Low solid phase strong inhibition calcium salt drilling fluid and preparation method thereof

Abstract

This invention provides a low-solids, strongly inhibiting calcium salt drilling fluid. Compared with existing technologies, the low-solids, strongly inhibiting calcium-based drilling fluid provided by this invention can utilize calcium ions (Ca) 2+ In an alkaline environment, carbonate and bicarbonate ions are neutralized, ensuring the stability of the drilling fluid's rheological properties; simultaneously, Ca... 2+ It undergoes irreversible absorption with clay particles, forming hydrated calcium silicate on the surface of the clay particles. Ion exchange and adsorption reduce the hydrophilicity and dispersibility of the clay particles, thereby inhibiting the hydration and dispersion of shale. Furthermore, the system has a low bentonite content and low solid phase content, with relatively low viscosity and shear force, which can accommodate a large amount of low-density solid phase. This ensures good and stable rheological properties of the drilling fluid, thereby giving the drilling fluid a strong anti-collapse effect and effectively controlling filtration loss.

Description

Technical Field

[0001] This invention belongs to the field of petroleum extraction technology, and particularly relates to a low-solids, high-inhibition calcium salt drilling fluid and its preparation method. Background Technology

[0002] Wellbore instability in shale formations is a major factor affecting drilling speed and cost, and is also one of the most common complex downhole situations encountered during drilling. The stratified shale formations are mainly composed of interbedded mudstone, sandstone, mudstone, and shale. The clay minerals are primarily montmorillonite, illite-montmorillonite mixed layers, and illite. The formations are poorly cemented, highly water-sensitive, and exhibit both dispersion and spalling after water absorption and expansion.

[0003] During drilling operations, clay minerals in shale are prone to absorbing water and expanding during their interaction with water-based drilling fluid. The seepage of drilling fluid and its filtrate along micro-fractures and bedding planes gradually reduces the strength of the shale formation. Under the action of pressure difference and hydration over a certain period of time, the formation becomes hydrated and dispersed, resulting in a decrease in the strength of the formation structure and causing complex situations such as wellbore collapse, stuck drill bit, and drill bit mud buildup.

[0004] Therefore, in efficient and safe drilling operations in layered shale formations, higher requirements are placed on the inhibition properties and rheological stability of water-based drilling fluids. To reduce the risk of wellbore instability in layered shale formations and improve contamination resistance, the research and development of low-solids, high-inhibition drilling fluid systems has become a key measure to solve this prominent problem.

[0005] Divalent calcium salt drilling fluid systems have outstanding advantages in inhibiting hydration and swelling of shale and stabilizing the wellbore, but due to the limitations of the calcium resistance of polymer treatment agents, they have not yet been widely applied. Chinese Patent Publication No. CN113583638A discloses a calcium-based polymer-based strong-inhibiting environmentally friendly drilling fluid base fluid, drilling fluid, and its preparation and application. The base fluid includes a base slurry, a calcium-based oligomer salt, a filtration loss reducer, a flow modifier, and sodium hydroxide. The base slurry includes a prehydrated sodium bentonite slurry or a slurry formed from water, sodium carbonate, and sodium bentonite. Based on the total volume of water in the prehydrated sodium bentonite slurry or slurry, the amount of calcium-based oligomer salt is 2-20 wt / v, the amount of filtration loss reducer is 0.8-4.5 wt / v, the amount of flow modifier is 0.5-2 wt / v%, and the amount of sodium hydroxide is 0.3-0.5 wt / v. The calcium-based oligomer salt is a compound formed by calcium salt and low-viscosity carboxymethyl cellulose sodium salt. The drilling fluid includes the base fluid and a plugging agent. The amount of plugging agent used is 1.2–5 wt / v%, calculated based on the total volume of the base fluid. High-calcium drilling fluid exhibits good anti-collapse effects during use, but due to the high concentration of Ca… 2+In certain environments, the effects of bentonite and conventional polymers weaken or even disappear, making it difficult to maintain the performance of drilling fluid systems. As a result, they have not been widely used, and there is relatively little patent information available for similar applications. Summary of the Invention

[0006] In view of this, the present invention provides a low-solids, strongly inhibiting calcium salt drilling fluid and its preparation method for addressing the problems of poor drilling fluid rheological properties and uncontrollable filtration loss caused by clay hydration expansion and alkaline contamination during drilling operations in shale formations and alkaline layers. This low-solids, strongly inhibiting calcium salt drilling fluid has a strong inhibitory and anti-collapse effect, can ensure stable drilling fluid rheological properties, and effectively control filtration loss. It can be applied to shale formations that produce mud and slurry, shale formations that are prone to spalling and flaking, and alkaline-rich formations, which is beneficial to wellbore stability during the drilling process, reduces downhole complexity, and reduces the average wellbore enlargement rate.

