CN113294131A

CN113294131A - Thin interbed lithologic reservoir surface active agent huff-puff oil recovery method

Info

Publication number: CN113294131A
Application number: CN202110428831.9A
Authority: CN
Inventors: 李俊; 罗陶涛; 向祖平; 程柯扬; 程婷婷; 朱诗杰
Original assignee: Chongqing University of Science and Technology
Current assignee: Chongqing University of Science and Technology
Priority date: 2021-04-21
Filing date: 2021-04-21
Publication date: 2021-08-24

Abstract

The invention belongs to the technical field of oil field exploitation, and discloses a surfactant huff and puff oil recovery method for a thin interbed lithologic reservoir, which optimizes a proper surfactant system aiming at the characteristics (generally deeper buried, low-porosity, medium-low permeability, thin oil layer and the like) of a target oil reservoir, wherein the system has the effects of increasing the number of capillary tubes, changing wettability and carrying out crude oil replacement in a well stewing process, and meets the requirement of the thin interbed lithologic reservoir on the improvement of crude oil recovery ratio; the influence of the injection mode (including concentration, speed and injection amount) is researched by applying a relatively corresponding physical model, and the influence of the difference of application parameters on the effect is determined; an application scheme of a set of injection parameters, a set of stuffy well characteristics and a set of extraction parameters is formulated: optimizing injection parameters; optimizing the parameters of the blind well; and (5) optimizing the extraction parameters. The invention realizes the high-efficiency development of the thin interbed oil reservoir; the low-pressure injection requirement of the oil reservoir can be met, the salt tolerance is realized, and the requirement of the formation water mineralization degree of the target oil reservoir is met; the stability is good, and the requirement of the target oil reservoir stratum temperature is met.

Description

Thin interbed lithologic reservoir surface active agent huff-puff oil recovery method

Technical Field

The invention belongs to the technical field of oilfield exploitation, and particularly relates to a thin interbed lithologic reservoir surfactant huff-and-puff oil production method.

Background

At present, the thin interbed lithologic reservoir geological reserve of the Tahe oil field is 809 multiplied by 10⁴Ton, cumulative oil production 110X 10⁴The production degree is 13.7% per ton, and the thin interbed of the tower and the river has the characteristics of ultra-deep burial (4800 + 5500m), low porosity, medium and low permeability and 3-8m of oil layer thickness, and belongs to a structure-lithology composite trap oil reservoir. At present, most wells of thin interbed lithologic oil reservoirs have low yield and low efficiency, but effective treatment means and measures are lacked; therefore, surfactant huff and puff technical research is developed, the thin interbed reservoir surfactant huff and puff mechanism is determined by researching and developing a temperature-resistant and salt-resistant surfactant system, and a technical direction is provided for efficient development of the thin interbed sandstone reservoir.

The application of the surfactant in oil exploitation dates from 20 to 30 years in the 20 th century. In the 20 th century, 60 s, microemulsion flooding was proposed, and in the 90 s, the surfactant oil displacement agent was greatly developed after two petroleum crises.

In 2006, polyoxyethylene ether sulfonate is synthesized in the prior art 1, and is compounded with cheap anionic surfactant residual oil sulfonate to obtain a temperature-resistant and salt-resistant compound surfactant oil-displacing system. The degree of mineralization is 41g/L, Ca at 80 DEG C²⁺And Mg²⁺The mass concentration of the system is 1g/L, and the system is used for crude oil in the Hongkong oil field, and the oil-water interfacial tension can be reduced to about 10^-3mN/m can meet the requirements of high-temperature and high-mineralization oil reservoirs in large-port oil fields on the surfactant for oil displacement.

In 2006, in the prior art 2, a self-made Gemini surfactant and polyoxyethylene ether sulfonate are compounded, and the mass concentration of salt is 10g/L in DaqingIn sewage, the interfacial tension between the compound surfactant and oil and water is reduced to 10^-2mN/m or so. Due to Ca²⁺And Mg²⁺An indoor evaluation experiment was conducted at a mass concentration of 410mg/L and a saturated crude oil viscosity of 25 mPaS. The experimental result shows that the single lauric polyether sodium sulfonate surfactant system can improve the recovery ratio by 4.2%.

In 2007, in prior art 3, aiming at the defect of poor interface characteristics of a single alkylphenol ethoxylate surfactant, two sulfobetaines are compounded, and under the condition that the mass fractions of the compounded system are 0.05%, 0.10% and 0.30%, the interfacial tension between the compounded system and crude oil in the Shengli oil field can reach 10^-2mN/m order of magnitude.

In 2009, in the prior art 4, polyoxyethylene ether sulfonate is used as a raw material, and nitric acid is used to synthesize an anionic surfactant, wherein the surfactant has good salt tolerance and high interfacial activity.

In 2012, the fatty alcohol polyoxyethylene ether sulfonate (AESO) anionic-nonionic amphoteric surfactant synthesized by the prior art 5 has good salt resistance, and is compounded with a cheap surfactant, namely heavy alkylbenzene sulfonate (the sum of the mass fractions of the two surfactants is 0.3%), or AESO (the mass fraction is 0.5%) is used alone, or the AESO, sodium hydroxide (the mass fraction is 0.1%) and a polyacrylamide aqueous solution (the mass fraction is 0.1%) form a ternary composite flooding system, and the mineralization degree is 89g/L, Ca g at the temperature of 85 DEG C²⁺And Mg²⁺The ultra-low oil-water interfacial tension can be achieved under the condition of the mass concentration of 1.150g/L, and the method is suitable for tertiary oil recovery of high-temperature and high-salinity oil reservoirs.

In 2013, in the prior art 6, fatty alcohol/alkylphenol polyoxyethylene ether is used as an initiator, and the fatty alcohol/alkylphenol polyoxyethylene ether sulfonate is obtained through halogenation and sulfonation reactions, and the result of an interfacial activity test shows that the single agent has the mass fraction of 0.2%, the temperature of 70 ℃ and the mineralization degree of 80g/L, Ca²⁺And Mg²⁺Under the condition of mass concentration of 1.1g/L, the stable value of the oil-water interfacial tension within 2h reaches 10^- ³mN/m order of magnitude.

In 2014, in the prior art 7, 7 series sulfonate anionic surfactants with different hydrophobic chain lengths and connecting group lengths are synthesized by taking series long-chain alkylene oxides and different short-chain diols as starting materials, have lower surface tension and critical micelle concentration, have good surface activity and very good monovalent and divalent salt resistance, and except that C16-C2-C16 can be separated out from a NaC1 solution with the mass fraction of more than 5%, the rest Gemini surfactants have salt resistance in a salt solution with the mass fraction of more than 20%.

In 2015, in the prior art 8, pentadecene is used as a raw material to synthesize a sulfonate surfactant, the sulfonate surfactant is compounded with petroleum sulfonate, and when the mass fraction of a compound system is 1%, the oil-water interfacial tension can be reduced to 10^-4mN/m. Thereby improving the recovery ratio of crude oil.

In 2016, in the prior art, 9 dibromoalkane is used as a raw material to synthesize a Gemini di-quaternary ammonium salt surfactant SL-1, and when the mass concentration of the SL-1 surfactant is 700-900 mg/L, the equilibrium interfacial tension between the surfactant and crude oil of five plants of the Shengli oilfield reaches 10^-3mN/m order of magnitude; the results of core simulation oil displacement tests show that the oil displacement efficiency can be improved by more than 8% by using the surfactant at most.

At present, the development of the surfactant for oil recovery focuses on the development of a temperature-resistant and salt-resistant surfactant under a high-temperature and high-salt oil reservoir, and the development of a novel surfactant not only focuses on the performance of reducing the interfacial tension, but also considers the stability and durability of the performance. Compared with the traditional surfactant, the novel Gemini surfactant has better surface activity and capability of reducing the tension of an oil-water interface, has better water solubility, lower adsorption loss and better temperature resistance and salt resistance, and can also increase the viscosity of the displacement fluid. The Gemini surfactant has good compatibility with other surfactants, the synergistic effect among the surfactants can improve the performance of a compound system, and simultaneously the dosage of the Gemini surfactant is reduced, so that the oil displacement cost is reduced, and therefore, the Gemini surfactant is a surfactant for high-temperature and high-salt oil reservoirs with good prospect.

