CN114873820A

CN114873820A - Treatment process of shale gas fracturing flowback fluid

Info

Publication number: CN114873820A
Application number: CN202210593706.8A
Authority: CN
Inventors: 杨寿冬; 刘云辉
Original assignee: Sichuan Huanke Meineng Environmental Protection Technology Co ltd
Current assignee: Sichuan Huanke Meineng Environmental Protection Technology Co ltd
Priority date: 2022-05-27
Filing date: 2022-05-27
Publication date: 2022-08-09

Abstract

The invention discloses a treatment process of shale gas fracturing flowback fluid, which comprises the following steps: pretreating raw water of shale gas fracturing flow-back fluid; carrying out ultrafiltration treatment on the pretreated shale gas fracturing flowback fluid; carrying out nanofiltration treatment on the ultrafiltered shale gas fracturing flow-back fluid; carrying out reverse osmosis treatment on the nanofiltration shale gas fracturing flow-back fluid; evaporating and crystallizing the reverse osmosis concentrated water; mixing the clear water after reverse osmosis with the evaporated condensate for discharging; the shale gas fracturing flow-back fluid is stably and efficiently treated, the pressure of a subsequent treatment system is reduced through pretreatment, and finally the crystallized salt reaches the industrial first-grade quality and the clear water reaches the standard of reclaimed water recycling through the mutual synergistic effect of nanofiltration and ultrafiltration as well as nanofiltration and reverse osmosis; the treatment cost is reduced while the treatment flow is simplified.

Description

Treatment process of shale gas fracturing flowback fluid

Technical Field

The invention relates to the technical field of sewage treatment, in particular to a treatment process of shale gas fracturing flowback fluid.

Background

Shale gas is an unconventional natural gas resource that is found in reservoir rock systems dominated by organic-rich shale. Shale gas development has the advantages of long mining life, high yield and long production period, and becomes a new bright point for exploration and development of global oil and gas resources.

But the development process of shale gas resources is greatly promoted, high efficiency and economy are sought, and meanwhile, the huge environmental problems possibly brought by shale gas exploitation cannot be ignored. According to the statistics of the United states environmental protection agency, the water consumption of a single-opening shale gas horizontal well is generally 7600-19000 m ³ And after the fracturing operation is finished, 15 to 80 percent of flowback liquid is discharged to the ground. Besides consuming a large amount of water resources, shale gas exploitation also has serious water pollution hidden danger, the injection of fracturing fluid containing chemical reagents into the underground may pollute the underground water, the return fluid contains highly mineralized formation water, if the treatment is improper, the environment is seriously polluted, the safety of surface drinking water sources can be influenced, and meanwhile, the influence on the surrounding soil environment can also be influenced. It can be said that how to reduce the water resource consumption and reasonably dispose a large amount of flowback liquid generated in the shale gas development becomes one of the bottleneck problems in the large-scale shale gas development.

In the process of treating the shale gas fracturing flowback fluid (Luxian), the shale gas fracturing flowback fluid is found to be easy to cause higher pressure to a treatment device, so that serious blockage is caused, and the treatment process of the shale gas fracturing flowback fluid cannot be stably carried out; meanwhile, the treatment process is complex and long, so that the treatment efficiency of the shale gas fracturing flowback fluid is slow, and the treatment cost is high.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, and provides a treatment process of shale gas fracturing flow-back fluid, which is used for stably and efficiently treating the shale gas fracturing flow-back fluid, and simultaneously simplifies the treatment process and reduces the treatment cost.

The purpose of the invention is realized by the following technical scheme: a treatment process of shale gas fracturing flowback fluid comprises the following steps:

s1, pretreating raw water of the shale gas fracturing flow-back fluid;

s2, carrying out ultrafiltration treatment on the pretreated shale gas fracturing flowback liquid (clear water), and treating sludge through a filter press;

s3, performing nanofiltration treatment on the ultrafiltered shale gas fracturing flow-back fluid (clear water), and returning concentrated water to the pretreatment stage for treatment;

s4, performing reverse osmosis treatment on the filtered shale gas fracturing flow-back fluid (clear water), and evaporating concentrated water;

s5, evaporating and crystallizing the concentrated water of the reverse osmosis shale gas fracturing flow-back fluid, wherein the clear water reaches the standard of reclaimed water reuse;

and S6, mixing the clear water after reverse osmosis with the evaporated condensate liquid for discharging.

