CN114427407A - A water injection huff and puff oil recovery method for low porosity and ultra-low permeability reservoirs - Google Patents

Abstract

The invention relates to a water injection huff and puff oil recovery method for a low-porosity and ultra-low permeability oil reservoir, belonging to the field of oilfield exploitation. The water injection huff and puff oil recovery method of the low-porosity and ultra-low permeability oil reservoir of the present invention comprises the following steps: 1) injecting the surfactant solution into the formation; the injection displacement of the surfactant solution is not less than the critical injection displacement for fracturing the formation; 2. ) simmer well; 3) open well for suction production. The water injection huff and puff oil recovery method of the low-porosity and ultra-low permeability oil reservoir of the present invention can effectively increase the reservoir pressure and change the oil-water well pattern in the low-porosity and ultra-low permeability reservoir, such as imperfect oil-water well pattern, poor physical properties and low natural productivity. The oil-water distribution in the small pores is replaced by the crude oil in the large pores to improve the oil recovery.

Description

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

technical field

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

Background technique

Water injection huff and puff oil recovery is an important technology to improve the effect of oilfield development in recent years. With the continuous exploitation, the reservoir pressure decreases and the production decreases. Water is injected from the oil well into the reservoir through the water injection huff and puff process, and the water injected into the reservoir preferentially enters favorable parts such as high porosity and high permeability. Under the action of capillary force, the injected aqueous 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, and then the well is opened for production, and the crude oil displaced to the high-porosity and high-permeability zone is recovered. Enhanced oil recovery.

The reservoirs in Weibei Oilfield have a burial depth of 300m to 650m, with an average burial depth of 550m. The sand bodies are thick and 3 sets of oil layers are developed. The main oil layer is the Chang 3 oil layer, the distribution of the interlayers of each oil layer varies greatly, 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; Among them, the Chang 3 reservoir has an oil-bearing area of 220.67km ² and a geological reserve of 10474.1×10 ⁴ t. After several years of exploitation, the reservoir pressure has been reduced and the deficit is serious; coupled with the high water injection pressure, low water injection system pressure, wellbore formation pollution and other factors, the water injection well is seriously under-injected, the oil well reservoir energy is insufficient, and the pressure is low, resulting in crude oil recovery. The yield is lower.

SUMMARY OF THE INVENTION

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

In order to achieve the above object, the technical scheme adopted in the present invention is:

A water injection huff and puff oil recovery method for a low porosity and ultra-low permeability oil reservoir, comprising the following steps:

1) The surfactant solution is injected into the formation; the injection displacement of the surfactant solution is not less than the critical injection displacement for fracturing the formation; 2) The well is soaked; 3) The well is pumped for production.

The water injection huff and puff oil recovery method of the low-porosity and ultra-low permeability oil reservoir of the present invention can effectively improve the reservoir pressure and change the oil-water well pattern in the low-porosity and ultra-low permeability reservoir, such as imperfect oil-water well pattern, poor physical properties and low natural productivity. The oil-water distribution in the small pores is replaced by the crude oil in the large pores to improve the oil recovery.

Medium-low porosity and ultra-low permeability oil reservoirs in the present invention refer to oil reservoirs with porosity < 15%, permeability < 1 mD, low natural productivity of oil wells (daily fluid production < 1 m ³ ) or no natural productivity. The critical displacement is the critical water injection displacement for fracturing to be put into production according to hydraulic fracturing simulation. The surfactant solution is obtained by mixing surfactant and water. Further, the mass concentration of the surfactant solution is 0.1%-0.4%. Further, the surfactant is a betaine-type surfactant.

In order to balance the concentration in the swept volume of water injection and improve the imbibition displacement efficiency, the surfactant solution is injected into the formation in a variable concentration mode of 0.4%-0.2%-0.1%.

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

When the form of formation fracture is a horizontal fracture, a temporary plugging agent is injected into the formation during the process of injecting the surfactant solution. The fracture complexity of the horizontal fractured reservoir is small, and the injection of temporary plugging agent can improve the complexity of the fracture and increase the contact area between the injected surfactant solution and the reservoir.

Further, the surfactant solution is injected into the formation according to the variable concentration of 0.4%-0.2%-0.1%, and the injection sequence of each concentration of surfactant solution and temporary plugging agent is 0.4% surfactant solution, temporary plugging agent, 0.2% surfactant solution, temporary plugging agent, 0.2% surfactant solution, 0.1% surfactant solution.

