Recycling and resource utilization system and method for deep coal bed gas fracturing flow-back fluid

Abstract

The invention discloses a system and method for treating deep coal bed gas fracturing flow-back fluid to facilitate resource utilization, the fracturing flow-back fluid passes through a pretreatment device, a carbon dioxide softening device and a special anti-blocking ultrafiltration device, and if the water quality of effluent of the special anti-blocking ultrafiltration device meets the water quality requirement of a required recycling way, the effluent is recycled; if the organic impurities (COD) or the mineralization degree of the effluent is still higher than the water quality requirement of the recycling way, the effluent enters the special anti-blocking nanofiltration device to be further treated, the water produced by the special anti-blocking nanofiltration device is recycled, and the concentrated water of the special anti-blocking nanofiltration device returns to the carbon dioxide softening device to be continuously treated; calcium carbonate generated in the carbon dioxide softening process is recycled and directly used as a drilling fluid additive. The invention provides the full-automatic treatment system and the full-automatic treatment process method which are short in flow; according to the method disclosed by the invention, the energy consumption, the agent dosage and the sludge yield are greatly reduced, and the whole-process recycling of the deep coal bed gas fracturing flow-back fluid, the sludge and the process precipitate (calcium carbonate) is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of waste liquid treatment, and more particularly to a system and method for recycling and utilizing deep coalbed methane fracturing flowback fluid. Background Art

[0002] Deep coalbed methane development uses hydraulic fracturing technology. After the fracturing construction is completed, the fracturing fluid pumped into the formation will flow back to the ground to become fracturing flowback fluid. Since the volume of deep coalbed methane fracturing flowback fluid is much larger than that of conventional fracturing flowback fluid (the flowback volume of a single well can reach 20,000 cubic meters), in addition to containing various fracturing fluid additives and mechanical impurities, it has higher mineralization and hardness than conventional fracturing flowback fluid, especially the hardness can exceed 30,000 mg / L (calculated as calcium carbonate), and it also contains fine coal powder. The water pollution is serious and cannot be discharged directly. It needs to be deeply treated for reuse (reuse) or harmless treatment to meet the standards before it can be discharged. At present, the post-treatment reuse (mainly reinjection) and post-treatment discharge of conventional fracturing flowback fluid require the removal of suspended matter, reduction of hardness and mineralization, COD and other treatment processes, but the removal degree is limited and the reuse ratio is low.

[0003] The existing technology mainly uses biological treatment and / or chemical oxidation to reduce COD, chemical flocculation and / or electroflocculation to flocculate and settle to remove suspended solids, chemical precipitation and / or ion exchange resin to reduce the content of high-valent metal ions, multi-stage filtration to further reduce the content of suspended solids, and reverse osmosis membrane treatment to reduce mineralization: biological treatment and reverse osmosis membrane treatment are mainly used for reuse of sewage after deep treatment or discharge to meet standards. Among them, the most common industrial application of conventional fracturing fluid is chemical oxidation + flocculation sedimentation + multi-stage filtration, and the effluent is reinjected with bactericides, scale inhibitors, and corrosion inhibitors; and reuse after deep treatment or discharge to meet standards requires the above-mentioned basic treatment units for reinjection treatment, and also requires advanced oxidation, biochemical treatment, softening, ultrafiltration membrane and reverse osmosis membrane treatment units.

[0004] The treatment process of the existing technology is long. The biological method has a certain adaptability to the mineralization degree and is extremely sensitive to water quality fluctuations. The electrocoagulation method has a poor separation effect on impurities, and the electrocoagulation plate is severely scaled and corroded, and the cleaning and replacement of the plate is labor-intensive and costly. The subsequent treatment pipelines, valves and subsequent process flows after chemical precipitation are severely scaled, resulting in frequent blockage of the fracturing return fluid treatment device, which requires high-frequency unblocking and backwashing, and a large amount of sludge production. The pure chemical flocculation and chemical precipitation methods use a large amount of reagents and produce a large amount of sludge. The ion exchange resin used in the relevant technology has strong selectivity for high-valent metal ions, but the amount used is large when treating high-hardness fracturing return fluid, the regeneration work intensity is high, and the on-site The implementation is difficult and leads to high costs; in the related technologies, the ultrafiltration membrane and reverse osmosis membrane treatment units have clear requirements on the mineralization and hardness of the influent water, and the influent water quality requirements are high. The large fluctuations in the water quality of the fracturing return fluid cause membrane pollution, scaling on the concentrate side, low recovery rate, and the need for further treatment of the concentrate. There are many practical problems in the on-site operation, and it is even more unsuitable for the treatment of deep coalbed methane fracturing return fluid with high mineralization and high hardness. Therefore, there is no system and method for the resource utilization of deep coalbed methane fracturing return fluid with high mineralization and high hardness, and there is no system and method for the resource utilization of treated effluent that can be reused in multiple ways. Summary of the invention

[0005] The first object of the present invention is to provide a system and method with a simple connection structure and capable of realizing resource recovery and utilization of deep coalbed methane fracturing return fluid.

