CN113464087B - A selective water shutoff method for high water cut oil wells in bottom water reservoirs - Google Patents

Abstract

The invention discloses a selective water plugging method for a bottom water reservoir high-water-cut oil well. And then the foam in the high permeability layer is cleaned by back drainage, so that the aims of temporarily blocking the low permeability and enabling the subsequent water plugging agent to enter the high permeability layer in an oriented manner are fulfilled. And then injecting a water shutoff agent, wherein the water shutoff agent establishes an artificial partition plate at a proper position in the water production layer to prevent bottom water from rising and inhibit bottom water coning. And finally, displacing the water shutoff agent out of a certain position near the well area through polymer solution displacement, ensuring certain liquid production capacity after plugging, preventing the injection pressure of the water injection well from being too high, and prolonging the effective period of the water shutoff agent. Under the combined action of the steps, the directional water shutoff is realized, and the problem that the yield is sharply reduced after the oil well is exposed to water in the early stage is solved.

Description

A selective water shutoff method for high water cut oil wells in bottom water reservoirs

technical field

The invention relates to the field of oil recovery engineering in bottom water reservoirs, in particular to a selective water shutoff method for high water content oil wells in bottom water reservoirs.

Background technique

After the oil and gas with water bodies migrate and accumulate, due to gravity differentiation, the oil in the reservoir is always above the water, and according to the oil-water contact relationship, such reservoirs can be divided into edge water reservoirs and bottom water reservoirs. Compared with other types of reservoirs, the oil-bearing area of the edge-bottom water reservoir will be in direct contact with the water body. In the middle and early stages of oilfield development, the edge and bottom water will provide certain energy for the development of the oil reservoir, making the oil field stable; The water tongue or cone advance makes the oil well start to see water, the water-free oil production period is shortened, the water cut rises faster, the oil production rate decreases, and the recovery degree decreases, so the reservoir development effect becomes worse. Therefore, how to suppress the intrusion and coning of the natural water body of edge and bottom water reservoirs is the focus of its development.

Traditional water shutoff methods mainly include mechanical water shutoff and chemical water shutoff. Mechanical water plugging can accurately seal the water-producing layer, and when the follow-up conditions permit, the blockage can be unblocked to continue oil production, well washing and other operations, but it requires an accurate understanding of the downhole water outlet point/layer, and the cost is high. Chemical water plugging is mainly to plug the water-producing layer by injecting chemicals downhole. Chemical water shutoff includes selective water shutoff and non-selective water shutoff. The water shutoff agent used in non-selective water shutoff can block both water layer and oil layer without selectivity. During construction, first find out the water level, select an appropriate process string, separate the oil layer from the water layer, and then squeeze the water shutoff agent into the high water-bearing layer to achieve the purpose of plugging; the non-selective water shutoff of oil wells is mainly used for Cement slurry, resin, etc. block the outlet layer at one time. Selective water shutoff is the use of chemical water shutoff agents to greatly reduce the permeability of the water phase, and the chemical water shutoff measures that reduce or do not reduce the permeability of the oil (gas) phase are called selective water shutoff; the mechanism is the use of water shutoff agents. Oil, water and rock properties, as well as the differences between oil-producing and water-producing layers, are used to achieve selective water shutoff.

Patent CN104629698A discloses a water plugging method for edge and bottom water reservoirs, which uses nitrogen-enhanced gel plugging agent to plug high-permeability layers, but if the injection pressure exceeds the start-up pressure of low-permeability layers, the plugging agent will flow into low-permeability layers , causing damage to the low-permeability layer. Therefore, it is necessary to invent a selective water shutoff method for high water cut oil wells in bottom water reservoirs.

Contents of the invention

The purpose of the present invention is to provide a selective water shutoff method for high water content oil wells in bottom water reservoirs in view of the current problem of difficult water shutoff and poor water shutoff effect in edge and bottom water reservoirs.

The method for selective water shutoff of high water-cut oil wells in bottom water reservoirs provided by the present invention has the following steps:

S1. Inject nitrogen gas into the formation at high speed and high pressure through the injection well, press down the bottom water cone, increase the pressure of the oil-producing layer, and make the follow-up water shutoff agent preferentially enter the high permeability.

