Water-based drilling fluid for deep coal bed gas horizontal well as well as preparation method and application of water-based drilling fluid

Abstract

The invention belongs to the technical field of oil and gas exploitation, and discloses a water-based drilling fluid for a deep coal bed gas horizontal well as well as a preparation method and application of the water-based drilling fluid. The water-based drilling fluid is prepared from the following components in percentage by mass: 3.0 to 9.0 percent of film-forming plugging agent, 1.0 to 3.0 percent of quick plugging agent, 1.0 to 3.0 percent of oil layer shielding temporary plugging agent, 2.0 to 4.0 percent of anti-collapse agent, 1.0 to 5.0 percent of filtrate reducer, 2.0 to 5.0 percent of solid lubricant, 3.0 to 5.0 percent of liquid lubricant, 3.0 to 6.0 percent of organic salt, 10 to 25 percent of inorganic salt, 0.1 to 0.5 percent of alkaline substance, 0.2 to 0.5 percent of flow pattern regulator and the balance of water. And the balance of weighting agent and water. The water-based drilling fluid provided by the invention has good plugging performance, lubricating performance and inhibition performance, and meets high requirements of stratums such as a deep coal bed gas horizontal well and a carbonaceous mudstone horizontal well on plugging and collapse prevention performance of the water-based drilling fluid.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas exploitation, and in particular relates to a water-based drilling fluid for a deep coalbed methane horizontal well and a preparation method and application thereof. Background Art

[0002] Generally, coalbed methane horizontal wells with a vertical depth of less than 1500m are called deep coalbed methane horizontal wells. Compared with conventional shallow coalbed methane horizontal wells, deep coal rocks are subjected to higher overburden pressure and are more prone to collapse. Deep coalbed methane horizontal wells have higher requirements for drilling fluids. The key is to ensure the stability of the well wall, lubrication, anti-stuck and anti-leakage. The problem of coal seam collapse in deep coalbed methane horizontal wells is a key issue restricting the exploration and development of deep coalbed methane.

[0003] In the past, when the problem of wellbore instability occurred during the construction of coalbed methane horizontal wells, the problem was usually solved by increasing the density of drilling fluid. However, the coal seams contain a large number of micropores and microcracks. The higher density drilling fluid is more likely to invade the micropores and microcracks of the formation, thereby accelerating the formation of microcracks in the formation, resulting in wellbore spalling, collapse and instability. When the drilling fluid has insufficient plugging capacity, a vicious cycle of "wellbore instability → increasing drilling fluid density → short-term stability of the wellbore → aggravated filtrate invasion → collapse and worsening" is likely to occur, resulting in the density of the drilling fluid used on site being higher and higher, the stability of the wellbore becoming worse and worse, and the problems of wellbore block falling and drill stuck being more prominent.

[0004] In summary, there are several main problems in the construction process of deep coalbed methane horizontal wells, which need to be overcome:

[0005] 1. Deep coalbed methane horizontal wells have greater vertical depth and higher overburden pressure. During the construction of the horizontal section, the coal seam is more likely to collapse under the action of overburden pressure and gravity.

[0006] 2. Simply increasing the density of drilling fluid is used to solve the problem of wellbore instability during the construction of coalbed methane horizontal wells. However, microcracks are developed in deep coal rocks, and higher-density drilling fluid is more likely to invade micropores and microcracks in the formation, thereby accelerating the generation of microcracks in the formation and causing the wellbore to peel off and collapse.

[0007] 3. The deep coal rock is highly brittle and contains a large amount of coal gangue, carbonaceous mudstone and mixed layers. These three rock layers are difficult to effectively seal, resulting in well wall collapse.

[0008] 4. Deep coalbed methane horizontal wells have a greater depth than conventional coalbed methane horizontal wells, resulting in greater friction and torque during drilling. Although the solid lubricants currently used are low-cost, the lubrication effect is not ideal. Liquid lubricants are often more effective, but the action time is short. Therefore, a single type of lubricant is difficult to meet the requirements of lubrication and drag reduction.

[0009] Therefore, providing a new type of water-based drilling fluid for coalbed methane horizontal wells and a preparation method thereof, so that the water-based drilling fluid has good plugging performance, lubrication performance, and inhibition performance, and meets the high requirements of deep coalbed methane horizontal wells, carbonaceous mudstone horizontal wells and other formations for the plugging and anti-collapse performance of water-based drilling fluids has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0010] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to provide a water-based drilling fluid for deep coalbed methane horizontal wells and a preparation method thereof with good plugging performance, lubrication performance and inhibition performance, so as to meet the high requirements of deep coalbed methane horizontal wells, carbonaceous mudstone horizontal wells and other formations for the plugging and anti-collapse performance of water-based drilling fluids.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] The invention discloses a water-based drilling fluid for a deep coalbed methane horizontal well. Taking the total weight of clean water used in preparing the water-based drilling fluid as 100%, the weight percentages of the components in the water-based drilling fluid are as follows: 3.0-9.0% of a film-forming plugging agent, 1.0-3.0% of a quick plugging agent, 1.0-3.0% of an oil layer shielding temporary plugging agent, 2.0-4.0% of an anti-collapse agent, 1.0-5.0% of a filtration loss reducer, 2.0-5.0% of a solid lubricant, 3.0-5.0% of a liquid lubricant, 3.0-6.0% of an organic salt, 10-25% of an inorganic salt, 0.1-0.5% of an alkali substance, 0.2-0.5% of a flow pattern regulator, and the remainder is a weighting agent and water.

