CN113604209A

CN113604209A - Nano-composite viscoelastic oil displacement agent produced on line

Info

Publication number: CN113604209A
Application number: CN202110913903.9A
Authority: CN
Inventors: 李翔; 于萌; 铁磊磊
Original assignee: China Oilfield Services Ltd
Current assignee: China Oilfield Services Ltd
Priority date: 2021-08-10
Filing date: 2021-08-10
Publication date: 2021-11-05

Abstract

The invention provides an online produced nanometer composite oil displacement agent, which comprises the following components in percentage by weight: 0.05 to 0.8 percent of surfactant and the balance of water; wherein the surfactant comprises erucamidopropylhydroxysultaine, or erucamidopropylbetaine, cetylamidopropylhydroxypropylsultaine, and tetradecylpropylsultaine. The compound oil displacement agent can also comprise at least one of tetradecylamidopropyl hydroxypropyl sulfobetaine and hexadecyl propyl sulfobetaine, and/or nano silicon dioxide with the content of not more than 0.05 percent, and/or sodium dodecyl benzene sulfonate with the content of not more than 0.03 percent, and/or polyether diamine with the content of 0.05 to 0.1 percent and salicylic acid with the content of 0.05 to 0.1 percent. For oil reservoirs with different degrees of mineralization and permeabilities, the viscosity and the interfacial tension of the nano-composite viscoelastic oil displacement agent in the oil reservoir are controllable; and inorganic ions in the formation injection water are fully utilized under the condition of ensuring on-line injection.

Description

Nano-composite viscoelastic oil displacement agent produced on line

Technical Field

The invention relates to the technical field of balanced oil displacement of offshore continental sandstone reservoirs, in particular to an online-produced nanometer composite viscoelastic oil displacement agent.

Background

At present, an effective means for improving the water drive development effect of an oil field is to enlarge the water wave and volume of injection. However, as the oil field gradually enters a development stage with medium-high water content or ultrahigh water content, the residual oil enrichment area is distributed in the deep part of the stratum, and the original profile control technology of the near wellbore area is difficult to meet the requirement of deep liquid flow steering of the mine field. In addition, aiming at oil reservoirs with strong heterogeneity or high mineralization degree, the injectability or salt resistance of the conventional polymer gel is difficult to adapt to the environmental requirements, and the salt-resistant modified polymer has higher cost, so that the profile control cost is obviously increased. In addition, the presence of solid suspensions in the oilfield injection water can reduce the injection performance of the polyacrylamide profile control agent. The inorganic gel profile control agent has low cost, but has quick inorganic reaction, weak inorganic gel shear resistance, difficult system to enter deep stratum and unsatisfactory plugging strength in the deep stratum.

Currently, there have been some studies in this regard. For example, the Chinese patent application with application number of 201811150954.5 discloses a profile control and flooding system and an oil displacement method suitable for carbonate weathering crust reservoirs. The oil displacement system comprises the following components in percentage by mass: 0.5 to 2 percent of nano silicon dioxide, 0.01 to 3.0 percent of quaternary ammonium salt surfactant and the balance of water. The Chinese patent application with the application number of 201310300604.3 discloses a salt-tolerant vermicular micelle system, a preparation method thereof and application thereof in oil displacement. Among these, a worm-like micellar system comprising an alkyl sulphobetaine, a sodium alkyl sulphate surfactant and optionally an adjuvant. Wherein the mole fraction of the sodium alkyl sulfate to the total mole amount of the sodium alkyl sulfate and the alkyl sulfobetaine is 0.2-0.6, preferably 0.2-0.4, and more preferably 0.2-0.3. Wherein the total mass fraction of the surfactant is 0.2-0.8%.

However, the above researches mainly refer to a polymer flooding technology and a conventional polymer profile control agent, and for a hypersalinity oil field, a salt-resistant polymer needs to be used, so that the cost investment is increased, online injection cannot be performed, and the injection property is difficult to reach an expected value.

Therefore, an oil displacement technology which can realize online injection, has good injectability, is salt-resistant and shear-resistant and effectively improves the deep oil displacement effect is urgently needed.

Disclosure of Invention

In order to solve all or part of the problems, the invention aims to provide an on-line produced nanometer composite viscoelastic oil displacement agent so as to effectively improve the deep oil displacement effect.

Specifically, the invention is realized by the following technical scheme:

a composite oil displacement agent comprises the following components in percentage by weight: 0.05 to 0.8 percent of surfactant and the balance of water; wherein the surfactant comprises erucamidopropylhydroxysultaine, erucamidopropylbetaine, cetylamidopropylhydroxypropylsultaine, and tetradecylpropylsultaine.

Preferably, the content of the surfactant is 0.3% to 0.8%.

Preferably, the erucamidopropylhydroxysultaine is present in the surfactant in an amount of no more than 45%, preferably from 18% to 45%, more preferably from 18% to 22.5%.

Preferably, the content of the cetylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine in the surfactant is not more than 10%.

Preferably, the surfactant further comprises tetradecylamidopropyl hydroxypropyl sulphobetaine and/or hexadecyl propyl sulphobetaine.

Preferably, the compound oil displacement agent also comprises nano silicon dioxide with the content not more than 0.05 percent; more preferably, the compound oil displacement agent comprises nano silicon dioxide with the content of 0.005-0.05%.

Preferably, the particle size of the nanosilica is from 15nm to 50nm, more preferably from 30nm to 50 nm.