Most suspended matters, colloids and scaling ions in the flowback liquid are removed through pretreatment (softening and hardness removal, flocculation and sedimentation and sand filtration), after the pretreatment, the COD of the raw water is removed by 48 percent, the hardness is removed by 79 percent, the pressure of the raw water on subsequent treatment is reduced, the condition of pollution and blockage cannot be generated, and the treatment process is stable to operate; ultrafiltration is carried out on clear water generated by pretreatment, filter pressing is carried out on generated sludge, and residual suspended matters and colloid substances in the back drainage liquid are removed by ultrafiltration; then, carrying out nanofiltration to separate salt, so that divalent ions are separated out, and the purity of sodium chloride is ensured; concentrating by reverse osmosis, and evaporating and crystallizing concentrated water; and finally, mixing the evaporated condensate with reverse osmosis clear water to reach the standard and discharging, wherein the crystallized salt reaches the first-grade quality of industry.

Further, the pretreatment comprises the following steps:

s11, introducing the shale gas fracturing flow-back fluid into a reaction tank, and adjusting the pH value of the shale gas fracturing flow-back fluid to 8-10 for softening;

s12, adding PAC with the mass concentration of 10% and PAM with the mass concentration of 0.1ppm into the softened shale gas fracturing flow-back fluid for flocculation, wherein the adding amount of PAC is 2-6 per mill of the mass of the shale gas fracturing flow-back fluid;

and S13, performing sand filtration on the flocculated shale gas fracturing flow-back fluid.

The raw water is beneficial to removing hardness by adjusting the pH of the raw water to be alkaline; PAC and PAM are added into the softened water body, so that shale gas fracturing flowback fluid becomes clear and transparent; and finally, adjusting the pH of the supernatant of the flocculated shale gas fracturing flow-back fluid to be acidic (the pH is 6-6.5), and performing sand filtration.

Further, in step S11, a sodium carbonate solution with a mass concentration of 10% is added into the reaction cell a to adjust the pH to 8-10, so that the hardness (<500mg/L) of the shale gas fracturing flow-back fluid meets the hardness requirement of the membrane.

Further, the pH value of the flocculated shale gas fracturing flow-back fluid is adjusted to 6-6.5 before sand filtration, so that sand filtration is facilitated.

Furthermore, the reverse osmosis uses a high-pressure RO membrane, so that the salt separation effect is ensured, and the contents of divalent ions such as sulfate radicals and hardness are extremely low, but the contents of the divalent ions have basic influence on the content of chloride.

Furthermore, the shale gas fracturing flowback fluid is Luxian shale gas fracturing flowback fluid, and relevant process and parameter design of the process is carried out according to the characteristics of the Luxian shale gas fracturing flowback fluid, so that the whole process flow is long and stable, the treatment efficiency of the Luxian shale gas fracturing flowback fluid is ensured, the operation cost is reduced, and the method is suitable for engineering application.

Further, the treatment process of the shale gas fracturing flowback fluid is carried out in a treatment system of the shale gas fracturing flowback fluid, the treatment system of the shale gas fracturing flowback fluid comprises a reaction tank, the output end of the reaction tank is communicated with a sand filtration device, the output end of the sand filtration device is communicated with an ultrafiltration device, the output end of the ultrafiltration device is communicated with a nanofiltration device, the output end of the nanofiltration device is communicated with a reverse osmosis device, the high pressure side of the reverse osmosis device is communicated with an evaporation device, the low pressure side of the reverse osmosis device is communicated with a discharge device, and a condensation pipe of the evaporation device is communicated with the discharge mechanism; the system can stably and permanently operate in the treatment process of the Luxian shale gas fracturing flowback liquid, and the problems of pollution, blockage and the like can not be caused.

The invention has the beneficial effects that: the method treats the Luxian shale gas fracturing flowback fluid through pretreatment, ultrafiltration, nanofiltration, reverse osmosis and evaporation, so that the final produced water reaches the discharge standard, the obtained crystalline salt also reaches the industrial first-level standard, and meanwhile, the stable and efficient operation of each stage in the process can be ensured; the medicine adding cost and the operation cost are reduced, and the method is suitable for engineering application.

