CN117105460A - Treatment system and treatment method for fracturing flowback fluid of oil and gas field - Google Patents

Abstract

The invention discloses an oil and gas field fracturing flowback liquid processing system and a processing method, which include: the oil and gas field fracturing flowback liquid enters an air flotation tank, and the separated floating oil is scraped into the oil pool by a slag scraper on the top of the tank, and the effluent enters the air flotation tank. Electrode oxidation tank, the effluent from the electrode oxidation tank enters the coagulation tank, the inclined plate sedimentation tank, and the filter unit in sequence, and is finally injected back into the ground; the sludge produced by the above tanks is transported out of the solid phase for treatment after passing through the sludge pump and centrifuge. This invention adopts the combined process of "air flotation + electrode catalytic oxidation + coagulation sedimentation + filtration" and is suitable for the treatment of fracturing flowback fluids such as guar gum fracturing flowback fluid and slick water systems that are common in oil fields. The equipment is designed as a skid and the entire process No strong oxidants are used. It mainly decomposes polymers and reduces viscosity through electrolysis, without secondary pollution. At the same time, it improves the efficiency of sewage treatment and reduces operating costs. It overcomes the inflexibility of existing technical equipment, high operating costs, and the danger of adding strong oxidants. The problem is that it is highly sensitive and the water discharge cannot stably meet the water injection standard.

Description

An oil and gas field fracturing flowback fluid treatment system and treatment method

Technical field

The invention relates to the technical field of oilfield wastewater treatment, and specifically relates to a high COD, high oil content, high viscosity oil and gas field fracturing flowback fluid treatment system and treatment method.

Background technique

With the continuous development of the domestic oil production industry, the number of fracturing flowback fluids is increasing year by year. As a major wastewater in oil field production, fracturing flowback fluids have high viscosity, high suspended matter content, high salinity, and oil-water properties. It is difficult to separate and has strong stability. If it is directly mixed into the produced water treatment system of the joint station, it will have an impact on the system, causing the effluent of the entire water treatment system to not meet the water injection standards.

Conventional treatment processes include "chemical oxidation-flocculation sedimentation-filtration", "oxidation-flocculation-potassium permanganate/Fenton oxidation-filtration", "chemical oxidation-flocculation magnetic separation-filtration".

For example, the Chinese patent application for CN108439712A uses sodium hypochlorite as the oxidant. After oxidation and gel breaking, the waste liquid is filtered and sterilized to meet the reinjection requirements. However, as oxidants such as sodium hypochlorite, these chemicals are hazardous chemicals. Procurement, transportation, storage, and use require a hazardous chemicals license. At the same time, hazardous chemicals pose great safety risks to operators, and their use is prohibited in some areas. In addition, due to the high viscosity of the waste liquid and the large dosage of chemicals, the gel breaking and viscosity reducing effect is not good. For example, the Chinese patent application of CN 115724517 A uses magnetic photocatalyst coupled Fenton oxidation and adds hazardous chemical hydrogen peroxide. The usage is large, and the amount of sludge produced by this process is higher than other processes.

Some other existing technologies use electrocatalytic oxidation processes, but electrocatalytic oxidation, ozone oxidation, chemical oxidation, etc. are used in series, resulting in lengthy processes and reduced efficiency. For example, the Chinese patent application of CN 111087108B uses a combination of advanced oxidation of ozone nano-microbubbles, ultrasonic waves, and electrocatalytic oxidation to treat fracturing flowback fluid. The combination of multiple high-tech equipment results in high equipment investment, high maintenance costs, and long process routes.

Therefore, it is very necessary to develop a fracturing flowback fluid treatment process that has a short process flow, high sewage treatment efficiency, low equipment investment and operating costs, little or no addition of strong oxidant, skid-mounted equipment, and stable effluent water quality. .

Contents of the invention

The purpose of the present invention is to provide a high COD, high oil content, high viscosity oil and gas field fracturing flowback fluid treatment system and treatment method, which can avoid the addition of strong oxidants, improve treatment efficiency and effluent water quality, and maximize the recovery of crude oil.

