Supersaturated brine drilling fluid as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of drilling fluid, and particularly relates to supersaturated brine drilling fluid as well as a preparation method and application thereof. The supersaturated salt water drilling fluid comprises water, a pH regulator, a tackifier, a filtrate reducer, a dispersant, a salt inhibitor, a powdery soluble salt and a soluble salt. The supersaturated salt water drilling fluid has a supersaturated functional characteristic, supersaturated salt suspends in the drilling fluid in the form of particles, dissolution of a salt-gypsum layer is prevented, salt particles have a temporary plugging function, reservoir damage can be prevented, and the supersaturated salt water drilling fluid has a very good reservoir protection effect.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling fluid, and in particular relates to a supersaturated brine drilling fluid and a preparation method and application thereof. Background Art

[0002] The reservoir damage problem has always restricted the construction of single well production capacity of oil and gas, especially the reservoir damage problem during the drilling and completion process. After drilling the reservoir, the drilling fluid directly contacts the reservoir, and the solid particles in the drilling fluid invade the reservoir pores and cause damage. The drilling fluid that drills the reservoir is generally called drilling fluid. How to avoid the reservoir damage problem of drilling fluid has always been the goal pursued by scientific researchers.

[0003] There are several main types of existing drilling fluids. One is solid-free drilling fluid, which is completely free of any solid phase, avoiding the clogging problem of solid phase particles, but it also brings about the problem of damage to the polymer solution. In order to prevent the polymer solution from invading the reservoir, a high-viscosity polymer solution is used in combination with a gel breaker pumped in later to reduce the viscosity of the polymer solution to eliminate the damage; the other is clay-free drilling fluid, which is based on the solid-free drilling fluid, introduces acid-soluble temporary plugging materials, and appropriately reduces the viscosity of the polymer solution to achieve the purpose of protecting the reservoir. This method can achieve direct flowback without the need for a gel breaker, and also has a good reservoir protection effect, but there is a risk of temporary plugging particles invading deep into the pores and causing damage.

[0004] In addition, the overlying rocks of some carbonate reservoirs are usually salt-gypsum layers. During the drilling process, the reservoir drilling fluid must inevitably pass through the salt-gypsum layer. The creep and dissolution of the salt-gypsum layer have a great influence on the performance of the drilling fluid.

[0005] Therefore, research and development of a supersaturated brine drilling fluid is needed to solve the problem of salt dissolution in the salt-gypsum layer and avoid the damage of acid-soluble materials such as calcium carbonate in the traditional clay-free drilling fluid, further enhancing the temporary plugging ability of the traditional solid-free drilling fluid system, which has important application significance for improving the single well production capacity of oil and gas wells. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides a supersaturated brine drilling fluid and a preparation method and application thereof, so as to overcome the shortcomings of the existing drilling fluid technology without solid phase or clay phase, and solve the problem of salt dissolution in salt-gypsum layer drilling.

[0007] Specifically, the present invention is achieved through the following technical solutions:

[0008] A supersaturated salt water drilling fluid comprises: water, a pH regulator, a viscosity enhancer, a fluid loss reducer, a dispersant, a salt inhibitor, a powdery soluble salt and a soluble salt.

[0009] The above-mentioned supersaturated brine drilling fluid includes, by weight: 100 parts of water, 0.1-0.5 parts of pH adjuster, 0.4-1.0 parts of viscosity enhancer, 2.0-4.0 parts of filtrate reducer, 0.5-2.0 parts of dispersant, 1.0-3.0 parts of salt inhibitor, 10.0-20.0 parts of powdered soluble salt, the soluble salt is not limited to a certain amount, and is added until saturation.

[0010] The above-mentioned supersaturated brine drilling fluid, the water is fresh water and / or sea water.

[0011] In the above-mentioned supersaturated brine drilling fluid, the pH regulator is sodium hydroxide and / or sodium carbonate.

[0012] In the above-mentioned supersaturated salt water drilling fluid, the viscosity increasing agent is at least one of xanthan gum, guar gum and fenugreek gum.

[0013] The above-mentioned supersaturated brine drilling fluid, the viscosity enhancer, calculated on a mass basis of 100 parts, includes 50-70 parts of xanthan gum, 20-40 parts of guar gum, and 0-30 parts of fenugreek gum.

[0014] In the above-mentioned supersaturated brine drilling fluid, the fluid loss reducer is pregelatinized starch and / or modified starch.

[0015] The above-mentioned supersaturated brine drilling fluid, based on 100 parts by mass, the pregelatinized starch includes 50-70 parts of pregelatinized potato starch and 30-50 parts of pregelatinized cassava starch.

[0016] The supersaturated brine drilling fluid mentioned above, based on 100 parts by mass, comprises 50-70 parts of carboxymethyl potato starch and 30-50 parts of carboxymethyl cassava starch.

[0017] The above-mentioned supersaturated brine drilling fluid, the dispersant is a polyetheramine graft copolymer.

