Troubleshooting Methods for Rising Pressure Difference of Coalescing Filters in Wellhead Crude Oil Purification

Troubleshooting Methods for Rising Pressure Difference of Coalescing Filters 

in Wellhead Crude Oil Purification

1. Overview of Working Condition Background and Pressure Difference Failure Hazards

1.1 Medium Characteristics of Wellhead Crude Oil Purification

Wellhead crude oil contains mixed impurities including formation sand, pipeline rust, scaling particles, emulsified water droplets, light hydrocarbon condensate and trace asphaltene colloid. Medium temperature fluctuates greatly with seasons, and the medium presents alternating gas-liquid-solid three-phase impact during intermittent pumping. High-performance Coalescer & Separator Cartridge undertakes dual functions of solid impurity interception and micro-water coalescence separation to guarantee qualified crude oil output. Sustained abnormal rise of filter cartridge pressure difference will bring multiple operation risks: System pipeline load increases, pump unit power consumption rises, and equipment energy consumption increases significantly; Excessive pressure difference causes flow channel compression inside filter media, fluid shear force surges, coalesced large water droplets are broken again into micro-emulsions, and outlet crude oil water content exceeds the standard; Long-term high differential pressure operation leads to pleat collapse, fiber delamination and skeleton deformation of filter cartridges, resulting in bypass leakage of unpurified crude oil and downstream equipment scaling and corrosion, which requires timely overhaul or replacement of the failed Coalescer & Separator Cartridge; Severe blockage triggers overpressure interlock shutdown of wellhead metering and purification system, interrupting continuous crude oil collection operation.

1.2 Classification of Pressure Difference Rise Types

According to field operation data, pressure difference faults ofCoalescer & Separator Cartridge are divided into three categories for targeted disposal: Slow and gradual pressure difference rise: Regular pollutant accumulation under normal working conditions, belonging to normal aging trend, which reminds operators to prepare spare Coalescer & Separator Cartridgefor periodic replacement; Rapid short-term pressure difference surge: Abnormal sudden increase of inlet pollution load or system parameter mismatch; Irregular fluctuating pressure difference: Caused by unstable gas cut, liquid level disorder and pipeline flow fluctuation. This paper sorts out step-by-step troubleshooting flow, root cause judgment standards and corresponding rectification schemes for all types of pressure difference rise faults, and summarizes daily preventive control measures.

2. Standard Step-by-Step Troubleshooting Process for Abnormal Pressure Difference Rise

Step 1: Instrument Calibration to Eliminate False Pressure Difference Data

Before checking filter cartridges and system equipment, eliminate measurement deviation caused by instrument failure first:

Close the sampling valves of differential pressure transmitter and pressure gauge, drain condensate and solid dirt blocked in sampling pressure guiding tubes; asphaltene and crude oil sludge easily block thin pressure guiding pipelines, leading to displayed pressure difference higher than actual value.

Disassemble and inspect pressure measuring components, compare with standard calibrated pressure gauges to complete calibration; replace damaged pressure sensors with signal drift.

After dredging pressure guiding tubes and calibrating instruments, resume operation and observe pressure difference changes; if the value returns to the normal baseline, the fault source is instrument blockage or calibration deviation.

Step 2: Check Front-End Pre-Separation Equipment Pollution State

Wellhead coalescing separators must be equipped with cyclone coarse separator and metal mesh pre-filter as primary interception devices, which are the first barrier to reduce filter cartridge pollution load:

Inspect the bottom ash hopper of the inlet cyclone separator, open the blowdown valve to discharge accumulated formation sand and large-particle rust; long-term non-blowdown leads to secondary entrainment of solid impurities into the coalescing tank.

Disassemble the secondary 20–50μm metal pre-filter screen, observe surface dirt accumulation degree and mesh breakage; if the screen is fully covered by sludge or has holes, replace the pre-filter screen immediately.

Judgment standard: If the pre-filter pressure difference exceeds 0.05MPa, it indicates that a large amount of solid pollutants pass through and accumulate on the coalescing filter media, which is the main inducement of rapid pressure difference rise.

Step 3: Inspect Separator Tank Internal Liquid Level and Exhaust Condition

Gas cut and excessive accumulated liquid inside the tank will occupy the effective filtration area of filter cartridges and raise overall pressure difference:

Check the liquid level reading of the bottom liquid collecting bin; if the liquid level exceeds 2/3 of the bin body, emulsified water mixed with crude oil will backwash the filter cartridge pleats, accelerate dirt adhesion and block fiber pores. Manually open the drain valve for full drainage.

