Water-based drilling fluid

Abstract

The present application relates to a water-based drilling fluid, the water-based drilling fluid comprises the following raw material components: a composite inhibitor, the composite inhibitor comprises a shale inhibitor, a surfactant and formate, the surfactant has a wetting reversal effect, and the chemical components of the shale inhibitor comprise potassium ions and / or ammonium ions; the composite plugging agent comprises a flexible plugging agent, a rigid plugging agent and a micro-nano plugging agent; wherein the weight ratio of the surfactant to the shale inhibitor to the formate is (1-2): (1-7): (5-7); the weight ratio of the flexible blocking agent to the rigid blocking agent to the micro-nano blocking agent is (2-3): (2-3): (1-5). The technical problem that when an existing sea-land transition phase shale horizontal well is drilled, the well wall is unstable is solved.

Description

Technical Field

[0001] This application relates to the technical field of oil and gas drilling, and particularly relates to an aqueous drilling fluid. Background Art

[0002] Shale gas is currently the focus of global resource exploration and development. Marine-continental transitional shale belongs to brittle shale, with low shale compressive strength, high fragmentation degree, sensitivity to bottom-hole pressure difference, and easy spalling and chipping after the new formation is drilled, resulting in pump jamming and top drive jamming during drilling; shale has bedding, and the width of microcracks is 2μm in the natural state, with strong self-absorption capillary effect. Due to self-absorption, the shale strength is reduced, and wellbore collapse is likely to occur; the proportion of clay minerals in the rock components is high, and the clay minerals are mainly kaolinite, illite-montmorillonite mixed layer and illite, without montmorillonite. The clay hydration is mainly surface hydration, and shale belongs to low expansion and low dispersion, and the hydration effect is generally weak.

[0003] Therefore, there is a problem of wellbore instability during the horizontal well drilling of existing marine-continental transitional shale. Summary of the Invention

[0004] This application provides an aqueous drilling fluid to solve the technical problem of wellbore instability during the horizontal well drilling of existing marine-continental transitional shale.

[0005] In a first aspect, this application provides an aqueous drilling fluid, and the raw material components of the aqueous drilling fluid include:

[0006] A composite inhibitor, the composite inhibitor includes a shale inhibitor, a surfactant, and formate. The surfactant has a wetting reversal effect, and the chemical composition of the shale inhibitor includes potassium ions and / or ammonium ions;

[0007] A composite plugging agent, the composite plugging agent includes a flexible plugging agent, a rigid plugging agent, and a micro-nano plugging agent; wherein,

[0008] The weight ratio of the surfactant, the shale inhibitor, and the formate is (1-2):(1-7):(5-7);

[0009] The weight ratio of the flexible plugging agent, the rigid plugging agent, and the micro-nano plugging agent is (2-3):(2-3):(1-5).

[0010] Optionally, the shale inhibitor includes at least one of the following: potassium chloride, potassium hydroxide, amino polyol, amino silanol.

[0011] Optionally, the surfactant includes at least one of the following: alkyl glycoside quaternary ammonium salt, organic amine.

[0012] Optionally, the formate includes at least one of the following: potassium formate, sodium formate, cesium formate.

[0013] Optionally, the flexible plugging agent includes at least one of the following: white asphalt, emulsified asphalt, sulfonated asphalt, and modified asphalt.

[0014] Optionally, the rigid plugging agent includes at least one of the following: micron calcium carbonate, quartz sand, and fiber.

[0015] Optionally, the micro-nano plugging agent includes at least one of the following: nano-silica emulsion, multi-vinyl polymer emulsion, and emulsified paraffin micro-emulsion.

[0016] Optionally, the raw material components of the water-based drilling fluid further include: bentonite, sodium carbonate, pH regulator, viscosifier, filtration reducer, lubricant, and weighting agent.

[0017] Optionally, the pH regulator includes at least one of the following: sodium hydroxide, potassium hydroxide; and / or,

[0018] The viscosifier includes at least one of the following: biopolymer xanthan gum, amphoteric composite ionic polymer; and / or,

[0019] The filtration reducer includes at least one of the following: polyanionic cellulose, starch, modified starch; and / or,

[0020] The lubricant includes at least one of the following: vegetable oil modified lubricant, graphite powder solid lubricant, polyhydric alcohol lubricant; and / or,

[0021] The weighting agent includes at least one of the following: barite, limestone.