[0006] The second object of the present invention is to provide a method for directly recycling calcium carbonate filter cake without further drying treatment, which greatly reduces energy consumption and environmental pollution of process by-products compared to conventional fracturing return fluid resource recycling processes, and can achieve the purpose of multi-path reuse.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A deep coalbed methane fracturing flowback fluid recovery and resource utilization system, comprising: a pretreatment device, a carbon dioxide softening device, a special anti-blocking ultrafiltration device, a special anti-blocking nanofiltration device, a sludge dehydration device, a calcium carbonate dehydration recovery device, an ultrafiltration product water tank and a nanofiltration product water tank;

[0009] Wherein, the pretreatment device, the carbon dioxide softening device, the special anti-clogging ultrafiltration device, the ultrafiltration product water tank, the special anti-clogging nanofiltration device and the nanofiltration product water tank are connected in sequence;

[0010] The pretreatment device is cyclically connected to the sludge dewatering device;

[0011] The pretreatment device is cyclically connected to the carbon dioxide softening device;

[0012] The carbon dioxide softening device is cyclically connected to the calcium carbonate dehydration recovery device;

[0013] The special anti-blocking ultrafiltration device is cyclically connected to the carbon dioxide softening device;

[0014] The special anti-clogging nanofiltration device is also connected to the carbon dioxide softening device.

[0015] Preferably, the pretreatment device comprises a regulating water tank, a pH regulating sedimentation tank, an air flotation oil removal device, and a dosing device;

[0016] The regulating water tank is connected to the pH regulating sedimentation tank, the flotation oil removal equipment and the carbon dioxide softening device in sequence; the dosing equipment is connected to the pH regulating sedimentation tank; the pH regulating sedimentation tank is connected to the sludge dewatering device; the sludge dewatering device is connected to the regulating water tank; the flotation oil removal equipment is connected to the carbon dioxide softening device in a circular connection;

[0017] The air flotation oil removal equipment is a shallow air flotation device, the gas source is carbon dioxide, and the gas is supplied from a carbon dioxide storage tank through a vaporizer.

[0018] Preferably, the carbon dioxide softening device comprises a primary softener, a secondary softener, a deep softener, a clarifier, a carbon dioxide storage tank, a vaporizer and a wide-range hardness online monitor;

[0019] The wide-range hardness online monitor includes a wide-range hardness online monitor 1 and a wide-range hardness online monitor 2;

[0020] The flotation oil removal equipment is connected to the primary softener, the secondary softener, the deep softener, the clarifier and the special anti-blocking ultrafiltration device in sequence; the clarifier is cyclically connected to the calcium carbonate dehydration recovery device; the carbon dioxide storage tank is connected to the vaporizer; the vaporizer is respectively connected to the primary softener, the secondary softener and the flotation oil removal equipment;

[0021] The wide-range hardness online monitor 1 is connected to the pipeline between the flotation oil removal equipment and the primary softener; the wide-range hardness online monitor 2 is connected to the pipeline between the clarification tank and the special anti-clogging ultrafiltration device; the special anti-clogging ultrafiltration device is circularly connected to the clarification tank, and the special anti-clogging nanofiltration device is connected to the primary softener.

[0022] Preferably, the special anti-clogging ultrafiltration device is a special anti-clogging inorganic membrane with a filtration accuracy of 100-200nm.

[0023] Preferably, the special anti-clogging nanofiltration device is a special anti-clogging organic membrane with a molecular weight cutoff of 150 to 300 Daltons.

[0024] Preferably, the sludge dewatering device is a high-pressure diaphragm plate and frame filter press.

[0025] Preferably, the calcium carbonate dehydration and recovery device is a high-pressure diaphragm plate and frame filter press.

[0026] A method for recycling and utilizing deep coalbed methane fracturing flowback fluid, comprising the following steps:

[0027] Step 1: Add the fracturing flowback fluid to the regulating water tank in the pretreatment device, homogenize and then pH adjust the sedimentation tank, then add pH adjuster and oxidant to the pretreatment device to obtain effluent and sludge;

[0028] Step 2: The effluent from the pH adjustment sedimentation tank in step 1 is sent to the flotation oil removal equipment, and the upper floating oil layer enters the shallow flotation device for oil-water separation to obtain floating oil with a high oil content and deoiled effluent, and the recovered floating oil can be reprocessed or blended for use as fuel, etc.;

[0029] Step 3: Send the deoiled water in step 2 to the primary softener in the carbon dioxide softening device, then introduce carbon dioxide gas and add pH regulator into the primary softener and secondary softener in the carbon dioxide softening device, and after reaction, enter the deep softener and clarifier to obtain softened water and calcium carbonate precipitate; the primary softener, the secondary softener and the deep softener are reaction equipment for gradually reducing the hardness of water, the clarifier is for removing most of the suspended matter in the water, the carbon dioxide storage tank is for storing and providing the liquid carbon dioxide and flotation gas source required for the entire process, the vaporizer is for converting carbon dioxide from liquid to gas and adding it to the primary softener, the secondary softener and the flotation oil removal equipment in the pretreatment device, the calcium carbonate dehydration and recovery device is for dehydrating and recovering the calcium carbonate precipitate at the bottom of the clarifier, and two wide-range hardness online monitors are used to monitor the hardness of the inlet and outlet water of the carbon dioxide softening device.