[0013] Furthermore, the rapid plugging agent includes the plugging agent G314 for drilling fluid,

[0014] Film-forming plugging agents include drilling fluid plugging agent G308,

[0015] Oil layer shielding temporary plugging agent includes drilling fluid shielding temporary plugging agent G325,

[0016] The mass ratio of the film-forming plugging agent, the rapid plugging agent and the oil layer shielding temporary plugging agent is 3-6:1:1.

[0017] Furthermore, the anti-collapse agent includes at least one of emulsified asphalt, modified asphalt and sulfonated asphalt.

[0018] Furthermore, the fluid loss reducer includes high temperature resistant micro-nano fluid loss reducer G352 for drilling fluid.

[0019] Further, the solid lubricant includes graphite powder and / or elastic graphite.

[0020] Furthermore, the liquid lubricant includes a wetting agent for oil-based drilling fluid G329.

[0021] Further, the organic salt includes at least one of sodium acetate, potassium acetate, sodium formate and potassium formate;

[0022] The inorganic salt includes at least one of potassium chloride, potassium sulfate, sodium chloride and potassium nitrate.

[0023] Furthermore, the alkaline substance includes sodium hydroxide and / or potassium hydroxide.

[0024] Furthermore, the flow pattern regulator includes at least one of locust bean gum, sesbania gum, guar gum, xanthan gum, hydroxypropyl sesbania gum, hydroxypropyl guar gum, carboxymethyl guar gum and carboxymethyl sesbania gum.

[0025] Further, the weighting agent includes at least one of barite, iron ore powder and limestone, and the amount of the weighting agent is determined according to the target density of the water-based drilling fluid.

[0026] In a second aspect, the present invention discloses a method for preparing a water-based drilling fluid, comprising:

[0027] Under stirring conditions, adding a quick plugging agent, a film-forming plugging agent, an oil layer shielding temporary plugging agent, an anti-collapse agent, a fluid loss reducer, a solid lubricant, a liquid lubricant, an inorganic salt, an organic salt, an alkali substance, a flow pattern regulator and a weighting agent into water according to a proportion, and stirring evenly to obtain a water-based drilling fluid;

[0028] Among them, taking the total weight of water used in preparing the water-based drilling fluid as 100%, the mass percentages of the components in the water-based drilling fluid are: 3.0-9.0% of film-forming plugging agent, 1.0-3.0% of quick plugging agent, 1.0-3.0% of oil layer shielding temporary plugging agent, 2.0-4.0% of anti-collapse agent, 1.0-5.0% of filtrate reducer, 2.0-5.0% of solid lubricant, 3.0-5.0% of liquid lubricant, 3.0-6.0% of organic salt, 10-25% of inorganic salt, 0.1-0.5% of alkali substance, 0.2-0.5% of flow pattern regulator, and the balance is weighting agent and water.

[0029] In a third aspect, the present invention discloses an application of a water-based drilling fluid for a deep coalbed methane horizontal well, and utilizes the water-based drilling fluid to perform horizontal well drilling construction.

[0030] Furthermore, the horizontal wells include horizontal wells in coal-bearing strata with a vertical depth greater than 1500m.

[0031] Technical effects and advantages of the present invention:

[0032] 1. The water-based drilling fluid provided by the present invention uses three different types of plugging agents, and the three different types of plugging agents have a synergistic effect. On this basis, the plugging performance of the water-based drilling fluid is effectively improved, especially its plugging performance for microcracks, micropores, etc., and the permeability of the plugging layer is reduced, thereby improving the anti-collapse plugging performance of the water-based drilling fluid, solving the problem of wellbore instability of horizontal wells such as coalbed methane with developed microcracks that restricts the current exploration and development of deep coalbed methane, etc., and meeting the needs of safe and rapid drilling of horizontal wells such as coalbed methane.

[0033] 2. The present invention uses the wetting agent for oil-based drilling fluid as the liquid lubricant in the water-based drilling fluid, and uses the liquid lubricant and the solid lubricant to cooperate with each other, so that the water-based drilling fluid has good lubrication and drag reduction properties, thereby significantly reducing the torque in drilling construction and reducing friction, solving the problem of lubrication and drag reduction of long horizontal sections in the previous deep coalbed methane horizontal well drilling process, so that the length of the horizontal section can be greatly extended, meeting the geological requirements for the length of the horizontal section.

