Introduction

The continuous growth of global energy demand has made oil and gas field development a critical component of modern industry1. However, this process generates significant waste, including water-based drilling fluids and WOM, which pose substantial environmental risks2. WOM, a hazardous drilling fluid containing organic compounds, mineral oils, diesel, and heavy metals, is classified as hazardous waste in China3,4. Direct disposal without proper treatment leads to severe environmental pollution and resource waste5. Consequently, the harmless and resource-efficient treatment of WOM aligns with both low-carbon economic goals and the principles of green development6,7.

Significant progress has been made in WOM treatment technologies, including physical (centrifugation, filtration, distillation), chemical (oxidation, demulsification), and biological methods (microbial degradation)8,9,10. Integrated approaches such as pyrolysis, hot washing, and incineration have even reached industrial-scale application in some oil fields11. For instance, Wu achieved a 68.1% mineral oil degradation rate using low-temperature plasma technology12, while Zhou demonstrated the feasibility of thermal distillation for oil recovery and residue reuse in ceramics13.

Despite these advances, critical challenges persist: high costs14, inefficient component separation15, secondary pollution16, excessive energy consumption17, and limited resource recovery18. Moreover, engineering scale-up difficulties and the absence of standardized metrics hinder widespread adoption19,20. Three key issues must be addressed: (1) the complex composition of WOM demands multifactorial treatment strategies21; (2) by-products require proper disposal to avoid secondary pollution22; and (3) energy-efficient and sustainable technologies are urgently needed23.

While significant research and industrial applications exist for oilfield WOM treatment, resource utilization and harmless treatment technologies for gasfield WOM remain underexplored24. This study addresses this gap by focusing on Yanchang gasfield WOM, employing an integrated approach combining chemical oxidation-demulsification and mechanical separation. The process achieves efficient dehydration and de-oiling, followed by deep treatment of centrifuged water for reuse in fracturing fluid preparation, while solidified DM meets environmental standards for construction applications. The study’s key innovations include: (1) a complete treatment chain enabling both resource recovery (recycled clean water and oil) and safe disposal (solidified DM); (2) closed-loop water reuse, reducing freshwater demand; (3) recovered oil repurposed as fuel; and (4) DM solidification producing compliant, reusable materials for infrastructure. By demonstrating a scalable solution for gasfield WOM, this work advances sustainable practices in oil and gas development, minimizing environmental harm while maximizing resource efficiency. The findings offer practical insights for industry applications and contribute to the theoretical framework for hazardous waste management in energy operations.

Materials and methods

Experimental materials

Analytical grade sodium hydroxide (NaOH, > 99% purity), concentrated sulfuric acid (H2SO4, > 98% purity), sodium hypochlorite(NaClO, 30% purity), hydrogen peroxide solution(H2O2, > 30% purity) were used in the experiment. Industrial grade poly aluminum chloride (PAC, > 30% purity), polyaluminium sulfate (PAS, > 17% purity), polymerization ferric chloride (PFC, > 35% purity), polymeric ferric sulfate (PFS, > 21% purity), CPAM (> 99% purity, molecular weight 14 million), APAM (> 99% purity, molecular weight 8–18 million) were used in this experiment. AR36 type demulsifier, portland cement, quicklime, fly ash, biomass (walnut shell) were used in the experiment. In this study, NaOH, PAC, PAS, PFC, PFS, APAM, CPAM were prepared as solutions with mass fractions of 20%, 1%, 1%, 1%, 1%, 0.1% and 0.1%, respectively. H2SO4 were prepared as solutions with volume fractions of 50%.

A vacuum oven (BYP-070GX), acidity meter (PHSJ-5T), tabletop centrifuge (TD4C, external dimensions 400 × 480 × 360 mm, maximum capacity during single tube centrifugation 100mL), infrared oil analyzer (LJ-HC500), vacuum circulating water pump (SHZD), UV spectrophotometer (HD-UV90), and universal pressure testing machine (TYE2000) were utilized in the experiment.