[0022] Optionally, in terms of parts by weight, relative to 1000 parts of water in the water-based drilling fluid,

[0023] the flexible plugging agent is 20 to 30 parts, the rigid plugging agent is 20 to 30 parts, the micro-nano plugging agent is 10 to 50 parts, the surfactant is 10 to 20 parts, the shale inhibitor is 10 to 70 parts, the formate is 50 to 70 parts, the bentonite is 20 to 40 parts, the sodium carbonate is 0.5 to 2 parts, the pH regulator is 1 to 2 parts, the viscosifier is 1 to 2 parts, the filtration reducer is 15 to 35 parts, the lubricant is 20 to 40 parts, and the weighting agent is 290 to 340 parts.

[0024] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0025] The water-based drilling fluid provided by the embodiment of the present application, the composite plugging agent includes a flexible plugging agent, a rigid plugging agent and a micro-nano plugging agent. The flexible plugging agent has no fixed-shaped plugging material and is extremely likely to deform or undergo a phase change when the temperature, pressure and other external environments change, so as to plug the micro-pores or fractures of the marine-terrestrial transitional shale; the rigid plugging agent bridges and fills the micro-fractures of the marine-terrestrial transitional shale reservoir with a size matching the micro-fractures, so as to form a dense plugging layer; the micro-nano plugging agent is a plugging agent with a particle size main peak distributed at the nano level, and can form a dense polymer film on the surface of the porous formation through filtration loss; the nano-emulsion can enter the nano-level micro-fractures and pores; by compounding plugging agents with different particle size distributions, the plugging of micro-fractures of marine-terrestrial transitional shale with different sizes can be realized, and a dense plugging layer is formed on the micro-fractures and the shale surface; the composite inhibitor includes a surfactant, a shale inhibitor and formate. The surfactant has a wetting reversal effect, and the chemical composition of the shale inhibitor includes potassium ions and / or ammonium ions; the surfactant with a wetting reversal effect can effectively reduce the surface tension of the drilling fluid filtrate, increase the wetting angle of the filtrate on the surface of the marine-terrestrial transitional shale, thereby reducing the capillary suction of the micro-fractures; the shale inhibitor containing potassium ions or ammonium ions uses its intercalation effect between the crystal layers in the clay minerals to reduce the hydration swelling of the clay minerals in the marine-terrestrial transitional shale, provide high salinity mineral ions for the drilling fluid, and strengthen the role of the activity regulator; the formate and the shale inhibitor interact with each other to adjust the activity of the drilling fluid to be equal to or less than the activity of the formation water, thereby realizing the reverse osmosis effect of the drilling fluid filtrate. In summary, through the synergistic effect of the composite plugging agent and the composite inhibitor, the technical problem of wellbore instability during the horizontal well drilling of the existing marine-terrestrial transitional shale is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The accompanying drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a microscopic image of the plugging effect of a water-based drilling fluid provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of this application. Apparently, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0030] The various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] In this application, unless otherwise stated, the orientation terms such as "upper" and "lower" specifically refer to the drawing directions in the accompanying drawings. Additionally, in the description of this application's specification, the terms "include", "comprise", etc. mean "include but not limited to". In this text, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. In this text, "and / or" describes the association relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone. Here, A and B may be singular or plural. In this text, "at least one" means one or more, and "multiple" means two or more. "At least one kind", "at least one of the following items", or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0032] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, equipment, etc. used in this application can be obtained through market purchases or can be prepared by existing methods.

[0033] The present application provides an aqueous drilling fluid, and the raw material components of the aqueous drilling fluid include:

[0034] A composite inhibitor, which includes a shale inhibitor, a surfactant, and formate. The surfactant has a wetting reversal effect, and the chemical composition of the shale inhibitor includes potassium ions and / or ammonium ions;

[0035] A composite plugging agent, which includes a flexible plugging agent, a rigid plugging agent, and a micro-nano plugging agent; wherein,

[0036] The weight ratio of the surfactant, the shale inhibitor, and the formate is (1-2):(1-7):(5-7);

[0037] The weight ratio of the flexible plugging agent, the rigid plugging agent, and the micro-nano plugging agent is (2-3):(2-3):(1-5).