One class of materials in which fluorocarbon surfactants can significantly reduce the surface tension of a solvent at very low concentrations is known as surfactants. The fluorocarbon surfactant is the most important variety of special surfactants, and means that hydrogen atoms in a hydrocarbon chain of the hydrocarbon surfactant are completely or partially replaced by fluorine atoms, namely, the fluorocarbon chain replaces the hydrocarbon chain, so that a non-polar group in the surfactant not only has hydrophobic property, but also has oleophobic property. The fluorocarbon surfactant is the surfactant with highest surface activity so far, can reduce the surface tension of water to 20mN/m when the mass fraction is 0.01 percent, has high capability of resisting strong base, strong acid and oxidant, and can be used in harsh environment.

Surfactants play an important role in oil recovery, but traditional single-head-based surfactants reduce the free energy of the system by spontaneously adsorbing to the interface or spontaneously aggregating to form micelles, mainly due to hydrophobic interactions between hydrocarbon chains. However, the charge repulsion between the ionic head groups or hydration causes repulsion between individual surfactant molecules, making them difficult to arrange closely in interfaces or molecular aggregates, resulting in low surface activity. Therefore, how to obtain a high-efficiency surfactant becomes a focus of research in the field of surfactants.

Through the above analysis, the problems and defects of the prior art are as follows: the surface activity of the existing surfactant is low, so that the huff and puff oil recovery efficiency is low.

The difficulty in solving the above problems and defects is: at present, for a structural-lithologic composite trap oil reservoir with ultra-deep burial, low oil layer thickness and higher reservoir mineralization degree, a temperature-resistant and salt-resistant surfactant system for improving the crude oil recovery rate is not mature. Most of the existing surfactant systems cannot be suitable for the oil reservoir conditions, and a single surfactant has the problems of poor temperature resistance, weak salt resistance, reduction of interfacial tension and poor wetting reversal capability.

The significance of solving the problems and the defects is as follows: by means of indoor tests and numerical simulation, the established surfactant compounding system and construction process parameters are optimized, a new idea can be provided for solving the technical problem of development of the oil and gas reservoir, the optimized surfactant system can bring considerable economic benefits for field production, and efficient development of oil and gas resources is realized. Meanwhile, technical ideas and development experiences can be provided for the development of oil reservoirs with similar stratum conditions.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a method for improving the crude oil recovery rate by injecting surface active agents into a thin interbed lithologic oil reservoir.

The invention is realized by firstly injecting a temperature-resistant salt-resistant surfactant system suitable for the stratum into the stratum through an injection well; then closing the injection well and stewing for a period of time; finally, the well is opened and the crude oil from the formation flows out of the formation under the action of the oil pressure and enters the wellbore to be produced to the surface. The thin interbed lithologic reservoir surfactant huff-puff oil recovery method comprises the following steps:

step 1: aiming at the characteristics of a target oil reservoir (ultra-deep burying, low oil layer thickness and higher reservoir mineralization degree), a proper surfactant is optimized (the number of capillary pipes can be increased, the wettability is changed, and crude oil replacement is carried out in the soaking process);

step 2: the influence of an injection mode on the final oil reservoir crude oil recovery ratio (including concentration, dosage, soaking time, throughput period and the like) is researched by applying a relatively corresponding physical model, and the influence of the difference of application parameters on the effect is determined;

and step 3: and making an application scheme containing construction parameters and a matched process. The method comprises the following steps: optimizing injection parameters; optimizing the parameters of the blank well; and (4) optimizing the extraction parameters.

The number of capillary tubes is increased by injecting the composite surfactant, the wettability is changed, and crude oil replacement is carried out in the soaking process, so that huff and puff oil recovery of the thin interbedded lithologic oil reservoir is realized.

Further, the injection amount of the composite surfactant was 0.5PV, and the concentration of the composite surfactant was 0.4%.

Further, the composite surfactant injection method comprises the following steps: at 30m³The composite surfactant injection is carried out at a speed of/d.

Further, the composite surfactant is obtained by compounding Gemini12-3-12 Gemini and fluorocarbon FT101329 according to the proportion of 2: 1.

By combining all the technical schemes, the invention has the advantages and positive effects that: the technology of optimizing well spacing, straight-flat combined fireflood, continuous oil pipe sand blasting perforation casing staged fracturing, separate-layer water injection, mechanical partial pressure pipe column, separate-layer acidification, subdivision control fracturing and the like is adopted at home and abroad to develop the thin interbed reservoir. The surfactant huff and puff technology has been effectively applied to closed small fault block oil reservoirs, large-port fault block heavy oil reservoirs, Puchensha-one oil reservoirs and Daqing oil fields. The basic mechanisms of surfactant huff and puff technology are: increasing the number of capillary tubes, changing the wettability and carrying out crude oil replacement in the process of soaking. In the S70 well region Karazaire group sand shale section, the electrical property of sand and conglomerate of the reservoir section is represented by a typical negative characteristic, and the wettability can be changed for a long time by utilizing the electrostatic adsorption reaction characteristic of anions and cations, so that the property of the rock surface of an oil layer is changed, and the huff and puff operation is facilitated; through preliminary screening, fine screening and compounding, the recommended use type of the huff and puff surfactant is compounded by Gemini12-3-12 and fluorocarbon FT101329, and the compounding ratio is 2: 1; combining the results of comprehensive physical modeling and numerical simulation, the optimization result of the dosage of the surfactant is as follows: 0.5 PV; combining the results of comprehensive physical model and numerical simulation while considering the loss in the surfactant injection process, the determined surfactant injection concentration is preferably 0.4%; synthesizing results of indoor physical models and numerical simulation, and finally determining the optimal result of the well closing time to be 12-14 days; according to the research results of the object model and the digital model, the recommended intermittent liquid drainage period is 50 days, and the liquid drainage times are three times; the injection speed is determined to be 30m by several modes and combining field practice³D; the increase of the injection pressure/speed is beneficial to forced dialysis to improve the recovery ratio at the initial stage, but the injection pressure is too large and is unfavorable to improve the recovery ratio; the larger the difference of the anisotropism of the permeability is, the worse the huff and puff effect of the surfactant is, which is not beneficial to huff and puff the surfactant to improve the recovery ratio; the injection of the gel plugging agent is beneficial to the change of the surfactant from high permeation to low permeation, and the throughput efficiency of the surfactant can be greatly improved.

The invention utilizes the surfactant to increase the number of capillary, change the wettability and carry out crude oil replacement in the soaking process, thereby realizing the high-efficiency development of the thin interbed oil reservoir. The composite surfactant can meet the low-pressure injection requirement of an oil reservoir, has certain salt tolerance, meets the requirement of the mineralization degree of formation water of the target oil reservoir, and is not easy to react with ions in the formation water to inactivate or generate precipitates; the stability is good, the requirement of the temperature of the target oil reservoir stratum is met, the flow in the stratum can be stably maintained for a long time, and the throughput validity period can be prolonged; the adsorption in the stratum of the production well is stable, and the wettability of rock can be changed for a long time, so that the validity period can be prolonged.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a schematic diagram of a simulated core water flooding relative permeability curve provided by an embodiment of the invention.

Fig. 2 is a schematic diagram of the relative permeability curves of a water flood and a surfactant flood provided by an embodiment of the present invention.

Fig. 3 is a schematic diagram of a surfactant flooding numerical simulation mechanism model provided in an embodiment of the present invention.

FIG. 4 is a comparative schematic of daily oil production per well for different Nc scenarios provided by an embodiment of the present invention.

FIG. 5 is a comparative schematic of the cumulative oil production per well for different Nc scenarios provided by an embodiment of the present invention.