[0018] The above-mentioned supersaturated brine drilling fluid, the polyetheramine graft copolymer is prepared by the following method:

[0019] (1) After the polyetheramine is heated to 60-70° C. under stirring conditions, maleic anhydride is slowly added to carry out an amidation reaction, the reaction temperature is controlled at 60-80° C., the reaction time is 1-2 h, and an amidation product is obtained;

[0020] (2) Cooling the amidation product to room temperature, then slowly adding deionized water and allyl polyethylene glycol, stirring for 0.5-1h, adding ammonium persulfate to initiate the polymerization reaction, and maintaining the reaction temperature at 50-65°C, controlling the temperature of the reaction system not to exceed 65°C, and reacting for 2-3h to obtain a polyetheramine graft copolymer.

[0021] The supersaturated brine drilling fluid comprises, by weight, 40-50 parts of the polyetheramine, 20-40 parts of maleic anhydride, 10-20 parts of allyl polyethylene glycol, 3-5 parts of ammonium persulfate and 100 parts of deionized water.

[0022] In the above-mentioned supersaturated brine drilling fluid, the salt inhibitor is sodium nitrilotriacetate and / or ammonium ferric citrate.

[0023] In the above-mentioned supersaturated brine drilling fluid, the soluble salt is sodium chloride; the powdered soluble salt is sodium chloride and / or potassium chloride.

[0024] On the other hand, the present invention provides a method for preparing the above-mentioned supersaturated brine drilling fluid, comprising: under stirring conditions, adding a pH regulator, a viscosity increaser, a filtration reducer, a dispersant, a salt inhibitor and a soluble salt to water in order by mass; after the soluble salt is added to saturation, adding a powdered soluble salt to obtain the supersaturated brine drilling fluid.

[0025] In another aspect, the present invention provides the use of the supersaturated brine drilling fluid in oil drilling engineering.

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

[0027] (1) The supersaturated brine drilling fluid provided by the present invention has a simple raw material composition, the raw materials are easily available, and the preparation method is simple, no special process conditions are required, and it is easy to promote and apply;

[0028] (2) The supersaturated salt water drilling fluid of the present invention has the functional characteristics of supersaturation. The supersaturated salt is suspended in the drilling fluid in the form of particles, which not only prevents the dissolution of the salt paste layer, but also has a temporary plugging function, which can prevent reservoir damage and has a good reservoir protection effect;

[0029] (3) The supersaturated brine drilling fluid of the present invention can solve the problem of salt dissolution in the salt-gypsum layer on the one hand, and avoid the damage of acid-soluble materials such as calcium carbonate in the traditional drilling fluid without clay phase on the other hand, and further enhance the temporary plugging ability of the traditional drilling fluid system without solid phase, thereby realizing reservoir protection, which has important application significance for improving the single well productivity of oil and gas wells;

[0030] (4) The supersaturated salt water drilling fluid provided by the present invention has good rheological properties, filtration properties and reservoir protection properties. The permeability recovery rate of the drilling fluid reaches more than 93.2%, and the permeability recovery rate after completion fluid treatment reaches more than 98.6%, which provides a guarantee for safe drilling and reservoir protection of salt-gypsum layers and reservoirs. DETAILED DESCRIPTION

[0031] In order to fully understand the purpose, features and effects of the present invention, the present invention is described in detail through the following specific embodiments. Except for the following contents, the process method of the present invention adopts conventional methods or devices in the art. Unless otherwise specified, the following terms have the meanings commonly understood by those skilled in the art.

[0032] The terms "the", "said", "one" and "an" as used herein do not indicate a limitation of quantity, but rather indicate the presence of at least one of the referenced object. The terms "include", "including", "have", "contain", and the like are open-ended terms, meaning including but not limited to. The terms "preferred", "more preferred", and the like refer to embodiments of the present invention that may provide certain beneficial effects in certain circumstances. However, other embodiments may also be preferred under the same or other circumstances. In addition, the description of one or more embodiments does not imply that other embodiments are not applicable, nor is it intended to exclude other embodiments from the scope of the present invention.

[0033] When a numerical range is disclosed herein, the above range is considered to be continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0034] In a first aspect, the present invention provides a supersaturated brine drilling fluid, comprising: water, a pH regulator, a viscosity enhancer, a fluid loss reducer, a dispersant, a salt inhibitor, a powdered soluble salt and a soluble salt.

[0035] The components of the supersaturated brine drilling fluid of the present invention are introduced in detail below:

[0036] water

[0037] The supersaturated salt water drilling fluid of the present invention has low requirements on water, and can be fresh water or sea water.

[0038] Among them, the fresh water includes river water, lake water, groundwater, recycled water, rainwater and the like.

[0039] pH Adjusters

[0040] pH regulator is used to adjust the pH of supersaturated brine drilling fluid.

[0041] In some preferred embodiments, the pH adjuster is sodium hydroxide and / or sodium carbonate.

[0042] In some preferred embodiments, based on 100 parts by weight of water, the pH regulator is added in an amount of 0.1-0.5 parts in the supersaturated brine drilling fluid of the present invention.

[0043] Optionally, the pH adjuster is added in an amount of 0.1 part, 0.2 part, 0.3 part, 0.4 part or 0.5 part.

[0044] Thickener

[0045] The viscosity enhancer used in drilling fluid can increase the viscosity of drilling fluid, improve the sand carrying capacity of drilling fluid, adjust the rheology of drilling fluid, reduce the friction resistance of drilling fluid, and assist in plugging and stopping leakage.

