CN112080269A - Micro-bubble fracturing fluid, preparation method and application - Google Patents

Abstract

The invention belongs to the technical field of fracturing fluid, and discloses a micro-bubble fracturing fluid, a preparation method and application thereof, wherein the micro-bubble fracturing fluid comprises the following components in formula: the adhesive consists of 0.2 percent of special-grade hydroxypropyl guanidine gum, 0.2 percent of organic boron crosslinking agent, 0.2 percent of Sodium Dodecyl Sulfate (SDS), 0.3 percent of dodecyl Sulphobetaine (SJT), 0.2 percent of dodecanol (SF-1) and the balance of water according to mass fraction; the microbubble fracturing fluid has the advantages that the diameter of the microbubbles is distributed between 30 and 100 mu m, and the microbubbles are very fine and uniform; the special 'one-core two-layer three-mold' microstructure has stable performance. The foam is tiny, fine and uniform, and has high compression resistance; the temporary plugging effect is achieved, the filtration of the fracturing fluid into tiny pores or natural cracks can be effectively reduced, and the efficiency of the fracturing fluid is improved; the sand-carrying agent has the characteristics of high temperature resistance and shear resistance and strong sand-carrying capacity; the foam has large mass and less liquid, can increase the backflow of laminated low-pressure ground, and reduce water sensitivity and adhesive residue damage.

Description

Micro-bubble fracturing fluid, preparation method and application

Technical Field

The invention belongs to the technical field of fracturing fluids, and particularly relates to a micro-bubble fracturing fluid, a preparation method and application thereof.

Background

Oil and gas resources are important strategic materials for the survival and safety of the country and also are important components for the national economic construction and life. Fracturing is one of the most effective measures for increasing the production of oil and gas reservoirs, and has been rapidly developed and widely applied at home and abroad. The high-pressure pump set is used for pumping high-viscosity non-Newtonian fluid containing high-concentration proppant into the stratum, high pressure is formed near a target layer, and when the pressure exceeds the fracture pressure of the stratum at the position, a crack is formed in the target layer and extends and expands. The fracturing fluid, which is used to transmit high pressure during the fracturing process, fracture the reservoir, form the fracture and ultimately carry proppant into the fracture, is the most important working fluid in the overall process. The fracturing fluid can directly influence the success of construction, the length of the pressed fracture, the flow conductivity of the supporting fracture and the production capacity of the oil and gas well after being pressed.

At present, the fracturing fluids widely used at home and abroad mainly comprise water-based fracturing fluids, oil-based fracturing fluids, foam fracturing fluids and emulsified fracturing fluids. Each fracturing fluid has different characteristics due to different compositions, and an appropriate fracturing fluid formula needs to be optimized by combining different characteristics of a reservoir stratum. According to the functional requirements of the fracturing technology on the fracturing fluid, the fracturing fluid usually needs to be well compatible with formation minerals, oil and water, so that the damage to a storage matrix is reduced; the fluid loss control agent has proper viscosity, low fluid loss characteristic and seam making capability; the temperature resistance, the shearing resistance and the sand carrying capacity are stronger; the rapid gel breaking capacity under the stratum condition reduces the damage to the flow conductivity of the support fracture. Therefore, the formation and development of the fracturing fluid technology will be further researched in the future on two main aspects of improving sand carrying performance and low damage performance. Foamed fracturing fluids have also undergone one such development as a two-phase gas-liquid containing fracturing fluid system.

The country where foam was first used in fracturing construction was the united states. It has been put into use as early as 1970, and the technology of foam fracturing fluids has matured by the end of the 80 s. In the early 70s, nitrogen foam fracturing fluid is used firstly, and the content of the proppant can only be 120kg/m according to the injection technology at that time³～140kg/m³The mortar is pumped into cracks, and the laying concentration of the propping agent is lower. Although the sand carrying capacity is not strong and the properties of the fracturing fluid are not good enough, a good yield increasing effect is obtained, and scientific researchers summarize and find that the flowback effect after the fracturing is improved due to the expansion characteristic of gas, so that the interest of people is aroused. During 1973-1976, the foam fracturing fluid was the initial stage of development, most construction was small-scale treatment, and the use of the foam fracturing fluid was still in the trial stage. During 1977-1978, foam fracturing fluid damage to the formation began to be considered and began to be reduced by the addition of methanol. 1979-1983 was the rapid development stage of the foam fracturing fluid process. The main development stage of the foam fracturing fluid is the middle of the 80 th century, the foam fracturing fluid has good effect on solving the problem of gas well fracturing, and more than 90% of gas well fracturing is applied foam fracturing fluid technology at that time. After decades of development and research, the foam fracturing fluid tends to be mature, which mainly shows the understanding of the properties of the foam fracturing fluid, the construction design aspect, the final productivity evaluation and the like.

From the development process of the foreign foam fracturing fluid technology, the method can be summarized into the following four processes:

(1) the main components of the first generation of foam fracturing fluid base fluid are water, brine, alcohols and crude oil, and bubbles are generated by using nitrogen and a foaming agent. The foam fracturing fluid has low filtration loss and high flowback rate, and has the defects of poor stability of formed foam, short half-life period of the foam, incapability of constructing high-temperature wells and deep wells, and control of construction scale in a small range.

(2) The second generation of foam fracturing fluid was modified by the addition of vegetable gums to stabilize the foam properties. Besides the stability of foam, the foam fracturing fluid also has improved viscosity and enhanced sand carrying capacity, so that the foam fracturing fluid meets more construction condition requirements than the first-generation foam fracturing fluid.

(3) The third-generation foam fracturing fluid is formed by adding a cross-linking agent on the basis of the second-generation foam fracturing fluid, and the cross-linking agent also has the main function of improving the viscosity of the sand-carrying fluid and further improving the stability of the fracturing fluid. The method of delaying crosslinking gel is adopted to further enable the bubbles to become uniform and stable, and the viscosity of the system is improved, so that the temperature resistance, the shearing resistance and the sand carrying capacity of the foam fracturing fluid are enhanced.

(4) The fourth generation of foam fracturing fluid has little difference with the third generation of foam fracturing fluid in the aspect of liquid composition, but the uniformity of foam is emphasized, the temperature resistance and the shearing resistance of a foam system are improved, and the content of a propping agent reaches 1440kg/m³Above, can satisfy the large-scale sand construction needs of adding.

The method is different from the development of foam fracturing fluid abroad, and the domestic development is mainly in the aspects of the composition of the foam fracturing fluid and the performance research and evaluation of additives. The method mainly comprises two stages: the first stage is non-crosslinked foam fracturing fluid research; the second stage is a crosslinked foam fracturing fluid study. Wherein the crosslinked foam fracturing fluid can be subdivided into acidic crosslinked CO according to different researches and applications₂Foam fracturing fluid and organic boron crosslinked N₂Two parts of foam fracturing fluid. The research of China on the foam fracturing fluid starts at the end of the 80 th years of the 20 th century. In the 1989 cooperation of the division of the oil exploration courtyard house with the CER company of the United states, a rheological circuit device was introduced, which is used to treat non-crosslinked CO₂The rheological property of the foam fracturing fluid is researched, rheological parameters of the fracturing fluid under different foam qualities are measured, and the flowing property of the foam fluid is researched; parameters such as foam quality, bubble size, half-life period and the like are tested, and decay mechanism of the foam is researched; and the apparent viscosity of the fracturing fluid, the settling rate of the proppant in the fracturing fluid, and the like; in 1989 Jiang Guzhou Hua introduced foam fracturing fluidPreferred tests for the foam agent and foam stabilizer, and the influence of inorganic salts, temperature and foaming speed on the foam parameters. In 1998, the construction of foam fracturing fluid was carried out for the first time in Liaohe oil field, and N was used₂And (4) foaming fracturing fluid. The flowing behavior characteristics of the foam fracturing fluid were studied in the year 2000 Yangdong by using a large multifunctional circuit device introduced from the CER corporation of America, and different CO were obtained₂Rheological parameters of foam quality fracturing fluid, and research on CO by using RS75 controlled stress rheometer₂The viscoelastic property of the foam fracturing fluid analyzes the relationship between the foam quality and the apparent viscosity, the viscoelasticity, the microstructure and the settling rate of the propping agent; the experimental result shows that the researched foam fracturing fluid has the characteristics of low density, low filtration loss, good rheological property, strong sand carrying capacity, low damage and the like. After 2000 years, CO₂And N₂The foam fracturing fluid is applied to a plurality of oil fields in China in a large amount, and has a good effect on a low-permeability reservoir; meanwhile, the indoor research is further deepened, the research and evaluation of the temperature resistance, the shearing resistance, the viscoelasticity, the friction resistance, the low damage characteristic and the like of the foam fracturing fluid are rapidly developed, and meanwhile, the in-situ self-generated foam fracturing fluid, the acid foam fracturing fluid, the surfactant foam fracturing fluid and the clean N are developed₂Foam fracturing fluids, foam-like fracturing fluids, and the like, SiO-containing fluids have been developed over the years₂、Al₂O₃The performance of the foam fracturing fluid is being improved.

