Nano-particle reinforced foam drilling fluid based on rigid and flexible characteristics and preparation method of foam drilling fluid

Abstract

The invention belongs to the technical field of drilling fluids in petroleum and natural gas development, and particularly relates to a rigid-flexible nanoparticle reinforced foam drilling fluid and a preparation method thereof. The foam drilling fluid comprises composite magnetic nanoparticles, potassium chloride, a surfactant, a nanocellulose material and deionized water, wherein the composite magnetic nanoparticle has a core-shell multi-layer structure which takes a magnetic material as an inner core and sequentially wraps a primary polymer layer, a porous carrier framework layer and a rigid-flexible composite shell layer on the outer layer, and the rigid-flexible composite shell layer consists of a flexible polymer matrix and a rigid polymer matrix. According to the foam drilling fluid, online optimization of viscosity and shear dilution characteristics of a foam drilling fluid system is realized, and dynamic regulation and control of rheological properties of the foam drilling fluid in a complex stratum environment are realized; and moreover, environmental pollution is reduced, and green well drilling and sustainable well drilling can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of drilling fluid technology in oil and gas development, specifically relating to a foam drilling fluid reinforced with rigid-flexible nanoparticles and its preparation method. Background Technology

[0002] In oil and gas development, drilling fluid is a core material for ensuring efficient and safe drilling operations, undertaking key functions such as carrying drill cuttings, cooling the drill bit, stabilizing the wellbore, and regulating formation pressure. Among these, rheological properties, as a core technical parameter of drilling fluid, directly determine drilling efficiency: at low shear rates, sufficient viscosity is required to ensure drill cuttings suspension and carrying capacity; at high shear rates, good shear thinning properties are required to reduce flow resistance and ensure drill bit rock-breaking efficiency. Achieving a dynamic balance between suspension and flow is the core objective of drilling fluid performance optimization.

[0003] Traditional drilling fluids primarily regulate their rheological properties by adding chemical additives. However, under complex conditions such as high temperature and pressure downhole (e.g., 130°C, 10MPa) and fractured formations, these chemical additives are prone to failure, leading to rapid degradation of the drilling fluid's performance. To maintain performance, the concentration of chemical additives needs to be increased, which not only increases drilling costs but also exacerbates environmental pollutant emissions, making it difficult to meet the industry requirements for green drilling.

[0004] In recent years, magnetic nanoparticles have emerged as novel functional materials for rheological control of drilling fluids due to their magnetic field responsiveness. Under the influence of an external magnetic field, magnetic nanoparticles can dynamically adjust their dispersion state, thereby altering the viscosity and shear thinning effect of the drilling fluid. Simultaneously, they can enhance the gas-liquid interface stability of foam systems, and exhibit high material recovery rates, aligning with green chemistry principles. However, current technologies for the application of magnetic nanoparticles in foam drilling fluids still face key bottlenecks: firstly, the lack of design for a "rigid-flexible composite structure" for the particles leads to easy aggregation and insufficient stability under high temperature and pressure; secondly, the magnetic field control methods are not matched to the working conditions of foam drilling fluids, making it difficult to achieve precise and dynamic optimization of rheological properties; and thirdly, the process details for particle recycling and reuse are not clearly defined, failing to fully leverage their green advantages. Therefore, developing a method for preparing and controlling the performance of foam drilling fluids that can operate stably under complex conditions, dynamically control performance, and meet green environmental protection requirements has significant practical application value. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a foam drilling fluid reinforced with rigid-flexible nanoparticles and its preparation method. This foam drilling fluid enables online optimization of the viscosity and shear dilution characteristics of the foam drilling fluid system, and allows for dynamic control of the rheological properties of the foam drilling fluid in complex formation environments. Furthermore, it reduces environmental pollution and enables green and sustainable drilling.

[0006] To overcome the shortcomings of the prior art, the present invention provides the following technical solution:

[0007] A foam drilling fluid reinforced with rigid-flexible nanoparticles includes composite magnetic nanoparticles, potassium chloride, surfactant, nanocellulose material, and deionized water. Based on 100 mL of deionized water, the potassium chloride content is 2-4 g, the surfactant content is 0.4-0.6 g, the nanocellulose content is 0.08-0.1 g, and the composite magnetic nanoparticle content is 1.5-2 g. The composite magnetic nanoparticles have a core-shell multilayer structure with a magnetic material core, an outer layer sequentially encapsulating a primary polymer layer, a porous carrier framework layer, and a rigid-flexible composite shell. The rigid-flexible composite shell is composed of a flexible polymer matrix and a rigid polymer matrix.

[0008] Furthermore, the magnetic material is selected from one or a mixture of two of nano-iron oxide and cobalt ferrite;

[0009] And / or, the flexible polymer matrix is ​​selected from one or a mixture of two of hydroxyl-terminated polybutadiene and polyether polyurethane;

[0010] And / or, the rigid polymer matrix is ​​selected from one or a mixture of two of polymethyl methacrylate and styrene-acrylonitrile copolymer;

[0011] And / or, the surfactant is camellia saponin, and the purity of camellia saponin is ≥95%; the nanocellulose material has a diameter of 50nm and a length of 1~3μm.

[0012] In addition, the present invention also provides a method for preparing foam drilling fluid based on rigid-flexible nanoparticle reinforcement as described above, comprising the following steps:

[0013] S1. Preparation of composite magnetic nanoparticles: First, primary magnetic responsive polymer microspheres are prepared, then a porous magnetic carrier framework is constructed using the primary magnetic responsive polymer microspheres as raw materials, and finally a rigid-flexible shell is composited on the porous magnetic carrier framework to obtain composite magnetic nanoparticles.

