Method for preparing water-based drilling fluid by using slickwater fracturing flow-back fluid as slurry preparation water

Abstract

The invention provides a method for preparing water-based drilling fluid by using slickwater fracturing flow-back fluid as slurry preparation water, which comprises the following steps: filtering the slickwater fracturing flow-back fluid, adjusting the pH value, adding a destabilizing agent, a flocculating agent and a chelating agent into the slickwater fracturing flow-back fluid, stirring, standing for layering, taking supernatant liquid, and adding a defoaming agent, a decolorizing agent and a sterilizing agent into the supernatant liquid to obtain the slurry preparation water; and adding the slurry preparation water, the macromolecular coating agent FA-367, the glycan treating agent and the weighting material into the drilling fluid base slurry to obtain the water-based drilling fluid. Wherein the mass ratio of the slickwater fracturing flow-back fluid to the destabilizing agent to the flocculating agent to the chelating agent to the defoaming agent to the decolorizing agent to the sterilizing agent is 1.0: (0.5-1.0): (0.5-2.0): (1.0-3.0): (0.1-0.5): (0.5-2.0): (0.1-1.0). The water-based drilling fluid system with strong inhibition, low friction resistance and high performance obtained by the invention has good rheological property, filtrate loss reduction property, inhibition property and lubricity. And the whole treatment process simultaneously meets the engineering requirements of resource utilization of the slickwater fracturing flow-back fluid and well drilling, and has a good application prospect.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, and in particular to a method for preparing water-based drilling fluid by using slick water fracturing flowback fluid as slurry preparation water. Background Art

[0002] With the continuous growth of global energy demand, the difficulty and cost of exploiting traditional oil and gas resources are also increasing. Hydraulic fracturing technology can develop and utilize unconventional oil and gas resources, such as shale gas and tight oil, providing new opportunities for energy development. Especially in the exploitation of unconventional oil and gas resources, hydraulic fracturing technology is one of the key technologies to improve the recovery rate. By injecting water, sand and chemical additives into the well, the rock is fractured with high pressure to form cracks, or the rock cracks are enlarged and form channels, which effectively improves the permeability characteristics and pore structure of the oil and gas reservoir, thereby greatly improving the recovery rate of oil and gas. At present, water-based fracturing fluid has strong applicability and low cost. Among them, slick water fracturing fluid is a new type of water-based fracturing fluid with the advantages of low friction, low viscosity, high permeability and low cost, and is currently widely used.

[0003] During the fracturing process, the liquid used for fracturing (fracturing fluid) will contact and mix with minerals, oil and gas and other substances in the formation. Part of the fracturing fluid will then be discharged from the well, which is called flowback fluid. A large amount of water resources are needed when preparing water-based fracturing fluid. The flowback fluid produced after fracturing using a slick water system is a kind of sewage composed of a variety of chemical agents. The main components are fracturing fluid additives such as demulsifiers, antibacterial agents, and viscosity regulators. The fracturing flowback fluid has complex components, high viscosity, strong stability, high mineralization and high content of suspended solids, and is very difficult to handle. In addition, the amount of waste liquid generated after fracturing is large, and it presents the characteristics of "three highs" (high COD, high TSS and high TDS). It is one of the main pollutants in oil and gas field production. If the flowback fluid is not effectively treated and directly discharged, it will cause serious environmental pollution. With the promulgation of my country's new Environmental Protection Law, waste generated by oil and gas production is required to be treated "not on the ground". How to effectively treat fracturing flowback fluid has become a key technical problem that needs to be solved urgently. At present, the treatment technology of fracturing return fluid is mainly divided into three categories: external discharge after treatment, reinjection after treatment and repeated preparation of fracturing fluid. Among them, the treatment methods of fracturing return fluid at home and abroad mainly include physical treatment method (precipitation, filtration, adsorption, etc.), chemical treatment method (chemical reaction, oxidation-reduction, etc.), biological treatment method (water quality treatment by aerobic microorganisms, anaerobic microorganisms, etc.), acidification and heat treatment method (acidification of fracturing return fluid to retain the available elements in it), but the current conventional treatment and reuse technology does not involve desalination, and it is difficult to solve the problems of high viscosity, severe emulsification, difficult separation, high handling difficulty and high transportation cost of slippery water fracturing return fluid. Moreover, repeated preparation of fracturing fluid often requires dilution with a large amount of clean water, the reuse ratio of return fluid is not high, and a large amount of water resources are consumed. However, the method of reinjection after treatment and repeated preparation of fracturing fluid has disadvantages: as the number of repeated preparations increases, the salt concentration and COD in the return fluid accumulate, the preparation performance decreases, and the cost becomes higher and higher. Moreover, as production enters the late stage of development, the demand for fracturing fluid reuse is relatively small. A large amount of remaining fracturing flowback fluid will eventually need to be deeply treated to meet the standards before being used for other purposes or discharged. As a result, the two methods of reinjection after treatment and repeated preparation of fracturing fluid are difficult to meet the demand in terms of processing volume. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a method for preparing water-based drilling fluid by using slickwater fracturing flowback fluid as slurry preparation water, wherein the slickwater fracturing flowback fluid is treated to obtain slurry preparation water, and the slurry preparation water is used to prepare high-performance water-based drilling fluid. The specific content of the invention is as follows:

