Foam base fluid, preparation method and preparation method of temperature-resistant and salt-resistant CO2 foam oil displacement system

Abstract

The invention discloses a foam base fluid, a preparation method and a preparation method of a temperature-resistant and salt-resistant CO2 foam flooding system.The foam base fluid comprises a foaming agent, a foam stabilizer and water, the foaming agent is a betaine type surfactant, and the foam stabilizer is a biological polysaccharide polymer. A temperature-resistant and salt-resistant foam base solution and a biological polysaccharide reinforced CO2 foam oil displacement system are obtained by introducing a biological polysaccharide polymer as a foam stabilizer and combining with a betaine type surfactant, so that the problem that the viscosity of polyacrylamide as a traditional foam stabilizer is reduced and even fails in a high-temperature and high-salt environment is effectively solved; the stability of CO2 foam can be obviously improved. Meanwhile, the biological polysaccharide polymer has the characteristics of environmental friendliness and degradability, and can effectively reduce the negative influence on the environment. In addition, due to rich resources and low price of the biological polysaccharide, the system is competitive in cost, and the economic benefit of the oil field can be further improved.

Description

Technical Field

[0001] The invention relates to the technical field of CO2 flooding and storage in oilfield development, and in particular to a foam base fluid, a preparation method and a preparation method of a temperature-resistant and salt-resistant CO2 foam flooding system. Background Art

[0002] Carbon capture, utilization and storage (CCUS) is one of the most effective ways to reduce carbon emissions. Among them, using captured CO2 for oil recovery can not only achieve the effective utilization of CO2, but also achieve the geological storage of CO2. Due to its unique physical and chemical properties, CO2 can interact strongly with crude oil under reservoir conditions, such as reducing crude oil viscosity, increasing crude oil volume and high miscibility, thereby significantly improving crude oil recovery. However, compared with reservoir liquids, CO2 is prone to viscous fingering and gravity separation, leading to excessive flow and crossflow problems. In addition, the presence of heterogeneous reservoirs and fractures further limits the utilization rate of CO2 and oil recovery. Therefore, how to effectively block CO2 and control its mobility has become a key challenge to improve the scope of CO2, oil recovery performance and storage efficiency.

[0003] In recent years, foam flooding technology has been regarded as a potential technology to solve the problems of gas channeling and low sweep efficiency in the CO2 flooding process. CO2 foam flooding technology is based on CO2 flooding and uses the Jamin effect of foam in porous media to inhibit CO2 gas channeling and expand the sweep range of the displacement phase. This technology not only has the advantages of foam flooding such as selective plugging, base fluid viscosity enhancement, and oil washing capabilities, but also uses less water, which is especially suitable for areas with scarce water resources. Therefore, CO2 foam flooding, as a multifunctional fluid with the three-in-one functions of "plugging", "flooding" and "washing", can greatly improve the recovery rate while achieving CO2 sequestration. However, the thermodynamic instability of foam has become a key factor restricting the sweep range, oil recovery performance and sequestration efficiency of CO2. Due to the decay behaviors of foam such as gravity liquid separation, coarsening and aggregation, the foam is unstable and defoams. In addition, in ordinary CO2 foam systems, the high CO2 solubility enhances the mass transfer capacity of CO2 molecules between foam liquid films and reduces the stability of foam. In addition, the harsh reservoir conditions (such as high temperature, high salinity, low permeability-heterogeneity) further aggravate the instability of foam.

[0004] With the increase in the exploration and exploitation of low-grade oil and gas resources (harsh reservoir conditions) in my country, the development of high-temperature and high-salinity CO2 foam systems has become an urgent need. In order to enhance the stability of foam, researchers have proposed the use of foam stabilizers such as polymers, nanoparticles, and gels, in order to reduce the liquid film separation rate and inhibit the mass transfer effect of gas molecules between liquid films, thereby prolonging the foam stability time. However, the existing foam stabilizer systems all have certain limitations. For example, although polymer enhanced foam flooding technology shows good performance under medium and low temperature conditions (≤75°C), high temperature environments will cause thermal degradation of polymers, thereby significantly reducing their foam stabilization effect; nanoparticles, as high-temperature resistant foam stabilizers, have the potential to improve foam stability, but in actual application scenarios, nanoparticles have poor dispersibility and are easy to agglomerate, which may not only lead to permanent plugging of the formation, but also cause irreversible damage to the reservoir structure, thereby limiting its application in actual working conditions; although gel foam has high strength and stability, the gelation time is uncontrollable, and cross-linking reactions are required under specific reservoir conditions, which limits its large-scale application. Therefore, in view of the various shortcomings of traditional foam stabilizers in high-temperature and high-salt CO2 foam systems, the development of new temperature-resistant and salt-resistant foam stabilizers has become a key issue that needs to be urgently addressed in the current oil and gas field development field.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention is to provide a foam base fluid, a preparation method and a preparation method of a temperature-resistant and salt-resistant CO2 foam flooding system, so as to overcome the problems that the existing foam base fluid has poor high temperature and high salt resistance and poor foaming and stability of the foam.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a foam base liquid, comprising a foaming agent, a foam stabilizer and water, wherein the foaming agent is a betaine-type surfactant, and the foam stabilizer is a biopolysaccharide polymer.