Drawings

FIG. 1 is a process flow diagram of the present invention.

Detailed Description

The technical solutions of the present invention are further described in detail below with reference to the accompanying drawings, but the scope of the present invention is not limited to the following.

Example 1

A treatment process of shale gas fracturing flowback fluid comprises the following steps:

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s11, introducing the shale gas fracturing flow-back fluid into a reaction tank, adding a sodium carbonate solution with the mass concentration of 10% to adjust the pH value of the shale gas fracturing flow-back fluid to 8, and softening;

s12, adding PAC with the mass concentration of 10% and PAM with the mass concentration of 0.1ppm into the softened shale gas fracturing flow-back fluid for flocculation, wherein the adding amount of PAC is 2 per mill of the mass of the shale gas fracturing flow-back fluid;

s13, adjusting the pH value of the flocculated shale gas fracturing flow-back fluid to 6, and carrying out sand filtration;

s5, evaporating and crystallizing the concentrated water of the reverse osmosis shale gas fracturing flow-back fluid, wherein the clear water reaches the standard of reclaimed water reuse; the reverse osmosis uses a high-pressure RO membrane;

Example 2

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s12, adding PAC with the mass concentration of 10% and PAM with the mass concentration of 0.1ppm into the softened shale gas fracturing flow-back fluid for flocculation, wherein the adding amount of PAC is 4 per mill of the mass of the shale gas fracturing flow-back fluid;

s13, adjusting the pH value of the flocculated shale gas fracturing flow-back fluid to 6.2, and carrying out sand filtration;

Example 3

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s11, introducing the shale gas fracturing flow-back fluid into a reaction tank, adding a sodium carbonate solution with the mass concentration of 10% to adjust the pH value of the shale gas fracturing flow-back fluid to 9, and softening;

s13, adjusting the pH value of the flocculated shale gas fracturing flow-back fluid to 6.5, and carrying out sand filtration;

Example 4

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s11, introducing the shale gas fracturing flow-back fluid into a reaction tank, adding a sodium carbonate solution with the mass concentration of 10% to adjust the pH value of the shale gas fracturing flow-back fluid to 10, and softening;

s12, adding PAC with the mass concentration of 10% and PAM with the mass concentration of 0.1ppm into the softened shale gas fracturing flow-back fluid for flocculation, wherein the adding amount of PAC is 6 per mill of the mass of the shale gas fracturing flow-back fluid;

Comparative example 1

s1, adjusting the pH value of the shale gas fracturing flow-back fluid to 6.2, and carrying out sand filtration;

Comparative example 2

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s4, performing reverse osmosis treatment on the ultrafiltered shale gas fracturing flow-back fluid (clear water), and evaporating concentrated water;

Comparative example 3

s1, pretreating raw water of the Luxian shale gas fracturing flowback liquid;

s2, carrying out nanofiltration treatment on the pretreated shale gas fracturing flow-back fluid (clear water), and returning concentrated water to the pretreatment stage for treatment;

s3, performing reverse osmosis treatment on the filtered shale gas fracturing flow-back fluid (clear water), and evaporating concentrated water;

s4, evaporating and crystallizing the concentrated water of the reverse osmosis shale gas fracturing flow-back fluid, wherein the clear water reaches the standard of reclaimed water reuse; the reverse osmosis uses a high-pressure RO membrane;

and S5, mixing the clear water after reverse osmosis with the evaporated condensate liquid for discharging.

Through comparison between the examples 1-4 and the comparative examples 1-3, the process flows related to the examples can be stably and long-term carried out, the treatment efficiency of the Luxian shale gas fracturing flowback liquid is guaranteed, meanwhile, clear water finally obtained by treating the Luxian shale gas fracturing flowback liquid reaches the standard of reclaimed water reuse, the obtained crystalline salt reaches the industrial grade quality, and a certain commercial value is created during sewage treatment. In the comparative example 1, the treatment efficiency of the whole process on the shale gas fracturing flow-back fluid is low, the related treatment system is seriously blocked and needs to be frequently cleaned; comparative example 2 nanofiltration and ultrafiltration, nanofiltration and reverse osmosis can not be synergistic, the treatment efficiency of COD is low, and the obtained crystalline salt can not reach the first-grade quality of industry; comparative example 3 no synergistic effect was obtained on nanofiltration and ultrafiltration, resulting in low treatment efficiency of COD, and the quality of the obtained crystalline salt was higher than that of comparative example 2 by synergistic effect of nanofiltration and reverse osmosis.