[0007] This invention provides a low-solids, high-inhibition calcium salt drilling fluid, comprising:

[0008]

[0009] Preferably, the thickener is selected from polyanionic cellulose and / or potassium polyacrylamide.

[0010] Preferably, the lubricant is selected from emulsified paraffin wax and / or white oil.

[0011] Preferably, the lubricant is emulsified paraffin wax and white oil; the mass ratio of the emulsified paraffin wax to white oil is (1.5-2):(0.5-2).

[0012] Preferably, the sulfonate filtration reducer is selected from sulfonate copolymer DSP-1 and / or sulfonate copolymer DSP-2.

[0013] Preferred, including:

[0014]

[0015]

[0016] Preferred, including:

[0017]

[0018] Preferably, it also includes a weighting agent; the amount of weighting agent added is such that the density of the low-solids, strongly inhibiting calcium salt drilling fluid is 1.15–1.25 g / cm³. 3 .

[0019] This invention also provides a method for preparing the above-mentioned low-solids, high-inhibition calcium salt drilling fluid, comprising the following steps:

[0020] Bentonite is mixed with water to obtain a bentonite-based slurry. Then, sodium hydroxide, calcium chloride, calcium-resistant filtration reducer, thickener, sulfonate filtration reducer and lubricant are added and mixed evenly. After sealing and curing, a low-solids, strongly inhibited calcium salt drilling fluid is obtained.

[0021] Preferably, the mixing time is 10 to 30 minutes; the sealed curing time is 15 to 30 hours.

[0022] This invention provides a low-solids, strongly inhibiting calcium salt drilling fluid, comprising: 100 parts by weight of water; 1-3 parts by weight of bentonite; 0.2-0.5 parts by weight of sodium hydroxide; 1-8 parts by weight of calcium chloride; 0.8-1.2 parts by weight of an anti-calcium filtration reducer; 0.3-1 parts by weight of a viscosity modifier; 0.4-0.8 parts by weight of a sulfonate filtration reducer; and 2-4 parts by weight of a lubricant. Compared with the prior art, the low-solids, strongly inhibiting calcium-based drilling fluid provided by this invention can be controlled by calcium ions (Ca). 2+ In an alkaline environment, carbonate and bicarbonate ions are neutralized to ensure the stability of the drilling fluid's rheological properties. Simultaneously, by continuously replenishing Ca... 2+ The concentration ensures the neutralization of carbonate and bicarbonate ions in the formation, reducing formation contamination and thus exhibiting strong resistance to alkali contamination; simultaneously, Ca... 2+ It undergoes irreversible absorption with clay particles, forming hydrated calcium silicate on the surface of the clay particles. Ion exchange and adsorption reduce the hydrophilicity and dispersibility of the clay particles, thereby inhibiting the hydration and dispersion of shale. Furthermore, the system has a low bentonite content and low solid phase content, with relatively low viscosity and shear force, which can accommodate a large amount of low-density solid phase. This ensures good and stable rheological properties of the drilling fluid, thus giving the drilling fluid a strong anti-collapse effect and effectively controlling filtration loss. It can be applied to shale formations that are prone to slag formations, easily detached shale formations, and alkaline-rich formations. It is beneficial for wellbore stability during the drilling process, reduces downhole complexity, and reduces the average wellbore enlargement rate. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This invention provides a low-solids, high-inhibition calcium salt drilling fluid, comprising:

[0025]

[0026] The low-solids, high-inhibition calcium salt drilling fluid of the present invention has strong inhibition, pollution resistance and stable rheological properties, and has a significant reusability, making it suitable for drilling operations in complex mudstone and shale formations and alkaline-rich formations.

