Background
After the oil and gas with water body are transferred into reservoir, the oil and gas are always on the top and under the bottom of the reservoir due to the action of gravity differentiation, and the reservoir can be divided into side water reservoir and bottom water reservoir according to the contact relation of oil and water. Compared with other types of reservoirs, the oil-bearing area of a bottom-edge water reservoir can be in direct contact with the water body. In the middle and early stages of oil field development, edge bottom water can provide certain energy for oil reservoir development, so that the oil field is stable in yield; however, as the production continues, the bottom water further invades the oil layer, which causes the front edge of the oil water to be broken through, the formation water to be pushed or tapered, the oil well starts to see water, the waterless oil production period is shortened, the water content is increased rapidly, the oil production is reduced, the production degree is reduced, and the oil deposit effect is poor. Therefore, how to inhibit invasion and coning of the own water body of the bottom water reservoir is the key point of development.
The traditional water plugging method mainly comprises mechanical water plugging and chemical water plugging. Mechanical water plugging can accurately plug a water producing layer, and unsealing is carried out when subsequent conditions allow for operations such as oil production, well flushing and the like, but accurate knowledge of downhole water outlet points/layers is required, and the cost is high. The chemical water plugging is mainly implemented by injecting chemicals into the underground to plug a water producing layer. The chemical water shutoff comprises selective water shutoff and non-selective water shutoff. The water shutoff agent used for non-selective water shutoff can cause blockage to both a water layer and an oil layer, and has no selectivity. During construction, a water layer position is found out, a proper process pipe column is selected, an oil layer is separated from a water layer, and then the water plugging agent is extruded into a high water-bearing layer to achieve the purpose of plugging; the non-selective water plugging of the oil well is mainly used for plugging a water outlet layer by cement paste, resin and the like at one time. The selective water shutoff is a chemical water shutoff measure which utilizes a chemical water shutoff agent to greatly reduce the water phase permeability and reduce or not reduce the oil (gas) phase permeability and is called selective water shutoff; the mechanism is that the water shutoff agent utilizes the properties of oil, water and rock and the difference between oil outlet layers and water outlet layers to achieve selective water shutoff.
Patent CN104629698A discloses a water plugging method for bottom water reservoir, which uses nitrogen to strengthen the gel plugging agent to plug the high permeability layer, but if the injection pressure exceeds the start pressure of the low permeability layer, the plugging agent will flow into the low permeability layer, causing damage to the low permeability layer. Therefore, a selective water plugging method for a bottom water reservoir high-water-cut oil well needs to be invented.
Disclosure of Invention
The invention aims to provide a selective water plugging method for a bottom water reservoir high-water-cut oil well, aiming at the problems of difficult water plugging and poor water plugging effect of the existing bottom water reservoir.
The invention provides a selective water plugging method for a bottom water reservoir high-water-cut oil well, which comprises the following steps:
and S1, injecting nitrogen into the stratum at high speed and high pressure through the injection well, pressing down a water cone at the bottom of the well, increasing the pressure of the produced oil layer, and enabling the subsequent water shutoff agent to enter high permeability preferentially.
S2, after a bottom water cone is pressed down, mixed solution of foaming agent, high molecular solution, foam stabilizer and cross-linking agent is injected into the well, and the mixed solution is mixed with the nitrogen injected in the step S1 in the porous medium to form gel foam in the stratum.
The high molecular solution is polyacrylamide solution with the mass percentage content of 0.3-0.4%. The foaming agent is fatty alcohol ether sodium sulfate. The foam stabilizer is hydrophobic modified nano SiO modified by brominated N, N-dimethyl ferrocenyl hexadecyl methyl ammonium salt2And (3) granules. The cross-linking agent is organic chromium and phenolThe composite cross-linking agent comprises aldehyde resin and a cross-linking agent, wherein the mass ratio of the aldehyde resin to the cross-linking agent is 3: 5; the crosslinking time of the composite crosslinking agent and the polyacrylamide is less than the half-life of a foam formed by the foaming agent and the gas.
And S3, opening the 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, leading the foam of the high-permeability layer to be preferentially flowback at low production pressure difference, and simultaneously temporarily plugging the low-permeability layer, so that the subsequent water plugging agent is favorably and preferentially entering the high-permeability layer.
And S4, injecting a water shutoff agent, wherein the water shutoff agent directionally enters a water production layer, and an artificial partition plate is established to realize intelligent selective water shutoff.
The screening of the water shutoff agent simultaneously needs to have the following conditions:
(1) the water shutoff agent is integrally solidified or gelled;
(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 a large production pressure difference;
(4) the far well uses the plugging agent with weak strength, and the near well uses the plugging agent with high strength.
The dosage of the water shutoff agent can be calculated according to the following formula:
q=π(2r)2hφ
in the formula: q-total amount of water shutoff agent, m3(ii) a r-plugging radius, m; phi-oil layer porosity,%; h-spacer thickness, m.
