Ⅰ  Process Principle

Pump suction reverse circulation well flushing is a high-efficiency and water-saving well flushing process suitable for medium-shallow water wells. The equipment generates stable negative pressure through a sand pump, driving the flushing fluid in the well to form directional circulating flow, which quickly extracts sediments such as bottom-hole sand, cuttings and sludge. The slag-containing wastewater can be recycled after sedimentation and purification on the ground, featuring thorough desilting, high construction efficiency, water conservation and environmental protection.

The overall operation flow is standardized and clear: the slag-containing water at the well bottom is collected intensively through the suction port of the drill bit, transported upward along the hollow drill pipe, guided into the sand pump via the swivel and outlet pipe, and finally discharged to the ground purification system for solid-liquid separation. Compared with the conventional forward circulation process, this technology has a shorter flow path, faster slag discharge and more thorough bottom-hole desilting effect.

Ⅱ Equipment Composition and Starting Methods

1. Complete Equipment Configuration

The complete set of well flushing equipment adopts a closed negative pressure integrated structure, featuring stable operation, low failure rate and strong continuity. Core configurations include the main sand pump, negative pressure suction pipeline, drilling swivel, thickened hollow drill pipe, drill bit slag suction structure, vacuum pressure stabilizing device and a full set of sealing accessories. The fully closed pipeline design effectively avoids air leakage, pressure loss and flow interruption, ensuring stable operation throughout the process.

2. Comparison of Equipment Starting Methods

The key to stable starting of the equipment is to evacuate air from the pipeline and establish constant negative pressure. Two starting methods are commonly used in the industry, among which vacuum negative pressure starting is the standardized preferred process.

（1）Water Filling and Air Exhaust Starting Method

The main pump is started after the pipeline is fully filled with water and completely evacuated by an auxiliary water pump. This method features low equipment investment and simple operation, but air tends to remain in the pipeline, resulting in poor negative pressure stability and relatively low starting success rate.

（2）Vacuum Negative Pressure Starting Method (Mainstream Preferred)

A vacuum pump and a vacuum pressure stabilizing tank work synergistically to actively extract air from the pipeline and establish stable negative pressure. The pressure stabilizing tank compensates for micro air leakage in the pipeline in real time, dynamically balances system pressure, eliminates unexpected shutdowns, and greatly improves construction continuity and stability.

（3） Overall Process Advantages

The vacuum negative pressure starting process achieves a starting success rate of over 98%, saves 15%–20% energy compared with the conventional water filling starting method, effectively avoids common failures such as air resistance, idling and shutdown, and is suitable for well flushing in most formation conditions.

Ⅲ Core Performance and Process Characteristics

All parameters of this process accurately match the construction conditions of medium-shallow water wells, with wide adaptability, strong stability and controllable construction effects.

（1）Effective Suction Head

The standard effective suction head of the equipment is ≥7 meters, which can stably suck bottom-hole sediments under conventional water level conditions, effectively avoiding residue accumulation and flow interruption to ensure desilting effect.

（2）Working Head

The process has low head requirements, and a conventional head of 10–20 meters can meet operation needs. No high-head pressurization equipment is required, resulting in lower overall power consumption and more energy-efficient operation.

（3） Diameter Specifications

The equipment is equipped with multiple standard diameters of 150mm, 200mm and 250mm, suitable for construction with different well diameters and sediment particle sizes. Equipped with a special double-vane impeller structure, it has strong impurity passing capacity and effectively reduces the probability of pipeline blockage.

（4） Pump Capacity and Flow Velocity

Standardized and controllable flow velocity design is adopted in construction to strictly control the optimal upward return velocity in the pipeline. On the premise of meeting sediment suspension and transportation requirements, it avoids resistance loss and energy waste caused by excessive flow velocity, ensuring balanced and stable construction efficiency.

Ⅳ Construction Key Points, Application Scope and Acceptance Standards

1.Application Scope

This process supports immediate operation upon startup without long-term pre-circulation, featuring high construction efficiency. It is standardly applicable to medium-shallow water wells with a depth of 60–80 meters, widely used in various medium-shallow water wells such as civil water intake wells and small engineering wells. For deep wells over 80 meters, the air lift reverse circulation process is recommended.

2. Key Construction Points

（1）Arrange equipment nearby, install the sand pump as close to the wellhead as possible to reduce pipeline loss and improve negative pressure utilization efficiency.

（2）Prioritize clean water as flushing medium, and adopt flushing fluid with corresponding parameters for different formations to effectively reduce equipment operation load.

（3）Conduct thorough sealing inspection throughout the process, focusing on pump body, flanges, swivel and drill pipe connections to eliminate air and liquid leakage.

（4）Stably control the liquid level in the well to avoid air intake caused by sudden water level drop and abnormal interruption of circulating flow.

（5）Equip a standard vacuum pressure stabilizing system to ensure long-term continuous operation and reduce shutdown failures.

（6）Provide sufficient circulating water tank for water supply, and keep the drill bit suspended 0.5–0.8 meters during construction to prevent pipeline blockage.

3. Inapplicable Scenarios

This process is not suitable for severely leaky formations, deep wells over 80 meters, extra-large diameter wells and complex working conditions with large impurities, which may cause water loss, circulation interruption and unqualified well flushing.

4.Construction Acceptance Standards

Upon completion of well flushing, the sand content of well water is ≤0.5%, water turbidity ≤10 NTU, the thickness of bottom-hole sediments conforms to industrial specifications, and the effluent quality and water intake efficiency of the well meet normal service standards.