[0027] The bentonite content in the low-solids strong-inhibiting calcium salt drilling fluid provided by the present invention is preferably 0.8 to 2.5 parts by weight, more preferably 0.8 to 2 parts by weight, and even more preferably 0.8 to 1.5 parts by weight; the bentonite can be any bentonite known to those skilled in the art, and there are no special restrictions. In the present invention, drilling-grade bentonite is preferred.

[0028] The sodium hydroxide content in the low-solids strong-inhibition calcium salt drilling fluid provided by the present invention is preferably 0.2 to 0.4 parts by weight, more preferably 0.2 to 0.3 parts by weight.

[0029] The calcium chloride content in the low-solids, strongly inhibited calcium salt drilling fluid provided by this invention is preferably 1-5 parts by weight, more preferably 1-4 parts by weight, and even more preferably 1.5-2 parts by weight. Through the compression of the double electric layer by calcium ions, the low-solids, strongly inhibited calcium salt drilling fluid of this invention has strong resistance to alkali contamination. Laboratory experiments show that its resistance to bicarbonate contamination is 2% sodium bicarbonate (theoretical bicarbonate concentration 14500 mg / L). During drilling operations, after carbonate and bicarbonate ions in the formation invade the polymer drilling fluid, the viscosity-shear value increases and the filtration loss rises due to the influence of electromotive force and gel structure; the rheological properties of the drilling fluid system deteriorate sharply, making flow difficult until it loses its fluidity. Compared with finely dispersed drilling fluid systems, the low-solids, strongly inhibited calcium-based drilling fluid can pass through the calcium ion Ca... 2+ In an alkaline environment, carbonate and bicarbonate ions are neutralized to ensure the stability of the drilling fluid's rheological properties. Simultaneously, by continuously replenishing Ca... 2+ The concentration ensures that carbonate and bicarbonate ions in the formation are neutralized, reducing formation contamination and giving the drilling fluid a strong ability to inhibit hydration and swelling of shale formations.

[0030] The content of the anti-calcium filtration reduction agent in the low solid phase strong inhibiting calcium salt drilling fluid provided by the present invention is preferably 0.9 to 1.5 parts by weight, more preferably 1 to 1.43 parts by weight; the anti-calcium filtration reduction agent is at least one of sulfonate copolymer, PAC-LV, NH4-HPAN, and anti-calcium filtration reduction agent (SMPFL).

[0031] The type of viscosifier in the low-solids, high-inhibition calcium salt drilling fluid provided by this invention can be any viscosifier well known to those skilled in the art, and there are no special limitations. In this invention, polyanionic cellulose and / or potassium polyacrylamide are preferred, and polyanionic cellulose or potassium polyacrylamide are more preferred. When the viscosifier is polyanionic cellulose, its content in the low-solids, high-inhibition calcium salt drilling fluid is preferably 0.5 to 1 part by weight. When the viscosifier is potassium polyacrylamide, its content in the low-solids, high-inhibition calcium salt drilling fluid is preferably 0.3 to 0.5 parts by weight, and more preferably 0.4 to 0.5 parts by weight.

[0032] The content of sulfonate filtration reducer in the low solids strong-inhibiting calcium salt drilling fluid provided by the present invention is preferably 0.4 to 0.6 parts by weight, more preferably 0.4 to 0.5 parts by weight, and even more preferably 0.4 to 0.43 parts by weight; the sulfonate filtration reducer is preferably sulfonate copolymer DSP-1 and / or sulfonate copolymer DSP-2.

[0033] The lubricant content in the low-solids, high-inhibition calcium salt drilling fluid provided by the present invention is preferably 2-3.5 parts by weight, more preferably 2.5-3.5 parts by weight, and even more preferably 2.5-3 parts by weight; the lubricant is preferably emulsified paraffin wax and / or white oil, more preferably emulsified paraffin wax and white oil; the mass ratio of the emulsified paraffin wax to white oil is preferably (1.5-2):(0.5-2), more preferably (1.5-2):(0.5-1.5), even more preferably (1.5-2):(0.5-1), and most preferably 2:0.5.

[0034] In this invention, preferably, the low-solids, strongly inhibiting calcium salt drilling fluid comprises:

[0035]

[0036] More preferably, including:

[0037]

[0038] Or preferably include:

[0039]

[0040] More preferably, including:

[0041]

[0042] According to the present invention, it preferably also includes a weighting agent, which can be used according to density requirements; the amount of weighting agent added in the present invention preferably results in a density of 1.15 to 1.25 g / cm³ for the low-solids, strongly inhibiting calcium salt drilling fluid. 3 More preferably 1.2 g / cm³ 3The type of weighting agent can be any weighting agent well known to those skilled in the art, and there are no special restrictions. In this invention, barite is preferred.