[0005] In a first aspect, the present invention provides a method for preparing a water-based drilling fluid using slickwater fracturing flowback fluid as slurry preparation water, the method comprising the following steps:

[0006] S1. After filtering and adjusting the pH of the slick water fracturing flowback fluid, adding a destabilizing agent, a flocculant and a chelating agent thereto, stirring, standing and stratifying, taking the upper clear liquid, and adding a defoaming agent, a decolorizing agent and a bactericide thereto to obtain slurry preparation water;

[0007] S2, adding the slurry preparation water, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material to the drilling fluid base slurry to obtain the water-based drilling fluid;

[0008] The mass ratio of the slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0: 0.5-1.0%: 0.5-2.0%: 1.0-3.0%: 0.1-0.5%: 0.5-2.0%: 0.1-1.0%.

[0009] Optionally, in step S1, the destabilizing agent is any one of polyvinyl alcohol, polyacrylamide, and polypropylene alcohol;

[0010] The flocculant is any one of polyaluminium chloride, polyferric sulfate and polyaluminium sulfate;

[0011] The chelating agent is any one of sulfite, EDTA and citric acid;

[0012] The defoaming agent is any one of polyacrylamide, sulfonate, phosphate and silicone oil;

[0013] The decolorizing agent is any one of activated carbon adsorbent, hydrogen peroxide, and sodium chlorate;

[0014] The bactericide is any one of sodium hypochlorite, sodium chloride, hydrogen peroxide and potassium permanganate.

[0015] Optionally, in step S1, the destabilizing agent is polyvinyl alcohol; the flocculant is polyferric sulfate; the chelating agent is EDTA; the defoaming agent is polyacrylamide; the decolorizing agent is hydrogen peroxide; and the bactericide is sodium hypochlorite.

[0016] Optionally, the mass ratio of the slick water fracturing flowback fluid, pH regulator, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0:0.6%:1.0%:1.0%:0.4%:1.5%:0.8%.

[0017] Optionally, before step S1, it is also necessary to perform component analysis on the color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD of the slick water fracturing flowback fluid.

[0018] Optionally, after step S1, it is also necessary to perform component analysis on the color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD of the slick water fracturing flowback fluid.

[0019] Optionally, in step S2, the polysaccharide treating agent is hydroxypropyl methylcellulose ether.

[0020] Optionally, in step S2, the mass ratio of the slurry preparation water, drilling fluid base slurry, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material is 1: 1.0-4.0%: 0.1-0.3%: 1-5%: 10-15%.

[0021] Optionally, in step S2, the method for preparing hydroxypropyl methylcellulose ether comprises:

[0022] Add 50-100 mL of toluene to a mixture of hydroxypropyl methylcellulose and an etherifying agent in a mass ratio of 1:(1-3), then stir at a speed of 300-500 r / min for 30 min, add an alkaline catalyst with a mass concentration of 5-8%, control the reaction temperature to 70-90° C., stir at a speed of 500 r / min for 60-70 min, filter, wash, dry and crush to obtain the hydroxypropyl methylcellulose ether; wherein the etherifying agent is any one of methyl, ethyl or propyl etherifying agents;

[0023] The alkaline catalyst is any one of sodium hydroxide, potassium hydroxide and sodium carbonate.

