Oil-based drilling and completion fluid for low-porosity and low-permeability reservoir as well as preparation method and application of oil-based drilling and completion fluid

Abstract

The invention relates to an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir as well as a preparation method and application of the oil-based drilling and completion fluid. The oil-based drilling and completion fluid comprises a base fluid and an additive, the additive is prepared from the following components in percentage by mass: 3.2 to 4.8 percent of main emulsifier, 0.8 to 1.2 percent of auxiliary emulsifier, 2.0 to 4.0 percent of alkalinity regulator, 1.5 to 3.0 percent of organic soil, 6.0 to 8.0 percent of filtrate reducer, 3.0 to 6.0 percent of blocking agent, 0.5 to 1.5 percent of shear strength improving agent, 1.0 to 3.0 percent of lubricant, 0 to 2.0 percent of wetting agent and 40.0 to 200.0 percent of weighting agent; the main emulsifier comprises a hyperbranched fatty acid amide compound. The oil-based well drilling and completion fluid provided by the invention can solve the contradiction among rheological property, reservoir protection and high-temperature stability in well drilling and completion of a low-porosity and low-permeability reservoir, realizes integrated application of well drilling and well completion, remarkably improves the operation efficiency, reduces reservoir damage, and is suitable for efficient development of complex oil and gas fields.

Description

Technical Field

[0001] The present invention relates to the technical field of oilfield chemistry in oil drilling engineering, and particularly relates to an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs, a preparation method thereof, and uses thereof. Background Art

[0002] With the continuous increase in the exploration and development efforts of offshore oil and gas, as well as the large-scale development of large heterogeneous oil and gas fields, high-difficulty wells such as extended reach wells and long horizontal section wells are frequently implemented, and the wellbore trajectory is extremely complex, resulting in a significant increase in the difficulty of drilling and completion engineering. For example, the drilling and completion operations of a single low-porosity and low-permeability extended reach well reservoir with a large thickness face huge challenges such as deep burial of oil and gas, high temperature and pressure (the temperature can reach 180 °C), variable lithology, and easy pollution of the reservoir. The development of the operation well is difficult, the productivity release is difficult, and the engineering cost is high. Traditional completion process technologies are difficult to apply. The open-hole completion process can not only greatly save the drilling and completion operation cycle, but also make the oil and gas layers fully exposed, effectively increase the seepage area, and better release the productivity of the reservoir section.

[0003] At present, the open-hole section drilling fluid commonly used offshore is generally a water-based drilling fluid or an oil-based drilling fluid system, and the completion fluid is generally a water-based completion fluid. The conventional open-hole completion method with a water-based drilling and completion fluid causes great damage to reservoirs with strong water sensitivity in low-porosity and low-permeability reservoirs, and can no longer meet the requirements of improving completion efficiency and productivity release. Using an oil-based drilling fluid as the drilling fluid in the horizontal open-hole section can greatly reduce the engineering difficulty. Implementing open-hole completion in this wellbore environment is more conducive to the lowering of the lower completion string, saving the completion construction period. The operation environment of using an oil-based drilling fluid throughout the open-hole section can also avoid the water lock effect of low-porosity and low-permeability water-sensitive reservoirs. Therefore, using an oil-based mud as the drilling fluid and completion fluid in the open-hole section has good engineering feasibility and necessity.

[0004] The open-hole section oil-based drilling fluid and oil-based completion fluid for low-porosity and low-permeability reservoirs require good rheological control, lubrication and drag reduction, and reservoir protection performance to improve the application effect of drilling and completion operations in the open-hole section, reduce reservoir damage, and improve the efficiency and economy of drilling operations. In view of the challenges faced by low-porosity and low-permeability reservoirs in offshore areas during the drilling and completion operations of extended reach wells and long horizontal section wells, the problems existing in the existing oil-based drilling fluids and completion fluids include: (1) Insufficient rheology and lubricity: The viscosity and shear force of traditional oil-based systems are high, making it difficult to meet the requirements of wellbore cleaning and pipe string lowering in extended reach wells; (2) Serious reservoir damage: The particle size of weighting agents is too small (such as D50 ≤ 2 μm), which is easy to block reservoir pores, and the water-based system causes the water lock effect; (3) Poor high-temperature stability: The existing systems settle and delaminate or the breakdown voltage drops after high-temperature static placement, affecting long-term stability; (4) Complex process: Different systems need to be switched during drilling and completion, increasing the operation cycle and cost.

[0005] For example, CN111748328A discloses an ultra-high temperature long-term stable oil-based completion fluid, which includes the following components: water-in-oil base fluid, primary emulsifier, secondary emulsifier, wetting agent, filtration reducer, alkalinity regulator, organophilic clay, weighting agent. Its core composition includes: mineral oil and 70% potassium formate as the water-in-oil base fluid, the primary emulsifier uses INVERMUL NT, a modified asphalt filtration reducer is used, and micronized manganese powder (D50≈5μm) is used as the weighting agent. Although the fluid can withstand a temperature of 200°C, with SSSI < 0.15 and good acidizing flowback performance, its rheological properties are not good, the yield point / plastic viscosity ratio > 0.6 Pa / Pa·s, and the high viscosity and shear problem is obvious, resulting in a high frictional resistance and unable to meet the pumping requirements of the horizontal section of extended reach wells.

[0006] CN111394073A discloses a high-temperature resistant oil-based well testing completion fluid, its preparation method and application. The completion fluid includes base oil, organophilic clay, high-temperature resistant primary emulsifier, high-temperature resistant secondary emulsifier, filtration reducer, calcium oxide, calcium chloride brine and weighting agent. Its core composition includes: using base oil and 25% CaCl2 aqueous solution as the base fluid, barite (D50≤2μm) as the weighting agent, and adding 1-3% of organophilic clay. Although it can achieve high temperature resistance and demulsification voltage, the particle size of the weighting agent is too small, resulting in the blockage of pore throats (average throat radius is about 1-5μm) after entering the reservoir, the permeability recovery value is only 70-75%, the yield point / plastic viscosity ratio is insufficient, the 6-rotation reading is less than 8, and the cutting bed removal efficiency is low, with the cutting bed thickness > 5 cm.

[0007] CN116410391A discloses a nanoemulsion, its preparation method, a high-temperature resistant high-density oil-based completion fluid and its application. The oil-based completion fluid includes base oil, primary emulsifier, secondary emulsifier, inorganic chloride brine solution, organophilic clay, alkalinity regulator, filtration reducer, stabilizer, weighting material. The core composition of the oil-based completion fluid includes: using a nanoemulsion stabilizer and barite (D90≤10μm) as the weighting material, and using oxidized asphalt as the filtration reducer. Although the density can reach 2.60 g / cm 3 3, with strong salt invasion resistance, at 200°C, the SF value is lower than 0.53, having stability, but the demulsification voltage is too low, at 180°C, the ES value is lower than 1000V, the emulsification film strength is insufficient, easily leading to wellbore instability, and the rheology is out of balance, the yield point / plastic viscosity ratio is lower than 0.25, the 6-rotation / 3-rotation reading ratio is lower than 1.5, and the cutting suspension ability is poor, with the cutting settlement rate exceeding 0.3 m / min.

[0008] In summary, providing an oil-based drilling and completion fluid for integrated use in low-porosity and low-permeability reservoirs, and enabling it to meet the requirements of rheology, filtration loss, lubricity, solid content and particle size, wettability and chemical stability is a technical problem that needs to be solved in the current field. Summary of the Invention

[0009] In view of the above problems, the object of the present invention is to provide an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs, its preparation method and uses. Compared with the prior art, the oil-based drilling and completion fluid provided by the present invention can solve the contradictions among rheology, reservoir protection and high-temperature stability in drilling and completion of low-porosity and low-permeability reservoirs, realize the integrated application of drilling and completion, significantly improve the operation efficiency and reduce reservoir damage, and is suitable for the efficient development of complex oil and gas fields.