[0014] S2. Preparation of foam drilling fluid: Dissolve potassium chloride in deionized water, add surfactant and stir until clear, add nanocellulose material in batches, stir at high speed to foam, add the composite magnetic nanoparticles and disperse evenly to obtain the foam drilling fluid.

[0015] Further, in step S1, the specific process for preparing primary magnetically responsive polymer microspheres is as follows: the first polymer matrix is ​​mixed and dissolved with deionized water, magnetic materials are added and ultrasonically dispersed, then the first crosslinking agent and the second crosslinking agent are added in sequence, the pH of the system is adjusted and the reaction is carried out; the reaction product is filtered, washed and dried to obtain primary magnetically responsive polymer microspheres.

[0016] Further, the first polymer matrix is ​​selected from one or a mixture of two of hydroxypropyl methylcellulose, gelatin, and polyvinylpyrrolidone; the first crosslinking agent is selected from one or a mixture of two of borax and ammonium zirconium carbonate; and the second crosslinking agent is selected from one or a mixture of two of glutaraldehyde and adipicaldehyde.

[0017] And / or, when preparing primary magnetically responsive polymer microspheres, the dissolution temperature is 70–95℃, the stirring speed is 200–500 rpm, and the stirring time is 30–50 min; the ultrasonic dispersion power is 300–500 W, and the ultrasonic dispersion time is 20–40 min; the system reaction pH is 8–10, the reaction temperature is 45–65℃, and the reaction time is 2–6 h;

[0018] And / or, the mass ratio of the first polymer matrix to deionized water is 1:(5-20); the mass ratio of the total mass of the mixture of the first polymer matrix and deionized water to the mass of the magnetic material is 1:(0.01-0.025); the mass ratio of the first crosslinking agent to the first polymer matrix is ​​1:(5-10); and the mass ratio of the second crosslinking agent to the first polymer matrix is ​​1:(12-18).

[0019] Further, in step S1, the specific process of constructing the porous magnetic support framework is as follows: immersing the primary magnetically responsive polymer microspheres in an aqueous solution containing the first initiator and stirring to react, filtering after the reaction, and freeze-drying the filtered product to obtain the porous magnetic support framework.

[0020] Further, the first initiator is one or a mixture of two of ammonium bicarbonate and ammonium carbonate; the mass ratio of the first initiator to deionized water is 1:(5-20).

[0021] And / or, when constructing a porous magnetic carrier framework, the stirring reaction temperature is 40–60℃, the stirring speed is 50–300 rpm, and the stirring reaction time is 4–8 h; the freeze-drying temperature is -90–-30℃, the pressure is 1–20 Pa, and the freeze-drying time is 12–24 h.

[0022] Further, in step S1, the specific process for preparing composite magnetic nanoparticles is as follows: the flexible polymer matrix and the rigid polymer matrix are dissolved in deionized water and stirred, a porous magnetic support framework is added and impregnated and stirred, a third crosslinking agent is added and the reaction continues, the reaction product is filtered, washed with ethanol and vacuum dried to obtain composite magnetic nanoparticles.

[0023] Further, the third crosslinking agent is one or a mixture of two of organotin T-12 and dibutyltin dilaurate; the mass ratio of the flexible polymer matrix to the rigid polymer matrix is ​​1:(0.4-0.65); the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the deionized water is 1:(15-25); the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the porous magnetic carrier skeleton is 1:(1.8-2.2); and the ratio of the third crosslinking agent to the total mass of the flexible polymer matrix, the rigid polymer matrix, and the porous magnetic carrier skeleton is 1:(10-30).

[0024] And / or, when preparing composite magnetic nanoparticles, the temperature for stirring and mixing the flexible polymer matrix and the rigid polymer matrix is ​​25–45℃, the stirring speed is 100–400 rpm, and the stirring time is 20–60 min; the temperature for impregnation and stirring is 45–65℃, the stirring speed is 400–800 rpm, and the impregnation and stirring time is 2–4 h; the reaction temperature after adding the third crosslinking agent is 50–70℃, and the reaction time is 1–4 h.

[0025] Further, in step S2, when preparing the foam drilling fluid, the amount of potassium chloride added is 3g / 100mL of deionized water, the stirring speed when dissolving potassium chloride is 300rpm, and the stirring time is 2min; the amount of surfactant added is 0.5g / 100mL of deionized water, and the stirring time after adding the surfactant is 15min; the amount of nanocellulose material added is 0.09g / 100mL of deionized water, added in three portions, with an interval of 5min between each addition; the high-speed stirring foaming speed is 7000 rpm, and the stirring time is 3min; the composite magnetic nanoparticles are dispersed by ultrasonication, with an ultrasonic power of 200W, an ultrasonic time of 10min, and an ultrasonic mode of 2s working and 1s intermittent pulse mode.

[0026] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0027] (1) In constructing the core-shell multilayer structure of composite magnetic nanoparticles, the present invention successfully prepared core-shell magnetic nanoparticles with multilevel structures by synergistic construction, namely, first preparing magnetically responsive gel microspheres, then constructing a porous carrier framework, and finally composite rigid and flexible shells.

[0028] (2) The present invention uses an external magnetic field to dynamically control the dispersion state of magnetic particles, so that the magnetic particles form a chain-like self-assembled skeleton structure, thereby realizing online optimization of the viscosity and shear dilution characteristics of the foam drilling fluid system and realizing dynamic control of the rheological properties of foam drilling fluid in complex formation environments.