[0009] In an optional embodiment, the mass fraction of the foaming agent is 0.2-0.4wt%;

[0010] And / or, the mass fraction of the foam stabilizer is 0.1-0.3wt%

[0011] In an optional embodiment, the foaming agent is selected from at least one of dodecyl dimethyl betaine, aramidopropyl betaine, octyl aramidopropyl betaine, lauryl aramidopropyl betaine, cocoamidopropyl betaine, oleamidopropyl betaine, erucamidopropyl betaine, lauryl hydroxypropyl sulfobetaine, coconut oil hydroxypropyl sulfobetaine, lauryl hydroxypropyl sulfobetaine, cocoamidohydroxypropyl sulfobetaine, dodecyl dimethyl hydroxypropyl sulfobetaine, hexadecyl dimethyl hydroxypropyl sulfobetaine, oleamidohydroxypropyl sulfobetaine and erucamidohydroxypropyl sulfobetaine.

[0012] In an optional embodiment, the foam stabilizer is selected from at least one of psyllium seed gum, tamarind gum, scleroglucan, diutan gum and xanthan gum.

[0013] In an optional embodiment, the mineralization degree of the foam base fluid is 0 to 2.0×10 5 mg / L;

[0014] And / or, the foam base liquid further comprises an inorganic salt, and the mass fraction of the inorganic salt is 0 to 20.0 wt %.

[0015] In an alternative embodiment, the inorganic salt comprises at least one of NaCl, CaCl2 and MgCl2.

[0016] In a second aspect, the present invention provides a method for preparing the foam base liquid as described in any one of the aforementioned embodiments, comprising: dissolving the foaming agent in water to obtain a surfactant solution; dissolving the foam stabilizer in the surfactant solution to obtain the foam base liquid.

[0017] In a third aspect, the present invention provides a method for preparing a CO2 foam flooding system, comprising: introducing the foam base fluid and CO2 gas described in any one of the aforementioned embodiments into a core to obtain the CO2 foam flooding system.

[0018] In an optional embodiment, the temperature of the foam base liquid is 20-130°C.

[0019] In an optional embodiment, the pressure of the CO2 gas is 0-20 MPa.

[0020] The present invention has the following beneficial effects:

[0021] The present invention introduces biopolysaccharide polymers as foam stabilizers and combines them with betaine-type surfactants to construct a temperature-resistant and salt-resistant biopolysaccharide-enhanced CO2 foam flooding system. The system effectively solves the problem of reduced viscosity or even failure of traditional foam stabilizer polyacrylamide in high-temperature and high-salt environments, and can significantly improve the stability of CO2 foam. At the same time, biopolysaccharide polymers have environmentally friendly and degradable characteristics, which can effectively reduce the negative impact on the environment. In addition, the abundant resources and low prices of biopolysaccharides make the system cost-competitive, which can further improve the economic benefits of oil fields. In summary, the present invention has significant technical innovation, economic benefits and environmental friendliness. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 High temperature and high pressure CO2 foam performance evaluation device;

[0024] Figure 2 The foaming volume of CO2 foam enhanced by different biopolysaccharides at different concentrations;

[0025] Figure 3 The lysis half-life of CO2 foam enhanced by different biopolysaccharides at different concentrations;

[0026] Figure 4 Comprehensive foam index of CO2 foam enhanced by different biopolysaccharides at different concentrations. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0028] The embodiment of the present invention provides a foam base liquid, comprising a foaming agent, a foam stabilizer and water, wherein the foaming agent is a betaine-type surfactant, and the foam stabilizer is a biopolysaccharide polymer.