[0034] 3. The water-based drilling fluid of the present invention has a good anti-collapse effect not only on coal seams, but also on carbonaceous mudstone and coal gangue associated with coal seams.

[0035] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram showing the comparison of the plugging performance between sample slurry 1 and sample slurries 10, 11, 12, and 13;

[0037] Figure 2 Schematic diagram showing the comparison of lubrication performance between sample slurry 2 and sample slurries 21, 22, and 23;

[0038] Figure 3 It is a schematic diagram showing the comparison of the linear expansion rates of the sample slurry 3 and the sample slurries 31 and 32;

[0039] Figure 4 Schematic diagram of comparison of coal dust recovery rates of sample slurry 3 and sample slurries 31 and 32. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The design idea of ​​the present invention is that, on the one hand, according to the characteristics of micro-cracks in deep coal seams, three different types of plugging agents are added to the water-based drilling fluid, namely, rapid plugging agent, film-forming plugging agent, and oil layer shielding temporary plugging agent. These three have different divisions of labor and work closely together:

[0042] ① During the drilling construction process, the rapid plugging agent is responsible for quickly adsorbing on the surface of the deep coal seam when drilling a new stratum, using its hydrophilic and lipophilic properties consistent with the deep coal seam, forming an adsorption layer, and quickly reducing the invasion of the filtrate into the rock formation. Its main feature is speed.

[0043] ② Based on the first plugging layer formed by the rapid plugging agent, the film-forming plugging agent undergoes a micro-crosslinking reaction under the action of the bottom hole temperature to form a second plugging layer, which enhances the plugging strength and strengthens the plugging effect. The main feature is high plugging strength. The film-forming plugging agent plays a major role in preventing the collapse of deep coal seams. For coal rocks with high brittleness, the proportion of the film-forming plugging agent should be appropriately increased.

[0044] ③ Oil layer shielding temporary plugging agent is mainly used to plug micron-sized cracks in deep coal seams and other strata. There are many micron-sized cracks in deep coal seams and the coal seams are easy to break. Oil layer shielding temporary plugging agent plays a supplementary role to rapid plugging agent and film-forming plugging agent, filling the larger micro cracks that are difficult to effectively plug with the above two plugging agents.

[0045] As shown above, the present invention effectively improves the plugging performance of water-based drilling fluid, especially its plugging performance for microcracks, micropores, etc., reduces the permeability of the plugging layer, and thus improves the anti-collapse plugging performance of water-based drilling fluid, that is, it relies on the effective plugging of microcracks, micropores, etc. to play an anti-collapse role, solves the problem of well wall instability of horizontal wells such as coalbed methane with developed microcracks that restricts the current exploration and development of deep coalbed methane, and meets the needs of safe and rapid drilling of horizontal wells such as coalbed methane. Moreover, it is usually inevitable to encounter carbonaceous mudstone and coal gangue in the construction of coalbed methane horizontal wells. Carbonaceous mudstone and coal gangue are often associated with coal seams, and both belong to formations that are extremely prone to collapse. The water-based drilling fluid provided by the present invention has a good anti-collapse effect not only on coal seams, but also on carbonaceous mudstone and coal gangue associated with coal seams.

[0046] On the other hand, deep coalbed methane horizontal wells have a greater well depth than shallow coalbed methane horizontal wells. For example, the 8# coal seam of the Benxi Formation in the Ordos Basin is usually buried at a depth of more than 3200m, and the completion depth reaches 5000m, resulting in large friction resistance, large torque during drilling, and easy to stop the top drive and cause underground accidents. The solid lubricant used in the water-based drilling fluid is usually low in cost, but the lubrication effect is not ideal, while the lubrication effect of the liquid lubricant is good, but the action time is short. It can be seen that a single type of lubricant is difficult to meet the lubrication and drag reduction requirements. For this reason, the present invention uses the wetting agent for oil-based drilling fluid as the liquid lubricant in the water-based drilling fluid. The wetting agent for the oil-based drilling fluid cooperates with the solid lubricant to make the water-based drilling fluid have good lubrication and drag reduction performance, thereby significantly reducing the torque in the drilling construction, reducing friction, and solving the problem of lubrication and drag reduction of long horizontal sections in the previous deep coalbed methane horizontal well drilling process, so that the length of the horizontal section can be greatly extended to meet the geological requirements for the length of the horizontal section.

[0047] The contents of the present invention are described in detail below.

[0048] The invention provides a water-based drilling fluid for a deep coalbed methane horizontal well. Taking the total weight of clean water used in preparing the water-based drilling fluid as 100%, the weight percentages of the components in the water-based drilling fluid are as follows: 3.0-9.0% of a film-forming plugging agent, 1.0-3.0% of a quick plugging agent, 1.0-3.0% of an oil layer shielding temporary plugging agent, 2.0-4.0% of an anti-collapse agent, 1.0-5.0% of a filtration loss reducer, 2.0-5.0% of a solid lubricant, 3.0-5.0% of a liquid lubricant, 3.0-6.0% of an organic salt, 10-25% of an inorganic salt, 0.1-0.5% of an alkali substance, 0.2-0.5% of a flow pattern regulator, and the remainder is a weighting agent and water.