In order to achieve the above goals, the present invention provides the following technical solutions:

The invention discloses an oil and gas field fracturing flowback fluid treatment system, which includes: an air flotation tank, an electrode oxidation tank, a coagulation tank, an inclined plate sedimentation tank, a pool and a filtering unit that are sequentially arranged along the oil and gas field fracturing flowback fluid treatment flow direction;

The upper floating oil and suspended matter in the air flotation tank and the upper floating oil in the electrode oxidation tank enter the oil pool through a slag scraper, and the oil outlet of the oil pool is connected to the dirty oil storage tank;

The bottom mud outlet of the electrode oxidation tank, oil tank, coagulation tank, inclined plate sedimentation tank and pool is connected to a centrifuge.

As a further improvement of the present invention, the water outlet of the air flotation tank is connected to the electrode oxidation tank.

As a further improvement of the present invention, the electrode oxidation tank is provided with an electrode plate and a water collecting pipe, wherein the anode is a titanium-coated ruthenium-iridium electrode titanium plate, the cathode is a titanium plate, and the outlet end of the water collecting pipe is connected to the coagulation tank. connected.

As a further improvement of the present invention, a stirrer is provided in the coagulation tank, and the dosing ports of the coagulation tank are respectively connected to the PAM dosing box and the PAC dosing box through dosing pumps.

As a further improvement of the present invention, when the water injection requirement is first-grade water quality, the filtration unit is a tubular membrane.

As a further improvement of the present invention, when the water injection requirement is secondary water quality, the filter unit is a walnut shell filter and a double filter material filter arranged in sequence.

As a further improvement of the present invention, the water inlet end of the filter unit is connected to a water collection pump, the oil inlet end of the dirty oil storage tank is connected to an oil collection pump, and the mud inlet end of the centrifuge is connected to a mud discharge pump.

As a further improvement of the present invention, the effluent from the filter unit is injected back into the ground, the oil from the dirty oil storage tank enters the joint station oil storage tank, and the sludge from the centrifuge is transported out for processing.

As a further improvement of the present invention, the oil and gas field fracturing flowback fluid treatment system is an integrated skid-mounted equipment.

The invention also discloses a method for treating oil and gas field fracturing flowback fluid, which adopts the above-mentioned oil and gas field fracturing flowback fluid processing system and includes:

The oil and gas field fracturing flowback fluid enters the air flotation tank to remove floating oil and some suspended solids. The effluent enters the electrode oxidation tank, where a redox reaction occurs through the electrode plate to generate hydroxyl radicals, a strong oxidizing substance, which oxidizes and decomposes the polymer substances in the wastewater, reducing the viscosity. Separate dirty oil and water;

The floating oil and suspended solids in the upper layer of the air flotation tank and the floating oil in the electrode oxidation tank enter the oil pool through the slag scraper, and after passing through the oil collection pump and the waste oil storage tank, enter the joint station oil storage tank for treatment;

The effluent from the electrode oxidation tank enters the coagulation tank, and coagulant and flocculant are added to the coagulation tank to cause the suspended matter in the water to flocculate and settle; the effluent from the coagulation tank enters the inclined plate sedimentation tank for solid-liquid separation. The upper part of the inclined plate sedimentation tank After the effluent passes through the pool, water collection pump, and filter unit, it is injected back into the ground;

The sludge at the bottom of the electrode oxidation tank, oil tank, coagulation tank, inclined plate sedimentation tank and pool is transported out of the solid phase for treatment after passing through the sludge pump and centrifuge.

As a further improvement of the present invention, the processing of the filter unit includes:

According to different water injection standards, the water effluent from the inclined plate sedimentation tank with the first-level water injection index enters the tubular membrane filtration, and the water effluent from the inclined plate sedimentation tank with the second-level water injection index and below enters the secondary filtration of the walnut shell filter and the double filter material filter.