[0029] (3) This invention innovatively introduces magnetic nanoparticles, which can be separated and recycled after drilling. The recycled particles can be reused after simple processing, which greatly reduces the use of traditional chemical additives, reduces environmental pollution, and enables green and sustainable drilling. Attached Figure Description

[0030] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0031] Figure 1-3 These are microscopic morphology images of gel-encapsulated iron oxide particles under different proportions according to the present invention;

[0032] Figure 4-6 It is a hysteresis loop diagram of pure nano-iron oxide and particles with different gel coating ratios;

[0033] Figure 7 , 8 The image shows a microscopic view of pure nano-iron oxide particles and gel-encapsulated nano-iron oxide particle foam.

[0034] Figure 9 , 10 The graph shows the relationship between the rheological index and consistency coefficient of the pure nano-iron oxide particles and the gel-encapsulated particle bubble system as a function of magnetic field strength.

[0035] Figure 11 , 12 It shows the distribution of gel-encapsulated nano-iron oxide particles in foam drilling fluid before and after magnetic field modulation. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0037] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0038] Facing the challenges of complex downhole operating environments and the dual demands of improving drilling efficiency and protecting the environment, this invention constructs a foam drilling fluid reinforced with rigid-flexible nanoparticles and its preparation method. The application of an external magnetic field can not only regulate the dispersion morphology of magnetic particles, but also optimize their linkage configuration. The improved rheological parameters of the foam drilling fluid are thus demonstrated, specifically by precise control of viscosity parameters and a significant reduction in shear thinning. Particularly noteworthy is that this scheme maintains the system's stable characteristics even under extreme high-temperature and high-pressure conditions, while exhibiting excellent transport capacity for bottom hole cuttings, providing technical feasibility verification for drilling operations under complex geological conditions. The specific technical solution adopted in this invention is as follows:

[0039] According to a first aspect of the present invention, a foam drilling fluid reinforced with rigid-flexible nanoparticles is provided, comprising composite magnetic nanoparticles, potassium chloride, surfactant, nanocellulose material, and deionized water. The components achieve synergistic effects through functional complementarity: potassium chloride provides an ionic environment to stabilize the wellbore; the surfactant is responsible for efficient foaming and reducing gas-liquid interfacial tension; nanocellulose interweaves into a network in the liquid phase, enhancing the overall structural strength and stability of the foam system; and the composite magnetic nanoparticles serve as the core functional unit, dynamically and precisely controlling the rheological properties of the system by changing their dispersion state under an applied magnetic field. Based on 100 mL of deionized water, the potassium chloride content is 2-4 g, the surfactant content is 0.4-0.6 g, the nanocellulose content is 0.08-0.1 g, and the composite magnetic nanoparticle content is 1.5-2 g. The composite magnetic nanoparticles have a core-shell multilayer structure with a magnetic material core, an outer layer sequentially encapsulating a primary polymer layer, a porous carrier framework layer, and a rigid-flexible composite shell. The rigid-flexible composite shell is composed of a flexible polymer matrix and a rigid polymer matrix. The rigid polymer matrix forms a robust framework, providing sufficient steric hindrance to prevent the magnetic core from directly approaching and agglomerating due to the strong magnetic dipole effect; while the flexible polymer matrix endows the shell with a certain degree of deformation capability and toughness, which can buffer external stress and avoid brittle fracture of the shell, thereby maintaining the integrity and dispersion stability of the particle structure under complex downhole conditions.

[0040] A heat- and corrosion-resistant polymer coating tightly encapsulates the magnetic core, establishing the enduring stability of this core-shell configuration. Examples demonstrate that this design effectively blocks the aggregation behavior caused by magnetic dipole moment interactions. Simultaneously, the particle dispersion uniformity index in the foam system is significantly improved, supporting this conclusion. Observations of the enhanced interfacial activity further confirm the preferential enrichment of nanoparticles in the foam interface region, thus exhibiting an order-of-magnitude increase in the stability duration of the foam structure.

[0041] In the aforementioned foam drilling fluid, as a preferred embodiment, the magnetic material includes, but is not limited to, one or a mixture of two of nano-ferric oxide and cobalt ferrite; optionally, the flexible polymer matrix includes, but is not limited to, one or a mixture of two of hydroxyl-terminated polybutadiene and polyether polyurethane; optionally, the rigid polymer matrix includes, but is not limited to, one or a mixture of two of polymethyl methacrylate and styrene-acrylonitrile copolymer; optionally, the surfactant is camellia saponin, and the purity of camellia saponin is ≥95%; the nanocellulose material has a diameter of 50 nm and a length of 1~3 μm.

[0042] According to a second aspect of the present invention, a method for preparing a foam drilling fluid reinforced with rigid-flexible nanoparticles as described above is provided, comprising the following steps:

[0043] Step 1: Prepare polymer microspheres with primary magnetic responsiveness

[0044] The first polymer matrix and deionized water were dissolved in a three-necked glass flask equipped with a stirrer and thermometer at a temperature of 70–95°C, a stirring speed of 200–500 rpm, and a stirring time of 30–50 min. After complete dissolution, the magnetic material was added and ultrasonically dispersed at a power of 300–500 W for 20–40 min. Subsequently, the first and second crosslinking agents were added sequentially, and the pH of the system (using a 1% sodium hydroxide solution) was adjusted to 8–10. The reaction was carried out at 45–65°C for 2–6 h. The first crosslinking agent interacted with the functional groups such as hydroxyl groups of the first polymer matrix through coordination or ionic bonds to form a preliminary physical crosslinking network. The subsequently added second crosslinking agent underwent a condensation reaction with the active groups on the polymer chain to form stable covalent chemical crosslinking bonds. This stepwise physical and chemical crosslinking together constructed a stable three-dimensional network structure, encapsulating and fixing the magnetic particles within it, thereby forming structurally stable primary magnetically responsive polymer microspheres.