Experimental methods

The overall idea of this experiment is to first dehydrate the WOM from the gas field through a volume reduction experiment. The water separated after dehydration is further treated, and finally the fracturing fluid is prepared again. The DM is subjected to solidification treatment experiments. The experiment is divided into three parts, among which the research group conducted a large number of experimental condition screenings for the dehydration of WOM. The optimal conditions for the dehydration experiment of WOM in this article are directly selected using the best experimental parameters screened by the research group. The specific screening process will not be described in detail. The focus of this article is on the deep treatment of water and solidification of sediment after the dehydration of WOM. In this article, the experimental data were obtained from triplicate independent tests, and the results are presented as mean values with error bars representing the standard deviation in all relevant figures25,26. The specific experimental methods for each part are as follows:

  1. (1)

    WOM dewatering experiment: Firstly, the pH of the WOM system was adjusted to 5–6 (H2SO4 solution, volume fraction of 50%), heated to 60 ℃, and 8 mg/L of AR36 type demulsifier and 0.5% biomass (walnut shell) were sequentially added to the mud. Then, stirring was carried out at 200 rpm for 40 min, and 60 mg/L of CPAM (molecular weight 14 million) was added to the stirred mud. After stirring, it is sent to a centrifuge with a speed of 3000 rpm and centrifuged for 20 min. The ORR, VRR, WC in the recovered oil, and OC in the DM are used as evaluation indicators.

  2. (2)

    IW cycle utilization experiment: After centrifugal treatment of the mud, the IW is subjected to deep treatment in order to use the CW for on-site preparation of fracturing fluid. The IW cycle utilization experiment adopts the idea of oxidation, coagulation, filtration, mainly screening the types and dosages of oxidants and coagulants. The experimental results show that the TR, SS, and OC of the upper layer of CW are the evaluation indicators. The CW was subjected to secondary preparation experiments of fracturing fluid, with the on-site requirements for the use of fracturing fluid as the evaluation index. TR is an initial screening tool in the experimental process, and the final suitability evaluation of CW needs to be combined with salinity and other physical and chemical analyses.

  3. (3)

    Mud solidification experiment: The solid phase of the centrifuged WOM is mixed with various solidification materials in a certain proportion, stirred and mixed evenly, and then injected into a square container with a length, width, and height of 7 cm for static solidification. After solidification, the compressive strength is measured after 7 days. Simultaneously measure the COD, chromaticity, heavy metal content, OC, and pH in the leachate of solidified blocks. The leachate experiment shall refer to the national standard “Horizontal Oscillation Method for Toxicity Leaching of Solid Waste”.

Analysis methods

The determination method of WC in oil shall be in accordance with the method specified in ‘Determination of water content in crude oil distillation method’ (GB/T 8929 − 2006). OC in water shall be determined according to the method specified in ‘Water quality determination of petroleum, animal and vegetable oils infrared spectrophotometry’ (HJ 637–2012). OC of DM shall be tested according to the method specified in the ‘Control limits for disposal and utilization of oily sludge’ (DB61/T 1025–2016).

The ORR was calculated by using the following Eq. (1):

$$ORR = \frac{m}{n} \times 100\%$$
(1)

where µ is ORR (%), m is volume of reduced separated oil (mL), n is volume of oil in crude WOM (mL).

The VRR was calculated by using the following Eq. (2):

$$VRR = \frac{x}{y} \times 100\%$$
(2)

where ρ is VRR (%), x is final residual solid sludge volume after centrifugation (mL), y is volume of crude WOM (mL).

WOM treatment process

Based on the experiments on WOM treatment, wastewater treatment and resource utilization, and mud solidification, the harmless and resource utilization processes for waste mud can be obtained. The process flow is shown in Fig. 1.

Given the involvement of multiple experimental components in this study, to enhance clarity and facilitate reader comprehension, we standardized the nomenclature of experimental materials at different stages. The original waste mud is referred to as WOM. The wastewater and solid waste produced following the dewatering of WOM are designated as IW and DM, respectively. Following advanced treatment, IW is referred to as CW.

Fig. 1
Fig. 1
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WOM treatment process flow.

Results and discussion

Analysis of sample properties

WOM samples were obtained from Fourth Gas Production Plant of Yanchang Oilfield in Shaanxi Province, China. These samples were stored in a refrigerator at 4℃ to minimize biological and chemical reactions as much as possible. The general characteristics of the WOM samples from the workplace were shown in Table 1.

Table 1 Characteristics of the WOM samples.
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Mud dewatering experiment

According to the method specified in 2.3 (1), the WOM from Quan122-1# gas well was treated. After the mud is dehydrated, the upper layer of floatation, IW and DM. The experimental results and process are shown in Table 2; Fig. 2.