[0038] In the embodiment of the present application, in the transitional marine-continental shale in the Daning Jixian block, brittle shale microfractures are well-developed, the capillary imbibition ability is strong, the formation water salinity is high, and the filtrate of the aqueous drilling fluid enters the deep formation along the microfractures under the action of three forces: capillary imbibition force, hydraulic pressure difference between the drilling fluid column and the formation pore pressure, and chemical potential difference between the formation water and the drilling fluid, resulting in the short-term expansion and extension of the microfractures under the hydration action, and the microfractures extend and communicate to form large shale fractures, which macroscopically manifests as wellbore failure and instability. Aiming at solving the technical problem of wellbore instability during the horizontal well drilling of existing brittle shale, through the synergistic effect of the composite plugging agent and the composite inhibitor, the effects of plugging microfractures, weakening capillary force, and achieving reverse osmosis are realized.

[0039] In the embodiment of the present application, physical methods are used to plug microfractures to prevent the filtrate of the aqueous drilling fluid from entering the deep formation; a shale inhibitor is added to inhibit the hydration of clay minerals in the transitional marine-continental shale, so that potassium ions or ammonium ions are embedded and replace water molecules to adsorb between the crystal layers of the shale clay minerals, reducing the hydration swelling force; the shale is regarded as a semi-permeable membrane, and by adding an activity regulator, the activity of the filtrate of the aqueous drilling fluid is made less than that of the formation water, and the principle of the osmotic membrane is used to achieve reverse osmosis, and the filtrate of the drilling fluid is prevented from entering the deep formation by chemical means; the surface of the transitional marine-continental shale is a hydrophilic surface, and the wetting reversal agent can effectively reduce the surface tension of the filtrate of the drilling fluid, increase the wetting angle of the filtrate of the drilling fluid on the shale surface, and thus reduce the capillary imbibition force of the microfractures.

[0040] By using a composite flexible plugging agent, a rigid plugging agent, and a micro-nano plugging agent, a physical plugging method is adopted. According to the different particle size distribution ranges of different plugging agents, broad-spectrum plugging of marine-continental transitional shale reservoirs is achieved, ensuring that the water-based drilling fluid can form a tight plugging layer to prevent filtrate from entering the deep formation. The flexible plugging agent has no fixed shape of the plugging material and is extremely easy to deform or undergo a phase change when the temperature, pressure, and other external environments change, thereby plugging the micro-pores or fractures of the marine-continental transitional shale; the rigid plugging agent bridges and fills the micro-fractures of the marine-continental transitional shale reservoir with a size matching the micro-fractures, thereby forming a tight plugging layer; the micro-nano plugging agent is a plugging agent with a particle size main peak distributed at the nano level, and can form a dense polymer film on the surface of the porous formation through filtration loss; the nano-emulsion can enter nano-scale micro-fractures and pores. It can achieve the plugging of micro-fractures in marine-continental transitional shale with different sizes and form a tight plugging layer on the micro-fractures and the shale surface. Figure 1 The microscopic image of the plugging effect of a water-based drilling fluid provided by an embodiment of the present application; please refer to Figure 1 Therefore, by compounding plugging agents with different particle size distributions, the water-based drilling fluid can achieve the plugging of micro-fractures in marine-continental transitional shale with different sizes and form a tight plugging layer on the micro-fractures and the shale surface.

[0041] By compounding a surfactant, a shale inhibitor, and formate; the surfactant has a wetting reversal effect, and the chemical composition of the shale inhibitor includes potassium ions and / or ammonium ions. By using a chemical inhibition method, the hydration of marine-continental transitional shale is inhibited and the filtrate is prevented from entering the deep formation. The shale inhibitor mainly provides potassium ions or ammonium ions, and uses their intercalation effect between the crystal layers in clay minerals to reduce the hydration swelling of clay minerals in marine-continental transitional shale, provide high salinity mineral ions for the drilling fluid, and strengthen the role of the activity regulator; formate can not only reduce the activity of the drilling fluid but also inhibit the hydration of clay; the surfactant can effectively reduce the surface tension of the drilling fluid filtrate, increase the wetting angle of the drilling fluid filtrate on the shale surface, and reduce the capillary suction force of the micro-fractures. Among them, formate is used to reduce the osmotic pressure difference caused by activity imbalance, the surfactant is used to reduce the capillary force caused by the imbibition effect of micro-fractures, and the shale inhibitor is used to eliminate the hydration clay swelling and dispersion that occur after the water molecules in the filtrate enter the deep formation, synergistically controlling the three hydration effects and facilitating wellbore stability.