Summarizing, the development and formation of the domestic foam concentrate technology comprise the following aspects:

(1) software simulation is carried out on the foam fracturing fluid under different construction conditions from the end of the 80 s to the middle of the 90 s, and the rheological property of the foam fracturing fluid in the construction process is researched.

(2) In the middle of the 90 s to 2003, the characteristics of the flow of the foam fluid in the fracture wall surface are researched, and it is deduced that the flow mode of the foam fracturing fluid in a reservoir fracture is more accurately described by using the equation of power-law laminar flow. However, the non-crosslinked foam fracturing fluid is only limited to research on the flow mechanism in China and is not applied on site. Acidic crosslinked CO₂Foam fracturing fluid and organic boron crosslinkingN₂The foam fracturing fluid has better application effect in practical application.

(3) From 2003 to 2008, the current CO is treated₂Foam fracturing fluid, N₂The performance evaluation and the application in mines of the foam fracturing fluid are increased, but a plurality of foam fracturing fluid systems such as self-generated foam fracturing fluid, low-molecular alcohol-based foam fracturing fluid, low-damage high-temperature-resistant foam fracturing fluid, acidic cross-linked foam fracturing fluid and the like are developed in a large amount at the same time, and corresponding mechanism research, performance evaluation and field application are developed at the same time, so that the foam fracturing fluid is developed for a period of time more quickly. However, for the foam fracturing fluid, the used foaming device and pressurizing equipment are expensive, so that the construction cost is greatly increased, and the difficulty of deep well construction is not solved. Therefore, the foam fracturing fluid is only used for research or part of well construction in China and is not popularized and applied in a large range.

(4) In addition to further performance optimization and field application of the above-described bulk fracturing fluid, in 2007, SiO was used₂、Al₂O₃Introduction of equal nanotechnology into CO₂In the foam fracturing fluid, the temperature resistance of the foam fracturing fluid is improved and the pipe column friction in the construction process is reduced by improving the arrangement structure of foam molecules, but at present, the foam fracturing fluid is not applied to a mine field, which is a new technical route of the foam fracturing fluid in recent years. The other new technical route is the introduction of the American Aphrons system, which treats the national circulating foam and the foreign Aphrons system as the microfoam drilling fluid, and in the following period of time, the systems are collectively called microfoam systems, and the microfoam is regarded as a microcosmic system with one core, one layer and three dies. By 2013, the research on the micro-foam system in China has been greatly advanced, more than 180 related academic papers exist, the main research field in the aspects of drilling and completion of wells has not been introduced into the fracturing technology as a foam fracturing fluid, and the main research direction of the micro-foam system comprises the rheological property, the fluid loss property, the stability and the like of the micro-foam system. The micro-foam system is developed by preparing a micro-foam system from a compound foaming agent, a high-efficiency foam stabilizer, a thickening agent and the like, and the foam quality is between 0.1 and 0.82Foam rheology, the herabar rheology model is believed to more accurately reflect the flow properties of the foamed fluid.

(5) After 2008, the Zheng Tong professor of the university of Petroleum in China (Beijing) has proposed the application of the micro-foam drilling fluid system used in the field, which is not the previously proposed structure of 'one core and one layer and three molds', but should be 'one core and two layers and three molds', on the structure of the micro-foam, and in the drilling, completion and leakage stoppage of the mine site.

The discussion of the microfoam microstructure needs to be further advanced and there are a number of problems to be solved. The term microvesicles was first introduced by Sebba in 1997, which was initially named Aphrons by Sebba. The micro-foam system is firstly applied to the petroleum and natural gas industry and is used as a micro-foam drilling fluid, which is a near-equilibrium drilling fluid with brand new application. In 1998 a recyclable foam system was developed by Brookey, known as Aphrons drilling fluid, and has received increasing attention. Subsequently, cga (colloidal gasaphrons) drilling fluid systems were developed, which have a strong shear-thinning ability, even like water during flow, and a certain viscosity at low flow rates. Due to the stable property of the micro-foam, the micro-foam is successfully applied to the field of petroleum and natural gas in recent years, firstly, a System applying the micro-foam with the special property is drilling fluid, and M-I and Acti-System companies of American drilling fluid companies jointly develop a near-equilibrium drilling fluid at the end of 20 th century, namely the unique property of the micro-foam is applied. Such drilling fluids do not require high pressure to squeeze in carbon dioxide, nitrogen or air. The fine foam, i.e., Aphrons system, can be generated by mechanical stirring at normal temperature and pressure. From this time, microfoam has begun to be widely used in various depleted reservoirs, highly permeable formations, and reservoirs in which natural fractures develop in the world, with great success. In China, the micro-foam system is firstly developed into a well completion fuzzy bag by the Zhengli professor of China Petroleum university (Beijing), and the micro-foam system is successfully applied to the plugging of a drilling and completion mine field of a coal bed methane reservoir and a fractured reservoir.

According to the development of foam fracturing fluid technology, the foam fracturing fluid which is mature in the past is collectively called conventional foam fracturing fluid. Summarizing the progress in foam fracturing fluid technology, it can be seen that these conventional foam fracturing fluids have the following advantages:

(1) has the characteristics of gas-liquid two-phase and higher viscosity, and particularly improves the temperature resistance and the shearing resistance and enhances the sand carrying capacity after a thickening agent is added and cross-linking is carried out.

(2) Has stronger expansibility, is beneficial to accelerating the flowback after pressing and reduces the damage to cracks and matrixes. The advantages of fracturing the low-pressure stratum are obvious.

(3) The high viscosity property enables fluid loss reduction, and damage of fluid loss to a reservoir matrix is reduced.

(4) The foam has certain foam quality, reduces the water quantity and the damage of the water quantity to the stratum, and particularly has obvious advantages to the water-sensitive stratum.

(5) The filter has bubble aggregation, can block partial large pores and natural fracture cracks, increases the main net pressure of the cracks while reducing filtration, and is beneficial to increasing the length of the cracks.

Of course, by analyzing the composition and characteristics of the foam fracturing fluid and summarizing the application and the progress of the technology of the foam fracturing fluid, the conventional foam fracturing fluid is also found to have some disadvantages:

(1) the foam has poor stability, and is easy to gather and quickly break. The main reasons are the simple structure of the foam, especially the large surface tension of the gas and liquid, the poor stability, the large and uneven foam.

(2) The construction of the mine site requires a special pressurizing device and a foaming device. Due to the two phases of gas and liquid, and the large size of the foam, the difficulty of compression, high pressure, increased expense and safety risk.

(3) The pipe flow friction resistance is large, and the construction pressure is higher. The friction of the gas-liquid two-phase flow of the foam fracturing fluid is large, and the pressure of a well head and construction equipment and cost are increased.

(4) Is not suitable for construction of deep wells. Limited by a liquid foam structure, even if a supercharging device is adopted, even two-stage supercharging is adopted, the device is basically suitable for well operation above 3500 m; and the two-phase flow has large friction resistance, which restricts the application range of the foam fracturing fluid.

(5) The cost is high. The gas used by the conventional foam fracturing fluid is N₂Or CO₂Both gases are difficult to prepare on site, need to be transported by special vehicles and then injected underground by large-scale special pump trucks, and the equipment cost is high. And the construction scale is limited, the number of special equipment is large, and the difficulty and the safety risk of well site placement are increased.