Fig. 6 is a graph of the increase trend of the recovery factor under different Nc schedules provided by the examples of the present invention.

FIG. 7 is a graph of the original oil saturation profile of the model provided by an embodiment of the present invention.

Fig. 8(a) is a depletion mode residual oil saturation profile provided by an embodiment of the present invention.

Fig. 8(b) shows surfactant displacement Nc ═ 10 for surfactant injection provided in the embodiments of the present invention^-6The model residual oil saturation profile.

Fig. 8(c) shows surfactant displacement Nc ═ 10 for surfactant injection provided in the embodiments of the present invention^-5The model residual oil saturation profile.

Fig. 8(d) shows surfactant displacement Nc ═ 10 for surfactant injection provided in the embodiments of the present invention^-4The model residual oil saturation profile.

Fig. 8(e) shows surfactant displacement Nc ═ 10 for surfactant injection provided in the embodiments of the present invention^-3The model residual oil saturation profile.

Fig. 8(f) shows surfactant displacement Nc ═ 10 for surfactant injection provided in the embodiments of the present invention^-2The model residual oil saturation profile.

Fig. 9 is a graph of variation trend of remaining oil saturation for different ncs provided by the embodiment of the present invention.

FIG. 10 is a comparative schematic of oil production per well for different wetting index conditions provided by an example of the present invention.

FIG. 11 is a graph comparing the effect of different wettabilities on recovery provided by examples of the present invention.

Fig. 12 is a schematic diagram of a single-well surfactant injection throughput model provided by an embodiment of the invention.

Fig. 13 is an average oil saturation profile before and after water injection according to various embodiments of the present invention.

FIG. 14 is a comparison graph of daily oil production per well for different production modes provided by an embodiment of the present invention.

FIG. 15 is a comparison graph of the cumulative oil production from a single well for different production modes provided by an embodiment of the invention.

FIG. 16 is a plot of average saturation of oil at different flooding strengths for different scenarios provided by an example of the present invention.

Fig. 17 is a schematic illustration of a comparative formation water compatibility provided by an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

Aiming at the problems in the prior art, the invention provides a thin interbed lithologic reservoir surfactant huff and puff oil recovery method, which is described in detail in the following with reference to the attached drawings.

The huff and puff oil recovery method of the surface active agent of the thin interbed lithologic reservoir provided by the embodiment of the invention comprises the following steps:

The injection amount of the composite surfactant provided by the embodiment of the invention is 0.5PV, and the concentration of the composite surfactant is 0.4%.

The composite surfactant injection method provided by the embodiment of the invention comprises the following steps: at 30m³The composite surfactant injection is carried out at a speed of/d.

The composite surfactant provided by the embodiment of the invention is obtained by compounding Gemini12-3-12 Gemini and fluorocarbon FT101329 according to the proportion of 2: 1.

The technical effects of the present invention will be further described with reference to specific embodiments.

Example 1:

overview of the invention 1

1.1 sources of

Geological reserve 809 multiplied by 10 of thin interbed lithologic reservoir of Tahe oil field⁴Ton, cumulative oil production 110X 10⁴The production degree is 13.7% per ton, and the thin interbed of the tower and the river has the characteristics of ultra-deep burial (4800 + 5500m), low porosity, medium and low permeability and 3-8m of oil layer thickness, and belongs to a structure-lithology composite trap oil reservoir. At present, most wells of thin interbed lithologic oil reservoirs have low yield and low efficiency, but effective treatment means and measures are lacked; therefore, surfactant huff and puff technical research is developed, the thin interbed reservoir surfactant huff and puff mechanism is determined by researching and developing a temperature-resistant and salt-resistant surfactant system, and a technical direction is provided for efficient development of the thin interbed sandstone reservoir.

1.2 content and index

1.2.1 contents

The method comprises the steps of preliminarily screening the types of the surface active agents, designing an experimental scheme of the surface active agents, carrying out performance test and comparison selection of the surface active agent system by researching a thin interbed lithologic oil reservoir and combining the research current situation of the surface active agents, the huff and puff mining application situation, the geology and development characteristics of a work area, and comprehensively optimizing the temperature-resistant and salt-resistant surface active agent system on the basis of salinity, temperature, formation water compatibility, formation crude oil, rock properties and the like. An oil increasing principle of the surfactant system is researched by using an oil reservoir numerical simulation method, huff and puff technological parameters are optimized, and a thin interbed lithologic reservoir surfactant huff and puff technical system is formed.

(1) Thin interbed lithologic reservoir development technology investigation

The method is characterized by comprising the following steps of firstly, researching high-efficiency development technology and application conditions of thin interbed lithologic oil reservoirs at home and abroad, and providing reference and guidance for development of thin interbed lithologic oil reservoirs of Tahe.

Secondly, the application conditions and the technical current situation of the temperature-resistant and salt-resistant surfactant system at home and abroad are investigated, wherein the application conditions comprise a medicament system, an application mechanism (oil displacement, huff and puff), an application scale and the like.

(2) Temperature-resistant and salt-resistant surfactant system research and development and performance evaluation

Firstly, a temperature-resistant and salt-resistant surfactant system suitable for harsh conditions of a Tahe oil field is developed, the evaluation of related performances such as interface (surface) tension, emulsifying property, wettability and the like is carried out, and a surfactant system with strong adaptability is screened.

Secondly, according to the screened surfactant system, the performance evaluation of temperature resistance, salt resistance, compatibility, adsorption influence and the like is carried out.

And thirdly, preferably selecting a temperature-resistant and salt-resistant surfactant system suitable for the characteristics of the Tahe oil field.

(3) Thin interbed surfactant throughput physical-analog-to-digital (IMD) studies

Firstly, a typical thin interbed reservoir physical model is established, and surfactant huff and puff physical model experimental research is developed aiming at a formed surfactant system.

Secondly, a typical thin interbed lithologic reservoir geological model is established, and a reservoir numerical simulation method is utilized to develop single-well huff and puff digital-analog research on surfactant injection, so that the huff and puff oil increasing mechanism of the surfactant is clarified.

Thirdly, throughput process parameters such as surfactant concentration, dosage, well stewing time, throughput period and the like are optimized by using an object model and a digital-analog method, and the process technology is completed to form a thin interbedded lithologic reservoir surfactant throughput technology system.

1.2.2 index

(1) 1 set of temperature-resistant and salt-resistant ultralow interfacial tension surfactant system is formed, and the temperature is 120 ℃ resistant and the salt resistance is 22 ten thousand mg/L;

(2) defining the huff and puff mechanism of the surface active agent of the thin interbed lithologic reservoir;

(3) and forming optimal process parameters of surfactant throughput technology.

1.3 Main workload to complete

The following work is mainly completed:

(1) the primary screening of the temperature-resistant and salt-resistant surfactant system comprises the following steps: on the basis of largely investigating and researching the temperature-resistant and salt-resistant surfactants used at home and abroad at present, the requirements of the throughput of the thin interbed reservoir surfactant on the performance of the surfactant are combined, 18 cationic surfactants are screened, the surface tension of the 18 surfactants under 9 different concentrations is tested, and the test data amount is 172. And then, carrying out compatibility experiments on the 10 surfactants which are primarily screened out, stripping the crude oil performance and influencing the experiments, and further screening out 6 surfactants which meet the requirements.

(2) In terms of further evaluation of temperature-resistant salt-tolerant surfactants: firstly, carrying out 10 interfacial tension test experiments with different concentrations and 4 different temperatures on 6 primarily screened surfactants, wherein 240 experimental test data points are obtained; testing wetting contact angles of 10 different concentrations of 6 surfactants, wherein the number of experimental data points is 60; testing foaming capacity of 6 surfactants under 9 concentrations, wherein foaming height and half-life period are included, and 144 experimental data points are included; fourthly, an emulsifying capacity test experiment is carried out on 6 surfactants under 9 concentrations, and 54 experimental data points are obtained; the experiment of influence of 120 ℃ on the interfacial tension of the surfactant shows that 18 data points are obtained; sixthly, the rock adsorption has 42 data points in the experiment on the influence of the interfacial tension of 6 surfactants; and (c) 36 data points in experiments on the influence of the mineralization degree on the interfacial tension of 6 surfactants.