[0029] The embodiment of the present invention adopts betaine-type surfactant as a foaming agent and introduces a biopolysaccharide polymer as a foam stabilizer to obtain a foam base fluid suitable for high-temperature and high-salinity oil reservoirs, thereby overcoming the problem that traditional foam stabilizers show a significant decrease in viscosity or even fail in the high-temperature and high-salinity oil reservoir environment.

[0030] In an optional embodiment, the mass fraction of the foaming agent is 0.2-0.4wt%;

[0031] And / or, the mass fraction of the foam stabilizer is 0.1-0.3wt%

[0032] In an optional embodiment, the foaming agent is selected from at least one of dodecyl dimethyl betaine, aramidopropyl betaine, octyl aramidopropyl betaine, lauryl aramidopropyl betaine, cocoamidopropyl betaine, oleamidopropyl betaine, erucamidopropyl betaine, lauryl hydroxypropyl sulfobetaine, coconut oil hydroxypropyl sulfobetaine, lauryl hydroxypropyl sulfobetaine, cocoamidohydroxypropyl sulfobetaine, dodecyl dimethyl hydroxypropyl sulfobetaine, hexadecyl dimethyl hydroxypropyl sulfobetaine, oleamidohydroxypropyl sulfobetaine and erucamidohydroxypropyl sulfobetaine.

[0033] In an optional embodiment, the foam stabilizer is selected from at least one of psyllium seed gum, tamarind gum, scleroglucan, diutan gum and xanthan gum.

[0034] The above-mentioned biological polysaccharide polymer is a high molecular polymer composed of multiple monosaccharides, and its main chain is formed by one or more monosaccharides connected by glycosidic bonds to form a long chain structure. The main chain is connected to side chains containing the same or other monosaccharides, and the side chains contain charged groups (such as carboxyl groups), which cause the polysaccharide molecules to present a polyanion / cation structure in aqueous solution. The introduction of side chains and their charged groups gives the polysaccharides complex helical, double helical and network structures, thereby showing excellent thickening properties and rheological properties. This type of polysaccharide shows excellent stability to environmental factors such as temperature, salinity, acid and alkali, and can maintain its properties and functions in a wide range of temperature and salinity.

[0035] In an optional embodiment, the mineralization degree of the foam base fluid is 0 to 2.0×10 5 mg / L;

[0036] And / or, the foam base liquid further comprises an inorganic salt, and the mass fraction of the inorganic salt is 0 to 20.0 wt %.

[0037] After foaming, the foam base liquid in the embodiment of the present application has a high foam comprehensive index in both high-salinity and low-salinity environments, even when the mineralization degree reaches 2.0×10 5It also shows excellent stability in a high-salt environment of 0.1 mg / L, with a higher foam comprehensive index retention rate (i.e. the ratio of the foam comprehensive index under high-salt conditions to the foam comprehensive index under low-salt conditions).

[0038] In an alternative embodiment, the inorganic salt comprises at least one of NaCl, CaCl2 and MgCl2.

[0039] By adding inorganic salts to the base fluid, formation water can be simulated and the performance of the foam base fluid under different salinity conditions can be studied.

[0040] An embodiment of the present invention further provides a method for preparing the foam base liquid described in any one of the aforementioned embodiments, comprising: dissolving the foaming agent in water to obtain a surfactant solution; dissolving the foam stabilizer in the surfactant solution to obtain the foam base liquid.

[0041] Specifically, in some embodiments, the method for preparing the foam base liquid comprises the following steps:

[0042] (1) Dissolving 1.0-20.0 wt% of inorganic salt in deionized water according to the mass fraction of each component to form simulated formation water A;

[0043] (2) dissolving 0.2% to 0.4% of a foaming agent in simulated formation water A and stirring for 10 to 15 minutes to form a surfactant solution B;

[0044] (3) Dissolve 0.1% to 0.3% of a foam stabilizer in surfactant solution B and stir for 60 to 80 minutes until the foam stabilizer is completely dissolved to form a foam base solution C.

[0045] An embodiment of the present invention further provides a method for preparing a CO2 foam flooding system, comprising: introducing the foam base fluid and CO2 gas described in any one of the aforementioned embodiments into a core to obtain the CO2 foam flooding system.

[0046] In an optional embodiment, the temperature of the foam base liquid is 20-130°C, and under the high temperature condition of 130°C, it still has a relatively high foam comprehensive index.