[0010] To achieve the object of the present invention, the following technical solutions are adopted:

[0011] In the first aspect, the present invention provides an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs, and the oil-based drilling and completion fluid comprises a base fluid and additives;

[0012] Calculated by mass percentage of the base fluid, the additives comprise: 3.2-4.8% of a main emulsifier, 0.8-1.2% of an auxiliary emulsifier, 2.0-4.0% of an alkalinity regulator, 1.5-3.0% of organophilic clay, 6.0-8.0% of a filtration reducer, 3.0-6.0% of a plugging agent, 0.5-1.5% of a viscosity increasing agent, 1.0-3.0% of a lubricant, 0-2.0% of a wetting agent and 40.0-200.0% of a weighting agent;

[0013] The main emulsifier comprises a hyperbranched fatty acid amide compound.

[0014] Compared with the prior art which requires the separate use of drilling fluid and completion fluid in different stages, the present invention can realize the integrated operation of drilling and open-hole completion by controlling the compounding of components such as the base fluid, main emulsifier, auxiliary emulsifier, alkalinity regulator, organophilic clay, filtration reducer, plugging agent, viscosity increasing agent, lubricant, wetting agent and weighting agent, reduce the system conversion, and shorten the construction period by more than 30%.

[0015] It should be noted that in the oil-based drilling and completion fluid provided by the present invention, a specific hyperbranched fatty acid amide compound is adopted. The hyperbranched structure forms a three-dimensional network (film thickness > 10 nm) at the oil-water interface, which can form a more stable oil-water interface film, the demulsification voltage (ES) ≥ 1500 V, and has good emulsification stability and high-temperature resistance performance; and it can reduce viscosity and shear force, increase the flexibility of molecular chains, control the dynamic-plastic ratio of the system at 0.3-0.56 Pa / Pa·s, and reduce the friction coefficient to 0.08.

[0016] In the present invention, the low-porosity and low-permeability reservoir refers to a reservoir with a porosity generally < 10% and a permeability generally < 1 mD.

[0017] In the present invention, the additive includes: 3.2 - 4.8% of a main emulsifier, which may be, for example, 3.2%, 3.4%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6% or 4.8%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 0.8 - 1.2% of an auxiliary emulsifier, which may be, for example, 0.8%, 0.9%, 1%, 1.1% or 1.2%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 2.0 - 4.0% of an alkalinity regulator, which may be, for example, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8% or 4%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 1.5 - 3.0% of organophilic clay, which may be, for example, 1.5%, 2%, 2.5% or 3%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 6.0 - 8.0% of a filtration reducer, which may be, for example, 6%, 6.5%, 7%, 7.5% or 8%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 3.0 - 6.0% of a plugging agent, which may be, for example, 3%, 3.5%, 4%, 4.5%, 5%, 5.5% or 6%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 0.5 - 1.5% of a viscosity increasing agent, which may be, for example, 0.5%, 1% or 1.5%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 1.0 - 3.0% of a lubricant, which may be, for example, 1%, 1.5%, 2%, 2.5% or 3%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 0 - 2.0% of a wetting agent, which may be, for example, 0%, 0.5%, 1%, 1.5% or 2%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable; 40.0 - 200.0% of a weighting agent, which may be, for example, 40%, 50%, 100%, 150% or 200%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0018] Preferably, the base fluid includes mineral oil or a mixture of mineral oil and an aqueous calcium chloride solution.

[0019] In the present invention, the mineral oil may be a commonly used mineral oil in the art, such as No. 3 white oil or gas - to - liquid oil, etc.

[0020] Preferably, the mass concentration of the aqueous calcium chloride solution is 20 - 30%, which may be, for example, 20%, 22%, 24%, 26%, 28% or 30%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0021] Preferably, the volume percentage of the calcium chloride aqueous solution in the base liquid ≤ 5%, for example, it can be 5%, 4%, 3%, 2%, 1% or 0%, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0022] Preferably, the preparation method of the main emulsifier includes:

[0023] (1) Mix tall oil fatty acid and methyl cocoate, carry out the first reaction under the condition of a catalyst, and then carry out the first purification to obtain fatty acid methyl ester;

[0024] (2) Mix the fatty acid methyl ester obtained in step (1) and an alkali solution to carry out the second reaction, and then carry out the second purification to obtain fatty acid;

[0025] (3) Mix the fatty acid, dimer acid and diethanolamine obtained in step (2), carry out the third reaction under the condition of a catalyst, and then carry out the third purification to obtain a hyperbranched fatty acid amide compound; mix the hyperbranched fatty acid amide compound and white oil to obtain the main emulsifier.

[0026] In the present invention, the dimer acid is a commonly used raw material in the art and can be obtained by purchase. For example, the dimer acid product produced by Zhongshan Dixin Chemical Industry can be used.

[0027] Preferably, by mass parts, in step (1), the tall oil fatty acid is 80 - 120 parts, for example, it can be 80 parts, 90 parts, 100 parts, 110 parts or 120 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the methyl cocoate is 40 - 60 parts, for example, it can be 40 parts, 45 parts, 50 parts, 55 parts or 60 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the catalyst is 1 - 4 parts, for example, it can be 1 part, 2 parts, 3 parts or 4 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0028] Preferably, the catalyst in step (1) includes sulfuric acid.

[0029] In the present invention, the sulfuric acid used as the catalyst in step (1) is generally sulfuric acid with a mass concentration of 75%.

[0030] Preferably, the temperature of the first reaction in step (1) is 120 - 150 °C, for example, it can be 120 °C, 125 °C, 130 °C, 135 °C, 140 °C, 145 °C or 150 °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0031] Preferably, the time of the first reaction in step (1) is 2 - 3 h. For example, it can be 2 h, 2.2 h, 2.4 h, 2.6 h, 2.8 h, or 3 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0032] Preferably, the first purification in step (1) includes: adjusting the pH value to neutral, and then performing solid - liquid separation to obtain fatty acid methyl ester.

[0033] In the present invention, the pH value regulator used for the first purification is generally sodium hydroxide solution.

[0034] In the present invention, the method of solid - liquid separation can adopt the conventional methods in the art. For example, it can be filtration.

[0035] Preferably, by mass parts, the fatty acid methyl ester in step (2) is 120 - 180 parts. For example, it can be 120 parts, 130 parts, 140 parts, 150 parts, 160 parts, 170 parts, or 180 parts, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable; the alkali solution is 240.5 - 541 parts. For example, it can be 240.5 parts, 250 parts, 280 parts, 300 parts, 350 parts, 400 parts, 450 parts, 500 parts, or 541 parts, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0036] Preferably, by mass parts, the alkali solution in step (2) includes 0.5 - 1 part of sodium hydroxide and 240 - 540 parts of water.

[0037] Preferably, the temperature of the second reaction in step (2) is 60 - 80 °C. For example, it can be 60 °C, 65 °C, 70 °C, 75 °C, or 80 °C, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0038] Preferably, the time of the second reaction in step (2) is 1 - 2 h. For example, it can be 1 h, 1.2 h, 1.5 h, 1.8 h, or 2 h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0039] Preferably, the second purification in step (2) includes: adjusting the pH value to neutral, then standing for layering, and collecting the lower layer component to obtain fatty acid.

[0040] In the present invention, the pH value regulator used for the second purification is generally 10% dilute hydrochloric acid by mass concentration, which is used to neutralize the excessive sodium hydroxide.

[0041] Preferably, by mass parts, the fatty acid in step (3) is 120-180 parts, for example, it can be 120 parts, 130 parts, 140 parts, 150 parts, 160 parts, 170 parts or 180 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the dimer acid is 50-70 parts, for example, it can be 50 parts, 55 parts, 60 parts, 65 parts or 70 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the diethanolamine is 48-72 parts, for example, it can be 48 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts or 72 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the catalyst is 1-2 parts, for example, it can be 1 part, 1.5 parts or 2 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable; the white oil is 10-20 parts, for example, it can be 10 parts, 12 parts, 14 parts, 16 parts, 18 parts or 20 parts, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0042] In the preparation method provided by the present invention, by preferably controlling the mass parts of the dimer acid and the fatty acid, the mass ratio of the dimer acid to the fatty acid is controlled, so that the density of crosslinking sites can be increased, which is more conducive to the formation of a hyperbranched structure; by preferably controlling the mass parts of the diethanolamine and the fatty acid, the mass ratio of the diethanolamine to the fatty acid is controlled, which can further ensure that the amino group is in excess to drive the branching reaction, so as to achieve a good degree of branching; by preferably controlling the mass parts of the catalyst, the degree of branching of the hyperbranched compound can be further adjusted, and finally the main emulsifier forms a more stable oil-water interfacial film. In the present invention, the addition of the white oil is used to adjust the flow state.