[0030] Step 4: The softened produced water in step 3 is quickly sent to a special anti-blocking ultrafiltration device for filtration to remove calcium carbonate in the water and prevent the generated calcium carbonate from dissolving back, so as to obtain produced water with SS ≤ 1 mg / L; the produced water is recycled to the ultrafiltration product water tank, and is reused if it meets the water quality requirements of the required reuse route; if the organic impurities or mineralization of the effluent water quality is still higher than the water quality requirements of the reuse route, it enters a special anti-blocking nanofiltration device for further treatment; the concentrated water is sent to the clarification tank in the carbon dioxide softening device;

[0031] Step 5: Send the produced water in step 4 to a special anti-clogging nanofiltration device to further reduce the organic impurities and mineralization in the water, obtain qualified produced water (according to the requirements of the reuse route) and concentrated water, and the produced water is recycled to the nanofiltration product water tank for recycling; the concentrated water is sent to the primary softener in the carbon dioxide softening device, and steps 3-4 are repeated;

[0032] Step 6: Send the sludge in the pH adjustment sedimentation tank in step 1 to the sludge dehydration device for filter pressing and dehydration to obtain a mud cake with a moisture content of less than 55%, and use it as raw material for downstream brick factories and other enterprises; the filtrate of the high-pressure diaphragm plate and frame filter press returns to the regulating water tank in the pretreatment device.

[0033] Step 7: The calcium carbonate precipitate in the clarification tank in the carbon dioxide softening device in step 3 is sent to a calcium carbonate dehydration recovery device, specifically, the calcium carbonate precipitate enters a high-pressure diaphragm plate and frame filter press for filtration and dehydration, and the obtained calcium carbonate is directly converted according to the water content and used as a drilling fluid additive without further drying treatment; the filtrate of the high-pressure diaphragm plate and frame filter press returns to the clarification tank in the carbon dioxide softening device.

[0034] Preferably, the pH adjuster in step 1 includes sodium hydroxide, and the pH of the fracturing flowback fluid is adjusted to 10-12; the oxidant includes sodium hypochlorite, and the concentration of the oxidant in the fracturing flowback fluid is 50-150 mg / L.

[0035] In step 1, the reaction equation of sodium hypochlorite and divalent iron (flowback liquid) is:

[0036] 2Fe 2+ +ClO - +4OH - +H2O=2Fe(OH)3+Cl -

[0037] The generated Fe(OH)3 acts as a flocculant to further assist in removing suspended matter and colloids in the fracturing flowback fluid.

[0038] Preferably, in step 3, a wide-range hardness online monitor is used to monitor the hardness of the inlet and outlet water in the carbon dioxide softening device. The wide-range hardness online monitor has a monitoring range of 20-50000 mg / L (in terms of calcium carbonate). The amount of carbon dioxide added is automatically calculated and controlled by monitoring the hardness value and the carbon dioxide conversion rate. The pH adjuster includes sodium hydroxide, and the pH of the fracturing return fluid is adjusted to 10-12.

[0039] Among them, the wide-range hardness online monitor 1 monitors the hardness of the incoming water, and the wide-range hardness online monitor 2 monitors the hardness of the outgoing water.

[0040] In step 3, carbon dioxide reacts with Ca in the effluent 2+Mg 2+ The reaction equation is:

[0041] Ca 2+ +2OH - =Ca(OH)2↓

[0042] Mg 2+ +2OH - =Mg(OH)2↓

[0043]

[0044] Preferably, the pressure at the feed inlet of the sludge dehydration device in step 6 and the calcium carbonate dehydration and recovery device in step 7 is ≥0.8 MPa.

[0045] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0046] 1. The present invention provides a system and a process method for recycling and utilizing deep coalbed methane fracturing flowback fluid. After the deep coalbed methane fracturing flowback fluid is treated by the method of the present invention, all produced water is recycled, and the recycled calcium carbonate is directly utilized as a drilling fluid additive, thereby eliminating the risk of secondary environmental pollution caused by discharge, reinjection or drying;

[0047] 2. The present invention provides a system with a simple connection structure; the equipment occupies a small area, operates fully automatically, is easy to operate, and has low cost;

[0048] 3. The carbon dioxide softening device in the present invention can effectively remove the hardness in the effluent, with low processing cost and can also achieve the "dual carbon" goal;

[0049] 4. The method of the present invention adopts a special anti-clogging ultrafiltration device, which has strong anti-pollution ability, high membrane flux, small footprint, good water quality, and effectively prevents calcium ions from dissolving back. If the produced water meets the water quality requirements of the desired reuse route, it will be reused, and the concentrated water will be sent to the clarification tank in the carbon dioxide softening device for further sedimentation, and the supernatant will enter the special anti-clogging ultrafiltration device; if the organic impurities or mineralization of the effluent are still higher than the water quality requirements of the reuse route, it will enter the special anti-clogging nanofiltration device for further treatment.