[0043] The low-solids, high-inhibition calcium-based drilling fluid provided by this invention can be controlled by calcium ions (Ca). 2+ In an alkaline environment, carbonate and bicarbonate ions are neutralized to ensure the stability of the drilling fluid's rheological properties. Simultaneously, by continuously replenishing Ca... 2+ The concentration ensures the neutralization of carbonate and bicarbonate ions in the formation, reducing formation contamination and thus exhibiting strong resistance to alkali contamination; simultaneously, Ca... 2+ It undergoes irreversible absorption with clay particles, forming hydrated calcium silicate on the surface of the clay particles. Ion exchange and adsorption reduce the hydrophilicity and dispersibility of the clay particles, thereby inhibiting the hydration and dispersion of shale. Furthermore, the system has a low bentonite content and low solid phase content, with relatively low viscosity and shear force, which can accommodate a large amount of low-density solid phase. This ensures good and stable rheological properties of the drilling fluid, thus giving the drilling fluid a strong anti-collapse effect and effectively controlling filtration loss. It can be applied to shale formations that are prone to slag formations, easily detached shale formations, and alkaline-rich formations. It is beneficial for wellbore stability during the drilling process, reduces downhole complexity, and reduces the average wellbore enlargement rate.

[0044] The present invention also provides a method for preparing the above-mentioned low-solids strong-inhibition calcium salt drilling fluid, comprising the following steps: mixing bentonite with water to obtain bentonite-based slurry, then adding sodium hydroxide, calcium chloride, anti-calcium filtration loss reducer, thickener, sulfonate filtration loss reducer and lubricant, mixing evenly, and then sealing and curing to obtain low-solids strong-inhibition calcium salt drilling fluid.

[0045] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0046] Bentonite is mixed with water to obtain bentonite-based slurry; the mixing method is preferably stirring, more preferably high-speed stirring; the mixing time is preferably 10-30 min, more preferably 15-25 min, and even more preferably 20 min; after mixing, it is preferably cured at room temperature in a sealed environment to obtain bentonite-based slurry; the curing time at room temperature in a sealed environment is preferably 10-24 h, more preferably 14-20 h, and even more preferably 16 h.

[0047] Then, sodium hydroxide, calcium chloride, calcium-resistant filtration reducer, thickener, sulfonate filtration reducer, and lubricant are added and mixed evenly. The mixture is then sealed and cured to obtain a low-solids, strongly inhibiting calcium salt drilling fluid. The mixing time is preferably 10-30 min, more preferably 15-25 min, and even more preferably 20 min. The sealed curing time is preferably 15-30 h, more preferably 18-26 h, and even more preferably 24 h.

[0048] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a low-solids, strongly inhibiting calcium salt drilling fluid and its preparation method.

[0049] All reagents used in the following examples are commercially available; caustic soda and sulfonate copolymer (DSP-2) were purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd.; liquid lubricant white oil, polyanionic fiber, and emulsified paraffin (SL-1) were purchased from Shandong Deshunyuan Petroleum Technology Co., Ltd.; barite was purchased from Liaoyang County Tuozhan Mineral Products Sales Co., Ltd.; and anti-calcium filtration loss reducer (SMPFL) was purchased from China Petroleum Engineering Technology Research Institute.

[0050] Example 1

[0051] a. Base slurry: Add 3g of bentonite to 350mL of distilled water, stir at high speed for 20min, and then cure at room temperature in a sealed environment for 16h.

[0052] b. Formulation: 350mL base slurry + 0.7g caustic soda + 5.25g calcium chloride + 3.5g anti-calcium filtration reducer + 1.75g ​​polyanionic cellulose + 1.5g sulfonate copolymer (DSP-2) + 7g emulsified paraffin + weighting agent (based on drilling fluid density 1.20g / cm³) 3 Add barite).

[0053] c. Preparation process: Under high-speed stirring, add different treatment agents sequentially to the high-speed stirring cup according to the formula, stir at high speed for 20 minutes, and then cure in a sealed environment for 24 hours. Measure the rheological properties and filtration loss of the drilling fluid.