[0043] Preferably, the catalyst in step (3) includes 4-dimethylaminopyridine.

[0044] Preferably, the temperature of the third reaction in step (3) is 100-120 °C, for example, it can be 100 °C, 105 °C, 110 °C, 115 °C or 120 °C, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0045] Preferably, the time of the third reaction in step (3) is 3-4 h, for example, it can be 3 h, 3.5 h or 4 h, but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0046] Preferably, the third purification in step (3) includes: solid-liquid separation to remove the catalyst to obtain a hyperbranched fatty acid amide compound.

[0047] In the present invention, by preferably controlling the temperature and time of the third reaction, the structure and degree of branching of the product can be optimized and regulated, so that the main emulsifier has good emulsifying stability and high-temperature resistance.

[0048] Preferably, the number-average molecular weight of the hyperbranched fatty acid amide compound is 2000-5000 Da, for example, it can be 2000 Da, 2500 Da, 3000 Da, 3500 Da, 4000 Da, 4500 Da or 5000 Da, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0049] Preferably, the degree of branching of the hyperbranched fatty acid amide compound > 60%, for example, it can be 65%, 68% or 70%, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0050] Preferably, the co-emulsifier includes alkyl polyamide surfactants.

[0051] In the present invention, the co-emulsifier can adopt alkyl polyamide surfactants commonly used in the art, for example, it can be PF-MOCOAT.

[0052] Preferably, the organoclay includes modified organoclay.

[0053] Preferably, the organoclay includes sodium bentonite.

[0054] Preferably, the modified organoclay includes sodium bentonite modified successively with sulfuric acid, quaternary ammonium salt and silane coupling agent.

[0055] In the present invention, the acidified sodium bentonite is doubly modified with quaternary ammonium salt and silane coupling agent. The silane coupling agent forms Si-O-Si bonds (thermal decomposition temperature > 250 °C) on the surface of the bentonite, and the ζ potential still remains -30 mV at 180 °C, preventing particle aggregation. After modification, the interlayer spacing of the organic clay layer increases from 1.2 nm to 2.5 nm (characterized by XRD), and SF ≤ 0.52 after standing at high temperature for 15 days. The modified organoclay of the present invention can enhance lipophilicity and high-temperature dispersibility, so as to ensure that the system can still remain uniform after standing at 180 °C for 15 days, and the sedimentation factor SF ≤ 0.52. The quaternary ammonium salt is a quaternary ammonium salt commonly used in the art, such as cetyltrimethylammonium bromide, and the silane coupling agent is a silane coupling agent commonly used in the art, such as KH550.

[0056] In the present invention, the method of modifying with sulfuric acid, quaternary ammonium salt and silane coupling agent is a conventional method in the art, and the preparation of the modified organoclay includes the following steps;

[0057] (I) Mix 80 - 120 parts by mass of sodium bentonite and sulfuric acid solution (20 - 50 parts by mass of sulfuric acid is added to 200 - 500 parts by mass of deionized water), react at room temperature (10 - 40 °C) for 1 - 2 h, then filter, and wash the filter cake with deionized water until neutral (pH 6 - 7) to obtain acidified bentonite;

[0058] (II) Mix 80 - 120 parts by mass of the acidified bentonite obtained in step (I), 100 - 200 parts by mass of solvent (volume ratio of deionized water to absolute ethanol = 1:4), and 5 - 10 parts by mass of quaternary ammonium salt, and react at a temperature of 60 - 80 °C for 2 - 3 h under the action of 1 - 2 parts by mass of isomeric tridecanol polyoxyethylene ether sulfate catalyst, then filter and wash the filter cake to obtain quaternary ammonium salt modified bentonite;

[0059] (III) Mix 80 - 120 parts by mass of the quaternary ammonium salt modified bentonite obtained in step (II), 100 - 200 parts by mass of solvent (volume ratio of deionized water to absolute ethanol = 1:1, and add an appropriate amount of sulfuric acid to adjust the pH value to 3 - 5), and 1 - 2 parts by mass of silane coupling agent, react at a temperature of 60 - 80 °C for 2 - 3 h, then filter and wash the filter cake, then dry at 105 - 110 °C, and then grind to obtain modified organic clay.

[0060] Preferably, the fluid loss reducer includes any one or at least two combinations of PF - MOHFR, PF - MOLSF, or PF - MOHFRHT.

[0061] Preferably, the fluid loss reducer includes a combination of PF - MOHFR and PF - MOLS or a combination of PF - MOHFRHT and PF - MOLS.

[0062] Preferably, in the combination of PF - MOHFR and PF - MOLS, the mass ratio of PF - MOHFR to PF - MOLS is 1:(1 - 2), for example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8, or 1:2, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0063] Preferably, in the combination of PF - MOHFRHT and PF - MOLS, the mass ratio of PF - MOHFRHT to PF - MOLS is 1:(1 - 2), for example, it can be 1:1, 1:1.2, 1:1.5, 1:1.8, or 1:2, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0064] Preferably, the plugging agent includes a modified styrene - acrylic polymer and a nano - micron - level wall - building agent.

[0065] Preferably, the mass ratio of the modified styrene acrylic polymer to the nano-micro solid wall agent is (1-2):(2-1), for example, it can be 1:2, 1:1 or 2:1, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0066] Preferably, the D50 particle size of the modified styrene acrylic polymer is 2-5 μm, for example, it can be 2 μm, 3 μm, 4 μm or 5 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0067] Preferably, the D50 particle size of the nano-micro solid wall agent is 0.1-1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.4 μm, 0.6 μm, 0.8 μm or 1 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0068] In the present invention, the plugging agent obtained by compounding the modified styrene acrylic polymer and the nano-micro solid wall agent, the polymer plugs macroscopic cracks (>5 μm), and the nano-micro solid wall agent fills micropores (0.1-1 μm). The two work together to form a multi-scale plugging layer, reduce the filtration loss, and make the HTHP filtration loss ≤4 mL. In addition, the plugging agent provided by the present invention can achieve wetting reversal, which contains carboxyl (-COOH) and sulfonic acid group (-SO3H), converting the reservoir contact angle from water-wet (θ<30°) to neutral-wet (θ≈90°), and the permeability recovery value ≥90%.

[0069] Preferably, the raw materials for preparing the modified styrene acrylic polymer include monomers and crosslinking modifiers.

[0070] Preferably, the monomers include methyl styrene, methyl methacrylate and butyl acrylate.

[0071] Preferably, the crosslinking modifier includes diallyl terephthalate.

[0072] Preferably, the raw materials for preparing the modified styrene acrylic polymer include, by mass, 20-40 parts of methyl styrene, for example, 20 parts, 25 parts, 30 parts, 35 parts or 40 parts, but not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable; 5-15 parts of methyl methacrylate, for example, 5 parts, 8 parts, 10 parts, 12 parts, 14 parts or 15 parts, but not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable; 50-70 parts of butyl acrylate, for example, 50 parts, 55 parts, 60 parts, 65 parts or 70 parts, but not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable; 0.1-0.5 parts of diallyl terephthalate, for example, 0.1 parts, 0.2 parts, 0.4 parts or 0.5 parts, but not limited to the listed values, and other values ​​not listed in the numerical range are equally applicable.

[0073] In the present invention, the preparation method of the modified styrene acrylic polymer is a conventional method in the art, and the preparation method comprises the following steps:

[0074] (a) mixing 20-40 parts of methyl styrene, 5-15 parts of methyl methacrylate, 50-70 parts of butyl acrylate, 0.1-0.5 parts of diallyl terephthalate and an emulsifier to obtain a monomer emulsion;

[0075] The emulsifier includes 1-2 parts by mass of sodium lauryl sulfate, 1-2 parts by mass of Tween80 and 40-50 parts by mass of deionized water;

[0076] (b) mixing 2.5-5 parts by weight of an initiator, 10-20 parts by weight of a monomer emulsion and a buffer solution, and reacting at 70-90° C. for 10-20 minutes to obtain a seed emulsion;

[0077] The initiator comprises 0.5-1 parts by mass of potassium persulfate and 20-30 parts by mass of deionized water, and the buffer solution comprises 20-40 parts by mass of deionized water and 1-2 parts by mass of sodium bicarbonate;

[0078] (c) slowly adding the remaining initiator and monomer emulsion to the seed emulsion within 3-5 hours to obtain a polymer emulsion, and purifying the polymer emulsion, wherein the purification treatment comprises: adding 0.1-0.3 parts by mass of a 65% tert-butyl hydroperoxide solution to the polymer emulsion for reaction for 15 minutes, then dropwise adding 2-3 parts by mass of a 4% bleaching powder solution for reaction for 15 minutes to remove residual monomers, and then spray drying at 110-120° C. to obtain a modified styrene acrylic polymer in the form of a white powder.