Table 2 Characteristics of dehydration treatment of WOM.
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Fig. 2
Fig. 2
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Different stages of WOM treatment.

Following demulsification and centrifugation treatment, the ORR and VRR of WOM reached 95.62% and 93.20%, respectively. The WC in the recovered oil was reduced to 0.40%, complying with the Chinese national standard for crude oil transportation (GB 50350 − 2015). Furthermore, the OC in the DM was reduced to 4.33%, making it suitable for subsequent solidification treatment. The detailed experimental results are presented in Table 2.

IW treatment experiment

After centrifugal dehydration, the water separated from the WOM appears yellow green and has poor water quality, as shown in Fig. 2c. The salinity and COD of water are 72454.26 mg/L and 2711.30 mg/L, respectively, and the SS is 250.50 mg/L, as shown in Table 3.

Table 3 Analysis of IW.
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According to the water quality requirements for preparing fracturing fluid at the drilling site, the water must be clean and free of solid impurities. IW cannot meet the water quality indicators for secondary fluid preparation27. Therefore, it is necessary to carry out deep treatment of the water separated from the WOM. The IW treatment experiment was conducted according to the method specified in 2.3 (2), and the pH value, type and dosage of oxidants, and type and dosage of coagulants were screened.

Effect of pH on IW treatment

Add 200mL of IW sample to seven 250mL beakers. Adjust the pH value of IW sample to 4–10 using H2SO4 (solution, volume fraction of 50%) separately. The experimental results were evaluated based on the COD and TR in CW at the top of the beaker. as shown in Fig. 3.

Fig. 3
Fig. 3
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The influence of pH.

Effect of oxidant types, dosages, and oxidation time on IW treatment

The COD of CW under acidic conditions is significantly lower than that under alkaline conditions, and the COD shows a decreasing trend with the decrease of pH, as shown in Fig. 3. After the pH value of the CW decreased to 6, the TR showed a decreasing trend. Judging from the experimental phenomenon, due to the gradual decrease in pH, the CW shows a trend of becoming clearer, but the chromaticity of the CW shows an increasing trend, resulting in a decrease in TR28. Therefore, the pH of the CW should be adjusted to 6 before oxidation, and the slightly acidic experimental conditions are more conducive to subsequent oxidation treatment.

NaClO and H2O2 were used as oxidants in the experiment. This section conducted three parts of experiments, which screened the types of oxidants, the amount of oxidants added, and the oxidation time.

Effect of oxidant types

Add 200mL of IW to fourteen 250mL beakers, adjust the pH of all IW to 6, and divide the experiment into two groups, with seven water samples in each group. In the first group of IW, 1000 mg/L to 4000 mg/L of NaClO was added sequentially, and in the second group of IW, 1000 mg/L to 4000 mg/L of H2O2 was added sequentially. The oxidation time for all experiments was 30 min, and the optimal type of oxidant is selected based on the COD and TR in CW at the top of the beaker. The experimental results are shown in Fig. 4.

Fig. 4
Fig. 4
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The influence of oxidant types.

From Fig. 4, it can be seen that under the same dosage of the two oxidants, NaClO has a better effect than H2O2. Therefore, NaClO was selected as the oxidant in the experiment. It is not difficult to infer from the experimental results that there may be oxidation and oxidized processes of H2O2, resulting in suboptimal oxidation efficiency of H2O2. NaClO is difficult to oxidized when added to this type of water, as it only undergoes an oxidation process, resulting in higher oxidation efficiency29.

Effect of oxidizing agent dosage

Add 200mL of IW to eight 250mL beakers, adjust the pH of IW to 6, and sequentially add 1000 mg/L to 8000 mg/L NaClO to each of the eight beakers. The oxidation time is 30 min, and the optimal amount of oxidant is selected based on the COD and TR in CW at the top of the beaker. The experimental results are shown in Fig. 5.

Fig. 5
Fig. 5
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The influence of oxidizing agent dosage.

From Fig. 5, it can be seen that with the gradual increase of NaClO dosage, the TR of CW increases significantly, while the COD in CW decreases significantly. When the NaClO dosage is 5000 mg/L, the COD decreases to the lowest 338.24 mg/L, and the TR can increase to 78.02%. Afterwards, with further increase of NaClO, there is no significant change in COD and TR. Therefore, the optimal dosage of NaClO was selected as 5000 mg/L.