[0046] In some preferred embodiments, the viscosity increasing agent is at least one of xanthan gum, guar gum and fenugreek gum.

[0047] Further preferably, the viscosity enhancer comprises 50-70 parts of xanthan gum, 20-40 parts of guar gum, and 0-30 parts of fenugreek gum based on 100 parts by mass.

[0048] Among them, the compound of xanthan gum and guar gum has a good synergistic effect. Compared with single xanthan gum or single guar gum, the viscosity is higher and the salt resistance is better, especially the ability to resist saturated salt water. Fenugreek gum also has a good synergistic effect with xanthan gum, and can further improve the salt resistance and temperature resistance when necessary.

[0049] In some preferred embodiments, based on 100 parts by weight of water, the amount of the viscosity enhancer added to the supersaturated brine drilling fluid of the present invention is 0.4-1.0 parts.

[0050] Optionally, the amount of the tackifier added is 0.4 part, 0.5 part, 0.6 part, 0.7 part, 0.8 part, 0.9 part or 1.0 part.

[0051] Practice has shown that when the amount of thickener added is too small, the viscosity of the drilling fluid will be too low, resulting in poor suspension stability of the drilling fluid, inability to suspend excessive salt particles and causing sedimentation, and also affecting the ability to carry cuttings during the drilling process; when the amount of thickener added is too large, the viscosity of the drilling fluid will be too high, affecting the fluidity of the drilling fluid and making it impossible to achieve field application.

[0052] Fluid Loss Control Agent

[0053] Fluid loss reducers are used to reduce the loss of drilling fluid into the formation.

[0054] In some preferred embodiments, the fluid loss reducer is pregelatinized starch and / or modified starch.

[0055] Potato starch and cassava starch have high content of amylopectin, which can help reduce the filtration loss of drilling fluid and the reservoir protection effect after pregelatinization. Therefore, pregelatinized starch and modified starch are both derived from potato starch and cassava starch.

[0056] In some preferred embodiments, the pregelatinized starch is a mixture of pregelatinized potato starch and pregelatinized cassava starch.

[0057] Further preferably, based on 100 parts by mass, the pregelatinized starch includes 50-70 parts of pregelatinized potato starch and 30-50 parts of pregelatinized cassava starch.

[0058] In some preferred embodiments, the modified starch is carboxymethyl starch.

[0059] Further preferably, the carboxymethyl starch is produced by compounding potato starch and cassava starch and then carboxymethylating them, or by compounding carboxymethyl potato starch and carboxymethyl cassava starch.

[0060] Further preferably, the starch raw materials used in the production of carboxymethyl starch include 50-70 parts of potato starch and 30-50 parts of cassava starch based on 100 parts by mass.

[0061] In some preferred embodiments, based on 100 parts by weight of water, the amount of the fluid loss reducer added to the supersaturated brine drilling fluid of the present invention is 2.0-4.0 parts.

[0062] Optionally, the amount of the filtrate reducer added is 2.0 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, 3.0 parts, 3.2 parts, 3.4 parts, 3.6 parts, 3.8 parts, or 4.0 parts.

[0063] Practice has shown that when the amount of filtrate reducer added is too small, the filtration loss of the drilling fluid will increase, deteriorating the drilling fluid performance and affecting the stability of the wellbore; when the amount of filtrate reducer added is too large, although the filtration loss will become smaller, the viscosity of the drilling fluid will be too high, affecting the fluidity of the drilling fluid and making it impossible to achieve field application.

[0064] Dispersants

[0065] Dispersants can be used to prevent the aggregation of solid particles in the drilling fluid, maintain rheological properties, and improve the chip-carrying capacity of the drilling fluid.

[0066] In some preferred embodiments, the dispersant used in the present invention is a polyetheramine graft copolymer.

[0067] Wherein, the preparation method of the polyetheramine graft copolymer comprises the following steps:

[0068] First, the polyetheramine is heated to 60-70°C under stirring conditions, and maleic anhydride is slowly added to carry out an amidation reaction. The temperature during the reaction is controlled at 60-80°C and the reaction time is 1-2h to obtain an amidation product.

[0069] Secondly, the amidation product is cooled to room temperature, and then deionized water and allyl polyethylene glycol are slowly added, stirred for 0.5-1h, and ammonium persulfate is added to initiate the polymerization reaction, and the reaction temperature is maintained at 50-65°C. At this time, the reaction is violent, and the temperature of the reaction system should be observed and controlled not to exceed 65°C. After a reaction time of 2-3h, a polyetheramine graft copolymer is obtained.

[0070] Further preferably, in parts by weight, the polyetheramine is 40-50 parts, the maleic anhydride is 20-40 parts, the allyl polyethylene glycol is 10-20 parts, the ammonium persulfate is 3-5 parts and the deionized water is 100 parts.

[0071] The polyetheramine is commercially available D230; the molecular weight of the allyl polyethylene glycol is 400-1000 Da.

