The aeration process is an innovative biochemical technology for the treatment of industrial organic wastewater. It features prominent advantages including cost-effectiveness, low investment cost, quick results, stable treatment performance and small floor occupation. First developed and applied abroad in the early 1970s, relevant researches in China commenced in 1978. The process passed ministerial appraisal in 1983 and was officially included in the scope of promotion and application. The deep well serves as the core structure of the deep well aeration system, and its process flow is shown in Figure 1.

Figure 1 Process Flow of Deep Aeration Sewage Treatment

Ⅰ.Well Structure

As illustrated in Figure 2, the well adopts a double-layer inner and outer steel pipe structure. The steel pipes with sealed bottom ends are lowered into the drilled well. After the steel pipes are installed, the gap between the outer pipe wall and the well wall shall be filled and poured with cement slurry at a water-cement ratio of 0.5, so as to ensure the structural stability of the well and meet the operational requirements of the aeration treatment process.

Figure 2 Deep Well for Deep Aeration Sewage Treatment

Ⅱ. Drilling Quality Requirements

1.Verticality Control: The verticality deviation of drilling shall be controlled within 0.2%. Targeted technical measures shall be adopted throughout the drilling process to guarantee well verticality. Given the floating pipe lowering method, when the well pipe is lowered close to the well bottom, the overall rotatability of the well pipe shall be ensured to improve pipe lowering accuracy.

2.Overburden Drilling: During overburden drilling, the performance of wall-protecting mud shall be strictly controlled to stabilize the well wall and eliminate potential safety hazards such as well wall collapse.

3.Well Pipe Lowering: Well pipe lowering shall be completed promptly after well completion to prevent well wall collapse. Therefore, the welding scheme of well pipes shall be elaborately designed and arranged in advance.

4.Wellhead Protection: Wellhead protection measures shall be implemented. Wellhead pipes shall be embedded and concrete shall be poured at the wellhead. The construction shall be coordinated with the overall project as much as possible to ensure a firm and reliable wellhead structure.

Ⅲ. Key Precautions for Drilling Construction

1.Verticality Management: The reduced-pressure drilling technology shall be strictly implemented to meet the verticality standard. Well verticality is the core factor determining the success of deep well aeration well construction. Taking a well diameter of 1.8 m and a well pipe outer diameter of 1.5 m as an example, the unilateral gap between the pipe and the well wall is merely 150 mm, and the center offset of a 100-meter-deep well shall not exceed 150 mm.

2.Well Logging Requirements: Well logging shall be conducted synchronously during drilling, with focused monitoring of two core parameters: well inclination and well diameter, to timely detect and correct construction deviations.

3.Zonal Drilling: If the drilling passes through both overburden and bedrock strata, the zonal drilling process shall be adopted. Drilling in the overburden shall extend to the weakly weathered or slightly weathered bedrock layer, with protective casing lowered. The pipe foot shall be sealed by underwater cement mortar pouring to prevent water and sand leakage.

4.Stratum Boundary Treatment: At the boundary between overburden and bedrock, a rapid drilling process shall be selected according to stratum characteristics to prevent massive mud loss and subsequent well wall collapse.

5.Well Diameter Control: Changes in well diameter shall be monitored throughout construction, and the over-drilling range shall be strictly restricted. Excessive well diameter will lead to increased consumption of backfill cement outside the pipes, thus raising construction costs and delaying the construction period.