Although the mechanism research of the conventional foam fracturing fluid is greatly advanced with the application of a mine field, and a micro-foam velvet bag system also has a good application effect in the plugging aspect of drilling and completion, no related report about the micro-bubble fracturing fluid exists in China at present. The project group develops indoor research and mine application of the foam liquid system for years, particularly tracks research progress of different stages of the foam fracturing liquid technology at home and abroad, and gradually forms some cognition and stage achievements about the micro-foam liquid system in the indoor research and mine test processes. Subject to the national fund project: the major national science and technology project 'multi-gas joint production well completion technology and reservoir protection' (2016ZX 050660020001), Chinese petroleum science and technology innovation fund project: the support of the crack steering expansion mechanical mechanism research under the displacement effect (2019D-5007-0206) further researches the structural characteristics, rheological characteristics and hydrodynamic property change of a microfoam system, a field test is carried out in a Tarim basin Tahe oil field in 2017 and research results, the effect of the microfoam villus temporary plugging agent for temporarily plugging and acidizing the carbonate deep well is evaluated for the first time, and the result shows that: the elastic modulus of the core is reduced after the micro-foam velvet bag is injected, the Poisson ratio is increased, and the elastic strain of the core is increased, so that the toughness and deformability of the core are improved; secondly, after the micro-foam velvet bags are temporarily plugged in the cracks of the carbonate rocks, the pressure bearing capacity of the cracks is gradually improved, a cliff type steep drop does not occur after the injection pressure reaches the peak value, and the micro-foam velvet bags form plugging belts to show strong plugging capacity; after the micro-foam velvet capsules block the cracks, the blocking pressure and the crack width grow in a negative exponential relationship, and the time for the blocking agent to bear the pressure to stabilize is shortened along with the increase of the crack width; the deformation capability of the rock is improved after the micro-foam velvet bag is plugged, the plugging fluid forms pressure building in the cracks, and when the net pressure in the cracks is larger than the maximum and minimum horizontal ground stress difference of the rock, the cracks are forced to turn to form new cracks, so that the purpose of fracturing by temporary plugging and turning is achieved; fifthly, the depth of the middle part of the reservoir of the field test well is 6330m, the temperature is 130 ℃, the construction is smooth and safe, and the micro-foam system can be applied to a high-temperature deep well, thereby the application range is expanded. And the research result of the application of the temporary villous sac plugging agent in the deep carbonate reservoir diversion fracturing is published in 2019 in the journal of science and technology of the natural gas industry, volume 39, and 12. Supported by the foundation of the national major and scientific research projects, the project group also researches the structural characteristics and rheological properties of the micro-foaming acid and the technical problem of how to combine the micro-foaming acid with acid liquids such as hydrochloric acid, hydrofluoric acid and the like, optimizes a foaming agent and a foam stabilizer with strong compound foamability and foam stabilizing ability and mass fractions thereof through a large number of experiments, contrasts and evaluates the characteristics of reaction speed, reaction series and the like of various acid liquid systems such as the micro-foaming acid, the gelled acid, the cross-linked acid and the like and rocks, researches the foamability, half-life period, micro-morphology, salt resistance and the like of the micro-foaming acid, obtains better evaluation results, finally forms the formula composition of the micro-foaming acid system and the preparation method thereof, becomes a novel acid liquid system in China, and obtains patent approval of the national intellectual property office in 3 months in 2020 to form an invention patent: a micro-foaming acid liquid and a preparation method thereof, the patent numbers are as follows: ZL 201710877063.9. Some experience training is obtained in the research process of the micro-foam acid liquid system and the micro-foam temporary plugging agent, particularly after some research cognition and achievements are obtained, a project group further considers whether a micro-foam fracturing liquid system can be developed and formed, a micro-foam structure system with foaming property, foam stability, flow resistance reduction, pressure resistance, temperature resistance, shear resistance, rheological property and sand carrying ratio is good is formed, and some defects in the conventional foam fracturing liquid are overcome. Through more than three years of experiments and exploration, the micro-bubble fracturing fluid formula and the specific preparation method thereof can overcome partial technical defects of the conventional foam fracturing fluid, and have optimized performance and wider application range.

In conclusion, the conventional foam fracturing fluid is limited by a liquid foam structure, the foam size difference is large, the foam is easy to gather and break, the stability is poor, the pressure resistance is low, and a special pressurizing device and a foaming device are required for construction; the liquid foam fluid is conventional gas-liquid two-phase flow, the pipe flow friction is large, the wellhead pressure is high, and the liquid foam fluid cannot be used for a deep well; the obvious defects of the two aspects restrict the application field of the conventional foam fracturing fluid. Therefore, the micro-bubble fracturing fluid of the research is supposed to improve the microstructure of the micro-bubble fracturing fluid by optimizing the formula composition of the foaming agent, the foam stabilizer, the thickening agent and the crosslinking agent, meet the basic characteristic requirements of the conventional fracturing fluid and the conventional foam fracturing fluid, enhance the pressure resistance of the conventional fracturing fluid and reduce the flow friction resistance of the conventional foam fracturing fluid, save a special supercharging device and enlarge the application field of the foam fracturing fluid.

It can be seen that the main problems and defects of the conventional foam fracturing fluid technology are as follows:

(1) the liquid foam has relatively simple structure, large foam size difference, easy aggregation and breaking, poor stability and insufficient functions.

(2) The pressure resistance is low, the pipe flow friction is large, the wellhead pressure is high, a special supercharging device is required for construction, the device cannot be used for construction of deep wells and mines, the cost and the safety risk are increased, the application field is limited, and the device is not suitable for the development of oil and gas energy sources to deep wells in the future in China, particularly the development of offshore deep wells.

The difficulty in solving the above problems and defects is:

how to select foaming agent and foam stabilizer with better foamability and foam stability from a plurality of surface active agents with foamability and foam stability, especially the foaming agent and foam stabilizer which can be prepared into foam with tiny and uniform foams, independent dispersion or point-to-point contact dispersion of micro-bubbles in liquid and lower gas-liquid surface tension characteristic; how to construct the foaming agent, the foam stabilizer, the thickening agent and the cross-linking agent to ensure that the foaming agent, the foam stabilizer, the thickening agent and the cross-linking agent have compression resistance and low friction resistance besides the basic rheological property and low damage property of the conventional fracturing fluid and the conventional foam fracturing fluid. Wherein the preference of the foaming agent and the foam stabilizer is critical.

The significance of solving the problems and the defects is as follows:

based on the action mechanism of the surfactant, the defects of the existing foam fracturing fluid technology are scientifically solved, and the fracturing fluid system and the technology series are enriched; through liquid foam structure optimization, the prepared micro-bubble fracturing fluid has high pressure resistance and low friction resistance, so that the low damage characteristic of the foam fracturing fluid, particularly the application advantages of being suitable for water-sensitive and energy-deficient strata are fully exerted, and the application field of the foam fracturing fluid technology is expanded; provides a development technology and a storage technology for the fracturing production increase of onshore deep-layer and ocean deep wells for national oil and gas energy construction.

Disclosure of Invention

Aiming at the problems of the existing foam fracturing fluid technology, the invention provides a micro-bubble fracturing fluid, a preparation method and application.

The invention is realized in such a way, and the preparation method and the application thereof are provided, wherein the micro-bubble fracturing fluid consists of 0.2% of special-grade hydroxypropyl guar gum, 0.2% of organic boron crosslinking agent, 0.2% of Sodium Dodecyl Sulfate (SDS), 0.3% of dodecyl Sulfobetaine (SJT), 0.2% of dodecanol (SF-1) and the balance of water according to mass fraction; the water is complemented to 100 percent

Another object of the present invention is to provide a method for preparing a micro-bubble fracturing fluid, the method comprising:

step one, respectively weighing 0.2g of special hydroxypropyl guar gum, 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 according to mass percentage;

step two, adding 100ml of tap water into a 1000ml volumetric flask, slowly dissolving 0.2g of the weighed special-grade hydroxypropyl guar powder into the water in the volumetric flask, and uniformly stirring until the special-grade hydroxypropyl guar powder is swelled for 45 min;

and step three, sequentially adding 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 into a volumetric flask, and continuously stirring until the mixture is uniform to form milky micro foam liquid, thus obtaining the microbubble fracturing liquid.

