Foam system capable of tackifying and stabilizing oil displacement after being stimulated by CO2 as well as preparation method and application of foam system

Abstract

The invention relates to the technical field of crude oil recovery, and particularly discloses a CO2 stimulated tackifying stable oil displacement foam system as well as a preparation method and application thereof. The foam system is prepared from diethylenetriamine, lauryl alcohol polyoxyethylene ether sodium sulfate and water, the diethylenetriamine is subjected to protonation after being stimulated by CO2 to carry positive charges, the diethylenetriamine can be combined with the lauryl alcohol polyoxyethylene ether sodium sulfate carrying negative charges, wormlike micelles are formed under the condition that the concentration exceeds the critical micelle concentration, and the water content is reduced. And the viscosity and viscoelasticity of the solution are improved. Along with the introduction and discharge of CO2, the wormlike micelles can realize reversible change from spherical or rod-like micelles to wormlike micelles, and the viscosity of the system correspondingly generates mutual transformation of low-viscosity fluid and high-viscosity fluid. When the solution is used for preparing foam, the viscosity and the stability of the foam can be greatly enhanced. The foam system is high in salt tolerance, and the viscosity and strength of the system are increased along with the increase of the mineralization degree; and the plugging agent has better plugging and oil displacement effects in a heterogeneous rock core.

Description

Technical Field

[0001] The present invention belongs to the technical field of crude oil recovery, and particularly relates to a foam system for enhanced viscosity and stability during CO2 stimulation for enhanced oil recovery, a preparation method thereof, and an application thereof. Background Art

[0002] Foam is a dispersion system in which gas is dispersed in a liquid phase in the form of bubbles. The flow and deformation of bubbles in pores can significantly increase the apparent viscosity of the gas and delay the breakthrough and channeling of the gas during the displacement process. Foam can effectively block high-permeability regions such as large pores and fractures, causing more displacement fluid to be diverted into low-permeability regions. The surfactant component therein can reduce the oil-water interfacial tension and emulsify the crude oil. Therefore, foam can not only increase the swept volume of the reservoir but also improve the oil displacement efficiency. Foam is a thermodynamically unstable system. Foam will become unstable due to liquid film drainage and gas diffusion. Therefore, the volume of the bulk foam will continuously shrink over time, which will cause the foam to not achieve the ideal effect in the reservoir. The traditional CO2 foam system is developed from the CO2 gas flooding technology and is a composite oil displacement technology. Although it has good plugging ability and mobility control ability, it has relatively high requirements for conditions such as reservoir temperature, pressure, and salinity.

[0003] Preparing CO2-stimuli responsive foam using CO2 intelligent responsive materials to endow it with special properties is one of the ways to solve the existing problems of CO2 foam. CO2-stimuli responsive materials use CO2 as a switch. Utilizing the acidity of CO2 gas, the pH of the solution is changed by gas injection, thereby causing a change in the hydrophilicity of some molecules in the system, and further changing the surface activity of the system. Currently, the common CO2-stimuli responsive groups mainly include amidino, guanidine, and amine groups. Amidino is highly sensitive to CO2 but expensive and not suitable for large-scale applications; guanidine has relatively strict requirements for reaction conditions and is difficult to apply in oil fields. Summary of the Invention

[0004] The purpose of the present invention is to provide, in view of the above deficiencies of the prior art, a foam system for enhanced viscosity and stability during CO2 stimulation for enhanced oil recovery, a preparation method thereof, and an application thereof. After the CO2 gas flooding or water flooding is completed, CO2 gas and the foam system for enhanced viscosity and stability during CO2 stimulation described in any one of the above steps are injected into the fractured long core of the reservoir in a gas-liquid co-injection or alternating injection manner. After injecting a certain amount of the foam system for enhanced viscosity and stability during CO2 stimulation, CO2 or water is continuously injected into the reservoir for oil displacement.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions: The first aspect of the present invention is to provide a foam system for enhanced viscosity and stability during oil displacement stimulated by CO2. The viscosity of the foam system increases under the condition of introducing CO2 and decreases after discharging CO2. The foam system is prepared from diethylenetriamine, sodium lauryl polyoxyethylene ether sulfate, and water, where the molar ratio of diethylenetriamine to sodium lauryl polyoxyethylene ether sulfate is 1:(1.3 - 8).