[0049] In some embodiments of the present invention, the rapid plugging agent includes the plugging agent G314 for drilling fluid.

[0050] It should be noted that the rapid plugging agent is an active particle, and its lipophilicity and hydrophilicity can be adjusted according to the characteristics of the applied formation. The lipophilicity and hydrophilicity of the plugging agent must match the lipophilicity and hydrophilicity of the applied formation, so that this type of plugging agent can be quickly adsorbed and deposited on the surface of the formation, reducing the damage of the drilling fluid to the coal seam, thereby quickly forming the first plugging film on the surface of the micro-cracks and micro-fissures of the coal seam. The particle size of the rapid plugging agent is 10-300nm. The plugging agent G314 includes two types: water-dispersible (hydrophilic) and oil-dispersible (lipophilic), which are selected according to the hydrophilicity and lipophilicity of the coal seam.

[0051] Film-forming plugging agents include drilling fluid plugging agent G308,

[0052] It should be noted that the film-forming plugging agent can undergo micro-cross-linking at above 50°C, thereby forming a dense plugging film on the basis of the adsorption and deposition film formed by the rapid plugging agent G314. The particle size of the film-forming plugging agent is 100-600nm.

[0053] Oil layer shielding temporary plugging agent includes drilling fluid shielding temporary plugging agent G325,

[0054] It should be noted that the oil layer shielding temporary plugging agent is modified paraffin. The oil-soluble particles form a third plugging film on the basis of the film-forming plugging layer, thereby improving the plugging and anti-collapse effect. It can also reduce the damage of drilling fluid to the reservoir and achieve the effect of reservoir protection. The particle size of the shielding temporary plugging agent G325 for drilling fluid is 0.1-5μm.

[0055] The mass ratio of film-forming plugging agent, rapid plugging agent and oil layer shielding temporary plugging agent is 3-6:1:1. For coal rock with high brittleness, the proportion of film-forming plugging agent should be appropriately increased.

[0056] In some embodiments of the present invention, the anti-collapse agent includes at least one of emulsified asphalt, modified asphalt and sulfonated asphalt.

[0057] In some embodiments of the present invention, the fluid loss reducer includes high temperature resistant micro-nano fluid loss reducer G352 for drilling fluid.

[0058] In some embodiments of the present invention, the solid lubricant includes graphite powder and / or elastic graphite.

[0059] In some embodiments of the present invention, the liquid lubricant includes a wetting agent for oil-based drilling fluid G329,

[0060] It should be noted that the wetting agent for oil-based drilling fluid is generally used in oil-based drilling fluid to wet the weighting material, improve the suspension stability of the drilling fluid, and prevent the weighting material from settling. The present invention uses it in water-based drilling fluid to play a lubricating role, and the lubricating effect is better than that of the commonly used lubricant for water-based drilling fluid.

[0061] In some embodiments of the present invention, the organic salt comprises at least one of sodium acetate, potassium acetate, sodium formate and potassium formate;

[0062] The inorganic salt includes at least one of potassium chloride, potassium sulfate, sodium chloride and potassium nitrate.

[0063] In some embodiments of the present invention, the alkaline substance includes sodium hydroxide and / or potassium hydroxide.

[0064] In some embodiments of the present invention, the flow pattern modifier includes at least one of locust bean gum, sesbania gum, guar gum, xanthan gum, hydroxypropyl sesbania gum, hydroxypropyl guar gum, carboxymethyl guar gum and carboxymethyl sesbania gum.

[0065] In some embodiments of the present invention, the weighting agent includes at least one of barite, iron ore powder and limestone, and the amount of the weighting agent is determined according to the target density of the water-based drilling fluid.

[0066] It should be noted that G308, G314, G325, G329, G339 and G352 used in the present invention are all commercially available conventional products.

[0067] In a second aspect, the present invention discloses a method for preparing a water-based drilling fluid for a deep coalbed methane horizontal well, comprising:

[0068] Under stirring conditions, adding a quick plugging agent, a film-forming plugging agent, an oil layer shielding temporary plugging agent, an anti-collapse agent, a fluid loss reducer, a solid lubricant, a liquid lubricant, an inorganic salt, an organic salt, an alkali substance, a flow pattern regulator and a weighting agent into water according to a proportion, and stirring evenly to obtain a water-based drilling fluid;

[0069] Wherein, taking the total weight of water used in preparing the water-based drilling fluid as 100%, the mass percentage of each component in the water-based drilling fluid is: 3.0-9.0% of film-forming plugging agent, 1.0-3.0% of quick plugging agent, 1.0-3.0% of oil layer shielding temporary plugging agent, 2.0-4.0% of anti-collapse agent, 1.0-5.0% of fluid loss reducer, 2.0-5.0% of solid lubricant, 3.0-5.0% of wetting agent for oil-based drilling fluid, 3.0-6.0% of organic salt, 10-25% of inorganic salt, 0.1-0.5% of alkali substance, 0.2-0.5% of flow pattern regulator, and the balance is weighting agent and water. The present invention does not make specific requirements on the order of adding each component and the stirring speed in the process of preparing the water-based drilling fluid, and can be reasonably adjusted according to the actual operation needs on site.

