New Treatment Process for Oilfield Produced Water with CDFU Technology: Process Flow, Features, and Application

1. Process Flow

Currently, commonly used water separation technologies are mainly implemented through a combination of single technologies such as gravity sedimentation, cyclone, air flotation, and thermochemical processes, or combinations of two or more of these methods. Representative technologies include inclined oil-water separation, serial hydraulic cyclone separation, high-efficiency three-phase separation, and low-temperature demulsification technologies. However, there is a lack of systematic research combining column-type cyclone separators with hydraulic cyclone separators, as well as a lack of design methods for matching parameters between integrated devices. 

The Shenzhen Clear Science & Technology Co., Ltd (SINOKLE) has designed two sets of short-flow treatment and reinjection processes for produced fluids at the wellhead, using the patented Cyclonic Dissolved Gas Flotation Unit (CDFU) as the core, supplemented by filters of varying precision. The process flow diagrams for the solutions are as follows: 

Pic 1. A general process flow diagram for the SINOKLE’s solution

· Solution 1: 

The produced fluid is pretreated by a three-phase separator. The water phase containing oily wastewater is sent to a two-stage CDFU for oil and suspended solids removal. The oily sludge enters the oil collection tank, and waste gas is directed to the flare or natural gas pipeline. The treated water passes through two stages of activated media filters, and once the water meets the reinjection standards, it enters the reinjection water tank. The backwash water from the filters is reused from the reinjection water tank. The filtered sludge is dewatered and pressed, with the resulting cake packed and transported out. 

· Solution 2:

The produced fluid is pretreated by a two-phase separator. The water phase containing oily wastewater enters a two-stage CDFU for oil and suspended solids removal. The oily sludge is collected in the oil collection tank, and the waste gas is sent to the flare or natural gas pipeline. The treated water is directed to a circulation water tank, and the concentrated water in the circulation tank is sent back to the CDFU. The floating sludge is dewatered and pressed, with the resulting cake packed and transported out. The CDFU effluent is returned to the circulation tank, where it is filtered by an SIC membrane filter. Once the treated water meets the reinjection standards, it is sent for reinjection.

2. Process Features

Compared to conventional processes, the two produced water treatment processes described above have the following features: 

· Short process flow, high efficiency, strong resistance to impact, and stable effluent that meets water quality requirements.

· No chemical agents; pure physical demulsification and separation technology, no aging oil, no secondary pollution, and good environmental benefits.

· Uses a two-stage dissolved gas flotation as pre-treatment, providing strong impact resistance and ensuring stable and reliable operation of subsequent processes. Advanced filtration technology with high precision, effective performance, strong resistance to impact, long filter material lifespan, and stable water quality that meets standards.

· Modular design, compact footprint, suitable for space-constrained environments such as offshore platforms.

· Fully automated and information-driven operation, remote monitoring capability, minimal labor required, and low operating and maintenance costs. 

3. Application Cases

Pic 2. Reinjection water treatment skid at a PetroChina joint station, along with treatment effect demonstration. The bottled water samples in the figure are arranged from right to left: influent, first-stage effluent, second-stage effluent, and final effluent.

A reinjection water treatment skid at a PetroChina joint station is shown below. This system achieves A1-level effluent with an oil content of ≤5mg/L and suspended solids ≤1mg/L, and A2-level effluent with an oil content of ≤6mg/L and suspended solids ≤2mg/L.