[0054] Example 2

[0055] a. Base slurry: Add 3g of bentonite to 350mL of distilled water, stir at high speed for 20min, and then cure at room temperature in a sealed environment for 16h.

[0056] b. Formulation: 350mL base slurry + 0.7g caustic soda + 5.25g calcium chloride + 5.0g anti-calcium filtration reducer + 1.75g ​​polyanionic cellulose + 1.5g sulfonate copolymer (DSP-2) + 7g emulsified paraffin + weighting agent (based on drilling fluid density 1.20g / cm³) 3 Add barite).

[0057] c. Preparation process: Add different treatment agents to the high-speed stirring cup in sequence according to the formula under high-speed stirring, stir at high speed for 20 minutes, and then cure in a sealed container for 24 hours.

[0058] The mudstone cuttings from the site were placed in an aging tank and heated at 100°C for 16 hours. The rheological properties and filtration loss of the drilling fluid were then measured. The sieved and dried mudstone cuttings were collected, and the inhibition performance of the drilling fluid was analyzed.

[0059] Example 3

[0060] a. Base slurry: Add 3g of bentonite to 350mL of distilled water, stir at high speed for 20min, and then cure at room temperature in a sealed environment for 16h.

[0061] b. Formulation: 350mL base slurry + 0.7g caustic soda + 5.25g calcium chloride + 3.5g anti-calcium agent + 1.75g ​​polyanionic cellulose + 1.5g sulfonate copolymer (DSP-2) + 7g emulsified paraffin wax + weighting agent (based on drilling fluid density 1.20g / cm³) 3 Add barite).

[0062] c. Preparation process: Under high-speed stirring, different treatment agents are added sequentially to the high-speed stirring cup according to the formula, stirred at high speed for 20 minutes, and then cured in a sealed container for 24 hours. 2% soil (by mass) and 4% soil are added sequentially to the drilling fluid, and the rheological properties of the drilling fluid are measured.

[0063] Performance tests were conducted using the drilling fluid from Example 1 as an example. The experimental results of other examples were comparable to those of Example 1. Drilling fluid performance and filtration loss were tested. The results are shown in Table 1 below.

[0064] Table 1. Drilling fluid performance test results of Example 1

[0065] Serial Number project Test value standard 1 <![CDATA[Density, g / cm 3 > 1.20 Drilling fluid testing standards 2 Plastic viscosity, mPa·s 21 Drilling fluid testing standards 3 Dynamic shear force, pa 3.0 Drilling fluid testing standards 4 Medium-pressure filtration loss (API filtration loss), mL 4.8 SY / T 6865-2012 5 pH value 9 Drilling fluid testing standards

[0066] The drilling fluid from Example 2 was used as an example for preparation. Two 50g portions of on-site mudstone cuttings were placed in an aging tank, and 350mL of the prepared drilling fluid and 350mL of clean water were added to each. The mixture was then heated at 100℃ for 16 hours. After cooling, the fluid was removed, and the rheological properties, filtration loss, and other indicators of the drilling fluid before and after aging, as well as the mass change of the cuttings before and after aging, were tested. The results are shown in Tables 2 and 3 below.

[0067] Table 2. Drilling fluid performance test results of Example 2

[0068]

[0069]

[0070] Table 3. Mass changes of rock cuttings before and after hot rolling in water and drilling fluid (Example 2).

[0071]

[0072] As shown in Tables 2 and 3, the plastic viscosity, dynamic shear force, and filtration loss of the drilling fluid in Example 2 did not change significantly before and after aging, indicating that the drilling fluid's performance remained stable after hot rolling. The cuttings recovery rate in clear water was 24.6%, while the cuttings recovery rate in Example 2 was 93.4%, indicating that the drilling fluid in Example 2 has a better ability to inhibit clay dispersion and hydration.

[0073] The drilling fluid of Example 3 was used as an example for preparation. 2% soil and 4% soil were added to the drilling fluid of Example 3 respectively, and the changes in the rheological properties of the drilling fluid were tested. The results are shown in Table 4.

[0074] Table 4 shows the test performance of soil with different proportions added in Example 3.