By combining all the technical schemes, the invention has the advantages and positive effects that:

the microbubble fracturing fluid is milky-white micro foam fluid, and the diameter of micro foam of the microbubble fracturing fluid is distributed between 30 and 100 mu m, so that the microbubble fracturing fluid is very fine and uniform; has a special microstructure of 'one core, two layers and three moulds' and stable performance. Different from the conventional foam liquid, a special foam generating device is not needed in the preparation process, the mixture is stirred indoors by a glass rod, and the liquid is circulated by a cement truck in a mine field; the foam is tiny, the high pressure resistance characteristic is realized, and a special pressurizing device is not needed in the construction process; the pipe flow friction resistance is small, the pressure of a wellhead is favorably reduced, and the device can be used for deep wells; the foam aggregation characteristic is kept under the reservoir condition, the temporary plugging effect is realized, the filtration loss of the fracturing fluid to tiny pores or natural cracks can be effectively reduced, and the fracturing fluid efficiency is improved; the high-temperature-resistant and shear-resistant sand carrier has high temperature resistance and strong sand carrying capacity in artificial cracks; the foam has large mass and less liquid, can increase the flowback after lamination in a low-pressure area and reduce the damage of water sensitivity and adhesive residue. The microbubble fracturing liquid system is particularly suitable for water-sensitive, low-pressure and fractured fluid loss strata, can be used for fracturing high-temperature deep well reservoirs, has wide application prospect, and provides development technology and storage technology for increasing the fracturing yield of onshore deep layers and ocean deep wells for oil and gas energy construction.

Drawings

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

FIG. 1 is a flow chart of a method for preparing a microbubble fracturing fluid according to an embodiment of the present invention

FIG. 2 evaluation experiment of foaming volume (ml) of different foaming agents

FIG. 3 evaluation experiment of half-lives (min) of different blowing agents

FIG. 4SDS and ABS compounded foaming volume (ml) evaluation experiment

FIG. 5SDS and OP-10 foaming volume (ml) evaluation experiment

FIG. 6 evaluation experiment of SDS and SJT compounded foaming volume (ml)

FIG. 7 evaluation experiment of half-life (min) of SDS and ABS compounded foaming liquid

FIG. 8 evaluation experiment of half-life (min) of SDS and OP-10 compounded foaming liquid

FIG. 9 evaluation experiment of half-life period (min) of SDS and SJT compounded foaming liquid

FIG. 10 evaluation experiment of foaming volume (ml) and half-life (min) of OA-12 foam liquid as foam stabilizer

FIG. 11 evaluation experiment of foam volume (ml) and half-life (min) of SF-1 foam stabilizer

FIG. 12 evaluation experiment of microbubble-based liquid thickener

FIG. 13 evaluation experiment of crosslinking agent for crosslinked foam liquid

FIG. 14 micro-foam fracturing fluid foamability and foam stability test chart

FIG. 15 is a graphical representation of different time periods for the micro-bubble fracturing fluid

FIG. 16 is a graph of the structural change of a microfoam at different times under quiescent conditions

FIG. 17 microfoam theoretical microstructure diagram

FIG. 18 comparison of conventional foam and microfoam microstructures

FIG. 19 is a diagram of the temperature and shear (90 deg.C) resistance of the micro-bubble fracturing fluid

FIG. 20 is a graph showing the temperature and shear resistance (120 ℃ C.) of the micro-bubble fracturing fluid

FIG. 21 pressure resistance test chart of micro-bubble fracturing fluid

FIG. 22 is a graph of friction tests of a micro-bubble fracturing fluid and several common fracturing fluids

FIG. 23 is a graph showing that 20-40 mesh quartz sand with a sand ratio of 30% stands for 24hr in a micro-bubble fracturing fluid

TABLE 1 proppant settling velocity experiments in several fracturing fluids

TABLE 2 micro-bubble fracturing fluid gel breaking experiment

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 micro-bubble fracturing fluid, a preparation method and application thereof, and the invention is described in detail below with reference to the accompanying drawings.

The microbubble fracturing fluid provided by the embodiment of the invention consists of 0.2% of special-grade hydroxypropyl guar gum, 0.2% of organic boron crosslinking agent, 0.2% of Sodium Dodecyl Sulfate (SDS), 0.3% of dodecyl Sulphobetaine (SJT), 0.2% of dodecanol (SF-1) and water according to mass fraction; the balance of water, and the water is complemented to 100 percent.

As shown in fig. 1, the preparation method of the microbubble fracturing fluid provided by the embodiment of the present invention includes:

s101, respectively weighing 0.2g of grade hydroxypropyl guar gum, 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 according to the proportion;

s102, adding 100ml of tap water into a 1000ml volumetric flask, slowly dissolving 0.2g of the weighed special-grade hydroxypropyl guar powder into the water in the volumetric flask, and uniformly stirring until the special-grade hydroxypropyl guar powder is swelled for 45 min;

s103, adding 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 which are weighed into a volumetric flask in sequence, and continuously stirring until the mixture is uniform to form milky micro foam liquid, thus obtaining the microbubble fracturing liquid.

The technical solution of the present invention is further illustrated by the following specific examples.

Example 1:

1 evaluation optimization of functional reagent of micro-bubble fracturing fluid formula system

1.1 blowing agent preference

The foaming agent is a main agent of the foam fracturing fluid, and the performance of the foaming agent directly influences the foaming capacity, stability, rheological property, sand carrying property, half-life period and flowback capacity of the foam fracturing fluid. The preference of the foaming agent in the micro-bubble fracturing fluid is of critical importance.

There are four main types of blowing agents widely used in industry: anionic surfactants, cationic surfactants, zwitterionic surfactants and nonionic surfactants. Wherein, the foaming capability of the anionic surfactant is usually the strongest, the price is the cheapest, and the industrial application is wider; the main defects are that the sensitivity to hard water is high, and foams are easy to break when meeting reservoirs with high mineral compositions. Cationic surfactants maintain good foaming ability under acidic and hard water formation conditions and have good foam stability, but are relatively expensive. The zwitterionic surfactant has the characteristics of strong foaming capacity of the anionic foaming agent and salt resistance of the cationic foaming agent; the nonionic surfactant is not greatly influenced by water quality and pH value, is usually good in compatibility with stratum, but is low in foaming rate.

1.1.1 Experimental reagents and instruments

The main experimental reagents are as follows: sodium Dodecyl Sulfate (SDS), sodium dodecyl benzene sulfonate (ABS), shanghai lai chemical ltd; FBM-4, New county Fubang technologies, Inc. of Henan; octyl phenol polyoxyethylene ether (OP-10), Jiayuan environmental protection, Inc. of Shandong Binzhou; lauryl alcohol carbonyl succinate (DLSK), dodecyl Sulphobetaine (SJT), Nanjing Jinling petrochemical research institute, Inc.; special grade hydroxypropyl guar, kyukan oil field chemical technology development company.

The main experimental apparatus: an electric heating air blast drying oven, a constant temperature water bath, an electronic balance, Beijing Oerseli scientific and technological development Limited company; electric stirrer, Shenzhen Cizhong Usche Spatz; stopwatch, thermometer, volumetric flask, graduated cylinder, beaker, pipette, glass rod, etc., by far Bo chemical trade company, Beijing Oriental.

1.1.2 foaming mechanism

The foam is a heterogeneous system in which insoluble gas enters liquid under the action of external force and is isolated by the liquid through gas-liquid contact and the action of surfactant in the system. After the liquid and the gas are contacted, the surface area is rapidly increased, the free energy in the system is also rapidly increased, and the bubbles are unstable; when the solution contains the surfactant, low molecules and small molecules in the solution are easy to diffuse to the surface of liquid and gas, hydrophilic groups and hydrophobic groups are adsorbed by bubble walls and regularly arranged on the surface of the liquid and gas to form an elastic film, so that the surface tension of the liquid and gas is reduced, the surface work required by generating foam is reduced, the free energy of the system is reduced, and the foam is easy to form and tends to be stable; and after the macromolecule and the macromolecule in the surfactant are adsorbed, a high-strength surface film can be formed on the liquid-gas surface, so that the effect of stabilizing foam is achieved. I.e. the foam is formed by the surface action of the gas and liquid.

Mechanical stirring is adopted in this experiment to foam, and the usable electric mixer of great container such as beaker foams, and less container such as graduated flask can the artifical rapid mixing bubble of glass stick. The foaming principle is that air enters the base liquid to form foam fluid through rotating and stirring in the foam base liquid.

