Integrated Flocculation and Solidification Technology for Waste Drilling Mud: Compliant Discharge, Waste-to-Waste Treatment, and Resource Utilization

During the extraction of oil, gas, and coalbed methane, substantial quantities of waste drilling mud—characterized by high water content, high Chemical Oxygen Demand (COD), and high chromaticity—are generated. If discharged directly, this waste poses significant environmental risks, including soil salinization, water body contamination, and heavy metal accumulation. Traditional treatment methods are plagued by issues such as high costs, inconsistent efficacy, and difficulty in meeting regulatory discharge standards. This paper presents a comprehensive process flow—comprising gel-breaking flocculation, solid-liquid separation, and slag-based solidification—to address these challenges. Through laboratory-scale experiments, the study identifies optimal chemical reagents and operating parameters, thereby achieving primary-level compliance for the liquid phase of the waste mud while ensuring the stable solidification of its solid phase. This research provides a mature technical solution for the harmless disposal and resource utilization of waste drilling mud generated in oilfields and coalbed methane fields.

I. Pollution Characteristics and Treatment Challenges of Waste Drilling Mud

1. Basic Characteristics of the Mud

The subject of this study is water-based waste drilling mud from a coalbed methane platform in Shanxi Province:

Water content: As high as 96.24%

CODₙᵣ: 2,824 mg/L (28 times the regulatory limit)

Suspended Solids: 497.5 mg/L (7 times the regulatory limit)

Chromaticity: 500 (10 times the regulatory limit)

pH: 8.61; contains trace amounts of petroleum hydrocarbons and total chromium

2. Shortcomings of Traditional Treatment Methods

Simple solidification requires excessive chemical dosages, incurs high costs, and results in insufficient structural strength.

Conventional flocculation and separation methods are often incomplete, making the direct discharge of the liquid phase difficult.

Cement-based solidification frequently leads to pH levels exceeding regulatory limits and a subsequent decline in structural strength over time.

It is difficult to achieve the dual objectives of 'liquid phase reuse + solid phase resource utilization.'

II. Core Treatment Process: Gel Breaking & Flocculation → Solid-Liquid Separation → pH Adjustment → Mud Cake Solidification

The overall process employs chemically enhanced solid-liquid separation combined with low-cost solidification to ensure compliance at each stage and render the entire process environmentally harmless:

Gel Breaking & Flocculation: Destabilizes colloidal structures to facilitate rapid separation of mud and water.

Solid-Liquid Separation: Treats the filtrate to meet discharge standards while dewatering the mud cake to reduce its volume.

pH Adjustment: Neutralizes the acidic filtrate to meet Class I discharge standards.

Mud Cake Solidification: Utilizes a slag-based curing agent to stabilize heavy metals and enhance structural strength.

Resource Utilization: The solidified material can be used for landfilling, road paving, or brick manufacturing.

III. Selection of Demulsification and Flocculation Agents: Optimal Combination + Optimal Dosage

Through a series of comparative experiments, the optimal combination was selected from a pool of three demulsifiers and three coagulant aids.

1. Selected Demulsifier: Aluminum Sulfate (Al₂(SO₄)₃)

Optimal Dosage: 2000 mg/L

Treatment Results: COD removal rate of 96.27%, Suspended Solids removal rate of 92.25%, Colority removal rate of 92.00%, and Filter Cake Moisture Content reduced to 84.46%.

2. Selected Coagulant Aid: Non-ionic Polyacrylamide (NPAM)

Optimal Dosage: 10 mg/L

When used synergistically with aluminum sulfate, it results in larger flocs, faster settling, and improved dewatering.

Filter Cake Moisture Content is further reduced to 78.64%.

3. Optimal Process Conditions (Optimized via Orthogonal Experiments)

Stirring Speed: 90 rpm

Stirring Time: 60 s

Settling Time: 5 min

→ Achieves maximum treatment efficiency, minimum processing time, and lowest energy consumption.