S2. After pressing down the bottom hole water cone, inject four kinds of mixed solutions of foaming agent, polymer solution, foam stabilizer and cross-linking agent into the well, and mix the mixed solution with the nitrogen injected in step S1 in the porous medium, Forms a gel foam.

The polymer solution is a polyacrylamide solution with a mass percent content of 0.3%-0.4%. The foaming agent is sodium fatty alcohol ether sulfate. The foam stabilizer is hydrophobically modified nano- _SiO2 particles modified by N,N-dimethylferrocenyl hexadecylmethylammonium bromide. The cross-linking agent is a composite cross-linking agent composed of organic chromium and phenolic resin in a mass ratio of 3:5; the cross-linking time of the composite cross-linking agent and polyacrylamide is less than the half-life of the foam formed by the foaming agent and gas.

S3. Start the well and flow back, change the small oil nozzle, and use the low production pressure difference to open the well for 3-8 hours to promote the formation of foam. At the same time, the low production pressure difference makes the foam in the high permeability layer flow back preferentially, and at the same time temporarily plug the low permeability layer , which is beneficial for the follow-up water blocking agent to preferentially enter the hyperpermeable layer.

S4. Inject the water shutoff agent, the water shutoff agent enters the water production layer in a directional manner, and establishes an artificial partition to realize intelligent selective water shutoff.

The screening of the water blocking agent needs to meet the following conditions at the same time:

(1) The water blocking agent is solidified or gelled as a whole;

(2) The water blocking agent is in the form of molecular or ion dispersion, and the reaction time is long;

(3) The plugging agent used near the well must ensure no production under large production pressure difference;

(4) The plugging agent with weak strength is used far from the well, and the plugging agent with high strength is used near the well.

The amount of water blocking agent can be calculated as follows:

q＝π(2r) ² hφ

In the formula: q-total amount of water blocking agent, m ³ ; r-plugging radius, m; φ-reservoir porosity, %; h-thickness of diaphragm, m.

S5. Use polymer solution for over-displacement to prevent the injection pressure of the water injection well from being too high and prolong the validity period of the water shutoff agent.

Through the above five steps, temporary plugging can be achieved to maintain the low-permeability oil layer, and at the same time, the ability of the water blocking agent to enter the high-permeability water-producing layer can be improved, and an artificial partition can be formed at a suitable position to effectively block water.

Compared with the prior art, the benefits of the present invention are:

(1) Nitrogen gas is injected downhole at high speed and high pressure, and the nitrogen gas enters to press down the water cone, so that the subsequent water shutoff agent can enter the high permeability layer;

(2) The nitrogen used for the compression of the cone becomes the gas source for the subsequent injection of the foam temporary plugging agent. The foam generated after the injection of the foaming agent can enhance the effect of the cone compression; the density of the foam formed by injecting the foaming agent solution is higher than that of nitrogen, and enters the produced water After the formation, it can further strengthen the cone pressure effect, and can temporarily plug and protect the oil layer to ensure that the follow-up water blocking agent can accurately enter the high-permeability water-producing layer;

(3) The injected mixed solution contains a foaming agent, a polymer solution, a foam stabilizer and a crosslinking agent to form a gel foam, which effectively increases the stability and strength of the foam, and at the same time increases its oil resistance.

Other advantages, objectives and features of the present invention will partly be embodied through the following descriptions, and partly will be understood by those skilled in the art through the study and practice of the present invention.

Description of drawings

Figure 1 is a schematic diagram of the stratum under the initial condition of water flooding.

Fig. 2 is a schematic diagram of formation conditions after nitrogen injection pressure cone.

Fig. 3 is a schematic diagram of the stratum after injecting the mixed solution of foaming agent, polymer solution, foam stabilizer and crosslinking agent.

Figure 4 is a schematic diagram of the formation situation when the oil nozzle is small and the flowback is low production pressure difference.

Figure 5 is a schematic diagram of the stratum after injection into the artificial partition.

In the figure, 1-low-permeability oil-producing layer, 2-high-permeability water-producing layer, 3-bottom water body, 4-nitrogen injection, 5-condensate produced after injection of foaming agent, polymer solution, foam stabilizer and cross-linking agent Adhesive foam, 6-artificial partition formed after injection of water blocking agent.

detailed description

The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described here are only used to illustrate and explain the present invention, and are not intended to limit the present invention.