1.1.3 preparation method of foaming liquid

Firstly, weighing 10g of foaming agent, placing the foaming agent in a 100ml volumetric flask, adding tap water to dilute the foaming agent to 100ml, and uniformly stirring to prepare a foaming agent standard solution with the content of 100 g/l; secondly, weighing 4g of special-grade hydroxypropyl guar powder according to a preparation method of a base fluid of the water-based fracturing fluid, slowly adding the special-grade hydroxypropyl guar powder into a 2000ml beaker containing water, and uniformly stirring to prepare a guar base fluid with the mass fraction of 0.2%; finally, measuring 1ml, 2ml, 3ml, 4ml, 5ml and 6ml of foaming agent standard solution respectively, placing the foaming agent standard solution into 6 measuring cylinders with 500ml respectively, adding 0.2% guanidine gum base solution to 100ml respectively, and preparing the foaming agent base solution with the foaming agent contents of 1g/l, 2g/l, 3g/l, 4g/l, 5g/l and 6g/l respectively.

If a compound foaming agent is selected for an experiment, adding another foaming agent standard solution after one foaming agent standard solution is added according to the method; other addition methods are the same as above.

1.1.4 measurement procedure

And (3) rapidly stirring the foam base liquid in a 500ml measuring cylinder indoors through a manual glass rod, finding that the foam in the liquid is gradually increased, the large foam is gradually reduced, the small foam is increased, the solution becomes an emulsion white fluid, until no obvious foam is seen, the volume of the foam liquid is not increased any more, then stopping stirring, starting recording the time and the initial volume (serving as the foaming volume) of the foam liquid, and observing. The time at which the liquid began to appear at the bottom of the cylinder was recorded until the liquid rose to 50ml, and the recording was stopped as the half-life of the foam liquid (the time required for half of the liquid to be precipitated by the foam).

According to the method for preparing the foam liquid and recording the measuring process, the foaming liquid with different foaming agents and different mass fractions of the foaming liquid are evaluated, the graph is drawn, the table analysis experiment result is made, and the foaming agent is optimized.

1.1.5 Experimental results and discussion

In the experiment, six foaming agents, namely sodium dodecyl benzene sulfonate (ABS), Sodium Dodecyl Sulfate (SDS), lauryl alcohol sulfosuccinate (DLSK), octyl phenol polyoxyethylene ether (OP-10), FBM-4 and SJT (dodecyl sulphobetaine), are mainly used for testing the foaming capacity.

(1) Evaluation of foaming Property of foaming agent

FIG. 2 shows the maximum foaming volumes of the 6 blowing agents at different contents when the foams were stable. It can be seen that the foaming volume of SDS after the content of SDS is greater than 1.5g/l is obviously greater than that of other 5 foaming agents, and the foaming volume after the content of SDS is greater than 3.0g/l is relatively stable, the foam statistics is basically about 350ml, and the rest is below 275 ml; secondly, in a common use content range of 2.0-4.0 g/l, the foaming capacity of FBM-4 is slightly better than that of other 4 types: DLSK, ABS, SJT, and OP-10. Thus SDS was chosen preferentially as the better blowing agent and FBM-4 was chosen second.

(2) Evaluation of foam stabilizing property of foaming agent

FIG. 3 shows the maximum time for which the 6 blowing agents mentioned above have been stable at different levels. As can be seen, the stabilization time of foam formation after the ABS is used in an amount of more than 4.0g/l is longest, 76min, which is slightly higher than 69min of SDS, and the other 4 types are obviously lower than 25 min; the foam produced by SDS has an increased foam volume stabilization time after use at levels greater than 2.0g/l, which is long lasting above 60min and relatively stable. In comparison, SDS produced foam with stability generally superior to ABS. The other 4 were relatively less stable. Therefore, SDS is preferred for stability, and ABS is selected as a better foaming agent for standby.

As can be seen from fig. 2 and 3, the above 6 foaming agents have the following characteristics in terms of foaming and foam stability:

there is an overall tendency for the foam volume to increase with increasing blowing agent content, but not for greater contents, the greater the foam volume, e.g., OP-10, and for substantially no change in bubble volume with increasing content.

② with the increase of the content of the foaming agent, not all the foams have increased stability and the half-life period is longer. Only SDS and ABS showed remarkable performance, other foaming agents showed no remarkable performance, wherein SJT and FBM-4 have a certain foaming capacity, but have extremely short half-life of less than 10 min.

Comprehensively comparing the foaming performance and the foam stabilizing performance of 6 foaming agents, wherein the sequence from large to small is as follows: SDS > OP-10> ABS > FBM-4> DLSK > SJT. Wherein, SDS can generate more exquisite and abundant foam; the foam liquid generated by ABS has higher viscosity but smaller foam volume; the foam generated by OP-10 has larger volume and longer stabilization time; both invoice and stabilization time for FBM-4 are general; the foams generated by DLSK are large but very unstable; and the foam generated by SJT has small volume and short stabilization time.

(3) Evaluation of foaming Property of Compound foaming agent

The surfactants are matched with each other for use or the surfactants are matched with other chemical substances for use, so that the properties of the mixed system can be enhanced, different use conditions can be adapted to, the mixed system has better properties than a system generated by a single surfactant, the requirements of users can be better met, the defects of the mixed system can be mutually compensated, the performance is more perfect, and sometimes, new performances can be provided, which is a great advantage. Therefore, the surfactant combination plays a very important role in both practical application and performance research, especially in practical application, a single surfactant is rarely used, and the surfactant combination is mostly used in the form of surfactant combination.

As can be seen from the performance test results of the single foaming agent, SDS can generate fine and rich foam with good stability, so that SDS is determined to be used as the main foaming agent to be respectively compounded with ABS, OP-10 and SJT, and the performance after compounding is evaluated. When the two components are used in a compounding way, the proportion influence is large, the proportion is different, and the difference of test results is obvious.

A is the combination of SDS and ABS

FIG. 4 shows the stable maximum foaming volume of two foaming agents of ABS and SDS in different contents after compounding. Therefore, when the SDS content is 1.0g/l, the volume of the compounded foaming is relatively small, namely about 450ml, even if the content change of the ABS is large; when the SDS content is 4.0g/l, the ABS content is only 1.0g/l, a relatively large foaming volume is formed, about 550ml is obtained, the advantage is not too large, the volume is reduced when the content is increased, about 400ml is obtained, and the application range is narrow; when the SDS content is within the range of 2.0-3.0 g/l, the foaming volume compounded with ABS with different contents is ideal, and when the SDS content is within the range of 2.0-550 ml, the SDS content is within the range of 550-600 ml when the SDS content is within the range of 3.0 g/l. Therefore, the SDS content in the range of 2.0-3.0 g/l can be temporarily used as the selection for compounding with ABS.

SDS and OP-10 are compounded

FIG. 5 shows the stable maximum foaming volumes of two foaming agents OP-10 and SDS in different contents. It can be seen that when the SDS content is 1.0g/l, the OP-10 content is increased, and although the compounded foaming volume is increased, the compounded foaming volume is not large and is less than 350 ml; a relatively maximum foaming volume of about 550ml for SDS content of 4.0g/l and OP-10 content of 2.0-3.0 g/l; when the SDS content is in the range of 2.0-3.0 g/l, the foaming volume compounded with OP-10 with different contents is 420-460 ml. Therefore, considering the foaming performance of the formulation, SDS of 4.0g/l and OP-10 of 2.0g/l are selected, and if considering the economy, SDS of 2.0g/l and OP-10 of 1.0g/l are selected. Can be used as the selection of the combination of the two.

Compounding of SDS and SJT

FIG. 6 shows the stable maximum foaming volume of SJT and SDS foaming agents with different contents after combination. Therefore, the foaming volume of the SDS and SJT compound is not changed greatly, and when the contents of the SDS and the SJT are both 2.0-3.0 g/l, the foaming volume of the compound is relatively large, about 400 ml; when the SDS content is 1.0g/l or 4.0g/l, and the SJT content is 1.0-3.0 g/l, the compounded foaming volume is smaller and is about 250 ml. Although the volume of the two compositions is not large, the foam is even, fine and milky compared with the foams of the other two compositions. Therefore, if a combination of both is to be considered, it is slightly better to select 3.0g/l for both SDS and SJT.