Effect of oxidation time

Add 200 mL of IW to six 250 mL beakers, adjust the pH of IW to 6, and then add 5000 mg/L NaClO. The oxidation time is 10–35 min, and the optimal oxidation time is selected based on the COD and TR in the CW at the top of the beaker. The results are shown in Fig. 6.

From Fig. 6, it can be seen that as the oxidation time prolongs, the TR gradually increases and COD gradually decreases. When the oxidation time was 25 min, the TR reached 78.32% and the COD decreased to 367.82 mg/L. When the oxidation time exceeds 25 min, the changes in TR and COD are no longer significant, indicating that the oxidation reaction has been completed. Therefore, the optimal oxidation time is 25 min.

Fig. 6
Fig. 6
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The influence of oxidation time.

Effect of types and dosages of coagulants on IW treatment

According to the general principles of wastewater treatment, adjusting the pH of the IW sample to alkaline or weakly alkaline conditions is the most effective in conducting coagulation and sedimentation experiments. Therefore, before conducting coagulation experiments, adjust the pH of the oxidized water sample to 9, and then conduct screening experiments on the type, dosage, and settling time of coagulants. The coagulants used in the experiment are APAM (molecular weight 8 million), PFS, PFC, PAC, and PAS. This section of the experiment is divided into two parts, namely the selection of coagulant types and the selection of coagulant dosage. The selection of coagulant dosage is further divided into PAC dosage screening, APAM dosage screening, and APAM molecular weight screening experiments.

Effect of type of coagulant

Take five parts of the water sample after oxidation and add five types of coagulants (APAM, PFS, PFC, PAC, PAS) in the same amount. Stir for 10 min and then settle for 20 min. The experimental phenomenon is shown in Fig. 7.

Fig. 7
Fig. 7
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Selection experiment of coagulant types.

From Fig. 7, it can be seen that the effectiveness of a single coagulant is poor and cannot play a role in water purification. Among them, PAC and APAM have the best effect, so the combination of coagulants PAC and APAM is used.

Effect of coagulant dosage

Based on the experimental phenomena and results during the selection of coagulant types, the combination addition scheme of coagulants was determined: PAC was added first, followed by APAM. Therefore, the screening of drug dosage experiments is divided into three parts, namely PAC dosage screening, APAM dosage screening, and APAM molecular weight screening experiments.

① Effect of PAC dosage

Add 200mL of oxidized water sample to five 250mL beakers. Add 60–140 mg/L of PAC in sequence to five beakers, then add 5 mg/L of APAM separately, stir for 10 min, and let it stand for 20 min. The TR, SS, and COD in the upper layer of CW in the beaker are used as evaluation indicators. The experimental results are shown in Fig. 8.

Fig. 8
Fig. 8
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PAC dosage screening experiment.

From Fig. 8, it can be seen that with the increase of PAC dosage, the TR has significantly increased, and the SS and COD have both decreased to varying degrees. When the PAC dosage is 120 mg/L, the TR of CW can reach 89.62%, and the SS and COD in CW decrease to 28.33 mg/L and 198.32 mg/L, respectively. When the dosage of PAC exceeds 120 mg/L, the TR decreases, while the SS and COD no longer show a significant decrease. Therefore, the optimal dosage of PAC is 120 mg/L.

② Effect of APAM dosage

Add 200mL of oxidized water sample to six 250mL beakers. Add 120 mg/L of PAC in six beakers, then add 2–10 mg/L of APAM separately, stir for 10 min, and let it stand for 20 min. The TR, SS, and COD in the upper layer of CW in the beaker are used as evaluation indicators. The experimental results are shown in Fig. 9.

Fig. 9
Fig. 9
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APAM dosage screening experiment.

From Fig. 9, it can be seen that with the increase of APAM dosage, the TR gradually increases, while the SS and COD gradually decreases. At an APAM dosage of 8 mg/L, the TR of CW reaches 96.76%, with SS and COD reduced to 15.05 mg/L and 153.87 mg/L, respectively. Increasing the APAM dosage beyond 8 mg/L yields no significant improvement in TR, SS, or COD values. Therefore, an APAM dosage of 8 mg/L was identified as the optimal condition.

