. Due to a decrease in the conductivity of highly permeable zones, the direction of the filtration flows will change, i.e. displacement coverage will increase. In general, the oil recovery coefficient will increase by 5-20 points, well productivity in oil will increase by 20-100%.

To implement the proposed method for the development of an oil reservoir, it is necessary to use a pump-ejector unit capable of creating a water-gas mixture with the required parameters.

Known pump-ejector installation, which can be used in the development of an oil field for injection into the reservoir of produced water and capable of simultaneously ensuring the utilization of associated petroleum gas. The installation consists of three separators, a pump, a liquid-gas ejector, interconnected by pipelines. Products coming from the field (oil, water, gas) are divided into its phases. The produced water is pumped into the injection well, and part of this water is directed to the working nozzle of the liquid-gas ejector, into the low-pressure chamber of which oil gas is supplied from the inlet separator. The gas-gas mixture from the liquid-gas ejector is sent to the liquid-gas separator, in which the gas is separated from the liquid (water) and sent to the consumer. Water from this separator can be sent for disposal (USSR Author's Certificate No. 1492097, class F 04 F 5/54, publ. 1989).

The disadvantage of this device is that it does not provide for increasing the pressure of the water leaving the liquid-gas separator to a value sufficient for injection into injection wells, and it is impossible to supply this water to the pump for compression before injection into the formation due to the presence of water dissolved petroleum gas, which can cause cavitation in the pump. At high pressure values of the produced water leaving the liquid-gas separator due to the restrictions of the pumps of the reservoir pressure maintenance system according to the inlet parameters, it is necessary to reduce the pressure of the water supplied to the booster pumps, which leads to irrational energy losses, as well as intensive release of dissolved in water gas already at the inlet to the pump, which complicates the operation of the pump.

Closest to the proposed invention in technical essence is a device for developing an oil field, including a liquid ejector, the low-pressure chamber of which is connected by a pipeline with a discharge water pipe of the liquid-gas separator, the working nozzle of the liquid ejector is communicated by a pipe with a pump discharge, and the outlet pipe of this ejector is connected by a pipe with a water injection well. The device is equipped with a second liquid-gas separator and a second liquid-gas ejector, the low-pressure chamber of which is connected by a pipe with a gas outlet of the first liquid-gas separator, the working nozzle of the second liquid-gas ejector is in communication with the pump outlet, and the outlet of this ejector is connected by a pipeline with the second a liquid-gas separator, the gas and water discharge pipes of which are connected by pipelines, respectively, to gas and water injection wells, or low pressure chamber of a liquid ejector (RF Patent No. 2046931, class E 21 B 43/00, publ. 10.27.95 - prototype).

In the known device, produced water leaving the liquid-gas separator is squeezed in a liquid ejector, at the outlet of which the pressure necessary for pumping water into the formation is maintained.

A disadvantage of the known device is the need to squeeze the produced water for injection into the reservoir. When using a water-gas mixture as a working agent, it becomes necessary to squeeze not only produced water, but also separated oil gas. In addition, the device is cumbersome, metal-intensive and does not provide a water-gas mixture with a given dispersion and stability.

The present invention is also the creation of a device that allows you to implement the proposed method for the development of oil deposits.

Such a device for implementing the method of developing an oil reservoir includes a jet pump with a conical nozzle on the central water supply pipe, a side gas supply pipe and a central water-gas mixture outlet. It is equipped with a hydrodynamic cavitation unit and a jet disperser, located sequentially behind the jet pump in a single housing. The hydrodynamic cavitation unit is made in the form of a chamber, on the end wall of which there is a glass having a central cavity and a tangential input for the gas-water mixture. The inkjet dispersant is made in the form of a chamber with a glass fixed to its end wall with a central cavity, radial inlets and a recess in the bottom of the glass. The cavities of the glasses of the cavitation unit and the jet dispersant are interconnected by means of a central channel, and the outlet of the dispersed water-gas mixture is made in the form of a centrally located nozzle fixed to the second end wall of the chamber of the jet dispersant.

The technical result that can be obtained by using the inventive device is to disperse associated petroleum gas in water to obtain a finely divided water-gas mixture with a gas content of from 1 to 80% and a diameter of gas bubbles in the MHSS from 1 μm to 100 μm.