[0079] Preferably, the nano-micron-scale wall-solidifying agent includes PF-MOHGW.

[0080] Preferably, the alkalinity regulator includes calcium oxide and / or calcium hydroxide.

[0081] Preferably, the viscosifier includes an epoxy soybean oil modified compound.

[0082] In the present invention, the viscosifier is obtained by using the preparation method of the viscosity increasing and viscosifying agent modified with epoxy soybean oil disclosed in CN116693408A, which can form a gel network, improve the dynamic plastic ratio, ensure the cuttings carrying capacity, and thus achieve good rheology and borehole cleaning ability.

[0083] Preferably, the wetting agent includes a modified vegetable oil fatty acid amide type compound.

[0084] In the present invention, the wetting agent is obtained by using the preparation method of the wetting agent for oil-based drilling fluid disclosed in CN106947441A.

[0085] Preferably, the lubricant includes a modified vegetable oil extreme pressure lubricant.

[0086] Preferably, the modified vegetable oil extreme pressure lubricant includes PF-LUBE.

[0087] In the present invention, the lubricant can reduce the friction coefficient by more than 30%, is suitable for long horizontal section drilling, and improves rheology and borehole cleaning ability.

[0088] Preferably, the weighting agent includes barite and / or calcium carbonate.

[0089] Preferably, the D90 particle size of the barite and calcium carbonate is independently ≥15 μm, for example, it can be 15 μm, 28 μm or 20 μm, but is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0090] In the present invention, by preferably controlling the D90 particle size of barite and calcium carbonate to be independently ≥15 μm, and the average pore size of the reservoir is 10 - 20 μm, the risk of low porosity and permeability reservoir plugging can be reduced, the permeability recovery value ≥90%, the bridging plugging efficiency >95% (invasion depth <5 cm), so that the reservoir protection effect is significant; it can also improve the sedimentation stability, and the grading of coarse particles (barite) and fine particles (calcium carbonate) can reduce the Stokes sedimentation rate by 30%. In the present invention, the compounding method of barite and calcium carbonate is adjusted according to the density requirement of the drilling and completion fluid. When the required density ≤1.5 g / cm 3 Calcium carbonate (D90≥15 μm) is used as the weighting agent; when the required density >1.5 g / cm 3 When, first use calcium carbonate to increase the weight to 1.5 g / cm 3, then add barite (D90≥15μm) to the target density.

[0091] Preferably, the density of the barite > 4.2 g / cm 3 , for example, it can be 4.3 g / cm 3 , 4.4 g / cm 3 or 4.5 g / cm 3 , but not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0092] In a second aspect, the present invention provides a preparation method of the oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs described in the first aspect of the present invention. The preparation method includes the following steps:

[0093] Mix the base fluid and additives according to the formula amounts and adjust to the target density by controlling the addition amount of the weighting agent to obtain the oil-based drilling and completion fluid.

[0094] In the preparation method provided by the present invention, by precisely compounding the base fluid and additives, the obtained oil-based drilling and completion fluid can be directly used for drilling and completion without converting the system, saving the construction period and operation efficiency.

[0095] Preferably, the preparation method specifically includes the following steps:

[0096] Mix mineral oil, main emulsifier, auxiliary emulsifier and viscosifier, stir at 10000 r / min on a high-speed stirrer for 20 min; then add the alkalinity regulator and stir at 10000 r / min on a high-speed stirrer for 10 min; then add organophilic clay, filtration reducer and plugging agent, stir at 10000 r / min on a high-speed stirrer for 20 min; then add calcium chloride aqueous solution, stir at 10000 r / min on a high-speed stirrer for more than 20 min, then add the weighting agent to the target density, continuously stir at 10000 r / min on a high-speed stirrer for more than 20 min, then add the wetting agent and stir for 10 min, and finally add the lubricant and stir for 10 min to obtain the oil-based drilling and completion fluid.

[0097] In a third aspect, the present invention provides a use of the oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs described in the first aspect of the present invention. The oil-based drilling and completion fluid is used for integrated drilling and open-hole completion operations.

[0098] Aiming at the drilling and completion operation difficulties of large-displacement wells in low-porosity and low-permeability reservoirs, the oil-based drilling and completion fluid provided by the present invention can achieve integrated drilling and open-hole completion operations, meeting the requirements of well completion efficiency improvement and productivity release for such reservoirs.

[0099] Compared with the prior art, the present invention has the following beneficial effects:

[0100] (1) The oil-based drilling and completion fluid provided by the present invention can be directly used for oil-based drilling and completion without converting the system, saving the construction period and operation efficiency, and shortening the construction period by more than 30%.

[0101] (2) The oil-based drilling and completion fluid provided by the present invention is compounded with components such as base fluid, main emulsifier, auxiliary emulsifier, alkalinity regulator, organophilic clay, filtration reducer, plugging agent, viscosity increasing agent, lubricant, wetting agent and weighting agent, and has good comprehensive properties, including emulsification stability, anti-settling performance, lubrication and drag reduction, wellbore stability, borehole cleaning effect and reservoir protection effect. Specifically, under relatively optimal conditions, the emulsification stability is good, ES≥1500V; the filtration property is good, the HTHP filtration volume ≤4mL; the reservoir protection effect is good, the permeability recovery value of the polluted sandstone core ≥90%; the viscosity and shear force are low, and the dynamic plastic ratio of the system is controlled at 0.3-0.56Pa / Pa·s (6-rotation reading 9-15); and the temperature resistance reaches 180°C and the slurry stability is good after standing at high temperature for 15d, and the sedimentation factor SF value ≤0.52; the application density range reaches 1.1-1.8g / cm 3 .

[0102] (3) The oil-based drilling and completion fluid system provided by the present invention can be recycled, reducing waste emissions. By reducing reservoir damage and improving the production capacity release efficiency, the operation cost can be reduced by more than 20%. Detailed Embodiments

[0103] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0104] Example 1

[0105] This example provides an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs. The oil-based drilling and completion fluid includes a base fluid and additives. The base fluid includes 3# white oil and an aqueous calcium chloride solution with a mass concentration of 25%, and the volume ratio of the two is 95:5;

[0106] Calculated by the mass percentage of the base fluid, the additives include: 4% of the main emulsifier, 1% of the auxiliary emulsifier, 3% of the alkalinity regulator, 2% of the organophilic clay, 7% of the filtration reducer, 4.5% of the plugging agent, 1% of the viscosity increasing agent, 2% of the lubricant, 1% of the wetting agent and 120% of the weighting agent;

[0107] The auxiliary emulsifier is PF-MOCOAT, the alkalinity regulator is calcium hydroxide, the filtrate reducer is PF-MOHFR and PF-MOLS with a mass ratio of 1:1, the plugging agent is a modified styrene acrylic polymer (D50 particle size is 2 - 5 μm) and a nano-micro solid wall agent PF-MOHGW (D50 particle size is 0.1 - 1 μm) with a mass ratio of 2:1, the viscosity increasing agent is an epoxy soybean oil modified compound, obtained by the method disclosed in Example 5 of CN116693408A, the lubricant is PF-LUBE, the wetting agent is a modified vegetable oil fatty acid amide type compound, obtained by the method disclosed in Example 2 of CN106947441A, and the weighting agent is calcium carbonate (D90 particle size ≥ 15 μm);

[0108] Among them, the main emulsifier is obtained by the following preparation method:

[0109] (1) Mix 100 parts of tall oil fatty acid and 50 parts of methyl cocoate, and under the condition of 2.5 parts of catalyst (75% sulfuric acid), carry out the first reaction at 135 °C for 2.5 h, then adjust the pH value to neutral, filter, and obtain fatty acid methyl ester;

[0110] (2) Mix 150 parts of the fatty acid methyl ester obtained in step (1) and an alkali solution (0.7 part of sodium hydroxide and 390 parts of water), carry out the second reaction at 70 °C for 1.5 h, then adjust the pH value to neutral, let it stand for stratification, collect the lower layer component, and obtain fatty acid;

[0111] (3) Mix 150 parts of the fatty acid obtained in step (2), 60 parts of dimer acid (dimer acid produced by Zhongshan Dixin Chemical Industry, industrial grade, purity 98%), and 60 parts of diethanolamine, and under the condition of 1.5 parts of 4-dimethylaminopyridine catalyst, carry out the third reaction at a temperature of 110 °C for 3.5 h, then filter to remove the catalyst, and obtain a hyperbranched fatty acid amide compound; mix the hyperbranched fatty acid amide compound and 15 parts of white oil to obtain the main emulsifier.