(3) The compounding experiment aspect of the temperature-resistant and salt-resistant surfactant system is as follows: testing performance experiments under different proportions of 2 kinds of optimized surfactants according to 3 different proportions, wherein the performance experiments comprise interface tension conditions under the conditions of 3 proportions, 9 concentrations and 4 temperatures, and 108 data points are obtained; ② 60 data points of wetting contact angles under the conditions of 3 proportions and 9 concentrations; testing foaming capacity under 3 proportioning conditions, wherein 15 data points are obtained; fourthly, testing the foaming capacity under 3 proportioning conditions, wherein 10 data points are obtained; testing the interfacial tension stability under 3 proportioning conditions, wherein 15 data points are obtained; sixthly, 35 data points are obtained in an experiment of influence of different rock adsorption on interfacial tension under 3 proportioning conditions; seventhly, in the test experiment of the influence of salinity on the stability of the interface tension under the conditions of 3 proportioning conditions, 30 data points are obtained; finally, an optimal performance active agent system is formed.

3 throughput surfactant system development

3.1 surfactant throughput mechanism

3.1.1 surfactant System brief introduction

(1) Essential properties of surfactants

A large class of organic compounds, which can greatly reduce the surface tension or liquid-liquid interfacial tension of an aqueous solution by adding a small amount of solute to the aqueous solution, is called surfactants. The molecules of the surfactant are composed of hydrophilic groups (also called lipophobic groups, polar groups) having affinity for water and lipophilic groups (also called hydrophobic groups, nonpolar groups) having affinity for oil. It is therefore soluble in both polar and non-polar solvents, and has amphiphilic properties, known as amphiphiles (ampphilesmolecule). Currently, there are about 20000 kinds of surfactants, and the surfactants can be classified into the following categories according to the dissociation of the surfactant molecules in water. This classification reflects some relationship of chemical structure to performance.

3.1.2 mechanism of surfactant to increase the number of capillaries

Of the many determining factors that affect oil recovery, sweep efficiency and wash efficiency of the displacement agent are the most important parameters. Improving the oil washing efficiency is generally achieved by increasing the capillary accuracy, while decreasing the oil-water interfacial tension is the main way to increase the capillary accuracy. The relationship between capillary norm and interfacial tension is shown in the following formula:

N_c＝νμ_w/σ_woformula 3.1

In the formula:

N_c-capillary accuracy, dimensionless;

v-displacement velocity, m/s;

μ_w-displacement fluid viscosity, mpa.s;

σ_wointerfacial tension between oil and displacement fluid, mN/m.

N_cThe larger the residual oil saturation, the higher the oil displacement efficiency. Increase of mu_wAnd v, lowering σ_woCan increase N_c. In which the interfacial tension σ is reduced_woIs the basic basis of surfactant flooding. In the later stages of development, N_cIs generally at 10^-7～10^-6Increased Nc will significantly increase oil recovery, N in the ideal case_cIs increased to 10^-2The recovery rate of crude oil can reach 100%. By reducing the oil-water interfacial tension, N can be reduced_cThere are 2-3 orders of magnitude changes. The oil-water interfacial tension is usually 20-30 mN/m, and the ideal surfactant can reduce the interfacial tension to (10)^-4～10^-3) mN/m, thereby greatly reducing or eliminating the capillary action of the stratum, reducing the adhesion force required by stripping the crude oil and improving the oil washing efficiency.

The simulation of the oil-water relative permeability curve characteristics of the core water flooding and the surfactant flooding shows that the surfactant effectively reduces the saturation of the residual oil in the water flooding; the water saturation at the isotonic point is shifted to the right, which shows that the surfactant can change the wettability of the oil layer to a certain extent and convert the wettability to the hydrophilic direction; after the surfactant flooding, the oil-water two-phase co-permeation area is widened, the oil displacement condition is improved, the wider the oil-water two-phase co-permeation area is, the higher the oil displacement efficiency is, and the oil displacement efficiency can be improved by the surfactant.

A surfactant flooding numerical simulation mechanism model (shown as a figure 3) is established by combining a surfactant oil-increasing mechanism and referring to geological parameters of a Tahe oilfield 3 zone, relevant parameters of the model are shown as a table 1, and 6 comparison schemes are designed for analyzing influences of different Nc on the surfactant flooding effect, and the method specifically comprises the following steps:

scheme 1: single well failure recovery-basic scenario;

scheme 2: surfactant flooding scheme-Nc 10^-6；

Scheme 3: surfactant flooding scheme-Nc 10^-5；

Scheme 4: surfactant flooding scheme-Nc 10^-4；

Scheme 5: surfactant flooding scheme-Nc 10^-3；

Scheme 6: surfactant flooding scheme-Nc 10^-2。

TABLE 1 numerical simulation of mechanism model parameters

Properties of	Reservoir model
		Mesh type	The number of grids: 40 × 40 × 3, 4800, K direction, down
Size of the grid	5m×5m
		Properties of the mesh	The top depth of the oil reservoir is 1600m, and the grid thickness is 3m multiplied by 5m multiplied by 3m
Native water saturation S_w,％	15
		Permeability, mD	110
Porosity, is%	17
		K_v/K_h	0.1
Crude oil Density, t/m³	0.844
		Geological reserve, 10⁴ t	4
Simulating well type	2 wells, injection well S70I and production well S70
		Number of years to predict	20

The effects of different schemes are predicted and contrasted through numerical simulation, and the following can be seen:

(1) compared with failure exploitation, the surface activator flooding injection can further improve the single-well exploitation effect.

Respectively predicting the production effect of the production well S70 in the scheme 1 and the schemes 2-6 for 20 years (as shown in figures 3-4 and tables 3-2), and obtaining the resultIt can be seen that in the case of single well failure recovery, the oil production is about 1.64X 10 after 20 years of production⁴t, the production degree is only 41.47%, and the oil production can be increased to 2.56X 10 by injecting surfactant⁴t, the extraction degree is improved to 64.43% or more, and the amplification reaches 23%. The comprehensive results show that the surfactant flooding injection mode can further effectively improve the recovery ratio on the basis of the failure recovery mode.

(2) The greater the Nc, the greater the accumulated oil and the greater the extent of production.

Comparing the production efficiency of the production wells under different Nc conditions in schemes 2-6 (see FIGS. 3-5, Table 2), it can be seen that the cumulative oil production gradually increases with increasing injection of surfactant to Nc, when Nc increases to 10^-2The extraction degree is improved to 67.86%, the amplification reaches 26.4%, and the extraction degree of the lower Nc scheme is improved by 3% -4%.

(3) The greater the Nc, the lower the remaining oil saturation.

The original oil saturation of the oil reservoir is 85%, the oil saturation is gradually reduced along with the extraction of crude oil, as can be seen from fig. 6 to 7, the larger the Nc is, the larger the swept area is, the higher the displacement efficiency is, the lower the residual oil saturation is, and when the Nc is increased to 10^-2The average remaining oil saturation of the oil reservoir (as shown in figure 8) is reduced to 25.3 percent at most, and is reduced by 28.3 percent compared with failure recovery.

The synthesis of the above results show that the surfactant flooding improves Nc by reducing interfacial tension, so as to achieve the purpose of improving the oil displacement efficiency, and the larger the Nc improvement range is, the better the oil displacement effect is relatively.

TABLE 2 statistical table of production effect of different mining schemes

3.1.3 surfactants alter the wettability mechanism

With the progressive research on the correlation of surfactant flooding, the importance of two mechanisms, namely lowering the oil-water interfacial tension and improving the rock wettability, of the surfactant is gradually recognized. Both the reduction of the flow resistance of the residual oil in the pores itself and the influence of wettability on the recovery factor are considered. Currently, more and more researchers are beginning to study the surfactant wetting reversal mechanism of hypotonic reservoirs.