(4) Evaluation of foam stabilizing performance of compound foaming agent

A is the combination of SDS and ABS

FIG. 7 shows the half-lives of two foaming agents, ABS and SDS, in different amounts when stabilized after compounding. The half-life period of the SDS and ABS compound foam liquid is greatly changed along with different usage amounts, and particularly after the ABS content reaches 2.0g/l, the good half-life period can reach more than 200 min; and when the SDS content is 2.0g/l, the foam stabilizing time of the ABS content between 2.0g/l and 4.0g/l is kept stable and basically maintained at 80min, and the ABS foam stabilizer has certain advantages in stability, but the half-life period is slightly shorter.

SDS and OP-10 are compounded

FIG. 8 shows the half-lives of two foaming agents OP-10 and SDS at different contents when they are stabilized after compounding. The difference between the half-life period and the use amount of the SDS and OP-10 compound foam liquid is small, the use amount of OP-10 is increased under the condition that the content of SDS is unchanged, the half-life period is basically unchanged, and for example, when the content of SDS is 1.0g/l or 4.0g/l, the half-life period is about 60 min; if the SDS content is 2.0g/l and the OP-10 content reaches 2.0g/l, the half-life period is about 95 min; the half-life was 95min when the SDS content was 3.0g/l and the OP-10 content reached 1.0g/l, after which the OP-10 content increased and the half-life decreased. The half-life is relatively good when the contents of SDS and OP-10 are both 2.0 g/l.

Compounding of SDS and SJT

FIG. 9 shows the half-lives of different amounts of SJT and SDS when stabilized after compounding. The half-life difference of the SDS and SJT compound foam liquid is larger, when the SDS content is 2.0g/l, the half-life of the foam liquid reaches 225min when the SJT content is 2.0g/l, 180min when the SJT content is 3.0g/l, and 170min when the SJT content is 4.0 g/l. And when the SDS is in other contents, the half-life period of the foam liquid with the changed SJT content is smaller and is below 70 min. Therefore, it is preferable to select SDS at 2.0g/l and SJT at 3.0g/l from the viewpoint of half-life.

Compared with the experimental results of the foamability and the foam stability of a single foaming agent and a compound foaming agent, the foamability and the foam stability after compounding are improved, and the compound foaming agent is preferably selected to be better than the single foaming agent; the foaming volume of SDS and ABS and SDS and OP-10 compounded in different proportions is much larger than that of SDS and SJT compounded, but the foam size and the uniform distribution degree of the compounded foam liquid are less than those of SDS and SJT compounded; when the SDS content is 2.0g/l and the SJT content is 3.0g/l, the foaming volume is 350-400 ml, the foaming capacity reaches more than 65% of the foam quality, and the foam stabilizing capacity reaches the maximum at 225min, so that the thickening effect is remarkable, the viscosity of the system is high, and the effect of strong foam stabilizing capacity is achieved; has better synergistic effect; meanwhile, one of the purposes of the development and research of the micro-bubble fracturing fluid is to have stronger pressure resistance, and the micro-bubble fracturing fluid can be used for a deep well by subtracting a supercharging device, and the micro-bubble fracturing fluid must keep a certain liquid content. After comprehensive analysis, the preferable compound foaming agent is 2.0g/LSDS +3.0g/L SJT.

1.2 foam stabilizers are preferred

1.2.1 Experimental reagents and instruments

The main experimental reagents are as follows: dodecyl dimethyl amine oxide (OA-12), Kingshima Longitude chemical Co., Ltd, Shanghai; dodecanol (SF-1), Letai chemical Co., Ltd, Tianjin development area.

The main experimental apparatus: the device is the same as the device for preparing the foam liquid in the foaming agent optimization.

1.2.2 mechanism of foam stabilization

Most of the conventional foaming agents are surfactants, and the generated foam system has larger surface free energy and is often unstable. The foam fracturing fluid has to have good stability to meet the requirement of sand carrying in oilfield field fracturing, so the foam stabilizing performance of a foam system is required to be researched, and the stability of the foam system is usually enhanced by adding a foam stabilizer.

The main causes of foam collapse are due to liquid film drainage thinning and gas diffusion within the bubbles. The density of the gas and the liquid are greatly different from each other in physical and chemical properties, so that the gas and the liquid are unstable after mixing, and tiny bubbles in the liquid always rise to the liquid surface and then are destroyed. The foam research finds that the foam stability is closely related to the strength of a liquid film wrapping a gas core and is mainly influenced by three factors: (1) the surface viscosity of the liquid film is large or small; (2) the surface tension of the liquid film is large or small; (3) the nature of the charge carried by the surface of the liquid film; the pressure and temperature of the system, the surface charge of the liquid film, and the like. The most important is the surface viscosity of the liquid film, which not only can ensure that the foam can not be easily broken when being subjected to a certain external force, but also can slow down the liquid discharge speed of the liquid film, thereby increasing the stability of the foam. There are two main effects by using foam stabilizers: the surface viscosity of the system can be improved to a certain extent, so that the half-life period of the foam is prolonged; meanwhile, the viscosity of the surfactant in the system is improved. Secondly, the strength of the foam liquid film can be improved, and the service life of the foam is prolonged.

1.2.3 foam liquid preparation method

The foam stabilizer is used to prepare the foam liquid in the same way as the (1.1.3) foam liquid in the foaming agent optimization.

1.2.4 measurement procedure

The volume and half-life of the foam stabilizer formulation foam were determined in the same manner as for the (1.1.4) foam stabilizer determination for the foaming agent optimization.

1.2.5 Experimental results and discussion

(1) Evaluation of OA-12 Performance of foam stabilizer

FIG. 10 shows evaluation experiments of foam volume and half-life of OA-12 foam liquid as foam stabilizer. As can be seen, the foam stabilizer OA-12 forms foam liquid with the maximum foaming volume and the longest half-life period of 193ml and 117min respectively when the dosage is 2.0 g/l; the foam volume was 200ml at an amount of 1.0g/l and the half-life was 83 min. Increasing the amount of OA-12 foam stabilizer does not increase the half-life and the foaming volume. The half-life period is longer and the foam stability is better when the dosage of OA-12 is 2.0 g/l. If selected, the content is preferably selected.

(2) Evaluation of SF-1 Performance of foam stabilizer

FIG. 11 shows evaluation experiments of foam volume and half-life of SF-1 foam stabilizer. As can be seen, the foam stabilizer SF-1 forms the foam liquid, when the dosage of the foam liquid is 2.0g/l, the foaming volume is the largest and is 206ml, and the corresponding half-life period is the longest and is 133 min; the amount of SF-1 is increased, and the foam volume and the half-life period are slowly reduced; the half-life at the amount of 1.0g/l was 94min, corresponding to a foaming volume of 185 ml. The half-life period is longer, the foam stability is better, and the corresponding foaming volume is moderate. If selected, the content is preferably 2.0 g/l.

The foam volume half-life evaluation experiments for the foam stabilizer forming foams of fig. 10 and 11 were compared. As can be seen, the foam volume of the foam stabilizer SF-1 is 206ml when the dosage is 2.0g/l, and the corresponding half-life period is 133 min; the foam stabilizer OA-12 is used in an amount of 2.0g/l, with a foaming volume of 193ml and a half-life of 117 min. If selected, SF-1 with a content of 2.0g/l is preferably used.

1.3 preferred thickeners and crosslinkers

1.3.1 Experimental reagents and instruments

The main experimental reagents are as follows: special grade hydroxypropyl guar, kyukan oil field chemical technology development company; organic boron crosslinker, Beijing Tuopan North science and technology development Limited.

The main experimental apparatus: HAAKE RS600 rheometer, available from Tianjin Series Automation technology, Inc., available from Haake, Germany; six-speed rotational viscometer HTD13145-6, Qingdao Haitoda Special instruments ltd; an electric heating air blast drying oven, a constant temperature water bath, an electronic balance, Beijing Oerseli scientific and technological development Limited company; electric stirrer, Shenzhen Cizhong Usche Spatz; stopwatch, thermometer, graduated cylinder, beaker, pipette, glass rod, etc., by far Bo chemical trade company, Beijing Oriental.

1.3.2 crosslinking mechanism

The organic boron complex firstly hydrolyzes multi-stage ionization to slowly generate borate ions, and then the borate ions react with cis-ortho hydroxyl on the vegetable glucan molecular chain to form three-dimensional net-shaped or body-shaped jelly glue. Wherein the organic ligand is mainly a polyhydroxy-containing low molecular compound. Therefore, the organic boron crosslinking agent and the vegetable gum crosslink to act as borate ions. If an excessive ligand is wrapped around the organic boron crosslinking agent, the borate ions are shielded, so that competition contention of orthoposition cis-hydroxyl on a polysaccharide molecular chain and the organic ligand in the organic boron crosslinking agent for the borate ions is delayed, the affinity of the organic ligand and the borate ions is influenced by the pH value of the solution, and the higher the pH value is, the stronger the affinity is. Therefore, the speed of crosslinking can be tested by adjusting the pH value of the system, and the time for delaying crosslinking can be controlled.