Operate the automatic exhaust valve at the top of the tank, discharge trapped gas inside the tank; a large amount of gas wrapped around the filter cartridge will reduce the effective contact area between crude oil and filter media, increase local flow velocity and pressure loss.

Record the gas volume fraction of wellhead incoming liquid; when instantaneous gas cut exceeds 20%, high-speed gas-liquid mixed flow scours filter media, accelerates pollutant compaction and pushes up pressure difference rapidly.

3. Root Cause Classification and Targeted Disposal Schemes for Pressure Difference Rise Faults

Category 1: Slow Gradual Pressure Difference Rise (Daily Pressure Difference Increase ≤0.006MPa)

Root Cause

Continuous accumulation of conventional trace solid impurities and emulsified droplets under stable wellhead medium conditions, normal consumption of filter cartridge dirt holding capacity.

Disposal Measures

Carry out standardized timed blowdown of front cyclone separator and tank bottom liquid bin according to shift schedule to reduce pollutant accumulation speed.

Appropriately reduce the system operating flow by 10% to lower surface flux and extend the service cycle of filter cartridges.

Record daily pressure difference change curve, calculate the remaining service life, and arrange batch replacement before the pressure difference reaches the replacement threshold of 0.15MPa.

No disassembly and cleaning allowed; only low-pressure internal back-blowing can be carried out once for early warning state to slightly reduce pressure difference.

Category 2: Rapid Surge of Pressure Difference (Daily Pressure Difference Increase ≥0.012MPa, Short-Term Exceeding Warning Value)

Root Cause 1: Sudden high pollution load of incoming liquid

Well washing, well overhaul, stratum water breakthrough lead to sharp increase of formation sand, water cut and asphaltene sludge.

Disposal: Open the bypass pipeline to reduce the load of the coalescing tank; increase the blowdown frequency of cyclone separator to once every 4 hours; disassemble and replace the blocked pre-filter screen; arrange filter cartridge replacement in advance if the pressure difference cannot drop after back-blowing.

Root Cause 2: Long-term overload operation with excessive flow

Wellhead pump output exceeds separator design flow, surface flux exceeds the standard limit.

Disposal: Adjust pump frequency to control flow within the rated range; open the bypass valve for flow division; add a spare coalescing tank to share the treatment load if the wellhead output is permanently high.

Root Cause 3: Front pre-separation device failure

Cyclone ash hopper blocked, pre-filter screen broken and invalid, a large number of solid particles directly enter the filter cartridge layer.

Disposal: Fully clean the cyclone ash hopper; replace the complete set of damaged pre-filter screens; increase daily inspection frequency of pre-separation equipment to once per shift.

Category 3: Irregular Fluctuating Pressure Difference (Alternating High and Low Pressure Difference Without Stable Growth Trend)

Root Cause 1: Unstable gas cut in wellhead crude oil

Intermittent gas surging from the stratum leads to periodic gas wrapping of filter cartridges inside the tank, effective filtration area fluctuates up and down.

Disposal: Increase the opening frequency of the tank top automatic exhaust valve; install a buffer tank at the separator inlet to stabilize gas-liquid mixed flow; properly reduce the single-tank processing flow to weaken gas-liquid impact.

Root Cause 2: Uncontrolled liquid level in the liquid collecting bin

Automatic drain valve jamming leads to periodic high liquid level, emulsified liquid backwashing filter cartridges intermittently.

Disposal: Disassemble and overhaul the drain valve, clear sludge jamming parts; set high liquid level interlock alarm to remind manual auxiliary drainage.

Root Cause 3: Unstable wellhead pumping flow

Reciprocating pump pulse flow causes instantaneous flow impact on filter cartridges, resulting in fluctuating pressure loss.

Disposal: Install pipeline flow stabilizer at the separator inlet; adjust pump operating parameters to reduce flow pulse amplitude.

Category 4: Permanent Irreversible High Pressure Difference (Pressure Difference Remains Above Warning Value After Back-Blowing and Parameter Adjustment)

Root Cause

Sticky asphaltene sludge and compact sand cake are embedded deep into filter media fiber pores; pleat collapse, fiber delamination and skeleton deformation occur after long-term high differential pressure.

Disposal Scheme

Carry out safe shutdown and tank opening operation to replace all filter cartridges in batches; thoroughly clean the sludge and sediment on the inner wall of the tank and tube plate before installing new filter cartridges to avoid secondary pollution of new cartridges.