③ Effect of APAM molecular weight

Add 200mL of oxidized water sample to six 250mL beakers. Add 120 mg/L of PAC to six beakers, then add 8 mg/L of APAM with different molecular weights (8–18 million), stir for 10 min, and let stand for 20 min. The TR, SS, and COD of the upper layer of CW in the beaker are used as evaluation indicators. The experimental results are shown in Fig. 10.

Fig. 10
Fig. 10
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APAM molecular weight screening experiment.

From Fig. 10, it can be seen that as the molecular weight of APAM increases, the TR gradually increases, while the SS and COD gradually decrease. When the molecular weight of APAM is 14 million, the TR of CW can reach 98.60%, and the SS and COD in CW decrease to 11.03 mg/L and 131.36 mg/L, respectively. When the molecular weight of APAM exceeds 14 million, as the molecular weight further increases, there is no significant change in TR, SS, and COD. Therefore, the optimal molecular weight for selecting APAM is 14 million.

In summary, the optimal process conditions for IW treatment are as follows: adjust the pH value of the IW to 6, add 5000 mg/L NaClO for oxidation for 25 min, then adjust the pH value of the IW to 9, add 120 mg/L PAC, and add 8 mg/L APAM with molecular weight of 14 million. Stir for 10 min and let it stand for 20 min. The TR of the upper layer of CW in the beaker can reach 98.60%, and the SS and COD can be reduced to 10.50 mg/L and 130.33 mg/L, respectively. Before and after IW treatment, as shown in Fig. 11.

Fig. 11
Fig. 11
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Different stages of sewage treatment.

Preparation experiment of fracturing fluid

CW quality analysis

From the experimental results in 3.3.2, it can be seen that the IW treatment has a good effect, and the CW is relatively clean, which can be used to reconfigure the fracturing fluid. The CW quality analysis is shown in Table 4.

Table 4 Analysis of CW quality.
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As shown in Table 4, the OC and SS are 3.63 mg/L and 12.33 mg/L, respectively, while TR reaches 98.89% and turbidity is measured at 4 NTU, collectively indicating excellent water quality. However, the water exhibits high salinity, reaching up to 43,780.04 mg/L. The impact of salinity on the crosslinking performance of fracturing fluids must therefore be carefully considered during formulation. The concentrations of Ca²⁺, Mg²⁺, Ba²⁺, Sr²⁺, B³⁺, and total iron are relatively low. Other heavy metal ions are below detection limits and are not expected to interfere with the re-formulation of fracturing fluids.

Reuse of CW for fracturing fluid preparation experiments

The fracturing fluid formula used in some well sites of the Yanchang gas field is shown in Table 5.

Table 5 Fracturing fluid formula.
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According to Tables 4 and 5, the CW was reformulated with fracturing fluid. Owing to the elevated salinity of 43,780.04 mg/L in the CW, the cross-linking efficiency of the fracturing fluid may be compromised, and scaling may occur upon contact with formation water or other fluid components. Therefore, 0.1% BE-2 scale inhibitor was incorporated during the preparation of fracturing fluid using CW. The addition of the scale inhibitor resulted in favorable cross-linking performance and compatibility with formation water. The various performance indicators of the prepared fracturing fluid are shown in Table 6.

Table 6 Performance indicators of fracturing fluid.
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From Table 6, it can be seen that the CW can be re formulated with fracturing fluid, and all indicators fully meet the performance requirements of the new fracturing fluid on site. Therefore, the water extracted from WOM can be recycled after deep treatment.

Mud solidification experiment

According to method 2.3 (3), solidification experiments were conducted on the DM after dewatering treatment of WOM. The solidification agent mainly consists of fly ash, cement, and quicklime. The solidifying agent was mixed with the sediment in different proportions, and the influence of various components of the solidifying agent on the solidification strength of the sediment was explored in each group of experiments with the same sediment quality. The range of adding proportions of three additives was determined, namely fly ash 5% -15%, cement 30% -50%, and quicklime 10% -20%. A three factor and three level orthogonal experimental table was designed, and the adding ratios of each factor were calculated based on the mass of the sediment. The experimental design is shown in Table 7, and the experimental results were evaluated based on compressive strength.