Preferably, the surfactant further comprises an anionic surfactant at a level of no more than 0.075%; more preferably, the surfactant further comprises an anionic surfactant in an amount of not more than 0.03%.

Preferably, the anionic surfactant is any one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium dodecyl polyoxyethylene ether sulfate; more preferably, the anionic surfactant is sodium dodecylbenzene sulfonate.

Preferably, the compound oil displacement agent further comprises polyether diamine and/or salicylic acid; more preferably, the compound oil displacement agent further comprises polyether diamine and salicylic acid; most preferably, the compound oil displacement agent comprises 0.05-0.1% of polyether diamine and 0.05-0.1% of salicylic acid.

Compared with the prior art, the invention has at least the following beneficial effects:

compared with the prior oil displacement system, the system has the advantages of enhancing the strength of the system, improving the migration performance of the system in the deep stratum, simplifying the construction process, reducing construction equipment and lowering the cost of medicament and operation, thereby obviously lowering the cost compared with the traditional surfactant oil displacement technology.

For oil reservoirs with different degrees of mineralization and permeability, the viscosity and the interfacial tension of the oil displacement agent in the oil reservoir can be controlled; and inorganic ions in the formation injection water are fully utilized under the condition of ensuring on-line injection.

Drawings

Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. In the drawings:

FIG. 1 shows the shear viscosity results for examples 1-1 to 1-3 and comparative example 1.

FIG. 2 shows the constant shear viscosity results for examples 1-1 through 1-3 and comparative example 1.

Figure 3 shows the effect of water sample composition on the viscosity of the displacement agent.

FIG. 4 shows the effect of surfactant concentration on the viscosity of an oil displacing agent when formulated with simulated water.

FIG. 5 shows the effect of surfactant concentration on the viscosity of an oil displacing agent when the oil displacing agent was formulated with injection water.

Figure 6 shows the viscosity of an oil displacing agent formulated with water injected as a function of temperature.

Figure 7 shows the viscosity of an oil displacing agent formulated with simulated water as a function of temperature.

FIG. 8 shows the effect of NaCl concentration on the viscosity of the displacement agent.

FIG. 9 shows NaHCO₃The effect of concentration on the viscosity of the oil-displacing agent.

FIG. 10 shows Na₂SO₄The effect of concentration on the viscosity of the oil-displacing agent.

FIG. 11 shows CaCl₂The effect of concentration on the viscosity of the oil-displacing agent.

FIG. 12 shows MgCl₂The effect of concentration on the viscosity of the oil-displacing agent.

Fig. 13 shows the relationship of the viscosity of the oil displacing agent with the kind and concentration of the electrolyte.

Fig. 14 shows the effect of the content of nano silica particles having a particle diameter of 15nm on the viscosity of the oil displacing agent.

Fig. 15 shows the effect of the content of nano silica particles having a particle diameter of 30nm on the viscosity of the oil-displacing agent.

Fig. 16 shows the effect of the content of nano silica particles having a particle diameter of 50nm on the viscosity of the oil-displacing agent.

Fig. 17 shows the relationship between the particle diameter and concentration of the nanosilica particles and the viscosity of the oil-displacing agent.

Figure 18 shows the constant shear viscosity results for systems with different mass fractions of SDBS to total surfactant.

Figure 19 shows the results of fitting the mass fraction of SDBS on total surfactant to the constant shear viscosity effect of the oil displacing agent system.

FIG. 20 shows the viscosity as a function of time and temperature after injection of the oil displacing agent of example 5.

FIG. 21 shows the pressure as a function of PV after injection of the oil displacing agent of example 5.

FIG. 22 shows production as a function of injected PV after injection of the displacement agent of example 5.

FIG. 23 shows the elastic modulus and viscous modulus of the samples in example 5.

FIG. 24 shows the elastic modulus and viscous modulus of polyacrylamide in example 5.

Detailed Description

The present invention will be described in detail with reference to the following embodiments in order to fully understand the objects, features and effects of the invention, but the present invention is not limited thereto. The process of the present invention employs conventional methods or apparatus in the art, except as described below.

In the present invention, "%" means "% by weight" and ratios mean weight ratios, unless otherwise specified.

Aiming at various problems of the conventional polymer oil displacement agent, the inventor of the invention carries out intensive research, thereby creatively providing a composite oil displacement agent which comprises the following components in percentage by weight: 0.05 to 0.8 percent of surfactant and the balance of water; wherein the surfactant comprises Erucamidopropylhydroxysultaine (EHSB), erucamidopropylbetaine (PEHSB), cetylamidopropylhydroxypropylsultaine, and tetradecylpropylsultaine; wherein the water can be tap water, injection water or simulated water.

The structural formula of the PEHSB adopted by the invention, namely the erucic amide propyl betaine, is as follows:

the structural formula of EHSB and erucamide propyl hydroxysulfobetaine adopted by the invention is as follows:

the hexadecyl amide propyl hydroxypropyl sulfobetaine adopted by the invention has the following structural formula:

the tetradecyl propyl sulfobetaine adopted by the invention has the following structural formula:

as a preferable embodiment, in the composite oil-displacing agent of the present invention, the content of the surfactant is 0.3% to 0.8%, for example, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or the like. As a more preferred embodiment, the content of EHSB is not more than 45%, preferably the content of EHSB is 18% to 45%, such as 18%, 20%, 23%, 25%, 28%, 30%, 33%, 35%, 38%, 40%, 43%, or 45%, etc., more preferably the content of EHSB is 18% to 22.5%, such as 18%, 19%, 20%, 21%, 22%, or 22.5%, etc., based on the total weight of the surfactant. As another more preferred embodiment, the sum of the contents of hexadecylamidopropyl hydroxypropyl sultaine and tetradecylpropyl sultaine does not exceed 10%, and the weight ratio of both hexadecylamidopropyl hydroxypropyl sultaine and tetradecylpropyl sultaine may be 3:7, 4:6, 5:5, 6:4, 7:3, etc.