[0112] The organophilic clay is obtained by the following preparation method:

[0113] (I) Mix 100 parts by mass of sodium bentonite and a sulfuric acid solution (35 parts of sulfuric acid added to 350 parts by mass of deionized water), react at room temperature (25 °C) for 1.5 h, then filter, and wash the filter cake with deionized water to neutrality to obtain acidified bentonite;

[0114] (II) 100 parts by mass of the acidified bentonite obtained in step (I), 150 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:4), and 7.5 parts by mass of cetyltrimethylammonium bromide are reacted under the action of 1.5 parts by mass of isomeric tridecanol polyoxyethylene ether sulfate catalyst at a temperature of 70 °C for 2.5 h, then filtered, and the filter cake is washed to obtain quaternary ammonium salt modified bentonite;

[0115] (III) 100 parts by mass of the quaternary ammonium salt modified bentonite obtained in step (II), 150 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:1, and an appropriate amount of sulfuric acid is added to adjust the pH value to 4), and 1.5 parts by mass of silane coupling agent KH550 are reacted at a temperature of 70 °C for 2.5 h, then filtered, and the filter cake is washed, then dried at 107 °C, and then ground to obtain modified organoclay.

[0116] The modified styrene acrylic polymer is obtained by the following preparation method:

[0117] (a) 30 parts of methylstyrene, 10 parts of methyl methacrylate, 60 parts of butyl acrylate, 0.3 part of diallyl terephthalate and an emulsifier are mixed to obtain a monomer emulsion;

[0118] The emulsifier includes 1.5 parts by mass of sodium dodecyl sulfate, 1.5 parts by mass of Tween 80 and 45 parts by mass of deionized water;

[0119] (b) 3.7 parts by mass of an initiator, 15 parts by mass of the monomer emulsion and a buffer solution are mixed and reacted at 80 °C for 15 min to obtain a seed emulsion;

[0120] The initiator includes 0.7 part by mass of potassium persulfate and 25 parts by mass of deionized water, and the buffer solution includes 30 parts by mass of deionized water and 1.5 parts by mass of sodium bicarbonate;

[0121] (c) The remaining initiator and the monomer emulsion are slowly added to the seed emulsion within 4 h to obtain a polymer emulsion, and the polymer emulsion is subjected to a purification treatment. The purification treatment includes: adding 0.2 part by mass of a 65% by mass tert-butyl hydroperoxide solution to the polymer emulsion for reaction for 15 min, then dropping 2.5 parts by mass of a 4% by mass sodium formaldehyde sulfoxylate solution for reaction for 15 min to remove residual monomers, and then spray drying at 115 °C to obtain a white powdery modified styrene acrylic polymer.

[0122] This embodiment also provides a preparation method of the above oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs. The preparation method includes: mixing 3# white oil, a main emulsifier, an auxiliary emulsifier, and a viscosifier, and stirring at 10,000 r / min on a high-speed stirrer for 20 min; then adding an alkalinity regulator and stirring at 10,000 r / min on the high-speed stirrer for 10 min; then adding organophilic clay, a filtration reducer, and a plugging agent, and stirring at 10,000 r / min on the high-speed stirrer for 20 min; adding an aqueous calcium chloride solution and stirring at 10,000 r / min on the high-speed stirrer for 20 min, then adding a weighting agent to the target density and continuously stirring at 10,000 r / min on the high-speed stirrer for 20 min, adding a wetting agent and stirring for 10 min, and finally adding a lubricant and stirring for 10 min to obtain the oil-based drilling and completion fluid.

[0123] Example 2

[0124] This embodiment provides an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs. The oil-based drilling and completion fluid includes a base fluid and additives. The base fluid includes 3# white oil and an aqueous calcium chloride solution with a mass concentration of 20%, and the volume ratio of the two is 96:4;

[0125] Calculated by the mass percentage of the base fluid, the additives include: 4.8% of the main emulsifier, 0.8% of the auxiliary emulsifier, 4% of the alkalinity regulator, 1.5% of the organophilic clay, 8% of the filtration reducer, 3% of the plugging agent, 1.5% of the viscosifier, 1% of the lubricant, 2% of the wetting agent, and 40% of the weighting agent;

[0126] The auxiliary emulsifier is PF-MOCOAT, the alkalinity regulator is calcium hydroxide, the filtration reducer is PF-MOHFR and PF-MOLS with a mass ratio of 1:2, the plugging agent is a modified styrene acrylic polymer (D50 particle size is 2 - 5 μm) and a nano-micro solid wall agent PF-MOHGW (D50 particle size is 0.1 - 1 μm) with a mass ratio of 1:2, the viscosifier is an epoxy soybean oil modified compound obtained by the method disclosed in Example 5 of CN116693408A, the lubricant is PF-LUBE, the wetting agent is a modified vegetable oil fatty acid amide type compound obtained by the method disclosed in Example 2 of CN106947441A, and the weighting agent is calcium carbonate (D90 particle size ≥ 15 μm);

[0127] Among them, the main emulsifier is obtained by the following preparation method:

[0128] (1) Mix 120 parts of tall oil fatty acid and 40 parts of methyl cocoate, and carry out a first reaction at 120 °C for 3 h under the condition of 4 parts of a catalyst (75% sulfuric acid), then adjust the pH value to neutral and filter to obtain fatty acid methyl ester;

[0129] (2) Mix 120 parts of the fatty acid methyl ester obtained in step (1) with an alkali solution (1 part of sodium hydroxide and 540 parts of water), carry out a second reaction at 80 °C for 1 h, then adjust the pH value to neutral, let it stand for stratification, and collect the lower layer component to obtain a fatty acid;

[0130] (3) Mix 180 parts of the fatty acid obtained in step (2), 50 parts of dimer acid (dimer acid produced by Zhongshan Dixin Chemical Industry, industrial grade, purity 98%), and 72 parts of diethanolamine. Under the condition of 1 part of 4-dimethylaminopyridine catalyst, carry out a third reaction at a temperature of 120 °C for 3 h, then filter to remove the catalyst to obtain a hyperbranched fatty acid amide compound; mix the hyperbranched fatty acid amide compound with 20 parts of white oil to obtain a main emulsifier.

[0131] The organoclay is obtained by the following preparation method:

[0132] (I) Mix 80 parts by mass of sodium-based bentonite with a sulfuric acid solution (20 parts of sulfuric acid added to 200 parts by mass of deionized water), react at room temperature (25 °C) for 1 h, then filter, and wash the filter cake with deionized water until neutral to obtain acidified bentonite;

[0133] (II) Mix 120 parts by mass of the acidified bentonite obtained in step (I), 200 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:4), and 10 parts by mass of cetyltrimethylammonium bromide. Under the action of 1 part by mass of isomeric tridecyl alcohol polyoxyethylene ether sulfate catalyst, react at a temperature of 80 °C for 2 h, then filter and wash the filter cake to obtain quaternary ammonium salt modified bentonite;

[0134] (III) Mix 120 parts by mass of the quaternary ammonium salt modified bentonite obtained in step (II), 200 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:1, and add an appropriate amount of sulfuric acid to adjust the pH value to 3), and 2 parts by mass of silane coupling agent KH550. React at a temperature of 80 °C for 2 h, then filter and wash the filter cake, then dry at 110 °C, and then grind to obtain modified organoclay.