The detection data of the stock solution of the Luxian shale gas fracturing flowback fluid are shown in Table 1.

Table 1:

name of water sample	Water sample 1	Water sample 2
			pH (dimensionless)	7.9	8.3
Conductivity (us/cm)	21500	21200
			COD(mg/L)	311	487
Chloride ion (mg/L)	8315	8315
			Hardness (mg/L)	680	661

The pretreatment tests for adjusting the Luxian shale gas fracturing flowback fluid are shown in tables 2-3.

Table 2: softening and hardness removal bench test data sheet

Table 2 shows that: the removal of hardness is facilitated by adjusting the pH to be slightly alkaline, but the hardness requirement (<500mg/L) for film penetration can be achieved by adding 7% o of sodium carbonate solution (10%).

Table 3: flocculation precipitation bench scale data

As can be seen from Table 3, the addition of 4 ‰ PAC (10%) and a small amount of PAM makes the fracturing flowback fluid clear and transparent, and generates obvious flocs, and the flocculated pH is adjusted to 6-6.5, and then the pH value enters a sand filtration system for filtration, so that the clear and transparent fracturing flowback fluid is obtained.

The water quality after pretreatment is shown in Table 4.

Table 4:

name of water sample	Water sample 1
		pH (dimensionless)	6.2
Conductivity (us/cm)	24800
		COD(mg/L)	160
Chloride ion (mg/L)	8290
		Hardness (mg/L)	146

As can be seen from Table 4, the pretreatment removes 48% of COD in the raw water and 79% of hardness, which greatly reduces the pressure of the subsequent treatment and ensures the stable and long-lasting operation of the subsequent process flow.

The ultrafiltration experiment, the invention develops 4 batches of ultrafiltration experiments, only carries out water backwashing after each batch of experiments, refers to the normal water production in engineering for about 1 hour and then backwashing for 3 minutes, checks the pollution and blockage condition of ultrafiltration, the data of the ultrafiltration experiment are shown in a table 5, and the data of water quality detection after ultrafiltration are shown in a table 6.

Table 5:

as can be seen from Table 5, no fouling was produced by ultrafiltration in the continuous ultrafiltration experiment, which indicates that the pretreated frac flowback fluid was very slight to foul the ultrafiltration.

Table 6:

as can be seen from Table 6, after the ultrafiltration, the indexes were unchanged except that the COD was slightly decreased, indicating that the ultrafiltration was able to intercept some colloidal substances, but the content of the colloidal substances was very low.

Nanofiltration experiments, the invention develops 4 batches of nanofiltration experiments, and the recovery rate of each batch is 90%. Cleaning is not carried out after each batch of experiment, the fouling and blocking condition of nanofiltration is checked, the nanofiltration experiment data are shown in a table 7, and the water quality condition after nanofiltration is shown in a table 8.

Table 7:

as can be seen from table 7, the nanofiltration did not cause fouling through the continuous ultrafiltration experiment, which indicates that the fouling of the ultrafiltrated fracturing flow-back fluid is very slight.

Table 8:

name of water sample	Concentrated water	Raw water	Produce water
				pH (dimensionless)	6.4	6.2	6.0
Conductivity (us/cm)	31800	24800	22300
				COD(mg/L)	152	152	71
Chloride ion (mg/L)	10075	8290	8170
				Hardness (mg/L)	146	146	18
Sulfate radical (mg/L)	468	58	14

As can be seen from Table 8, after nanofiltration, the content of chloride in produced water is not greatly influenced, and the content of divalent ions such as sulfate radicals and hardness is low, which indicates that the salt separation effect is good.

Reverse osmosis experiments, 4 batches of reverse osmosis experiments are carried out by using a high-pressure RO membrane, and the recovery rate of each batch is 70 percent. After each batch of experiments, the fouling and blocking conditions of the high-pressure RO membrane are checked; the reverse osmosis experimental data are shown in Table 9, and the water quality after reverse osmosis is shown in Table 10.