The inventors of the present invention have conducted intensive studies on PEHSB and EHSB, and have found that both of them have the ability to rapidly increase the viscosity of injected water when used alone, and exhibit good thickening properties under conditions of high and low temperatures, that is, have the viscosity properties typical of viscoelastic oil-displacing agents. However, the viscosity characteristics of the PEHSB injection water sample and the viscous oil displacement agent are not completely the same, the micelle structure of the PEHSB injection water sample in a certain temperature range is hardly changed, and the structural characteristics of the viscoelastic oil displacement agent are still kept at high temperature; for an EHSB injected water sample, the viscoelastic oil displacement agent is formed at low temperature, but at high temperature, the viscoelastic oil displacement agent structure is destroyed and converted into smaller aggregates such as spherical micelles, thereby causing the viscosity of the system to be reduced sharply. From a temperature resistance perspective, PEHSB is more temperature resistant than EHSB, and PEHSB is almost temperature independent of either static viscosity or constant shear viscosity.

Based on the above research, the inventors of the present invention propose to use PEHSB and EHSB in oil displacement agents after the compatibility. Further studies have found that when the amounts of PEHSB and EHSB are within the range of the present invention, the viscosity of the oil displacing agent decreases with increasing shear rate, which is a typical shear viscosity characteristic of viscoelastic oil displacing agent systems. More importantly, the static viscosity of the oil displacement agent is increased and then decreased along with the change of the weight ratio of the PEHSB to the EHSB, which shows that the two surfactants of the PEHSB and the EHSB have synergistic effect in the aspect of viscosity increasing.

When the dosage of the PEHSB and the EHSB is within the range of the invention, the oil displacement agent can achieve better effects in the aspects of temperature resistance, salt resistance and viscosity increasing effect on injected water, particularly the static viscosity is the maximum, which shows that the PEHSB and the EHSB have strong synergistic effect.

The viscosity of the oil displacement agent is greatly influenced by temperature, and the viscosity of an oil displacement agent system obtained by diluting the surfactant with water at low temperature and high temperature by adopting the same equipment condition is completely different. The characteristic of the oil displacement agent of the invention just meets different requirements on the viscosity of the oil displacement agent in different stages in the application process of actual water injection yield increase.

The whole recovery process can be roughly divided into three major stages, namely water injection, oil displacement and oil extraction, and the application of the oil displacement agent relates to the water injection and oil displacement stages. The injection process of the first stage requires that the injectability of the fluid is good, i.e. the viscosity of the injected fluid is relatively small; in the oil displacement process of the second stage, the injected fluid is required to have higher viscosity under the conditions of high-temperature and high-salt oil deposit.

In practical application, on-line preparation can be adopted. Specifically, when the oil displacement agent of the present invention is actually injected, in the first stage, the surfactant composed of PEHSB and EHSB in the above ratio is diluted to the concentration range of the present invention by using the injected water, and in this process, an additional heat source is not introduced to heat the dilution process except the residual temperature of the injected water itself, and the viscosity of the obtained oil displacement agent system is very small, which just meets the requirement of small viscosity in the first stage. In the second stage, under the condition of high-temperature and high-salt oil reservoir, the viscosity of the oil displacement agent system is remarkably increased, namely, the phenomenon of high-temperature induced in-situ thickening occurs, and the process just meets the requirement of the second stage oil displacement process on high viscosity.

In view of the characteristic that the viscosity of the oil displacement agent of the invention changes with temperature, the inventors of the invention have further conducted intensive studies and found that:

it is known from the above-mentioned structural features of the molecules of PEHSB and EHSB that the hydrophobic tail chain of the surfactant is up to 22 carbon atoms, and the molecules are hydrophilicThe water head group is small, the hydrophobic tail chain is large, and the molecular stacking parameter is greater than 1/3 from the viewpoint of the molecular stacking parameter, so that the two molecules have the characteristic of strongly forming a viscoelastic oil displacement agent in a solution. On the other hand, the hydrophilic head groups of the two molecules are simultaneously charged with positive electricity and negative electricity, and are typical zwitterionic surfactants, so that they exist in the form of internal salts, and the whole molecule is electrically neutral, similar to nonionic surfactants. Their Krafft temperature is actually very high due to their too long hydrophobic tail-chains-for both compounds pure, their solubility in boiling water is not great. If, however, electrolytes such as NaCl, CaCl are introduced into their aqueous solutions₂For example, the destruction of the internal salt structure by the counter ion adsorption results in an ionic surfactant, and the solubility property is rapidly increased, which is also a factor of the salt resistance of these two substances.

As described above, these two substances have strong property of forming viscoelastic oil displacement agent, so that they form a very large self-assembly structure in solution state, and the process of diluting them needs to break up and uniformly disperse the intertwined viscoelastic oil displacement agent structure, and this process must overcome the strong electrostatic interaction between molecules and aggregates, so that it needs to be completed by vigorous stirring and sufficient time at normal temperature. If the stirring is insufficient and the stirring time is insufficient, the concentrated aggregates will only disperse into "particles" of different sizes and the viscosity of the system as a whole will not be large. The final viscosity value of the system is related to the stirring mode, the stirring speed and the stirring time, namely, the viscosity of the process is controlled by dynamics.