[0135] The modified styrene-acrylic polymer is obtained by the following preparation method:

[0136] (a) Mix 40 parts of methylstyrene, 15 parts of methyl methacrylate, 70 parts of butyl acrylate, 0.5 part of diallyl terephthalate, and an emulsifier to obtain a monomer emulsion;

[0137] The emulsifier includes 1 part by mass of sodium dodecyl sulfate, 2 parts by mass of Tween 80, and 40 parts by mass of deionized water;

[0138] (b) Mix 5 parts by mass of the initiator, 20 parts by mass of the monomer emulsion, and the buffer solution, and react at 90 °C for 10 min to obtain a seed emulsion;

[0139] The initiator includes 1 part by mass of potassium persulfate and 30 parts by mass of deionized water, and the buffer solution includes 20 parts by mass of deionized water and 1 part by mass of sodium bicarbonate;

[0140] (c) Slowly add the remaining initiator and monomer emulsion to the seed emulsion within 3 h to obtain a polymer emulsion, and purify the polymer emulsion. The purification treatment includes: adding 0.3 part by mass of a 65% by mass tert-butyl hydroperoxide solution to the polymer emulsion and reacting for 15 min, then dropping 3 parts by mass of a 4% by mass Rongalite solution and reacting for 15 min to remove residual monomers, and then spray drying at 120 °C to obtain a white powdery modified styrene-acrylic polymer.

[0141] This example also provides a preparation method for the oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs described above. The preparation method includes: mixing white oil No. 3, the main emulsifier, the auxiliary emulsifier, and the viscosifier, and stirring at 10000 r / min on a high-speed stirrer for 20 min; then adding the alkalinity regulator and stirring at 10000 r / min on a high-speed stirrer for 10 min; then adding organophilic clay, the filtration reducer, and the plugging agent, and stirring at 10000 r / min on a high-speed stirrer for 20 min; then adding the calcium chloride aqueous solution and stirring at 10000 r / min on a high-speed stirrer for 20 min, then adding the weighting agent to the target density and continuously stirring at 10000 r / min on a high-speed stirrer for 20 min, then adding the wetting agent and stirring for 10 min, and finally adding the lubricant and stirring for 10 min to obtain the oil-based drilling and completion fluid.

[0142] Example 3

[0143] This example provides an oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs. The oil-based drilling and completion fluid includes a base fluid and additives. The base fluid includes white oil No. 3 and a 30% by mass calcium chloride aqueous solution, and the volume ratio of the two is 97:3;

[0144] Calculated according to the mass percentage of the base fluid, the additives include: 3.2% of the main emulsifier, 1.2% of the auxiliary emulsifier, 2% of the alkalinity regulator, 3% of the organophilic clay, 6% of the filtration reducer, 6% of the plugging agent, 0.5% of the viscosifier, 3% of the lubricant, 0.5% of the wetting agent, and 200% of the weighting agent;

[0145] The co-emulsifier is PF-MOCOAT produced by China Oilfield Services Chemical Co., Ltd., the alkalinity regulator is calcium hydroxide, the filtration reducer is PF-MOHFR and PF-MOLS produced by China Oilfield Services Chemical Co., Ltd. and the mass ratio is 1:2. The plugging agent is a modified styrene acrylic polymer (D50 particle size is 2 - 5 μm) and a nano-micro solid wall agent PF-MOHGW produced by China Oilfield Services Chemical Co., Ltd. (D50 particle size is 0.1 - 1 μm) and the mass ratio is 2:1. The viscosifier is an epoxy soybean oil modified compound, obtained by the method disclosed in Example 5 of CN116693408A. The lubricant is PF-LUBE produced by China Oilfield Services Chemical Co., Ltd. The wetting agent is a modified vegetable oil fatty acid amide type compound, obtained by the method disclosed in Example 2 of CN106947441A. The weighting agents are barite and calcium carbonate (D90 particle size is independently ≥15 μm), and the mass ratio is 0.55:1.45;

[0146] Among them, the main emulsifier is obtained by the following preparation method:

[0147] (1) Mix 80 parts of tall oil fatty acid and 60 parts of methyl cocoate, under the condition of 1 part of catalyst (75% sulfuric acid), carry out the first reaction at 150 °C for 2 h, then adjust the pH value to neutral, filter to obtain fatty acid methyl ester;

[0148] (2) Mix 180 parts of the fatty acid methyl ester obtained in step (1) and an alkali solution (0.5 part of sodium hydroxide and 240 parts of water), carry out the second reaction at 60 °C for 2 h, then adjust the pH value to neutral, let it stand for stratification, collect the lower layer component to obtain fatty acid;

[0149] (3) Mix 120 parts of the fatty acid obtained in step (2), 70 parts of dimer acid (dimer acid produced by Zhongshan Dixin Chemical Industry, industrial grade, purity 98%) and 48 parts of diethanolamine, under the condition of 2 parts of 4-dimethylaminopyridine catalyst, carry out the third reaction at 100 °C for 4 h, then filter to remove the catalyst to obtain a hyperbranched fatty acid amide compound; mix the hyperbranched fatty acid amide compound and 10 parts of white oil to obtain the main emulsifier.

[0150] The organophilic clay is obtained by the following preparation method:

[0151] (I) Mix 120 parts by mass of sodium bentonite and a sulfuric acid solution (50 parts of sulfuric acid added to 500 parts by mass of deionized water), react at room temperature (25 °C) for 2 h, then filter, and wash the filter cake with deionized water to neutral to obtain acidified bentonite;

[0152] (II) 80 parts by mass of the acidified bentonite obtained in step (I), 100 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:4), and 5 parts by mass of cetyltrimethylammonium bromide are reacted at 60 °C for 3 h under the action of 2 parts by mass of isomeric tridecanol polyoxyethylene ether sulfate catalyst, and then filtered, and the filter cake is washed to obtain quaternary ammonium salt modified bentonite;

[0153] (III) 80 parts by mass of the quaternary ammonium salt modified bentonite obtained in step (II), 100 parts by mass of a solvent (volume ratio of deionized water to absolute ethanol = 1:1, and an appropriate amount of sulfuric acid is added to adjust the pH value to 5), and 1 part by mass of silane coupling agent KH550 are reacted at 60 °C for 3 h, then filtered, and the filter cake is washed, and then dried at 105 °C and then ground to obtain modified organoclay.

[0154] The modified styrene acrylic polymer is obtained by the following preparation method:

[0155] (a) 20 parts of methylstyrene, 5 parts of methyl methacrylate, 50 parts of butyl acrylate, 0.1 part of diallyl terephthalate and an emulsifier are mixed to obtain a monomer emulsion;

[0156] The emulsifier includes 2 parts by mass of sodium dodecyl sulfate, 1 part by mass of Tween 80 and 50 parts by mass of deionized water;

[0157] (b) 2.5 parts by mass of an initiator, 10 parts by mass of the monomer emulsion and a buffer solution are mixed and reacted at 70 °C for 20 min to obtain a seed emulsion;

[0158] The initiator includes 0.5 part by mass of potassium persulfate and 20 parts by mass of deionized water, and the buffer solution includes 40 parts by mass of deionized water and 2 parts by mass of sodium bicarbonate;

[0159] (c) The remaining initiator and monomer emulsion are slowly added to the seed emulsion within 5 h to obtain a polymer emulsion, and the polymer emulsion is subjected to a purification treatment, and the purification treatment includes: adding 0.1 part by mass of a 65% by mass tert-butyl hydroperoxide solution to the polymer emulsion for reaction for 15 min, and then dropping 2 parts by mass of a 4% by mass sodium formaldehyde sulfoxylate solution for reaction for 15 min to remove residual monomers, and then spray drying at 110 °C to obtain a white powdery modified styrene acrylic polymer.

[0160] This embodiment also provides a preparation method of the oil-based drilling and completion fluid for the low-porosity and low-permeability reservoir, and the preparation method includes: mixing white oil No. 3, a main emulsifier, an auxiliary emulsifier and a viscosifier, and stirring at 10,000 r / min on a high-speed stirrer for 20 min; then adding an alkalinity regulator and stirring at 10,000 r / min on the high-speed stirrer for 10 min; thereafter adding organophilic clay, a filtration reducer and a plugging agent, and stirring at 10,000 r / min on the high-speed stirrer for 20 min; adding an aqueous calcium chloride solution and stirring at 10,000 r / min on the high-speed stirrer for 20 min, then adding a weighting agent to the target density and continuously stirring at 10,000 r / min on the high-speed stirrer for 20 min, adding a wetting agent and stirring for 10 min, and finally adding a lubricant and stirring for 10 min to obtain the oil-based drilling and completion fluid.