[0024] Optionally, in step S2, the drilling fluid base slurry is obtained by mixing sodium bentonite and water, adding Na2CO3, and then sealing and curing for 24 hours;

[0025] Wherein, the mass ratio of the sodium bentonite to Na2CO3 is 1:0.3%.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention provides a method for preparing a water-based drilling fluid using a slick water fracturing flowback fluid as slurry preparation water, comprising adding a destabilizing agent, a flocculant and a chelating agent to the slick water fracturing flowback fluid, stirring, standing and stratifying, taking the upper clear liquid, and adding a defoaming agent, a decolorizing agent and a bactericide thereto to obtain slurry preparation water. Experimental results show that compared with untreated slick water fracturing flowback fluid, the slick water fracturing flowback fluid provided in the embodiment of the present application has greatly reduced organic pollutants, suspended matter, soluble inorganic salt content, calcium ions and magnesium ions after treatment, while its density and pH value remain unchanged. Specifically, the COD of the slick water fracturing flowback fluid before treatment is 2.347 W / cm2. CrThe concentration was 16122 mg / L, and it was 180 mg / L after treatment; the suspended matter content of the slickwater fracturing flowback fluid before treatment was reduced from 1057 mg / L to 2.06 mg / L after treatment; the mineralization of the slickwater fracturing flowback fluid before treatment was reduced from 36579 to 1843 after treatment; in addition, the calcium content in the slickwater fracturing flowback fluid before treatment was 2378 mg / L, and the magnesium content was 145 mg / L, and after treatment, they were reduced to very low levels (calcium was 157 mg / L, magnesium was 0 mg / L). Therefore, the treatment of the slickwater flowback fluid successfully removed organic pollutants, suspended solid particles, soluble inorganic salts and metal ions, and had no significant effect on its density and acidity and alkalinity. The slurry water obtained after treatment can meet the requirements for preparing water-based drilling fluid, which is conducive to the resource utilization of slickwater fracturing flowback fluid.

[0028] The present invention uses the slurry water obtained after treating the slick water fracturing flowback fluid to prepare a water-based drilling fluid, adds the drilling fluid base slurry to the slurry water, and selects auxiliary agents to maintain the stability of the drilling fluid, thereby obtaining a water-based drilling fluid with strong inhibition, low friction and high performance. The drilling fluid system has good rheological properties, fluid loss reduction, inhibition and lubricity. In addition, the entire treatment process simultaneously meets the engineering requirements of resource utilization of slick water fracturing flowback fluid and drilling, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 A flow chart of a method for preparing water-based drilling fluid using slick water fracturing flowback fluid as slurry preparation water provided by an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means a limitation on the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts falls within the scope of protection of the present invention. In addition, all other embodiments obtained by ordinary technicians in this field without carrying out creative work belong to the scope of protection of the present invention.

[0032] In the embodiment, no specific experimental steps or conditions are indicated, and the operation or conditions of the conventional experimental steps described in the prior art in this field can be carried out. The reagents used and other instruments that do not indicate the manufacturer are conventional reagent products that can be obtained commercially. In addition, the accompanying drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the figures represent the same or similar parts, and thus their repeated description will be omitted. Some block diagrams shown in the accompanying drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0033] Technologies, methods, and apparatus known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, such technologies, methods, and apparatus should be considered part of the authorization specification.