If the oil displacement agent sample is placed under the condition of high temperature, the thermal motion of molecules is intensified, the solubility of the surfactant in water is increased, so that the viscoelasticity oil displacement agent which is uniformly dispersed can be spontaneously formed in a short time, the high viscosity of the oil displacement agent system is ensured, the viscosity of the process is a process controlled by thermodynamics, the constant shear rate viscosity finally reached by the system is determined by the composition of the sample, and the method is irrelevant to whether the sample is subjected to strong shear before testing. Even if the viscosity of the sample fluctuates to some extent due to the strong shearing and the constant shearing rate in a short time, the viscosity can be rapidly recovered, which is determined by the thermodynamic properties of the viscoelastic oil displacement agent.

And, when hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecyl propyl sulfobetaine are further added to the above PEHSB and EHSB, the salt tolerance of the system can be significantly enhanced.

As a more preferred embodiment, the complex oil displacement agent of the present invention further comprises tetradecylamidopropyl hydroxypropyl sulfobetaine and/or hexadecylpropyl sulfobetaine.

The tetradecylamidopropyl hydroxypropyl sulphobetaine adopted by the invention has the following structural formula:

the structural formula of the hexadecyl propyl sulfobetaine adopted by the invention is as follows:

the inventor of the invention discovers through research that by further adding one or two of tetradecylamidopropyl hydroxypropyl sulfobetaine and hexadecylpropyl sulfobetaine into the composite oil displacement agent, the salt tolerance of a system can be further improved for a reservoir (2-5 ten thousand mg/L) with high mineralization degree in an offshore oil field while the viscoelasticity of the composite oil displacement agent is ensured. The surfactants can be added in a small amount to further improve the salt resistance of the system.

In the present invention, erucamidopropylhydroxysultaine, erucamidopropylbetaine, cetylamidopropylhydroxypropylsultaine, tetradecylamidopropylhydroxypropylsultaine, hexadecylpropylsultaine and tetradecylpropylsultaine are commercially available, and the present invention has no particular requirement for these surfactants, and commercially available erucamidopropylhydroxysultaine, erucamidopropylbetaine, hexadecylamidopropylhydroxypropylsultaine, tetradecylamidopropylsultaine, hexadecylpropylsultaine and tetradecylpropylsultaine can be used in the present invention. For example, tetradecylamidopropyl hydroxypropyl sulfobetaine, hexadecylpropyl sulfobetaine, tetradecylpropyl sulfobetaine are available from Guangzhou Tiancigao, Shanghai nusonsong, Shanghai silver clever, etc.; cetyl amidopropyl hydroxypropyl sulfobetaine is commercially available from shanghai nusonde, shanghai kumquat, etc.

As a more preferable embodiment, the composite oil displacement agent of the present invention further comprises nano silica. The content of the nano-silica is not more than 0.05%, preferably 0.005% to 0.05%, for example, 0.005%, 0.01%, 0.02%, 0.03%, 0.04%, or 0.05%. The particle size of the nano-silica is 15nm to 50nm, for example, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm or 50nm, preferably 30nm to 50nm, for example, 30nm, 32nm, 34nm, 36nm, 38nm, 40nm, 42nm, 44nm, 46nm, 48nm or 50 nm.

The inventor of the invention believes through research that the surfactant adopted by the oil displacement agent is a zwitterionic surfactant, although the whole oil displacement agent is neutral, the hydrophilic head group of the oil displacement agent is simultaneously loaded with positive electricity and negative electricity, and the surfactant and the nanoparticles are combined together through electrostatic action by introducing the nano-silica into the hydrophilic head group to form a space network structure, so that the viscosity and the elasticity of the oil displacement agent system are improved.

Further research shows that when the content of the nano silicon dioxide in the oil displacement agent is 0.005-0.05%, the viscosity of the oil displacement agent can be obviously improved, and particularly, when the content of the nano silicon dioxide is 0.01%, the maximum viscosity improvement of the oil displacement agent can be realized. In addition, the nanosilica size has an effect on the degree of thickening, with nanosilica at 15nm being less effective than nanosilica at 30nm to 50 nm. When the particle size of the nano-silica reaches 30nm, the effect of the size of the nano-particles on the viscosity is nearly the same at the same concentration.

As another more preferred embodiment, the surfactant in the composite oil-displacing agent of the present invention further includes an anionic surfactant. The anionic surfactant is present in an amount of no more than 0.075%, preferably no more than 0.03%, by weight of the total surfactant. The anionic surfactant may be any one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and sodium dodecylpolyoxyethylene ether sulfate, and preferably, the anionic surfactant is sodium dodecylbenzene sulfonate (SDBS). Particularly preferably, the surfactant in the composite oil displacement agent comprises sodium dodecyl benzene sulfonate with the content of not more than 0.03 percent based on the total weight of the surfactant.

The inventors considered through studies that Sodium Dodecylbenzenesulfonate (SDBS) has an influence on the viscosity and stability of the nanoparticle-viscoelastic oil-displacing agent system of the present invention, i.e., the oil-displacing agent comprising nanosilica of the present invention. SDBS exhibits good stability to nanoparticles and can improve the dispersibility of nanoparticle-viscoelastic oil displacement agent systems, but may cause a decrease in system viscosity. After further research, the inventor believes that the surfactant containing sodium dodecyl benzene sulfonate with the content not more than 0.03% can effectively improve the dispersibility of the oil displacement agent system while ensuring the expected viscosity of the system.