[0042] A composite surfactant, a shale inhibitor, and formate are used to inhibit the hydration of marine-continental transitional shale and prevent filtrate from entering the deep formation by chemical inhibition methods. The potassium ions and / or ammonium ions in the shale inhibitor play a role in inhibiting the hydration swelling and dispersion of clay minerals in marine-continental transitional shale. If the content of the shale inhibitor is too high, the inhibition effect has reached saturation; if the content of the shale inhibitor is too low, its inhibition effect will be weakened to a certain extent. The formate adjusts the activity of the drilling fluid to be equal to or less than the activity of the formation water, thereby realizing the reverse osmosis effect of the drilling fluid filtrate; if the content of the formate is too high, the activity of the drilling fluid tends to level off as the activity regulator increases, and the cost of the drilling fluid increases; if the content of the formate is too low, the reverse osmosis effect cannot be achieved, and the chemical potential difference causes the drilling fluid filtrate to enter the formation; the surfactant has a wetting reversal effect, effectively reducing the surface tension of the drilling fluid filtrate, increasing the wetting angle of the filtrate on the surface of marine-continental transitional shale, and thus reducing the capillary suction force of microcracks; if the content of the surfactant is too high, it will increase the cost of the drilling fluid to a certain extent and will not change the wetting reversal effect; if the content of the surfactant is too low, its best effect cannot be achieved to a certain extent, resulting in a poor wetting reversal effect. Specifically, the weight ratio of the surfactant, the shale inhibitor, and the formate can be 1:1:5, 2:5:5, 2:5:5, 2:7:7, 1:3:5, etc.

[0043] The flexible plugging agent, the rigid plugging agent, and the micro-nano plugging agent not only have different plugging principles, but also have different particle size distribution ranges, and they play complementary roles to jointly achieve the broad-spectrum plugging of the entire scale of the wellbore of marine-continental transitional shale by the drilling fluid. By evaluating the plugging performance of the micro-nano level filter membrane indoors and adopting the above composite ratio range, the plugging effect and the filtrate loss reduction effect of the drilling fluid can reach the best; if the content of a certain type of plugging agent is too large, it will thicken the viscosity of the drilling fluid and deteriorate the flow pattern to a certain extent, and it is easy to cause other complex situations; if the content of a certain type of plugging agent is too small, it will affect its plugging effect to a certain extent, causing the filtrate to enter the deep formation and leading to wellbore instability. Specifically, the weight ratio of the above flexible plugging agent, rigid plugging agent, and micro-nano plugging agent can be 2:2:5, 3:3:4, 1:1:1, 3:3:5, etc.

[0044] In some embodiments, the shale inhibitor includes at least one of the following: potassium chloride, potassium hydroxide, amino polyol, and amino silanol.

[0045] In some embodiments, the surfactant includes at least one of the following: alkyl glycoside quaternary ammonium salt, organic amine.

[0046] In some embodiments, the formate includes at least one of the following: potassium formate, sodium formate, cesium formate.

[0047] In the embodiments of the present application, potassium chloride and potassium hydroxide can provide potassium ions, and amino polyalcohol and amino silanol can provide ammonium ions, which play a role in inhibiting the hydration swelling and dispersion of clay minerals in marine-continental transitional shale.

[0048] In the embodiments of the present application, alkyl glycoside quaternary ammonium salts and organic amines are selected as surfactants, which can effectively reduce the surface tension of the drilling fluid filtrate and increase the wetting angle of the filtrate on the surface of marine-continental transitional shale.

[0049] In the embodiments of the present application, potassium formate, sodium formate, and cesium formate, as formates and organic salts, can mainly improve the salinity of the drilling fluid and regulate the activity of the drilling fluid, so that the activity of the drilling fluid is lower than that of formation water.

[0050] In some embodiments, the flexible plugging agent includes at least one of the following: white asphalt, emulsified asphalt, sulfonated asphalt, and modified asphalt.

[0051] In some embodiments, the rigid plugging agent includes at least one of the following: micron calcium carbonate, quartz sand, and fiber.

[0052] In some embodiments, the micro-nano plugging agent includes at least one of the following: nano-silica emulsion, multi-vinyl polymer emulsion, and micro-emulsion of emulsified paraffin.