[0034] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0035] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0036] Based on the existing treatment technology of slickwater fracturing backflow fluid, there are problems such as great difficulty in treatment, high transportation cost, low reuse ratio of fracturing backflow fluid, and inability to treat a large amount of residual fracturing backflow fluid. By comparing and analyzing the backflow fluid and water-based drilling fluid, it is found that the components contained in the backflow fluid are the same as the components of the treatment agents such as filtrate reducers, inhibitors and lubricants commonly used in water-based drilling fluids. By further analyzing the mechanism of action of the residual substances in the backflow fluid and the drilling fluid treatment agent, it is found that the salt in the fracturing backflow fluid can be used as an additive to improve the inhibition performance of the water-based drilling fluid. The unconsumed chemical additives (such as surfactants, friction reducers, etc.) in the fracturing backflow fluid can improve the rheology, inhibition, filtrate reduction and lubrication performance of the water-based drilling fluid and improve the stability of the wellbore. Therefore, some of the additives remaining in the slickwater fracturing fluid can be used as an effective component in the water-based drilling fluid. The fracturing backflow fluid can be treated as the slurry water of the water-based drilling fluid, which can effectively utilize the salt and unconsumed chemical additives in the backflow fluid. From the perspective of cost or environmental protection, the resource utilization of fracturing flowback fluid is the development trend of the oil and gas field industry in the future. Therefore, the present invention proposes a method for preparing a low-friction water-based drilling fluid using slippery water fracturing flowback fluid as slurry preparation water, by adding a destabilizing agent, a flocculant and a chelating agent to the slippery water fracturing flowback fluid, stirring, standing and stratifying, taking the upper clear liquid, and adding a defoaming agent, a decolorizing agent and a bactericide thereto to obtain slurry preparation water. Compared with the untreated slippery water fracturing flowback fluid, the slurry preparation water obtained after treating the slippery water fracturing flowback fluid provided in the embodiment of the present application has greatly reduced organic pollutants, suspended matter, soluble inorganic salt content, calcium ions and magnesium ions, and its density and pH value remain unchanged, meeting the requirements for preparing water-based drilling fluid. By adding drilling fluid base slurry to the slurry preparation water, and selecting auxiliary agents to maintain the stability of the drilling fluid, a water-based drilling fluid with strong inhibition of low friction and high performance is obtained. The drilling fluid system has good rheology, fluid loss reduction, inhibition and lubricity. Therefore, the method for preparing water-based drilling fluid by using slick water fracturing flowback fluid as slurry preparation water provided by the present invention satisfies both resource utilization of fracturing flowback fluid and engineering requirements of drilling, and has good application prospects.

[0037] The specific implementation methods are as follows:

[0038] In a first aspect, the present invention provides a method for preparing a water-based drilling fluid using slickwater fracturing flowback fluid as slurry preparation water. Figure 1 The flow chart of the method for preparing water-based drilling fluid by using the slick water fracturing flowback fluid provided in Examples 1 and 2 of the present invention as slurry preparation water is shown. Figure 1 As shown, the application includes the following steps:

[0039] S1. After filtering and adjusting the pH of the slick water fracturing flowback fluid, adding a destabilizing agent, a flocculant and a chelating agent thereto, stirring, standing and stratifying, taking the upper clear liquid, and adding a defoaming agent, a decolorizing agent and a bactericide thereto to obtain slurry preparation water;

