Method for improving recovery ratio after bottom water channeling of super heavy oil reservoir

Abstract

The invention relates to a method for improving the recovery ratio after bottom water channeling of a super heavy oil reservoir, and belongs to the technical field of oil exploitation. The method comprises the following steps that (1) nitrogen is injected, water near a shaft is pushed away, bottom water propelling is slowed down, and then a protection slug is injected; (2) a gel plugging agent is injected to form a plugging slug, finally, a sealing slug is injected, and the well is closed for cement waiting; (3) nitrogen foam is injected to block a slug; and (4) sequentially injecting a viscosity reducer and nitrogen to form a nitrogen composite viscosity reduction oil washing slug, and soaking. According to the method for improving the recovery ratio after bottom water channeling of the super heavy oil reservoir, the synergistic effect of the nitrogen slug, the plugging slug, the nitrogen foam slug and the viscosity reduction slug is utilized, and water pushing away, water plugging and oil reservoir crude oil viscosity reduction in the near wellbore area are achieved in sequence; physical water pushing and chemical plugging are combined, so that pushing of bottom water of the horizontal well of the super heavy oil reservoir is effectively inhibited, the viscosity reduction effect is improved, and the purpose of increasing yield and oil is finally achieved.

Description

Technical Field

[0001] The present invention relates to a method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs, belonging to the technical field of petroleum exploitation. Background Art

[0002] The heavy oil thermal recovery in Chunguang belongs to ultra - heavy oil reservoirs with extremely high porosity and permeability, having the characteristics of "medium - deep burial (about 925m - 980m), thin oil layers (0.3m - 3m), viscous oil (crude oil viscosity about 28000mPa·s - 70000mPa·s, difficult to flow in formations and wellbores), loose cementation (serious sand production), and adjacent to water layers (1m - 4m)". There are water layers both above and below the heavy oil reservoir in Chunguang Oilfield. The distance from the upper water layer is far and the interlayer shielding is good, while the interlayer between the oil layer and the lower water layer is thin and a physical property interlayer, and there is no interlayer in some areas. Therefore, the breakthrough between the oil layer and the lower water layer is the main reason for high water cut in heavy oil.

[0003] With the increase of the number of huff - and - puff cycles, water breakthrough intensifies, and the difficulty of water breakthrough control increases. The adaptability of mature technologies such as nitrogen water inhibition and nitrogen foam water shutoff gradually deteriorates, and the effect of high water - cut treatment becomes significantly worse. Through the cycle comparison of comparable wells, the daily oil production per cycle decreases from 3.6 tons / day in the first cycle to 0.7 tons / day in the fifth cycle. In recent years, domestic scholars have carried out a large number of research and field test works on viscosity reduction and cold production to improve the recovery factor in extra - heavy oil reservoirs, while the research on ultra - heavy oil reservoirs with bottom water breakthrough is very few. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs, and solve the problem that there is less research on bottom water breakthrough in ultra - heavy oil wells in the prior art.

[0005] In order to achieve the above purpose, the technical solution adopted by the method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs of the present invention is as follows:

[0006] A method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs, comprising the following steps:

[0007] (1) Inject nitrogen to push the water body near the wellbore away, slow down the bottom water advance, and then inject a protection slug;

[0008] (2) Inject a gel water - shutoff agent to form a plugging slug, and finally inject a sealing slug, then shut in the well and wait for setting;

[0009] (3) Inject a nitrogen foam plugging slug;

[0010] (4) Inject a viscosity - reducing agent and nitrogen in sequence to form a nitrogen composite viscosity - reducing and oil - washing slug, and then soak the well.

[0011] The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs of the present invention utilizes the synergistic effect of nitrogen slug, plugging slug, nitrogen foam slug, and viscosity - reducing slug, and successively realizes pushing the water in the near - wellbore area away, water plugging, and reducing the viscosity of crude oil in the reservoir. By combining physical water pushing and chemical plugging, it effectively inhibits the bottom water advancement at the bottom of the horizontal well in the ultra - heavy oil reservoir, reduces the dilution of the subsequent injected plugging agent by the formation water body, improves the plugging effect and viscosity - reducing effect, achieves the purpose of increasing production and oil production, ultimately improves the reservoir recovery factor, and moreover, the composite nitrogen in the viscosity - reducing and oil - washing slug has a certain energy - increasing effect during the back - production process.

