CN114293959A - A solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery - Google Patents

Abstract

The invention provides a solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery, and relates to the technical field of oil reservoir development. The present invention injects non-condensable gas and/or steam into the injection well in the later stage of solvent-assisted steam oil recovery, and is produced by the horizontal production well. During this process, on the one hand, the non-condensable gas and/or steam displaces the solvent in the gas cavity gas, thereby recovering solvent gas; on the other hand, with the injection of non-condensable gas and/or steam, the partial pressure of the solvent gas in the gas chamber decreases, thereby reducing the solubility of the solvent in the oil phase, and the solvent is flash vaporized by the liquid phase It becomes gas and is produced by horizontal production wells. By using the method provided by the invention, the solvent gas remaining in the steam chamber and the solvent dissolved in the remaining oil in the reservoir can be recovered, so that the solvent can be recycled, thereby improving the economic benefit of ES-SAGD.

Description

A solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery

technical field

The invention relates to the technical field of oil reservoir exploitation, in particular to a solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery.

Background technique

Steam Assisted Gravity Drainage (SAGD) technology has been successfully applied in the exploitation of heavy oil reservoirs in Canada's oil sands mining area, my country's Liaohe Oilfield, and Xinjiang Oilfield. SAGD technology reduces the viscosity of crude oil by injecting high dryness steam into the reservoir, the viscosity of crude oil is reduced, and the condensed water flows downward under the action of gravity, and is produced from the horizontal production well at the bottom of the reservoir.

However, SAGD technology still has some deficiencies. In the process of steam injection, a large amount of CO ₂ is produced by the combustion of the boiler, and the environmental protection problem is prominent. The solvent-assisted steam flooding (ES-SAGD) technology is an improvement on the SAGD technology. The solvent and steam are injected together, and the synergistic viscosity reduction effect of the steam and the solvent is used to further improve the oil production rate and reduce _CO2 emissions. According to field tests in Canada, in the ES-SAGD process, a part of the solvent is dissolved in the remaining oil in the reservoir, which is difficult to recover, which directly affects the economic benefits of ES-SAGD.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery. The method of the present invention can effectively recover the solvent remaining in the formation in the later stage of ES-SAGD, so that the solvent can be recycled, thereby improving ES-SAGD. economic benefits.

In order to achieve the above-mentioned purpose of the invention, the present invention provides the following technical solutions:

The invention provides a solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery, comprising the following steps:

(1) In the later stage of solvent-assisted steam oil recovery, a solvent recovery well group is deployed, and each solvent recovery well group includes an injection well and at least one horizontal production well; the horizontal depth of the injection well is less than that of the horizontal production well depth; the injection well and the horizontal production well are not on the same vertical line;

(2) Non-condensable gas and/or steam are injected simultaneously or alternately through injection wells, and mixed gas is recovered from horizontal production wells; The pressure difference between the well and the horizontal production well is 50-200kPa;

(3) Separating the solvent gas and the non-condensable gas in the mixed gas and recycling; when the content of the solvent gas is lower than the set value, stop injecting the non-condensable gas and/or steam.

Preferably, the injection well is a horizontal injection well or a vertical injection well.

Preferably, when there are two horizontal production wells in each solvent recovery well group, the injection well is located above the midpoint of the connecting line between the two horizontal production wells.

Preferably, the non-condensable gas includes one or more of N ₂ , O ₂ , CH ₄ , CO ₂ , air and flue gas.

Preferably, when the solvent to be recovered is a water-oil-soluble solvent, steam is injected after the non-condensable gas is injected into the injection well.

Preferably, the method for gradually decreasing the injection pressure includes: decreasing the injection pressure by 5-20% every preset time period until the injection pressure decreases to the initial pressure of the reservoir.

Preferably, when the injection well is a horizontal injection well, in the same solvent recovery well group, the vertical distance between the horizontal injection well and the horizontal production well is 4-6 m; The horizontal distance is 70-100m.

Preferably, when injecting non-condensable gas, the gas injection rate of the horizontal injection well is 20000-30000 m ³ /d;

When steam is injected, in terms of cold water equivalent, the gas injection rate of the horizontal injection well is 100-600 m ³ /d.