[0040] When this step is implemented, it is necessary to first conduct a component analysis on the slick water fracturing flowback fluid collected from different wellheads or other collection equipment. The indicators that need to be determined in the analysis include: color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD of the slick water flowback fluid. Then, the slick water fracturing flowback fluid is pretreated, that is, solid particles and large suspended matter are removed by filtering; then, the pH value of the slick water fracturing flowback fluid is adjusted (pH=6.5-8.5) with an acid-base regulator (sodium hydroxide, potassium hydroxide, sodium carbonate, hydrochloric acid, etc.); then, a destabilizer, a flocculant and a chelating agent are added to aggregate the suspended matter into larger clusters to facilitate subsequent precipitation and filtration; the flocculated liquid is allowed to stand for a period of time to allow the suspended matter to settle to the bottom to form a supernatant and a precipitate, and the supernatant is passed through a filtering device, such as a filter screen or a filter cloth, to further remove solid particles and suspended matter; the supernatant is taken and a defoaming agent is added thereto until it is completely defoamed; a decolorizing agent is added according to the color and appearance of the slick water fracturing flowback fluid; and the treated slick water fracturing flowback fluid is sterilized to ensure water quality safety. The mass ratio of the slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0: 0.5-1.0%: 0.5-2.0%: 1.0-3.0%: 0.1-0.5%: 0.5-2.0%: 0.1-1.0%. The destabilizer is added to destroy the stability of suspended matter and colloidal particles in the slick water flowback fluid, so that they aggregate into larger particles, which is convenient for subsequent precipitation and separation. The added destabilizer is any one of polyvinyl alcohol, polyacrylamide and polypropylene alcohol. The flocculant is added to promote the aggregation and precipitation of solid phase particles in the slick water flowback fluid, making it easier to separate. The added flocculant is any one of polyaluminum chloride, polyferric sulfate and polyaluminum sulfate. The chelating agent can combine with metal ions in the slick water flowback fluid to prevent them from reacting or precipitating. The added chelating agent is any one of sulfite, EDTA and citric acid. The defoamer is added because the slippery water return fluid may produce foam during the treatment process, and these foams will affect the subsequent treatment processes such as filtration, precipitation, and centrifugation. Therefore, defoaming treatment is required to eliminate or reduce the foam to an acceptable level to ensure the normal progress of the subsequent treatment process. The type and amount of defoamer are selected according to the component analysis of the slippery water return fluid. The added defoamer is any one of polyacrylamide, sulfonate, phosphate, and silicone oil. The decolorizer is added to remove colored organic substances that may be contained in the slippery water return fluid, such as naphthalene, aromatic hydrocarbons, etc. The added decolorizer is any one of activated carbon adsorbent, hydrogen peroxide, and sodium chlorate. The decolorization treatment is performed by adsorbing or oxidizing the colored organic substances to precipitate them.The bactericide is added to treat the large amount of organic matter and microorganisms contained in the slick water fracturing return fluid to ensure the performance of the subsequent drilling fluid as slurry water. The amount of bactericide added needs to be selected according to the water quality component analysis of the slick water return fluid. The amount of bactericide added should be as small as possible to avoid the influence of the bactericide on the treatment effect, and should be adjusted according to the experimental results. The added bactericide is any one of sodium hypochlorite, sodium chloride, hydrogen peroxide, and potassium permanganate. In the preferred embodiment, the destabilizer is polyvinyl alcohol, the flocculant is polyferric sulfate, the chelating agent is EDTA, the defoamer is polyacrylamide, the decolorizer is hydrogen peroxide, and the bactericide is sodium hypochlorite; the mass ratio of the selected slick water fracturing return fluid, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0: 0.6%: 1.0%: 1.0%: 0.4%: 1.5%: 0.8%. After the slickwater fracturing flowback fluid is treated with the above-mentioned auxiliary agent, the color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD need to be analyzed for composition. When the conductivity is in the range of 1.5-4.0mS / cm, the suspended matter content is ≤20mg / L, the organic matter content is ≤200mg / L, the salinity is in the range of 120-180g / L, and the oil content is ≤50mg / L, clean water is added to the treated slickwater fracturing flowback fluid according to the drilling fluid formulation direction to dilute it, and the slurry water for configuring the drilling fluid can be obtained. The ratio of clean water to the treated flowback fluid is 4:6 to 6:4. Table 1 shows the comparison of the physical and chemical components of the slickwater fracturing flowback fluid before and after treatment provided in Example 1 of the present invention.

[0041] Slickwater fracturing flowback fluid Before treatment After treatment Color and appearance Light Brown colorless <![CDATA[COD Cr (mg / L)]]> 16122 180 Suspended matter (mg / L) 1057 2.06 Mineralization 36579 1843 Calcium (mg / L) 2378 157 Magnesium (mg / L) 145 0 density 1.002 1.001 pH 6.5 6.5 Solid content 119 18.5

[0042] It can be seen that the slickwater fracturing flowback fluid was light brown before treatment, and the treated fluid was colorless. The treatment process successfully removed color impurities. CrThe concentration was reduced from 16122 mg / L to 180 mg / L after treatment, and the treatment process effectively reduced the content of organic pollutants; the suspended matter content was reduced from 1057 mg / L to 2.06 mg / L after treatment, and the treatment process successfully removed suspended solid particles. The mineralization was reduced from 36579 to 1843 after treatment, and the treatment process significantly reduced the content of soluble inorganic salts in the water; the calcium content in the slickwater fracturing return fluid before treatment was 2378 mg / L, and the magnesium content was 145 mg / L. After treatment, they were reduced to very low levels (calcium was 157 mg / L and magnesium was 0 mg / L), indicating that the treatment process successfully removed these two metal ions. The density and pH value of the slickwater fracturing return fluid before and after treatment remained unchanged, at 1.002 and 6.5, respectively, indicating that the treatment process had no significant effect on the density and acidity of the liquid. In summary, the treatment of slickwater flowback fluid successfully removed organic pollutants, suspended solid particles, soluble inorganic salts and metal ions. The slickwater flowback fluid after treatment can meet the requirements of preparing water-based drilling fluid.