[0006] Further, the molar concentration of the diethylenetriamine is 0.05 mol / L - 0.15 mol / L.

[0007] Further, the molar concentration of the sodium lauryl polyoxyethylene ether sulfate is 0.2 mol / L - 0.4 mol / L.

[0008] Further, the foam system further includes sodium chloride.

[0009] Further, in the foam system, the concentration of the sodium chloride is 0.017 - 0.068 mol / L.

[0010] Further, the resistance factor of the foam system for enhanced viscosity and stability during oil displacement stimulated by CO2 in high-permeability cores is greater than that in low-permeability cores.

[0011] The second aspect of the present invention is to provide a preparation method of a foam system. Dissolve sodium lauryl polyoxyethylene ether sulfate in water to obtain a first solution, and then add diethylenetriamine to the first solution and stir to dissolve it to obtain the foam system foaming liquid.

[0012] The third aspect of the present invention is to provide a preparation method of a foam system. Dissolve sodium lauryl polyoxyethylene ether sulfate in water to obtain a first solution, then add diethylenetriamine to the first solution and stir to dissolve it to obtain a second solution, and then add NaCl to the second solution and stir to dissolve it to obtain the foam system foaming liquid.

[0013] The fourth aspect of the present invention is to provide an oil displacement method. After the CO2 gas flooding or water flooding is completed, inject CO2 gas and the CO2-responsive viscosity-enhancing oil displacement foam system described in any one of the above steps into the fractured long core of the reservoir formation in a gas-liquid co-injection or alternating injection manner. After injecting a certain amount of the foam system for enhanced viscosity and stability during oil displacement stimulated by CO2, continue to inject CO2 or water into the reservoir for oil displacement.

[0014] Further, the use temperature of the foam system for enhanced viscosity and stability during oil displacement stimulated by CO2 is 30°C - 45°C; the conditions for introducing CO2 are: gas injection rate 15 mL / min - 25 mL / min, and gas injection time 10 min - 20 min.

[0015] Compared with the prior art, the beneficial effects brought by the technical solution provided by the present invention are as follows: (1) A foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 provided by the present invention is prepared from diethylenetriamine, sodium lauryl polyoxyethylene ether sulfate and water. After being stimulated by CO2, diethylenetriamine undergoes protonation to carry a positive charge, which can combine with sodium lauryl polyoxyethylene ether sulfate carrying a negative charge to form worm-like micelles under the condition of exceeding the critical micelle concentration (CMC), improving the viscosity and viscoelasticity of the solution. With the introduction and discharge of CO2, the worm-like micelles can achieve a reversible change from spherical or rod-like micelles to worm-like micelles, and the viscosity of the system correspondingly undergoes an interconversion between low-viscosity fluid and high-viscosity fluid. Using this solution to prepare foam can greatly enhance the foam viscosity and stability, while taking into account the controllable action time.

[0016] (2) The foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 provided by the present invention has strong salt tolerance, and the viscosity and strength of the system increase with the increase of salinity; (3) The foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 provided by the present invention has better plugging and oil displacement effects in heterogeneous cores; (4) The foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 provided by the present invention has strong shear resistance. There is no obvious shear thinning behavior within the shear rate range of 0 - 25 s -1 When the shear rate reaches 100 s -1 the viscosity still remains above 500 mPa·s, meeting the viscosity usage requirements.

[0017] (5) The CO2-responsive foam system for enhanced viscosity and oil displacement provided by the present invention does not contain toxic substances and is an environmentally friendly chemical system. The CO2 gas is inexpensive and easy to obtain. Injecting CO2 and the said system into the ground helps with the utilization and sequestration of CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a graph showing the change of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 and the half-life with salinity in the present invention; Figure 2 It is a graph showing the change of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 and the half-life with temperature in the present invention; Figure 3 It is a viscoelasticity curve of the foaming liquid of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 in the present invention; Figure 4 It is a rheological property curve of the foaming liquid of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 in the present invention Figure 5 It is a test curve of the mobility control ability of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 in the present invention; Figure 6 This is a comparison of the oil saturation after water injection and foam injection in the microfluidic experiment of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 in the present invention. Specific Embodiments To make the objectives, technical solutions, and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention in combination with specific examples and the accompanying drawings. For those not specified in the examples regarding specific testing methods, instrument equipment, or conditions, they are all carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. For the reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0019] In the present invention, diethylenetriamine (purity 99%) and sodium lauryl polyoxyethylene ether sulfate (purity 70%) are both from Shanghai Aladdin Biochemical Technology Co., Ltd., and the CO2 gas has a purity of 99.9% and is a commercially available product. The static foam stability test uses the Waring-Blender method, and the foaming liquid is stirred at 8000 rpm / min for 2 min to obtain foam.