The surface active agent substance contained in the crude oil is adsorbed on the pore wall surface, so that the pore wall surface becomes oleophilic, and the injected surface active agent is adsorbed on the wall surface of oleophilic rock when migrating in the pores, so that the pore wall surface is converted from oleophilic to hydrophilic, the adhesion work of the crude oil on the wall surface is reduced, the crude oil on the wall surface is easy to be taken away by the displacement fluid, the share of the mobile oil is increased, the flow space in the pores is increased, the flow is increased, the liquid production capacity of an oil well is increased, and the recovery ratio is improved.

The wettability of the rock wall surface is an important parameter influencing the seepage characteristic of the fluid, in an oleophylic capillary, the direction of a capillary is opposite to the water drive direction, and the capillary force is the oil displacement resistance; in the hydrophilic capillary, the direction of capillary force is the same as the water drive direction, and capillary force is the oil displacement power. When the surfactant flooding is carried out, active agent molecules are adsorbed on the wall surface of the pores, so that the lipophilicity of the wall surface is changed into the hydrophilicity, the capillary force is changed from oil displacement resistance into oil displacement power, and the aim of improving the recovery ratio is fulfilled.

The wettability of the rock can be characterized by a wettability index by combining a surfactant oil-enriching mechanism and wettability characteristics. In order to analyze the influence of wettability on the production effect, an oil increasing effect prediction scheme with different wetting indexes is designed on the basis of surfactant flooding numerical simulation established at 3.1.2, and the method specifically comprises the following steps:

scheme 1: surfactant flooding-WI ═ -1, completely oily;

scheme 2: surfactant flooding-WI ═ 0.5, oil wet;

scheme 3: surfactant flooding-WI ═ 0, moderate wetting;

scheme 4: surfactant flooding-WI ═ 0.5, water wet;

scheme 5: surfactant flooding-WI ═ 0.5, completely wet with water.

Predicting the 20-year recovery effect of the production wells in schemes 1-5, as shown in Table 3, and FIGS. 10-11, it can be seen that the cumulative oil production changes from 2.37X 10 as the wettability changes from lipophilic to hydrophilic⁴t increased to 2.81×10⁴t, the recovery efficiency is gradually improved (from 0.6 to 0.71), and the maximum improvement amplitude is about 11%. The recovery rate is gradually increased along with the change of the wettability to the hydrophilicity, and the crude oil recovery effect can be further improved by changing the wettability of the rock through surfactant injection and flooding.

TABLE 3 statistical Table of the production effectiveness of different wettability protocols

Wetting index WI	Wettability	Cumulative oil production, 10⁴t	Relative recovery factor, f
				-1.0	Complete oil wetting	2.37	0.60
-0.5	Oil wetting	2.64	0.66
				0	Neutral wetting	2.68	0.67
0.5	Wetting with water	2.74	0.69
				1.0	Completely wet with water	2.81	0.71

3.1.4 throughput enhanced recovery mechanism

The active water injection huff and puff oil production technology is a new oil field development technology and mainly aims at the later development of oil fields. When stratum energy is insufficient and liquid quantity is low, active water is injected into an oil well to raise oil layer pressure, then the oil well is stewed, crude oil is replaced under the self-absorption action of capillary force, then the oil well is opened to produce, and a mixed liquid of the crude oil and the injected water is produced. It is very effective for the development of small-sized oil reservoirs without energy supplement.

The single well active water injection huff and puff oil extraction technology is an oil extraction technology in which active water injection and oil extraction are carried out in the same oil layer of the same well. The general approach is: when the pressure of the oil layer is low, active water is injected into the oil layer to enable the formation pressure to rise, then the well is stewed, and the well is opened again for production after a period of time. The active water injection huff-and-puff oil extraction is to inject active water into an oil layer, wherein the injected water is filled with high-porosity and high-permeability parts preferentially; after the well is shut in, active water is injected to replace oil gas in the medium, small pore throat or matrix due to capillary force, so that oil and water in the oil layer are rearranged, the pressure is reduced by production, and the oil gas replaced to a high permeability zone, high porosity, large pore throat or crack enters the shaft along with the injected water. Therefore, wettability, interfacial tension, petrophysical properties, oil-water viscosity, and shut-in time affect water injection throughput oil production. Because the oil-water cross-permeation effect is a long-acting process, and the swept radius and the oil-washing efficiency of the injected active water are limited, the active water injection huff and puff of the oil reservoir needs to be carried out in 3 stages of water injection, well closing and oil extraction, and a huff and puff period is formed.

In order to analyze the oil increasing mechanism of surfactant stimulation, a single-well surfactant stimulation model (as shown in figure 11) is established on the basis of 3.1.2 model parameters, and two schemes of failure recovery and surfactant stimulation recovery are designed and are predicted for 20 years respectively. The throughput stage dynamics are analyzed as follows.

(1) Stage of injecting active water

After the oil well is produced by natural energy, the formation pressure is greatly reduced, and the liquid supply of the oil well is seriously insufficient. At this point, the first stage is entered-activated water injection, raising the formation pressure. The general trend is that the oil saturation of most stratum is gradually reduced along with the increase of the formation pressure, the reduction range near the bottom of the well is maximum, and the oil saturation near the boundary of the stratum is slightly increased, because the injected active water has displacement effect on crude oil.

As shown in fig. 12, the oil saturation distribution before and after water injection predicted by numerical simulation under two production schemes of depletion production and surfactant injection stimulation, it can be seen that with the injection of surfactant, the oil saturation around the stimulation well is obviously reduced, the reduction range near the bottom of the stimulation well is maximum, and the oil saturation at the far position from the stimulation well is slightly improved due to the displacement effect of surfactant.

(2) Well (oil-water exchange stage)

The main purpose of the soaking is to utilize the hydrophilicity of the oil layer, fully exert the functions of capillary water absorption and oil discharge, and exchange injected active water with the formation crude oil while diffusing with the formation pressure, so that the saturation distribution of the underground fluid is changed, and the extraction of the crude oil is facilitated. Studies have shown that the formation oil saturation changes as the shut-in time increases. The time required for the fluid saturation at each location of the formation to reach equilibrium is mainly influenced by the oil-water capillary force and the oil layer permeability. The stronger the capillary force, the greater the formation permeability, and the relatively shorter the time required for the subsurface fluid to rebalance. Therefore, the oil layer water injection throughput efficiency is high, the oil-water capillary force and the oil layer permeability are small, the time required for injection and balance is long, and the throughput effect is poor. The rebalancing effect of water injection velocity and fluid properties on subsurface fluid saturation is relatively much less.

Because the oil-water cross-infiltration process is quite slow, a certain well closing time is beneficial to improving the oil reservoir recovery ratio. At the moment, the formation pressure is redistributed to form a new pressure field, and meanwhile, the hydrophilicity of the reservoir layer is favorable for fully playing the role of capillary force water absorption and oil drainage, so that the one-way convection motion of water absorption and oil drainage is formed, the waterline is gradually pushed to the far part of the oil layer, the injected water is exchanged with the crude oil in the formation while the formation pressure is diffused, the oil is separated, when the oil and the water reach the new distribution and balance, the saturation of the underground fluid is changed, the waterline stops being pushed forward, and the extraction of the crude oil is favorable.

(3) Oil recovery stage

The oil recovery stage is an energy release process, the mechanism of which is the same as the energy depletion method in the primary oil recovery stage without energy supplementation. The difference is that the original single-phase flow in the formation is changed into oil-water two-phase flow at the beginning of production, and as most injected water is gathered near the bottom of the well, the water injection throughout production is characterized by high water content in the initial stage, gradually decreases along with the increase of the production time, and then slowly rises. The daily oil production rises to a certain peak at the initial stage and then gradually decreases.