[0045] After the reaction was complete, the product was filtered, washed with deionized water until neutral, and dried to obtain primary magnetically responsive polymer microspheres. The mass ratio of the first polymer matrix to deionized water was 1:(5-20), the mass ratio of the total mass of the mixture of the first polymer matrix and deionized water to the mass ratio of the magnetic material was 1:(0.01-0.025), the mass ratio of the first crosslinking agent to the first polymer matrix was 1:(5-10), and the mass ratio of the second crosslinking agent to the first polymer matrix was 1:(12-18).

[0046] Step 2, constructing a porous magnetic carrier framework

[0047] The primary magnetically responsive polymer microspheres obtained in step 1 were immersed in an aqueous solution containing the first initiator and slowly stirred at 50–300 rpm for 4–8 h at 40–60 °C. After filtration, the product was immediately transferred to a freeze dryer and freeze-dried at -90–-30 °C and 1–20 Pa for 12–24 h to obtain a porous magnetic support framework. The mass ratio of the first initiator to deionized water was 1:(5–20).

[0048] Step 3: Prepare composite magnetic nanoparticles with rigid and flexible shells.

[0049] The flexible and rigid polymer matrices were dissolved in deionized water and stirred for 20–60 min at 25–45 °C and 100–400 rpm. The porous magnetic support framework prepared in step 2 was added, and the mixture was impregnated and stirred at 45–65 °C for 2–4 h at a stirring speed of 400–800 rpm. Finally, a third crosslinking agent was added, and the reaction was continued for 1–4 h at 50–70 °C. The flexible polymer matrix provides flexible long chains, while the rigid polymer matrix acts as rigid nodes. The added third crosslinking agent catalyzes the crosslinking reaction between the active end groups on the flexible chains and the functional groups on the rigid polymer chains and the active sites on the surface of the porous support framework, forming a three-dimensional network shell containing both flexible chain segments and rigid nodes. This covalently crosslinked structure, combining rigidity and flexibility, not only provides steric hindrance to prevent particle proximity through the rigid portion but also utilizes the deformation capacity of the flexible portion to buffer external forces, thereby synergistically improving the structural integrity and stability of the shell.

[0050] After the reaction, the product was filtered, washed 2-3 times with ethanol, and dried in a vacuum drying oven (60℃, 50KPa) to obtain composite magnetic nanoparticles with a rigid-flexible shell. The mass ratio of the flexible polymer matrix to the rigid polymer matrix was 1:(0.4-0.65), the mass ratio of the flexible polymer matrix, the rigid polymer matrix, and deionized water was 1:(15-25), the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the porous magnetic carrier framework was 1:(1.8-2.2), and the ratio of the third crosslinking agent to the total mass of the flexible polymer matrix, the rigid polymer matrix, and the porous magnetic carrier framework was 1:(10-30).

[0051] In the preparation method of this invention, the precise design of the external magnetic field parameters makes it possible to form a chain-like self-assembled skeleton structure between magnetic particles, thereby achieving online adjustment and optimization of the viscosity and shear dilution characteristics of the foam drilling fluid system. Dynamic optimization of the rheological properties of the foam drilling fluid under complex downhole conditions is achieved, effectively solving many problems in the prior art, and significantly improving the overall performance of the drilling fluid.

[0052] In the above preparation method, as a preferred embodiment, the first polymer matrix in step 1 includes, but is not limited to, one or a mixture of two of hydroxypropyl methylcellulose, gelatin, and polyvinylpyrrolidone;

[0053] The magnetic material includes, but is not limited to, one or a mixture of two of nano-ferric oxide and cobalt ferrite; the first crosslinking agent includes, but is not limited to, one or a mixture of two of borax and ammonium zirconium carbonate; the second crosslinking agent includes, but is not limited to, one or a mixture of two of glutaraldehyde and adipaldehyde.

[0054] Preferably, the dissolution temperature is 80–90℃, the stirring speed is controlled at 400–500 rpm, and the stirring time is 30–40 min. The ultrasonic dispersion power is 300–400 W, and the ultrasonic dispersion time is 30–40 min. The reaction pH of the system is 9–10, the temperature is controlled at 50–60℃, and the reaction time is 4–5 h.

[0055] More preferably, the mass ratio of the first polymer matrix to deionized water is 1:(10-15), the mass ratio of the total mass of the mixture of the first polymer matrix and deionized water to the mass ratio of the magnetic material is 1:(0.01-0.02), the mass ratio of the first crosslinking agent to the first polymer matrix is ​​1:(6-8), and the mass ratio of the second crosslinking agent to the first polymer matrix is ​​1:(15-17).

[0056] In the above preparation method, as a preferred embodiment, the first initiator mentioned in step 2 includes, but is not limited to, one or a mixture of two of ammonium bicarbonate and ammonium carbonate.

[0057] Preferably, the reaction temperature is 50–60°C, the reaction time is 6–7 h, and the stirring speed is controlled at 10–200 rpm. The freeze dryer temperature is controlled at -50–-30°C, the pressure is controlled at 10–20 Pa, and the freeze drying time is 12–15 h. More preferably, the mass ratio of the first initiator to deionized water is 1:(10–15).

[0058] In the above preparation method, as a preferred embodiment, the flexible polymer matrix in step 3 includes, but is not limited to, one or a mixture of two of hydroxyl-terminated polybutadiene and polyether-type polyurethane; the rigid polymer matrix includes, but is not limited to, one or a mixture of two of polymethyl methacrylate and styrene-acrylonitrile copolymer. The third crosslinking agent includes, but is not limited to, one or a mixture of two of organotin T-12 and dibutyltin dilaurate.