[0050] 5. The method of the present invention adopts a special anti-clogging nanofiltration device, which has strong anti-pollution ability and small footprint. The produced water is directly recycled as a higher reuse route with higher water quality requirements, and the concentrated water is then processed in a carbon dioxide softening device. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] 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 embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0052] Figure 1 This is a process flow chart of the recycling and resource utilization system of deep coalbed methane fracturing flowback fluid;

[0053] Figure 2 Comparison photos of the appearance of water samples before and after pretreatment in step 1 of Example 1 of the present invention;

[0054] Figure 3 This is the particle size distribution diagram of calcium carbonate recovered in step 3 of Example 1 of the present invention;

[0055] Figure 4 This is an appearance diagram of the drilling fluid prepared for recovering calcium carbonate in step 3 of Example 1 of the present invention;

[0056] Figure 5 This is a comparison diagram of the appearance of softened water produced in step 4 of Example 1 of the present invention (left) and ultrafiltration water produced (right);

[0057] Figure 6 This is a comparison diagram of ultrafiltration water production (left) and nanofiltration water production (right) in step 5 of Example 1 of the present invention;

[0058] Figure 7 Appearance of guar gum fracturing fluid prepared with tap water (left) and nanofiltration produced water (right) in step 5 of Example 1 of the present invention;

[0059] Figure 8 Appearance of guar gum fracturing fluid degumming liquid prepared with tap water (left) and nanofiltration produced water (right) in step 5 of Example 1 of the present invention;

[0060] Fig. 9 This is a comparison diagram of the appearance of water samples before and after pretreatment in step 1 of Example 2 of the present invention;

[0061] Fig.10 This is the calcium carbonate particle size distribution diagram of step 3 of Example 2 of the present invention;

[0062] Fig.11 This is a comparison diagram of the appearance of softened water produced in step 4 of Example 2 of the present invention (left) and ultrafiltration water produced (right);

[0063] Fig.12 A comparison diagram of polymer fracturing fluids prepared with tap water (left) and ultrafiltration produced water (right) in step 5 of Example 2 of the present invention;

[0064] Fig.13Appearance diagram of polymer fracturing fluid degelling liquid prepared with tap water (left) and ultrafiltration produced water (right) in step 5 of Example 2 of the present invention;

[0065] Fig.14 This is a structural diagram of the pretreatment device of the present invention;

[0066] Fig.15 This is a structural diagram of the carbon dioxide softening device of the present invention. DETAILED DESCRIPTION

[0067] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Example 1

[0069] This embodiment provides a deep coalbed methane fracturing flowback fluid (hereinafter referred to as fracturing flowback fluid) recovery and resource utilization system, including: a pretreatment device, a carbon dioxide softening device, a special anti-blocking ultrafiltration device, a special anti-blocking nanofiltration device, a sludge dehydration device, a calcium carbonate dehydration recovery device, an ultrafiltration product water tank and a nanofiltration product water tank;

[0070] Among them, the pretreatment device, the carbon dioxide softening device, the special anti-clogging ultrafiltration device, the ultrafiltration product water tank, the special anti-clogging nanofiltration device and the nanofiltration product water tank are connected in sequence;

[0071] The pretreatment device is cyclically connected with the sludge dewatering device;

[0072] The pretreatment device is cyclically connected to the carbon dioxide softening device;

[0073] The carbon dioxide softening device is cyclically connected with the calcium carbonate dehydration recovery device;

[0074] The special anti-blocking ultrafiltration device is cyclically connected with the carbon dioxide softening device;

[0075] The special anti-clogging nanofiltration device is also connected to the carbon dioxide softening device.

[0076] In this embodiment, the pretreatment device includes a water conditioning tank, a pH adjustment sedimentation tank, an air flotation oil removal device, and a dosing device;

[0077] The regulating water tank is connected to the pH regulating sedimentation tank, the flotation oil removal equipment and the primary softener in the carbon dioxide softening device in sequence; the dosing device is connected to the pH regulating sedimentation tank; the pH regulating sedimentation tank is connected to the sludge dehydration device; the regulating water tank is connected to the sludge dehydration device; the flotation oil removal equipment is connected to the vaporizer neutralized by the carbon dioxide softening device;

[0078] The dosing equipment is used to add pH regulator and oxidant to the pH regulating sedimentation tank;

[0079] The flotation oil removal equipment is a shallow flotation device whose gas source is carbon dioxide, which is supplied by a carbon dioxide storage tank through a vaporizer to remove and recover oil in the water.