[0053] In the embodiments of the present application, when white asphalt, emulsified asphalt, sulfonated asphalt, and modified asphalt are selected as the flexible plugging agent, they can emulsify with water and clay, and can form tough particles at different temperatures to block the micro-fractures of the formation and the pores of the permeable formation, playing a role in reducing fluid loss, preventing formation collapse, and protecting the oil and gas reservoir. When micron calcium carbonate, quartz sand, and fiber are selected as the rigid plugging agent, the micron-sized rigid plugging agent plays a role in filling and bridging, and can well complement and support the flexible plugging agent in the formation fractures to jointly form a tight plugging layer. The calcium carbonate with 1200 mesh can be selected for the micron calcium carbonate. When nano-silica emulsion, multi-vinyl polymer emulsion, and micro-emulsion of emulsified paraffin are selected as the micro-nano plugging agent, this type of plugging agent is mainly distributed in the particle size range of 0.5 - 1 μm, which can plug the micro-fractures of the shale formation and prevent the filtrate from entering the deep part of the formation.

[0054] In some embodiments, the raw material components of the water-based drilling fluid further include: bentonite, sodium carbonate, pH regulator, viscosifier, fluid loss reducer, lubricant, and weighting agent.

[0055] In some embodiments, the pH regulator includes at least one of the following: sodium hydroxide, potassium hydroxide; and / or

[0056] The tackifier includes at least one of the following: biopolymer xanthan gum, amphoteric composite ionic polymer; and / or,

[0057] The fluid loss reducer includes at least one of the following: polyanionic cellulose, starch, modified starch; and / or,

[0058] The lubricant includes at least one of the following: vegetable oil modified lubricant, graphite powder solid lubricant, polyhydric alcohol lubricant; and / or,

[0059] The weighting agent includes at least one of the following: barite, limestone.

[0060] In the embodiments of the present application, the tackifier improves the rheological properties of the drilling fluid, enhances the rock-carrying capacity of the drilling fluid, and ensures the safety of drilling operations; the fluid loss reducer can effectively control the fluid loss of the water-based drilling fluid and improve the filter cake quality by adding a fluid loss reducer to the water-based drilling fluid, thereby preventing excessive filtrate from entering the deep formation; the lubricant effectively reduces the frictional torque during drilling and ensures the safe drilling and extension of the horizontal wellbore of shale gas in the marine-terrestrial transitional facies; the pH regulator stabilizes the performance of the drilling fluid; the weighting agent is used to weight the drilling fluid to the designed density, bentonite is the main mud-making raw material, and sodium carbonate is used to modify the bentonite slurry to improve the hydration mud-making ability of bentonite.

[0061] In some embodiments, based on parts by weight, relative to 1000 parts of water in the water-based drilling fluid,

[0062] The flexible plugging agent is 20 parts to 30 parts, the rigid plugging agent is 20 parts to 30 parts, the micro-nano plugging agent is 10 parts to 50 parts, the alkyl glycoside quaternary ammonium salt is 10 parts to 20 parts, the shale inhibitor is 10 parts to 70 parts, the formate is 50 parts to 70 parts, the bentonite is 20 to 40 parts, the sodium carbonate is 0.5 to 2 parts, the pH regulator is 1 to 2 parts, the tackifier is 1 to 2 parts, the fluid loss reducer is 15 to 35 parts, the lubricant is 20 to 40 parts, and the weighting agent is 290 to 340 parts.

[0063] In the embodiments of the present application, with respect to the water in 1000 parts of the above water-based drilling fluid, the composition of the raw materials is reasonably controlled to achieve a water-based drilling fluid with excellent performance. Specifically, the above flexible plugging agent can be 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, etc.; the above rigid plugging agent can be 20 parts, 22 parts, 24 parts, 26 parts, 28 parts, 30 parts, etc.; the above micro-nano plugging agent is 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, etc.; the above surfactant can be 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts, etc.; the above shale inhibitor can be 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts, 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, etc.; the above formate can be 50 parts, 55 parts, 60 parts, 65 parts, 70 parts, etc.; the above bentonite can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, etc.; the above pH regulator can be 1 part, 1.5 parts, 2 parts, etc.; the above sodium carbonate can be 0.5 part, 1 part, 2 parts; the above viscosifier can be 1 part, 1.5 parts, 2 parts, etc.; the above filtration reducer can be 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, etc.; the above lubricant can be 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, etc.; the above weighting agent can be 290 parts, 300 parts, 310 parts, 320 parts, 330 parts, 340 parts, etc.

