Environment-friendly water-based drilling fluid suitable for tight gas as well as preparation method and application of environment-friendly water-based drilling fluid

Abstract

The invention discloses an environment-friendly water-based drilling fluid suitable for tight gas as well as a preparation method and application thereof, and relates to the technical field of oil and gas field drilling, the environment-friendly water-based drilling fluid comprises the following components: bentonite slurry, sodium hydroxide, xanthan gum, a zwitterionic polymer coating agent, a filtrate reducer, a plugging agent, an inhibitor, potassium chloride, a lubricant, a defoaming agent, a viscosity reducer and barite. The preparation cost is low, the wide application of the environment-friendly water-based drilling fluid is promoted, and the environment-friendly treatment agent for the environment-friendly water-based drilling fluid suitable for tight gas is completely environment-friendly; the lubricating oil has excellent rheological filtration property, lubricating property and sedimentation stability; the water-based drilling fluid has the advantages that the water-based drilling fluid has excellent temperature-resistant stability, the fluctuation of the rheological property along with the temperature rise is small, meanwhile, the water-based drilling fluid system has excellent gas cut prevention capability and degassing effect, and the system performance is stable in the continuous methane injection process; the shale inhibitor has excellent inhibition performance and reservoir protection performance, and can effectively inhibit hydration and dispersion of shale.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field drilling, and in particular to an environmentally friendly water-based drilling fluid suitable for tight gas, a preparation method thereof and an application thereof. Background Art

[0002] Due to the increasing attention paid to environmental protection issues, new and stricter requirements have been put forward for the environmental performance of drilling fluids, requiring drilling fluids to be non-toxic, degradable, and not polluting the surrounding environment. Compared with oil-based drilling fluids, water-based drilling fluids have significant advantages in terms of good environmental protection and low cost. Statistics show that 80% of drilling projects use water-based drilling fluids. With the deep exploration and development of oil and gas resources, as well as the implementation of hot dry rock drilling and deep scientific drilling projects, the temperature of the formations encountered during drilling is getting higher and higher, which puts forward higher requirements on the temperature resistance of drilling fluids.

[0003] Methyl glucoside drilling fluid is also known as imitation oil-based drilling fluid. It can prevent shale hydration by forming a semi-permeable membrane. It has good lubricity and compatibility, is environmentally friendly, has stable rheological properties, and can effectively carry cuttings and clean wellbore. However, the amount of methyl glucoside added to the drilling fluid is large and the inhibition is insufficient.

[0004] A lot of work has been done in the research and application of environmentally friendly water-based drilling fluids at home and abroad, and some important results have been achieved. However, the existing environmentally friendly water-based drilling fluid systems suitable for tight gas still generally have the following problems:

[0005] (1) The developed environmentally friendly treatment agent has insufficient temperature resistance, which to some extent restricts the application temperature range of environmentally friendly water-based drilling fluids.

[0006] (2) Most temperature-resistant and environmentally friendly drilling fluid systems need to be compounded with treatment agents with poor environmental performance (such as sulfonated treatment agents) to achieve better performance, which affects the overall environmental performance of the drilling fluid to a certain extent. Summary of the invention

[0007] The technical problem to be solved by the present invention is that the current water-based drilling fluid has insufficient temperature resistance and environmental protection performance. The purpose is to provide an environmentally friendly water-based drilling fluid suitable for tight gas and its preparation method and application, which solves the problem that the current water-based drilling fluid has insufficient temperature resistance and environmental protection performance.

[0008] The present invention is achieved through the following technical solutions:

[0009] In a first aspect, the present application provides an environmentally friendly water-based drilling fluid suitable for tight gas, comprising the following components: permethrin slurry, sodium hydroxide, xanthan gum, zwitterionic polymer coating agent, filtrate reducer, plugging agent, inhibitor, potassium chloride, lubricant, defoamer, viscosity reducer and barite.