[0080] In this embodiment, the carbon dioxide softening device includes a primary softener, a secondary softener, a deep softener, a clarifier, a carbon dioxide storage tank, a vaporizer and a wide-range hardness online monitor;

[0081] The wide-range hardness online monitor includes a wide-range hardness online monitor 1 and a wide-range hardness online monitor 2;

[0082] The flotation oil removal equipment in the pretreatment device is connected to the primary softener, the secondary softener, the deep softener, the clarifier and the special anti-clogging ultrafiltration device in sequence; the clarifier is circularly connected to the calcium carbonate dehydration recovery device; the carbon dioxide storage tank is connected to the vaporizer; the vaporizer is respectively connected to the primary softener, the secondary softener and the flotation oil removal equipment; the wide-range hardness online monitor 1 is connected to the pipeline between the flotation oil removal equipment and the primary softener; the wide-range hardness online monitor 2 is connected to the pipeline between the clarifier and the special anti-clogging ultrafiltration device.

[0083] The special anti-clogging ultrafiltration device is circularly connected to the clarification tank.

[0084] In this embodiment, the special anti-clogging ultrafiltration device is a special anti-clogging inorganic membrane with a filtration accuracy of 100-200nm.

[0085] In this embodiment, the special anti-clogging nanofiltration device is a special anti-clogging organic membrane with a molecular weight cutoff of 150 to 300 Daltons.

[0086] In this embodiment, the sludge dewatering device is a high-pressure diaphragm plate and frame filter press.

[0087] In this embodiment, the calcium carbonate dehydration and recovery device is a high-pressure diaphragm plate and frame filter press.

[0088] Example 2

[0089] This embodiment provides a method for recycling and utilizing deep coalbed methane fracturing flowback fluid (hereinafter referred to as fracturing flowback fluid), which is specifically as follows:

[0090] Deep coalbed methane fracturing flowback fluid in a well site, Q = 6m 3 / h, mineralization: 65377mg / L, COD: 2650mg / L, Ca 2 + :4133mg / L,Mg 2+ :661mg / L,SO4 2- :3mg / L,SS:2780mg / L,Fe 2+ :4mg / L,Fe 3+ :95mg / L, Oil:124mg / L.

[0091] A method for recycling and utilizing deep coalbed methane fracturing flowback fluid, comprising the following steps:

[0092] Step 1: Add the fracturing return fluid to the regulating water tank in the pretreatment device, send it to the pH adjustment reaction sedimentation tank after homogenization, add the pH adjuster to adjust the pH of the fracturing return fluid to 10-12; then add 1.08Kg / h of oxidant; make the fracturing return fluid undergo a chemical reaction to remove iron, suspended matter and colloids in the fracturing return fluid to obtain effluent and sludge; then send the effluent to the flotation oil removal equipment, and the upper floating oil layer enters the shallow flotation device for oil-water separation to obtain floating oil and deoiled effluent; the specific removal effect is shown in Table 1:

[0093] Table 1 Pretreatment inlet and outlet water quality analysis table

[0094]

[0095] Sludge production is 0.57m 3 / h, the sludge is sent to the sludge dewatering device for filter pressing and dehydration (no conditioning is required); the pressure at the feed inlet of the sludge dewatering device is 0.8MPa, and after pressing for 1h, a mud cake with a moisture content of 48.6% is obtained, which is transported to downstream brick factories and other enterprises for use as raw materials; the filtrate from the high-pressure diaphragm plate and frame filter press returns to the pretreatment regulating water tank.

[0096] Step 2: The deoiled water in step 1 is sent to the primary softener in the carbon dioxide softening device, and then carbon dioxide gas is introduced into the primary softener and the secondary softener in the carbon dioxide softening device and a pH regulator is added to adjust the pH of the fracturing flowback fluid to 10-12. After the reaction, the water enters the deep softener and the clarification tank to remove the hardness in the water, and softened water and calcium carbonate precipitation are obtained; the specific removal effect is shown in Table 2:

[0097] In the carbon dioxide softening device (the following embodiments are the same and will not be repeated), the primary softener, the secondary softener and the deep softener are reaction equipment for gradually reducing the hardness of water, the clarifier is for removing part of the suspended matter in the water, the carbon dioxide storage tank is for storing and providing the liquid carbon dioxide and the flotation gas source required for the whole process, the vaporizer is for converting the carbon dioxide from liquid to gas and adding it to the primary softener, the secondary softener and the flotation oil removal equipment in the pretreatment device, the calcium carbonate dehydration recovery device is for dehydrating and recovering the calcium carbonate precipitate at the bottom of the clarifier, and two wide-range hardness online monitors are for online real-time monitoring of the inlet and outlet hardness of the carbon dioxide softening device;