As another more preferred embodiment, the composite oil displacement agent of the present invention further comprises polyether diamine and/or salicylic acid. Preferably, the composite oil displacement agent comprises polyether diamine and salicylic acid at the same time. More preferably, the compound oil displacement agent comprises 0.05-0.1% of polyether diamine and 0.05-0.1% of salicylic acid.

The inventor believes through research that polyether diamine and salicylic acid have an in-situ thickening effect. The polyether diamine and the salicylic acid are added into the composite oil-displacing agent, so that the viscosity of an oil-displacing agent system is further improved, and the composite oil-displacing agent has the obvious advantages of remarkably improving the dispersibility of the oil-displacing agent and ensuring that the oil-displacing agent has good fluidity.

Examples

The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.

Examples 1 to 1

The oil displacing agent of this example was an injection aqueous solution having a surfactant concentration of 0.5% in which the surfactant was composed of PEHSB, EHSB, cetylamidopropylhydroxypropylsulfobetaine, and tetradecylpropylsulfobetaine in a weight ratio of 72:18:6: 4. The oil displacing agent system of this example was 100 mL.

The preparation method of the oil displacement agent of the embodiment comprises the following steps: firstly, mixing PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulphobetaine and tetradecyl propyl sulphobetaine according to a proportion, then dissolving 0.5g of the mixture in injected water, stirring at a constant temperature of 60 ℃ for 30min, and preparing 100mL of oil displacement agent with 0.5% of surfactant concentration.

Examples 1 to 2

The oil displacing agent of this example was an injection aqueous solution having a surfactant concentration of 0.5%, wherein the surfactant consisted of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine, and tetradecylpropyl sulfobetaine in a weight ratio of 67.5:22.5:6: 4. The oil displacing agent system of this example was 100 mL.

The oil-displacing agent of this example was prepared in the same manner as in example 1-1 except that the proportions of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine were adaptively adjusted.

Examples 1 to 3

The oil displacing agent of this example was an injection aqueous solution having a surfactant concentration of 0.5%, wherein the surfactant consisted of PEHSB, EHSB, cetylamidopropylhydroxypropylsulfobetaine, and tetradecylpropylsulfobetaine in a weight ratio of 45:45:6: 4. The oil displacing agent system of this example was 100 mL.

Examples 1 to 4

The oil displacing agent of this example was a simulated aqueous solution having a surfactant concentration of 0.5% where the surfactant consisted of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine, and tetradecylpropyl sulfobetaine in a weight ratio of 67.5:22.5:6: 4. The oil-displacing agent system of this comparative example was 100 mL.

The preparation method of the oil displacement agent of the embodiment comprises the following steps:

mixing PEHSB and EHSB with hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecyl propyl sulfobetaine according to a proportion, dissolving 0.5g of the mixture in simulated water, and stirring at a constant temperature of 60 ℃ for 30min to prepare 100mL of oil displacement agent with 0.5% of surfactant concentration. The main parameter indexes of the simulated water used in this embodiment are as follows:

examples 1 to 5

The oil-displacing agent of this example was a pure aqueous solution with a surfactant concentration of 0.3%, wherein the surfactant consisted of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine, and tetradecylpropyl sulfobetaine at a weight ratio of 67.5:22.5:6: 4. The oil displacing agent system of this example was 100 mL.

The oil-displacing agent of this example was prepared in the same manner as in example 1-1 except that the proportions of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine and the water used were adjusted adaptively.

Comparative example 1

The oil-displacing agent of this comparative example was an injection aqueous solution having a surfactant concentration of 0.5%, in which the surfactant was composed of PEHSB, EHSB, cetylamidopropylhydroxypropylsulfobetaine, and tetradecylpropylsulfobetaine in a weight ratio of 36:54:6: 4. The oil-displacing agent system of this comparative example was 100 mL.

The oil-displacing agent of this comparative example was prepared in the same manner as in example 1-1 except that the proportions of PEHSB, EHSB, hexadecylamidopropylhydroxypropylsulfobetaine and tetradecylpropylsulfobetaine were adaptively adjusted.

And (3) effect testing:

1. the samples of examples 1-1 to 1-3 and comparative example 1 were tested for viscosity using a hakke viscotest q rheometer with a clamp Z5 at a temperature of 60 ℃. The shear viscosity and the constant shear viscosity can be read directly using a rheometer.

The results obtained for shear viscosity are shown in FIG. 1, and for constant shear viscosity in FIG. 2. In FIGS. 1 and 2, Sample A, Sample B, Sample C, and Sample D correspond to the samples of example 1-1, example 1-2, example 1-3, and comparative example 1, respectively.

As can be seen from fig. 1, the oil-displacing agent has excellent static viscosity when the ratio of PEHSB, EHSB, cetylamidopropyl hydroxypropyl sulfobetaine, and tetradecylpropyl sulfobetaine is 72:18:6:4 (example 1-1) or 67.5:22.5:6:4 (example 1-2); when the ratio of PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine, and tetradecylpropyl sulfobetaine is 45:45:6:4 (examples 1-3), the oil-displacing agent still achieves a better static viscosity; however, when the proportion of EHSB exceeds 50%, for example, the proportion of PEHSB, EHSB, hexadecylamidopropylhydroxypropylsulfobetaine and tetradecylpropylsulfobetaine is 36:54:6:4 (comparative example 1), the static viscosity of the oil-displacing agent is drastically reduced. Therefore, from the viewpoint of increasing the static viscosity, the content of EHSB in the total surfactant is selected to be not more than 45%, and preferably less than 45%.