[0047] In an optional embodiment, the pressure of the CO2 gas is 0-20 MPa.

[0048] Specifically, in some embodiments, the foaming of the CO2 foam flooding system under laboratory simulated flooding conditions specifically includes the following steps:

[0049] (1) Pass CO2 gas into the high temperature and high pressure foam evaluation instrument to make the equipment completely filled with CO2 atmosphere;

[0050] (2) injecting the foam base liquid C into the high temperature and high pressure foam evaluation instrument using a Luer injection;

[0051] (3) Turn on the heating device and use electric heating to heat the foam base liquid inside the evaluation device to a target temperature in the range of 20-130° C. through a temperature control system;

[0052] (4) Turn on the pressurizing device, use the CO2 gas booster pump, and pressurize the CO2 gas pressure inside the evaluation device to the target pressure through the pressure control system, with the pressure range of 0-20 MPa;

[0053] (5) Turn on the mixer, adjust the stirring speed and control the stirring time, and obtain the CO2 foam flooding system through shear foaming by the rotor inside the equipment.

[0054] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0055] Embodiment 1:

[0056] The preparation and performance testing process of biopolysaccharide enhanced CO2 foam flooding system is divided into the following three steps:

[0057] (1) Preparation of foam base fluid: In the experiment, NaCl, CaCl2, and MgCl2·6H2O were weighed according to the simulated formation water formula in Table 1 to prepare a foam base fluid with a mineralization of 1×10 5 mg / L simulated formation water A. Weigh 0.4 g of oleamide hydroxypropyl sulfobetaine (OHSB) and dissolve it in 100 mL of simulated formation water A, stir for 10-15 minutes to form surfactant solution B. Weigh 0.2 g of psyllium seed gum and dissolve it in surfactant solution B, stir for 60-80 minutes until the psyllium seed gum is completely dissolved to form foam base fluid C.

[0058] (2) Preparation of CO2 foam system: First, CO2 is introduced into a high temperature and high pressure foam evaluation instrument ( Figure 1 ) Expel air to ensure CO2 atmosphere; use the liquid inlet to inject 100mL of foam base liquid C into the foam evaluator; turn on the heating device and heat to the target temperature of 110°C through the temperature control system; turn on the pressurizing device and pressurize to the target pressure of 10MPa through the pressure control system; use the Waring Blender foaming method, turn on the blender switch, adjust the speed to 3000rpm, and the foaming time to 1min to obtain the CO2 foam system.

[0059] (3) CO2 foam performance test: When the foam is fully expanded, the foam volume is recorded as V max ; At the same time, observe the foam effluent situation, and when the foam effluent volume reaches 50mL, record the effluent half-life as t 1 / 2Each group of experiments was measured three times and the average value was taken. According to different foam stabilizers, the foam comprehensive index FCI (Formula 1) was introduced to simultaneously characterize the foamability and stability of CO2 foam.

[0060] FCI=0.75×V max ×t 1 / 2 Formula 1

[0061] Where V max Indicates the maximum foaming volume, t 1 / 2 Indicates the time required for the foam to precipitate to half of the total volume.

[0062] The results showed that the foaming volume of the psyllium seed gum enhanced CO2 foam was 388 mL and the half-life was 79.89 min. Under the same conditions, the foaming volume of the traditional polyacrylamide KYPAM-6S enhanced CO2 foam was 440 mL and the half-life was 16.5 min. Compared with the KYPAM-6S system, the foaming volume of the psyllium seed gum system was reduced, which was attributed to the high viscosity of the psyllium seed gum solution, which increased the energy consumption required for foaming, resulting in a decrease in the foaming volume of the system. However, the psyllium seed gum system significantly increased the half-life, which was due to the increase in the viscosity of the foam liquid film of the system, which slowed down the liquid film drainage rate, thereby enhancing the stability of the CO2 foam. This shows that the addition of the foam stabilizer reduces the foaming performance to a certain extent, but significantly improves the stability of the foam, revealing that there is an optimal foaming performance in the biopolysaccharide enhanced CO2 foam system.