Compared with the prior art, the beneficial effects of the present invention are:

The oil and gas field fracturing flowback fluid treatment system and treatment method of the present invention adopt an organic combination of multi-stage technologies of "air flotation + electrode catalytic oxidation + coagulation and sedimentation + filtration". The process is simple and highly automated, and there is no need to add enhanced oxidants during operation. , reduce the risk of operational hazards. At the same time, after electrode catalytic oxidation in this process, the colloid content is reduced, and the oil-water-solid three-phase separation effect is good. Only a small amount of conventional coagulant is added. At the same time, it is equipped with a centrifugal dehydrator, and the mud production is reduced by more than 60% compared with the traditional process. , reduce hazardous waste treatment costs. The equipment is skid-mounted and can be transported between multiple operating points and operated flexibly. According to different water injection indicators, the type of filter can be adjusted to ensure stable water quality and meet various water injection indicators.

Description of drawings

Figure 1 is a schematic structural diagram of an oil and gas field fracturing flowback fluid treatment system disclosed in Embodiment 1 of the present invention;

Figure 2 is a schematic structural diagram of an oil and gas field fracturing flowback fluid treatment system disclosed in Embodiment 2 of the present invention.

In the picture:

1. Air flotation tank; 10. Electrode oxidation tank; 11. Electrode plate; 12. Slag scraper; 13. Water collection pipe; 20. Oil tank; 30. Coagulation tank; 31. PAM dosing box; 32. PAC dosing box; 33. Mixer; 34. Dosing pump; 40. Inclined plate sedimentation tank; 50. Pool; 60. Waste oil storage tank; 61. Oil collection pump; 70. Tubular membrane; 71. Water collection pump; 80. Centrifugal machine; 81. Mud discharge pump; 90. Walnut shell filter; 91. Double filter material filter.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without any creative work fall within the scope of protection of the present invention.

The present invention will be described in further detail below in conjunction with the accompanying drawings:

In order to achieve the first-level water injection index, as shown in Figure 1, the present invention provides an oil and gas field fracturing flowback fluid treatment system, including: an air flotation tank 1, an electrode oxidation tank 10, an oil tank 20, a coagulation tank 30, and a sloping plate sedimentation tank. Pool 40, pool 50, waste oil storage tank 60, tubular membrane 70 and centrifuge 80; among them,

The air flotation tank 1 of the present invention is equipped with an aeration device. Oil and gas field fracturing flowback fluid enters the air flotation tank 1 and removes part of the suspended solids and floating oil through air flotation, thereby reducing the risk of subsequent electrode plate clogging. The floating oil in the air flotation tank is scraped The slag machine 12 enters the oil pool 20 .

The electrode oxidation tank 10 of the present invention is provided with cathode and anode electrode plates 11 and a water collection pipe 13, and a slag scraper 12 is provided above the electrode oxidation tank 10; the effluent from the air flotation tank 1 enters the electrode oxidation tank 10, and the cathode and anode electrode plates 11. The oxidation-reduction reaction occurs when electricity is applied to generate a hydroxyl radical (·OH) intermediate. The hydroxyl radical (·OH) interacts with polymers, colloids and other high molecular substances in the oil and gas field fracturing flowback fluid in the water, thereby reducing the viscosity and making the pollution Oil separates from water. The generated upper layer floating oil enters the oil pool 20 through the slag scraper 12, and the lower layer sewage enters the coagulation tank 30 through the water collecting pipe 13. Furthermore, the anode is a titanium-coated ruthenium-iridium electrode titanium plate, and the cathode is a titanium plate. Compared with commonly used aluminum plates, the titanium plate has better electrical conductivity, smaller pole pitch changes, stronger corrosion resistance, good mechanical strength and processing performance, and longer service life. It is long, low-cost and has good electrocatalytic performance, which plays a huge role in improving the efficiency and effect of sewage treatment.

The oil pool 20 of the present invention is used to collect the floating oil in the air flotation tank 1 and the electrode oxidation tank 10, and enters the dirty oil storage tank 60 through the oil collecting pump 61. The dirty oil collected in the dirty oil storage tank 60 can be transported to the joint station for storage. Oil tanks are centrally processed.