[0072] Among them, the dispersant prepared according to the method of the present invention has two polyether branched structures based on the long-chain polymer molecules, one of which contains an amide group. These branches have extremely strong hydrophilicity and adsorption, and can be adsorbed on the salt particles in the supersaturated state, so that the salt particles can be better suspended and dispersed. In addition, the dispersant also has a strong inhibitory performance, which can inhibit the expansion of clay in the formation, prevent hydration expansion from causing reservoir damage, and further protect the reservoir; the dispersant also has the function of dispersing the salt-containing drill cuttings that enter the drilling fluid from the formation salt gypsum layer.

[0073] In some preferred embodiments, based on 100 parts by weight of water, the amount of dispersant added to the supersaturated brine drilling fluid of the present invention is 0.5-2.0 parts.

[0074] Optionally, the amount of the dispersant added is 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1.0 parts, 1.1 parts, 1.2 parts, 1.3 parts, 1.4 parts, 1.5 parts, 1.6 parts, 1.7 parts, 1.8 parts, 1.9 parts, or 2.0 parts.

[0075] Practice has shown that when the amount of dispersant added is too small, it is difficult to achieve the dispersion effect, and the salt or rock cuttings will aggregate into clumps; when the amount of dispersant added is too large, the drilling fluid will be over-dispersed, reducing the viscosity of the drilling fluid and affecting the suspension stability of the solid phase.

[0076] Salt inhibitor

[0077] Although the drilling fluid provided by the present invention is a supersaturated solution, and the salt particles exist in a suspended and dispersed state, the dissolution and crystallization of salt is a dynamic process, especially with the change of temperature. Therefore, the addition of salt inhibitor is to ensure that when the dynamic process of salt dissolution and crystallization occurs, the crystallized salt is in the form of fine and loose particles, which ensures that the crystallization of salt will not cause blockage on the one hand, and ensures that the particle size of the salt particles can better temporarily block the reservoir pores on the other hand.

[0078] In some preferred embodiments, the salt inhibitor of the present invention is sodium nitrilotriacetate and / or ammonium ferric citrate.

[0079] In some preferred embodiments, based on 100 parts by weight of water, the amount of salt inhibitor added to the supersaturated brine drilling fluid of the present invention is 1.0-3.0 parts.

[0080] Optionally, the amount of the salt inhibitor added is 1.0 parts, 1.2 parts, 1.4 parts, 1.6 parts, 1.8 parts, 2.0 parts, 2.2 parts, 2.4 parts, 2.6 parts, 2.8 parts, or 3.0 parts.

[0081] Practice has shown that when the amount of salt inhibitor added is too small, the salt crystallization process cannot be effectively inhibited, causing the salt to become hard particles, affecting the dispersion of the salt; when the amount of salt inhibitor added is too large, the inhibitory effect on salt crystallization is minimal.

[0082] Salt

[0083] The salt used in the present invention is divided into powder soluble salt and soluble salt. In the process of preparing drilling fluid, soluble salt is first added to saturation, and then powder soluble salt is added.

[0084] In the present invention, supersaturated salt is suspended in the drilling fluid in the form of particles, which not only prevents the dissolution of the salt-gypsum layer, but also has a temporary plugging function, can prevent reservoir damage, and has a good reservoir protection effect.

[0085] In some preferred embodiments, the particle size of the powdered soluble salt is 0.038-0.074 microns.

[0086] According to practice, if the particle size of the powdered soluble salt used in the present invention is too large, it will not pass through the vibrating screen (generally 0.089 microns) during drilling, resulting in loss; if the particle size of the powdered soluble salt is too small, it will penetrate deep into the reservoir and lose the temporary plugging effect. Therefore, the present invention preferably limits the particle size of the powdered soluble salt to between 0.038-0.074 microns.

[0087] In some preferred embodiments, the soluble salt is sodium chloride; the powdered soluble salt is sodium chloride and / or potassium chloride.

[0088] When the soluble salt is in a saturated state, adding powdered soluble salts such as sodium chloride or potassium chloride will not continue to dissolve, while adding other powdered soluble salts such as sodium formate will cause solubilization, making it difficult to achieve a supersaturated state.

[0089] In some preferred embodiments, based on 100 parts by weight of water, the amount of powdered soluble salt added to the supersaturated brine drilling fluid of the present invention is 10.0-20.0 parts.

[0090] Optionally, the added amount of the powder-soluble salt is 10 parts, 11 parts, 12 parts, 13 parts, 14 parts, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, or 20 parts.

[0091] Through practice, in the present invention, adding too little powdered soluble salt will cause the drilling fluid to become undersaturated during the underground heating process, resulting in a series of wellbore stability problems such as dissolution of formation salt rock; adding too much powdered soluble salt will result in too many salt particles affecting the rheological properties of the drilling fluid, so the present invention preferably limits the addition amount of powdered soluble salt to the above parameter range.

[0092] In a second aspect, the present invention also provides a method for preparing the above-mentioned supersaturated brine drilling fluid, comprising: under stirring conditions, adding a pH regulator, a viscosity enhancer, a filtration reducer, a dispersant, a salt inhibitor and a soluble salt to water in sequence according to their mass fractions; after the soluble salt is added to saturation, adding a powdered soluble salt to obtain the supersaturated brine drilling fluid.