1.3.3 preparation method of guar gum base liquid and cross-linking liquid

Preparing base fluid according to 5.2 of a SYT 5107-2005 water-based fracturing fluid performance evaluation method of the oil and gas industry standard of the people's republic of China, preparing cross-linking fluid 5.3, and preparing jelly 5.4. Adding 100ml of water into 4 1000ml beakers, slowly adding 0.1g, 0.15g, 0.2g and 0.3g of special grade hydroxypropyl guar powder, and swelling for 45 min; then 0.2g SDS and 3.0g SJT were added to each beaker to form a foam base containing extra grade hydroxypropyl guar.

Repeating the above method, firstly preparing the foam base solution containing the special grade hydroxypropyl guar gum in 4 beakers, then sequentially adding 0.1g, 0.2g, 0.3g and 0.4g of organic boron crosslinking agent, and finally adding 0.2g of SDS and 3.0g of SJT into each beaker to form the foam solution containing the special grade hydroxypropyl guar gum and the organic boron crosslinking agent.

1.3.4 measurement procedure

(1) And respectively measuring the foaming volume when the stable volume of the foam base liquid is stable and the time elapsed when 10ml of water is discharged from the bottom of the beaker for the foam base liquid containing the special grade hydroxypropyl guar gum, namely the foaming volume and the time elapsed when 10% of the water is discharged.

(2) Respectively measuring the time from the time when the stable volume of the foam liquid is stable to the time when 10ml of water is discharged from the bottom of the beaker, namely the time for discharging 10% of the water.

1.3.5 Experimental results and discussion

(1) Thickener Performance evaluation

The viscosity of the system can be greatly improved by adding a proper amount of thickening agent guar gum, so that the foam is stabilized, and a foam base liquid experimental diagram formed by the super-grade hydroxypropyl guar gum with the mass fraction of 0.1-0.3%, the foaming agent and the foam stabilizer which are preferably selected in the foregoing is shown in figure 12. It can be seen that as the mass fraction of guar gum increases, the volume of the foam tends to increase and then decrease, but the foam stabilizing capacity, i.e. the time for 10ml of liquid to appear, tends to increase. In consideration of two aspects, the fracturing requirement can be met when the mass fraction of the special grade hydroxypropyl guar gum is 0.2%.

(2) Evaluation of Cross-linker Performance

The fracturing crosslinking agent applied on site at present mainly comprises borax, organic boron and organic zirconium, and the selection is mainly based on the temperature resistance and gel breaking performance of the crosslinking liquid, the temperature resistance focuses on investigating the sand carrying capacity of the crosslinking liquid, and the gel breaking performance focuses on investigating the damage of the crosslinking liquid to a reservoir and a crack after gel breaking. The borax is mainly used for fracturing construction of medium-low temperature shallow well layers, and the organic zirconium is mainly used for high-temperature deep wells and ultra-deep wells. The research aims at developing the micro-bubble fracturing fluid aiming at the fracturing of the medium-deep well, so that an organic boron crosslinking agent is selected as the optimal direction of a formula; after the micro-bubble fracturing fluid field test obtains the effect, the micro-bubble fracturing fluid is further attacked towards the fracturing direction of the ultra-deep well, and then the cross-linking agents such as organic zirconium and the like used for the ultra-high temperature stratum are selected.

FIG. 13 is a test result of cross-linking agents with different mass fractions and guanidine gum with different mass fractions under the condition of optimizing a foaming agent and a foam stabilizer, and it can be seen that when the mass fractions of the super-hydroxypropyl guar gum and the organic boron cross-linking agent are both 0.2%, the time for 10ml of liquid to appear in the foam liquid reaches more than 300min, and the foam stabilizing performance is good; further increase in the crosslinker mass fraction, the effect increase is no longer significant. Therefore, the organic boron crosslinking agent is used in an amount of 0.2% by mass.

FIG. 14 shows the foam volume of the prepared micro-bubble fracturing fluid and the tapping time of the cup bottom. Therefore, the foaming volume is still kept at 660ml above 300min, liquid is separated from 90min, 10ml of liquid is separated from the cup bottom until 310min, the liquid is slowly separated, the half-life period of the liquid is very long, and the stability of the micro-bubble fracturing fluid is very good. In summary, the preferred formulation is 0.2% extra hydroxypropyl guar plus 0.2% organoboron crosslinker.

1.4 primary selection of micro-bubble fracturing fluid formula

The optimization is carried out according to the evaluation experiments of the foaming agent, the foam stabilizer, the thickening agent and the crosslinking agent; considering that the content of each functional reagent is very low, most of the functional reagent is clear water, and the density of the fracturing fluid is about 1.0g/cm³Therefore, the formula of the micro-bubble fracturing fluid is provided according to the mass percentage after the g/l is converted, and the micro-bubble fracturing fluid comprises the following components:

0.2% of special hydroxypropyl guar gum, 0.2% of organic boron crosslinking agent, 0.2% of Sodium Dodecyl Sulfate (SDS) + 0.3% of dodecyl Sulphobetaine (SJT) + 0.2% of dodecanol (SF-1), and the balance of water.

Example 2:

preparation method of 2-microbubble fracturing fluid system

The first step is as follows: respectively weighing 0.2g of special hydroxypropyl guar gum, 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 according to the mixture ratio;

the second step is that: adding 100ml of tap water into a 1000ml volumetric flask, slowly dissolving 0.2g of the weighed special-grade hydroxypropyl guar gum into the water in the volumetric flask, and uniformly stirring until the mixture swells for 45 min;

the third step: and sequentially adding 0.2g of organic boron crosslinking agent, 0.2g of SDS, 0.3g of SJT and 0.2g of SF-1 into a volumetric flask, and continuously stirring until the mixture is uniform to form milky micro foam liquid, thus obtaining the microbubble fracturing fluid.

Example 3:

3 evaluation of Performance of micro-bubble fracturing fluid System

3.1 micro-bubble fracturing fluid morphology

The shape of the microbubble fracturing fluid prepared according to the optimized formula and the preparation process thereof is shown in fig. 15, visible microfoam is milky white, the size of the microbubble is invisible to naked eyes, the color is uniform, the distribution of the displayed foam is uniform, the foaming volume is 650ml, the stabilization time is long, and the microbubble fracturing fluid is not obviously changed even in 200 min. FIG. 16 shows structural changes of the micro-foam at different times under a static condition, the size of the micro-foam is generally 30-300 μm, the micro-foam cannot be visually detected by naked eyes, and the micro-foam changes very slowly. Fig. 17 is a theoretical microscopic structure diagram of the micro-foam, which is composed of "one core, two layers and three films" and ensures foamability, stability, pressure resistance and low friction resistance of the foam. Fig. 18 shows a comparison of the microstructure of the conventional foam and the microfoam, which shows the differences in size and distribution.

3.2 temperature and shear resistance of the micro-bubble fracturing fluid

FIG. 19 is a 90 ℃ temperature and shear resistance test experiment of the prepared microbubble fracturing fluid. It can be seen that at 90 ℃ and 170s^-1The apparent viscosity of 75mPa.s is still maintained after 120min of shear, and the apparent viscosity of the microbubble liquid slowly decreases along with the extension of the shear time at 90 ℃, so that the microbubble liquid has better stability and meets the requirements of site fracturing construction on the sand-carrying liquid.

FIG. 20 shows the temperature and shear resistance test of the prepared micro-bubble fracturing fluid at 120 ℃. It can be seen that, at 170s^-1The apparent viscosity of 61mPa.s is kept after 120min of shear, and the decrease of the apparent viscosity of the microbubble liquid is very slow along with the increase of the shear time at the high temperature of 120 ℃, so that the microbubble liquid shows better high-temperature stability, and completely meets the requirements of site fracturing construction on the sand carrying liquid.