[0043] S2, adding the slurry preparation water, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material to the drilling fluid base slurry to obtain the water-based drilling fluid;

[0044] When this step is implemented, the mass ratio of the selected slurry water, drilling fluid base slurry, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material is 1: 1.0-4.0%: 0.1-0.3%: 1-5%: 10-15%. In step S2, the drilling fluid base slurry is obtained by mixing sodium bentonite and water, adding Na2CO3, and then sealing and curing for 24 hours; wherein the mass ratio of the sodium bentonite and Na2CO3 is 1: 0.3%. The selected polysaccharide treatment agent is hydroxypropyl methylcellulose ether. The preparation method of hydroxypropyl methylcellulose ether is as follows: 50-100 mL of toluene is added to a mixture of hydroxypropyl methylcellulose and an etherifying agent in a mass ratio of 1:(1-3), and then the mixture is stirred at a speed of 300-500 r / min for 30 min, an alkaline catalyst with a mass concentration of 5-8% is added, the reaction temperature is controlled to be 70-90°C, and the mixture is stirred at a speed of 500 r / min for 60-70 min, and the mixture is filtered, washed, dried, and crushed to obtain hydroxypropyl methylcellulose ether; wherein the etherifying agent is any one of methyl, ethyl or propylated etherifying agents; and the alkaline catalyst is any one of sodium hydroxide, potassium hydroxide, and sodium carbonate.

[0045] As a sugar, hydroxypropyl methylcellulose can provide lubrication itself, form a lubricating layer or film, and reduce the friction between the well wall and the drill pipe. It also has good inhibition performance and can be adsorbed on the well wall to form a protective film to prevent the well wall from swelling and decomposing, and improve the stability of the well wall. In addition, it can also improve the filtration performance of the drilling fluid, reduce the filtration of solid particles into the well wall, and maintain the stability of the wellbore. The etherification modification of hydroxypropyl methylcellulose is based on the properties of the treated return fluid (containing sodium, calcium, magnesium ions, etc.), so that the modified hydroxypropyl methylcellulose ether has good salt and calcium resistance, and can maintain stability and effectiveness in salt environments such as sodium chloride and calcium chloride.

[0046] Table 2 shows the rheological properties and filtration performance test results of the low friction drilling fluid system prepared by treating the slick water fracturing flowback fluid provided in Example 2 of the present invention.

[0047]

[0048] It can be seen that with the increase of temperature, the apparent viscosity of the low friction drilling fluid system gradually decreases, the plastic viscosity shows a downward trend, and the dynamic shear force is relatively stable. Under high temperature conditions (150 / 180℃), the overall viscosity of the system decreases, the fluidity increases, and the API filtration loss increases, but the rheological properties and filtration loss properties are still within the controllable range, indicating that the basic formula of the water-based drilling fluid constructed with the treated slickwater flowback fluid and polysaccharide treatment agent has good rheological and filtration loss properties.

[0049] Table 3 shows the inhibition performance test results of the low friction drilling fluid system prepared by treating slick water fracturing flowback fluid provided in Example 2 of the present invention.

[0050]

[0051]

[0052] It can be seen that within the experimental temperature range, as the temperature gradually increases, the rolling recovery rate of the low friction drilling fluid system decreases from 78.82% to 72.88%, which indicates that the basic formula of the drilling fluid has a strong ability to inhibit the hydration and dispersion of clay under high temperature conditions. Within the experimental temperature range, the linear expansion rate of the system increases slightly (gradually from 32.97% to 45.35%), and compared with clean water, it remains in a lower range, indicating that the basic formula of the drilling fluid can effectively control the hydration and expansion of clay under high temperature conditions.

[0053] Table 4 shows the lubricity test results of the low friction drilling fluid system prepared by treating the slick water fracturing flowback fluid provided in Example 2 of the present invention.

[0054]

[0055] It can be seen that compared with the 4% sodium-based bentonite-based slurry, the lubricating performance of the basic formula of the low-friction drilling fluid system obtained in Example 2 is better, and as the temperature increases to 180° C., the reduction rate of the friction coefficient is still greater than 80%.

[0056] In order to enable those skilled in the art to more clearly understand the present invention, the method for preparing water-based drilling fluid using slick water fracturing flowback fluid as slurry preparation water according to the present invention is now described in detail through the following examples.