Further, in order to send the temporary plugging agent into the ground fractures more fully and effectively, the injection method of the temporary plugging agent is to inject the original glue liquid into the formation first, and then inject the mixture of the original glue liquid and the temporary plugging agent, Finally, inject the original glue. The first injection of raw glue can replace the surfactant solution in the wellbore; the last injection of raw glue can replace the temporary plugging agent to the fracture end, open new fractures, and increase the contact area between the injected surfactant solution and the reservoir. The injection volume of the raw glue solution in the three stages is respectively the volume of the construction wellbore, the volume of the liquid volume in 2 minutes under the current displacement, and 1.5 times the volume of the fracture expansion under the current construction.

The original 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 original gum liquid are 0.2%, 1 %, 0.2% and 0.2%. The surfactant in the original glue solution is 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 its performance is better than that of the amino acid-type amphoteric surfactant. Type surfactant is made by reacting single long chain alkyl dimethyl tertiary amine and sodium chloroacetate as the main raw material.

Further, the injection volume of the surfactant solution is 0.12-0.15 times the pore volume of the reservoir within the scope of water injection. When the void volume of the reservoir is 1PV, the injection volume of the surfactant solution is 0.12-0.15PV. After the surfactant solution is injected into the formation, ensure that the reservoir pressure can reach 0.8 to 1.2 times the original pressure of the reservoir, thereby expanding the swept volume of the injected surfactant solution and increasing the contact area between the injected surfactant solution and the reservoir.

Further, the injection pressure of the surfactant solution is not less than the critical pressure for fracturing the formation, and not greater than the critical pressure for the bottom hole casing to resist internal pressure.

If there is a trial injection, the liquid volume of the trial injection surfactant solution is included in the injection volume of the surfactant solution.

Further, in order to fully diffuse the injected water in the reservoir and perform imbibition replacement with the crude oil, the time of the well soaking is 30-60 days.

Description of drawings

1 is a schematic diagram of the oil recovery mechanism of water injection huff and puff according to an embodiment of the present invention;

FIG. 2 is a simulation diagram of a water injection sweep range in an embodiment of the present invention.

Detailed ways

The technical solution of the present invention will be described in detail below with reference to the WB-1 well of 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 anion part of the carboxylate-type surfactant, specifically a single long-chain alkyl dimethyl tertiary amine and sodium chloroacetate. It is formed by the reaction of the main raw materials.

Example

The water injection huff and puff oil recovery method of the low porosity and ultra-low permeability oil reservoir in this embodiment, the water injection huff and puff oil recovery mechanism is shown in Figure 1, including the following contents:

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

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

Rock properties: permeability 0.82×10 ^-3 μm ² ; porosity 12.4%; oil saturation 38.5%.

Logging parameters: resistivity 23.8Ω·m; acoustic time difference 260.8μs/m.

(2) Adopt water injection huff and puff process

A. Injection volume: According to the hydraulic fracturing simulation, the fracturing horizontal fracture length is 80m, and the injection water sweeps the formation volume of 42390m ³ . According to the calculation that the injection volume is 0.15 times the pore volume of the reservoir, the injected water volume is 790m ³ , and the water injection sweep range is simulated. as shown in picture 2;

B. When the fracturing of Well WB-1 was put into production, the stratum was fractured at a displacement of 1.0 m ³ /min before fracturing, and the displacement of the main fracturing operation was 2.2 to 3.1 m ³ /min, taking into account the construction environment and operating costs in the Weibei area. After problems such as (vehicle cost), the injection displacement of the surfactant solution in Well WB-1 is 1.0-2.4 m ³ /min;

C. When the fracturing of Well WB-1 is put into production, the pre-fracture test fracturing pump pressure is 21 MPa, the bottom hole fracturing pressure is 24.7 MPa (that is, the critical pressure for fracturing the formation), the wellhead extension pressure is 11 MPa, and the formation extension pressure is 14.7 MPa. The construction environment, operating cost (vehicle cost), liquid friction (surfactant solution friction along the way 2.7MPa) and construction pressure limit (30MPa) in the north area, etc., the predicted injection pressure of Well WB-1 is 23.5MPa, and the predicted well The inner pressure of the bottom casing is 24.7MPa;

D. Considering the dilution effect of the reservoir fluid and the high permeability near the wellbore, the concentration of the surfactant solution is injected into the formation with a variable concentration of 0.4%-0.2%-0.1%, so that the concentration in the swept volume of water injection is balanced and the imbibition replacement is improved. efficiency;

E. Well WB-1 was fracturing and put into production. The artificial fractures were horizontal fractures. The water injection huff and puff exceeded the formation fracture pressure. Temporary plugging agents were added to improve the complexity of the fractures and expand the imbibition swept volume.