[0070] In a third aspect, the present invention further discloses an application of a water-based drilling fluid for a deep coalbed methane horizontal well, and horizontal well drilling construction is performed using the water-based drilling fluid for a deep coalbed methane horizontal well.

[0071] In some embodiments of the present invention, the horizontal well includes a deep coal-bearing formation horizontal well, wherein the deep coal-bearing formation horizontal well refers to a coal-bearing formation horizontal well with a vertical depth greater than 1500m.

[0072] In order to better illustrate the present invention, the following examples and comparative examples are provided.

[0073] Example 1

[0074] This embodiment provides a water-based drilling fluid for a deep coalbed methane horizontal well, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0075] Film-forming plugging agent G308: 3.0%, fast plugging agent G314: 1.0%, oil layer shielding temporary plugging agent G325: 1.0%,

[0076] Drilling fluid anti-collapse agent G339: 2.0%, high temperature resistant micro-nano filtration reducer G352: 2.0%, solid lubricant graphite powder: 2.0%, liquid lubricant G329: 3.0%, sodium formate: 3.0%, potassium chloride: 10.0%, sodium hydroxide: 0.1%, flow pattern regulator xanthan gum: 0.2%, barite: 5% and clean water.

[0077] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0078] Under the condition of high-speed stirring, film-forming plugging agent G308 for drilling fluid, plugging agent G314 for drilling fluid, temporary plugging agent G325 for oil layer shielding, anti-collapse agent G339 for drilling fluid, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, which was recorded as sample slurry 1.

[0079] Comparative Example 1

[0080] This comparative example provides a blank water-based drilling fluid without the three plugging agents G325, G314 and G308, wherein, based on the total weight of clean water used to prepare the blank water-based drilling fluid as 100%, the blank water-based drilling fluid comprises:

[0081] Anti-collapse agent G339: 2.0%, high temperature resistant micro-nano filtration reducer G352: 2.0%, solid lubricant graphite powder: 2.0%, liquid lubricant G329: 3.0%, organic salt sodium formate: 3.0%, inorganic salt potassium chloride: 10.0%, alkaline substance sodium hydroxide: 0.1%, flow pattern regulator xanthan gum: 0.2%, weighting agent barite: 5% and clean water.

[0082] The blank water-based drilling fluid provided in this comparative example is prepared by a preparation method comprising the following specific steps:

[0083] Under high-speed stirring conditions, anti-collapse agent G339, high-temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in order according to the proportion, and the blank water-based drilling fluid was prepared after stirring evenly, which was recorded as sample slurry 10.

[0084] Comparative Example 2

[0085] This comparative example provides a water-based drilling fluid to which only one plugging agent, G308, is added, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0086] Film-forming plugging agent G308: 3.0%, anti-collapse agent G339: 2.0%, high temperature resistant micro-nano filtration reducer G352: 2.0%, solid lubricant graphite powder: 2.0%, liquid lubricant G329: 3.0%, sodium formate: 3.0%, potassium chloride: 10.0%, sodium hydroxide: 0.1%, flow pattern regulator xanthan gum: 0.2%, barite: 5% and clean water.

[0087] The water-based drilling fluid provided in this comparative example is prepared by a preparation method comprising the following specific steps:

[0088] Film-forming plugging agent G308, anti-collapse agent G339, high-temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to clean water in sequence according to the proportions, and the water-based drilling fluid was prepared after stirring evenly, which was recorded as sample slurry 11.

[0089] Comparative Example 3

[0090] This comparative example provides a water-based drilling fluid to which only the rapid plugging agent G314 is added, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0091] Quick plugging agent G314: 1.0%, anti-collapse agent G339: 2.0%, high temperature resistant micro-nano filtration reducer G352: 2.0%, solid lubricant graphite powder: 2.0%, liquid lubricant G329: 3.0%, sodium formate: 3.0%, potassium chloride: 10.0%, sodium hydroxide: 0.1%, flow pattern regulator xanthan gum: 0.2%, barite: 5% and clean water.

[0092] The water-based drilling fluid provided in this comparative example is prepared by a preparation method comprising the following specific steps:

[0093] Under high-speed stirring conditions, quick plugging agent G314, anti-collapse agent G339, high-temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after stirring evenly, which was recorded as sample slurry 12.