As can be seen from fig. 2, the viscosity of all four samples increased with decreasing shear rate. Samples of examples 1-1 and 1-2 were taken at 7.34s^-1The viscosity of the system is stabilized at 60 mPa.s. With PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropylThe ratio of the sulfobetaine was increased to 45:45:6:4 (examples 1-3), 7.34s^-1A significant viscosity reduction of the viscosity of the system occurs. In this case, the static viscosity does not change much as seen from the shear rate-viscosity graph (FIG. 1). From the viewpoint of increasing the constant shear viscosity, the content of EHSB in the total surfactant is selected to be not more than 45%, and preferably less than 45%.

2. Influence of water sample composition on viscosity of oil displacement agent

Using rheometer, test 7.34s^-1Constant shear viscosity.

The results are shown in FIG. 3. It can be seen from the figure that the viscosity of the injected water formulated sample (60 mpa.s, examples 1-2) is slightly higher than the viscosity of the simulated water sample (40 mpa.s, examples 1-4) at 60 ℃, but the relevant viscosity results all meet the requirements in actual production. The results show that the oil displacement agent of the present invention is somewhat resistant to changes in the composition of the aqueous phase.

3. Effect of surfactant concentration on oil-displacing agent viscosity

The samples of examples 1 to 4 were diluted with simulated water to concentrations of 0.3%, 0.2% and 0.1% in this order, and then the viscosity (60 ℃ C.) was measured, and the results are shown in FIG. 4.

The samples of examples 1-2 were diluted to concentrations of 0.3%, 0.2% and 0.1% in this order with water injection, and then the viscosities (60 ℃ C.) were measured, and the results are shown in FIG. 5.

From the viscosities of the different concentrations of the simulated water samples of FIG. 4, it can be seen that as the concentration of the system is reduced from 0.5 wt% to 0.3 wt%, the viscosity of the system is reduced from 40mPa.s to 10 mPa.s; the surfactant concentration decreases and the viscosity decreases. Corresponding to the injected water sample, it is clear from FIG. 5 that the sensitivity of the surfactant concentration to the decrease in the viscosity of the injected water is reduced, and that 7.34s is obtained when the total surfactant concentration is reduced to 0.2 wt%^-1The retained viscosity is still higher than 10 mpa.s. It can be seen that the oil displacement agent of the invention has better effect in injected water compared with simulated water.

4. Effect of temperature on oil-displacing agent viscosity

The constant shear viscosity at 7.34s-1 was measured using a rheometer.

The results are shown in FIGS. 6 and 7, respectively, using the samples of examples 1-2 and examples 1-4 as examples.

As can be seen from FIG. 6, the higher the temperature at high shear rate, the lower the viscosity of the oil displacing agent system, but at 7.34s^-1The viscosity of the system changes little when the temperature rises from 60 ℃ to 80 ℃. A similar phenomenon can also be seen in samples formulated with simulated water (fig. 7). Therefore, the oil displacement agent shows good temperature resistance from the viewpoint of viscosity.

5. Influence of degree of mineralization on viscosity of oil-displacing agent

Five electrolytes mainly contained in simulated water were studied: NaCl, NaHCO₃、Na₂SO₄、CaCl₂And MgCl₂The influence on the viscosity of the viscoelastic oil-displacing agent system of the oil-displacing agent of the invention under different concentration conditions. The oil-displacing agent samples of examples 1 to 5 were used and the concentration of the electrolyte therein was varied from 0mg/L to 100000mg/L under the test conditions of 7.34s^-1And 65 ℃.

FIG. 8 shows the effect of NaCl concentration on the viscosity of the displacement agent. FIG. 9 shows NaHCO₃The effect of concentration on the viscosity of the oil-displacing agent. FIG. 10 shows Na₂SO₄The effect of concentration on the viscosity of the oil-displacing agent. FIG. 11 shows CaCl₂The effect of concentration on the viscosity of the oil-displacing agent. FIG. 12 shows MgCl₂The effect of concentration on the viscosity of the oil-displacing agent. As can be seen from fig. 8 to 12, the viscosity of the oil displacement agent does not change significantly with the increase of the electrolyte concentration, which indicates that the type and content of the electrolyte do not have a significant effect on the viscosity of the viscoelastic oil displacement agent system, i.e. the oil displacement agent of the present invention can still be stable under the condition of high salinity.

To better compare the effect of the electrolyte, the mean values after 200s of each test were plotted against the different electrolyte concentrations, see FIG. 13, where the surfactant concentration was 0.3% and the test conditions were 7.34s^-1And 65 ℃. As can be seen from the figure, of the five electrolytes studied, only Na was present₂SO₄For viscoelastic oil displacementThe viscosity of the agent system has a significant influence, the higher the concentration the lower the viscosity, and the viscosity almost completely disappears above-70 g/L. However, this phenomenon is not significant in reagent systems because divalent calcium and magnesium ions bind to sulfate ions and the concentration of the salt formed is limited and cannot reach the measured concentration range. In addition, when NaHCO is used₃At concentrations above-50 g/L, the viscosity may be reduced, possibly in combination with a high concentration of NaHCO₃The resulting change in solution pH is relevant. As for the remaining three electrolytes, an increase in concentration not only does not lead to a decrease in viscosity but also contributes to an increase in viscosity, especially divalent calcium and magnesium salts.