[0059] Preferably, the mixing temperature is 40–45℃, the stirring speed is 200–300 rpm, and the stirring time is 20–30 min. The impregnation stirring temperature is 50–60℃, the stirring time is 3–4 h, and the stirring speed is 600–800 rpm. The reaction temperature is 60–70℃, and the reaction time is 1–2 h.

[0060] More preferably, the mass ratio of the flexible polymer matrix to the rigid polymer matrix is ​​1:(0.5-0.6), the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the deionized water is 1:(20-25), the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the porous magnetic carrier skeleton is 1:(2-2.2), and the ratio of the third crosslinking agent to the total mass of the flexible polymer matrix, the rigid polymer matrix, and the porous magnetic carrier skeleton is 1:(10-15).

[0061] After the preparation process of the magnetic nanoparticles was completed, their morphological characteristics and magnetic properties were evaluated. Transmission electron microscopy (TEM) was used to observe the experiments, revealing the particle size distribution and aggregation degree of the nanoparticles, while also verifying the integrity of the core-shell encapsulation layer. The results of the vibrational sample magnetometer (VSM) test showed that the values ​​of the saturation magnetization and the morphological characteristics of the hysteresis loop in the magnetization curve were clearly distinguishable. The examples demonstrate that the response characteristics of this material under magnetic field conditions meet the expected standards.

[0062] In the construction of the foam drilling fluid system, the introduction of magnetic nanoparticles was achieved through direct dispersion, and their dispersion state in the liquid medium was systematically optimized.

[0063] The formation of fine and stable foam depends on the addition of foaming agents, while the enhancement of the mechanical strength of the foam structure is achieved through the action of stabilizers. Magnetic nanoparticles are responsible for regulating the rheological properties under the influence of a magnetic field.

[0064] Magnetic nanoparticles were added to the foam drilling fluid during the experiment. This ensured the avoidance of local aggregation or sedimentation effects. The improved stability of the magnetic nanoparticles in the foam drilling fluid was achieved by adjusting their distribution. Agglomeration or separation phenomena that might occur under high temperature and high pressure conditions were effectively prevented. Continuous functionality during the flow process was thus guaranteed, as evidenced by the stable performance maintained in complex environments.

[0065] To systematically investigate the rheological properties of foam drilling fluid under the influence of external magnetic fields, a novel testing system was designed. This system consists of two parts: a ring coil assembly and a wellbore simulation rheological measurement unit. The former generates a uniform static magnetic field environment, while the latter is used to measure the viscosity parameters and shear thinning phenomenon of the foam drilling fluid under different operating conditions. Significant changes in the spatial distribution of magnetic nanoparticles were observed after applying external magnetic fields of varying intensities. The rheological behavior of the foam drilling fluid changed accordingly with the magnetic field conditions. During the experiment, pre-prepared foam drilling fluid was injected into the wellbore simulation device. The relationship between pressure drop and flow rate data was recorded in detail when the ring coil applied a gradient magnetic field. The shear thinning characteristics of the foam drilling fluid in the magnetic field environment were analyzed by calculating the mathematical relationship between shear stress and shear rate.

[0066] This study, for the first time, constructively proposes a method for preparing a foam-type drilling fluid system based on nanoscale rigid-flexible coupling particles and its performance regulation mechanism. The implementation involved a series of experimental verifications under simulated high-temperature and high-pressure conditions, with the core objective focusing on evaluating the adaptability of this method to extreme downhole operating conditions. The dispersion state and structural linkage characteristics of the magnetic particles, which can be effectively controlled by applying an external magnetic field, were observed. The viscosity index and shear thinning phenomenon of the foam drilling fluid system exhibit significant controllable dynamic characteristics, as confirmed by experimental data. Examples demonstrate that the implementation of this research scheme opens up a new technical approach for drilling operations under complex geological conditions. This provides reliable technical support for achieving both intelligent development and green environmental protection requirements.

[0067] The present invention will now be described in detail with reference to embodiments thereof. These examples are provided by way of explanation and not by way of limitation. In fact, those skilled in the art will recognize that modifications and variations can be made to the present invention without departing from its scope or spirit. For example, a feature shown or described as part of one embodiment may be used in another embodiment to produce yet another embodiment. Therefore, it is desirable that the present invention encompass such modifications and variations that fall within the scope of the appended claims and their equivalents.

[0068] In the embodiments of the present invention, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0069] Example 1

[0070] Step 1: Prepare polymer microspheres with primary magnetic responsiveness

[0071] 10 g of hydroxypropyl methylcellulose and 120 g of deionized water were dissolved in a three-necked glass flask equipped with a stirrer and thermometer at 80 °C. The stirring speed was controlled at 500 rpm for 35 min. After complete dissolution, 2 g of nano-ferric oxide was added, and the mixture was ultrasonically dispersed at 300 W for 40 min. Subsequently, 1.4 g of borax and 0.6 g of glutaraldehyde were added sequentially, and the pH of the system was adjusted to 10. The reaction was carried out at 50 °C for 5 h. After the reaction was completed, the product was filtered, washed with deionized water until neutral, and dried to obtain primary magnetically responsive polymer microspheres.

[0072] Step 2, constructing a porous magnetic carrier framework

[0073] 15 g of the primary magnetically responsive polymer microspheres obtained in step 1 were immersed in 120 g of an aqueous solution containing 8 g of ammonium bicarbonate and slowly stirred at 100 rpm for 6 h at 60 °C. After filtration, the product was immediately transferred to a freeze dryer and freeze-dried at -40 °C and 20 Pa for 15 h to obtain a porous magnetic support framework.