[0093] In some preferred embodiments, the preparation method of the supersaturated brine drilling fluid of the present invention comprises: injecting water into a container by mass, turning on the agitator, adding a pH adjuster into the container, and stirring for 10 minutes; slowly adding a viscosity enhancer, and continuously stirring for 30 minutes; slowly adding a filtration reducer, and continuously stirring for 30 minutes; adding a dispersant and a salt inhibitor, and continuously stirring for 20 minutes; adding a soluble salt, and continuously stirring for more than 40 minutes until the soluble salt is completely dissolved, and finally adding a powdered soluble salt, and continuously stirring for more than 20 minutes to obtain the supersaturated brine drilling fluid.

[0094] In a third aspect, the present invention also provides the use of the above-mentioned supersaturated brine drilling fluid in oil drilling engineering.

[0095] The supersaturated salt water drilling fluid provided by the present invention can meet the reservoir protection requirements of open hole completion on the one hand, and can prevent the dissolution of salt rock in the salt-gypsum layer from causing instability of the well wall on the other hand. In addition, the supersaturated salt water drilling fluid of the present invention, the salt solution itself is in a supersaturated state, and after the salt rock in the salt-gypsum layer invades the drilling fluid, on the one hand, it will not dissolve into the drilling fluid to affect the performance, and the dispersant provided in the drilling fluid can also evenly disperse the salt rock to ensure the stability of the drilling fluid performance; on the other hand, after the drilling fluid and its filtrate invade the formation, the salt rock deep in the formation will not dissolve to cause instability of the well wall, thereby ensuring the stability of the wellbore. The supersaturated salt water drilling fluid of the present invention also has a good reservoir protection effect. The artificially added salt particles in a supersaturated state can temporarily block the pores of the reservoir to prevent the drilling fluid from further invading the reservoir pores, thereby protecting the reservoir. After the drilling fluid has completed the drilling footage, a completion fluid of an unsaturated salt solution can be pumped in for completion. The unsaturated salt solution can dissolve the salt particles temporarily blocking the reservoir pores, thereby achieving the purpose of unblocking the pore throats, ensuring that the reservoir pore throat channels are unobstructed and avoiding reservoir damage. Moreover, even if the salt particles invade deep into the formation, they will come into contact with the formation water contained in the formation and dissolve, and will not damage the reservoir.

[0096] The supersaturated salt water drilling fluid provided by the present invention has good rheological properties, filtration properties and reservoir protection properties. The permeability recovery rate of the drilling fluid reaches more than 93.2%, and the permeability recovery rate after completion fluid treatment reaches more than 98.6%, which provides a guarantee for safe drilling and reservoir protection of salt-gypsum layers and reservoirs.

[0097] Example

[0098] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions. The raw materials used in the following examples are all conventionally purchased.

[0099] Example 1

[0100] This embodiment provides a supersaturated brine drilling fluid, which is composed of the following components in parts by weight:

[0101] Water: 100 parts

[0102] pH adjuster: 0.5 parts

[0103] Thickener: 1.0 part

[0104] Fluid loss reducer: 4.0 parts

[0105] Dispersant: 2.0 parts

[0106] Salt inhibitor: 3.0 parts

[0107] Soluble salt: add until saturated

[0108] Powdered soluble salt: 20.0 parts.

[0109] Wherein, water is seawater;

[0110] The pH adjuster is sodium carbonate;

[0111] The viscosity enhancer is a mixture of xanthan gum and guar gum in a mass ratio of 7:3;

[0112] The fluid loss reducer is pregelatinized starch, specifically a mixture of pregelatinized potato starch and pregelatinized cassava starch in a mass ratio of 7:3;

[0113] The dispersant is a polyetheramine graft copolymer, which is composed of the following raw materials in parts by weight: 50 parts of polyetheramine, 40 parts of maleic anhydride, 10 parts of allyl polyethylene glycol, 5 parts of ammonium persulfate and 100 parts of deionized water.

[0114] The preparation method of the polyetheramine graft copolymer is as follows:

[0115] First, polyetheramine is added into a three-necked flask under stirring conditions, and after the temperature is raised to 70° C., maleic anhydride is slowly added to carry out an amidation reaction. The temperature during the reaction process is controlled at 80° C. and the reaction time is 1-2 hours to obtain an amidation product;

[0116] Secondly, cool the three-necked flask containing the amidation product to room temperature, slowly add deionized water and allyl polyethylene glycol, stir for 1 hour, add ammonium persulfate to initiate the polymerization reaction, and maintain the reaction temperature at 65°C. At this time, the reaction is violent, and the temperature in the three-necked flask should be observed and controlled not to exceed 65°C. After a reaction time of 3 hours, a polyetheramine graft copolymer is obtained.

[0117] The salt inhibitor is sodium nitrilotriacetate;

[0118] The soluble salt is sodium chloride.

[0119] The powdered soluble salt is sodium chloride; the particle size of the powdered soluble salt is 0.038-0.074 microns.

[0120] This embodiment also provides a method for preparing the supersaturated brine drilling fluid, which comprises the following steps:

[0121] First, inject water into the container according to the mass fraction, turn on the agitator, add the pH adjuster into the container, stir for 10 minutes, then slowly add the viscosity enhancer, continue stirring for 30 minutes, slowly add the filtration reducer, continue stirring for 30 minutes, add the dispersant and salt inhibitor, continue stirring for 20 minutes, add the soluble salt, continue stirring for more than 40 minutes, until the soluble salt is completely dissolved, finally add the powdered soluble salt, continue stirring for more than 20 minutes, and obtain the supersaturated brine drilling fluid.