Table 9:

as can be seen from table 9, continuous reverse osmosis experiments show that no fouling is generated by reverse osmosis, which indicates that the high-pressure RO membrane is slightly fouled by the fracturing flow-back fluid after nanofiltration.

Table 10:

name of water sample	Concentrated water	Produce water
			pH (dimensionless)	6.2	6.0
Conductivity (us/cm)	81200	370
			COD(mg/L)	192	12
Chloride ion (mg/L)	27264	45
			Hardness (mg/L)	51	Not detected out
Sulfate radical (mg/L)	40	Not detected out

As can be seen from Table 10, after SWRO, the produced water meets the standard of reclaimed water reuse, and the concentrated water has high salinity and low hardness, and meets the requirement of evaporation.

And (3) an evaporative crystallization experiment, wherein the concentrated water subjected to reverse osmosis is subjected to evaporative crystallization, the experimental data of the crystallized salt are shown in a table 11, and the water quality index of the condensed water is shown.

Table 11:

item	Numerical value	Industry first class standard
			Sodium chloride content (g/100g)	99.4	99.1
Moisture (g/100g)	0.2	0.3
			Water insoluble matter (g/100g)	0.01	0.05
Total amount of calcium and magnesium ions (g/100g)	Not detected out	0.25
			Sulfate ion (g/100g)	Not detected out	0.3

Table 12:

name of water sample	Condensed water
		pH (dimensionless)	7
Conductivity (us/cm)	38
		COD(mg/L)	12
Chloride ion (mg/L)	Not detected out
		Ammonia nitrogen (mg/L)	15

As can be seen from tables 11 and 12, the crystallized salt reached the first grade standard of industrial salt, and the condensed water reached the emission standard of the third grade.

The foregoing is illustrative of the preferred embodiments of this invention, and it is to be understood that the invention is not limited to the precise form disclosed herein and that various other combinations, modifications, and environments may be resorted to, falling within the scope of the concept as disclosed herein, either as described above or as apparent to those skilled in the relevant art. And that modifications and variations may be effected by those skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. The treatment process of the shale gas fracturing flowback fluid is characterized by comprising the following steps of:

s1, pretreating raw water of the shale gas fracturing flow-back fluid;

s2, carrying out ultrafiltration treatment on the pretreated shale gas fracturing flowback fluid;

s3, performing nanofiltration treatment on the ultrafiltered shale gas fracturing flow-back fluid;

s4, performing reverse osmosis treatment on the nanofiltration shale gas fracturing flow-back fluid;

s5, evaporating and crystallizing the reverse osmosis concentrated water;

2. The treatment process of the shale gas fracturing flowback fluid of claim 1, wherein: the pretreatment comprises the following steps:

3. The treatment process of the shale gas fracturing flowback fluid as claimed in claim 2, wherein: in step S11, sodium carbonate solution with the mass concentration of 10% is added into the reaction tank A to adjust the pH value to 8-10.

4. The treatment process of the shale gas fracturing flowback fluid as claimed in claim 2, wherein: and before sand filtration, the pH value of the flocculated shale gas fracturing flow-back fluid is adjusted to 6-6.5.

5. The treatment process of the shale gas fracturing flowback fluid of claim 1, wherein: the reverse osmosis uses a high pressure RO membrane.

6. The treatment process of the shale gas fracturing flowback fluid of claim 1, wherein: : the shale gas fracturing flowback fluid is Luxian shale gas fracturing flowback fluid.

7. The treatment process of the shale gas fracturing flowback fluid as claimed in claims 1-7, wherein: the shale gas fracturing flow-back fluid treatment process is carried out in a shale gas fracturing flow-back fluid treatment system, the shale gas fracturing flow-back fluid treatment system comprises a reaction tank, the output end of the reaction tank is communicated with a sand filtration device, the output end of the sand filtration device is communicated with an ultrafiltration device, the output end of the ultrafiltration device is communicated with a nanofiltration device, the output end of the nanofiltration system is communicated with a reverse osmosis device, the high-pressure side of the reverse osmosis device is communicated with an evaporation device, the low-pressure side of the reverse osmosis device is communicated with a discharge device, and a condensation pipe of the evaporation device is communicated with a discharge mechanism.