A water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs

Abstract

The present invention relates to a water injection and huff-and-puff oil production method for a low-porosity and ultra-low permeability oil reservoir, and belongs to the field of oilfield exploitation. The water injection and huff-and-puff oil production method for a low-porosity and ultra-low permeability oil reservoir of the present invention comprises the following steps: 1) injecting a surfactant solution into the formation; the injection displacement of the surfactant solution is not less than the critical injection displacement that causes the formation to rupture; 2) well soaking; 3) opening the well for pumping and production. The water injection and huff-and-puff oil production method for a low-porosity and ultra-low permeability oil reservoir of the present invention can effectively increase the reservoir pressure, change the oil and water distribution in the reservoir, replace the crude oil in the small pores with the large pores, and improve the crude oil recovery rate, in order to solve the problems of imperfect oil and water well network, poor physical properties, and low natural production capacity in low-porosity and ultra-low permeability reservoirs.

Description

Technical Field

[0001] The invention relates to a water injection and huff-and-puff oil production method for a low-porosity and ultra-low-permeability oil reservoir, and specifically belongs to the field of oilfield exploitation. Background Art

[0002] Water injection and huff-and-puff oil recovery is an important technology to improve the effect of oil field development in recent years. With continuous exploitation, the reservoir pressure of the oil reservoir decreases and the output decreases. Water is injected from the oil well into the reservoir through the water injection and huff-and-puff process. The water injected into the reservoir preferentially enters favorable parts such as high porosity and high permeability. After the well is shut down, under the action of capillary force, the injected water solution is replaced with the crude oil in the medium and small pore throats, so that the oil and water in the reservoir are redistributed. Then the well is opened for production, and the crude oil that has been displaced to the high porosity and high permeability zone is produced, thereby improving the recovery rate of crude oil.

[0003] The reservoir burial depth of Weibei Oilfield is 300m to 650m, with an average burial depth of 550m. The sand body is thick and has three sets of oil layers. The main oil layer is Chang 3 oil layer. The distribution of each oil layer is very different. The stress difference between the reservoir and the interlayer is small. The average porosity is 7.2% and the average permeability is 0.76×10 -3 μm 2 , which is a low-porosity and ultra-low-permeability reservoir; the oil-bearing area of ​​Chang 3 reservoir is 220.67km 2 , geological reserves of 10474.1×10 4 t. After several years of exploitation, the reservoir pressure decreased and the deficit was serious; coupled with the influence of factors such as high water injection pressure, low water injection system pressure, and wellbore formation pollution, the water injection wells were seriously under-injected, the oil well reservoir energy was insufficient, and the pressure was low, resulting in a low crude oil recovery rate. Summary of the invention

[0004] The object of the present invention is to provide a water injection and huff-and-puff oil production method for a low-porosity and ultra-low-permeability oil reservoir, which can effectively improve the crude oil recovery rate.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A water injection and huff-and-puff oil production method for a low-porosity and ultra-low-permeability oil reservoir comprises the following steps:

[0007] 1) Injecting the surfactant solution into the formation; the injection rate of the surfactant solution is not less than the critical injection rate that causes the formation to rupture; 2) Soaking the well; 3) Opening the well for pumping and production.

[0008] The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs of the present invention can effectively increase reservoir pressure, change the oil and water distribution in the reservoir, replace crude oil in small pores into large pores, and improve crude oil recovery rate, in order to solve the problems of imperfect oil and water well network, poor physical properties and low natural productivity in low-porosity and ultra-low-permeability reservoirs.

[0009] The low porosity and ultra-low permeability reservoir in the present invention refers to a reservoir with a porosity of less than 15%, a permeability of less than 1mD, and a low natural productivity of the oil well (daily liquid production of less than 1m 3 ) or oil reservoirs without natural productivity. The critical displacement is the critical water injection displacement of hydraulic fracturing simulation production fracturing. The surfactant solution is obtained by mixing a surfactant and water. Further, the mass concentration of the surfactant solution is 0.1% to 0.4%. Furthermore, the surfactant is a betaine type surfactant.

[0010] In order to balance the concentration in the injected volume and improve the imbibition displacement efficiency, the surfactant solution is injected into the formation in a variable concentration manner of 0.4%-0.2%-0.1%.

[0011] In order to further improve the imbibition displacement efficiency of the formation, the injection volume ratio of 0.4% surfactant solution, 0.2% surfactant solution and 0.1% surfactant solution is (25-35): (40-60): (10-15).

[0012] When the stratum fracture is in the form of horizontal fracture, a temporary plugging agent is injected into the stratum during the injection of the surfactant solution. The fracture complexity of the horizontal fracture reservoir is small, and the injection of the temporary plugging agent can increase the complexity of the fracture and increase the contact area between the injected surfactant solution and the reservoir.