[0161] Example 4

[0162] This embodiment provides an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir. The only difference compared with that of Example 1 is that the dimer acid used in step (3) of the preparation method of the main emulsifier is 40 parts.

[0163] Example 5

[0164] This embodiment provides an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir. The only difference compared with that of Example 1 is that the dimer acid used in step (3) of the preparation method of the main emulsifier is 80 parts.

[0165] Example 6

[0166] This embodiment provides an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir. The only difference compared with that of Example 1 is that the diethanolamine used in step (3) of the preparation method of the main emulsifier is 40 parts.

[0167] Example 7

[0168] This embodiment provides an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir. The only difference compared with that of Example 1 is that the diethanolamine used in step (3) of the preparation method of the main emulsifier is 80 parts.

[0169] Example 8

[0170] This embodiment provides an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir. The only difference compared with that of Example 1 is that the crosslinking modifier diallyl terephthalate is not added in step (a) of the preparation method of the plugging agent modified styrene acrylic polymer.

[0171] Comparative Example 1

[0172] This comparative example provides a conventional water-based drilling and completion fluid, including seawater bentonite slurry with a mass concentration of 2%. By weight percentage of the seawater bentonite slurry, it also includes 0.3% caustic soda, 0.2% soda ash, 0.5% gum protector PF-PACLV, 1.0% phenolic resin filtrate reducer PF-SMP HT, 1.0% lignite resin filtrate reducer PF-SPNH HT, 1.5% asphalt filtrate reducer PF-LSF, 2.5% fiber swelling resin plugging agent PF-HMF, 7.0% polyol bonding agent PF-HBA, 2.0% nano-micelle plugging agent PF-HSM, 12.0% sodium chloride, 3.0% potassium formate, 0.1% viscosity increasing and gel strength enhancing agent PF-XC, 0.5% coating agent PF-PLUS, 2.5% lubricant LUBE168, 2.5% micro-nano wall-building agent PF-HGW, 2.0% ultra-fine calcium carbonate EZCARB, and 28.6% barite.

[0173] Comparative Example 2

[0174] This comparative example provides a drilling and completion fluid of a typical oil-in-water emulsion system, including a base fluid and additives. The base fluid uses 3# white oil and an aqueous calcium chloride solution with a concentration of 25%, and the volume ratio of the two is 80:20. By weight percentage of the base fluid, the additives include: 4.0% main emulsifier, 1.0% auxiliary emulsifier, 3.0% alkalinity regulator, 1.5% organophilic clay, 6.0% filtrate reducer, 4.0% plugging agent, 1.0% gel strength enhancer, 2.0% lubricant, 0.5% wetting agent, 90.6% weighting agent. The main emulsifier uses PF-MOEMUL produced by China Oilfield Services Limited. The alkalinity regulator is calcium oxide. The plugging agent is the modified styrene-acrylic polymer provided in Example 1 (D50 particle size is 2 - 5 μm) and the nano-micro wall-building agent PF-MOHGW (D50 particle size is 0.1 - 1 μm) with a mass ratio of 1:1. The lubricant is the modified vegetable oil extreme pressure lubricant PF-LUBE OB produced by China Oilfield Services Limited. The weighting agent is calcium carbonate, D 90 is more than 15 μm, and the rest of the auxiliary emulsifier, organophilic clay, filtrate reducer, gel strength enhancer, wetting agent, etc. are the same as those in Example 1.

[0175] Comparative Example 3

[0176] This comparative example provides a traditional oil-based completion fluid, and the traditional oil-based drilling and completion fluid system is obtained by the method in Example 1 of CN111748328A.

[0177] Performance tests were conducted on the drilling and completion fluids provided in Examples 1-8 and the completion fluids provided in Comparative Examples 1-3. The results are shown in Table 1. The demulsification voltage was measured using a demulsification voltage meter (ES), the HTHP filtration loss was measured using a high-temperature and high-pressure rheometer (HTHP), the core permeability was measured using a core permeability tester (R S )), and the rheological properties were evaluated using a six-speed rotational viscometer (YP / PV, 6-rotation reading). Among them, according to the oil-based drilling fluid test procedure (GB / T 16783.2-2012), performance tests were carried out before and after rolling aging, and the core permeability recovery value was measured according to SY / T 6540-2021 "Indoor Evaluation Method for Drilling and Completion Fluids Damaging Oil Reservoirs"; the static settlement stability of the drilling and completion fluid was evaluated by measuring the density difference between the upper and lower layers of the drilling and completion fluid: First, the drilling and completion fluid was added to a stainless steel tank, and after standing statically at a specific temperature for a period of time, the density ρ top of the upper part (lower layer of free liquid) of the drilling and completion fluid column and the density ρ bottom of the bottom were measured respectively, and the density difference between the upper and lower layers, that is, the static density difference, could be obtained. The magnitude of the static settlement stability was expressed by the static settlement factor SF (Static Stratification factor), SF = ρ bottom / (ρ bottom + ρ top ). The closer the static settlement factor value is to 0.5, the better the settlement stability, and vice versa, the worse the settlement stability of the drilling and completion fluid.

[0178] Table 1

[0179]

[0180] In Table 1, " / " indicates that there is no or no relevant data is required.

[0181] It can be seen from the data in Table 1 that:

[0182] (1) It can be seen from the data in Examples 1-3 that under relatively optimal conditions, the oil-based drilling and completion fluid provided by the present invention has a demulsification voltage ES > 1999, an HTHP filtration loss ≤ 3.2 mL, a permeability recovery value ≥ 91.6%, a settlement factor SF ≤ 0.515, a yield point / plastic viscosity ratio between 0.48 - 0.52 Pa / Pa·s, and a 6-rotation reading between 9 - 12.

[0183] (2) It can be seen from the comparison between Example 1 and Examples 4-5 that the difference between Examples 4-5 and Example 1 lies only in that the amount of dimer acid adjusted is not within the preferred range of the present invention, which changes the ratio of the amount of dimer acid to the amount of fatty acid, resulting in a decrease in the demulsification voltage, an increase in the fluid loss, a decrease in the permeability recovery value, a decrease in the yield point / plastic viscosity ratio and the 6-rotation reading in Examples 4-5. Thus, it can be seen that by preferably controlling the mass fractions of dimer acid and fatty acid, and thereby controlling the mass ratio of dimer acid to fatty acid, the present invention can increase the density of crosslinking sites, which is more conducive to the formation of a hyperbranched structure, thereby enhancing the emulsion stability of the drilling and completion fluid, reducing the damage to the reservoir, and having better rheological properties.

[0184] (3) It can be seen from the comparison between Example 1 and Examples 6-7 that the difference between Examples 6-7 and Example 1 lies only in that the amount of diethanolamine adjusted is not within the preferred range of the present invention, which changes the ratio of the amount of diethanolamine to the amount of fatty acid, resulting in a decrease in the demulsification voltage in Example 6 and a decrease in the permeability recovery value in Examples 6-7. Thus, it can be seen that by preferably controlling the mass fractions of diethanolamine and fatty acid, and thereby controlling the mass ratio of diethanolamine to fatty acid, the present invention can further ensure an excess of amino groups to drive the branching reaction, so as to achieve a good degree of branching, and further enhance the emulsion stability of the drilling and completion fluid and reduce the damage to the reservoir.

[0185] (4) It can be seen from the comparison between Example 1 and Example 8 that the difference between Example 8 and Example 1 lies only in that the styrene acrylic polymer is not crosslinked and modified. In Example 8, the demulsification voltage decreases and the permeability recovery value decreases. Thus, it can be seen that by preferably using a modified styrene acrylic polymer, the present invention can enhance the emulsion stability of the drilling and completion fluid and reduce the damage to the reservoir.