Table 7 Orthogonal design and results of curing experiment.
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From Table 7, the cumulative values kb of the same level experimental groups in each column can be calculated, thereby calculating the range R and minimum range Re of the k values in each column. When R/Re>1.5, it is confirmed that this column of factors is the main influencing factor, with the larger kb being the better level. According to the experimental results in Table 7, R1 = 0.198 in the first column, R2 = 0.334 in the second column, R3 = 0.267 in the third column, and Re=0.198 (taking the minimum value from the three columns), cement were determined as the main influencing factors.

The optimal levels of each factor were: 10% fly ash added in Factor 1, 30% cement added in Factor 2, and 20% quicklime added in Factor 3. Three parallel experiments were conducted based on the optimal levels of various factors selected through orthogonal experiments, and the experimental results are shown in Table 8.

Table 8 Parallel experiments at orthogonal optimal levels.
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From Table 8, it can be seen that when 10% fly ash, 30% cement, and 20% quicklime are added to the sediment, the average compressive strength of the solidified mud block can reach 16.22 MPa. The experimental phenomena at intervals of 1, 3, 5, and 7 days during mud solidification are shown in Fig. 12.

Fig. 12
Fig. 12
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Experimental process of sediment solidification.

In order to verify the solidification effect of the mud, a leaching solution experiment was conducted on the solidified block. The experimental plan followed the experimental method specified in 2.3 (3), mainly detecting various heavy metals, COD, OC, chromaticity, pH, etc. in the leaching solution. The detection results are shown in Table 9.

Table 9 Extraction liquid detection experiment of solidified blocks.
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From Table 9, it can be seen that all heavy metal contents in the solidified leachate are below the detection limit, and the COD, OC, chromaticity, pH and other indicators in the leachate meet the discharge requirements of ‘Comprehensive wastewater discharge standard’ (GB 8978 − 1996). Therefore, the solidified mud block can be fully used for laying well sites or roads in oil and gas fields.

In summary, the DM of WOM can be solidified in a ratio of 10%: 30%: 20% for fly ash: cement: quicklime. The compressive strength of the solidified block after solidification can reach 16.22 MPa, and all indicators in the leachate of the solidified block meet the discharge requirements of ‘Comprehensive wastewater discharge standard’. This solidified block can be used for laying well sites or roads in oil and gas fields.

The absence of detectable heavy metals in both the CW and the leachate of the solidified block during the experiment suggests that the majority of heavy metals were immobilized within the solid matrix and are not readily released through short-term water immersion. To validate this hypothesis, the solidified block was crushed and subjected to immersion testing, which revealed a significant presence of heavy metals in the leachate. Accordingly, subsequent research will focus on elucidating the solidification mechanisms and release dynamics of heavy metals.

Comparative analysis of cost and technology

Cost analysis

This article proposes a new method for harmless treatment of gas field waste mud. From the experimental results, it can be seen that the CW can be reused, and the treated solidified blocks can be used as materials for laying oil and gas field well sites or roads, all of which meet the standard requirements. However, due to the complex processing of WOM, its application in industry may increase certain costs, and there is little information on the treatment of gas field WOM in the network or literature. Therefore, in order to further demonstrate the feasibility of this approach in treating gas field WOM, it is necessary to conduct an economic analysis. Therefore, this technology also needs to be economically compared with relevant technologies mentioned in the network or literature, so that it has practical application and promotion value in both technical and economic aspects.

This study incorporates several assumptions in the economic analysis, including a WOM processing capacity of 2,000 m³ per well, a daily treatment capacity of 80 m³, and an annual treatment capacity of 24,000 m³ for the WOM treatment system, with a total capital investment of USD 170,000 and a total installed power of 105 kW. Based on these assumptions, the economic assessment primarily evaluated the costs associated with chemicals, water, electricity, labor, equipment depreciation, and maintenance. By comparing the operating economy analysis of the process in this article with similar processes reported in literature, Table 10 demonstrates that the lowest operating economy of the process in this article can reach 8.06 USD/m3. This finding suggests promising application and promotion prospects.

Technical comparative analysis

To further underscore the advantages of the WOM treatment technology presented in this study, a comparative analysis was conducted against other existing WOM treatment technologies. Assuming a daily treatment capacity of 10 m³, the comparison focused on treatment principles, technological maturity, capital investment, operational costs, treatment efficiency, potential for secondary pollution, oil recovery efficiency, resource recycling, disposal methods, and long-term performance. Details of the comparison are provided in Table 11.