[0064] The preparation method of the above water-based drilling fluid: Add bentonite and stir under electric stirring at normal temperature, then add sodium carbonate and stir. Pre-hydrate under normal temperature and pressure. When preparing the mud, first stir the pre-hydrated bentonite slurry, and then add the medicaments in a slow addition manner with the high-speed stirrer speed; then add the viscosifier and the filtration reducer and stir; then add the composite plugging agent and stir; then add the composite inhibitor and stir; then add the lubricant and stir; then add barite to adjust the density of the drilling fluid to; finally, use the pH regulator to adjust the system, and then let it stand for use to obtain the water-based drilling fluid.

[0065] A water-based drilling fluid provided by the present application has at least the following beneficial effects:

[0066] (1) It can specifically solve the problem of wellbore instability in horizontal wells of marine-continental transitional shale gas in the Daning Jixian block;

[0067] (2) The cost of the water-based drilling fluid of this innovative achievement is lower than that of the oil-based drilling fluid, and it has good economy.

[0068] Specifically, the water-based drilling fluid of the embodiments of the present application has supported the completion of 4 horizontal wells in the marine-terrestrial transitional shale gas block in Daning-Jixian County. The average total depth of the completed wells is 3,701 m, the average horizontal section length is 1,451.75 m, and the average mechanical drilling rate of the horizontal section is 7.60 m / h. The system has good performance during use and stable wellbore. The successful application of this system effectively supports the shale gas production in the marine-terrestrial transitional zone of the Daning-Jixian County block.

[0069] The following further elaborates the present application in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application. The experimental methods without specific conditions noted in the following embodiments are generally determined according to national standards. If there is no corresponding national standard, they are carried out according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0070] Example 1

[0071] A water-based drilling fluid is prepared from the following raw material components in parts by weight:

[0072] 20 parts of bentonite, 0.5 part of sodium carbonate, 1 part of sodium hydroxide, 1 part of biopolymer xanthan gum, 20 parts of starch, 10 parts of polyanionic cellulose, 70 parts of potassium chloride, 50 parts of potassium formate, 10 parts of alkyl glycoside quaternary ammonium salt inhibitor, 20 parts of white asphalt, 30 parts of 1200-mesh calcium carbonate, 20 parts of microemulsion of emulsified paraffin wax, 10 parts of multi-vinyl polymer emulsion, 40 parts of vegetable oil-modified lubricant, 1000 parts of water.

[0073] Example 2

[0074] A water-based drilling fluid is prepared from the following raw material components in parts by weight:

[0075] 20 parts of bentonite, 0.5 part of sodium carbonate, 2 parts of sodium hydroxide, 2 parts of biopolymer xanthan gum, 20 parts of starch, 5 parts of polyanionic cellulose, 50 parts of potassium chloride, 50 parts of potassium formate, 10 parts of alkyl glycoside quaternary ammonium salt inhibitor, 20 parts of white asphalt, 20 parts of 1200-mesh calcium carbonate, 20 parts of microemulsion of emulsified paraffin wax, 10 parts of multi-vinyl polymer emulsion, 20 parts of vegetable oil-modified lubricant, 1000 parts of water.

[0076] Example 3

[0077] A water-based drilling fluid is prepared from the following raw material components in parts by weight:

[0078] 20 parts of bentonite, 0.5 part of sodium carbonate, 2 parts of sodium hydroxide, 2 parts of biopolymer xanthan gum, 20 parts of starch, 10 parts of polyanionic cellulose, 50 parts of potassium chloride, 70 parts of potassium formate, 20 parts of alkyl glycoside quaternary ammonium salt inhibitor, 20 parts of white asphalt, 30 parts of 1200-mesh calcium carbonate, 30 parts of emulsified paraffin microemulsion, 10 parts of multi-vinyl polymer emulsion, 40 parts of vegetable oil modified lubricant, 1000 parts of water.