[0010] Furthermore, the components of the water-based drilling fluid are calculated in the following mass percentages: 2% to 4% bentonite slurry, 0.2% sodium hydroxide, 0 to 0.2% xanthan gum, 0.2% to 0.3% zwitterionic polymer coating agent, 4% to 6% fluid loss reducer, 4% plugging agent, 0.2% to 0.3% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoaming agent and 1% to 2% viscosity reducer, and the balance is barite.

[0011] Furthermore, when used for a density of 1.7 g / cm 3 In an environment of , the components of the water-based drilling fluid are calculated according to the following mass percentages: 4% bentonite slurry, 0.2% sodium hydroxide, 0.2% xanthan gum, 0.3% zwitterionic polymer coating agent, 6% fluid loss reducer, 4% plugging agent, 0.3% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoamer and 1% viscosity reducer, and the balance is barite.

[0012] Furthermore, when used for a density of 2.3 g / cm 3 In an environment of , the components of the water-based drilling fluid are calculated according to the following mass percentages: 2% bentonite slurry, 0.2% sodium hydroxide, 0.2% zwitterionic polymer coating agent, 4% fluid loss reducer, 4% plugging agent, 0.2% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoamer and 2% viscosity reducer, and the balance is barite.

[0013] Furthermore, the density of the barite is 4.3 g / cm 3 .

[0014] Furthermore, the zwitterionic polymer coating agent is a zwitterionic polymer strong coating agent for drilling fluid (FA-367); the fluid loss reducer is an environmentally friendly fluid loss reducer (JY-1B); the plugging agent is an environmentally friendly plugging agent (JHS-01); the inhibitor is an environmentally friendly inhibitor (YFKN); the lubricant is a lubricant for drilling fluid (JHL-03); the defoamer is a general-purpose silicone defoamer (AT-920); and the viscosity reducer is a silicone-fluorine high-temperature viscosity reducer (SF260).

[0015] In a second aspect, the present application provides a method for preparing an environmentally friendly water-based drilling fluid suitable for tight gas using the above formula, comprising the following steps:

[0016] Step 1: Add bentonite and sodium hydroxide into water and stir to mix well to prepare base slurry;

[0017] Step 2: Add xanthan gum, zwitterionic polymer coating agent, fluid loss reducer, plugging agent and inhibitor to the base slurry in sequence and stir evenly;

[0018] Step 3: Continue to add potassium chloride latex and stir evenly;

[0019] Step 4: Continue to add lubricant, defoamer, viscosity reducer and barite and stir evenly.

[0020] Furthermore, it is characterized in that each treatment agent added in step 2 is stirred for 5 minutes.

[0021] Furthermore, each time a treatment agent is added in step 4, stirring is performed for 5 minutes, and finally stirring is performed for 10 minutes.

[0022] In a third aspect, the present application provides a water-based drilling fluid with the above formula or a water-based drilling fluid prepared by the above method for preparing the water-based drilling fluid, and its use in deepwater and ultra-deepwater oil and gas field drilling.

[0023] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0024] (1) The environmentally friendly water-based drilling fluid of the present invention has a low production cost, which is conducive to promoting the widespread application of environmentally friendly water-based drilling fluids, and realizes the full environmental protection of environmentally friendly water-based drilling fluid treatment agents suitable for tight gas;

[0025] (2) The environmentally friendly water-based base well fluid provided by the present invention has excellent rheological filtration, lubricity and sedimentation stability, a plastic viscosity of 25mPa.s to 47mPa.s, an API water loss of 2.4ml to 2.8ml, an initial shear of 3Pa to 3.5Pa, a final shear of 5Pa to 9Pa, and a dynamic shear of 10Pa to 11Pa;

[0026] (3) The environmentally friendly water-based drilling fluid provided by the present invention has excellent temperature resistance stability, and the rheological properties fluctuate less with increasing temperature. At the same time, the water-based drilling fluid system has excellent gas invasion resistance and degassing effect. During the continuous methane injection process, the system performance is stable;

[0027] (4) The environmentally friendly water-based drilling fluid provided by the present invention has excellent inhibitory and reservoir protection properties, can effectively inhibit the hydration and dispersion of shale, and the permeability damage rate of dense sandstone core is 18.66%, which is lower than the original system;