[0012] To improve the plugging effect on water breakthrough and prevent the back - vomiting of the water - plugging agent, preferably, the gel - type water - plugging agent and the sealing slug in step (2) both include hydrolyzed polyacrylamide and phenolic cross - linker; the concentrations of hydrolyzed polyacrylamide and phenolic cross - linker in the sealing slug are both higher than those in the gel - type water - plugging agent.

[0013] Preferably, the mass fraction of hydrolyzed polyacrylamide in the gel - type water - plugging agent is 0.5 - 0.7%, and the mass fraction of phenolic cross - linker is 0.3 - 0.4%; the mass fraction of hydrolyzed polyacrylamide in the sealing slug is 0.6 - 0.8%, and the mass fraction of phenolic cross - linker is 0.4 - 0.5%.

[0014] Preferably, the volume ratio of the protection slug, the plugging slug, and the sealing slug is 1:(10 - 12):(2 - 3). The three slugs cooperate with each other to expand the plugging radius and improve the plugging effect. Preferably, in step (3), the nitrogen foam plugging slug is obtained by injecting a foaming agent and nitrogen successively for underground foaming to plug the water - producing layers that are not well plugged by the gel - type water - plugging agent.

[0015] To improve the reservoir recovery factor, preferably, in step (4), the viscosity - reducing agent is injected in at least two rounds, the concentration of the viscosity - reducing agent in the previous round is not lower than that in the subsequent round, and the injection volume of the viscosity - reducing agent in the previous round is not lower than that in the subsequent round.

[0016] To increase the stirring power and improve the viscosity - reducing effect at low temperatures, preferably, the concentration of the viscosity - reducing agent in the first round is 1.5 - 1.7%, the concentration of the viscosity - reducing agent in the second round is 1.0 - 1.2%, and the concentration of the viscosity - reducing agent in the third round is 1.0 - 1.2%.

[0017] Preferably, the volume ratio of the viscosity - reducing agent in the first round, the viscosity - reducing agent in the second round, and the viscosity - reducing agent in the third round is (2 - 2.5):(2 - 2.5):1. These three rounds of viscosity - reducing agents cooperate with each other to improve the viscosity - reducing effect.

[0018] To make nitrogen foam better for foaming and achieving the plugging effect, preferably, the volume ratio of the foaming agent to nitrogen in the nitrogen foam plugging slug is 1:(100 - 110).

[0019] Preferably, the volume ratio of the viscosity reducer to nitrogen in the nitrogen composite viscosity-reducing washing slug is 3:(200 - 250). BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the gelation morphology diagram of the plugging slug in Example 1;

[0021] Figure 2 It is the oil-water emulsion state of heavy oil A added with BCHX-12 in Example 1 after oscillating for 3 h and 6 h;

[0022] Figure 3 It is the oil-water emulsion state of heavy oil B added with BCHX-12 in Example 1 after oscillating for 3 h and 6 h. DETAILED DESCRIPTION OF THE INVENTION

[0023] The technical solutions of the present invention will be further described below in conjunction with the specific embodiments. Unless otherwise specified, the percentages mentioned in the embodiments are all mass fractions.

[0024] The specific embodiments of the method for improving the recovery factor after bottom water breakthrough in ultra-heavy oil reservoirs of the present invention are as follows:

[0025] Example 1

[0026] The method for improving the recovery factor after bottom water breakthrough in ultra-heavy oil reservoirs in this example adopts the following steps:

[0027] This example is directed to a horizontal well in an ultra-heavy oil reservoir. The reservoir temperature of this well is 38 °C, the crude oil viscosity is about 28000 mPa·s - 70000 mPa·s, and the salinity is about 86676 mg / L.