[0020] Example 1 The experimental temperature is 30 °C. 130 mL of deionized water is filled in a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, placed on a magnetic stirrer, a magnetic stir bar is put in, the rotation speed is set at 300 r / min, and stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2.

[0021] 30 mL of the foaming liquid is taken out, CO2 gas is introduced at a ventilation rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 863.3 mPa·s.

[0022] The remaining foaming liquid is transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid is stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a ventilation rate of 20 mL / min to obtain the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2, which is used as Test Sample 1.

[0023] Example 2 The experimental temperature was 30 °C. 130 mL of deionized water was placed in a clean and dry beaker; 0.4 mol / L of sodium lauryl polyoxyethylene ether sulfate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was put in, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine was added to the first solution, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the second solution, which was the foaming liquid of the foam system for enhanced viscosity and stability during CO2-stimulated oil displacement.

[0024] 30 mL of the foaming liquid was taken out, CO2 gas was introduced at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid was measured to be 890.6 mPa·s.

[0025] The remaining foaming liquid was transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid was stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during CO2-stimulated oil displacement, which was used as Test Sample 2.

[0026] Example 3 The experimental temperature was 30 °C. 130 mL of deionized water was placed in a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was put in, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the first solution; 0.05 mol / L of diethylenetriamine was added to the first solution, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the second solution, which was the foaming liquid of the foam system for enhanced viscosity and stability during CO2-stimulated oil displacement.

[0027] 30 mL of the foaming liquid was taken out, CO2 gas was introduced at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid was measured to be 340.5 mPa·s.

[0028] The remaining foaming liquid was transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid was stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during CO2-stimulated oil displacement, which was used as Test Sample 3.

[0029] Example 4 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.1 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO₂.

[0030] Take out 30 mL of the foaming liquid, introduce CO₂ gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 120.3 mPa·s.

[0031] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and introduce CO₂ gas at the same time at a gas flow rate of 20 mL / min, then the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO₂ is obtained, which is used as test sample 4.

[0032] Example 5 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.2 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO₂.

[0033] Take out 30 mL of the foaming liquid, introduce CO₂ gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 855.1 mPa·s.

[0034] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and introduce CO₂ gas at the same time at a gas flow rate of 20 mL / min, then the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO₂ is obtained, which is used as test sample 5.

[0035] Example 6 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.017 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for viscosity increasing and stability enhancing in oil displacement after being stimulated by CO2.

[0036] 30 mL of the foaming liquid is taken out, CO2 gas is introduced at a ventilation rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 1411.8 mPa·s.

[0037] The remaining foaming liquid is transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid is stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a ventilation rate of 20 mL / min, thus obtaining the foam system for viscosity increasing and stability enhancing in oil displacement after being stimulated by CO2, which is used as test sample 6.

[0038] Example 7 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.034 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for viscosity increasing and stability enhancing in oil displacement after being stimulated by CO2.

[0039] 30 mL of the foaming liquid is taken out, CO2 gas is introduced at a ventilation rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 2750.5 mPa·s.

[0040] The remaining foaming liquid is transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid is stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a ventilation rate of 20 mL / min, thus obtaining the foam system for viscosity increasing and stability enhancing in oil displacement after being stimulated by CO2, which is used as test sample 7.

[0041] Example 8 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.051 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2.

[0042] Take out 30 mL of the foaming liquid, introduce CO2 gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 4505.2 mPa·s.

[0043] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and introduce CO2 gas at the same time at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2, which is used as test sample 8.

[0044] Example 9 The experimental temperature is 30 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.068 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2.

[0045] Take out 30 mL of the foaming liquid, introduce CO2 gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 6250.9 mPa·s.

[0046] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and introduce CO2 gas at the same time at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2, which is used as test sample 9.

[0047] Example 10 The experimental temperature is 30°C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.085 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for viscosity increase and stability during oil displacement stimulated by CO2.