[0063] In order to comprehensively evaluate the effects of different foam stabilizers on foam performance, this example introduces the Foam Comprehensive Index (FCI), which can simultaneously reflect the foamability and stability of CO2 foam. Specifically, the FCI value of the psyllium seed gum system is 23248 mL·min, while that of the KYPAM-6S system is 5445 mL·min. Comparative analysis shows that the half-life of the psyllium seed gum system is 4.8 times that of the KYPAM-6S system, and its FCI value is 4.3 times higher than the latter, indicating the advantage of psyllium seed gum in improving foam stability.

[0064] Table 1. Formation water formulations with different mineralizations

[0065]

[0066]

[0067] Embodiment 2:

[0068] The difference between this embodiment and embodiment 1 is that the concentration of the foam stabilizer in step (1) is changed.

[0069] (1) Preparation of foam base fluid: In the experiment, NaCl, CaCl2, and MgCl2·6H2O were weighed according to the simulated formation water formula in Table 1 to prepare a foam base fluid with a mineralization of 1×10 5 mg / L simulated formation water A. Weigh 0.4 g of oleamide hydroxypropyl sulfobetaine (OHSB) and dissolve it in 100 mL of simulated formation water A, stir for 10-15 minutes to form surfactant solution B. Weigh 0.25 g of psyllium seed gum and dissolve it in surfactant solution B, stir for 60-80 minutes until the psyllium seed gum is completely dissolved to form foam base fluid C.

[0070] Step (2) and step (3) and parameters are the same as those in Example 1.

[0071] The results show that the foaming volume of CO2 foam strengthened by psyllium seed gum is 335 mL, the half-life is 88.45 min, and the comprehensive foam index is 22223 mL min. Under the same conditions, the foaming volume of CO2 foam strengthened by polyacrylamide KYPAM-6S is 428 mL, the half-life is 19.6 min, and the comprehensive foam index is 6292 mL min. Therefore, the half-life of the psyllium seed gum system is 4.5 times that of the KYPAM-6S system, and the comprehensive foam index is 3.5 times that of the latter.

[0072] Embodiment 3:

[0073] The difference between this embodiment and embodiment 1 is that the type of foam stabilizer in step (1) is changed.

[0074] (1) Preparation of foam base fluid: In the experiment, NaCl, CaCl2, and MgCl2·6H2O were weighed according to the simulated formation water formula in Table 1 to prepare a foam base fluid with a mineralization of 1×10 5 mg / L simulated formation water A. Weigh 0.4 g of oleamide hydroxypropyl sulfobetaine (OHSB) and dissolve it in 100 mL of simulated formation water A, stir for 10-15 minutes to form surfactant solution B. Weigh 0.2 g of tamarind gum and dissolve it in surfactant solution B, stir for 60-80 minutes until the plantain gum is completely dissolved to form foam base liquid C.

[0075] Step (2) and step (3) and parameters are the same as those in Example 1.

[0076] The results show that the foaming volume of tamarind gum-enhanced CO2 foam is 415 mL, the half-life is 45.67 min, and the foam comprehensive index is 14215 mL min. Under the same conditions, the foaming volume of traditional polyacrylamide KYPAM-6S-enhanced CO2 foam is 440 mL, the half-life is 16.5 min, and the foam comprehensive index is 5445 mL min. Therefore, the half-life of the xanthan gum system is 2.8 times that of the KYPAM-6S system, and the foam comprehensive index is 2.6 times that of the latter.

[0077] Embodiment 4:

[0078] The difference between this embodiment and embodiment 1 is that the type of foaming agent in step (1) is changed.

[0079] (1) Preparation of foam base fluid: In the experiment, NaCl, CaCl2, and MgCl2·6H2O were weighed according to the simulated formation water formula in Table 1 to prepare a foam base fluid with a mineralization of 1×10 5 mg / L simulated formation water A. Weigh 0.4 g of oleamide hydroxypropyl sulfobetaine (OAB) and dissolve it in 100 mL of simulated formation water A, stir for 10-15 minutes to form surfactant solution B. Weigh 0.2 g of psyllium seed gum and dissolve it in surfactant solution B, stir for 60-80 minutes until the psyllium seed gum is completely dissolved to form foam base fluid C.

[0080] Step (2) and step (3) and parameters are the same as those in Example 1.

[0081] The results show that the foaming volume of CO2 foam strengthened by psyllium seed gum is 400 mL, the half-life is 76.34 min, and the comprehensive foam index is 22902 mL·min. Under the same conditions, the foaming volume of CO2 foam strengthened by traditional polyacrylamide KYPAM-6S is 445 mL, the half-life is 16.15 min, and the comprehensive foam index is 5390 mL·min. Therefore, the half-life of the psyllium seed gum system is 4.7 times that of the KYPAM-6S system, and the comprehensive foam index is 4.2 times that of the latter.