[0074] Step 3: Prepare composite magnetic nanoparticles with rigid and flexible shells.

[0075] 6.5 g of polyether polyurethane and 3.5 g of polymethyl methacrylate were dissolved in 200 g of deionized water and stirred at 40 °C and 300 rpm for 25 min. 20 g of the porous magnetic support framework prepared in step 2 was added, and the mixture was impregnated and stirred at 50 °C for 4 h at a stirring speed of 700 rpm. Finally, 3 g of organotin T-12 was added, and the reaction was continued at 70 °C for 2 h. After the reaction was complete, the product was filtered, washed with ethanol, and dried in a vacuum drying oven to obtain composite magnetic nanoparticles with a rigid-flexible shell.

[0076] Test column 1

[0077] The morphological characteristics of the iron oxide particles coated in the example system were characterized and analyzed using transmission electron microscopy. Figure 1-3 The results shown are from the experiment. Figure 1 When the mass ratio of the first polymer matrix and deionized water mixture to the magnetic material is 1:0.02, the encapsulated nanoparticles exhibit significant agglomeration. Figure 2 When the mass ratio of the first polymer matrix and deionized water mixture to the magnetic material is 1:0.015, the encapsulated nanoparticles exhibit good dispersion and no obvious aggregation. Figure 3When the mass ratio of the first polymer matrix to deionized water mixture to the magnetic material is 1:0.01, no agglomeration of the coated nanoparticles is observed, but the outer shell encapsulating the nanoparticles thickens further. Examples show that successful coating of iron oxide particles is achieved through a hydroxypropyl methylcellulose system, and the uniformity of the core-shell structure is well maintained. Improvements in mechanical stability and heat resistance are particularly significant after the formation of this core-shell structure. Improved dispersibility in the foam drilling fluid system is also observed, thus confirming the reduction in sedimentation.

[0078] Test column 2

[0079] The hysteresis loop of the particles was measured using a vibrating sample magnetometer (VSM) to analyze their magnetic field response. The test results are as follows: Figure 4-6 As shown, Figure 4 The hysteresis curve of pure nano-iron oxide particles has a saturation magnetization of 66.97 emu / g. Figure 5 The magnetic hysteresis curve of the nano-Fe3O4 particles is shown when the mass ratio of the total mass of the first polymer matrix and deionized water mixture to the mass of the magnetic material is 1:0.015, and the saturation magnetization value reaches 51.68 emu / g. Figure 6 The figure shows the hysteresis curve of the nano-Fe3O4 particles when the mass ratio of the first polymer matrix and deionized water mixture to the magnetic material is 1:0.01, with a saturation magnetization of 38.27 emu / g. This example demonstrates that when the mass ratio is 1:0.01, the presence of the coating layer significantly affects the magnetic properties of the nanoparticles.

[0080] Preparation of foam drilling fluid: Take 100 mL of deionized water, add 3 g of potassium chloride (KCl, analytical grade), and stir with a magnetic stirrer at 300 rpm for 2 minutes until completely dissolved. Then, add 0.5 g of camellia saponin surfactant (purity ≥95%), and continue stirring for 15 minutes until the solution is clear and transparent to ensure that the surfactant is fully dispersed and reduces surface tension.

[0081] During the preparation process, a step-by-step addition method was adopted to prevent component agglomeration, which would affect stability. The total amount of nanocellulose material (50 nm in diameter, 1–3 μm in length) was 0.09 g, added in three separate additions, with each addition spaced 5 minutes apart. This resulted in uniform distribution of the cellulose component, thus avoiding agglomeration. The foam stability and rheological properties were significantly improved using this method.

[0082] Ferric oxide nanoparticles were slowly added to the foam-based liquid system. To achieve uniform particle dispersion, an ultrasonic dispersion instrument was selected as the auxiliary treatment method, with parameters set to 200W power and a processing time of 10 minutes (pulse mode: alternating 2s working cycle and 1s interval). The mechanical vibration effect of ultrasound can significantly reduce the probability of particle agglomeration, thereby improving the uniformity and stability of the foam system.

[0083] The foam base liquid is stirred and foamed based on the Waring Blender principle. The variable frequency high-speed stirrer operates at a speed of 7000 rpm and the continuous stirring time is set to 3 minutes. This operation ensures the generation of an initial foam system with homogeneous characteristics.

[0084] In the static stability test of foam, the enhancing effect of hydroxypropyl methylcellulose-encapsulated iron oxide nanoparticles on foam stability was evaluated. The experiment is as follows: Figure 7 This indicates that pure nano-ferric oxide particles mainly exist in the foam liquid film, and the particles are easily attracted to each other, leading to large-scale aggregation, which in turn inhibits the stability of the foam. In contrast, ferric oxide nanoparticles encapsulated in hydroxypropyl methylcellulose... Figure 8 As shown, the hydroxyl groups (-OH) of the hydroxypropyl methylcellulose coating layer of the iron oxide nanoparticles form hydrogen bonds with the hydroxyl groups (-OH) of the nanocellulose, actively adsorbing at the gas-liquid interface to form a protective mechanism, enhancing the mechanical strength of the bubble film and improving the foam's resistance to rupture. On the other hand, the iron oxide particles can interact with the foam liquid skeleton, slowing down the liquid discharge rate, thereby delaying foam decay and enhancing the foam's stability.