[0079] Example 4

[0080] An aqueous drilling fluid is prepared from the following raw material components in parts by weight:

[0081] 40 parts of bentonite, 2 parts of sodium carbonate, 1 part of sodium hydroxide, 1 part of biopolymer xanthan gum, 10 parts of starch, 10 parts of low-viscosity polyanionic cellulose, 70 parts of potassium chloride, 50 parts of potassium formate, 10 parts of alkyl glycoside quaternary ammonium salt inhibitor, 30 parts of white asphalt, 20 parts of 1200-mesh calcium carbonate, 20 parts of emulsified paraffin microemulsion, 20 parts of multi-vinyl polymer emulsion, 20 parts of vegetable oil modified lubricant, 1000 parts of water.

[0082] Example 5

[0083] An aqueous drilling fluid is prepared from the following raw material components in parts by weight:

[0084] 40 parts of bentonite, 2 parts of sodium carbonate, 1 part of sodium hydroxide, 1 part of biopolymer xanthan gum, 10 parts of starch, 15 parts of low-viscosity polyanionic cellulose, 70 parts of potassium chloride, 70 parts of potassium formate, 20 parts of alkyl glycoside quaternary ammonium salt inhibitor, 30 parts of white asphalt, 30 parts of 1200-mesh calcium carbonate, 30 parts of emulsified paraffin microemulsion, 20 parts of multi-vinyl polymer emulsion, 40 parts of vegetable oil modified lubricant, 1000 parts of water.

[0085] Comparative Example 1

[0086] An aqueous drilling fluid is prepared from the following raw material components in parts by weight:

[0087] 20 parts of bentonite, 0.5 part of sodium carbonate, 1 part of sodium hydroxide, 1 part of biopolymer xanthan gum, 20 parts of starch, 10 parts of low-viscosity polyanionic cellulose.

[0088] Comparative Example 2

[0089] The difference from Example 1 is that potassium chloride, potassium formate and alkyl glycoside quaternary ammonium salt inhibitor are not added to the aqueous drilling fluid system.

[0090] Comparative Example 3

[0091] The difference from Example 1 is that white asphalt, 1200-mesh calcium carbonate, emulsified paraffin microemulsion and multi-vinyl polymer emulsion are not added to the aqueous drilling fluid system.

[0092] Refer to the standard B / T 16783.1-2014 "Petroleum and natural gas industries - Field testing of drilling fluids - Part 1: Water-based drilling fluids" to test the performance of the drilling fluid system; refer to the standard SY / T 5613-2016 "Test method for physical and chemical properties of mud shale in drilling fluid testing" to test the linear expansion rate and rolling recovery rate of marine-terrestrial transitional shale after immersion in the drilling fluid.

[0093] The effects of the water-based drilling fluids in Examples 1 to 5 and Comparative Examples 1 to 3 are described below.

[0094] 1. Experimental results of the conventional properties of the water-based drilling fluid system

[0095] The average reservoir temperature in the Daning-Jixian block is 65°C, and the thermal rolling test condition is thermal rolling at 80°C for 16 h. The rheological properties of the drilling fluid system in the examples of this application change little before and after aging, and the filtration loss decreases slightly. Therefore, this drilling fluid system has good temperature resistance and can meet the requirements of on-site construction for the performance of the drilling fluid. For specific details, please refer to the rheological property test results of the system before and after aging shown in Table 1.

[0096] Table 1 Rheological property test results of the water-based drilling fluid system before and after aging

[0097]

[0098]

[0099] 2. Experimental results of the inhibition performance of the water-based drilling fluid system

[0100] The inhibition performance experiment of the water-based drilling fluid system was carried out using the marine-terrestrial transitional shale rock samples in the Daning-Jixian block. By analyzing the experimental results of the examples and comparative examples, it can be seen that the rolling recovery rate of the marine-terrestrial transitional shale rock samples in the examples is > 98% and the linear expansion rate is < 2% after immersion, while in Comparative Example 1 and Comparative Example 2, the rolling recovery rate is close to 95% and the linear expansion rate is close to 5%. This is because the various inhibitors in the water-based drilling fluid system in the examples of this application act synergistically, which will significantly increase the inhibition performance of the drilling fluid system. For specific details, please refer to the inhibition performance test results of the water-based drilling fluid shown in Table 2.