[0028] (1) System selection

[0029] 1.1 Foaming agent selection: Since the reservoir temperature is 38 °C, the foaming agent GD-05 is selected. This foaming agent is a foaming agent for nitrogen, and the recommended concentration of the system is 0.5% by mass percentage. The evaluation results are shown in Table 1.

[0030] Table 1 0.5% foaming agent screening experiment

[0031]

[0032] 1.2 Plugging system selection: According to the reservoir temperature of 38 °C, the salinity of about 86676 mg / L, and the permeability of 0.732 μm 2, under conditions such as a porosity of 29.2%, considering the characteristics of the wire-wrapped screen sand control string, a relatively mature organic phenolic gel was preferably selected as the plugging system for this plugging system to block the main flow line channel of the water flow. According to the target reservoir conditions, gel systems with different strengths can be formed by adjusting the concentrations of the polymer and the cross-linking agent, and the gel can be formed stably at 38°C. The experimental results are shown in Table 2. Among them, the polymer is polyacrylamide and its derivatives.

[0033] Table 2 Gelation time and gelation strength of phenolic gels under different formulation concentrations (the solvent is produced water, 38°C)

[0034]

[0035] Based on the evaluation results of the gelation experiment, an organic phenolic gel system with a polymer concentration of 5000 mg / L + a cross-linking agent concentration of 3600 mg / L (i.e., 0.5% polymer by mass fraction + 0.36% phenolic resin cross-linking agent by mass fraction) was selected as the plugging slug, and an organic phenolic gel system with a polymer concentration of 8000 mg / L + a cross-linking agent concentration of 4800 mg / L (i.e., 0.8% polymer by mass fraction + 0.48% phenolic resin cross-linking agent by mass fraction) was used as the sealing slug. Figure 1 It is the gelation morphology diagram of the plugging slug system.

[0036] 1.3 Selection of heavy oil viscosity reduction system: According to the crude oil properties of this well, a hyperbranched temperature- and salt-resistant extra-heavy oil nano-viscosity reducer BCHX-12 was preferably used. This system was formed by modifying the end positions of POSS cores with different end groups synthesized and polymerizing with AM monomers, anionic (or cationic / non-ionic / amphoteric ionic) active monomers, etc. to form a series of hyperbranched nano-viscosity reducers. By monomer selection, the emulsification, penetration and dispersion, anti-aggregation and other properties of the material can be regulated.

[0037] Using the national standard Q / SY 118-2013, the viscosity reduction effects of BCHX-12 on heavy oil A (at 40°C, the viscosity is 33124 mPa·s; at 50°C, the viscosity is 12512 mPa·s) and heavy oil B (at 38°C, the viscosity is 48970 mPa·s; at 50°C, the viscosity is 19286 mPa·s) were evaluated. The results are shown in Table 3. Figure 2 , 3 as shown.

[0038] From Figure 2 , 3 it can be seen that the viscosity reducer of the present invention is stable after being mixed with heavy oil A and heavy oil B for 6 h, forming a relatively stable oil-in-water emulsion.

[0039] Table 3 Evaluation of the viscosity reduction performance of BCHX-12 on Xinjiang heavy oil A and heavy oil B

[0040]

[0041] (2) Dosage calculation

[0042] 2.1 Design of dosage of nitrogen foam slug

[0043] Dosage of nitrogen: The underground nitrogen dosage is 307.5 m 3 .

[0044] The surface temperature of this well is 20 °C, the surface pressure is 0.1 MPa, the underground temperature is 38.73 °C, and the formation pressure is 9.1 MPa. Substituting into the gas state equation:

[0045]

[0046] Among them, P 1 is the surface pressure, P 2 is the formation pressure, V 1 is the surface volume of nitrogen, V 2 is the underground nitrogen volume, T 1 is the surface Kelvin temperature, T 2 is the underground Kelvin temperature, where Kelvin temperature = Celsius temperature + 273.15. It is calculated that the nitrogen compression ratio is 85.53 times. By calculating, the standard cubic volume of nitrogen under the surface pressure condition is: 26301.1 Nm 3 , and the designed surface nitrogen injection volume is 30000 Nm 3 , among which the pre - nitrogen slug is 10000 Nm 3 , and the nitrogen foam slug is 20000 Nm 3 .