Example 1

The selective water shutoff method of the high water-cut oil well in the bottom water reservoir of the present invention is specifically as follows:

As shown in Fig. 1, with long-term water injection production, the oil well enters the stage of high water cut, and the bottom water invades seriously, resulting in water cone and water flooding in the lower high permeability layer.

At this time, as shown in Figure 2, nitrogen gas is injected downhole at high speed and high pressure through the tubing. At this time, nitrogen gas preferentially enters the hyperpermeable layer to increase the pressure of the hyperpermeable layer. The entry of nitrogen gas drives the intrusive water to the lower part to reach the pressure of the water cone. The purpose is to create conditions for the entry of subsequent water blocking agents. Since nitrogen is injected into the formation at high speed and high pressure, some nitrogen enters the low-permeability layer, and this part of nitrogen further increases the intralayer pressure of the low-permeability layer itself. Compared with the high-permeability layer, the pressure conduction of the low-permeability layer is slower per unit time, and the pressure drop rate is slower, which leads to the gradual increase of the pressure difference between the high- and low-permeability layers after gas injection, which makes the subsequent water plugging The agent can enter the high-permeability water-producing layer in a certain direction under a certain injection pressure.

Then inject the mixed solution (mixed solution of foaming agent, polymer solution, foam stabilizer and crosslinking agent) downhole at high speed, as shown in Fig. 3 . After the foaming agent enters the formation, it mixes with the nitrogen injected from the previous plug to form a gel foam in the porous medium. After the foam is formed in the hyperpermeable layer, the density of the foaming agent and the foam itself is greater than that of nitrogen, which can further strengthen the nitrogen pressure. cone effect. At the same time, due to the formation of foam in the high-permeability layer, which reduces its own permeability, the mixed solution begins to enter the low-permeability layer, and mixes with nitrogen in the low-permeability layer to generate foam, which produces temporary plugging protection for the low-permeability layer. Preferably, the polymer solution may be 0.3%-0.4% HPAM solution. The foaming agent is fatty alcohol ether sulfate sodium salt (AES). The foam stabilizer is hydrophobically modified nano-SiO ₂ particles modified with N,N-dimethylferrocenyl hexadecylmethylammonium bromide (Fc16AB). The crosslinking agent is a composite crosslinking system (organic chromium: phenolic resin = 3:5). The cross-linking time of the composite cross-linking agent and polyacrylamide is shorter than the half-life of the foam formed by the foaming agent and gas, ensuring that the cross-linking agent and polyacrylamide can undergo cross-linking reaction when only a small amount of foam is broken.

After injecting a certain amount of mixed solution, replace the nozzle with a small oil nozzle, and start the production for 3-8 hours with low production pressure difference, as shown in Figure 4. Both the high-permeability layer and the low-permeability layer tend to be produced during flowback, and the fluid in the formation flows toward the wellbore. Since the viscosity of nitrogen gas is much smaller than that of the mixed solution and the gel foam produced, nitrogen migration is easier. Move from a little distance away from the wellbore to the vicinity of the wellbore and further fully mix with foaming agent and other solutions to improve the quality of foam generation and strengthen the effect of temporary plugging and cone pressure; During production with low production pressure difference, the foam in the high-permeability layer will flow back preferentially, and the pressure in the high-permeability layer will decrease, which will increase the pressure difference between the low-permeability layer and the high-permeability layer, which is beneficial for the subsequent water shutoff agent to enter the high Seepage layer.

As shown in Figure 5, after the above steps, the water blocking agent is injected into the formation to establish an artificial partition, and the water blocking agent is directed into the water-producing layer to realize intelligent and selective water blocking. The screening conditions of the water blocking agent are as follows:

(1) It is an integral water blocking agent, that is, the blocking agent is solidified or gelled as a whole.

(2) The water blocking agent used is preferably in the form of molecular or ion dispersion, and the reaction time should be long enough.

(3) The water blocking agent should be combined, and the strength of the blocking agent should be as high as possible.

(4) The water shutoff agent used near the well must ensure no production under large production pressure difference.