[0101] Table 2 Inhibition performance test results of the water-based drilling fluid

[0102] Example Rolling recovery rate / % Linear expansion rate / % Example 1 98.81 1.03 Example 2 98.83 1.12 Example 3 98.56 1.05 Example 4 99.01 1.10 Example 5 98.51 1.07 Comparative Example 1 94.22 5.33 Comparative Example 2 95.63 4.85

[0103] 3. Experimental results of the plugging performance of the water-based drilling fluid system

[0104] The filtration loss of the drilling fluid systems of Examples 1 to 5 and Comparative Examples 1 to 3 was measured indoors using a 2-μm microporous filter membrane. Compared with Comparative Example 1 and Comparative Example 3, the filtration loss of the drilling fluid systems of the examples of the present application was significantly reduced, indicating good plugging performance. After the experiment, the filter cake had good compactness, and the tight filter cake could effectively prevent the drilling fluid from entering the formation. For specific details, please refer to the plugging performance test results of the water-based drilling fluid shown in Table 3.

[0105] Table 3 Plugging Performance Test Results of Water-Based Drilling Fluid

[0106] Example Medium pressure filtration loss volume in 30 min / mL Example 1 2.6 Example 2 3.4 Example 3 2.8 Example 4 3.0 Example 5 2.4 Comparative Example 1 8.5 Comparative Example 3 7.8

[0107] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A water-based drilling fluid, characterized in that, The raw material components of the water-based drilling fluid include: A composite inhibitor, which includes a shale inhibitor, a surfactant, and a formate. The surfactant has a wetting reversal effect, and the chemical composition of the shale inhibitor includes potassium ions and / or ammonium ions; A composite plugging agent, which includes a flexible plugging agent, a rigid plugging agent, and a micro-nano plugging agent; wherein, The weight ratio of the surfactant, the shale inhibitor, and the formate is (1-2):(1-7):(5-7); The weight ratio of the flexible plugging agent, the rigid plugging agent, and the micro-nano plugging agent is (2-3):(2-3):(1-5).

2. The water-based drilling fluid according to claim 1, characterized in that, The shale inhibitor includes at least one of the following: potassium chloride, potassium hydroxide, amino polyol, amino silanol.

3. The water-based drilling fluid according to claim 1, characterized in that, The surfactant includes at least one of the following: alkyl glycoside quaternary ammonium salt, organic amine.

4. The water-based drilling fluid according to claim 1, characterized in that, The formate includes at least one of the following: potassium formate, sodium formate, cesium formate.

5. The water-based drilling fluid according to claim 1, characterized in that, The flexible plugging agent includes at least one of the following: white asphalt, emulsified asphalt, sulfonated asphalt, modified asphalt.

6. The water-based drilling fluid according to claim 1, characterized in that, The rigid plugging agent includes at least one of the following: micron calcium carbonate, quartz sand, fiber.

7. The water-based drilling fluid according to claim 1, characterized in that, The micro-nano plugging agent includes at least one of the following: nano-silica emulsion, multi-vinyl polymer emulsion, emulsified paraffin microemulsion.

8. The water-based drilling fluid according to any one of claims 1 to 7, characterized in that, The raw material components of the water-based drilling fluid further include: bentonite, sodium carbonate, a pH regulator, a viscosifier, a filtration reducer, a lubricant, and a weighting agent.

9. The water-based drilling fluid according to claim 8, characterized in that, The pH regulator includes at least one of the following: sodium hydroxide, potassium hydroxide; and / or, The viscosifier includes at least one of the following: biopolymer xanthan gum, amphoteric composite ionic polymer; and / or, The filtration reducer includes at least one of the following: polyanionic cellulose, starch, modified starch; and / or, The lubricant includes at least one of the following: vegetable oil modified lubricant, graphite powder solid lubricant, polyol lubricant; and / or, The weighting agent includes at least one of the following: barite, limestone.

10. The water-based drilling fluid according to claim 8, characterized in that, In parts by weight, relative to 1000 parts of water in the water-based drilling fluid, The flexible plugging agent is 20 parts to 30 parts, the rigid plugging agent is 20 parts to 30 parts, the micro-nano plugging agent is 10 parts to 50 parts, the surfactant is 10 parts to 20 parts, the shale inhibitor is 10 parts to 70 parts, the formate is 50 parts to 70 parts, the bentonite is 20 to 40 parts, the sodium carbonate is 0.5 to 2 parts, the pH regulator is 1 to 2 parts, the viscosifier is 1 to 2 parts, the filtration reducer is 15 to 35 parts, the lubricant is 20 to 40 parts, and the weighting agent is 290 to 340 parts.

Images