[0122] Example 2

[0123] This embodiment provides a supersaturated brine drilling fluid, which is composed of the following components in parts by weight:

[0124] Water: 100 parts

[0125] pH adjuster: 0.1 part

[0126] Thickener: 0.4 parts

[0127] Fluid loss reducer: 2.0 parts

[0128] Dispersant: 0.5 parts

[0129] Salt inhibitor: 1.0 part

[0130] Soluble salt: add until saturated

[0131] Powdered soluble salt: 10.0 parts.

[0132] Among them, water is fresh water;

[0133] The pH adjuster is sodium hydroxide;

[0134] The viscosity enhancer is a mixture of xanthan gum, guar gum and fennel gum in a mass ratio of 5:2:3;

[0135] The fluid loss reducer is carboxymethyl starch; the carboxymethyl starch is obtained by compounding carboxymethyl potato starch and carboxymethyl cassava starch in a mass ratio of 7:3.

[0136] The dispersant is a polyetheramine graft copolymer, which is composed of the following raw materials in parts by weight: 40 parts of polyetheramine, 20 parts of maleic anhydride, 20 parts of allyl polyethylene glycol, 5 parts of ammonium persulfate and 100 parts of deionized water.

[0137] The preparation method of the polyetheramine graft copolymer is as follows:

[0138] First, polyetheramine was added into a three-necked flask under stirring conditions, and after the temperature was raised to 60°C, maleic anhydride was slowly added to carry out an amidation reaction. The temperature during the reaction was controlled at 60°C and the reaction time was 1h to obtain an amidation product.

[0139] Secondly, cool the three-necked flask containing the amidation product to room temperature, slowly add deionized water and allyl polyethylene glycol, stir for 0.5h, add ammonium persulfate to initiate the polymerization reaction, and maintain the reaction temperature at 50°C. At this time, the reaction is violent, and the temperature in the three-necked flask should be observed and controlled not to exceed 65°C. After 2h of reaction time, a polyetheramine graft copolymer is obtained.

[0140] The salt inhibitor was ammonium ferric citrate;

[0141] The soluble salt is sodium chloride.

[0142] The powdered soluble salt is potassium chloride; the particle size of the powdered soluble salt is 0.038-0.074 microns.

[0143] This embodiment also provides a method for preparing the supersaturated brine drilling fluid, which comprises the following steps:

[0144] First, inject water into the container according to the mass fraction, turn on the agitator, add the pH adjuster into the container, stir for 10 minutes, then slowly add the viscosity enhancer, continue stirring for 30 minutes, slowly add the filtration reducer, continue stirring for 30 minutes, add the dispersant and salt inhibitor, continue stirring for 20 minutes, add the soluble salt, continue stirring for more than 40 minutes, until the soluble salt is completely dissolved, finally add the powdered soluble salt, continue stirring for more than 20 minutes, and obtain the supersaturated brine drilling fluid.

[0145] Example 3

[0146] This embodiment provides a supersaturated brine drilling fluid, which is composed of the following components in parts by weight:

[0147] Water: 100 parts

[0148] pH adjuster: 0.3 parts

[0149] Thickener: 0.6 parts

[0150] Fluid loss reducer: 3.0 parts

[0151] Dispersant: 1.0 part

[0152] Salt inhibitor: 2.0 parts

[0153] Soluble salt: unlimited amount, add until saturated

[0154] Powdered soluble salt: 15.0 parts.

[0155] Among them, water is fresh water;

[0156] The pH regulator is a mixture of sodium hydroxide and sodium carbonate in a mass ratio of 2:3;

[0157] The viscosity enhancer is a mixture of xanthan gum, guar gum, and fennel gum in a mass ratio of 6:3:1;

[0158] The fluid loss reducer is a compound of 50 parts of pregelatinized starch and 50 parts of carboxymethyl starch; wherein the pregelatinized starch is a mixture of pregelatinized potato starch and pregelatinized cassava starch in a mass ratio of 3:2; the carboxymethyl starch is a mixture of carboxymethyl potato starch and carboxymethyl cassava starch in a mass ratio of 3:2;

[0159] The dispersant is a polyetheramine graft copolymer, which is composed of the following raw materials in parts by weight: 45 parts of polyetheramine, 30 parts of maleic anhydride, 15 parts of allyl polyethylene glycol, 4 parts of ammonium persulfate and 100 parts of deionized water.

[0160] The preparation method of the polyetheramine graft copolymer is as follows:

[0161] First, polyetheramine was added into a three-necked flask under stirring conditions, and after the temperature was raised to 65°C, maleic anhydride was slowly added to carry out an amidation reaction. The temperature during the reaction was controlled at 70°C and the reaction time was 1.5h to obtain an amidation product.

[0162] Secondly, the three-necked flask containing the amidation product was cooled to room temperature, deionized water and allyl polyethylene glycol were slowly added, and the mixture was stirred for 0.8 h. Ammonium persulfate was added to initiate the polymerization reaction, and the reaction temperature was maintained at 60°C. At this time, the reaction was violent, and the temperature in the three-necked flask should be carefully observed to control the temperature not exceeding 65°C. After 2.5 h of reaction time, a polyetheramine graft copolymer was obtained.