[0098] Among them, the wide-range hardness online monitor has a monitoring range of 20-50000 mg / L (calculated as calcium carbonate), and automatically calculates and controls the amount of carbon dioxide added by monitoring the hardness value and carbon dioxide conversion rate; the wide-range hardness online monitor 1 monitors the hardness of the water entering the primary softener, and the wide-range hardness online monitor 2 monitors the hardness of the effluent from the clarifier;

[0099] Table 2 Carbon dioxide softening water quality analysis table

[0100]

[0101] The calcium carbonate precipitation yield is 0.24m 3 / h, the calcium carbonate precipitate is sent to the calcium carbonate recovery device for filter pressing and dehydration; the pressure at the feed inlet of the calcium carbonate recovery device is 0.8, and the pressing is 1h to obtain calcium carbonate with a water content of 15.89%. The particle size distribution of the recovered calcium carbonate is shown in Figure 5 , calcium carbonate is bagged and used as a drilling fluid additive; the filtrate from the high-pressure diaphragm plate and frame filter press returns to the clarification tank in the carbon dioxide softening device.

[0102] The calcium carbonate generated by carbon dioxide softening is directly used as an additive for compound drilling fluid. The dynamic-plastic ratio of the compound drilling fluid is tested by adding the required concentration of recycled calcium carbonate according to the water content. The experimental results are as follows:

[0103] Table 3 Comparison of conventional properties of drilling fluids between the experimental group and the control group

[0104]

[0105] It can be seen that the drilling fluid compounded with calcium carbonate has excellent filtration performance, and the dynamic plastic ratio meets the requirement of 0.36-0.48Pa / (mPa·s). The recovered calcium carbonate can be directly used as a drilling fluid additive.

[0106] Step 3: The softened water produced in step 2 is quickly sent to a special anti-clogging ultrafiltration device for filtration to remove suspended solids in the water, mainly calcium carbonate. The produced water is sent to the ultrafiltration product water tank for recycling, and the concentrated water is sent to the clarification tank in the carbon dioxide softening device. The specific removal effect is shown in Table 4:

[0107] Table 4 Anti-blocking ultrafiltration inlet and outlet water quality analysis table

[0108]

[0109] Step 4: Send the water in the ultrafiltration product water tank to the special anti-clogging nanofiltration device; further remove the organic matter and mineralization in the water, the special anti-clogging nanofiltration device has a recovery rate of 65%, a retention rate of mineralization of 15%, and a retention rate of COD of 60%; the produced water is sent to the nanofiltration product water tank for recycling; the concentrated water is sent to the primary softener in the carbon dioxide softening device; the specific removal effect is shown in Table 5:

[0110] Table 5 Analysis of water quality of inlet and outlet water of anti-blocking nanofiltration device

[0111]

[0112] The guar fracturing fluid was prepared with 0.4% (w / w) guar gum and 0.8% (w / w) cross-linking agent in the nanofiltration water. -1 The viscosity of the shearing fluid is not less than 95 mPa·s after 90 minutes of shearing. The fluid can be completely broken within 60 minutes with an addition of 0.3‰ (w / w) of ammonium persulfate. The residue content of the broken fluid is 343 mg / L, the surface tension is 31.3 mN / m, and the anti-swelling rate is 63.1%, which meets the requirements of SY / T7627-2021 "Technical Requirements for Water-Based Fracturing Fluids".

[0113] The experimental results of the base fluid viscosity of the fracturing fluid prepared with tap water and nanofiltration water, the viscosity of the supernatant after gel breaking, the surface tension, the residue content, and the anti-swelling rate are shown in Table 6:

[0114] Table 6 Comparison of fracturing fluid performance prepared with tap water and nanofiltration produced water

[0115]

[0116] It can be seen from the above table that the fracturing fluid prepared with nanofiltration produced water meets the requirements of plant jelly fracturing fluid residue content <600mg / L, surface tension <32mN / m, and anti-swelling rate >60%.

[0117] Example 3

[0118] This embodiment provides a method for recycling and utilizing deep coalbed methane fracturing flowback fluid (hereinafter referred to as fracturing flowback fluid) to treat the fracturing flowback fluid, as follows:

[0119] Deep coalbed methane fracturing flowback fluid in a well site, Q: 6m 3 / h, mineralization: 98310mg / L, COD: 2302mg / L, Ca 2+ :16282mg / L,Mg 2+ :1737mg / L,SO4 2- : 42mg / L, SS: 2550mg / L, Fe 2+ :40mg / L,Fe 3+ :24mg / L,Oil:150mg / L

[0120] Step 1: Add the fracturing flowback fluid to the regulating water tank in the pretreatment device, send it to the pH adjustment reaction sedimentation tank after homogenization, add the pH adjuster to adjust the pH of the fracturing flowback fluid to 10-12; 0.72kg / h of oxidant; make the fracturing flowback fluid undergo a chemical reaction to remove iron, suspended matter and colloids in the fracturing flowback fluid to obtain effluent and sludge; then send the effluent from the pH adjustment reaction sedimentation tank to the flotation oil removal equipment, and the upper floating oil layer enters the shallow flotation device for oil-water separation to obtain floating oil and deoiled effluent; the specific removal effect is shown in Table 7:

[0121] Table 7 Pretreatment inlet and outlet water quality analysis table

[0122]

[0123] Sludge output is 1.2m 3 / h, the sludge is sent to the sludge dewatering device for filter pressing and dehydration (no conditioning is required); the pressure at the feed inlet of the sludge dewatering device is 0.8MPa, and after pressing for 1h, a mud cake with a moisture content of 52.6% is obtained, which is transported to downstream brick factories and other enterprises for use as raw materials.