[0186] (5) It can be seen from the comparison between Example 1 and Comparative Examples 1-2 that the HTHP fluid loss in Example 1 is significantly lower than that in Comparative Example 1, and the permeability recovery value is significantly higher than that in Comparative Examples 1-2. Thus, it can be seen that the oil-based system provided by the present invention can reduce the entry of drilling fluid into the reservoir and reduce the damage to the reservoir compared with the existing conventional water-based drilling fluid system and the typical oil-in-water emulsion system, and has more excellent reservoir protection effect. It can be seen from the comparison between Example 1 and Comparative Example 3 that the demulsification voltage in Example 1 is significantly higher than that in Comparative Example 3, and the HTHP fluid loss and the 6-rotation reading are significantly lower than those in Comparative Example 3. Thus, it can be seen that the oil-based drilling and completion fluid provided by the present invention has more excellent emulsion stability, reservoir protection performance and rheological properties compared with the traditional oil-based completion fluid. Therefore, compared with Comparative Examples 1-3, the oil-based drilling and completion fluid provided by the present invention has better rheological and water filtration properties, reservoir protection performance and high-temperature static settlement stability, which is beneficial to the integrated application of drilling and completion in low-permeability reservoirs.

[0187] In summary, the oil-based drilling and completion fluid provided by the present invention can resolve the contradictions among rheology, reservoir protection, and high-temperature stability in drilling and completion operations for low-porosity and low-permeability reservoirs. It has good emulsification stability, anti-settling performance, lubrication and drag reduction properties, wellbore stability, wellbore cleaning effect, and reservoir protection effect. It can achieve integrated application of drilling and completion, significantly improve operation efficiency, and reduce reservoir damage, and is suitable for the efficient development of complex oil and gas fields.

[0188] The applicant declares that the above description is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by any person skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. An oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs, characterized in that: The oil-based drilling and completion fluid comprises a base fluid and an additive; The additives include, by mass percentage of the base fluid: 3.2-4.8% of a primary emulsifier, 0.8-1.2% of an auxiliary emulsifier, 2.0-4.0% of an alkalinity regulator, 1.5-3.0% of an organic soil, 6.0-8.0% of a fluid loss reducer, 3.0-6.0% of a plugging agent, 0.5-1.5% of a shearing agent, 1.0-3.0% of a lubricant, 0-2.0% of a wetting agent, and 40.0-200.0% of a weighting agent; The primary emulsifier includes a hyperbranched fatty acid amide compound.

2. The oil-based drilling and completion fluid according to claim 1, characterized in that: The base fluid includes mineral oil or a mixture of mineral oil and calcium chloride aqueous solution; Preferably, the mass concentration of the calcium chloride aqueous solution is 20-30%; Preferably, the volume percentage of the calcium chloride aqueous solution in the base liquid is ≤5%.

3. The oil-based drilling and completion fluid according to claim 1 or 2, characterized in that: The preparation method of the primary emulsifier comprises: (1) mixing tall oil fatty acid and methyl coconut oil, performing a first reaction under the condition of a catalyst, and then performing a first purification to obtain fatty acid methyl ester; (2) mixing the fatty acid methyl ester obtained in step (1) with an alkaline solution to conduct a second reaction, and then conduct a second purification to obtain fatty acids; (3) mixing the fatty acid, dimer acid and diethanolamine obtained in step (2), performing a third reaction under the condition of a catalyst, and then performing a third purification to obtain a hyperbranched fatty acid amide compound; mixing the hyperbranched fatty acid amide compound and white oil to obtain a primary emulsifier; Preferably, in step (1), the tall oil fatty acid is 80-120 parts, the methyl cocoate is 40-60 parts, and the catalyst is 1-4 parts, calculated by weight. Preferably, the catalyst in step (1) comprises sulfuric acid; Preferably, the temperature of the first reaction in step (1) is 120-150°C; Preferably, the first reaction time in step (1) is 2-3 h; Preferably, the first purification in step (1) comprises: adjusting the pH value to neutral, and then performing solid-liquid separation to obtain fatty acid methyl esters; Preferably, in terms of weight parts, the fatty acid methyl ester in step (2) is 120-180 parts, and the alkaline solution is 240.5-541 parts; Preferably, the alkaline solution in step (2) comprises 0.5-1 parts of sodium hydroxide and 240-540 parts of water, calculated by weight; Preferably, the temperature of the second reaction in step (2) is 60-80°C; Preferably, the time of the second reaction in step (2) is 1-2h; Preferably, the second purification in step (2) comprises: adjusting the pH value to neutral, then standing to separate the layers, collecting the lower layer components, and obtaining fatty acids; Preferably, in terms of weight, the fatty acid in step (3) is 120-180 parts, the dimer acid is 50-70 parts, the diethanolamine is 48-72 parts, the catalyst is 1-2 parts, and the white oil is 10-20 parts; Preferably, the catalyst in step (3) comprises 4-dimethylaminopyridine; Preferably, the temperature of the third reaction in step (3) is 100-120°C; Preferably, the time of the third reaction in step (3) is 3-4h; Preferably, the third purification in step (3) comprises: removing the catalyst by solid-liquid separation to obtain a hyperbranched fatty acid amide compound; Preferably, the number average molecular weight of the hyperbranched fatty acid amide compound is 2000-5000Da; Preferably, the branching degree of the hyperbranched fatty acid amide compound is >60%; Preferably, the auxiliary emulsifier includes an alkyl polyamide surfactant.

4. The oil-based drilling and completion fluid according to any one of claims 1 to 3, characterized in that: The organic soil includes modified organic soil; Preferably, the organic soil comprises sodium bentonite; Preferably, the modified organic soil comprises sodium bentonite modified in sequence with sulfuric acid, quaternary ammonium salt and silane coupling agent.

5. The oil-based drilling and completion fluid according to any one of claims 1 to 4, characterized in that: The fluid loss reducer includes any one of PF-MOHFR, PF-MOLSF or PF-MOHFRHT or a combination of at least two thereof; Preferably, the fluid loss additive comprises a combination of PF-MOHFR and PF-MOLS or a combination of PF-MOHFRHT and PF-MOLS; Preferably, the mass ratio of PF-MOHFR to PF-MOLS in the combination of PF-MOHFR and PF-MOLS is 1:(1-2); Preferably, the mass ratio of PF-MOHFRHT to PF-MOLS in the combination of PF-MOHFRHT and PF-MOLS is 1:(1-2).

6. The oil-based drilling and completion fluid according to any one of claims 1 to 5, characterized in that: The plugging agent includes a modified styrene acrylic polymer and a nano-micron-level wall-fixing agent; Preferably, the mass ratio of the modified styrene acrylic polymer to the nano-micron-scale wall-solidifying agent is (1-2):(2-1); Preferably, the D50 particle size of the modified styrene acrylic polymer is 2-5 μm; Preferably, the D50 particle size of the nano-micron-scale wall-fixing agent is 0.1-1 μm; Preferably, the raw materials for preparing the modified styrene acrylic polymer include monomers and a cross-linking modifier; Preferably, the monomers include methyl styrene, methyl methacrylate and butyl acrylate; Preferably, the cross-linking modifier comprises diallyl terephthalate; Preferably, the raw materials for preparing the modified styrene acrylic polymer include, by weight, 20-40 parts of methyl styrene, 5-15 parts of methyl methacrylate, 50-70 parts of butyl acrylate, and 0.1-0.5 parts of diallyl terephthalate; Preferably, the nano-micron-scale wall-solidifying agent includes PF-MOHGW.

7. The oil-based drilling and completion fluid according to any one of claims 1 to 6, characterized in that: The alkalinity regulator includes calcium oxide and / or calcium hydroxide.

8. The oil-based drilling and completion fluid according to any one of claims 1 to 7, characterized in that: The shearing agent includes an epoxidized soybean oil modified compound; Preferably, the wetting agent comprises a modified vegetable oil fatty acid amide type compound; Preferably, the lubricant comprises a modified vegetable oil extreme pressure lubricant; Preferably, the modified vegetable oil extreme pressure lubricant comprises PF-LUBE; Preferably, the weighting agent comprises barite and / or calcium carbonate; Preferably, the D90 particle size of the barite and calcium carbonate is independently ≥15 μm; Preferably, the density of the barite is >4.2 g / cm 3 .

9. A method for preparing an oil-based drilling and completion fluid for a low-porosity and low-permeability reservoir as claimed in any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: The base fluid and additives are mixed according to the formula and the target density is adjusted by controlling the amount of weighting agent added to obtain an oil-based drilling and completion fluid.

10. A use of the oil-based drilling and completion fluid for low-porosity and low-permeability reservoirs as claimed in any one of claims 1 to 8, characterized in that: The oil-based drilling and completion fluid is used for integrated drilling and open hole completion operations.

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