[0082] Embodiment 5:

[0083] The difference between this embodiment and embodiment 1 is that the experimental temperature in step (2) is changed.

[0084] (2) Preparation of CO2 foam system: First, pass CO2 into the foam evaluation instrument to exhaust the air to ensure CO2 atmosphere; use the liquid inlet to inject 100 mL of foam base liquid C into the foam evaluation instrument; turn on the heating device and heat to the target temperature of 130°C through the temperature control system; use the Waring Blender foaming method, turn on the pressurizing device, and pressurize to the target pressure of 10 MPa through the pressure control system; turn on the mixer switch, adjust the speed to 3000 rpm, and the foaming time to 1 min to obtain the CO2 foam system.

[0085] Step (1) and step (3) and parameters are the same as those in Example 1.

[0086] The results show that the foaming volume of CO2 foam strengthened by psyllium seed gum is 440 mL, the half-life is 28.15 min, and the comprehensive foam index is 9290 mL min. In comparison, the foaming volume of CO2 foam strengthened by traditional polyacrylamide KYPAM-6S is 450 mL, the half-life is 10.34 min, and the comprehensive foam index is 3490 mL min. Therefore, the half-life of the psyllium seed gum system is 2.8 times that of the KYPAM-6S system, and the comprehensive foam index is 2.7 times that of the latter.

[0087] By comparing Example 1 and Example 5, it can be seen that as the temperature increases, the FCI value of the psyllium seed gum system decreases from 23248 mL·min in Example 1 to 9290 mL·min in Example 5, but is still higher than the FCI value of the KYPAM-6S system in Example 1.

[0088] Embodiment 6:

[0089] The difference between this embodiment and embodiment 1 is that the salinity of the simulated formation water in step (1) is changed.

[0090] (1) Preparation of foam base fluid: In the experiment, NaCl, CaCl2, and MgCl2·6H2O were weighed according to the simulated formation water formula in Table 1 to prepare foam base fluids with mineralizations of 0 and 1×10 4 , 5×10 4 , 1×10 5 , 1.5×10 5 , 2×10 5 mg / L simulated formation water A. Weigh 0.4 g of oleamide hydroxypropyl sulfobetaine (OHSB) and dissolve it in 100 mL of simulated formation water A, stir for 10-15 minutes to form surfactant solution B. Weigh 0.2 g of psyllium seed gum and dissolve it in surfactant solution B, stir for 60-80 minutes until the psyllium seed gum is completely dissolved to form foam base fluid C.

[0091] Step (2) and step (3) and parameters are the same as those in Example 1.

[0092] The results show that the mineralization is 0, 1×10 4 , 5×10 4 , 1.5×10 5 , 2×10 5 Under the conditions of 2×10 mg / L, the foaming volumes of CO2 foams strengthened by psyllium seed gum were 405, 395, 385, 370, and 360 mL, respectively, the half-lives were 57.75, 62.03, 71.74, 94.85, and 115.45 min, and the comprehensive foam indexes were 17542, 18376, 20715, 26321, and 31172 mL·min. In contrast, the traditional polyacrylamide KYPAM-6S had a high foaming capacity of 1.247 W / m2 at 2×105 The foaming volume of CO2 foam under the condition of 1.5 mg / L is 445 mL, the half-life is 9.89 min, and the comprehensive foam index is 3301 mL min. Therefore, the half-life of the psyllium seed gum system is 11.7 times that of the KYPAM-6S system, and the comprehensive foam index is 9.4 times that of the latter.

[0093] By comparing Example 1 and Example 6, it can be seen that with the increase of mineralization, the FCI value of the psyllium seed gum system gradually increases from 17542 mL·min when the mineralization is 0 to 2×10 5 mg / L at 31172 mL·min; the FCI value of the KYPAM-6S system is 2×10 5 Under the condition of 100 mg / L, it was 3301 mL·min, which was lower than 5445 mL·min in Example 1. In comparison, the psyllium seed gum system had better salt tolerance.

[0094] Comparative Example 1:

[0095] The difference between this comparative example and Example 1 is that the type of surfactant is changed, and the experimental steps and conditions are the same as those of Example 1. Different types of surfactants are used as foaming agents, and the surfactants are: cationic surfactant dodecyltrimethylammonium bromide (DTAB), anionic surfactant sodium dodecyl sulfate (SDS), and nonionic surfactant alkyl polyglycoside (APG-10).