[0094] Comparative Example 4

[0095] This comparative example provides a water-based drilling fluid to which only one plugging agent, oil layer shielding temporary plugging agent G325, is added, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid as 100%, the water-based drilling fluid comprises:

[0096] Oil layer shielding temporary plugging agent G325: 1.0%, anti-collapse agent G339: 2.0%, high temperature resistant micro-nano filtration reducer G352: 2.0%, solid lubricant graphite powder: 2.0%, liquid lubricant G329: 3.0%, sodium formate: 3.0%, potassium chloride: 10.0%, sodium hydroxide: 0.1%, flow pattern regulator xanthan gum: 0.2%, barite: 5% and clean water.

[0097] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0098] Under the condition of high-speed stirring, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after stirring evenly, which was recorded as sample slurry 13.

[0099] Example 2

[0100] This embodiment provides a water-based drilling fluid, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0101] Film-forming plugging agent G308: 6.0%, quick plugging agent G314: 2.0%, oil layer shielding temporary plugging agent G325: 2.0%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, liquid lubricant G329: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0102] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0103] Under high-speed stirring conditions, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in order according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, recorded as sample slurry 2.

[0104] Comparative Example 5

[0105] This comparative example provides a water-based drilling fluid without adding liquid lubricant G329, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid as 100%, the water-based drilling fluid comprises:

[0106] Film-forming plugging agent G308: 6.0%, quick plugging agent G314: 2.0%, oil layer shielding temporary plugging agent G325: 2.0%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0107] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0108] Under high-speed stirring conditions, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, recorded as test slurry 21.

[0109] Comparative Example 6

[0110] This comparative example provides a water-based drilling fluid using oleic acid ester as a lubricant for water-based drilling fluid, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0111] Film-forming plugging agent G308: 6.0%, fast plugging agent G314: 2.0%, oil layer shielding temporary plugging agent G325: 2.0%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, lubricant oleate for water-based drilling fluid: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0112] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0113] Under the condition of high-speed stirring, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, lubricant oleate for water-based drilling fluid, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, recorded as test slurry 22.

[0114] Comparative Example 7

[0115] This comparative example provides a water-based drilling fluid using a drilling fluid lubricant vegetable oil, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0116] Film-forming plugging agent G308: 6.0%, fast plugging agent G314: 2.0%, oil layer shielding temporary plugging agent G325: 2.0%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, lubricant vegetable oil for water-based drilling fluid: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0117] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0118] Under the condition of high-speed stirring, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, drilling fluid lubricant vegetable oil, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, recorded as test slurry 23.

[0119] Example 3

[0120] This embodiment provides a water-based drilling fluid, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0121] Film-forming plugging agent G308: 8.0%, quick plugging agent G314: 2.0%, oil layer shielding temporary plugging agent G325: 2.0%, the total amount of three plugging agents is 12%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, liquid lubricant G329: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0122] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0123] Under high-speed stirring conditions, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in order according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, recorded as sample slurry 3.

[0124] Comparative Example 8

[0125] This comparative example provides a water-based drilling fluid in which the mass ratio of three plugging agents is lower than 3:1:1, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0126] Film-forming plugging agent G308 for drilling fluid: 4.0%, quick plugging agent G314 for drilling fluid: 4.0%, temporary plugging agent for oil layer shielding G325: 4.0%, the total addition amount of three plugging agents is 12%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, liquid lubricant G329: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0127] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0128] Under the condition of high-speed stirring, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, which was recorded as sample slurry 31.

[0129] Comparative Example 9

[0130] This comparative example provides a water-based drilling fluid in which the mass ratio of the three plugging agents is higher than 6:1:1, wherein, based on the total weight of clean water used to prepare the water-based drilling fluid being 100%, the water-based drilling fluid comprises:

[0131] Film-forming plugging agent G308: 10.0%, quick plugging agent G314: 1.0%, oil layer shielding temporary plugging agent G325: 1.0%, the total amount of three plugging agents is 12%, anti-collapse agent G339: 3.0%, high temperature resistant micro-nano filtration reducer G352: 3.0%, solid lubricant graphite powder: 3.0%, liquid lubricant G329: 4.0%, sodium formate: 4.0%, potassium chloride: 12.0%, sodium hydroxide: 0.2%, flow pattern regulator xanthan gum: 0.3%, barite: 5% and clean water.

[0132] The water-based drilling fluid provided in this embodiment is prepared by a preparation method comprising the following specific steps:

[0133] Under the condition of high-speed stirring, film-forming plugging agent G308, quick plugging agent G314, oil layer shielding temporary plugging agent G325, anti-collapse agent G339, high temperature resistant micro-nano filtration reducer G352, solid lubricant graphite powder, liquid lubricant G329, sodium formate, potassium chloride, sodium hydroxide, flow pattern regulator xanthan gum and barite were added to the clean water in sequence according to the proportion, and the water-based drilling fluid was prepared after uniform stirring, which was recorded as sample slurry 32.