The coagulation tank 30 of the present invention is provided with a stirrer 33, and the dosing ports of the coagulation tank 30 are respectively connected to the PAM dosing box 31 and the PAC dosing box 32 through the dosing pump 34; the sewage transported by the electrode oxidation tank 10 enters the mixing tank. In the coagulation tank 30, under the stirring action of the agitator 33, the PAM and PAC in the PAM dosing box 31 and PAC dosing box 32 are added to the coagulation tank 30 through the dosing pump 34, and the suspended solids in the wastewater are mixed with each other. Flocculation and sedimentation are performed to remove suspended solids; the effluent from the coagulation tank 30 enters the inclined plate sedimentation tank 40 .

The inclined plate sedimentation tank 40 of the present invention is equipped with an inclined plate assembly with an inclination angle of 60 degrees above the sludge suspended layer, so that the suspended solids in the raw water or the floc alum formed after adding coagulant can be deposited on the bottom side of the inclined plate. The surface accumulates into a thin mud layer, which slides back to the suspended mud layer by gravity, and then sinks into the mud collecting bucket; the supernatant gradually rises to the water collecting pipe and is discharged into the pool 50 . The inclined plate sedimentation tank 40 adopts the principle of laminar flow, which increases the sedimentation area of the sedimentation tank, improves the processing capacity of the sedimentation tank, and saves the volume of the skid-mounted equipment.

The pool 50 of the present invention is used to collect the effluent from the inclined plate sedimentation tank 40 and transport it to the tubular membrane 70 through the water collection pump 71. After being filtered by the tubular membrane 70, the effluent reaches the first-level water injection index and is injected back into the ground.

The bottom mud outlet of the electrode oxidation tank 10, the oil tank 20, the coagulation tank 30, the inclined plate sedimentation tank 40 and the pool 50 of the present invention enters the centrifuge 80 through the mud discharge pump 81. After centrifugation, the solid phase is transported out. deal with.

Electrode oxidation tank 10, oil tank 20, coagulation tank 30, inclined plate sedimentation tank 40, pool 50, waste oil storage tank 60, tubular membrane 70 and centrifuge 80 as well as corresponding pump bodies, agitators and valves of the present invention , pipelines and other components adopt skid-mounted integrated design to facilitate on-site operations.

Based on the above treatment system, the present invention provides an oil and gas field fracturing flowback fluid treatment method, including:

Step 1. The oil and gas field fracturing flowback fluid enters the air flotation tank 1 with a gas-water ratio of 1: (2-3) and a hydraulic retention time of (15-20) min. Part of the suspended solids and floating oil are removed through air flotation to reduce the subsequent There is a risk of electrode plate clogging. The floating oil in the air flotation tank enters the oil pool 20 through the slag scraper 12 and passes through the oil collection pump 61 and the dirty oil storage tank 60 before entering the joint station oil storage tank for treatment;

Step 2: The water from the air flotation tank 1 enters the electrode oxidation tank 10, the treatment time is (30-50) min, the voltage is (5-10) V, and the current density is (300-1100) A/m ² . The oxidation-reduction reaction of the electrode plate generates hydroxyl radicals, a strong oxidizing substance, which oxidizes and decomposes the polymer substances in the waste water, reduces the viscosity, and separates the dirty oil and water; the floating oil in the electrode oxidation tank 10 enters the oil pool 20 through the scraper 12 , and after passing through the oil collection pump 61 and the dirty oil storage tank 60, it enters the joint station oil storage tank for processing;

Step 3: The effluent from the electrode oxidation tank 10 enters the coagulation tank 30, and coagulant and flocculant are added to the coagulation tank 30 to cause the suspended matter in the water to flocculate and settle. The coagulation time is 15 minutes; the effluent from the coagulation tank enters the inclined plate to settle. The solid-liquid separation is carried out in the tank 40, and the hydraulic retention time is (40-50) min. After the effluent from the upper part of the inclined plate sedimentation tank 40 is filtered by the pool 50, the water collection pump 71 and the tubular membrane 70, the oil and suspended matter are further removed, so that the effluent reaches First-level water injection index and back-injection into the ground;

Step 4. The bottom sludge in the electrode oxidation tank 10, the oil tank 20, the coagulation tank 30, the inclined plate sedimentation tank 40 and the pool 50 enters the centrifuge 80 for dehydration treatment through the sludge discharge pump 81. The output of solid pollutants is reduced by 60%. Reduces hazardous waste treatment costs and environmental pollution risks.