[0028] (5) The environmentally friendly water-based drilling fluid suitable for tight gas provided by the present invention can further improve the drilling efficiency and downhole construction safety, thereby reducing the tight gas drilling cycle and playing an important role in the safe and fast drilling of tight gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0030] Figure 1 This is a static sedimentation stability effect diagram of an environmentally friendly water-based drilling fluid system suitable for tight gas in Example 1 of the present invention;

[0031] Figure 2 This is a static sedimentation stability effect diagram of an environmentally friendly water-based drilling fluid system suitable for tight gas in Example 2 of the present invention;

[0032] Figure 3 The recovery rate results of the inhibition ability of different systems on the hydration and dispersion of reservoir cuttings, where the environmentally friendly drilling fluid refers to the original system (i.e., Example 3), and the optimized system refers to the system suitable for a density of 1.7 g / cm 3 An environmentally friendly water-based drilling fluid system in an environment of (i.e., Example 1);

[0033] Figure 4 The linear expansion rate results of different systems' inhibition ability on reservoir cuttings hydration dispersion, where the environmentally friendly drilling fluid refers to the original system (i.e., Example 3), and the optimized system refers to the system suitable for a density of 1.7 g / cm 3 An environmentally friendly water-based drilling fluid system in an environment of (i.e., Example 1);

[0034] Figure 5 The core photos of the original system environmentally friendly water-based drilling fluid system in Example 3 before and after pollution, where the left picture is before pollution and the right picture is after pollution;

[0035] Figure 6 These are photos of cores before and after contamination of an environmentally friendly water-based drilling fluid system suitable for tight gas in Example 1, where the left picture is before contamination and the right picture is after contamination. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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.

[0037] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0038] The room temperature of the present invention refers to 25±2° C.; in the embodiments of the present invention, unless otherwise specified, “%” refers to mass percentage.

[0039] Example 1

[0040] This embodiment provides a method suitable for a density of 1.7 g / cm 3 Environmentally friendly water-based drilling fluid, the raw materials are composed of the following components according to mass percentage:

[0041] 4% bentonite slurry, 0.2% sodium hydroxide (NaOH), 0.2% xanthan gum (XC), 0.3% zwitterionic polymer coating agent FA367, 6% environmentally friendly fluid loss reducer JY-1B, 4% environmentally friendly plugging agent JHS-01, 0.3% environmentally friendly inhibitor YFKN, 8% potassium chloride (KCl), 2% lubricant JHL-03, 0.1% defoamer AT920 and 1% viscosity reducer SF260, the balance is barite (density 4.3g / cm 3 ).

[0042] The preparation method is:

[0043] Step 1: Take 400 ml of water, add bentonite and sodium hydroxide, stir at 10000 rpm for 20 minutes, and stand at room temperature for 24 hours as the experimental slurry;

[0044] Step 2: Add the above-mentioned amount of xanthan gum (XC), zwitterionic polymer coating agent FA367, environmentally friendly fluid loss reducer JY-1B, environmentally friendly plugging agent JHS-01, and environmentally friendly inhibitor YFKN to the base slurry prepared in step 1 in sequence, and stir for 5 minutes after adding each treatment agent;

[0045] Step 3: Continue to add the above amount of potassium chloride (KCl) and stir for 10 minutes;

[0046] Step 4: Continue to add the above amount of lubricant JHL-03, defoamer AT920, viscosity reducer SF260 and barite, stir for 5 minutes after adding each treatment agent, and finally stir for 10 minutes.

[0047] Example 2

[0048] This embodiment provides a method suitable for a density of 2.3 g / cm3 Environmentally friendly water-based drilling fluid, the raw materials are composed of the following components according to mass percentage:

[0049] 2% Pengrun soil slurry, 0.2% sodium hydroxide (NaOH), 0.2% zwitterionic polymer coating agent FA367, 4% environmentally friendly fluid loss reducer JY-1B, 4% environmentally friendly plugging agent JHS-01, 0.2% environmentally friendly inhibitor YFKN, 8% potassium chloride (KCl), 2% lubricant JHL-03, 0.1% defoamer AT920 and 2% viscosity reducer SF260, the balance is barite (density 4.3g / cm 3 ).