[0013] Furthermore, the surfactant solution is injected into the formation at a variable concentration of 0.4%-0.2%-0.1%, and the injection order of surfactant solutions of different concentrations and temporary plugging agents is 0.4% surfactant solution, temporary plugging agent, 0.2% surfactant solution, temporary plugging agent, 0.2% surfactant solution, and 0.1% surfactant solution.

[0014] Furthermore, in order to deliver the temporary plugging agent more fully and effectively into the ground fracture, the injection method of the temporary plugging agent is to first inject the original glue liquid into the formation, then inject the mixture of the original glue liquid and the temporary plugging agent, and finally inject the original glue liquid. The first injection of the original glue liquid can displace the surfactant solution in the wellbore; the final injection of the original glue liquid can displace the temporary plugging agent to the end of the fracture, open a new fracture, and increase the contact area between the injected surfactant solution and the reservoir. The injection volume of the original glue liquid in the three stages is respectively the construction wellbore volume, the liquid volume in 2 minutes at the current displacement, and 1.5 times the volume of the fracture expansion under the current construction.

[0015] The raw gum liquid is obtained by mixing guar gum, potassium chloride, bactericide, surfactant and water, and the mass concentrations of guar gum, potassium chloride, bactericide and surfactant in the raw gum liquid are 0.2%, 1%, 0.2% and 0.2% respectively. The surfactant in the raw gum liquid is a betaine type surfactant. Preferably, the betaine type surfactant in the present invention is composed of the cationic part of the quaternary ammonium salt type surfactant and the anionic part of the carboxylate type surfactant, and has better performance than the amino acid type amphoteric surfactant. The betaine type surfactant is formed by reacting a mono-long chain alkyl dimethyl tertiary amine with sodium chloroacetate as the main raw materials.

[0016] Furthermore, the injection volume of the surfactant solution is 0.12 to 0.15 times the pore volume of the reservoir within the water injection sweep range. When the reservoir pore volume is 1PV, the injection volume of the surfactant solution is 0.12 to 0.15PV. After the surfactant solution is injected into the formation, it is ensured that the reservoir pressure can reach 0.8 to 1.2 times the original reservoir pressure, thereby expanding the swept volume of the injected surfactant solution and increasing the contact area between the injected surfactant solution and the reservoir.

[0017] Furthermore, the injection pressure of the surfactant solution is not less than the critical pressure for rupturing the formation and not greater than the critical pressure for the bottom hole casing to resist internal pressure.

[0018] If there is a trial injection, the amount of the trial injected surfactant solution is included in the injection amount of the surfactant solution.

[0019] Furthermore, in order to allow the injected water to fully diffuse in the reservoir and to perform imbibition replacement with the crude oil, the soaking time is 30 to 60 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of a water injection and huff-and-puff oil production mechanism according to an embodiment of the present invention;

[0021] Figure 2 This is a simulation diagram of the water injection coverage in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described in detail below in conjunction with the WB-1 well in a certain oil reservoir in the Weibei area. The betaine type surfactant in the embodiment is composed of the cationic part of the quaternary ammonium salt type surfactant and the anionic part of the carboxylate type surfactant, and is specifically formed by reacting a mono-long chain alkyl dimethyl tertiary amine with sodium chloroacetate as the main raw materials.

[0023] Example

[0024] The water injection and huff-and-puff oil production method of the low-porosity and ultra-low-permeability oil reservoir of this embodiment has a water injection and huff-and-puff oil production mechanism as follows: Figure 1 As shown, including the following:

[0025] (1) Characteristics of low-porosity and ultra-low-permeability reservoirs

[0026] The target layer is an oil-water layer with a burial depth of 391.0-396.0m and a reservoir temperature of 31°C. There is no corresponding water injection well on the plane.

[0027] Rock properties: permeability 0.82×10 -3 μm 2 ; Porosity 12.4%; Oil saturation 38.5%.

[0028] Logging parameters: resistivity 23.8Ω·m; sonic time difference 260.8μs / m.

[0029] (2) Using water injection and huff-and-puff technology

[0030] A. Injection volume: According to the hydraulic fracturing simulation, the horizontal fracture length is 80m, and the volume of the injected water affecting the formation is 42390m 3 Calculated based on the injection volume being 0.15 times the reservoir pore volume, the required water injection volume is 790m 3 , the water injection sweep range is simulated as follows Figure 2 As shown;

[0031] B. When the WB-1 well was put into production by fracturing, the pre-fracturing test was carried out at 1.0m 3 / min displacement for fractured formation, main fracturing operation displacement 2.2~3.1m 3 / min. After comprehensively considering the construction environment in Weibei area, operation cost (vehicle group cost) and other issues, the injection displacement of surfactant solution in WB-1 well is 1.0~2.4m 3 / min;

[0032] C. When the WB-1 well was put into production by hydraulic fracturing, the pre-fracturing test showed that the fracture pump pressure was 21MPa, the bottom hole fracture pressure was 24.7MPa (i.e., the critical pressure for formation fracture), the wellhead extension pressure was 11MPa, and the formation extension pressure was 14.7MPa. Taking into account the construction environment in Weibei area, the operation cost (vehicle group cost), the liquid friction (the friction of the surfactant solution along the way was 2.7MPa) and the construction pressure limit (30MPa), the injection pressure of the WB-1 well was predicted to be 23.5MPa, and the bottom hole casing was predicted to withstand an internal pressure of 24.7MPa.