[0047] Dosage of foaming agent: The dosage of foaming agent is 200 m 3 .

[0048] 2.2 Design of dosage of gel plugging system slug

[0049] The horizontal section of this well is completed with a screen pipe. When the plugging system is injected, it diffuses radially along the well axis. The dosage of the plugging system is calculated using the following formula:

[0050] Q = a(2b 1 h - πb 2 2 )Φe (1)

[0051] In the formula: Q—Dosage of the system, m 3 ;

[0052] a—Length of the horizontal well section, 170 m (the water - channeling section for temperature measurement and water - finding is about 100 m);

[0053] b 1 —Horizontal radial penetration depth of the system along the well axis, 6 m;

[0054] b 2 — Horizontal radial displacement depth along the well axis, 2 m;

[0055] h— Effective thickness of the oil reservoir, 6 m;

[0056] Φ— Porosity of the treatment layer, 26.7%;

[0057] e— Dosage coefficient, take 0.3.

[0058] Calculated by the formula, the dosage of the high-strength gel plugging system is 476.11 m 3 , the designed dosage is 500 m 3 . In addition, the designed sealing slug is 100 m 3 .

[0059] 2.3 N 2 Design of the dosage of the composite heavy oil nano-viscosity-reducing system slug

[0060] The dosage of this system slug is calculated using the following formula:

[0061] Q = πr 2 LΦ (2)

[0062] In the formula: Q— Dosage of the system, m 3 ;

[0063] r— Treatment radius, 3.5 m;

[0064] L— Length of the horizontal section, 170 m;

[0065] Φ— Porosity of the treatment layer, 26.7%.

[0066] Calculated by the formula, the dosage of the system is 1745.9 m 3 , the designed dosage of the heavy oil nano-viscosity-reducing agent BCHX-12 is 1800 m 3 (content 0.5%), the dosage of the nano-viscosity-reducing agent BCHX-12 is 9.0 t. Design N 2 dosage 10000 Nm 3 .

[0067] (3) Slug design, the results are shown in Table 4

[0068] 3.1 Nitrogen slug: Inject 10000 Nm 3 nitrogen, and control the injection speed at 600 - 1000 Nm 3 / h to push the water in the near-well area away.

[0069] 3.2 Plugging slug: First, prepare a 0.6% polymer (hydrolyzed polyacrylamide) solution of 50 m with clear water 3Conduct a trial injection with it as a protective slug, and then prepare 500 m of a high-strength gel water plugging agent with on-site sewage 3 (0.5% HPAM (hydrolyzed polyacrylamide) + 0.36% phenolic crosslinking agent) for injection. Finally, inject 100 m of a high-strength sealing slug prepared with on-site sewage 3 (0.8% HPAM + 0.48% phenolic crosslinking agent) to prevent the plugging agent from flowing back. Control the injection rate at 6 - 8 m 3 / h, and then inject 10.73 m 3 of sewage as a displacement slug, with an injection rate of 10 - 15 m 3 / h. Shut in the well and wait for setting for 7 days.

[0070] 3.3 Nitrogen foam slug: Inject alternately in two rounds. First, inject 100 m of foaming agent GD - 05 (concentration 0.5%) 3 and 10000 Nm 3 of nitrogen as one round, and control the injection rate at 8 - 10 m 3 / h. Among them, the main component of the foaming agent is triethoxybutane.

[0071] 3.4 Nitrogen composite viscosity reduction slug: Inject alternately in three rounds. In the first round, inject 300 m of BCHX - 12 heavy oil nano viscosity reducer 3 (concentration 1.5%), in the second round, inject 300 m of BCHX - 12 heavy oil nano viscosity reducer 3 (concentration 1.0%), and in the third round, inject 150 m of BCHX - 12 heavy oil nano viscosity reducer 3 (concentration 1.0%) and inject N 2 10000 Nm 3 , and control the injection rate at 8 - 10 m 3 / h. Injecting the viscosity reducer in rounds is to enable the viscosity reducer to contact the crude oil more fully, fully reduce the viscosity of the crude oil in the oil layer, improve the flow performance of the crude oil in the formation and wellbore, and at the same time, the injection of nitrogen has a certain energy - increasing effect during production.

