Pulling Procedure

Pulling the equipment out of a well involves essentially the reverse process of the installation procedure.

If the equipment failure is judged to be premature, the condition of cable, flat cable, pump rotation, and motor/protector fluid will be useful in determining the cause of the failure. 10.1.4. Troubleshooting

This section outlines a recommendations to identify typical ESP problems and provide solutions. The sole method that a failure can be analysed and its cause determined, is by data collection. When problems occur, obtaining as much data as possible is essential. Data Collection

Information that should be routinely compiled on each ESP installation includes:

• Production data (such as water, oil, and gas rates)

• Run life in days

• Number of unit start ups and stoppages

• Dynamic and static fluid levels

• Pump setting depth

• Perforation depths.

Information also should be obtained on:

• Ammeter charts

• Well conditions (abrasives, corrosives, H2S, etc.)

• Electric power quality (surges, sags, balance, negative sequence voltages, etc.)

• Visual observations of equipment and cable condition on prior workovers

• Reasons for equipment workover (failure, workover, size change, etc.)

• BHT recordings

When an ESP well is first placed on production, data should be collected daily for the first week, weekly for the first month, and a minimum of monthly after the first month. Production data during the first month are very important because they will indicate whether the pump is performing as designed. If a downhole pressure instrument is installed, operating BHP is equally if not more important.

The major source of information when troubleshooting an ESP installation is the recording ammeter. The recording ammeter is a circular strip-chart accessory mounted in the switchboard that records the amperage drawn by the ESP motor. A number of changes in operating conditions can be diagnosed by interpreting ammeter records. The following addresses ammeter chart ‘reading’ and typical problem situations.

Normal Operation

A normal chart is smooth, with amperage at, or near to the motor specification amperage draw. Actual operation may be, either, slightly above or below the specification amperage, however, as long as the curve is symmetric and consistent over a period of time, operation is considered normal.

Normal Start-up

The start-up ‘spike’ is caused by the inrush surge as the pump comes up to operating speed. The subsequent amperage draw is high but trending towards the normal level. This is principally a result of the fluid level being drawn down to the design TDH, resulting in a high but declining amperage draw. Using the modern variable speed units this problem has been overcome.

Power Fluctuations

Operating ESP amperage will vary inversely with voltage. If system voltage fluctuates, the ESP amperage will fluctuate inversely to maintain a constant load. The most common cause of this type of fluctuation is a periodic heavy load on the primary power system. This load usually occurs when starting up another ESP or other large electric motor.

Simultaneous start-up of several motors should be avoided to minimise the impact on the primary power system.

Ammeter spikes also can occur during a thunderstorm that is accompanied by lightning strikes.

Gas Locking

Gas locking occurs as fluid level drawdown approaches the pump intake and intake pressure is lower than the bubble-point. There are three possible remedies for gas locking:

• Install a gas intake and/or a motor shroud

• Lower the setting depth of the pump (but not lower than the perforation unless the motor is shrouded)

• Reduce the production rate of the pump by using a surface choke (but ensure that the production rate remains within the recommended range for that pump). It is entirely feasible that none of these solutions is satisfactory, then the pump should be replaced with a pump that does not draw down the fluid level or reduce intake pressure below the bubble-point.

Another possible solution is to add a variable speed drive (VSD) to the existing system. The VSD controls the speed of the pump, which in turn controls the pump capacity. Thus the pump output can be fine-tuned to protect against pump-off and gas lock while contributing to improved pump life.

If the problem is confirmed to be due to reservoir conditions, then a stimulation operation may be considered to reinstate the original PI and therefore allow operation of the current ESP design.

Fluid Pump-Off

Fluid pump-off occurs typically when an ESP is too large in relation to the inflow capacity of the well. The remedial actions are much the same as those listed for a gas lock and, in addition, a well simulation treatment may increase the well’s productivity closer to a match with the pump.

In general, cycling an ESP will have an adverse effect on optimal run life. As a temporary measure, the amount of time delay before automatic restart can be increased if the switchboard is equipped with a Redalert Motor Controller. This may allow the fluid volume to build up to prevent a high frequency of shutdown occurrence. Nevertheless, the pump and well are not compatible and the pump size should be checked on the next change-out or the well worked over to improve productivity.

Gassy Conditions Or Emulsion

Continuos amperage fluctuation results from alternating free gas and heavy fluid pumping. Generally this condition results in a reduction of stock tank barrels in relation to the pump design rate.

This is also typical of emulsion conditions. The fluctuations are caused by the frequent, temporary blockage of the pump intake. If it is an emulsion block, spikes are normally lower or below the normal amperage line.

Solids and Debris

When solids or debris are produced in a well, the amperage will display fluctuations immediately after start-up. Typically, when solids such as sand, scale, or weighted mud are produced, special care must be taken on start-up to avoid pump damage. It may be necessary to apply back-pressure on the well to prevent excess amperage until the kill fluid is removed and/or sand production begins to decline to a safe volume.

Overload Shutdown

A pump will automatically shut down when it reaches an overload condition. When an overload condition shutdown does occur the unit must not be restarted until the cause of the overload has been identified and corrected. Some motor controller overload-detection circuits contain a built-in time delay, ranging from 1 to 5 secs at 500% of the set point to 2 to 30 secs at 200% of the set point. However, they will not automatically restart the unit on an overload condition. A restart attempt in an overload condition can destroy the downhole equipment if the cause of the overload is not identified and corrected first.

The most common causes of overload conditions are:

• Fluid pump-off

• Increased fluid specific gravity

• Sand production

• Emulsion formation

• Scale

• Electric power supply problems

• Worn equipment

• Lightning damage