Preferably, when injecting non-condensable gas, the gas injection rate of the vertical injection well is 400-600 m ³ /d;

When injecting steam, in terms of cold water equivalent, the gas injection rate of the vertical injection well is 20-120 m ³ /d.

Preferably, the recycling includes: performing solvent-assisted steam oil recovery on the separated solvent gas; injecting the separated non-condensable gas into a solvent recovery well group for solvent recovery.

The present invention provides a solvent recovery method suitable for the late stage of solvent-assisted steam oil recovery. In the present invention, in the late stage of solvent-assisted steam oil recovery, non-condensable gas and/or steam are injected into the injection well and produced from the horizontal production well. , on the one hand, the non-condensable gas and/or steam displaces the solvent gas in the gas chamber, thereby recovering the solvent gas; on the other hand, with the injection of the non-condensable gas and/or steam, the partial pressure of the solvent gas in the gas chamber decreases , thereby reducing the solubility of the solvent in the oil phase, and the solvent is flashed from the liquid phase into a gas, which is produced by the horizontal production well. By adopting the method provided by the invention, the solvent gas remaining in the steam chamber and the solvent dissolved in the remaining oil in the reservoir can be recovered, so that the solvent can be recycled, thereby improving the economic benefit of ES-SAGD.

Description of drawings

Fig. 1 is the schematic diagram of ES-SAGD horizontal well injection-production well pattern;

Fig. 2 is the schematic diagram of solvent recovery well group in embodiment 1;

Fig. 3 is a graph showing the quality change of solvent remaining in the reservoir during ES-SAGD oil recovery and solvent recovery;

4 is a schematic diagram of a solvent recovery well group in Example 2;

5 is a schematic diagram of the mechanism of solvent recovery in Example 1.

Detailed ways

The invention provides a solvent recovery method suitable for the later stage of solvent-assisted steam oil recovery, comprising the following steps:

(1) In the later stage of solvent-assisted steam oil recovery, a solvent recovery well group is deployed, and each solvent recovery well group includes an injection well and at least one horizontal production well; the horizontal depth of the injection well is less than that of the horizontal production well depth; the injection well and the horizontal production well are not on the same vertical line;

(2) Non-condensable gas and/or steam are injected simultaneously or alternately through injection wells, and mixed gas is recovered from horizontal production wells; The pressure difference between the well and the horizontal production well is 50-200kPa;

(3) Separating the solvent gas and the non-condensable gas in the mixed gas and recycling; when the content of the solvent gas is lower than the set value, stop injecting the non-condensable gas and/or steam.

In the present invention, the conditions in the later stage of solvent-assisted steam oil recovery are preferably that the oil production decreases while the gasoline ratio increases, more preferably, the oil production keeps dropping and the gasoline ratio keeps increasing for more than 50 consecutive days. In the present invention, in the later stage of solvent-assisted steam oil recovery, the content of the solvent in the horizontal production well is preferably lower than 10 mol%.

In the present invention, the solvent recovery well group is preferably deployed on the basis of the original horizontal well injection and production well pattern. In the present invention, the original horizontal injection-production well pattern consists of several horizontal injection-production well pairs; each horizontal injection-production well pair consists of a horizontal injection well and a Composition of horizontal production wells.

In the present invention, in the same horizontal injection-production well pair, the vertical distance between the horizontal injection well and the horizontal production well is preferably 4-6 m, more preferably 5 m; the horizontal distance between the adjacent horizontal injection-production well pairs Preferably it is 70-100m, More preferably, it is 80-90m. In a specific embodiment of the present invention, the well spacing is related to the overall well layout of the reservoir.

In the present invention, each group of the solvent recovery well group includes one injection well and at least one horizontal production well; the horizontal depth of the injection well is smaller than the horizontal depth of the horizontal production well; the injection well and the horizontal production well Wells are not on the same vertical line. In the present invention, the injection well is preferably a horizontal injection well or a vertical injection well. In the present invention, when there are two horizontal production wells in the solvent recovery well group in each group, the injection well is located above the midpoint of the connecting line of the two horizontal production wells; the non-condensable gas and/or the non-condensable gas injected through the injection well Or steam, the solvent is recovered separately from two horizontal production wells on either side of the injection well.