[0057] Example 1

[0058] a. Pre-treat the slickwater fracturing flowback fluid by filtering to remove solid particles and large suspended matter;

[0059] b. Add acid-base regulator to the slick water fracturing flowback fluid to adjust the pH value of the flowback fluid to 7;

[0060] c. Add destabilizing agent (polyvinyl alcohol), flocculant (polyferric sulfate) and chelating agent (EDTA) to the slick water fracturing flowback fluid to aggregate the suspended matter into larger clusters;

[0061] d. Let the flocculated liquid stand for 24 hours to allow the suspended matter to settle to the bottom, forming a supernatant and a precipitate. Pass the supernatant through a filtering device, such as a filter screen or filter cloth, to further remove solid particles and suspended matter. After separation, take the supernatant to detect the content of suspended solid matter. If the content of suspended solid matter is greater than 20 mg / L, repeat steps c and d.

[0062] e. Add defoamer (polyacrylamide) to the supernatant and stir, repeat several times until the foam is completely eliminated;

[0063] f. Add decolorizing agent (hydrogen peroxide) according to the color and appearance of the slippery water return liquid and stir, repeat several times until it is completely decolorized;

[0064] g. After adding the fungicide (sodium hypochlorite), take samples for testing. If the organic matter content is > 200 mg / L, add the fungicide repeatedly.

[0065] The treated slickwater fracturing flowback fluid is diluted and used as slurry water for preparing drilling fluid.

[0066] The mass ratio of the selected slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoaming agent, decolorizing agent and bactericide is 1.0: 0.6%: 1.0%: 1.0%: 0.4%: 1.5%: 0.8%.

[0067] Example 2

[0068] The steps for preparing water-based drilling fluid are:

[0069] Low friction drilling fluid is an aqueous solution containing the following components in percentage by mass:

[0070] Weigh 4.0% sodium bentonite, add it to the treated slick water fracturing flowback fluid, add 0.3% Na2CO3 under high-speed stirring conditions, adjust the pH value to 7, stir thoroughly and seal and cure for 24 hours to obtain 4.0% bentonite-based slurry;

[0071] In a 4.0% bentonite-based slurry, add 0.1% FA-367 (macromolecule coating agent) and 5% polysaccharide treatment agent, and then add weighted crystals to adjust the system density to 1.20 g / cm 3 .

[0072] Example 3

[0073] a. Pre-treat the slickwater fracturing flowback fluid by filtering to remove solid particles and large suspended matter;

[0074] b. Add acid-base regulator to the slick water fracturing flowback fluid to adjust the pH value of the flowback fluid to 7;

[0075] c. Add destabilizing agent (polyacrylamide), flocculant (polyaluminium chloride) and chelating agent (sulfite) to the slick water fracturing flowback fluid to aggregate the suspended matter into larger clusters;

[0076] d. Let the flocculated liquid stand for 24 hours to allow the suspended matter to settle to the bottom, forming a supernatant and a precipitate. Pass the supernatant through a filtering device, such as a filter screen or filter cloth, to further remove solid particles and suspended matter. After separation, take the supernatant to detect the content of suspended solid matter. If the content of suspended solid matter is greater than 20 mg / L, repeat steps c and d.

[0077] e. Add defoamer (silicone oil) to the supernatant and stir, repeat several times until the foam is completely eliminated;

[0078] f. Add decolorizing agent (sodium chlorate) according to the color and appearance of the slippery water flowback and stir, repeat several times until it is completely decolorized;

[0079] g. After adding the fungicide (potassium permanganate), take samples for testing. If the organic matter content is > 200 mg / L, add the fungicide repeatedly.

[0080] The treated slickwater fracturing flowback fluid is diluted and used as slurry water for preparing drilling fluid.

[0081] The mass ratio of the selected slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoaming agent, decolorizing agent and bactericide is 1.0: 0.8%: 1.5%: 2.0%: 0.3%: 1.0%: 0.5%.

[0082] Example 4

[0083] The steps for preparing water-based drilling fluid are:

[0084] Low friction drilling fluid is an aqueous solution containing the following components in percentage by mass:

[0085] Weigh 4.0% sodium bentonite, add it to the treated slick water fracturing flowback fluid, add 0.3% Na2CO3 under high-speed stirring conditions, adjust the pH value to 7, stir thoroughly and seal and cure for 24 hours to obtain 4.0% bentonite-based slurry;

[0086] In a 4.0% bentonite-based slurry, add 0.1% FA-367 (macromolecule coating agent) and 5% polysaccharide treatment agent, and then add weighted crystals to adjust the system density to 1.20 g / cm 3 .