Example 2-1

The oil displacement agent of the embodiment comprises the following components: 0.3% of surfactant (consisting of 67.5:22.5:6:4 PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine in weight ratio), nano-silica having a particle size of 15nm, and the balance of water.

Wherein, the content of the nano silicon dioxide in the oil displacement agent is respectively 0.005%, 0.0075%, 0.01%, 0.02%, 0.03% and 0.05%, so as to obtain different oil displacement agent samples.

Each sample was tested at 65 ℃ and 7.34s^-1The viscosity under the conditions is compared with that of the oil displacement agent without the nano silicon dioxide, and the result is shown in FIG. 14. As can be seen from fig. 14, the introduction of the nano silica particles can increase the viscosity of the oil-displacing agent system, and the viscosity reaches the maximum value when the content of the nano silica is 0.01%.

Examples 2 to 2

The oil displacement agent of the embodiment comprises the following components: 0.3% of surfactant (consisting of 67.5:22.5:6:4 PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine in weight ratio), nano-silica having a particle size of 30nm, and the balance of water.

Wherein, the content of the nano silicon dioxide in the oil displacement agent is respectively 0.005%, 0.0075%, 0.01%, 0.02%, 0.03%, 0.04% and 0.05%, so as to obtain different oil displacement agent samples.

Each sample was tested at 65 ℃ and 7.34s^-1The viscosity under the conditions is compared with that of the oil displacement agent without the nano silicon dioxide, and the result is shown in FIG. 15. As can be seen from fig. 15, the introduction of the nano silica particles can increase the viscosity of the oil-displacing agent system, and the viscosity reaches the maximum value when the content of the nano silica is 0.01%.

Examples 2 to 3

The oil displacement agent of the embodiment comprises the following components: 0.3% of surfactant (consisting of 67.5:22.5:6:4 PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine in weight ratio), nano-silica having a particle size of 50nm, and the balance of water.

Wherein the content of the nano silicon dioxide in the oil displacement agent is 0.0062%, 0.0105%, 0.02%, 0.03% and 0.04%, respectively, so as to obtain different oil displacement agent samples.

Each sample was tested at 65 ℃ and 7.34s^-1The viscosity under the conditions is compared with that of the oil displacement agent without the nano silicon dioxide, and the result is shown in FIG. 16. As can be seen from fig. 16, the introduction of the nano silica particles can increase the viscosity of the oil-displacing agent system, and the viscosity reaches the maximum value when the content of the nano silica is 0.02%.

The viscosity averages for each of the samples of examples 2-1, 2-2 and 2-3 were compared, using the same shear rate and time, and the results are shown in FIG. 17. As can be seen from FIG. 17, the size of the nanosilica particles has an effect on the degree of viscosification, the 15nm system is not as good as the 30nm and 50nm systems, and the size of the nanoparticles has approximately the same effect on viscosity at the same concentration after the nanosilica size reaches 30 nm.

Example 3

The oil displacement agent of the embodiment comprises the following components:

PEHSB, EHSB, hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine at a weight ratio of 67.5:22.5:6: 4: 0.3 percent of

Nano silica having a particle size of 30 nm: 0.01 percent

SDBS

The balance of water

Where the SDBS mass fraction of total surfactant (i.e., the sum of PEHSB, EHSB, SDBS, cetylamidopropylhydroxypropylsultaine, and tetradecylpropylsultaine) was 0.025%, 0.05%, and 0.075%, respectively, resulting in different oil-displacing agent samples.

Each sample was tested at 65 ℃ and 7.34s^-1The viscosity under the conditions, as compared with the oil-displacing agent containing no SDBS, is shown in FIG. 18, wherein m is_SDBS/m_totalRepresenting the mass ratio of SDBS to total surfactant. Figure 18 shows the constant shear viscosity results for systems with different mass fractions of SDBS to total surfactant, and it can be seen that the viscosity of the oil displacing agent system decreases as the mass fraction of SDBS increases.

Each sample was tested at 65 ℃ and 7.34s^-1The constant shear viscosity under the conditions, as compared with the oil-displacing agent without SDBS, is shown in FIG. 19, where m is_SDBS/m_totalRepresenting the mass ratio of SDBS to total surfactant. Figure 19 shows the results of fitting the mass fraction of SDBS on total surfactant to the constant shear viscosity effect of the oil displacing agent system. As can be seen from FIG. 19, when, m_SDBS/m_totalWhen the viscosity is less than 0.03%, the viscosity of the oil displacement agent system can meet the offline constant shear viscosity of 10mPa.s of the target viscosity, and the dispersibility of the oil displacement agent system is good.

Example 4

The samples were first prepared according to the following composition:

67.5:22.5:6:4 PEHSB, EHSB, hexadecylamidopropylhydroxypropylsultaine and tetradecylpropylsultaine: 20 percent of

Nano silica having a particle size of 30 nm: 1 percent of

Polyether diamine D-230: 4.6 percent

Salicylic acid: 5.4 percent

Water: balance of

The sample is observed after being placed for 12 hours, phase separation occurs, but the fluidity is very good, and the phase-separated nano particles can be re-dispersed by simply shaking.

The sample was diluted so that the content of the surfactant (PEHSB, EHSB, hexadecylamidopropylhydroxypropylsulfobetaine, and tetradecylpropylsulfobetaine) was 0.3%, and dispersibility was observed and good. Comparing it with the oil displacing agent samples containing only 0.3% of the surfactant (PEHSB, EHSB, cetylamidopropylhydroxypropyl sulfobetaine, and tetradecylpropylsulfobetaine), it was found that it was more easily dispersed and the viscosity was not lost than the oil displacing agent samples containing only 0.3% of the surfactant (PEHSB, EHSB, cetylamidopropylhydroxypropyl sulfobetaine, and tetradecylpropylsulfobetaine).