IV. Liquid Phase Treatment: Meeting Grade I Discharge Standards for Direct Reuse

Following demulsification, flocculation, and pH adjustment: 0.8 mL of a 5% NaOH solution was added per 100 mL of filtrate.

pH Adjusted to: 6.07

Final Effluent Parameters: CODₙᵣ: 38.45 mg/L

Suspended Solids: 30.50 mg/L

Colority: 20 times dilution

Petroleum Hydrocarbons and Total Chromium: Far below standard limits.

Complies with the Grade I discharge standards for wastewater (GB8978-1996) and can be reused for slurry preparation and site flushing.

V. Filter Cake Solidification: Slag-based Solidifier—An Economical 'Waste-Treating-Waste' Approach

For the filter cake separated during treatment, a self-developed slag-based solidifier (comprising slag, cement, fly ash, and a composite activator) was employed to achieve low-cost, high-efficiency solidification. 1. Solidification Performance (at a 25% dosage, cured for 28 days)

Compressive Strength: 0.64 MPa (Meets requirements for landfilling and road paving applications)

Leachate COD: 53.26 mg/L

Chromaticity: 10-fold dilution

Suspended Solids: 37.80 mg/L

Petroleum Hydrocarbons / Total Chromium: Not detected

2. Comparison with Cement: Distinct Advantages

At an equivalent dosage of 25%:

The slag-based solidifier exhibits higher strength and achieves strength growth more rapidly.

Leachate pH levels remain within regulatory limits (whereas cement-based systems often result in persistently high pH levels).

Lower levels of COD, suspended solids, and chromaticity in the leachate.

Reduces cement consumption, resulting in lower overall costs.

Enables 'waste-treating-waste'—utilizing waste materials to treat other waste—yielding significant environmental benefits.

VI. Mechanism of Action: Revealing Technical Advantages at the Microscopic Level

1. Demulsification and Flocculation Mechanism

Aluminum Sulfate: Induces destabilization via charge neutralization, forming a skeletal floc structure.

NPAM: Facilitates long-chain bridging, netting, and sweeping effects, forming large, dense flocs → Rapid settling and deep dewatering.

2. Solidification Mechanism

In an alkaline environment, the slag undergoes hydration to generate C-A-H and C-A-S-H gels.

These gels interlock with one another, encapsulating solid particles and filling interstitial pores.

The resulting structure is dense, possesses high strength, and effectively locks in pollutants.

→ In contrast, cement-based systems generate expansive AFt crystals, which lead to internal micro-cracking, a decline in structural strength, and an increased susceptibility to pollutant leaching.

VII. Technical Advantages and Engineering Value

**Compliance Across the Entire Process**

The liquid phase meets Class I discharge standards; the solid phase meets leaching standards; and heavy metals are stably solidified.

**Significant Cost Reduction**

Slag-based solidifiers replace the majority of cement requirements, and chemical dosages are optimized to ensure high cost-effectiveness.

**High Treatment Efficiency**

Flocculation requires a settling time of only 5 minutes, making the process suitable for skid-mounted, on-site operations with a minimal footprint.

**Resource Utilization**

The filtrate can be reused; the solidified filter cake can be utilized for road paving, brick manufacturing, or landfill reclamation.

**Broad Applicability**

Suitable for treating various types of water-based waste drilling muds generated in oil and gas fields, coalbed methane fields, and shale gas fields.

**Conclusion:** The integrated treatment technology for waste drilling mud—combining 'demulsification-flocculation' with 'slag-based solidification'—achieves direct, compliant discharge of the liquid phase and stable solidification of the solid phase through the precise selection of chemical agents and the optimization of operating conditions. This technology not only resolves complex pollution challenges but also embodies the principles of 'using waste to treat waste' and resource utilization. It represents an economical, efficient, and reliable solution for the environmentally sound treatment of drilling waste, providing robust technical support for green oilfield development.