CDOF Ozone Catalytic Oxidation Technology: An Efficient Solution for Gel Breaking and Viscosity Reduction of Oilfield Fracturing Flowback Fluid

As global oil and gas development extends into unconventional fields such as deep reservoirs, shale oil, and tight gas, horizontal-well staged fracturing has become the core technology for production enhancement and stable output. At the same time, the difficulty of treating fracturing flowback fluid keeps rising. This kind of wastewater contains large amounts of high-molecular polymers such as guar gum, hydroxypropyl guar gum, and polyacrylamide, which form a stable three-dimensional network colloidal structure through molecular entanglement, hydrogen bonding, and electrostatic interaction, with viscosity reaching tens to hundreds ofmPa.s, making solid-liquid separation difficult-a recognized technical difficulty in oilfield water treatment.

For a long time, the industry has mainly relied on traditional processes that add chemical oxidants and gel breakers to treat this wastewater, but it has always faced problems such as high cost, large sludge volume, and secondary pollution.CDOFThe emergence of ozone catalytic oxidation technology provides a better solution path for this problem.

Through optimized reactor-structure design, this technology achieves efficient ozone activation and utilization, and without additional chemical agents can complete gel breaking and viscosity reduction, oil removal, and COD degradation of fracturing flowback fluid, providing technical support for green and efficient oilfield development.

I. Limitations of the Traditional Gel-Breaking Process

The core treatment goal of fracturing flowback fluid is to destroy the colloidal system formed by high-molecular polymers, reduce wastewater viscosity, and achieve oil-water-solid three-phase separation. Current mainstream treatment processes all have varying shortcomings, making it hard to balance treatment effect, operating cost, and environmental requirements.

1. Chemical oxidation gel-breaking method: high cost and high pollution coexist

This is the most widely used process at present. It destroys polymer molecular chains by adding oxidants such as ammonium persulfate and sodium hypochlorite, then cooperates with coagulants and flocculants to achieve solid-liquid separation. Its limitations are mainly reflected in:

·High and volatile chemical cost: treating 1m³ fracturing flowback fluid requires adding2-6kg various chemical agents, with a per-ton agent cost ofyuan, and the composition of flowback fluid varies greatly among different blocks and batches, requiring frequent adjustment of agent ratios, further increasing operating costs.

·Large chemical-sludge production: agent addition produces large amounts of chemical sludge; each treatment of 1000m³ wastewater produces25-60m³ of sludge, and hazardous-waste disposal cost accounts for60%-70%of total operating cost, becoming a heavy burden on oilfields.

·High secondary-pollution risk: residual chemical agents corrode downstream equipment and pipelines and are difficult to biodegrade; after entering the reinjection formation they may cause formation damage, leading to increased injection-well pressure and reduced injectivity.

·Unstable treatment effect: when incoming water quality fluctuates greatly, gel breaking is often incomplete, causing filter-media clogging in the subsequent filtration unit and affecting normal system operation.

2. Physical separation method: cannot solve the fundamental problem

Physical methods such as hydrocyclones, centrifugal separation, and induced air flotation can only remove free-state oil and large-particle suspended solids by density difference, and are ineffective against dissolved-state high-molecular polymers and stable colloidal systems. The treated wastewater still has high viscosity and cannot meet reinjection requirements; the equipment also easily scales and clogs, with heavy maintenance workload.

3. Biological treatment method: poor applicability

Fracturing flowback fluid contains large amounts of refractory organic matter and bactericides, and theB/C ratio is usually below 0.1, with extremely poor biodegradability. Biological treatment requires tens of hours of residence time, occupies a large area, and has extremely unstable treatment effect, unable to adapt to the continuous-production needs of oilfields.

II.CDOFPrinciple of Ozone Catalytic Oxidation Technology

CDOFThe core of ozone catalytic oxidation technology lies in ozone multi-path catalytic oxidation. The reactor is filled with high-efficiency heterogeneous catalysts (such as silica-alumina-based and carbon-based catalysts), and a small amount of homogeneous catalyst is added. After wastewater and ozone are mixed under pressure (0.2-0.4 MPa), a hydrodynamic cavitation effect is generated through a special flow channel; the local high temperature and pressure released by cavitation-bubble collapse further promote ozone decomposition. On the catalyst surface, ozone is efficiently converted into hydroxyl radicals (OH) with an oxidation potential as high as 2.8 V, which attack the main and side chains of high-molecular polymers non-selectively, breaking long-chain molecules such as guar gum and polyacrylamide into short-chain small molecules, and finally mineralizing them into carbon dioxide and water. At the same time, cyclonic dissolved-air flotation rapidly separates the non-dissolved products generated by the reaction, realizing integrated gel breaking, oil removal, and COD reduction.

III. Technical Features

CDOFThe ozone catalytic oxidation technology requires no addition of any chemical agents and features stable treatment effect, low operating cost, and low sludge production; it has been applied in multiple oilfield fracturing-flowback-fluid treatment projects in China.

Thorough gel breaking and viscosity reduction:After treatment, wastewater viscosity can drop below 1 mPa.s, gel-breaking rate >=99%, and solid-liquid separation performance is greatly improved.
Synchronous multi-effect treatment:While breaking gel and reducing viscosity, it can effectively remove oil and COD from the wastewater; oil content can drop below 6 mg/L, and COD removal rate >=60%.
Low operating cost:No traditional chemical oxidants or gel breakers are needed, only a small amount of catalyst and flocculant (dosing <=30 ppm); per-ton operating cost is reduced by over 60% compared with the traditional chemical gel-breaking process.
Low sludge production:From the source it avoids the generation of large amounts of chemical sludge; sludge volume is reduced by over 90% compared with the traditional process, greatly lowering hazardous-waste disposal costs.
High ozone utilization:Ozone utilization is as high as over 99%, with short reaction time (total residence time <15 min) and a footprint only 1/5 that of the traditional process.
Strong shock-load resistance:Good adaptability to water-quality fluctuations, maintaining stable treatment effect.
High degree of automation:The system can achieve fully automatic operation without dedicated attendance.

IV.Comparison with Traditional Processes

V. Technology Development and Application Prospects

As environmental regulations become increasingly strict and the concept of green development in oilfields deepens, oilfield water-treatment technology is developing toward reduction, resource recovery, and harmlessness.CDOFAs an efficient and green treatment process, ozone catalytic oxidation technology has broad application prospects.

In the future, the technology will further develop toward large-scale and intelligent directions, developing modular equipment with larger daily treatment capacity, and combining with Internet-of-Things technology to achieve remote monitoring and intelligent O&M. At the same time, through integration with membrane separation, electrochemistry, and other technologies, a more complete treatment system can be formed to realize deep treatment and resource-recovery reuse of wastewater.

Under the background of the green transformation of the oil and gas industry,CDOFozone catalytic oxidation technology provides a reliable solution for oilfield fracturing-flowback-fluid treatment, helping reduce the environmental-protection cost of oilfield development and promoting high-quality, sustainable industry development.