F. Liquid formula:

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

b. The original glue solution is obtained by mixing guar gum, potassium chloride, bactericide, betaine-type surfactant and clear water. The mass concentrations were 0.2%, 1%, 0.2% and 0.2%, respectively.

G. Pump injection procedure, the specific process parameters are shown in Table 1:

a. Test injection with 0.4% surfactant solution;

b. Inject 230m ³ of 0.4% surfactant solution;

c, replace the original glue 2m ³ ;

d. Add 125kg of temporary plugging agent with ^3m3 original glue solution;

e. Use 20m ³ of original glue to send the temporary plugging agent into the joint;

f. Inject 220m ³ of 0.2% surfactant solution;

g, replace the original glue solution 2m ³ ;

h. Add 175kg of temporary plugging agent with 3m ³ original glue solution;

i. Use 20m ³ of the original glue to send the temporary plugging agent into the joint;

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

k. Inject 100m ³ of 0.1% surfactant solution;

h. Boil the well for 30 days, so that the injected water can be fully diffused in the reservoir and imbibed and replaced with the crude oil;

i. Drilling and pumping production.

Table 1 Injection process pumping procedure

The water injection huff and puff oil recovery method of the low porosity and ultra-low permeability oil reservoir of the present invention can improve the single well recovery rate by 10% to 15%, while the single well recovery rate of the conventional water injection huff and puff oil recovery method without surfactant can be improved 5% or so.

Claims (10)

1. a water injection huff and puff oil recovery method of a low-porosity ultra-low permeability oil reservoir, is characterized in that, comprises the following steps: 1) Inject the surfactant solution into the formation; the injection displacement of the surfactant solution is not less than the critical injection displacement for breaking the formation; 2) Stew the well; 3) Open well for suction production. 2. The waterflooding huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 1, is characterized in that, the mass concentration of described surfactant solution is 0.1%～0.4%; Described surfactant is betaine type surfactant. 3 . The water injection huff and puff oil recovery method for low porosity and ultra-low permeability oil reservoirs according to claim 2 , wherein the surfactant solution is injected into the formation in a variable concentration mode of 0.4%-0.2%-0.1%. 4 . 4. The water injection huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 3, wherein the concentration is 0.4% surfactant solution, 0.2% surfactant solution, 0.1% surfactant solution The ratio of the injection volume of the solution was (25-35):(40-60):(10-15). 5. The water injection huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 2 or 3, is characterized in that, when the form of formation rupture is horizontal fracture, in the process of injecting surfactant solution, inject temporarily into formation blocking agent. 6. The water injection huff and puff oil recovery method for low-porosity and ultra-low permeability oil reservoirs according to claim 5, wherein the surfactant solution is injected into the formation at variable concentrations of 0.4%-0.2%-0.1%, and each concentration The injection sequence of the surfactant solution and the temporary plugging agent is 0.4% surfactant solution, temporary plugging agent, 0.2% surfactant solution, temporary plugging agent, 0.2% surfactant solution, and 0.1% surfactant solution. 7. The water injection huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 5, is characterized in that, the injection method of described temporary plugging agent is to inject original glue liquid in formation first, then inject original glue liquid and The mixture of temporary plugging agent is finally injected into the original glue solution. 8 . The waterflooding huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 1 , wherein the injection volume of the surfactant solution is 0.12-0.15 of the pore volume of the reservoir within the scope of water injection. 9 . times. 9. The water injection huff and puff oil recovery method of low porosity and ultra-low permeability oil reservoir according to claim 1, wherein the injection pressure of the surfactant solution is not less than the critical pressure for fracturing the formation, and is not more than the bottom hole casing The critical pressure at which the pipe resists internal pressure. 10 . The water injection huff and puff oil recovery method for a low-porosity and ultra-low permeability oil reservoir according to claim 1 , wherein the time for the well-holding is 30-60 days. 11 .

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