[0050] The preparation method is:

[0051] Step 1: Take 400 ml of water, add pentane and sodium hydroxide, stir at 10000 rpm for 20 minutes, and stand at room temperature for 24 hours as the experimental slurry;

[0052] Step 2: Add the above-mentioned amount of zwitterionic polymer coating agent FA367, environmentally friendly fluid loss reducer JY-1B, environmentally friendly plugging agent JHS-01, and environmentally friendly inhibitor YFKN to the base slurry prepared in step 1 in sequence, and stir for 5 minutes after adding each treatment agent;

[0053] Step 3: Continue to add the above amount of potassium chloride (KCl) and stir for 10 minutes;

[0054] Step 4: Continue to add the designed amount of lubricant JHL-03, defoamer AT920, viscosity reducer SF260 and barite, stir for 5 minutes after adding each treatment agent, and finally stir for 10 minutes.

[0055] Comparative Example (Original System)

[0056] This embodiment provides a water-based drilling fluid, wherein the raw materials are composed of the following components in terms of mass percentage:

[0057] 4% bentonite slurry, 0.2% sodium hydroxide (NaOH), 6% environmentally friendly filtration reducer JY-1B, 4% environmentally friendly plugging agent JHS-01, 0.3% environmentally friendly inhibitor YFKN, 8% potassium chloride (KCl), 2% lubricant JHL-03, and the balance is barite.

[0058] The preparation method is:

[0059] Step 1: Take 400 ml of water, add bentonite and sodium hydroxide (NaOH), stir at 10000 rpm for 20 minutes, and stand at room temperature for 24 hours as the experimental slurry;

[0060] Step 2: Add the above-mentioned amounts of environmentally friendly fluid loss reducer JY-1B, environmentally friendly plugging agent JHS-01, and environmentally friendly inhibitor YFKN to the experimental base slurry prepared in step 1 in sequence, and stir for 5 minutes after adding each treatment agent;

[0061] Step 3: Continue to add the above amount of potassium chloride (KCl) and stir for 10 minutes;

[0062] Step 4: Continue to add the above amount of lubricant JHL-03 and barite, stir for 5 minutes after adding each treatment agent, and finally stir for 10 minutes.

[0063] Performance Testing

[0064] 1) The rheological filtration test was performed on the water-based drilling fluids prepared by the formulations and preparation methods of Example 1, Example 2 and the comparative example.

[0065] The test results of rheological filtration performance of the optimized environmentally friendly water-based drilling fluid system (i.e., the environmentally friendly water-based drilling fluid system prepared in Example 1 and Example 2) and the original system of the comparative example are shown in Table 1.

[0066] Table 1 Rheological filtration properties of environmentally friendly water-based drilling fluid

[0067]

[0068] It can be seen from the data in Table 1 that the rheological filtration properties of the environmentally friendly water-based drilling fluids prepared by the formulations and preparation methods of Examples 1 and 2 are significantly improved compared to the comparative example. At the same time, it can be seen from Table 1 that after the formulation is adjusted and optimized, the system (density 1.7 g / cm 3 ~2.3g / cm 3 )'s rheological filtration properties meet the following requirements: plastic viscosity (PV) ≤ 50mPa.s, API water loss ≤ 5ml, initial shear 2-5Pa, final shear 3-10Pa, dynamic shear force (YP) 5-12Pa, meeting the requirements of oilfield drilling design.

[0069] 2) The lubricity performance of the water-based drilling fluids prepared using the formulations and preparation methods of Example 1, Example 2 and the comparative example was tested.

[0070] The lubrication performance test results of the optimized environmentally friendly water-based drilling fluid system (i.e., the environmentally friendly water-based drilling fluid system prepared in Example 1 and Example 2) and the original system of the comparative example are shown in Table 2.