As shown in fig. 13-15, table 3, the numerical simulation predicts the development effect for 20 years (about 1 year per cycle) for both depleted production and surfactant injection throughput production scenarios, as can be seen:

(1) the injection surfactant huff and puff mining mode can further improve the mining rate on the basis of the failure mode.

As can be seen from fig. 14 and table 4, the recovery degree of the surfactant injection huff-and-puff recovery mode is 48.70%, while the failure mode is about 36.52%, and the surfactant injection huff-and-puff mode is improved by about 12.18%, as can be seen from fig. 16, the oil saturation at the end of each period after surfactant injection huff-and-puff is obviously lower than that of the failure mode, which indicates that the surfactant injection huff-and-puff mode can effectively reduce the residual oil saturation, and further improve the development effect.

(2) The daily oil production at the initial stage of huff and puff of the huff and puff agent is in an ascending trend, and the daily oil production is decreased gradually after reaching a high peak value.

As can be seen from FIG. 14 and Table 3, the oil production on the day of huff and puff reaches the peak value in the 2 nd cycle, which is 14m on average³D rises to 15.8m³D, then begins to fall, step of cycle 2The extraction degree of the section (5.71%) is improved by 0.51% compared with the 1 st period (5.2%). Generally, the daily oil yield increases and then gradually decreases with the increase of the throughput period of the injection and swallowing emetics.

TABLE 4 statistical table of stage production effect of different mining modes

3.2 surfactant System development

3.2.1 surfactant throughput screening principle

Surfactant throughput is different from surfactant flooding and the required surfactant performance is also different. In the process of surfactant huff and puff, the same injection and production port is used for gas injection and oil production after soaking. And surfactant flooding is separate from injection and production wells. Although both require lowering the oil-water interfacial tension and increasing the wetting angle of the rock and crude oil, oil recovery still relies on formation energy because of surfactant stimulation. In the surfactant huff and puff process, multiple mechanisms coexist, and the surfactant is required to have low interfacial tension, strong wettability, high-temperature stability and high salt resistance; and meanwhile, in order to avoid blocking damage caused by airlock and Jamin effect on the stratum near the production well, the surfactant also has low foam and low emulsifying property. Surfactant throughput conventional screening principles:

(1) the molecular weight of the surfactant cannot be too large, the low-pressure injection requirement of an oil reservoir must be met, the stratum is not easy to block, and the concentration of a surfactant system is not too large;

(2) the surfactant has certain salt tolerance, meets the requirement of the mineralization degree of formation water of a target oil reservoir, and is not suitable for reacting with ions in the formation water to inactivate or generate precipitates;

(3) the surfactant has good stability, meets the requirement of the temperature of the stratum of a target oil reservoir, and can stably exist for a long time when flowing in the stratum, so that the effective period of huffing and puff is prolonged;

(4) the surfactant is stably adsorbed in the stratum of the production well, and the wettability of rock can be changed for a long time, so that the effective period can be prolonged for a long time.

The invention determines two compound surfactants through twice performance screening, obtains three different surfactant systems through different proportions of compounding, and screens the third performance of the three systems and the second screened surfactant to finally obtain the best compound surfactant system.

3.2.2 Primary selection of surfactants

The invention prepares 18 kinds of surfactants, the invention measures the surface tension of 0, 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1% at 30 ℃ according to the nineteen kinds of surfactants, and 10 kinds of surfactants are screened according to the surface tension.

The surface tensions of the nineteen surfactants were arranged from large to small at a concentration of 1% as shown in table 5. Since the smaller the surface tension, the better the performance, the latter 10 surfactants were screened out. For ease of labeling, the ten surfactants 12-3-12; 16-3-16; YND 1233; YND 1633; 101005, respectively; 101328, respectively; 101336, respectively; 101329, respectively; 101335, respectively; 101338 are numbered sequentially as surfactant Nos. 1-10, as in Table 6.

TABLE 5 surface tension of eighteen surfactants

TABLE 6 numbering of the ten surfactants

Number 1	Number 2	No. 3	Number 4	Number 5
					Gemini12-3-12	Gemini16-3-16	YND1233	YND1633	FT101005
Number
	6	No. 7	Number 8	Number 9	Number 10
FT101328						FT101336	FT101329	FT101335	FT101338

3.2.3 check of surfactant

1. Research on compatibility of surfactant and formation water

And (3) researching the compatibility of the surfactant and the formation water, observing whether the surfactant and the formation water generate precipitates or not, and if no precipitates are separated out, showing better stability and compatibility with injected water by the system.

1) Testing an instrument: ten beakers, pipettors.

2) The testing steps are as follows:

(1) ten beakers were taken and 100ml of formation water was placed.

(2) Ten kinds of surfactants, 0.5ml, were added to prepare solutions with a concentration of 0.5%.

(3) Standing for 48h, and observing color change of the ten solutions, with or without precipitate.

Surfactants No. 4 and 6 produced white precipitates with formation water during the test, and surfactant No. 10 produced flocculent layers under simulated formation water conditions during the test, as shown in fig. 6, thus excluding surfactants No. 4, 6, and 10.

2. Testing of crude oil Peel Properties

1) Testing an instrument: eleven beakers, stratum sand and stratum crude oil.

2) The method comprises the following steps: (1) respectively adding 20g of stratum soil and 10ml of crude oil into eleven beakers, and sealing by using a plastic film after fully stirring; (2) then placing the mixture into an oven to be baked for 24 hours at the temperature of 60 ℃; taking out, respectively adding ten 0.5% solutions of 100ml surfactants and formation water, and hermetically baking for 24h at 60 deg.C; (3) and finally, comparing the amount of crude oil stripped from different types of surfactant solutions, and judging the stripping degree of the crude oil.

Surfactant No. 2 produced floc after high temperature aging with crude oil during the test, indicating that surfactant No. 2 was unstable in the presence of crude oil. It can also be seen from the oil sand stripping experiment of crude oil that the distribution form after soaking in two different solutions has a great difference, the oil sand that has soaked in the surfactant solution with high surface activity wets and subsides more fully, and a lot of oil drops desorb with the oil sand and disperse in aqueous solution automatically, and the oil sand that has soaked in aqueous solution wets and does not change significantly.

3.2.4 selection of surfactants

According to the experiment in 3.2.3, only the remaining six surfactants were evaluated, since the surfactants No. 2, No. 4, No. 6 and No. 10 were not compatible with formation water and crude oil.

1. Testing of temperature resistance

1) The apparatus tested: XY-6 type high-temperature oven, polyvinyl fluoride bottle.

2) The testing method comprises the following steps: (1) taking 100ml of 6 surfactant solutions with the concentration of 0.2% respectively and putting the surfactant solutions into a polytetrafluoroethylene bottle; (2) heating to 120 ℃ by an oven and keeping for 24 h; (3) the six solutions were then taken out and their interfacial tensions at 30 ℃ were measured, in order to compare the temperature resistance of the individual surfactants.

TABLE 7 comparison of temperature resistance

Surfactant numbering	1	3	5	7	8	9
							Normal temperature before preparation	0.08	0.17	0.01	0.36	0.16	0.41
After heating	0.09	0.19	0.05	0.54	0.17	0.45
							Rate of change/%)	12.5	11.76	400	50	6.25	9.75

From the change rate of temperature resistance, except the surfactants 5 and 7, the other four surfactants have higher temperature resistance and smaller influence on the performances under high temperature conditions.

2. Effect of rock on surfactant adsorption

1) Testing an instrument: six beakers, electronic balance, pipettor, stratum sandstone.

2) The method comprises the following steps: (1) six kinds of surfactant solutions with the concentration of 0.2% are prepared, and six bottles are respectively prepared; (2) 5g of sandstone, 10g of sandstone, 15g of sandstone, 20g of sandstone and 25g of sandstone are added respectively; (3) standing for 12 h. The interfacial tension after adsorption of the sand with different qualities is respectively measured at 30 ℃.