[0085] Test column 3

[0086] A simulated wellbore rheological testing device was used. This experimental system mainly consists of four parts: a gas-liquid supply unit, a foam generation and visualization unit, a rheological testing unit, and a system control and data acquisition unit. The equipment includes a temperature control system, a pressure control system, a simulated wellbore, and sensors.

[0087] In this experiment, a toroidal coil device generated an external magnetic field. The rheological properties of the magnetic nanoparticles were observed and analyzed under different magnetic field intensities. In the setup of the experimental apparatus, a toroidal electromagnetic coil was preferred. The DC power supply system was set to an adjustable voltage range of 0-30V. Foam drilling fluid was injected into the simulated wellbore, and the temperature was set at 120℃ and the pressure at 10MPa, stabilizing for 30 minutes. Different magnetic field intensities (0-800 mT) were applied through the toroidal coil.

[0088] The results are as follows Figure 9 , 10As shown, within a magnetic field range of 0-800 mT, the two nanoparticle-reinforced foam drilling fluids exhibit distinctly different rheological behavior evolution patterns.

[0089] For unencapsulated nanoparticle systems ( Figure 9 In the 0-150 mT range, the n value slightly decreased from 0.71 to 0.63, and the K value increased from 16 mPa·s to 23.9 mPa·s, showing a slight optimization effect; however, after 150 mT, its performance underwent a fundamental reversal, with the n value continuing to rise to 0.708 and the K value decreasing to 16.3 mPa·s, and the optimization effect was completely lost.

[0090] For encapsulated nanoparticle systems ( Figure 10 The rheological properties of the sample can be divided into three stages: In the 0-500 mT range, the rheological index n continuously decreased from 0.69 to 0.26, while the consistency coefficient K increased significantly from 18 mPa·s to 71.8 mPa·s, indicating that the shear dilution and system viscosity were synergistically enhanced; In the 500-550 mT range, the n value continued to decrease to the lowest point of 0.21, while the K value reached a peak of 76.9 mPa·s; In the 550-800 mT range, the n value rebounded to 0.39, while the K value decreased to 38.2 mPa·s, indicating that the rheological properties deteriorated.

[0091] For the encapsulation system, without the application of a magnetic field, the particles are stably and uniformly dispersed in the foam system through the adsorption between the gel shell and the liquid film. Figure 11 When a magnetic field of 0-550 mT is applied, the particles overcome steric hindrance under the action of magnetic dipoles and assemble in an orderly manner into a uniform, reversible chain-like framework structure. Figure 12 This structure significantly increases the internal resistance to fluid flow, manifested as an increase in the consistency coefficient K. Simultaneously, this framework is prone to breakage and reorganization under shear forces, exhibiting strong shear dilution with a decreasing rheological index n. Until 550 mT, excessively strong magnetic interactions begin to overcome the steric hindrance of the gel layer, causing the chain structure to collapse and form irreversible coarse aggregates. This disrupts structural homogeneity and reversibility, leading to performance degradation.

[0092] For the unencapsulated system, due to the lack of protection, the magnetic dipole interaction directly leads to severe irreversible aggregation of particles at a relatively low field strength of 150 mT. The resulting aggregates are irregular in shape and large in size, which not only fails to construct an effective chain-like support structure but also destroys the homogeneity of the system, thus resulting in weak rheological control capabilities and premature failure.

[0093] This comparison confirms that the gel encapsulation layer significantly delays magnetic aggregation by providing steric hindrance and allows for the regulation of the system's viscosity and shear dilution properties.

[0094] In actual drilling operations, the use of an external magnetic field during the recovery of nano-ferric oxide particles has proven to have both significant economic benefits and environmental advantages. The specific operational process is as follows: First, a settling process is required in the drilling fluid system containing quartz sand components. Under gravity, the quartz sand components gradually settle or form clear stratification. Next, a strong magnet is used near the drilling fluid. The adsorption of dispersed magnetic nanoparticles is achieved through the magnetic field, while the original positions are maintained by the non-magnetic quartz sand components, which are unaffected by magnetic forces. Scraping is then performed on the particles adhering to the magnet surface. After collection, centrifugation and deionized water washing are carried out successively, thus thoroughly removing impurities from the drilling fluid. The final stage involves drying the washed particles at low temperatures to restore them to a powder state, facilitating their subsequent re-dispersion in the drilling fluid system.

[0095] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Any technical solutions obtained by means of equivalent substitution or equivalent transformation should be covered within the protection scope of the present invention.

Claims

1. A foam drilling fluid reinforced with rigid-flexible nanoparticles, characterized in that, The product comprises composite magnetic nanoparticles, potassium chloride, surfactant, nanocellulose material, and deionized water; based on 100 mL of deionized water, the potassium chloride content is 2-4 g, the surfactant content is 0.4-0.6 g, the nanocellulose content is 0.08-0.1 g, and the composite magnetic nanoparticle content is 1.5-2 g; wherein, the composite magnetic nanoparticles have a core-shell multilayer structure with a magnetic material core, and an outer layer sequentially wrapped with a primary polymer layer, a porous carrier framework layer, and a rigid-flexible composite shell layer, and the rigid-flexible composite shell layer is composed of a flexible polymer matrix and a rigid polymer matrix.

2. The foam drilling fluid reinforced with rigid-flexible nanoparticles according to claim 1, characterized in that, The magnetic material is selected from one or a mixture of two of nano-iron oxide and cobalt ferrite. And / or, the flexible polymer matrix is ​​selected from one or a mixture of two of hydroxyl-terminated polybutadiene and polyether polyurethane; And / or, the rigid polymer matrix is ​​selected from one or a mixture of two of polymethyl methacrylate and styrene-acrylonitrile copolymer; And / or, the surfactant is camellia saponin, and the purity of camellia saponin is ≥95%; the nanocellulose material has a diameter of 50nm and a length of 1~3μm.