[0124] Step 2: The effluent from the oil removal device in step 1 is sent to the primary softener in the carbon dioxide softening device, and then carbon dioxide gas and pH regulator are introduced into the primary softener and the secondary softener in the carbon dioxide softening device. After the reaction, the effluent enters the deep softener and the clarification tank to remove the hardness in the water, and softened water and calcium carbonate precipitation are obtained; the specific removal effect is shown in Table 8:

[0125] Table 8 Carbon dioxide softening water quality analysis table

[0126]

[0127]

[0128] The calcium carbonate precipitation yield is 0.84m 3 / h, the calcium carbonate precipitate is sent to the calcium carbonate recovery device for filter pressing and dehydration; the pressure at the feed inlet of the calcium carbonate recovery device is 0.8MPa, and after pressing for 1h, calcium carbonate with a water content of 16.76% is obtained, and the calcium carbonate is utilized as a drilling fluid additive;

[0129] Step 3: The softened water produced in step 2 is quickly sent to a special anti-clogging ultrafiltration device for filtration to remove suspended solids in the water, mainly calcium carbonate. The produced water is sent to the ultrafiltration product water tank for recycling, and the concentrated water is sent to the clarification tank in the carbon dioxide softening device. The specific removal effect is shown in Table 9:

[0130] Table 9 Anti-blocking ultrafiltration device inlet and outlet water quality analysis table

[0131]

[0132] The treated water from the fracturing flowback fluid was used to prepare the polymer fracturing fluid under the conditions of 1% (w / w) polymer thickener and 0.2% (w / w) crosslinking agent crosslinking ratio; 80°C, 170s -1 The viscosity is not less than 80mPa·s after shearing for 90 minutes. The gel can be completely broken within 120 minutes at an addition of 0.3‰ of ammonium persulfate. The residue content of the broken gel liquid is 98mg / L, the surface tension is 31.0mN / m, and the anti-swelling rate is 71.7%. It is compatible with formation water and meets the requirements of SY / T7627-2021 "Technical Requirements for Water-Based Fracturing Fluids".

[0133] The experimental results of base fluid viscosity of polymer fracturing fluid prepared with tap water and ultrafiltration water, viscosity of supernatant after gel breaking, surface tension, residue content, and anti-swelling rate are shown in the following table:

[0134] Table 10 Viscosity of polymer fracturing fluid base fluid and performance of degelling fluid prepared with tap water and ultrafiltration produced water

[0135]

[0136] It can be seen from the above table that the polymer fracturing fluid degelling liquid prepared by ultrafiltration produced water meets the requirements of polymer fracturing fluid residue content <200 mg / L, surface tension <32 mN / m, and anti-swelling rate >60%.

[0137] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0138] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A system for recycling and utilizing deep coalbed methane fracturing flowback fluid, characterized in that: include: Pretreatment device, carbon dioxide softening device, special anti-clogging ultrafiltration device, special anti-clogging nanofiltration device, sludge dehydration device, calcium carbonate dehydration recovery device, ultrafiltration product water tank and nanofiltration product water tank; Wherein, the pretreatment device, the carbon dioxide softening device, the special anti-clogging ultrafiltration device, the ultrafiltration product water tank, the special anti-clogging nanofiltration device and the nanofiltration product water tank are connected in sequence; The pretreatment device is cyclically connected to the sludge dewatering device; The pretreatment device is cyclically connected to the carbon dioxide softening device; The carbon dioxide softening device is cyclically connected to the calcium carbonate dehydration recovery device; The special anti-blocking ultrafiltration device is cyclically connected to the carbon dioxide softening device; The special anti-clogging nanofiltration device is connected to the carbon dioxide softening device.

2. A system for recycling and utilizing deep coalbed methane fracturing flowback fluid according to claim 1, characterized in that: The pretreatment device comprises a regulating water tank, a pH regulating sedimentation tank, an air flotation oil removal device, and a dosing device; The regulating water tank is connected to the pH regulating sedimentation tank, the flotation oil removal equipment and the carbon dioxide softening device in sequence; the dosing device is connected to the pH regulating sedimentation tank; the pH regulating sedimentation tank is connected to the sludge dewatering device; the sludge dewatering device is connected to the regulating water tank; the flotation oil removal equipment is connected to the carbon dioxide softening device in a circular connection; The air flotation oil removal equipment is a shallow air flotation device, the gas source is carbon dioxide, and the gas is supplied from a carbon dioxide storage tank through a vaporizer.