And S5, replacing by adopting a polymer solution, preventing the injection pressure of the water injection well from being overhigh, and prolonging the effective period of the water shutoff agent.
Through the five steps, temporary plugging can be realized to keep a low-permeability oil layer, the capability of the water plugging agent for directionally entering a high-permeability water production layer is improved, and an artificial partition plate is formed at a proper position to effectively plug water.
Compared with the prior art, the invention has the advantages that:
(1) injecting nitrogen into the underground at high speed and high pressure, wherein the nitrogen enters to press the water cone, so that the subsequent water plugging agent can conveniently enter a high permeability layer;
(2) nitrogen used by the pressure cone becomes an air source for injecting the foam temporary plugging agent subsequently, and foam generated after the foaming agent is injected can enhance the effect of the pressure cone; by injecting a foaming agent solution and forming foam with density higher than that of nitrogen, the cone pressing effect can be further enhanced after the foam enters a water producing layer, a protective oil layer can be temporarily blocked, and a subsequent water blocking agent is ensured to accurately enter a high-permeability water producing layer;
(3) the injected mixed solution contains foaming agent, high molecular solution, foam stabilizer and cross-linking agent simultaneously to generate gel foam, thereby effectively increasing the stability and strength of the foam and simultaneously increasing the oil resistance of the foam.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Detailed Description
The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.
Example 1
The selective water plugging method for the bottom water reservoir high-water-cut oil well comprises the following specific steps:
as shown in figure 1, with the long-time water injection production, the oil well enters a high water-cut stage, bottom water invasion is serious, water cones are generated, and water flooding occurs in a lower high-permeability layer.
At the moment, as shown in fig. 2, nitrogen is injected into the underground at high speed and high pressure through the oil pipe, at the moment, the nitrogen preferentially enters the high-permeability layer, the pressure of the high-permeability layer is improved, the invaded water is driven to the lower part by the entering of the nitrogen, the purpose of pressing the water cone downwards is achieved, and conditions can be created for the entering of the subsequent water plugging agent. Since nitrogen is injected into the formation at high velocity and high pressure, a portion of the nitrogen also enters the hypotonic layer, which further increases the pressure within the hypotonic layer itself. Compared with a high permeability layer, the low permeability layer has slower pressure conduction and slow pressure drop speed in unit time, which leads to the gradual increase of the difference of the internal pressures of the high and low permeability layers after gas injection, so that the subsequent water plugging agent can directionally enter a high permeability water production layer under certain injection pressure.
Then, a mixed solution (a mixed solution of a foaming agent, a polymer solution, a foam stabilizer and a crosslinking agent) is injected into the well at a high speed, as shown in fig. 3. After the foaming agent enters the stratum, the foaming agent and nitrogen injected from the upper section of plug are mixed in the porous medium to form gel foam, and after foam is formed in the high permeability layer, the foaming agent and the foam have the density larger than that of the nitrogen, so that the effect of the nitrogen pressure cone can be further enhanced. Meanwhile, the high-permeability layer forms foam, so that the permeability of the high-permeability layer is reduced, the mixed solution starts to enter the low-permeability layer and is mixed with nitrogen in the low-permeability layer to generate foam, and temporary blocking protection is generated on the low-permeability layer. Preferably, the polymer solution may be a 0.3% to 0.4% HPAM solution. The foaming agent is fatty alcohol ether sodium sulfate (AES). The foam stabilizer is hydrophobically modified nano SiO modified by using brominated N, N-dimethylferrocenyl hexadecyl methyl ammonium salt (Fc16AB)2And (3) granules. The cross-linking agent is a composite cross-linking system (organic chromium: phenolic resin: 3: 5). The crosslinking time of the composite crosslinking agent and the polyacrylamide is less than the half-life of foam formed by the foaming agent and gas, so that the crosslinking agent and the polyacrylamide can be subjected to crosslinking reaction only when a small amount of foam is broken.
After a certain amount of mixed solution is injected, the choke nozzle is changed, and the well is opened to produce for 3-8 hours at low production pressure difference, as shown in figure 4. During flowback, the high-permeability layer and the low-permeability layer both have output trends, fluid in the stratum flows towards the direction of a shaft, the nitrogen is easier to transport because the viscosity of the nitrogen is far less than that of a mixed solution and generated gel foam, and the nitrogen is transported to the vicinity of the shaft from a position slightly far away from the shaft during flowback and is further fully mixed with solutions such as foaming agents and the like, so that the foam generation quality is improved, and the temporary plugging and cone pressing effects are enhanced; in addition, because the starting pressure difference of the high permeability layer is smaller than that of the low permeability layer, when the low production pressure difference is used for production, foam in the high permeability layer can be preferentially discharged back, the pressure in the high permeability layer is reduced, the pressure difference between the low permeability layer and the high permeability layer is improved, and the subsequent directional entering of the water plugging agent into the high permeability layer is facilitated.