3.3 micro-bubble fracturing fluid pressure resistance

FIG. 21The test result of the density of the micro-bubble fracturing fluid with the system pressure of 1.0MPa to 20.0MPa at the temperature of 30-120 ℃ is shown. It can be seen that at the same temperature, as the system pressure increases, the density of the microbubble fracturing fluid increases; at the same pressure, the density of the microbubble fracturing fluid decreases as the temperature increases. The density of the microbubble fracturing fluid at 30 ℃ and 120 ℃ under the system pressure of 20MPa is 0.8963g/cm³And 0.8370g/cm³The microbubble fracturing fluid has strong pressure resistance, still contains a certain amount of gas even under high pressure, and changes along with the temperature, thereby providing experimental basis and technical support for application in deep wells and ultra-deep wells.

3.4 micro-bubble fracturing fluid drag reduction

FIG. 22 compares the friction of microfoam fracturing fluid with several common fracturing fluids at 2-7/8 "tubing (62mm ID), as seen by the friction coefficient, the greater the displacement, the greater the friction, and the greater its increase with displacement; the clear water has the largest friction resistance and is often used as an object for comparing the friction resistance of other fracturing fluids; a 0.10% polymer fracturing fluid having a minimum friction, about 22% to 35% of clean water; secondly, 0.35 percent of guar gum fracturing fluid which is about 35 to 50 percent of clear water; the friction resistance of a conventional foam fracturing fluid is reduced compared with the prior art, and is about 55 to 80 percent of that of clear water; the friction resistance of the micro-bubble fracturing fluid formed in the research is about 45-60% of that of clear water. The data show that under specific conditions, the friction resistance of the micro-bubble fracturing fluid is still greater than that of the polymer fracturing fluid and the guar gum fracturing fluid, but the friction resistance of the micro-bubble fracturing fluid is obviously reduced compared with that of the conventional foam fracturing fluid, about 70 percent of the friction resistance and greatly reduced compared with that of clear water, which shows that the micro-bubble fracturing fluid has better resistance reduction performance, and has resistance reduction conditions for reducing the construction pressure of a wellhead and being applied to deep wells and ultra-deep wells.

3.5 micro-bubble fracturing fluid sand carrying property

Table 1 shows a specification of 30 mesh with a density of 1.62g/cm³The free settling experiment results of the quartz sand in the 5 kinds of liquid show that the settling speed of the quartz sand in clear water is the fastest; secondly, the concentration of the polymer in 0.10 percent of high molecular polymer fracturing fluid is 0.769 cm/min; in conventional CO₂Foam fracturing fluidThe middle is 0.184 cm/min; the fracturing fluid is 0.535cm/min in 0.35 percent special grade guanidine gum fracturing fluid; the sedimentation rate of the microbubble fracturing fluid formed in the research is 0.107cm/min, and obviously the sedimentation rate is the slowest due to the high viscosity of the microbubble fracturing fluid at rest, the uniform foam distribution and the high elasticity of the crosslinked foam fluid. The settlement result of the micro-bubble fracturing fluid proppant is far lower than the industrial requirement (1.08cm/min) of the fracturing fluid, and the micro-bubble fracturing fluid proppant has good sand carrying property. FIG. 23 is a shape chart of 20-40 mesh quartz sand with a sand ratio of 30% standing in a micro-bubble fracturing fluid for 6hr, after 4hr, a small amount of foam is accumulated at the upper part due to the precipitation of a small amount of water in the micro-bubble fluid, and the rest part of quartz sand is uniformly distributed in the micro-bubble fracturing fluid, so that suspended sand is stable. Therefore, the quartz sand is very slow to settle in the micro-bubble fracturing fluid, has better sand carrying capacity, and meets the requirements of site fracturing construction on sand carrying and sand suspending.

3.6 gel breaking Property of micro-bubble fracturing fluid

Table 2 shows the results of gel breaking experiments for the micro-bubble fracturing fluids. Under the action of atomic oxygen of the 0.1% potassium persulfate gel breaker, the microbubble fracturing crosslinking liquid is broken and hydrated, the apparent viscosity of the system is 15.4 mPas after 2 hours, and the apparent viscosity is reduced to 8.5 mPas after 3 hours; the water content of the system is increased, the stability of the foam is reduced, the defoaming is started, and 176min is needed for complete defoaming. After the defoaming agent is added, the complete defoaming time is only 25min, the apparent viscosity of the system is 5.5 mPas after 2hr, and the apparent viscosity is reduced to 3.8 mPas after 3 hr. If the in-situ crude oil is used as the defoaming agent, the complete defoaming takes 77min, the apparent viscosity of the system is 6.3 mPas after 2hr, and the apparent viscosity is reduced to 4.9 mPas after 3 hr. Therefore, the gel breaking performance of the micro-bubble fracturing fluid meets the industrial requirements, and the damage to the stratum can be reduced.

TABLE 1 proppant settling velocity experiments in several fracturing fluids

TABLE 2 micro-bubble fracturing fluid gel breaking experiment

The microbubble fracturing fluid has the advantages that the diameter of the microbubbles is distributed between 30 and 100 mu m, and the microbubbles are very fine and uniform; the special 'one-core two-layer three-mold' microstructure has stable performance. The microbubble fracturing fluid is different from the conventional foam fracturing fluid, a special foam generating device is not needed in the preparation process, the air source is air in the atmosphere, the microbubble fracturing fluid is stirred indoors by a glass rod, and the microbubble fracturing fluid is circulated by a cement truck in a mine field; a special supercharging device is not needed in the construction process, the foam is tiny, fine and uniform, and the high-pressure-resistant characteristic is achieved; the foam aggregation characteristic is utilized under the reservoir condition, the temporary plugging effect is realized, the filtration loss of the fracturing fluid to tiny pores or natural cracks can be effectively reduced, and the fracturing fluid efficiency is improved; the high-temperature-resistant and shear-resistant sand carrier has high temperature resistance and strong sand carrying capacity in artificial cracks; the foam has large mass and less liquid, can increase the backflow of laminated low-pressure ground, and reduces the damage of water sensitivity and adhesive residue. The microbubble fracturing liquid system is particularly suitable for water-sensitive, low-pressure and fractured fluid loss formations, can be used for high-temperature deep wells in the future, and has wide application prospects.

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 (6)

1. The microbubble fracturing fluid is characterized by comprising 0.2% of special-grade hydroxypropyl guar gum, 0.2% of organic boron crosslinking agent, 0.2% of Sodium Dodecyl Sulfate (SDS), 0.3% of dodecyl Sulfobetaine (SJT), 0.2% of lauryl alcohol (SF-1) and water in percentage by mass; the balance of water, and the water is complemented to 100 percent.

2. A method for preparing the microbubble fracturing fluid according to claim 1, comprising:

step one, respectively weighing special-grade hydroxypropyl guanidine gum, an organic boron crosslinking agent, sodium dodecyl sulfate, lauryl sodium sulfate, lauryl sulfobetaine and dodecanol according to the mass fraction of 0.2% special-grade hydroxypropyl guanidine gum, 0.2% organic boron crosslinking agent, 0.2% sodium dodecyl sulfate SDS, 0.3% lauryl sulfobetaine SJT and 0.2% dodecanol SF-1;

adding tap water into the volumetric flask, slowly dissolving the weighed special-grade hydroxypropyl guar powder into the water in the volumetric flask, and uniformly stirring until the special-grade hydroxypropyl guar powder is swelled;

and step three, adding the weighed organic boron crosslinking agent, sodium dodecyl sulfate, dodecyl sulphobetaine and dodecanol into a volumetric flask in sequence, and continuously stirring until the mixture is uniform to form milky micro foam liquid, thus obtaining the microbubble fracturing liquid.

3. The preparation method of the microbubble fracturing fluid as claimed in claim 2, wherein in the second step, 100ml of tap water is added into a 1000ml volumetric flask, and the weighed special grade hydroxypropyl guar powder is slowly dissolved in the volumetric flask water and is stirred uniformly until the swelling is carried out for 45 min.

4. The method for preparing the micro-bubble fracturing fluid according to claim 2, wherein in the third step, the weighed 0.2% sodium dodecyl sulfate SDS, 0.3% dodecyl sulfobetaine SJT and 0.2% dodecanol SF-1 are added into a volumetric flask in sequence.

5. Use of the microbubble fracturing fluid of claim 1 in a water sensitive, low pressure, fractured fluid loss formation.

6. Use of the microbubble fracturing fluid of claim 1 in a high temperature deep well.

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