[0072] 3.5 Shut - in well and production recovery: Inject 10.73 m 3 of sewage as a displacement slug, with an injection rate of 10 - 15 m 3 / h. After shutting in the well for 7 days, start production recovery.

[0073] Table 4 Results table of slug design

[0074]

[0075] According to the optimized design plan: injection gas volume 3×10 4 m 3, 1 t of foaming agent, 9 t of viscous crude oil nano-viscosity reducer (Table 5), viscosity reduction and cold production increase oil production by 500 t, the process implementation cost is 480,000 yuan, and the increased oil production generates benefits of 605,000 yuan, with remarkable effects. Therefore, the method of using nitrogen and plugging agent to plug water and then implementing viscosity reduction and cold production in the present invention can inhibit the advancement of bottom water, improve the viscosity reduction effect, and ultimately realize the effective utilization of watered-out reserves, which is feasible for ultra-viscous crude oil bottom water coning reservoirs.

[0076] Table 5 Construction Material Consumption Table

[0077]

Claims

1. A method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs, characterized in that, it includes the following steps: (1) Inject nitrogen to push the water body near the wellbore away, slow down the bottom water advance, and then inject a protection slug; (2) Inject a gel - type water - plugging agent to form a plugging slug, and finally inject a sealing slug, then shut in the well and wait for setting; (3) Inject a nitrogen foam plugging slug; (4) Inject a viscosity - reducing agent and nitrogen in sequence to form a nitrogen composite viscosity - reducing and oil - washing slug, and soak the well.

2. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 1, characterized in that, both the gel - type water - plugging agent and the sealing slug in step (2) include hydrolyzed polyacrylamide and phenolic cross - linking agent; the concentrations of hydrolyzed polyacrylamide and phenolic cross - linking agent in the sealing slug are both higher than those in the gel - type water - plugging agent.

3. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 1, characterized in that, the mass fraction of hydrolyzed polyacrylamide in the gel - type water - plugging agent is 0.5 - 0.7%, and the mass fraction of phenolic cross - linking agent is 0.3 - 0.4%; the mass fraction of hydrolyzed polyacrylamide in the sealing slug is 0.6 - 0.8%, and the mass fraction of phenolic cross - linking agent is 0.4 - 0.5%.

4. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to any one of claims 1 - 3, characterized in that, the volume ratio of the protection slug, the plugging slug and the sealing slug is 1:(10 - 12):(2 - 3).

5. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 1, characterized in that, in step (3), the nitrogen foam plugging slug is formed by injecting a foaming agent and nitrogen successively.

6. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 1, characterized in that, in step (4), the viscosity - reducing agent is injected in at least two rounds, the concentration of the viscosity - reducing agent in the previous round is not lower than that in the subsequent round, and the injection volume of the viscosity - reducing agent in the previous round is not lower than that in the subsequent round.

7. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 6, characterized in that, the concentration of the first - round viscosity - reducing agent is 1.5 - 1.7%, the concentration of the second - round viscosity - reducing agent is 1.0 - 1.2%, and the concentration of the third - round viscosity - reducing agent is 1.0 - 1.2%.

8. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 7, characterized in that, the volume ratio of the first - round viscosity - reducing agent, the second - round viscosity - reducing agent and the third - round viscosity - reducing agent is (2 - 2.5):(2 - 2.5):

1.

9. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 5, characterized in that, the volume ratio of the foaming agent to nitrogen in the nitrogen foam plugging slug is 1:(100 - 110).

10. The method for improving the recovery factor after bottom water breakthrough in ultra - heavy oil reservoirs according to claim 1, characterized in that, the volume ratio of the viscosity - reducing agent to nitrogen in the nitrogen composite viscosity - reducing and oil - washing slug is 3:(200 - 250).

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