After the solvent recovery well group is deployed in the present invention, non-condensable gas and/or steam are injected simultaneously or alternately through injection wells, and mixed gas is recovered from horizontal production wells. The invention forms a displacement channel through a solvent recovery well group, injects non-condensable gas and/or steam through the injection well, and the non-condensable gas and/or steam carries the solvent and is produced by the horizontal production well to realize solvent recovery.

In the present invention, when the injection well is a horizontal injection well, the method for deploying a solvent recovery well group preferably includes: closing the horizontal injection well at a spatial interval, and keeping the open horizontal injection well and the adjacent horizontal injection well Production wells form groups of solvent recovery wells. In the present invention, the closing of horizontal injection wells at intervals specifically refers to closing one horizontal injection well every other horizontal injection well. In the present invention, the horizontal production well just below the closed horizontal injection well is kept in an open state; the horizontal production well just below the horizontal injection well in the open state is kept in a closed state. In the present invention, in the same solvent recovery well group, the vertical distance between the horizontal injection well and the horizontal production well is preferably 4-6 m; the horizontal distance between the horizontal injection well and the horizontal production well is preferably 70-100 m.

In a specific embodiment of the present invention, as shown in FIG. 5 , on the basis of the ES-SAGD horizontal injection-production well pair, the horizontal injection wells are kept in an open state at intervals, and the horizontal production wells directly below them are closed; The horizontal injection wells of the adjacent horizontal injection wells are closed, and the horizontal production wells of the adjacent horizontal injection-production wells remain open; the horizontal injection wells that remain open and the adjacent horizontal production wells are used as solvent recovery well groups, and non-condensable injection wells are injected into the horizontal injection wells. Gas and/or steam, mixed gas is produced from adjacent horizontal production wells.

In the present invention, when injecting non-condensable gas, the gas injection rate of the horizontal injection well is preferably 20000-30000 m ³ /d; when injecting steam, in terms of cold water equivalent, the gas injection rate of the horizontal injection well is preferably It is 100～600m ³ /d.

In the present invention, when the injection wells are vertical injection wells, the method for deploying the solvent recovery well group preferably includes: closing the horizontal injection wells, and arranging a plurality of vertical injection wells on both sides perpendicular to the pair of horizontal injection and production wells, Vertical injection wells and adjacent horizontal production wells form solvent recovery well groups. In the present invention, in the same solvent recovery well group, the vertical distance between the vertical injection well and the horizontal production well is preferably 5-20 m; the horizontal distance between the vertical injection well and the horizontal production well is preferably 35-20 m. 50m. In the present invention, the distance between the vertical injection wells is preferably 150-200 m. In the present invention, the vertical injection wells form well rows; the spacing between the vertical injection wells and the well rows is preferably 70-100 m.

In the present invention, the vertical injection well has better recovery effect than the horizontal injection well, because the vertical injection well is located in the upper part of the oil reservoir, which is beneficial to increase the sweeping range of the injected gas.

In the present invention, when injecting non-condensable gas, the gas injection rate of the vertical injection well is preferably 400-600 m ³ /d; when injecting steam, in terms of cold water equivalent, the gas injection rate of the vertical injection well is preferably 20 to 120 m ³ /d (cold water equivalent).

In the present invention, the non-condensable gas refers to the gas that does not condense under the temperature and pressure conditions of the oil well, preferably including one or more of N ₂ , O ₂ , CH ₄ , CO ₂ , air and flue gas , more preferably CH ₄ or CO ₂ .

In the present invention, when the solvent to be recovered is a water-oil-soluble solvent, steam is injected after the non-condensable gas is injected into the injection well. In the present invention, the water-oil amphoteric solvent is preferably an ether solvent, more preferably dimethyl ether. By adopting the method in the present invention, the recovery efficiency of the water-oil-soluble solvent can be further improved.