SUMMARY OF THE INVENTION

When developing an oil reservoir, the injected water only partially displaces the oil and does not cover the entire volume of the productive part of the reservoir, so oil recovery rarely exceeds 50%, and very often drops to 20-30%.

The proposed method solves the problem of increasing oil recovery deposits and intensification of oil production. The problem is solved as follows.

A finely dispersed water-gas mixture (MVGS) is injected into the formation, which, having less mobility, increases the coverage of the formation by the displacement process. Due to the growth of pressure gradients in the formation, an increase in the volumetric coefficient and a decrease in the viscosity of oil when gas is dissolved in it, as well as due to gas segregation in the near-bed parts of the formation, the oil recovery increases and the productivity of the wells in oil increases. By changing the size of the gas bubbles and the gas content in the water-gas mixture, the displacement process is adapted to the specific geological and field characteristics of the formation in the area of the location of a particular injection well.

Enhanced oil recovery can be achieved by changing the direction of the filtration flows, which in the described method is achieved by alternately injecting a water-gas mixture and ordinary water. The water-gas mixture reduces the conductivity of the most permeable zones, the segregated gas displaces oil from the low-permeability cover parts of the reservoir, and the injected ordinary water displaces the oil from the bottom of the formation.

Figure 1 presents the device (longitudinal section), through which receive a fine water-gas mixture at the mouth of the injection well before injection into the reservoir.

The device includes a housing 1, divided inside by a partition 2 with an axial conical opening 3, in which a conical nozzle 4 is located, located on the central pipe 5 of the water supply. A side pipe 6 for supplying gas is connected to the housing. This compartment compartment, separated by a partition 2, forms a jet pump that sucks in gas and delivers the resulting gas-gas mixture to a hydrodynamic cavitation unit located in series behind the jet pump in a single housing 1. The hydrodynamic cavitation unit is made in the form of a chamber 7, on the end wall 8 which fixed the glass 9 having a Central cavity 10 and a tangential inlet 11 for a gas-liquid mixture. Next, the gas-water mixture is sent to the jet dispersant, which is made in the form of a chamber 12 with a glass 14 with a central cavity 15 fixed on its end wall 13, radial inlet openings 16 and a recess 17 in the bottom of the glass 14. The cavity of the glasses 9 of the cavitation unit and 14 of the jet dispersant are communicated interconnected by means of a central channel 18. The dispersed water-gas mixture is discharged through a centrally located pipe 19 fixed to the second end wall 20 of the jet disperser chamber 12.

A device for producing a finely divided water-gas mixture works as follows.

Gas is pumped through the gas inlet 6, water is pumped through the axial water inlet 5. Due to the conical surfaces 3.4, the speed of the water jet increases, providing ejection of gas through the annular channel formed by the surfaces 3.4. The first mixture of gas and water occurs. Next, the mixture of gas and water through the tangentially located side holes 11 enters the glass 9 and twists. There is a message to the flow of the rotational component of the velocity, the presence of which leads to the appearance of centrifugal mass forces in the flow and the formation of a radial gradient of static pressure. The flow velocity vector deviates from the axial direction, and the main characteristic of the swirling flow is the swirl angle between its total velocity vector and the channel axis. The dynamic (instantaneous) velocity vector consists of the axial, radial and tangential components, and due to the redistribution of the axial component into the tangential and radial components, a cavitation cavity is formed. The vector of the dynamic velocity of the water-gas mixture in the glass significantly exceeds the average consumption rate (in this case, the maximum speed develops near the wall of the cavitation cavity, and the minimum speed near the wall of the glass). The axis has a reverse flow zone, a sharp drop in pressure and the release of tiny air bubbles from the liquid and cavitation phenomena that contribute to intense gas dispersion. A high specific contact surface of the phases and the intensity of mixing is achieved due to the action of the centrifugal force field on the gas-water mixture, which contributes to the intense fragmentation of gas bubbles and the renewal of the interfacial surface. As a result, an axial cavitation cavity is formed in the internal volume of the glass 9 and cavitation processes are realized, which lead to efficient crushing of gas bubbles and homogenization of the resulting finely divided water-gas mixture. The size of gas bubbles in water decreases. The resulting mixture through the axial hole 18 enters the glass 14. In this case, part of the energy of the turbulent flooded jet is converted into the energy of acoustic waves and the process of formation of a pulsating cavitation region is formed between the axial hole 18 and the bottom of the recess 17. Further dispersion and homogenization of the finely dispersed water-gas mixture takes place. which through the side holes 15 of the glass 14 and the pipe 19 is sent to the well.