[0033] D. Considering the dilution effect of reservoir fluid and the high permeability of the near-wellbore zone, the surfactant solution is injected into the formation at a concentration of 0.4%-0.2%-0.1% to balance the concentration in the injected volume and improve the efficiency of imbibition replacement;

[0034] E. Well WB-1 was put into production after fracturing. The artificial fractures were horizontal in shape. Water injection was performed at a pressure exceeding the formation fracture pressure. Temporary plugging agents were added to increase the complexity of the fractures and expand the volume of the imbibition wave.

[0035] F. Liquid formula:

[0036] a. The surfactant solution is obtained by mixing a betaine-type surfactant and clean water, and the mass concentration of the surfactant in the surfactant solution is 0.1% to 0.4%;

[0037] b. The original rubber solution is obtained by mixing guar gum, potassium chloride, a bactericide, a betaine-type surfactant and clean water. The mass concentrations of guar gum, potassium chloride, a bactericide and a betaine-type surfactant in the original rubber solution are 0.2%, 1%, 0.2% and 0.2%, respectively.

[0038] G. Pump injection procedure, specific process parameters are shown in Table 1:

[0039] a. Test injection with 0.4% surfactant solution;

[0040] b. Inject 0.4% surfactant solution for 230 m 3 ;

[0041] c. Replace the original glue liquid 2m 3 ;

[0042] d. Use 3m 3 Add 125kg of temporary plugging agent to the original glue solution;

[0043] e. Use 20m 3 The original glue liquid delivers the temporary plugging agent into the seam;

[0044] f. Inject 220m3 of 0.2% surfactant solution 3 ;

[0045] g, replace the original glue 2m 3 ;

[0046] h. Use 3m 3 Add 175kg of temporary plugging agent to the original glue solution;

[0047] i. Use 20m 3 The original glue liquid delivers the temporary plugging agent into the seam;

[0048] j. Inject 220m of 0.2% surfactant solution 3 ;

[0049] k. Inject 100m3 of 0.1% surfactant solution 3 ;

[0050] h. Keep the well shut for 30 days to allow the injected water to fully diffuse in the reservoir and to undergo imbibition replacement with the crude oil;

[0051] i. Open the well and start pumping production.

[0052] Table 1 Injection process pumping program

[0053]

[0054]

[0055] The water injection and huff and puff oil production method for low-porosity and ultra-low-permeability oil reservoirs of the present invention can increase the single-well recovery rate by 10% to 15%, while the single-well recovery rate of the conventional water injection and huff and puff oil production method without adding surfactant can be increased by about 5%.

Claims

1. A water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs, characterized in that: The following steps are involved: 1) Injecting surfactant solution into the formation; The injection rate of the surfactant solution is not less than the critical injection rate that causes the formation to break; 2) Stew well; 3) Open the well for pumping and production; The surfactant is a betaine-type surfactant; the stratum fracture is in the form of a horizontal fracture, and a temporary plugging agent is injected into the stratum during the process of injecting the surfactant solution; The injection method of the temporary plugging agent is to first inject the original glue liquid into the formation, then inject the mixture of the original glue liquid and the temporary plugging agent, and finally inject the original glue liquid; the soaking time is 30 to 60 days, so that the injected water can fully diffuse in the reservoir and perform imbibition replacement with the crude oil.

2. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 1, characterized in that: The mass concentration of the surfactant solution is 0.1% to 0.4%.

3. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 2, characterized in that: The surfactant solution is injected into the formation in a concentration varying from 0.4% to 0.2% to 0.1%.

4. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 3, characterized in that: The injection volume ratio of 0.4% surfactant solution, 0.2% surfactant solution, and 0.1% surfactant solution is (25~35):(40~60):(10~15).

5. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 1, characterized in that: The surfactant solution is injected into the formation at a variable concentration of 0.4%-0.2%-0.1%, and the injection order of surfactant solutions of different concentrations and temporary plugging agents is 0.4% surfactant solution, temporary plugging agent, 0.2% surfactant solution, temporary plugging agent, 0.2% surfactant solution, and 0.1% surfactant solution.

6. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 1, characterized in that: The injection volume of the surfactant solution is 0.12 to 0.15 times the pore volume of the reservoir within the water injection sweep range.

7. The water injection and huff-and-puff oil production method for low-porosity and ultra-low-permeability oil reservoirs according to claim 1, characterized in that: The injection pressure of the surfactant solution is not less than the critical pressure for rupturing the formation and not greater than the critical pressure for the bottom hole casing to resist internal pressure.

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