[0096] The results show that the foaming volumes of CO2 foams in the systems of DTAB + psyllium seed gum, SDS + psyllium seed gum, APG-10 + psyllium seed gum, and OHSB + psyllium seed gum are 385, 403, 392, and 388 mL, respectively, with half-lives of 36.63, 56.15, 66.34, and 79.89 min, and comprehensive foam indexes of 10577, 16971, 19503, and 23248 mL min. Among the four surfactants tested, the compounding system of betaine-type surfactant OHSB and psyllium seed gum showed the best foam stabilizing effect. Therefore, it can be considered that there is a significant synergistic foam stabilizing effect between betaine-type surfactants and psyllium seed gum, and it is the most suitable choice among the surfactants tested for compounding with psyllium seed gum to improve the stability of CO2 foam. Comparative Example 2:

[0097] The difference between this comparative example and Example 1 is that the combination of the surfactant and the foam stabilizer is changed, the experimental steps are the same as those of Example 1, the experimental conditions change the solution mineralization to 0 (i.e., pure water), and the other experimental conditions are the same as those of Example 1. Different types of surfactants are combined with different types of foam stabilizers, and the combinations of surfactants and foam stabilizers are: SDS+xanthan gum, SDS+plantagin seed gum, OHSB+xanthan gum, and OHSB+plantagin seed gum.

[0098] The results showed that the foaming volume of CO2 foam in SDS+xanthan gum, SDS+plantagin seed gum, OHSB+xanthan gum, and OHSB+plantagin seed gum systems were 418, 415, 410, and 405 mL, respectively, the half-life was 43.50, 40.67, 53.89, and 57.75 min, and the foam comprehensive index was 13637, 12659, 16571, and 17542 mL·min. Under the same conditions, in the SDS system, the combination of xanthan gum was slightly better than that of plantagin seed gum in terms of comprehensive performance. In the OHSB system, the combination of plantagin seed gum was slightly better than that of xanthan gum in terms of comprehensive performance. The half-life and foam comprehensive index of the OHSB+plantagin seed gum system were the highest among all the combinations, and the combination of betaine OHSB and plantagin seed gum showed a better effect in stabilizing foam.

[0099] Comparative Example 3:

[0100] The difference between this comparative example and Example 1 is that the type and concentration of the foam stabilizer in step (1) are changed.

[0101] In this comparative example, a CO2 foam system is composed of foam stabilizers such as KYPAM-6S, psyllium seed gum, tamarind gum, xanthan gum, scleroglucan, and diutan. Foam base liquids with foam stabilizer concentrations of 0.05wt%, 0.1wt%, 0.15wt%, 0.2wt%, 0.25wt%, and 0.3wt% are prepared, respectively, to carry out foam performance experiments.

[0102] Step (2) and step (3) and parameters are the same as those in Example 1.

[0103] This example investigates the foam performance of CO2 foam system composed of foam stabilizers such as comb polymer (KYPAM-6S), psyllium seed gum, tamarind gum, xanthan gum, scleroglucan, and diutan gum. The foaming volume of CO2 foam strengthened by different biopolysaccharide polymers at different concentrations is shown in Figure 2. Figure 2 As shown in the figure, compared with KYPAM-6S, the foaming volume of the biopolysaccharide polymer decreases with increasing concentration. Due to the excessively high viscosity of the foam base liquid at high concentration, more energy is required for foaming, resulting in a gradual decrease in the volume of bubbles in the system. The order of the volume of CO2 foams enhanced by different biopolysaccharides is: KYPAM-6S> diutan gum> scleroglucan> tamarind gum> xanthan gum> psyllium gum.

[0104] The half-life of the effluent of different biopolysaccharide-enhanced CO2 foams at different concentrations is as follows Figure 3 As shown in the figure, the half-life of the liquid precipitation of all polymer systems gradually increases. Because the viscosity of the system increases with the concentration under the action of the polymer, the viscosity of the foam liquid film generated is large, and the liquid film liquid precipitation speed decreases, so the stability of CO2 foam increases. The order of volume size of CO2 foam enhanced by different biopolysaccharides is: psyllium seed gum>xanthan gum>tamarind gum>scleroglucan>diutan gum>KYPAM-6S. When the concentration is 3000 mg / L, the stability of psyllium seed gum, xanthan gum, tamarind gum, scleroglucan, and diutan gum are 4.8 times, 3.7 times, 2.6 times, 2.3 times, and 1.9 times that of KYPAM-6S, respectively.