The ratio of the liquid and gas phases (ejection coefficient) and the diameter of the gas bubbles in the finely dispersed water-gas mixture is regulated by moving the nozzle 4 of the water inlet in the axial direction in order to change the area of the passage section of the annular gap of the jet pump and changing the flow rate of water and associated petroleum gas supplied to the device using valves located respectively on the pipelines for supplying water and gas (not shown in figure 1).

Case Studies

Example 1. The proposed method and device were tested in laboratory conditions on a bulk model of the reservoir with the characteristics presented in table 1:

Table 1
The main characteristics of the reservoir model The parameters of the porous medium packing composition,% (sand fraction 0.25 ... 0.5) 8% marshallite + 92% sand geometrical dimensions of the reservoir model, m ⌀0.0382 × 3.075 porosity,% 0.320 methane permeability, m 1440 · 10 ^-15 reservoir model pore volume, m 1128.510 ^-6 Fluid parameters water-salt solution (HRV) 1.3% solution of NaCl in distilled water oil model kerosene (GOST 10227-88) finely divided water-gas mixture (MVGS) a mixture of a 1.3% solution of NaCl in distilled water and methane in various ratios

Experimental studies included the following steps:

1. Saturation of the reservoir model with water-salt solution (HRV) in order to determine the permeability coefficient of the reservoir model for HRV. The permeability coefficient was equal to 1.85 · 10 ^-12 m ² .

2. The replacement of HRV with kerosene until the complete removal of HRV with the aim of modeling the conditions of the oil reservoir, in a fragment of which the residual oil reserves are blocked. The critical water saturation was 36.05%.

3. Filtration of HRV through the reservoir model until the complete removal of kerosene in order to simulate the conditions of the reservoir, in a fragment of which there are residual oil reserves. Residual reserves amounted to 27.2%.

4. Injection of MFGS into the reservoir model for stimulating the formation in order to study the effects of MFGS with different gas phase contents on the simulated oil reservoir. The fourth stage consisted of three sub-stages.

The first sub-step was to download a 10% MVGS. In this case, the viscosity was measured using a standard capillary viscometer (an increase in viscosity of 16% was recorded compared to the viscosity of salt water). It was pumped 2.6 pore volume MVGS, the coefficient of additional extraction of kerosene was 2.7%. The injection of a 10% MVGS was stopped after the complete removal of kerosene from the reservoir model.

After stopping the release of kerosene using 10% MHF, the tests were continued using a 20% mixture (20% methane in MHF), which led to the resumption of displacement.

The second sub-step was to download a 20% MVGS. 6.3 pore volume of the MHC was pumped, while the coefficient of additional extraction of kerosene was 7.6% of residual kerosene.

At the third stage, after appropriate modernization of both the dispersion unit and the reservoir model, the obtained MHF was injected directly into the model, bypassing the standard intermediate storage capacity of the model, which is closest to the actual conditions of application of the proposed technology. When resuming injection of a 20% mixture in this way, an intense release of kerosene was detected at the output of the model almost immediately after the injection began.

To measure the dispersion of the gas phase in the mixture under a pressure of 15.0 MPa, a transparent section of the circulation system and an MBS-10 microscope were used. Using analytical microscopy, it was recorded that a spectrum of bubbles with sizes ranging from less than 5 microns to 50 microns is present in the MHSS. The bulk of the free gas phase is made up of small bubbles ranging in size from less than 5 microns to 15-20 microns.