[0071] Table 2 Lubrication properties of environmentally friendly water-based drilling fluid

[0072] system Clean water readings Sample reading Correction Factor Lubrication coefficient <![CDATA[Example 1 (ρ = 1.7 g / cm 3 )]]> 32.10 11.3 1.0592 0.1197 <![CDATA[Example 2 (ρ = 2.3 g / cm 3 )]]> 35.33 10.5 0.9624 0.1010 <![CDATA[Comparative example (ρ = 1.6 g / cm 3 )]]> 35.85 18.2 0.9484 0.1726

[0073] It can be seen from the test data in Table 2 that the environmentally friendly water-based drilling fluids prepared by the formulations and preparation methods of Examples 1 and 2 have good lubricity and are superior to the environmentally friendly water-based drilling fluids prepared by the formulations and preparation methods of the comparative examples.

[0074] 3) The sedimentation stability test was conducted on the water-based drilling fluids prepared by the formulations and preparation methods of Example 1, Example 2 and the comparative example. The upper and lower density differences of the environmentally friendly water-based drilling fluids prepared by the formulations and preparation methods of Example 1 and Example 2 after hot rolling and standing for 24 hours were measured to determine their sedimentation stability.

[0075] The sedimentation stability test of the environmentally friendly water-based drilling fluid system of the optimized system (i.e., the environmentally friendly water-based drilling fluid system prepared in Example 1 and Example 2) and the original system of the comparative example is shown in Table 3, Figure 1 and Figure 2 shown.

[0076] Table 3 Results of sedimentation stability test of environmentally friendly water-based drilling fluid

[0077]

[0078] According to the data in Table 3 and Figure 1 , Figure 2 It can be seen that the environmentally friendly water-based drilling fluid prepared by the formula and preparation method of Example 1 and Example 2 has no obvious stratification phenomenon after standing for 24 hours, and the density difference between the upper and lower layers of the system is low, indicating that the environmentally friendly water-based drilling fluid prepared by the formula and preparation method of Example and Example 2 has excellent sedimentation stability.

[0079] 4) The rheological properties of the water-based drilling fluids prepared by the formulations and preparation methods of Examples 1 and 2 were tested as a function of density / temperature.

[0080] The environmentally friendly water-based drilling fluid systems prepared by the formulations and preparation methods of Example 1 and Example 2 were used to test the rheological properties of the two systems at different temperatures (25° C., 70° C., 80° C., and 90° C.). The results are shown in Table 4.

[0081] Table 4 Effect of temperature on rheological properties of environmentally friendly water-based drilling fluid system

[0082]

[0083] From the test results in Table 4, it can be seen that with the increase of density, the viscosity and shear force of the water-based drilling fluid system prepared by the formulation and preparation method of Example 1 and Example 2 increase, but both are within a controllable range. At the same time, at different temperatures, the rheological properties of the water-based drilling fluid system prepared by the formulation and preparation method of Example 1 and Example 2 fluctuate less with increasing temperature, showing better temperature resistance stability.

[0084] 5) A gas invasion test was performed on the water-based drilling fluid prepared using the formulation and preparation method of Example 1 and Example 2.

[0085] The water-based drilling fluids prepared by the formula and preparation method of Example 1 and Example 2 were respectively taken, and methane gas was continuously introduced at a rotation speed of 1000 rpm to simulate the gas invasion process. After gas injection for 5 minutes, 10 minutes, 20 minutes, and 30 minutes, the rheological properties and density changes of the test system were tested. The test results are shown in Table 5.

[0086] Table 5 Effect of methane gas invasion on the rheological properties of environmentally friendly water-based drilling fluids in the optimized system

[0087]

[0088] It can be seen from Table 5 that during the continuous injection of methane gas, the viscosity and shear force of the water-based drilling fluid prepared by the formulation and preparation method of Example 1 and Example 2 did not change significantly, indicating that the system has excellent gas invasion prevention ability and degassing effect.