As shown in Table 11, pyrolysis and thermal distillation technologies exhibit high treatment efficiency but are associated with high capital and operating costs, along with the risk of secondary pollution from flue gas emissions. Although microbial treatment methods incur low operational costs, their treatment efficiency is insufficient, the processing cycle is prolonged, the land footprint is substantial, and they are incapable of timely WOM remediation. In comparison with pyrolysis, thermal distillation, and microbial approaches, the treatment process proposed in this study demonstrates advantages including low capital investment, reduced operational costs, high treatment efficiency, a short processing cycle, comprehensive remediation, absence of secondary pollution, compact footprint, on-site applicability, and robust long-term stability.

Technical limitations

(1) Scalability: Although laboratory-scale experiments confirmed the effectiveness of WOM treatment, we recognize that scaling up to industrial operations (typically 1–10 m³/d) may present challenges in maintaining uniform mixing, ensuring consistent heat transfer in larger reactors, and achieving stable performance under varying sludge compositions.

(2) Energy consumption: The proposed process does not require thermal input, and energy consumption primarily stems from equipment operation.

(3) Chemical additives and secondary pollution: The environmental implications of chemical usage have been further explored as follows:

NaClO: While effective for oxidation, its use may result in chloride accumulation (150–200 mg/L in treated effluent), necessitating additional treatment measures.

APAM: Although a low dosage (8 mg/L) was employed, further research is needed to assess long-term ecotoxicity and to investigate bio-based flocculant alternatives.

Based on the above analyses, specific recommendations and challenges have been identified for future research directions. In upcoming work, our research group will focus on pilot-scale validation to assess scalability, energy optimization through process integration, and the development of environmentally friendly chemical alternatives.

Future perspectives and research directions

To further advance the outcomes of this study, several avenues for future research are proposed:

  1. (1)

    Field trials and real-world validation: Controlled laboratory experiments should be extended to field-scale trials to evaluate the practical applicability and operational robustness of the proposed method under diverse environmental conditions.

  2. (2)

    Long-term performance evaluation: Future investigations should assess the long-term durability and operational efficiency of the system to ensure sustained performance and to identify potential degradation pathways.

  3. (3)

    Scaling mitigation strategies: Further research is needed to optimize large-scale implementation, encompassing cost-benefit analysis, logistical constraints, and necessary modifications for industrial or commercial deployment.

  4. (4)

    Environmental impact monitoring: Comprehensive ecological assessments should be conducted to evaluate potential secondary effects on surrounding ecosystems, ensuring that mitigation strategies do not introduce unintended consequences.

These future studies will enhance the practical relevance of this work and strengthen its foundation for real-world application.

Table 10 Economic comparative analysis (USD/m3).
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Table 11 Technical comparative analysis.
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Summary and conclusion

(1) This study successfully developed an integrated treatment system for WOM, achieving both resource recovery and environmentally safe disposal. The chemical demulsification-mechanical dehydration process attained 95.62% oil recovery and 93.20% volume reduction, with residual oil and water contents of 0.40% and 4.33% in DM, respectively. The treated IW demonstrated 98.6% transmittance, suitable for fracturing fluid preparation, while solidified blocks exhibited 16.22 MPa compressive strength with compliant leachate.

(2) The proposed method shows superior cost-effectiveness (8.06 USD/m³) compared to conventional pyrolysis (9.10 USD/m³) and thermal distillation, featuring: eliminated thermal energy requirements, optimized chemical consumption through pH-mediated oxidation, and complete phase separation without secondary pollution. The modular design proves particularly suitable for remote gas field applications.

(3) Our three-stage treatment system addresses critical industry challenges: enhanced demulsification efficiency for stable emulsions, breakthrough NaClO oxidation-coagulation synergy for high-salinity wastewater clarification, and innovative fly ash-cement-lime formulation simultaneously meeting mechanical and environmental standards.

(4) This technology provides a near-zero discharge solution: recovered oil serves as fuel, purified water replaces freshwater in fracturing operations, and solidified products enable wellpad construction. The compact system demonstrates strong potential for field deployment, especially in space-constrained drilling sites.

(5) Further research will focus on: pilot-scale validation, long-term stability assessment under extreme climates, AI-driven dosing control development, and photovoltaic-powered operation exploration to enhance sustainability and adaptability.