(5) The configuration and construction of the water blocking agent should be simple and easy to operate, and the construction risk is small.

(6) The cost of water blocking agent is low and the source is wide.

(7) The plugging agent for establishing the partition can use weak water blocking agent in the far well, and use high strength water blocking agent in the near well.

The amount of water blocking agent can be calculated as follows:

q＝π(2r) ² hφ

In the formula: q-total dosage of plugging agent, m ³ ; r-plugging radius, m; φ-reservoir porosity, %; h-baffle thickness, m.

Finally, polymer solution is used for over-displacement, which also displaces the water-blocking agent from a certain position near the wellbore to ensure a certain liquid production capacity after plugging, prevent the injection pressure of the water injection well from being too high, and prolong the life of the water-blocking agent. expiration date.

Under the combined action of the above steps, intelligent selective water shutoff of high water cut oil wells in bottom water reservoirs can be realized, and the problem of sharp decline in production after water breakthrough in oil wells can be solved.

Example 2

The water shutoff method of the present invention is applied to a specific high water cut oil well in a certain bottom water reservoir. The specific method is as follows:

S1. Inject nitrogen gas into the well at high speed and high pressure, so that nitrogen gas enters the high-permeability water-producing layer. The entry of nitrogen gas drives the intrusive water to the lower part, achieving the purpose of pressing down the water cone and providing conditions for subsequent operations. According to the study of the gel foam system, the optimum nitrogen dosage is twice the volume of the mixed solution injected in step S2, the volume calculation formula of the mixed solution: Q=πR ² hφ, where R=10m, h=2m, φ=0.3 . The amount of nitrogen injection is converted to ground volume using the state equation PV=nRT, the gas injection rate is controlled at 600-900m ³ /h, and the gas injection pressure is higher than the formation pressure.

S2. Inject a mixed solution of foaming agent, HPAM, cross-linking agent and foam stabilizer into the well, wherein the foaming agent is fatty alcohol ether sulfate sodium salt with a mass concentration of 1%; the mass concentration of HPAM is 0.3%-0.4% ; The cross-linking agent is a composite cross-linking system (organic chromium: phenolic resin = 3:5). The cross-linking time of the composite cross-linking agent and polyacrylamide is less than the half-life of the foam formed by the foaming agent and gas, so that the cross-linking agent can react with polyacrylamide when only a small amount of foam is broken, and the mass concentration is 0.1%; Foam stabilizer is the use of N,N-dimethylferrocenyl hexadecyl methylammonium bromide (Fc16AB) modified hydrophobically modified nano-SiO ₂ particles, the mass concentration is 0.1%. The injection volume of the mixed solution is calculated according to the formula in step S1, and the injection volume is about 188.4 m ³ .

S3. After the injection of the mixed solution is completed, change the oil nozzle to a production pressure difference slightly greater than the start-up pressure difference of the hyperpermeable layer, and open the well for 3-8 hours to fully mix the nitrogen in the formation with the foaming agent, and discharge the hyperpermeable Inner foam.

S4. After completing the above steps, inject the water shutoff agent into the partition, and the water shutoff agent adopts the temperature-resistant, salt-resistant and high-temperature self-crosslinking in-situ polymerized water shutoff gel in the patent CN104449618B. The amount of water shutoff agent is calculated using the formula q=π(2r) ² hφ, where r=10m, h=2m, φ=0.3, and the injection volume is about 753.6m ³ . Since the low-permeability layer is temporarily plugged, after the plugging agent is injected into the formation, it will only enter the high-permeability layer and extend laterally in the high-permeability layer to establish an artificial partition at a suitable position. The breakthrough pressure gradient of the plugging agent in the core is greater than 9MPa/m, and the plugging rate reaches 99%.

S5. Use HPAM polymer solution for over-displacement. The viscosity of the over-displacement fluid is greater than that of the displaced fluid. Over-displacement will also displace the plugging agent from a certain position near the wellbore to ensure a certain fluid production capacity after plugging and prevent water injection wells. The injection pressure is too high and the validity period of the water shutoff agent is extended.

Using the above-mentioned technology, the water content of the well is reduced by 18.9%, and the water plugging effect is good.