3. A system for recycling and utilizing deep coalbed methane fracturing flowback fluid according to claim 2, characterized in that: The carbon dioxide softening device comprises a primary softener, a secondary softener, a deep softener, a clarifier, a carbon dioxide storage tank, a vaporizer and a wide-range hardness online monitor; The wide-range hardness online monitor includes a wide-range hardness online monitor 1 and a wide-range hardness online monitor 2; The flotation oil removal equipment is connected to the primary softener, the secondary softener, the deep softener, the clarifier and the special anti-blocking ultrafiltration device in sequence; the clarifier is cyclically connected to the calcium carbonate dehydration recovery device; the carbon dioxide storage tank is connected to the vaporizer; the vaporizer is respectively connected to the primary softener, the secondary softener and the flotation oil removal equipment; The wide-range hardness online monitor 1 is connected to the pipeline between the flotation oil removal equipment and the primary softener; the wide-range hardness online monitor 2 is connected to the pipeline between the clarifier and the special anti-blocking ultrafiltration device; the special anti-blocking ultrafiltration device is cyclically connected to the clarifier, and the special anti-blocking nanofiltration device is connected to the primary softener; The special anti-blocking ultrafiltration device is a special anti-blocking inorganic membrane with a filtration accuracy of 100-200nm; The special anti-clogging nanofiltration device is a special anti-clogging organic membrane with a molecular weight cutoff of 150 to 300 Daltons; The sludge dewatering device is a high-pressure diaphragm plate and frame filter press; The calcium carbonate dehydration and recovery device is a high-pressure diaphragm plate and frame filter press.

4. A method for recycling and utilizing deep coalbed methane fracturing flowback fluid, characterized in that: The system of claim 3 comprises the following steps: Step 1: Add deep coalbed methane fracturing flowback fluid into the regulating water tank, and after homogenization, enter the pH regulating sedimentation tank, and then add pH regulator and oxidant into the pH regulating sedimentation tank to obtain effluent and sludge; Step 2: The effluent from step 1 is sent to the flotation oil removal equipment, and the upper floating oil layer enters the shallow flotation device for oil-water separation to obtain floating oil and deoiled effluent; Step 3: sending the deoiled water in step 2 to a primary softener, then introducing carbon dioxide gas and adding a pH regulator into the primary softener and the secondary softener, and after reaction, entering a deep softener and a clarifier to obtain softened water and calcium carbonate precipitation; Step 4: The softened produced water in step 3 is quickly sent to a special anti-clogging ultrafiltration device for filtration to obtain produced water and concentrated water; the produced water is sent to the ultrafiltration product water tank, and if it meets the water quality requirements of the required reuse route, it is reused; if the organic impurities or mineralization of the effluent is still higher than the water quality requirements of the reuse route, it enters the special anti-clogging nanofiltration device for further treatment, and the concentrated water is sent to the clarification tank; Step 5: The produced water in step 4 enters a special anti-clogging nanofiltration device to obtain produced water and concentrated water; the produced water is sent to a nanofiltration product water tank for recycling; the concentrated water is sent to a primary softener, and steps 3-4 are repeated; Step 6: sending the sludge in step 1 to a sludge dehydration device for filter pressing and dehydration to obtain a mud cake; the generated filtrate is sent to a regulating water tank; Step 7: The calcium carbonate precipitate described in step 3 is sent to a calcium carbonate dehydration recovery device, and the calcium carbonate precipitate is dehydrated by filter pressing to obtain a filter cake of calcium carbonate, which is directly converted according to the water content and used as a drilling fluid additive without further drying treatment. The generated filtrate is returned to the clarification tank in the carbon dioxide softening device.

5. The method for recycling and utilizing deep coalbed methane fracturing flowback fluid according to claim 4, characterized in that: In step 1, the pH regulator comprises sodium hydroxide, which adjusts the pH of the fracturing flowback fluid to 10-12; the oxidant comprises sodium hypochlorite, and the concentration of the oxidant in the fracturing flowback fluid is 50-150 mg / L.

6. The method for recycling and utilizing deep coalbed methane fracturing flowback fluid according to claim 4, characterized in that: In step 3, two wide-range hardness online monitors are used to monitor the hardness of the water entering and exiting the carbon dioxide softening device; in terms of calcium carbonate, the wide-range hardness online monitor has a monitoring range of 20-50000 mg / L, and the amount of carbon dioxide added is automatically calculated and controlled by monitoring the hardness value and the carbon dioxide conversion rate; The pH adjuster includes sodium hydroxide, which adjusts the pH of the fracturing flowback fluid to 10-12.

7. The method for recycling and utilizing deep coalbed methane fracturing flowback fluid according to claim 4, characterized in that: The pressure at the feed inlet of the sludge dehydration device in step 6 and the calcium carbonate dehydration recovery device in step 7 is ≥0.8MPa.

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