[0048] Take out 30 mL of the foaming liquid, introduce CO2 gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 9435.3 mPa·s.

[0049] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and at the same time introduce CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for viscosity increase and stability during oil displacement stimulated by CO2, which is used as test sample 10.

[0050] Example 11 The experimental temperature is 40°C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.085 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for viscosity increase and stability during oil displacement stimulated by CO2.

[0051] Take out 30 mL of the foaming liquid, introduce CO2 gas at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid is measured to be 3236.2 mPa·s.

[0052] Transfer the remaining foaming liquid to the stirring cylinder of a high-speed stirrer, stir the foaming liquid at 5000 rpm / min for 15 min, and at the same time introduce CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for viscosity increase and stability during oil displacement stimulated by CO2, which is used as test sample 11.

[0053] Example 12 The experimental temperature was 50 °C. 130 mL of deionized water was placed in a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was put in, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine was added to the first solution, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the second solution; 0.085 mol / L of NaCl was added to the solution to obtain the third solution, which was the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2.

[0054] 30 mL of the foaming liquid was taken out, CO2 gas was introduced at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid was measured to be 886.2 mPa·s.

[0055] The remaining foaming liquid was transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid was stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2, which was used as test sample 12.

[0056] Example 13 The experimental temperature was 60 °C. 130 mL of deionized water was placed in a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was put in, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine was added to the first solution, the rotation speed was set at 300 r / min, and it was stirred until completely dissolved to obtain the second solution; 0.085 mol / L of NaCl was added to the solution to obtain the third solution, which was the foaming liquid of the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2.

[0057] 30 mL of the foaming liquid was taken out, CO2 gas was introduced at a gas flow rate of 20 mL / min for 15 min, and the viscosity of the foaming liquid was measured to be 145.6 mPa·s.

[0058] The remaining foaming liquid was transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid was stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for enhanced viscosity and stability during oil displacement after being stimulated by CO2, which was used as test sample 13.

[0059] Example 14 The experimental temperature is 70 °C. 130 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution; 0.085 mol / L of NaCl is added to the solution to obtain the third solution, which is the foaming liquid of the foam system for viscosity increase and stability improvement in enhanced oil recovery after being stimulated by CO2.

[0060] 30 mL of the foaming liquid is taken out, and CO2 gas is introduced at a gas flow rate of 20 mL / min for 15 min. The viscosity of the foaming liquid is measured to be 31.4 mPa·s.

[0061] The remaining foaming liquid is transferred to the stirring cylinder of a high-speed stirrer, and the foaming liquid is stirred at 5000 rpm / min for 15 min while introducing CO2 gas at a gas flow rate of 20 mL / min to obtain the foam system for viscosity increase and stability improvement in enhanced oil recovery after being stimulated by CO2, which is used as test sample 14.

[0062] Example 15 The experimental temperature is 30 °C. 100 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for viscosity increase and stability improvement in enhanced oil recovery after being stimulated by CO2, and is used as test sample 15. N2 gas is introduced at a gas flow rate of 20 mL / min for 15 min. The viscosity of the foaming liquid is measured to be 2.7 mPa·s.

[0063] Example 16 The experimental temperature is 30 °C. 100 mL of deionized water is filled into a clean and dry beaker; 0.3 mol / L of sodium lauryl polyoxyethylene ether sulfate is added, and it is placed on a magnetic stirrer. A magnetic stir bar is put in, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine is added to the first solution, the rotation speed is set at 300 r / min, and it is stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for viscosity increase and stability improvement in enhanced oil recovery after being stimulated by CO2, and is used as test sample 16.

[0064] Acetic acid is added dropwise to the solution to adjust the pH of the solution to be the same as that of the solution after introducing CO2 gas in Example 1.

[0065] The measured viscosity of the sample is 820.2 mPa·s. Comparative Example 1 At an experimental temperature of 30 °C, 30 mL of deionized water was placed in a clean and dry beaker; 0.3 mol / L of sodium α-olefin sulfonate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was added, and the rotation speed was set at 300 r / min and stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine was added to the first solution, and the rotation speed was set at 300 r / min and stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2.

[0066] CO2 gas was introduced into the foaming liquid at a gas flow rate of 20 mL / min for 15 min, and the rheological behavior of the foaming liquid was measured at a shear rate in the range of 0.1 - 100 s -1 range.