In the present invention, in the recovery stage, the injection pressure of the non-condensable gas and/or steam is gradually decreased. In the present invention, the stepwise decreasing method preferably includes: decreasing the injection pressure by 5-20% every preset time period until the injection pressure decreases to the initial reservoir pressure. In the present invention, the preset time period is preferably 3-6 months. In the present invention, the pressure difference between the injection well and the horizontal production well is 50-200 kPa; the pressure of the injection well is greater than the pressure of the horizontal production well.

In the present invention, in the process of non-condensable gas or steam injection, the injection pressure is gradually reduced, and the recovery efficiency of the solvent is further increased.

After the mixed gas is recovered from the horizontal production well, the present invention separates the solvent gas and the non-condensable gas in the mixed gas for recycling. In the present invention, the recycling preferably includes: performing solvent-assisted steam oil recovery on the separated solvent gas; injecting the separated non-condensable gas into the solvent recovery well group for solvent recovery. In the present invention, when the content of the solvent gas in the mixed gas is lower than the set value, the injection of the non-condensable gas and/or steam is stopped. In the present invention, the set value is preferably that the content of the solvent gas is 3 to 8 wt %.

In the present invention, the method for solvent-assisted steam oil recovery preferably includes solvent-assisted steam flooding (ES-SAGD), solvent-assisted steam huff and puff or steam-assisted gravity drainage (SAGD).

In the present invention, it is preferable to satisfy the condition of shutting down the horizontal injection well that the oil production decreases while the gasoline ratio increases, and more preferably, the oil production keeps dropping and the gasoline ratio keeps increasing for more than 50 consecutive days.

In the present invention, the crude oil viscosity of the heavy oil in the formation is preferably greater than 10000 mPa·s, more preferably 15000 mPa·s. In the present invention, heavy oil is recovered by injecting solvent gas, and then solvent is recovered by injecting non-condensable gas and/or steam, so as to achieve the purpose of recycling solvent.

The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

The reservoir in this example is 280m deep, the original reservoir pressure is 1800kPa, the porosity is 0.3, the horizontal permeability is 5000mD, the average thickness of the oil layer is 30m, and the crude oil viscosity is 15000mPa·s under initial reservoir conditions.

Deployment of horizontal injection-production well pattern: ES-SAGD is used for the horizontal injection-production well pattern. The location of the well pattern is shown in Figure 1. The vertical spacing between the horizontal injection well and the horizontal production well in the same horizontal injection-production well pair is 5m. The production well is 1m away from the bottom of the oil layer, the spacing between adjacent horizontal injection and production well pairs is 100m, and the length of the horizontal injection well and the horizontal production well is 800m. In the ES-SAGD process, the injection pressure was 2300 kPa, hexane (C6) and steam were injected together, the mole fraction of C6 was 2%, and the steam dryness was 0.95.

In the later stage of ES-SAGD, the oil production decreased and the gasoline ratio increased. The injection of steam and solvent gas was stopped, and the solvent recovery well group was deployed on the basis of the original horizontal well injection-production well pattern, as shown in Fig. 2. The horizontal injection wells of the production well pair are closed; the horizontal production wells below the horizontal injection wells that remain open are closed, and the horizontal production wells of the horizontal injection-production well pairs are solvent recovery production wells; The adjacent horizontal production wells form solvent recovery well groups, establish solvent gas displacement channels, and carry out solvent recovery. In the solvent recovery stage, inject CH ₄ , the injection pressure starts from 2300kPa, and decreases by 50kPa every 3 months, until the injection pressure drops to the initial reservoir pressure of 1800kPa, or the solvent content at the production end is lower than 3-8wt%, stop injecting CH _4. Shut off all horizontal injection wells and horizontal production wells.

Figure 3 shows the mass of solvent remaining in the reservoir during ES-SAGD recovery and during solvent recovery. It can be seen from FIG. 3 that the present invention can recover 86% of the solvent remaining in the oil reservoir by depressurizing and injecting non-condensable gas.

Example 2

In the ES-SAGD oil production stage, the reservoir conditions, horizontal well injection-production well pattern deployment, and operating conditions are the same as those in Example 1. In the solvent recovery stage, several vertical injection wells are deployed on both sides of the horizontal injection-production well, and the original horizontal injection well is closed at the same time, and the original horizontal production well is used as the production well in the solvent recovery stage. In the solvent recovery stage, CO ₂ is injected into the vertical injection well, the injection pressure is 2300kPa, and the injection pressure is decreased by 50kPa every 3 months until the injection pressure drops to the initial reservoir pressure of 1800kPa, or the solvent content at the production end is lower than 3-8wt%, The _CO2 injection was stopped and all vertical injection and horizontal production wells were shut down.