[0087] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification.

[0088] For the method embodiments, for the sake of simplicity, they are all described as a series of action combinations, but those skilled in the art should know that the present invention is not limited by the order of the actions described, because according to the present invention, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily required by the present invention.

[0089] The above is a detailed introduction to the method for preparing water-based drilling fluid using a slick water fracturing flowback fluid as slurry mixing water provided by the present invention. Specific examples are used herein to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present invention.

Claims

1. A method for preparing water-based drilling fluid using slickwater fracturing flowback fluid as slurry preparation water, characterized in that: The method comprises the following steps: S1. After filtering and adjusting the pH of the slick water fracturing flowback fluid, adding a destabilizing agent, a flocculant and a chelating agent thereto, stirring, standing and stratifying, taking the upper clear liquid, and adding a defoaming agent, a decolorizing agent and a bactericide thereto to obtain slurry preparation water; S2, adding the slurry preparation water, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material to the drilling fluid base slurry to obtain the water-based drilling fluid; The mass ratio of the slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0: 0.5-1.0%: 0.5-2.0%: 1.0-3.0%: 0.1-0.5%: 0.5-2.0%: 0.1-1.0%.

2. The method according to claim 1, characterized in that In step S1, the destabilizing agent is any one of polyvinyl alcohol, polyacrylamide, and polypropylene alcohol; The flocculant is any one of polyaluminium chloride, polyferric sulfate and polyaluminium sulfate; The chelating agent is any one of sulfite, EDTA and citric acid; The defoaming agent is any one of polyacrylamide, sulfonate, phosphate and silicone oil; The decolorizing agent is any one of activated carbon adsorbent, hydrogen peroxide, and sodium chlorate; The bactericide is any one of sodium hypochlorite, sodium chloride, hydrogen peroxide and potassium permanganate.

3. The method according to claim 2, characterized in that In step S1, the destabilizing agent is polyvinyl alcohol; the flocculant is polyferric sulfate; the chelating agent is EDTA; the defoaming agent is polyacrylamide; the decolorizing agent is hydrogen peroxide; and the bactericide is sodium hypochlorite.

4. The method according to claim 1, characterized in that: The mass ratio of the slick water fracturing flowback fluid, destabilizer, flocculant, chelating agent, defoamer, decolorizer and bactericide is 1.0:0.6%:1.0%:1.0%:0.4%:1.5%:0.8%.

5. The method according to claim 1, characterized in that Before step S1, it is also necessary to perform component analysis on the color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD of the slick water fracturing flowback fluid.

6. The method according to claim 1, characterized in that After step S1, it is also necessary to perform component analysis on the color and appearance, density, pH value, calcium ion content, magnesium ion content, total mineralization, solid content, and COD of the slurry preparation water.

7. The method according to claim 1, characterized in that In step S2, the polysaccharide treating agent is hydroxypropyl methylcellulose ether.

8. The method according to claim 1, characterized in that In step S2, the mass ratio of the slurry preparation water, drilling fluid base slurry, macromolecular coating agent FA-367, polysaccharide treatment agent and weighting material is 1: 1.0-4.0%: 0.1-0.3%: 1-5%: 10-15%.

9. The method according to claim 7, characterized in that: In step S2, the preparation method of hydroxypropyl methylcellulose ether comprises: Add 50-100 mL of toluene to a mixture of hydroxypropyl methylcellulose and an etherifying agent in a mass ratio of 1:(1-3), then stir at a speed of 300-500 r / min for 30 min, add an alkaline catalyst with a mass concentration of 5-8%, control the reaction temperature to 70-90° C., stir at a speed of 500 r / min for 60-70 min, filter, wash, dry and crush to obtain the hydroxypropyl methylcellulose ether; Wherein, the etherifying agent is any one of methyl, ethyl or propyl etherifying agents; The alkaline catalyst is any one of sodium hydroxide, potassium hydroxide and sodium carbonate.

10. The method according to claim 1, characterized in that In step S2, the drilling fluid base slurry is obtained by mixing sodium bentonite and water, adding Na2CO3, and then sealing and curing for 24 hours; Wherein, the mass ratio of the sodium bentonite to Na2CO3 is 1:0.3%.

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