[0067] Comparative Example 2 At an experimental temperature of 30 °C, 30 mL of deionized water was placed in a clean and dry beaker; 0.3 mol / L of sodium dodecyl sulfate was added, and it was placed on a magnetic stirrer. A magnetic stir bar was added, and the rotation speed was set at 300 r / min and stirred until completely dissolved to obtain the first solution; 0.1 mol / L of diethylenetriamine was added to the first solution, and the rotation speed was set at 300 r / min and stirred until completely dissolved to obtain the second solution, which is the foaming liquid of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2.

[0068] CO2 gas was introduced into the foaming liquid at a gas flow rate of 20 mL / min for 15 min, and the rheological behavior of the foaming liquid was measured at a shear rate of 0.1 - 100 s -1 range.

[0069] Comparing Comparative Example 1 and Examples 2 - 5 shows that the molar ratio of sodium lauryl polyoxyethylene ether sulfate to diethylenetriamine of 3:1 is the optimal ratio.

[0070] Comparing Comparative Example 1 and Example 15 shows that CO2 is the stimulation source of the system, and N2 has no stimulating effect on the system.

[0071] Comparing Comparative Example 1 and Example 16 shows that the change in pH is the main mechanism for triggering the change in system performance, and the role of CO2 is to change the pH of the solution.

[0072] Comparative Example 1 shows that under the condition of the same concentration, the viscosity of the sodium lauryl polyoxyethylene ether sulfate system is similar to that of the sodium α-olefin sulfonate system at low shear rates, and higher than that of the sodium α-olefin sulfonate system at high shear rates, indicating that the sodium lauryl polyoxyethylene ether sulfate system has a larger shear rate adaptation range.

[0073] Comparative Example 2 shows that, under the same concentration condition, the viscosity of the sodium lauryl polyoxyethylene ether sulfate system is higher than that of the sodium dodecyl sulfonate system, indicating that the sodium lauryl polyoxyethylene ether sulfate system has a stronger plugging effect.

[0074] To better illustrate the intelligent regulation of viscosity and foam stability of the foam system for enhanced viscosity and stability during CO2 stimulation for oil displacement and its application effect in oil displacement, the applicant also conducted the following research: (1) The foaming ratio and half-life of the foam system for enhanced viscosity and stability during CO2 stimulation for oil displacement vary with temperature and salinity.

[0075] Examples 1, 6 - 10 show the influence of salinity on the system.

[0076] Examples 10 - 14 show the influence of temperature on the system.

[0077] The experimental results are as Figure 1 and Figure 2 shown, the stability of the foam system increases with the increase of NaCl concentration and decreases with the increase of temperature.

[0078] (2) Study on the viscoelastic properties of the foam system for enhanced viscosity and stability during CO2 stimulation for oil displacement.

[0079] As Figure 3 shown, the viscoelasticity of the foaming liquid in Example 1 was measured using a rheometer. As the angular frequency increases, the elasticity of the system weakens and the viscosity increases.

[0080] (3) Study on the anti-shear properties of the foam system for enhanced viscosity and stability during CO2 stimulation for oil displacement.

[0081] The rheological properties of the foaming liquids in Comparative Examples 1 and 2 were measured using a rheometer. The sodium lauryl polyoxyethylene ether sulfate system has the highest viscosity and the best anti-shear performance.

[0082] (4) Mobility control ability of the foam system for enhanced viscosity and stability during CO2 stimulation for oil displacement.

[0083] The measurement method is as follows: ① Homogeneous core injection experiment (low-permeability core 140 mD, high-permeability core 500 mD); ② Inject a NaCl solution with a concentration of 0.054 mol / L into the core at a certain flow rate and record the pressure change; ③ Inject the foaming liquid in Example 8 and CO2 gas into the core in a gas-liquid co-injection manner and record the pressure change; ④ Calculate the resistance factor.

[0084] As Figure 5As shown, the results indicate that after being stimulated by CO2, the foam system for enhanced viscosity and stable oil displacement has a greater resistance factor in high-permeability cores, indicating that this system is more conducive to plugging high-permeability channels.