4. Standardized Back-Blowing Pressure Difference Reduction Operation Specification (Only for Early Warning Blockage)

Applicable Restrictions

Only applicable when pressure difference reaches the early warning value of 0.10–0.12MPa, outlet crude oil water content is qualified, and no pleat collapse is observed; the whole service cycle allows back-blowing operation at most twice.

Switch the crude oil purification system to bypass operation to ensure uninterrupted crude oil collection at the wellhead.

Close the inlet and outlet cut-off valves of the coalescing tank, open the exhaust and drain valves to reduce the tank pressure to normal pressure.

Adopt dry oil-free compressed air as back-blowing medium, air source dew point ≤-20℃, back-blowing pressure controlled at 0.25–0.30MPa, single blowing duration 0.18s, intermittent blowing 6–10 times per operation.

After back-blowing is completed, close the exhaust and drain valves, slowly inject crude oil into the tank, exhaust internal air, and gradually restore to rated operating flow.

Record the pressure difference drop amplitude after back-blowing; if the pressure difference rebounds to the early warning threshold within 3 working days, judge the filter cartridge to have irreversible blockage and arrange replacement.

Strictly Prohibited Operations That Aggravate Filter Cartridge Blockage

Forbid washing blocked filter cartridges with water or organic solvent: Crude oil sludge mixed with sand will solidify into hard blocks inside fiber layers, and the surface hydrophilic-lipophilic balance coalescing film will be damaged, permanently losing separation performance.

Forbid long-term high-pressure back-blowing: Excessive airflow impact will tear composite filter media and cause fiber shedding leakage.

Forbid continuous overload operation after pressure difference early warning: Accelerate pleat deformation and shorten the service life of filter cartridges by more than half.

5. Preventive Control Measures to Avoid Recurring Pressure Difference Rise Faults

Shift regular blowdown mechanism: Discharge accumulated sand and liquid of front cyclone separator and tank bottom liquid bin every shift to reduce pollutant accumulation baseline.

Weekly pre-filter maintenance: Disassemble, clean and inspect the secondary metal pre-filter screen to ensure the primary interception function is intact.

Real-time flow monitoring: Limit the maximum processing flow of the separator, and open bypass flow division in time when instantaneous flow exceeds the standard.

Seasonal parameter adjustment: In winter, crude oil viscosity rises, appropriately reduce the operating flow to lower surface flux and extend the dirt holding cycle of filter cartridges.

Well working condition linkage adjustment: After well washing, perforation and other operations with sudden sand production, reduce the single-tank treatment load and increase equipment inspection frequency.

Instrument daily maintenance: Dredge pressure guiding tubes of differential pressure measuring instruments every week to eliminate false pressure difference data interference.

6. Post-Fault Handling Acceptance Standards

After completing fault disposal, continuous stable operation for more than 4 hours is required for acceptance judgment, and the following indicators must meet the standards simultaneously:

Filter cartridge operating pressure difference drops back to the normal stable interval (below 0.08MPa);

Outlet crude oil water content is stable below the design index, no fluctuation exceeding the standard;

Wellhead pump operating power consumption returns to the daily average normal level;

No abnormal flow fluctuation, gas surging and liquid level alarm inside the coalescing tank.

7. Summary

The rising pressure difference fault of wellhead crude oil coalescing filter cartridges is divided into gradual rise, rapid surge and fluctuating rise according to field performance. Troubleshooting shall follow the sequence of instrument calibration → pre-separation equipment inspection → tank liquid level and exhaust check → flow parameter verification → medium sampling test → filter cartridge disassembly inspection to locate the root cause step by step.

Slow pressure difference rise only needs routine blowdown and flow optimization; rapid pressure difference surge is mostly caused by sudden pollution load or pre-filter failure and requires early replacement of filter cartridges; fluctuating pressure difference mainly comes from unstable gas cut and liquid level disorder, which can be eliminated by optimizing exhaust and drainage equipment. Back-blowing can only relieve mild early warning blockage, and irreversible compact sludge blockage must be solved by batch replacement of filter cartridges.

Long-term standardized blowdown, pre-filter maintenance and flow limit control can effectively reduce the frequency of abnormal pressure difference faults, stabilize the purification index of wellhead crude oil, reduce the number of shutdown maintenance, and guarantee the stable operation of the wellhead crude oil gathering and purification system.