[0163] The salt inhibitor is a mixture of sodium nitrilotriacetate and ferric citrate in a mass ratio of 1:1;

[0164] The soluble salt is sodium chloride.

[0165] The powdered soluble salt is sodium chloride; the particle size of the powdered soluble salt is 0.056-0.074 microns.

[0166] This embodiment also provides a method for preparing the supersaturated brine drilling fluid, which comprises the following steps:

[0167] First, inject water into the container according to the mass fraction, turn on the agitator, add the pH adjuster into the container, stir for 10 minutes, then slowly add the viscosity enhancer, continue stirring for 30 minutes, slowly add the filtration reducer, continue stirring for 30 minutes, add the dispersant and salt inhibitor, continue stirring for 20 minutes, add the soluble salt, continue stirring for more than 40 minutes, until the soluble salt is completely dissolved, finally add the powdered soluble salt, continue stirring for more than 20 minutes, and obtain the supersaturated brine drilling fluid.

[0168] Example 4

[0169] This embodiment provides a supersaturated brine drilling fluid, which is composed of the following components in parts by weight:

[0170] Water: 100 parts

[0171] pH adjuster: 0.4 parts

[0172] Thickener: 0.8 parts

[0173] Fluid loss reducer: 3.5 parts

[0174] Dispersant: 1.5 parts

[0175] Salt inhibitor: 2.5 parts

[0176] Soluble salt: unlimited amount, add until saturated

[0177] Powdered soluble salt: 18.0 parts.

[0178] Wherein, water is seawater;

[0179] The pH regulator is a mixture of sodium hydroxide and sodium carbonate in a mass ratio of 3:7;

[0180] The thickener is a mixture of xanthan gum, guar gum and fenugreek gum in a mass ratio of 5:2:3.

[0181] The fluid loss reducer is a compound of 30 parts of pregelatinized starch and 70 parts of carboxymethyl starch; wherein the pregelatinized starch is a mixture of pregelatinized potato starch and pregelatinized cassava starch in a mass ratio of 1:1; the carboxymethyl starch is a mixture of carboxymethyl potato starch and carboxymethyl cassava starch in a mass ratio of 7:3;

[0182] The dispersant is a polyetheramine graft copolymer, which is composed of the following raw materials in parts by weight: 40 parts of polyetheramine, 40 parts of maleic anhydride, 20 parts of allyl polyethylene glycol, 5 parts of ammonium persulfate, and 100 parts of deionized water.

[0183] The preparation method of the polyetheramine graft copolymer is as follows:

[0184] First, polyetheramine was added into a three-necked flask under stirring conditions, and after the temperature was raised to 70°C, maleic anhydride was slowly added to carry out an amidation reaction. The temperature during the reaction was controlled at 70°C and the reaction time was 2h to obtain an amidation product.

[0185] Secondly, cool the three-necked flask containing the amidation product to room temperature, slowly add deionized water and allyl polyethylene glycol, stir for 1 hour, add ammonium persulfate to initiate the polymerization reaction, and maintain the reaction temperature at 55°C. At this time, the reaction is violent, and the temperature in the three-necked flask should be observed and controlled not to exceed 65°C. After a reaction time of 3 hours, a polyetheramine graft copolymer is obtained.

[0186] The salt inhibitor is a mixture of sodium nitrilotriacetate and ammonium ferric citrate in a mass ratio of 3:7;

[0187] The soluble salt is sodium chloride.

[0188] The powdered soluble salt is potassium chloride; the particle size of the powdered soluble salt is 0.038-0.056 microns.

[0189] This embodiment also provides a method for preparing the supersaturated brine drilling fluid, which comprises the following steps:

[0190] First, inject water into the container according to the mass fraction, turn on the agitator, add the pH adjuster into the container, stir for 10 minutes, then slowly add the viscosity enhancer, continue stirring for 30 minutes, slowly add the filtration reducer, continue stirring for 30 minutes, add the dispersant and salt inhibitor, continue stirring for 20 minutes, add the soluble salt, continue stirring for more than 40 minutes, until the soluble salt is completely dissolved, finally add the powdered soluble salt, continue stirring for more than 20 minutes, and obtain the supersaturated brine drilling fluid.

[0191] The supersaturated brine drilling fluid (referred to as drilling fluid) prepared in Examples 1-4 above was evaluated according to GB / T16783.1-2014 "Field Test of Drilling Fluids in Petroleum and Natural Gas Industry Part 1: Water-Based Drilling Fluids", and the results are shown in Table 1.

[0192] Table 1 Rheological and filtration properties of drilling fluid

[0193] T state PV YP Φ3 API HFZ HFZ-S Example 1 100 16 hours later 28 13 11 4.8 93.2 98.8 Example 2 120 16 hours later 18 8 7 4.6 94.4 98.6 Example 3 140 16 hours later 25 12 11 2.4 94.7 99.2 Example 4 150 16 hours later 27 10 10 2.2 93.5 99.8

[0194] Note: T: drilling fluid aging temperature, °C; PV: drilling fluid plastic viscosity, mPa·s; YP: drilling fluid dynamic shear force, Pa; Φ3: 3-turn reading of six-speed rotary viscometer, dimensionless; API: medium-pressure water loss of drilling fluid (0.7 MPa, 30 min), mL; HFZ: permeability recovery rate after drilling fluid directly contaminates the core, %; HFZ-S: permeability recovery rate after the core is contaminated by drilling fluid and then contaminated by 10% potassium chloride solution, %.