[0089] 6) Wellbore stability evaluation

[0090] The first and second sandstone cuttings of the reservoir of Yongqian 3-1-H2 well were selected and processed into two specifications of 2-5 mm and 100 mesh. The water-based drilling fluid prepared in Example 1 was evaluated by rolling dispersion test (90°C / 16h) and linear expansion rate test (ρ=1.7 g / cm 3 ) on the ability to inhibit the hydration and dispersion of reservoir cuttings, and compared with the water-based drilling fluid and clean water prepared in the comparative example, the recovery rate results are as follows Figure 3 The linear expansion rate results are shown as Figure 4 As shown. Figure 3 and Figure 4 It can be seen that the water-based drilling fluid prepared by the formulation and preparation method of Example 1 has excellent inhibition ability, can increase the cuttings recovery rate to more than 66%, and reduce the cuttings expansion rate to less than 3.2%.

[0091] 7) Reservoir protection performance evaluation

[0092] A tight sandstone core was selected to test the gas permeability of the water-based drilling fluid system prepared in Example 1 before and after contamination, and to investigate the reservoir protection performance of the water-based drilling fluid system prepared by the formula and method of Example 1. The core contamination method refers to the core damage evaluation method for tight oil and shale oil in SY / T 6540-2021, and the specific steps are as follows:

[0093] ① After the core is washed and dried, the initial permeability K is tested in the forward direction. g1 ;

[0094] ② Load the core into the core holder in reverse, place it in the contamination kettle, and add drilling fluid;

[0095] ③ Seal the kettle, increase the surrounding pressure to 4.5MPa, and raise the temperature to 90℃.

[0096] ④After the temperature reaches the specified value, adjust the pollution pressure difference to 3.5MPa and adjust the speed to 300s -1 , dynamic pollution for 125 minutes. Record the dynamic filtration loss during the pollution process.

[0097] ⑤After the pollution is over, take out the core and test the core permeability K in the forward direction g2 .

[0098] Permeability recovery value R d Calculate as follows:

[0099]

[0100] In formula (1), R d is the dynamic permeability recovery value; K g1 is the initial gas permeability, 10 -3 μm 2 ; K g2 is the core permeability after damage, 10 -3 μm 2 .

[0101] The core usage information is shown in Table 6.

[0102] Table 6 Core information for pollution experiment

[0103]

[0104] The experimental results are shown in Table 7 below.

[0105] Table 7 Pollution test results

[0106]

[0107]

[0108] From the test results in Table 7, it can be seen that after the core was contaminated by the original system drilling fluid on site, the permeability decreased from 0.4205mD to 0.2575mD, and the damage rate was as high as 38.77%. This shows that the original system environmentally friendly drilling fluid has poor reservoir protection performance and cannot form a better plugging layer, resulting in serious blockage of pore throats and cracks inside the core. At the same time, according to the effect diagram before and after the core pollution ( Figure 5), it can also be seen that the drilling fluid has deep invasion traces. After the core was contaminated by the optimized system (Example 1), the permeability changed slightly, from 0.3087mD to 0.2511mD, and the damage rate was 18.66%, which was much lower than the damage rate of the original system (Comparative Example). This shows that the optimized system (Example 1) has better reservoir protection performance. On the one hand, the system can form a good plugging layer and reduce the invasion depth (such as Figure 6 ), on the other hand, the defoaming agent introduced into the system reduces the surface tension of the filtrate, which helps the filtrate to flow back and restore the permeability.

[0109] In summary, from the above content we can know:

[0110] 1. The environmentally friendly water-based drilling fluid prepared by the formula and preparation method of Example 1 and Example 2 has excellent rheological filtration, lubricity and sedimentation stability, plastic viscosity of 25mPa.s~47mPa.s, API water loss of 2.4-2.8mL, initial shear 3-3.5Pa, final shear 5-9Pa, dynamic shear force 10-11Pa.

[0111] 2. The environmentally friendly water-based drilling fluid prepared by the formula and preparation method of Example 1 and Example 2 has excellent temperature stability, and its rheological properties fluctuate less with increasing temperature. It also has excellent gas intrusion prevention and degassing effect. During the continuous methane injection process, the system performance is stable.