As shown in fig. 5, after the above steps, injecting a water plugging agent into the stratum to establish an artificial partition plate, and enabling the water plugging agent to directionally enter a water producing layer to realize intelligent selective water plugging. The water shutoff agent screening conditions are as follows:
(1) the blocking agent is an integral water blocking agent, namely the blocking agent is integrally solidified or gelled.
(2) The water shutoff agent used is preferably in the form of a molecular or ionic dispersion, and the reaction time should be sufficiently long.
(3) The water plugging agent is of a combined type, and the strength of the water plugging agent is high enough.
(4) The plugging agent used near the well must ensure that it is not produced at large production pressure differentials.
(5) The configuration and construction of the water shutoff agent are simple and easy to operate, and the construction risk is small.
(6) The water shutoff agent has low cost and wide source.
(7) The plugging agent for establishing the partition plate can be used as a plugging agent with weak strength in a far well and used as a plugging agent with high strength in a near well.
The dosage of the water shutoff agent can be calculated according to the following formula:
q=π(2r)2hφ
in the formula: q-total amount of blocking agent, m3(ii) a r-plugging radius, m; phi-oil layer porosity,%; h-spacer thickness, m.
And finally, using a polymer solution for replacing, and replacing the water plugging agent out of a certain position near the well area by replacing, so that certain liquid production capacity is ensured after plugging, the over-high injection pressure of the water injection well is prevented, and the effective period of the water plugging agent is prolonged.
Under the combined action of the steps, intelligent selective water shutoff of the oil well with high water content in the bottom water reservoir can be realized, and the problem that the yield is sharply reduced after water breakthrough in the oil well is solved.
Example 2
The water plugging method is applied to a specific high-water-cut oil well of a bottom water reservoir. The specific method comprises the following steps:
and S1, injecting nitrogen into the well at high speed and high pressure to enable the nitrogen to enter a high-permeability water production layer, and driving the invaded water to the lower part by the entering of the nitrogen to achieve the purpose of pressing down the water cone and provide conditions for subsequent operation. According to the gel foam system study, the optimum amount of nitrogen gas is twice the volume of the mixed solution injected in step S2, and the volume of the mixed solution is calculated by the formula: q ═ pi R2h phi, wherein R is 10m, h is 2m, and phi is 0.3. The nitrogen injection quantity is converted into the ground volume by adopting the equation of state PV ═ nRT, and the gas injection speed is controlled at 600-3The gas injection pressure is higher than the formation pressure.
S2, injecting a mixed solution of a foaming agent, HPAM, a cross-linking agent and a foam stabilizer into the well, wherein the foaming agent is fatty alcohol ether sodium sulfate, and the mass concentration of the foaming agent is 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 crosslinking time of the composite crosslinking agent and the polyacrylamide is less than the half-life of foam formed by a foaming agent and gas, so that the crosslinking agent and the polyacrylamide can be subjected to crosslinking reaction only when a small amount of foam is broken, and the mass concentration is 0.1%; the foam stabilizer is hydrophobically modified nano SiO modified by N, N-dimethylferrocenyl hexadecyl methylammonium bromide (Fc16AB)2The mass concentration of the particles is 0.1 percent. The injection amount of the mixed solution was calculated by the formula in step S1 and was about 188.4m3。
S3, after the mixed solution is injected, changing a small oil nozzle, opening the well for production for 3-8 hours by the production pressure difference slightly larger than the starting pressure difference of the high permeability layer, fully mixing nitrogen in the stratum with a foaming agent, and discharging foam in the high permeability layer.
S4, before completionAfter the steps, a partition board water plugging agent is injected, and the water plugging agent adopts the temperature-resistant salt-tolerant high-temperature self-crosslinking in-situ polymerization water plugging gel in the patent CN 104449618B. The dosage of the water shutoff agent adopts a formula q ═ pi (2r)2h phi is calculated, where r is 10m, h is 2m, phi is 0.3, and the implantation amount is about 753.6m3. Because the low-permeability layer is temporarily blocked, the blocking agent only enters the high-permeability layer after being injected into the stratum, transversely extends in the high-permeability layer, and establishes the artificial partition plate at a proper position. The breakthrough pressure gradient of the plugging agent in the rock core is more than 9MPa/m, and the plugging rate reaches 99 percent.
S5, replacing the plugging agent with HPAM polymer solution, wherein the viscosity of the replacing fluid is higher than that of the replaced fluid, and the replacing also replaces the plugging agent at a certain position close to the well area, so that certain fluid production capacity is ensured after plugging, the over-high injection pressure of the water injection well is prevented, and the effective period of the plugging agent is prolonged.
By adopting the process, the water content of the well is reduced by 18.9 percent, and the water plugging effect is good.
In summary, the water shutoff method of the invention is to inject the nitrogen pressure cone into the wellbore, and then inject the mixed solution of the foaming agent, the polymer solution, the foam stabilizer and the cross-linking agent, so as to form gel foam in the stratum. 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.
Although the present invention has been described with reference to a preferred embodiment, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.