Using the method of this embodiment, the solvent recovery rate is 88%.

Example 3

In the ES-SAGD oil production stage, the reservoir conditions and the horizontal well injection-production well pattern are the same as those in Example 1, and the injected solvent is dimethyl ether. In the solvent recovery stage, the solvent recovery well group in Example 1 is used in the well layout, and CH ₄ is injected into the horizontal injection well. The injection pressure starts from 2300kPa and decreases by 50kPa every 3 months until the injection pressure drops to the initial reservoir pressure. 2000kPa, then inject steam, the injection pressure decreases by 50kPa every 3 months, until the injection pressure drops to the initial reservoir pressure of 1800kPa, or the solvent content at the production end is lower than 3-8wt%, stop injecting steam, close all horizontal injection wells and Horizontal production wells. Using the method of this embodiment, the recovery rate of dimethyl ether is 93%.

The invention can effectively improve the recovery degree of the solvent, promote the recycling of the solvent, and improve the economic benefit of ES-SAGD.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (10)

1. A solvent recovery method applicable to the later stage of solvent-assisted steam oil recovery, comprising the following steps: (1) In the later stage of solvent-assisted steam oil recovery, a solvent recovery well group is deployed, and each solvent recovery well group includes an injection well and at least one horizontal production well; the horizontal depth of the injection well is less than that of the horizontal production well depth; the injection well and the horizontal production well are not on the same vertical line; (2) Non-condensable gas and/or steam are injected simultaneously or alternately through injection wells, and mixed gas is recovered from horizontal production wells; The pressure difference between the well and the horizontal production well is 50-200kPa; (3) Separating the solvent gas and the non-condensable gas in the mixed gas and recycling; when the content of the solvent gas is lower than the set value, stop injecting the non-condensable gas and/or steam. 2 . The solvent recovery method according to claim 1 , wherein the injection well is a horizontal injection well or a vertical injection well. 3 . 3 . The solvent recovery method according to claim 1 , wherein when there are two horizontal production wells in each group of the solvent recovery well group, the injection well is located at the midpoint of the connecting line between the two horizontal production wells. 4 . above. 4 . The solvent recovery method according to claim 1 , wherein the non-condensable gas comprises one or more of N ₂ , O ₂ , CH ₄ , CO ₂ , air and flue gas. 5 . 5 . The solvent recovery method according to claim 1 , wherein when the solvent to be recovered is a water-oil soluble solvent, after injecting non-condensable gas into the injection well, steam is injected. 6 . 6 . The solvent recovery method according to claim 1 , wherein the method for gradually decreasing the injection pressure comprises: decreasing the injection pressure by 5-20% at every preset time period until the injection pressure decreases to the initial stage of the reservoir. 7 . pressure. 7. The solvent recovery method according to claim 2, wherein when the injection well is a horizontal injection well, in the same solvent recovery well group, the vertical distance between the horizontal injection well and the horizontal production well is 4-6m; the horizontal distance between the horizontal injection well and the horizontal production well is 70-100m. The solvent recovery method according to claim 2 or 7, characterized in that, when non-condensable gas is injected, the gas injection rate of the horizontal injection well is 20000-30000 m ³ /d; When steam is injected, in terms of cold water equivalent, the gas injection rate of the horizontal injection well is 100-600 m ³ /d. 9 . The solvent recovery method according to claim 2 , wherein when non-condensable gas is injected, the gas injection rate of the vertical injection well is 400-600 m ³ /d; 9 . When injecting steam, in terms of cold water equivalent, the gas injection rate of the vertical injection well is 20-120 m ³ /d. 10 . The solvent recovery method according to claim 1 , wherein the recycling comprises: performing solvent-assisted steam oil recovery on the separated solvent gas; injecting the separated non-condensable gas into a solvent recovery well group for solvent recovery. 11 . .

Images