[0075]

[0076] As shown in Table 4, the addition of 2% and 4% soil in Example 3 resulted in slight changes in the plastic viscosity and dynamic shear force of the drilling fluid, while the rheological properties of the drilling fluid remained stable, indicating that Example 3 has a good ability to accommodate low-density solid phases.

[0077] Well Da 126 is an oil reservoir appraisal well with a designed depth of 2540m and a completed depth of 2556m. Located near an alkaline mineral deposit, bicarbonate contamination was predicted during drilling. The well used the low-solids, strongly inhibiting calcium salt drilling fluid from Example 1, with an actual drilling density of 1.14–1.25 g / cm³. 3 This is 0.03 g / cm³ lower than the average drilling fluid density of the wells constructed in this block. 3 The properties of the drilling fluid are shown in Table 5.

[0078] Table 5. Application Effects of Drilling Fluid

[0079]

[0080] As shown in Table 5, the drilling fluid of the embodiment has the following advantages when applied in the field: ① Good rheological stability, low filtration loss, easy adjustment and maintenance; stable calcium ion content, no viscosity change caused by bicarbonate contamination, and the viscosity is always maintained between 42-46S; ② Strong drilling fluid inhibition, and uniform and regular return of cuttings; ③ Good mud cake quality, strong lubrication performance, no stuck phenomenon during tripping, stable well wall without collapse, and regular well diameter.

[0081] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A low solid, high inhibitive calcium salt drilling fluid, characterized in that, It consists of the following components: 100 parts by weight of water; 0.8 to 3 parts by weight of bentonite; Sodium hydroxide 0.2~0.5 parts by weight; Calcium chloride 1-8 parts by weight; 0.8-1.5 parts by weight of anti-calcium filtration loss reducer; Thickening agent 0.3~1 parts by weight; Sulfonate-based filtration loss reducers: 0.4-0.8 parts by weight; 2-4 parts by weight of lubricant; The thickener is selected from polyanionic cellulose and / or potassium polyacrylamide; The lubricant is emulsified paraffin wax and white oil; the mass ratio of the emulsified paraffin wax to white oil is (1.5~2):(0.5~2).

2. The low solid, high inhibited calcium salt drilling fluid of claim 1, wherein, The sulfonate-based filtration reducer is selected from sulfonate copolymer DSP-1 and / or sulfonate copolymer DSP-2.

3. The low solid, high inhibited calcium salt drilling fluid of claim 1, wherein, It consists of the following components: 100 parts by weight of water; 0.8 to 3 parts by weight of bentonite; Sodium hydroxide 0.2~0.5 parts by weight; Calcium chloride 1-8 parts by weight; 0.8-1.5 parts by weight of anti-calcium filtration loss reducer; 0.5 to 1 part by weight of polyanionic cellulose; Sulfonate-based filtration loss reducers: 0.4-0.8 parts by weight; Emulsified paraffin wax, 1.5-2 parts by weight; 0.5 to 2 parts by weight of white oil.

4. The low solid, high inhibited calcium salt drilling fluid of claim 1, wherein, It consists of the following components: 100 parts by weight of water; 0.8 to 3 parts by weight of bentonite; Sodium hydroxide 0.2~0.5 parts by weight; Calcium chloride 1-8 parts by weight; 0.8-1.5 parts by weight of anti-calcium filtration loss reducer; Potassium polyacrylamide salt, 0.3~0.5 parts by weight; Sulfonate-based filtration loss reducers: 0.4-0.8 parts by weight; Emulsified paraffin wax, 1.5-2 parts by weight; 0.5 to 2 parts by weight of white oil.

5. The low solid, high inhibited calcium salt drilling fluid of claim 1, wherein, It also includes a weighting agent; the amount of the weighting agent added is such that the density of the low-solids, strongly inhibiting calcium salt drilling fluid is 1.15~1.25 g / cm³. 3 .

6. A method for preparing the low-solids, high-inhibition calcium salt drilling fluid according to claim 1, characterized in that, Includes the following steps: Bentonite is mixed with water to obtain a bentonite-based slurry. Then, sodium hydroxide, calcium chloride, calcium-resistant filtration reducer, thickener, sulfonate filtration reducer and lubricant are added and mixed evenly. After sealing and curing, a low-solids, strongly inhibited calcium salt drilling fluid is obtained.

7. The preparation method according to claim 6, characterized in that, The mixing time is 10-30 min; the sealed curing time is 15-30 h.