[0134] The plugging effect, lubrication performance and anti-collapse performance of the sample slurries prepared in the examples and comparative examples were tested.

[0135] First, the OFITE permeability plugging instrument was used to test the plugging capacity of test slurry 1 and sample slurries 10, 11, 12 and 13, and the plugging capacity under ceramic filter loss disks with different permeabilities was examined to analyze and compare the plugging performance of the water-based drilling fluid obtained before and after adding different plugging agents. Among them, the plugging performance comparison between sample slurry 1 and sample slurries 10-13 is shown in the figure. Figure 1 As shown, from Figure 1 It can be seen that compared with the plugging amount of sample slurry 1 obtained by adding three plugging agents (G308, G314 and G325) in Example 1, the plugging amounts of sample slurries 10-13 are significantly higher, and the plugging amount of sample slurry 10 without adding the three plugging agents G308, G314 and G325 is the highest. Although the three types of plugging agents can also reduce the plugging amount to varying degrees and have a certain plugging effect when used alone, they are far inferior to the plugging effect of using the three plugging agents at the same time. Only when three different types of plugging agents are used at the same time can the best plugging effect be achieved.

[0136] Then, the lubrication performance of test slurry 2 and sample slurries 21, 22, and 23 were tested respectively according to the SY-T 6094-1994 drilling fluid lubricant evaluation procedure. The tested parameter was the extreme pressure lubrication coefficient, and the lubrication performance of the water-based drilling fluid obtained before and after the addition of lubricants was analyzed and compared. Among them, the lubrication performance comparison between test slurry 2 and sample slurries 21, 22, and 23 is shown in the figure. Figure 2 As shown, from Figure 2 It can be seen that the lubrication performance of the water-based drilling fluid obtained by adding the oil-based drilling fluid wetting agent G329 in Example 2, that is, sample slurry 2, is significantly improved, which is specifically manifested in that the extreme pressure lubrication coefficient is greatly reduced, and the extreme pressure lubrication coefficient is lower than that of sample slurries 22 and 23 to which the water-based drilling fluid lubricant is added, and even lower than that of sample slurry 21 to which no water-based drilling fluid lubricant is added, indicating that the lubrication performance of the oil-based drilling fluid wetting agent G329 is better than that of the commonly used water-based drilling fluid lubricant.

[0137] Finally, the existing method for testing linear expansion and recovery rate in the art was used to test the anti-collapse performance of sample slurry 3, sample slurries 31, 32 and clean water on coal rock. The comparison of linear expansion of sample slurry 3, sample slurries 31, 32 and clean water is shown in the figure. Figure 3 As shown in FIG. 1 , the coal powder is pressed into a standard coal column at 40 MPa, and the linear expansion amount of the coal column in the sample slurry is tested using a linear expansion instrument commonly used in the art. Figure 3 It can be seen that the expansion amount of sample slurry 32 with a mass ratio of the three types of plugging agents higher than 6:1:1 is the lowest. This does not mean that the plugging performance of sample slurry 32 is the best. On the contrary, the coal pillar corresponding to sample slurry 32 collapsed first, indicating that the plugging performance of sample slurry 32 is the worst. This is because the amount of rapid plugging agent added is insufficient, resulting in the rapid plugging agent unable to quickly adsorb and deposit on the formation surface, reduce the damage of drilling fluid to the coal seam, and unable to quickly form the first plugging film on the surface of micro-cracks and micro-fissures in the coal seam, resulting in the collapse of the coal pillar; the expansion amount of sample slurry 31 with a mass ratio of the three types of plugging agents lower than 3:1:1 is low at the beginning, but the coal pillar collapsed after 3 hours, resulting in a decrease in the later expansion amount. The reason is that the amount of film-forming plugging agent added is insufficient, resulting in the inability of the film-forming plugging agent to form a dense plugging film. As time goes by, the drilling fluid filtrate gradually invades the coal pillar and eventually collapses. Although the total dosage of the three types of plugging agents is the same, all 12%, the plugging performance of sample slurry 3 with a mass ratio between 3:1:1-6:1:1 is significantly better than that of the other two sample slurries. That is, the water-based drilling fluid with a ratio not within the range of 3:1:1-6:1:1 does not meet the anti-collapse performance of the coal seam and there is a greater risk of well collapse.