[0112] 3. The environmentally friendly water-based drilling fluid prepared by the formula and preparation method of Example 1 has excellent inhibitory and reservoir protection properties, can effectively inhibit the hydration and dispersion of shale, and the permeability damage rate of dense sandstone core is 18.66%, which is lower than that of the original system.

[0113] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An environmentally friendly water-based drilling fluid suitable for tight gas, characterized in that: The invention comprises the following components: roentgen slurry, sodium hydroxide, xanthan gum, zwitterionic polymer coating agent, fluid loss reducer, plugging agent, inhibitor, potassium chloride, lubricant, defoamer, viscosity reducer and barite.

2. The environmentally friendly water-based drilling fluid suitable for tight gas according to claim 1, characterized in that: The components of the water-based drilling fluid are calculated in the following mass percentages: 2% to 4% bentonite slurry, 0.2% sodium hydroxide, 0 to 0.2% xanthan gum, 0.2% to 0.3% zwitterionic polymer coating agent, 4% to 6% fluid loss reducer, 4% plugging agent, 0.2% to 0.3% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoamer and 1% to 2% viscosity reducer, and the balance is barite.

3. The environmentally friendly water-based drilling fluid suitable for tight gas according to claim 1, characterized in that: When used for density 1.7g / cm 3 In an environment of , the components of the water-based drilling fluid are calculated according to the following mass percentages: 4% bentonite slurry, 0.2% sodium hydroxide, 0.2% xanthan gum, 0.3% zwitterionic polymer coating agent, 6% fluid loss reducer, 4% plugging agent, 0.3% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoamer and 1% viscosity reducer, and the balance is barite.

4. The environmentally friendly water-based drilling fluid suitable for tight gas according to claim 1, characterized in that: When used for density 2.3g / cm 3 In an environment of , the components of the water-based drilling fluid are calculated according to the following mass percentages: 2% bentonite slurry, 0.2% sodium hydroxide, 0.2% zwitterionic polymer coating agent, 4% fluid loss reducer, 4% plugging agent, 0.2% inhibitor, 8% potassium chloride, 2% lubricant, 0.1% defoamer and 2% viscosity reducer, and the balance is barite.

5. The environmentally friendly water-based drilling fluid suitable for tight gas according to claim 1, characterized in that: The density of the barite is 4.3 g / cm 3 .

6. The environmentally friendly water-based drilling fluid suitable for tight gas according to claim 1, characterized in that: The zwitterionic polymer coating agent is a zwitterionic polymer strong coating agent for drilling fluid; the fluid loss reducer is an environmentally friendly fluid loss reducer; the plugging agent is an environmentally friendly plugging agent; the inhibitor is an environmentally friendly inhibitor; the lubricant is a lubricant for drilling fluid; the defoaming agent is a general-purpose silicone defoaming agent; and the viscosity reducer is a silicone-fluorine high-temperature viscosity reducer.

7. A method for preparing an environmentally friendly water-based drilling fluid suitable for tight gas according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Add bentonite and sodium hydroxide into water and stir to mix well to prepare base slurry; Step 2: Add xanthan gum, zwitterionic polymer coating agent, fluid loss reducer, plugging agent and inhibitor to the base slurry in sequence and stir evenly; Step 3: Continue to add potassium chloride latex and stir evenly; Step 4: Continue to add lubricant, defoamer, viscosity reducer and barite and stir evenly.

8. The method for preparing an environmentally friendly water-based drilling fluid suitable for tight gas according to claim 7, characterized in that: In step 2, each treatment agent is stirred for 5 minutes.

9. The method for preparing an environmentally friendly water-based drilling fluid suitable for tight gas according to claim 7, characterized in that: In step 4, each treatment agent was stirred for 5 minutes, and finally stirred for 10 minutes.

10. Use of the water-based drilling fluid according to any one of claims 1 to 6 or the water-based drilling fluid prepared by the method for preparing the water-based drilling fluid according to any one of claims 7 to 9 in deepwater and ultra-deepwater oil and gas field drilling.

Images