3. A method for preparing foam drilling fluid reinforced with rigid-flexible nanoparticles as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Preparation of composite magnetic nanoparticles: First, primary magnetic responsive polymer microspheres are prepared, then a porous magnetic carrier framework is constructed using the primary magnetic responsive polymer microspheres as raw materials, and finally a rigid-flexible shell is composited on the porous magnetic carrier framework to obtain composite magnetic nanoparticles. S2. Preparation of foam drilling fluid: Dissolve potassium chloride in deionized water, add surfactant and stir until clear, add nanocellulose material in batches, stir at high speed to foam, add the composite magnetic nanoparticles and disperse evenly to obtain the foam drilling fluid.

4. The preparation method according to claim 3, characterized in that, In step S1, the specific process for preparing primary magnetically responsive polymer microspheres is as follows: the first polymer matrix is ​​mixed and dissolved with deionized water, magnetic materials are added and ultrasonically dispersed, then the first crosslinking agent and the second crosslinking agent are added in sequence, the pH of the system is adjusted and the reaction is carried out; the reaction product is filtered, washed and dried to obtain primary magnetically responsive polymer microspheres.

5. The preparation method according to claim 4, characterized in that, The first polymer matrix is ​​selected from one or a mixture of two of hydroxypropyl methylcellulose, gelatin, and polyvinylpyrrolidone; the first crosslinking agent is selected from one or a mixture of two of borax and ammonium zirconium carbonate; the second crosslinking agent is selected from one or a mixture of two of glutaraldehyde and adipaldehyde. And / or, when preparing primary magnetically responsive polymer microspheres, the dissolution temperature is 70–95℃, the stirring speed is 200–500 rpm, and the stirring time is 30–50 min; the ultrasonic dispersion power is 300–500 W, and the ultrasonic dispersion time is 20–40 min; the system reaction pH is 8–10, the reaction temperature is 45–65℃, and the reaction time is 2–6 h; And / or, the mass ratio of the first polymer matrix to deionized water is 1:(5-20); the mass ratio of the total mass of the mixture of the first polymer matrix and deionized water to the mass of the magnetic material is 1:(0.01-0.025); the mass ratio of the first crosslinking agent to the first polymer matrix is ​​1:(5-10); and the mass ratio of the second crosslinking agent to the first polymer matrix is ​​1:(12-18).

6. The preparation method according to claim 3, characterized in that, In step S1, the specific process of constructing the porous magnetic support framework is as follows: immerse the primary magnetically responsive polymer microspheres in an aqueous solution containing the first initiator and stir to react. After the reaction, filter the solution and freeze-dry the filtered product to obtain the porous magnetic support framework.

7. The preparation method according to claim 6, characterized in that, The first initiator is one or a mixture of two of ammonium bicarbonate and ammonium carbonate; the mass ratio of the first initiator to deionized water is 1:(5-20). And / or, when constructing a porous magnetic carrier framework, the stirring reaction temperature is 40–60℃, the stirring speed is 50–300 rpm, and the stirring reaction time is 4–8 h; the freeze-drying temperature is -90–-30℃, the pressure is 1–20 Pa, and the freeze-drying time is 12–24 h.

8. The preparation method according to claim 3, characterized in that, In step S1, the specific process for preparing composite magnetic nanoparticles is as follows: a flexible polymer matrix and a rigid polymer matrix are dissolved in deionized water and stirred. A porous magnetic support framework is added and then impregnated and stirred. A third crosslinking agent is added to continue the reaction. The reaction product is filtered, washed with ethanol, and vacuum dried to obtain composite magnetic nanoparticles.

9. The preparation method according to claim 8, characterized in that, The third crosslinking agent is one or a mixture of two of organotin T-12 and dibutyltin dilaurate; the mass ratio of the flexible polymer matrix to the rigid polymer matrix is ​​1:(0.4-0.65); the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the deionized water is 1:(15-25); the mass ratio of the total mass of the flexible polymer matrix and the rigid polymer matrix to the porous magnetic carrier skeleton is 1:(1.8-2.2); the ratio of the third crosslinking agent to the total mass of the flexible polymer matrix, the rigid polymer matrix, and the porous magnetic carrier skeleton is 1:(10-30). And / or, when preparing composite magnetic nanoparticles, the temperature for stirring and mixing the flexible polymer matrix and the rigid polymer matrix is ​​25–45℃, the stirring speed is 100–400 rpm, and the stirring time is 20–60 min; the temperature for impregnation and stirring is 45–65℃, the stirring speed is 400–800 rpm, and the impregnation and stirring time is 2–4 h; the reaction temperature after adding the third crosslinking agent is 50–70℃, and the reaction time is 1–4 h.

10. The preparation method according to claim 3, characterized in that, In step S2, when preparing the foam drilling fluid, the amount of potassium chloride added is 3g / 100mL of deionized water, the stirring speed when dissolving potassium chloride is 300rpm, and the stirring time is 2min; the amount of surfactant added is 0.5g / 100mL of deionized water, and the stirring time after adding surfactant is 15min; the amount of nanocellulose material added is 0.09g / 100mL of deionized water, added in three portions, with an interval of 5min between each addition; the high-speed stirring foaming speed is 7000 rpm, and the stirring time is 3min; the composite magnetic nanoparticles are dispersed by ultrasonication, the ultrasonic power is 200W, the ultrasonic time is 10min, and the ultrasonic mode is a pulse mode with 2s working and 1s intermittent.

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