TABLE 8 comparative results of rock adsorptive stability

The experimental results show that the difference of the change rate of the interfacial tension of different surfactants after the adsorption of the rock is large, the adsorption of stratum sandstone to the surfactants of No. 1, 3 and 5 is large, and the adsorption change of the stratum sandstone to other three surfactants is not obvious.

3. Evaluation of salt resistance of surfactant

1) Testing an instrument: five beakers, anhydrous CaCl₂A pipette.

2) The testing steps are as follows: (1) preparing six surfactant solutions with the concentration of 0.1% in five bottles respectively; (2) respectively adding 1%, 5%, 10%, 15%, 2% by weight0% of CaCl₂(ii) a (3) Interfacial tension was measured at 30 ℃ for different salinity respectively.

TABLE 9 comparison of salt tolerance of surfactants

With the increase of salinity, the surface activity of the surfactant is reduced, the interfacial tension is gradually increased, wherein the change of No. 5 is larger, and the changes of the other five surfactants are basically doubled.

4. Evaluation of interfacial tension and temperature stability

1) Testing an instrument: JJ2000B interfacial tension tester, syringe, small test tube, formation crude oil, beaker, pipettor.

2) The method comprises the following steps: (1) preparing mother liquor with the concentration of 1% for six surfactants, and further diluting the mother liquor into sub-liquors with the concentrations of 0.005%, 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.5% and 0.8% respectively; (2) the different concentrations of the subpool were injected into the capillary for measurement using a 5ml syringe. Measuring the interfacial tension, measuring the amount of injected liquid which is 1-2mm away from the pipe orifice, adding crude oil, and inserting a plug after ensuring that no air bubbles exist; (3) then screwing the capillary tube into a rotating shaft of the interface tension tester, and setting the rotating speed at 6000r/min for measurement; (4) the surface tension and interfacial tension were measured at respective concentrations of each surfactant at 30 deg.C, 50 deg.C, 60 deg.C, and 80 deg.C, as shown in Table 10.

Table 10 interfacial tension test results

From the results of the experiment shown in Table 10, it can be seen that at a low concentration, the interfacial tension increases with the increase in temperature, the activity of the surfactant increases, and the interfacial tension also increases, and that when the concentration is increased to a certain level, the interfacial tension does not increase any more and becomes stable with the increase in temperature.

5. Contact Angle testing of surfactants

1) Testing an instrument: contact angle tester, syringe.

2) The method comprises the following steps: (1) the surfactant solution was taken from the syringe and dropped on the rock. (2) After photographing with a contact angle tester, the contact angle was measured on the computer side.

TABLE 11 comparison of wetting contact angles

The smaller the contact angle, the easier the crude oil will leave the formation rock from previous mechanistic analysis. The contact angle test results show that the influence of the concentration of the surfactant is very obvious and is very close to the trend of interfacial tension, wherein the wettability of the No. 1 surfactant is the best.

6. Surfactant foamability test

1) Testing an instrument: high speed mixer, beaker, pipettor, graduated cylinder, timer.

2) The method comprises the following steps: (1) preparing 200ml of six surfactant solutions with the concentration of 0.5%, pouring the solutions into a stirring cup, placing the stirring cup on a stirrer, and adjusting the height; (2) starting the stirrer to stir at the rotating speed of 6000r/min, and stopping stirring after one minute; (3) and pouring the stirred surfactant solution into a measuring cup, recording the volume of the foam, simultaneously observing the condition of water separated out from the measuring cup, and stopping timing when 100ml of water is separated out to obtain the half-life period of the foam. The foam integrated value is the foam height multiplied by the half life as in table 12.

TABLE 12 comparison results of foaming Properties

From the results of the foaming performance experiments, it was found that when the surfactant concentrations were all 0.5%, the surfactant No. 1 had the lowest overall foam value and the lowest foamability.

7. Surfactant emulsifying Capacity test

1) Testing an instrument: high speed mixer, beaker, pipettor, graduated cylinder, timer, diesel oil.

2) The method comprises the following steps: (1) preparing 100ml of six surfactant solutions with the concentration of 0.5%, pouring the solutions into a stirring cup, adding 100ml of diesel oil, placing the stirring cup on a stirrer, and adjusting the height; (2) starting the stirrer to stir at a rotating speed of 3000r/min, and stopping stirring after two minutes; (3) the stirred solution was poured into a measuring cup, and the time for precipitating 25ml of water was recorded to compare the emulsifying ability.

TABLE 13 results of comparing emulsifying abilities

The results of the emulsification experiments show that except the surfactant 5 with a certain concentration for too long time, the emulsifying property is too good, and the emulsification stability of other four surfactants has a small difference.

3.2.5 combination of surfactants

1. Comprehensive evaluation of surfactants

In the surfactant huff and puff process, multiple mechanisms coexist, and the surfactant is required to have low interfacial tension, strong wettability, high-temperature stability and high salt resistance; and meanwhile, in order to avoid blocking damage caused by airlock and Jamin effect on the stratum near the production well, the surfactant also has low foam and low emulsifying property. Therefore, the comprehensive performance of 100 percent is set, the interface tension assigned specific gravity is set to be 30 percent, the wetting contact angle assigned specific gravity is set to be 25 percent, the emulsifying capacity assigned specific gravity is set to be 15 percent, the foaming capacity assigned specific gravity is set to be 15 percent, the temperature stability assigned specific gravity is set to be 5 percent, the salinity stability assigned specific gravity is set to be 5 percent, and the stability assigned specific gravity after rock adsorption is set to be 5 percent.

The six surfactants are ranked according to the performances of the six surfactants, and are sequentially scored from good to bad to be 6 to 1, and the performances are multiplied by specific weights to obtain a comprehensive score.

TABLE 14 ranking of six surfactant Properties

TABLE 15 ranking of the six surfactants

From the properties of various surfactants, the surfactant marked with the number 1 has higher interfacial activity, wettability, low foaming and salt stability resistance, and the surfactant No. 8 has low emulsification and better temperature stability, and the two are compounded to exert respective advantages.

2. Testing and comparing of compounding system performance

The surfactant 1 and the surfactant 8 are compounded in a ratio of 1:2, a ratio of 1:1 and a ratio of 1:2 respectively, and are used as three new surfactant systems to be compared with the surfactant 1 and the surfactant 8 with the highest scores in performance respectively. The optimal surfactant system is determined by the size of the final score.

TABLE 16 results of comparison of interfacial tensions

The present invention selects a comparison of the interfacial tensions of the surfactants at 50 deg.C and a concentration of 0.5%, as shown in tables 3-16. With varying proportions, the interfacial tension floats between the two formulated surfactants. Wherein the ratio of the compound system is 2:1, and the best effect is obtained. According to the advantages and disadvantages of the five systems, 5 to 1 points are sequentially assigned.

TABLE 17 comparison of wetting contact angles

From Table 17, the five systems were compared at 30 ℃ and 0.5% concentration. The contact angle of the three systems compounded is smaller than that of No. 8, the contact angles of the complex systems are all relatively close, the change of the contact angle can enable the crude oil in the stratum to be separated from the rock more easily, and the values are sequentially assigned to 5 to 1 from small to large.

TABLE 18 comparative results of foaming Properties

Surfactant type	Height of foaming	Half life	Characteristic value of foam	Assignment of value
					2:1	355	63	22365	5 points of
1:1	370	65	24050	4 is divided into
					1:2	390	68	26520	3 points of
1	640	53	33920	2 is divided into
					8	570	313	178410	1 minute (1)

From Table 18, it can be seen that the comprehensive value of the foam after compounding is reduced remarkably, wherein the compounding ratio of 2:1 is reduced most remarkably, and because the selected surfactant needs to be subjected to huff and puff construction, the surfactant is required to have low foamability so as to prevent the surfactant from generating a large amount of foam to block capillaries of a stratum and further reduce the air lock permeability. The values are assigned for 5 to 1 in turn from small to large.