Example 5

1. Preparation of samples

Sample 1 was prepared with the following composition:

67.5:22.5:6:4 PEHSB, EHSB, hexadecylamidopropylhydroxypropylsultaine and tetradecylpropylsultaine: 0.3 percent of

Injecting water: make up to 100%

Sample 2 was prepared with the following composition:

Nano silica having a particle size of 30 nm: 0.01 percent

Injecting water: make up to 100%

2. Oil displacement performance experiment (three-layer heterogeneous core)

Firstly, vacuumizing an artificial three-layer heterogeneous rock core, saturating and simulating formation water, and calculating porosity;

connecting rock core displacement experimental equipment, detecting flow tightness, and heating the device to 65 ℃;

thirdly, saturating the crude oil, and calculating the original oil saturation degree when the oil drives water to an outlet end and does not discharge water;

fourthly, stopping water flooding when the water content of the outlet end reaches 95 percent after the oil is displaced by water;

recording the volume of the effluent of the oil water, and calculating the oil displacement efficiency;

replacing three layers of artificial heterogeneous rock core, repeating the steps, and stopping water drive when water content reaches 95% at outlet end. 0.35PV oil displacement agent solution (0.8%) was injected first at a flow rate of 0.5mL/min and then water-displaced to 95% water content.

The results are shown in fig. 20, 21 and 22.

Fig. 20 shows the change in viscosity with time and temperature after the injection of the oil-displacing agent, illustrating that the oil-displacing agent of the present invention has good environmental responsiveness.

Fig. 21 shows the pressure as a function of PV, illustrating the good injectability of the displacement agent of the present invention.

FIG. 22 shows production as a function of injected PV illustrating good heterogeneous displacement performance of the displacement agent of the present invention.

3. Rheological Property test

Testing the rheological property of the oil displacement agent by adopting an Antopa rheometer at 65 ℃ and with the shear rate of 7.34s^-1Under the conditions that the viscosities of the

samples

1 and 2 and the injected water were measured, the main parameters of the injected water used were as follows

The steady-state shearing test adopts a shear rate control mode, and the shear rate range is 0.1-1000 s^-1。

Dynamic viscoelasticity test: and selecting an oscillation test mode, and selecting a proper oscillation angular frequency to perform stress scanning through experimental verification within the range of 0.628 rad/s-6.28 rad/s to determine a linear viscoelastic region. A stress value is selected in the linear viscoelastic region, oscillation time scanning is carried out, the scanning time is 3 min-5 min, and the change of the elastic modulus G 'and the viscous modulus G' with the time t of the sample 2 and polyacrylamide (1500mg/L) with the hydrolysis degree of 26% and the molecular weight of 1400 ten thousand are respectively tested.

The results for sample 2 are shown in fig. 23. The results for polyacrylamide are shown in FIG. 24.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other substitutions, modifications, combinations, changes, simplifications, etc., which are made without departing from the spirit and principle of the present invention, should be construed as equivalents and included in the protection scope of the present invention.

Claims

1. The composite oil displacement agent is characterized by comprising the following components in percentage by weight: 0.05 to 0.8 percent of surfactant and the balance of water; wherein the surfactant comprises erucamidopropylhydroxysultaine, erucamidopropylbetaine, cetylamidopropylhydroxypropylsultaine, and tetradecylpropylsultaine.

2. The composite oil-displacing agent according to claim 1, wherein the content of the surfactant is 0.3% to 0.8%.

3. Composite oil-displacing agent according to claim 1 or 2, characterized in that the erucamidopropylhydroxysultaine content in the surfactant is no more than 45%, preferably 18-45%, more preferably 18-22.5%.

4. A composite oil-displacing agent according to claim 3, characterized in that the content of hexadecylamidopropyl hydroxypropyl sulfobetaine and tetradecylpropyl sulfobetaine in the surfactant is not more than 10%.

5. A composite oil-displacing agent according to any one of claims 1 to 4, characterized in that the surfactant further comprises tetradecylamidopropyl hydroxypropyl sulfobetaine and/or hexadecylpropyl sulfobetaine.

6. The compound oil displacement agent according to any one of claims 1 to 4, further comprising nano silica with a content of not more than 0.05%; preferably, the compound oil displacement agent comprises nano silicon dioxide with the content of 0.005-0.05%.

7. The composite oil-displacing agent according to claim 6, wherein the particle size of the nano-silica is 15nm to 50nm, preferably 30nm to 50 nm.

8. A composite oil-displacing agent according to claim 6 or 7, characterized in that the surfactant further comprises an anionic surfactant in an amount of not more than 0.075%; preferably, the surfactant further comprises an anionic surfactant in an amount of not more than 0.03%.

9. The compound oil displacement agent according to claim 8, wherein the anionic surfactant is any one or more of sodium dodecyl sulfate, sodium dodecyl benzene sulfonate and sodium dodecyl polyoxyethylene ether sulfate; preferably, the anionic surfactant is sodium dodecylbenzenesulfonate.

10. The compound oil-displacing agent according to claim 6 or 7, which further comprises polyether diamine and/or salicylic acid; preferably, the compound oil displacement agent further comprises polyether diamine and salicylic acid;

more preferably, the compound oil displacement agent comprises 0.05-0.1% of polyether diamine and 0.05-0.1% of salicylic acid.