In summary, the water plugging method of the present invention is to inject a mixed solution of foaming agent, polymer solution, foam stabilizer and crosslinking agent after injecting nitrogen pressure cone into the wellbore to form gel foam in the formation. Then, the foam in the high-permeability layer is cleaned by flowback to achieve the purpose of temporary plugging and low-permeability, so that the subsequent water blocking agent can enter the high-permeability layer in a directional manner. Next, water shutoff agent is injected, and water shutoff agent is used to establish artificial partitions at appropriate positions in the water-producing layer to prevent bottom water from escaping and suppress bottom water coning. Finally, through polymer solution over-displacement, the water blocking agent is displaced from a certain position near the wellbore to ensure a certain liquid production capacity after plugging, prevent the injection pressure of the water injection well from being too high, and prolong the validity period of the water blocking agent.

The above description is only a preferred embodiment of the present invention, and does not limit the present invention in any form. Although the present invention has been disclosed as above with preferred embodiments, it is not intended to limit the present invention. Anyone familiar with this field Those skilled in the art, without departing from the scope of the technical solution of the present invention, can use the technical content disclosed above to make some changes or modify equivalent embodiments with equivalent changes. Any simple modifications, equivalent changes and modifications made to the above embodiments by the technical essence still belong to the scope of the technical solution of the present invention.

Claims (7)

1. The selective water plugging method for the high-water-cut oil well of the bottom water reservoir is characterized by comprising the following steps

S1, injecting nitrogen into a stratum through an injection well, and pressing down a well bottom water cone;

s2, injecting four mixed solutions of a foaming agent, a high molecular solution, a foam stabilizer and a cross-linking agent into the well, mixing the mixed solution with the nitrogen injected in the step S1 in a porous medium, and forming gel foam in the stratum;

s3, opening a well for flowback, replacing a small oil nozzle, opening the well for production for 3-8 hours at low production pressure difference, promoting the formation of foam, and simultaneously leading the foam of a high-permeability layer to preferentially flowback due to the low production pressure difference so as to temporarily block the low-permeability layer;

s4, injecting a water shutoff agent, enabling the water shutoff agent to directionally enter a water production layer, and establishing an artificial partition plate to realize intelligent selective water shutoff;

and S5, performing displacement, preventing the injection pressure of the water injection well from being too high, and prolonging the validity period of the water shutoff agent.

2. The selective water plugging method for the bottom water reservoir high water cut oil well as claimed in claim 1, wherein the polymer solution is 0.3-0.4% by mass of polyacrylamide solution.

3. The selective water shutoff method for the bottom water reservoir high water cut oil well according to claim 2, characterized in that the foaming agent is a sodium salt of fatty alcohol ether sulfate.

4. The selective water shutoff method for the bottom water reservoir high-water-cut oil well as defined in claim 3, characterized in that the foam stabilizer is nanometer SiO hydrophobically modified by N, N-dimethyl ferrocenyl hexadecyl methyl ammonium bromide ₂ And (3) granules.

5. The selective water shutoff method for the bottom water reservoir high water cut oil well according to claim 4, characterized in that the cross-linking agent is a composite cross-linking agent of organic chromium and phenolic resin according to a mass ratio of 3; the crosslinking time of the composite crosslinking agent and the polyacrylamide is less than the half-life of the foam formed by the foaming agent and the gas.

6. The selective water shutoff method for the bottom water reservoir high water cut oil well according to claim 1, wherein the amount of the water shutoff agent is calculated according to the following formula:

q＝π(2r) ² hφ

in the formula: q-total amount of water shutoff agent, m ³ (ii) a r-plugging radius, m; phi-oil layer porosity,%; h-spacer thickness, m.

7. The selective water plugging method for the bottom water reservoir high water cut oil well according to claim 6, wherein the water plugging agent screening simultaneously needs to meet the following conditions:

(1) The water shutoff agent is integrally solidified or gelatinized;

(2) The water shutoff agent is in a molecular or ion dispersion form, and the reaction time is long;

(3) The plugging agent used near the well must ensure that the plugging agent is not produced under large production pressure difference;

(4) The far well uses a plugging agent with weak strength, and the near well uses a plugging agent with high strength.

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