The main conditions and results of experimental studies (Table 2) are presented below:

1. Temperature 58 ° C 2. Pressure, MPA 15,2 3. The volume of kerosene before displacement by water, cm ³ 721.7 4. The volume of kerosene displaced by water, cm ³ 525.4 5. The volume of residual kerosene after displacement by water, cm ³ 196.2 6. The volume of kerosene, displaced MVGS, cm ³ 20.29 7. The coefficient of water displacement,% 72.80 8. The total coefficient of displacement by water and MVGS,% 75.61 9. The growth rate of displacement,% 2.81

table 2 No. Gas content (% vol.) MVG pumping volume Pumping speed (cm ³ / min) Suppression of kerosene cm ³ pore volume Volume (cm ³ ) To _draw water and MVGS (%) ΔK MVGS (%) 1 10 2934 2.6 5.08-7.1 5.32 73.54 0.74 2 twenty 7110 6.3 7.1 20.29 75.61 2.81

Example 2. An oil reservoir is developed with the following characteristics: the reservoir is represented by alternating sand-siltstone and clay layers with a thickness of several meters to tens of meters, oil-saturated thickness of 8 m, absolute marks of the roof 1665-1705 m, permeability up to 4 * 10 ^-1 μm ² , the average effective pore diameter of the reservoir reservoir is 150 μm, the injectivity of injection wells without a nozzle is 500-1000 m ³ / day, the average injectivity of injection wells is maintained by plating at 500 m ³ / day, the oil viscosity is 2.4 MPa · s

Current recoverable reserves are estimated at 4.5-5.0 million tons with an annual production of 0.3 million tons. Cumulative oil production at the site since the start of development is 22030.2 thousand tons, liquids - 198369.3 thousand tons . Extraction is carried out by electric submersible pumps and gas-lift method. According to the current state, the stock of producing wells in the area is 90 pcs., Injection - 28 pcs. The average daily oil production rate of operating wells is 9.6 tons / day, liquids - 303.9 tons / day, the water cut of the existing stock reaches 96.5%.

At the selected site, a finely dispersed water-gas mixture is obtained, obtained by dispersing associated petroleum gas in produced water at a produced water pressure of about 10-11 MPa and a gas pressure of up to ± 20% of the produced water pressure, i.e. from 8.0 to 13.2 MPa. For the formation of a finely dispersed mixture using the device according to the drawing. The finely dispersed water-gas mixture obtained at the mouth of the injection well is pumped into the formation either continuously or in cycles due to pressure in the RPM system. At the same time, the finely dispersed water-gas mixture is injected until the well injectivity in the mixture decreases by more than 50% of the initial water injectivity of the well. The gas content of the mixture at a pressure of its formation (about 10.0 MPa) varies from 10 to 40 percent and depends on the injectivity of the well, as well as the pressure drop across the nozzle. When the volume of microbubbles of gas, comprising from 10 to 40% of the volume of produced water, the average density of the solution is from 820 to 920 kg / m ³ .

Fine water-gas mixture is pumped for 1 year through injection wells, oil is taken through production wells. For 1 year, the estimated additional oil production will amount to 21.0 thousand tons.

Example 3. Perform as example 2. Alternate injection through injection wells after 30 days of finely dispersed water-gas mixture and produced water of the developed reservoir. For 1 year, the estimated additional oil production will be 27.0 thousand tons.

Claims (3)

1. A method of developing an oil reservoir, including the selection of liquid through production wells and pumping a gas-water mixture into the injection wells, which is obtained by ejecting gas into the jet pump, while the gas-water mixture is dispersed and homogenized, for which this mixture is fed into the hydrodynamic pump cavitation unit and further into a jet disperser for converting the energy of the jets into the energy of acoustic waves and the formation of pulsating cavitation. 2. The method according to p. 1, characterized in that the dispersed water-gas mixture is pumped into the injection wells periodically, while water is pumped between the periods of the gas-water mixture injection. 3. A device for implementing the development of an oil reservoir, comprising a jet pump with a conical nozzle on the central water supply pipe, a gas supply side pipe and a central gas-liquid mixture outlet, characterized in that it is equipped with a hydrodynamic cavitation unit and a jet disperser located in series behind the jet pump in a housing unified with it, while the hydrodynamic cavitation unit is made in the form of a chamber, on the end wall of which is fixed a glass having a central cavity and an angular entry for a gas-liquid mixture, the jet dispersant is made in the form of a chamber with a glass attached to its end wall with a central cavity, radial inlet openings and a recess in the bottom of the glass, the cavities of the glasses of the cavitation unit and the jet dispersant are interconnected via a central channel, and the output for dispersed gas-liquid mixture is made in the form of a centrally located nozzle mounted on the second end wall of the chamber of the jet dispersant.