[0085] (5)Testing the oil displacement performance of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 The measurement method for microfluidic experiments is as follows: ① Saturate the microfluidic chip with crude oil and age it for 24 h; ② Inject an NaCl solution with a concentration of 0.054 mol / L into the microfluidic chip at a flow rate of 0.0083 cc / min for 2 h; ③ Inject the foaming liquid in Example 8 and CO2 gas into the microfluidic chip simultaneously at flow rates of 0.02 cc / min and 0.2 cc / min respectively for 3 h; ④ Observe the change in the crude oil saturation in the chip.

[0086] Water flooding can only affect the crude oil in the fractures. After injecting the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2 in the present invention, the sweep efficiency is significantly improved, and most of the crude oil in the matrix and fractures is displaced out of the chip.

[0087] The measurement method for core flooding is as follows: Fractured long core displacement experiment (core size 30 cm × φ2.5 cm, matrix porosity 18.35%, matrix permeability 70 mD, fracture width 0.5 μm), crude oil viscosity 50 mPa·s, initial oil saturation 68.95%, experimental temperature 45°C. After water flooding until the water cut reaches 98%, the solution in Example 8 is injected into the core by the method of co-injecting gas and liquid, and then water flooding is carried out.

[0088] The final recovery rate is increased by 36.42% compared with water flooding. As Figure 6 shown, comparison of the oil saturation after water injection and foam injection in the microfluidic experiment of the foam system for enhanced viscosity and stable oil displacement after being stimulated by CO2.

[0089] Without conflict, the above embodiments and the features in the embodiments in this article can be combined with each other.

[0090] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A foam system for oil displacement that increases viscosity and stabilizes oil after being stimulated by CO2, characterized in that: The viscosity of the foam system increases when CO2 is introduced and decreases after CO2 is discharged. The foam system is prepared from diethylenetriamine, sodium lauryl polyoxyethylene ether sulfate and water, wherein the molar ratio of diethylenetriamine to sodium lauryl polyoxyethylene ether sulfate is 1: (1.3~8).

2. The foam system for stable oil displacement with viscosity increase after CO2 stimulation as claimed in claim 1, characterized in that: The molar concentration of the diethylenetriamine is 0.05 mol / L to 0.15 mol / L.

3. The foam system for stable oil displacement with viscosity increase after CO2 stimulation as claimed in claim 2, characterized in that: The molar concentration of the sodium lauryl polyoxyethylene ether sulfate is 0.2 mol / L to 0.4 mol / L.

4. The foam system for stable oil displacement after viscosity increase by CO2 stimulation as claimed in claim 3, characterized in that: The foam system also includes sodium chloride.

5. The foam system for stable oil displacement after viscosity increase by CO2 stimulation as claimed in claim 4, characterized in that: In the foam system, the concentration of sodium chloride is 0.017-0.068 mol / L.

6. The foam system for stable oil displacement with viscosity increase after CO2 stimulation as claimed in claim 4, characterized in that: The resistance factor of the foam system for viscosifying and stabilizing oil displacement after being stimulated by CO2 in a high-permeability core is greater than that in a low-permeability core.

7. A method for preparing a foam system as claimed in any one of claims 1 to 3, characterized in that: The sodium lauryl polyoxyethylene ether sulfate is dissolved in water to obtain a first solution, and then diethylenetriamine is added to the first solution and stirred to dissolve, so as to obtain a foaming liquid of the foam system.

8. A method for preparing a foam system as claimed in any one of claims 4 to 6, characterized in that: Sodium lauryl polyoxyethylene ether sulfate is dissolved in water to obtain a first solution, and then diethylenetriamine is added to the first solution and stirred to dissolve to obtain a second solution. Subsequently, NaCl is added to the second solution and stirred to dissolve to obtain a foaming liquid of a foam system.

9. An oil displacement method, characterized in that: After the CO2 gas drive or water drive is completed, CO2 gas and the foam system for stable oil recovery after being stimulated by CO2 as described in any one of claims 1-6 are injected into the fractured long core of the oil reservoir by gas-liquid co-injection or alternating injection. After a certain amount of the foam system for stable oil recovery after being stimulated by CO2 is injected, CO2 or water is continuously injected into the reservoir to drive oil.

10. The oil displacement method according to claim 9, characterized in that: The use temperature of the foam system for viscosity-enhancing and stable oil displacement after CO2 stimulation is 30°C~45°C; the conditions for introducing CO2 are: ventilation speed 15 mL / min~25 mL / min, ventilation time 10 min~20 min.

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