[0138] The coal dust with a particle size of 6-10 mesh was used as the object of recovery test. The recovery rate method commonly used in the field was used to test the recovery rate of coal dust in the sample slurry. The test temperature was 120℃ and the hot rolling time was 16h. The test results are as follows: Figure 4 As shown by Figure 4 It can be seen that the first expansion of sample slurry 32 with a mass ratio of the three types of plugging agents higher than 6:1:1 is the lowest, indicating that the plugging performance of sample slurry 32 is the worst in the initial stage. This is due to the insufficient amount of rapid plugging agent, which leads to the rapid plugging agent not being able to quickly adsorb and deposit on the formation surface, reduce the damage of drilling fluid to the coal seam, and cannot quickly form the first plugging film on the surface of micro-cracks and micro-cracks in the coal seam. The coal dust was hydrated and dispersed in the early stage of the test; the second recovery rate of sample slurry 31 with a mass ratio of the three types of plugging agents lower than 3:1:1 is the lowest. The reason is that the amount of film-forming plugging agent is insufficient, which leads to the inability of film-forming plugging agent to form a dense plugging film. As time goes by, the drilling fluid filtrate gradually invades the coal dust, and the coal dust is hydrated and dispersed in the later stage of the test. Although the total amount of the three types of plugging agents is the same, all 12%, the first recovery rate and second recovery rate of sample slurry 3 with a mass ratio between 3:1:1 and 6:1:1 are significantly better than the other two sample slurries.

[0139] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A water-based drilling fluid for deep coalbed methane horizontal wells, characterized in that: Taking the total weight of clean water used in preparing the water-based drilling fluid as 100%, the mass percentages of the components in the water-based drilling fluid are: 3.0-9.0% of a film-forming plugging agent, 1.0-3.0% of a quick plugging agent, 1.0-3.0% of an oil layer shielding temporary plugging agent, 2.0-4.0% of an anti-collapse agent, 1.0-5.0% of a fluid loss reducer, 2.0-5.0% of a solid lubricant, 3.0-5.0% of a liquid lubricant, 3.0-6.0% of an organic salt, 10-25% of an inorganic salt, 0.1-0.5% of an alkali substance, 0.2-0.5% of a flow pattern regulator, and the remainder is a weighting agent and water.

2. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The rapid plugging agent includes the plugging agent G314 for drilling fluid, The film-forming plugging agent includes the plugging agent G308 for drilling fluid, The oil layer shielding temporary plugging agent includes drilling fluid shielding temporary plugging agent G325, The mass ratio of the film-forming plugging agent, the rapid plugging agent and the oil layer shielding temporary plugging agent is 3-6:1:

1.

3. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The anti-collapse agent includes at least one of emulsified asphalt, modified asphalt and sulfonated asphalt.

4. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The fluid loss reducer includes high temperature resistant micro-nano fluid loss reducer G352 for drilling fluid.

5. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The solid lubricant includes graphite powder and / or elastic graphite.

6. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The liquid lubricant includes G329, a wetting agent for oil-based drilling fluid.

7. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The organic salt includes at least one of sodium acetate, potassium acetate, sodium formate and potassium formate; The inorganic salt includes at least one of potassium chloride, potassium sulfate, sodium chloride and potassium nitrate.

8. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The alkaline substance includes sodium hydroxide and / or potassium hydroxide.

9. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The flow pattern regulator includes at least one of locust bean gum, sesbania gum, guar gum, xanthan gum, hydroxypropyl sesbania gum, hydroxypropyl guar gum, carboxymethyl guar gum and carboxymethyl sesbania gum.

10. The water-based drilling fluid for deep coalbed methane horizontal well according to claim 1, characterized in that: The weighting agent includes at least one of barite, iron ore powder and limestone, and the amount of the weighting agent is determined according to the target density of the water-based drilling fluid.

11. A method for preparing a water-based drilling fluid for a deep coalbed methane horizontal well, characterized in that: include: Under stirring conditions, adding a quick plugging agent, a film-forming plugging agent, an oil layer shielding temporary plugging agent, an anti-collapse agent, a fluid loss reducer, a solid lubricant, a liquid lubricant, an inorganic salt, an organic salt, an alkali substance, a flow pattern regulator and a weighting agent to water according to a proportion, and stirring evenly to obtain the water-based drilling fluid; Wherein, taking the total weight of water used in preparing the water-based drilling fluid as 100%, the mass percentages of the components in the water-based drilling fluid are: 3.0-9.0% of film-forming plugging agent, 1.0-3.0% of quick plugging agent, 1.0-3.0% of oil layer shielding temporary plugging agent, 2.0-4.0% of anti-collapse agent, 1.0-5.0% of filtrate reducer, 2.0-5.0% of solid lubricant, 3.0-5.0% of liquid lubricant, 3.0-6.0% of organic salt, 10-25% of inorganic salt, 0.1-0.5% of alkali substance, 0.2-0.5% of flow pattern regulator, and the balance is weighting agent and water.

12. An application of water-based drilling fluid for deep coalbed methane horizontal wells, characterized in that: Horizontal well drilling construction is carried out using the water-based drilling fluid described in any one of claims 1 to 10.

13. The use of a water-based drilling fluid for deep coalbed methane horizontal wells according to claim 12, characterized in that: The horizontal wells include horizontal wells in coal-bearing strata with a vertical depth greater than 1500m.

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