[0105] This shows that the addition of polymers inhibits the foaming of CO2 foam but increases its stability, indicating that the biopolysaccharide-enhanced CO2 foam system has the best foaming performance. Therefore, the foam comprehensive index (FCI) is introduced to characterize the foam performance. The size of FCI can simultaneously reflect the foaming and stability of biopolysaccharide-enhanced CO2 foam. For a higher foam comprehensive index FCI, there is an optimal biopolysaccharide combination and optimal concentration. Figure 4 As shown in the figure, FCI increases with the increase of biopolysaccharide concentration. The FCI of CO2 foams enhanced by different biopolysaccharides is in the following order: psyllium seed gum>xanthan gum>tamarind gum>scleroglucan>diutan gum>KYPAM-6S. When the concentration is 3000 mg / L, the FCI values ​​of psyllium seed gum, xanthan gum, tamarind gum, scleroglucan, and diutan gum are 3.5 times, 3.0 times, 2.3 times, 2.1 times, and 1.8 times that of KYPAM-6S, respectively.

[0106] In summary, under high-temperature and high-salinity reservoir conditions, biopolysaccharide foam stabilizers show significant improvement in enhancing CO2 foam stability compared to traditional polyacrylamide. Biopolysaccharide polymers are not only environmentally friendly and biodegradable, effectively reducing the environmental burden, but also their rich natural resource base and low cost price give the system significant economic advantages, thereby promoting the economic benefits of oil field exploitation. Therefore, biopolysaccharides are expected to replace traditional polyacrylamide polymers in oil fields.

[0107] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, 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 base liquid, characterized in that: The invention comprises a foaming agent, a foam stabilizer and water, wherein the foaming agent is a betaine type surfactant and the foam stabilizer is a biopolysaccharide polymer.

2. The foam base liquid according to claim 1, characterized in that: The mass fraction of the foaming agent is 0.2-0.4wt%; And / or, the mass fraction of the foam stabilizer is 0.1-0.3wt%.

3. The foam base liquid according to claim 1, characterized in that: The foaming agent is selected from at least one of dodecyl dimethyl betaine, aramidopropyl betaine, octyl aramidopropyl betaine, lauroamidopropyl betaine, cocamidopropyl betaine, oleamidopropyl betaine, erucamidopropyl betaine, lauryl hydroxypropyl sulfobetaine, coconut hydroxypropyl sulfobetaine, lauramide hydroxypropyl sulfobetaine, cocamidopropyl sulfobetaine, dodecyl dimethyl hydroxypropyl sulfobetaine, hexadecyl dimethyl hydroxypropyl sulfobetaine, oleamidohydroxypropyl sulfobetaine and erucamidohydroxypropyl sulfobetaine.

4. The foam base liquid according to claim 1, characterized in that: The foam stabilizer is selected from at least one of psyllium seed gum, tamarind gum, scleroglucan, diutan gum and xanthan gum.

5. The foam base liquid according to claim 1, characterized in that: The mineralization degree of the foam base liquid is 0 to 2.0×10 5 mg / L; And / or, the foam base liquid further comprises an inorganic salt, and the mass fraction of the inorganic salt is 0 to 20.0 wt %.

6. The foam base liquid according to claim 5, characterized in that: The inorganic salt includes at least one of NaCl, CaCl2 and MgCl2.

7. A method for preparing a foam base liquid according to any one of claims 1 to 6, characterized in that: include: dissolving the foaming agent in water to obtain a surfactant solution; The foam stabilizer is dissolved in the surfactant solution to obtain the foam base liquid.

8. A method for preparing a heat-resistant and salt-resistant CO2 foam flooding system, characterized in that: include: The foam base fluid described in any one of claims 1 to 6 and CO2 gas are introduced into the core to obtain a CO2 foam flooding system.

9. The method for preparing the heat-resistant and salt-resistant CO2 foam flooding system according to claim 8, characterized in that: The temperature of the foam base liquid is 20-130°C.

10. The method for preparing the heat-resistant and salt-resistant CO2 foam flooding system according to claim 8, characterized in that: The pressure of the CO2 gas is 0-20MPa.

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