In order to achieve the water injection index of Level 2 or below, as shown in Figure 2, the present invention provides an oil and gas field fracturing flowback fluid treatment system. The difference between it and Embodiment 1 is that the tubular membrane 70 is replaced with sequentially arranged Walnut shell filter 90 and dual media filter 91.

Based on the above treatment system, the present invention provides an oil and gas field fracturing flowback fluid treatment method, which differs from Example 1 in that:

In step 3, the effluent from the upper part of the inclined plate sedimentation tank 40 is filtered through the pool 50, the water collection pump 71, the walnut shell filter 90 and the double filter material filter 91, and then further removes oil and suspended solids, so that the effluent reaches the second level or The water injection index is below level 2 and injected back into the ground.

Example 1:

The above-mentioned treatment methods were used to treat high-viscosity fracturing flowback fluid in the middle stage of pressure operation in an oil field. The waste liquid indicators are: viscosity 8.2mPa·s, COD 2300mg/L, oil content 240mg/L, suspended solids 320mg/L, median particle size 42um, pH 6.5. The processing includes:

The oil and gas field fracturing flowback fluid enters the air flotation tank, and the container ratio is adjusted according to the water volume. The gas-water ratio is 1:2, the reaction time is 15 minutes, and the scraper separates the floating oil on the water surface;

The effluent from the air flotation tank enters the electrode oxidation tank, the treatment time is 50 minutes, the voltage is 8V, and the current density is 800A/㎡. The oxidation-reduction reaction of the electrode plate generates hydroxyl radicals, a strong oxidizing substance, which oxidizes and decomposes the polymer substances in the wastewater, reduces the viscosity, and separates the dirty oil and water;

The effluent from the electrode oxidation tank enters the coagulation tank, and coagulant and flocculant are added to the coagulation tank to cause the suspended matter in the water to flocculate and settle. The coagulation time is 15 minutes;

The effluent from the coagulation tank enters the inclined plate sedimentation tank for solid-liquid separation. The hydraulic retention time is 45 minutes. The effluent from the upper part of the inclined plate sedimentation tank passes through the water pool and water collection pump and enters the activated carbon filter and double filter material filter to detect the final filter effluent quality.

Example 2:

The above-mentioned treatment methods were used to treat high-viscosity fracturing flowback fluid from a certain operating area in the North China Oilfield. The waste liquid indicators are: viscosity 8.2mPa·s, COD 2300mg/L, oil content 240mg/L, suspended solids 320mg/L, median particle size 42um, pH 6.5. The processing includes:

The entire treatment process is similar to Example 1, except for the filtration stage. The water from the water collection pump enters the tubular membrane, and the quality of the tubular membrane outlet water is detected.

Example 3:

The above-mentioned treatment methods were used to treat high-viscosity fracturing flowback fluid in the late stage of fracturing operations in an oil field. The waste liquid indicators are: viscosity 65mPa·s, COD 5500mg/L, oil content 870mg/L, suspended solids 920mg/L, median particle size 58um, pH 6. The processing includes:

The entire treatment process is the same as in Example 1, and the quality of the final filter effluent is tested.

Example 4:

The above-mentioned treatment methods were used to treat high-viscosity fracturing flowback fluid in the late stage of fracturing operations in an oil field. The waste liquid indicators are: viscosity 65mPa·s, COD 5500mg/L, oil content 870mg/L, suspended solids 920mg/L, median particle size 58um, pH 6. The processing includes:

The entire treatment process is the same as in Example 2, and the quality of the tubular membrane effluent is detected.

The water sample detection data of Examples 1 to 4 are shown in the table below.