TABLE 19 comparison of emulsification Properties

It can be seen from table 19 that the precipitation time is significantly reduced and the emulsifying ability is reduced when the formulation ratio is 2:1, and because the surfactant selected by the present invention needs to be subjected to huff and puff construction, the surfactant is required to have low emulsifying property, so as to prevent emulsified oil droplets from blocking capillaries of a stratum to cause a Jamin effect and reduce the permeability of the stratum, and the surfactant with low emulsifying property is selected by the present invention. Wherein the emulsifying capacity is sequentially assigned to 5 to 1 points from small to large.

TABLE 20 comparison of temperature stability

Compound system	2:1	1:1	1:2	1	8
						Normal temperature before preparation	0.09	0.11	0.13	0.08	0.41
After heating	0.09	0.13	0.16	0.09	0.45
						Rate of change/%)	0	18.18	23.07	12.5	9.75
Assignment of value	5	2	1	3	4

It can be seen from table 20 that the effects of the surfactant systems are different at high temperature, wherein the temperature is very stable and almost unchanged at a compounding ratio of 2:1, and the interfacial tension of the other four systems is reduced, which may be due to the reduction of the stability and the reduction of the activity of the surfactant at high temperature and high pressure. The temperature stability is assigned with values of 5 to 1 from high to low in sequence.

TABLE 21 comparison of rock adsorption stability

It can be seen from table 21 that the interfacial tension of the surfactant increases to different extents for each system as the amount of sand increases, probably because the adsorption of sand decreases the concentration of surfactant, resulting in an increase in interfacial tension, with the adsorption of rock having minimal effect on the system formulation ratio of 2: 1. And assigning values of 5 to 1 in sequence from low to high.

TABLE 22 comparison of salinity effects

From the table 22, it can be seen that the interfacial tension of the surfactants of each system increases to different degrees with the increase of salinity, the activity of the surfactants decreases due to the increase of mineralization, wherein the influence of salinity on the surfactant system with the compounding ratio of 2:1 is relatively small, and the surfactant systems with small salinity change rate are sequentially assigned to 5 to 1 points from small to large.

3. Final selection of surfactant systems

TABLE 23 Total score of seven Properties

The performances of the three compound systems are compared with those of the

surfactant

1 and 8. And finally, calculating: the composite score is given as 35% × interfacial tension assigned + 25% × surface tension assigned + 15% × non-emulsifying capacity assigned + 15% × non-foaming capacity assigned + 5% × temperature impact assigned + 5% × salinity impact assigned + 5% × rock stability assigned in table 22.

From the comprehensive scores of the five compound surfactant systems, the finally suggested surfactant is compounded by Gemini12-3-12 and FT101329, and the compounding ratio is 2: 1.

6 results

(1) The technology of optimizing well spacing, straight-flat combined fireflood, continuous oil pipe sand blasting perforation casing staged fracturing, separate-layer water injection, mechanical partial pressure pipe column, separate-layer acidification, subdivision control fracturing and the like is adopted at home and abroad to develop the thin interbed reservoir.

(2) The surfactant huff and puff technology has been effectively applied to closed small fault block oil reservoirs, large-port fault block heavy oil reservoirs, Puchensha-one oil reservoirs and Daqing oil fields.

(3) The basic mechanisms of surfactant huff and puff technology are: increasing the number of capillary tubes, changing the wettability and carrying out crude oil replacement in the process of soaking.

(4) In the S70 well region Karazaire group sand shale section, the electrical property of sand and conglomerate of the reservoir section is represented by a typical negative characteristic, and the wettability can be changed for a long time by utilizing the electrostatic adsorption reaction characteristic of anions and cations, so that the property of the rock surface of an oil layer is changed, and the huff and puff operation is facilitated;

(5) through preliminary screening, fine screening and compounding, the recommended use type of the huff and puff surfactant is compounded by Gemini12-3-12 and fluorocarbon FT101329, and the compounding ratio is 2: 1;

(6) combining the results of comprehensive physical modeling and numerical simulation, the optimization result of the dosage of the surfactant is as follows: 0.5 PV;

(7) combining the results of comprehensive physical model and numerical simulation while considering the loss in the surfactant injection process, the determined surfactant injection concentration is preferably 0.4%;

(8) synthesizing results of indoor physical models and numerical simulation, and finally determining the optimal result of the well closing time to be 12-14 days;

(9) according to the research results of the object model and the digital model, the recommended intermittent liquid drainage period is 50 days, and the liquid drainage times are three times;

(10) the injection speed is determined to be 30m by several modes and combining field practice³/d；

(11) The increase of the injection pressure/speed is beneficial to forced dialysis to improve the recovery ratio at the initial stage, but the injection pressure is too large and is unfavorable to improve the recovery ratio;

(12) the larger the difference of the anisotropism of the permeability is, the worse the huff and puff effect of the surfactant is, which is not beneficial to huff and puff the surfactant to improve the recovery ratio;

(13) the injection of the gel plugging agent is beneficial to the change of the surfactant from high permeation to low permeation, and the throughput efficiency of the surfactant can be greatly improved;

(14) the three surfactants can greatly change the interfacial tension and the contact angle, which shows that the three surfactants have good surface activity;

(15) compared with foaming performance and emulsion stability, the betaine amphoteric ionic surfactant has stronger foaming and emulsion stability, and has the risks of allergy and emulsion blockage in surfactant huff and puff construction;

(16) compared with the evaluation of surfactant stability in temperature and saline water, the compound surfactant GF-2:1 has higher stability, and the betaine surfactant BS-12 has better stability;

(17) the injection of the active water communicates with the water layer at the lower part of the carboniferous system, and the surfactant has good capability of reducing the flowing pressure and increasing the fluidity, so that the water layer is produced along with the production. When the surfactant is gradually discharged along with produced fluid, the concentration in the stratum is reduced, the flowing capability of a water source is deteriorated, and the capability of plugging crude oil is deteriorated. The situation that the water production is reduced and the oil production is increased is presented.

The above description is only for the purpose of illustrating the present invention and the appended claims are not to be construed as limiting the scope of the invention, which is intended to cover all modifications, equivalents and improvements that are within the spirit and scope of the invention as defined by the appended claims.

Claims

1. The method for increasing the recovery ratio of the thin interbed lithologic reservoir by injecting the surfactant is characterized by comprising the following steps of:

aiming at the characteristics of a target oil reservoir, a proper surfactant system is optimized, and the system has the effects of increasing the number of capillary pipes, changing wettability and carrying out crude oil replacement in a soaking process, so that the requirement of improving the crude oil recovery ratio of a thin interbedded lithologic oil reservoir is met;

applying a relatively corresponding physical model to determine the influence of the difference of the application parameters on the effect;

the application scheme of making injection parameters, stuffy well characteristics and extraction parameters comprises the following steps: optimizing injection parameters; optimizing the parameters of the blank well; and (4) optimizing the extraction parameters.

2. The thin interbed lithologic reservoir surfactant huff and puff oil recovery method of claim 1, wherein the composite surfactant injection amount is 0.5PV and the composite surfactant concentration is 0.4%.

3. The thin interbed lithologic reservoir surfactant huff and puff oil recovery method of claim 1, wherein the complex surfactant injection method comprises: at 30m³Speed of/d is repeatedAnd injecting a surfactant.

4. The thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method of claim 1, wherein the huff-and-puff surfactant of the thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method is compounded by Gemini12-3-12 Gemini and fluorocarbon FT101329, and the compounding ratio is 2: 1.

5. The thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method of claim 1, wherein the thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method comprises the following surfactant amounts: 0.5 PV.

6. The thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method of claim 1, wherein the thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method has a surfactant injection concentration of 0.4%.

7. The thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method of claim 1, wherein the thin interbed lithologic reservoir surfactant huff-and-puff oil recovery method lasts 12-14 days.

8. The thin interbed lithologic reservoir surfactant huff and puff oil recovery method of claim 1, wherein the thin interbed lithologic reservoir surfactant huff and puff oil recovery method has an intermittent drainage cycle of 50 days and three times of drainage; the injection speed is 30m³/d。