[0195] It can be seen from Table 1 that the drilling fluids prepared in Examples 1-4 of the present invention all have good rheological properties and filtration properties. After the drilling fluids prepared in Examples 1-4 of the present invention directly contaminated the core, the permeability recovery rate using the direct flowback method reached more than 93.2%, and after the core was contaminated again using 10% potassium chloride brine as the completion fluid, the permeability recovery rate was able to recover to more than 98.6%, indicating that the salt particles can be dissolved by the completion fluid and relieve damage.

[0196] The present invention has been disclosed above with preferred embodiments, but those skilled in the art should understand that these embodiments are only used to describe the present invention and should not be understood as limiting the scope of the present invention. It should be noted that all changes and substitutions equivalent to these embodiments should be deemed to be included in the scope of the claims of the present invention. Therefore, the scope of protection of the present invention should be based on the scope defined in the claims.

Claims

1. A supersaturated brine drilling fluid, characterized in that: include: Water, pH adjuster, viscosity enhancer, fluid loss reducer, dispersant, salt inhibitor, powder soluble salt and soluble salt.

2. The supersaturated brine drilling fluid according to claim 1, characterized in that: Calculated by weight, it includes: 100 parts of water, 0.1-0.5 parts of pH adjuster, 0.4-1.0 parts of viscosity enhancer, 2.0-4.0 parts of fluid loss reducer, 0.5-2.0 parts of dispersant, 1.0-3.0 parts of salt inhibitor, 10.0-20.0 parts of powdered soluble salt, there is no limit on the number of soluble salts, and it is added until saturation.

3. The supersaturated brine drilling fluid according to claim 1, characterized in that: The water is fresh water and / or sea water.

4. The supersaturated brine drilling fluid according to claim 1, characterized in that: The pH regulator is sodium hydroxide and / or sodium carbonate.

5. The supersaturated brine drilling fluid according to claim 1, characterized in that: The viscosity increasing agent is at least one of xanthan gum, guar gum and fenugreek gum.

6. The supersaturated brine drilling fluid according to claim 5, characterized in that: The viscosity enhancer comprises 50-70 parts of xanthan gum, 20-40 parts of guar gum and 0-30 parts of fenugreek gum in 100 parts by mass.

7. The supersaturated brine drilling fluid according to claim 1, characterized in that: The fluid loss reducer is pregelatinized starch and / or modified starch.

8. The supersaturated brine drilling fluid according to claim 7, characterized in that: Based on 100 parts by mass, the pregelatinized starch includes 50-70 parts of pregelatinized potato starch and 30-50 parts of pregelatinized cassava starch.

9. The supersaturated brine drilling fluid according to claim 7, characterized in that: Based on 100 parts by mass, the modified starch includes 50-70 parts of carboxymethyl potato starch and 30-50 parts of carboxymethyl tapioca starch.

10. The supersaturated brine drilling fluid according to claim 1, characterized in that: The dispersant is a polyetheramine graft copolymer.

11. The supersaturated brine drilling fluid according to claim 1, characterized in that: The polyetheramine graft copolymer is prepared by the following method: (1) After the polyetheramine is heated to 60-70° C. under stirring conditions, maleic anhydride is slowly added to carry out an amidation reaction, the reaction temperature is controlled at 60-80° C., the reaction time is 1-2 h, and an amidation product is obtained; (2) Cooling the amidation product to room temperature, then slowly adding deionized water and allyl polyethylene glycol, stirring for 0.5-1h, adding ammonium persulfate to initiate the polymerization reaction, and maintaining the reaction temperature at 50-65°C, controlling the temperature of the reaction system not to exceed 65°C, and reacting for 2-3h to obtain a polyetheramine graft copolymer.

12. The supersaturated brine drilling fluid according to claim 11, characterized in that: In parts by weight, the polyetheramine is 40-50 parts, the maleic anhydride is 20-40 parts, the allyl polyethylene glycol is 10-20 parts, the ammonium persulfate is 3-5 parts, and the deionized water is 100 parts.

13. The supersaturated brine drilling fluid according to claim 1, characterized in that: The salt inhibitor is sodium nitrilotriacetate and / or ammonium ferric citrate.

14. The supersaturated brine drilling fluid according to claim 1, characterized in that: The soluble salt is sodium chloride; the powdered soluble salt is sodium chloride and / or potassium chloride.

15. The method for preparing the supersaturated brine drilling fluid according to any one of claims 1 to 14, characterized in that: Under stirring conditions, pH regulator, viscosity enhancer, fluid loss reducer, dispersant, salt inhibitor and soluble salt are added to water in order by mass; after the soluble salt is added to saturation, powdered soluble salt is added to obtain the supersaturated brine drilling fluid.

16. Use of the supersaturated brine drilling fluid according to any one of claims 1 to 14 in oil drilling engineering.