It can be seen from the results in the above table that the treatment process of the present invention is effective in treating fracturing flowback fluid. After the secondary filtration process, the oil content, suspended solids, and median particle size all reach the secondary water injection standard. The tubular membrane filtration process is Afterwards, the oil content, suspended solids, and median particle size all reached the first-level water injection standard. Moreover, the process flow is simple, can be skid-mounted, has a high degree of automation, does not add strong oxidizing properties, and has high processing efficiency.

The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. An oil and gas field fracturing flow-back fluid treatment system, comprising: an air floatation tank, an electrode oxidation tank, a coagulation tank, an inclined plate sedimentation tank, a water tank and a filtering unit which are sequentially arranged along the treatment flow direction of the fracturing flowback fluid of the oil and gas field;

the upper layer floating oil and suspended matters of the air floatation tank and the upper layer floating oil of the electrode oxidation tank enter an oil tank through a slag scraping machine, and an oil outlet of the oil tank is connected with a dirty oil storage tank;

and the bottom mud outlets of the electrode oxidation tank, the oil tank, the coagulation tank, the inclined plate sedimentation tank and the water tank are connected with a centrifugal machine.

2. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein an electrode plate and a water collecting pipe are arranged in the electrode oxidation tank, an anode in the oxidation tank is a titanium plate of a titanium-coated ruthenium-iridium electrode, a cathode is a titanium plate, and a water outlet end of the water collecting pipe is connected with the coagulation tank.

3. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein a stirrer is arranged in the coagulation tank, and a dosing port of the coagulation tank is connected with a PAM dosing tank and a PAC dosing tank through dosing pumps respectively.

4. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein said filtration unit is a tubular membrane when the water injection requirement is primary water quality.

5. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein when the water injection requirement is secondary water quality, the filter unit is a walnut shell filter and a double filter material filter which are sequentially arranged.

6. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein the water inlet end of the filtering unit is connected with a water collecting pump, the oil inlet end of the dirty oil storage tank is connected with an oil collecting pump, and the mud inlet end of the centrifuge is connected with a mud pump.

7. The oil and gas field fracturing flow-back fluid treatment system of claim 1, wherein the effluent of said filtration unit is reinjected into the ground, the effluent of said dirty oil storage tank enters a co-station storage tank, and the effluent of said centrifuge is processed for export.

8. The oil and gas field fracturing flow-back fluid treatment system of any one of claims 1-7, wherein said oil and gas field fracturing flow-back fluid treatment system is an integrated skid-mounted device.

9. A method for treating a flowback fluid from an oil and gas field, comprising the steps of:

the fracturing flowback fluid of the oil and gas field enters an air floatation tank to remove floating oil and part of suspended matters, the effluent enters an electrode oxidation tank, and the electrode plate is used for carrying out oxidation-reduction reaction to generate hydroxyl free radicals of strong oxidation substances, so that high polymer substances in the wastewater are oxidized and decomposed, the viscosity is reduced, and dirty oil and water are separated;

the upper layer floating oil and suspended matters of the air floatation tank and the floating oil of the electrode oxidation tank enter the oil tank through the slag scraping machine, and enter the oil storage tank of the combined station for treatment after passing through the oil collecting pump and the dirty oil storage tank;

the effluent of the electrode oxidation pond enters a coagulation pond, and coagulant and flocculant are added into the coagulation pond to flocculate and precipitate suspended matters in the water; the effluent of the coagulation tank enters an inclined plate sedimentation tank for solid-liquid separation, and the upper effluent of the inclined plate sedimentation tank is reinjected into the ground after passing through a water tank, a water collecting pump and a filtering unit;

and (3) carrying out solid-phase outward transportation treatment on the bottom sludge of the electrode oxidation tank, the oil tank, the coagulation tank, the inclined plate sedimentation tank and the water tank through a sludge discharge pump and a centrifugal machine.

10. The method for treating a frac flowback fluid in an oil and gas field of claim 9, wherein said treating of said filter unit comprises:

according to different water injection standards, the water discharged from the first-stage water injection index inclined plate sedimentation tank enters tubular membrane filtration, and the water discharged from the second-stage water injection index inclined plate sedimentation tank and below enter the second-stage filtration of the walnut shell filter and the double-filter material filter.