ESP - RCFA vs. PM

Preventive Maintenance of ESP's and its Relationship to Root Cause of Failure Analysis

* Determine the failure mode. This is commonly mistaken for the root cause of failure. Mode of failure is how the failure surfaces, not why the failure happened. It is very common that people accept the statement “motor burnt” without asking what caused it.

* Determine the failure cause. Root Cause of Failure answers the question "Why?" and at the same time explains “how” it happened.

* Estimate the extent of the damage and the likelihood of additional failures. It is important to search for other potential ESP failures caused by the same Root Cause of Failure.

* Design and implement the appropriate corrective action; and follow-up to ensure that the corrective action is first implemented and verify its effectiveness in preventing another failure.

HISTORY

RCFA - Review previous Root Cause of Failure (RCF) for the given well. In many cases, a failure trend specific to, for example, the well conditions or the field service technician involved in the equipment installation or to the operating procedure has been identified, etc.

INSTALLATIONS PULLS - Review previous pull history. It is often possible that some damage from previous installations was not caught during equipment testing and the current failure is actually the result of damage caused from the previous installation. A good example is motor failure due to insulation fatigue resulting from overheating due to a plugged pump.

DRIVE SETTINGS - Compare drive start-up documentation attached to installation report with drive settings before failure. In many cases, especially with gassy wells, it has been observed that underload settings on the drive were changed and prevented shut down of the drive when the pump gas locked. Another example of need for review of documentation resides with the common practice to use an oversized motor in low flow and hot wells to prevent motor overheating. Unfortunately, in these cases it is possible that the motor operating current can be very close to idling current, and thus the UL settings will not protect the equipment in case of pump plugging. In these cases, it is recommended use a flow switch at the wellhead to improve equipment protection.

OPERATION

PRODUCTION DATA - Perform drive amp-chart analysis, or analysis of data available from data collectors or directly from the drive itself, in the case of the GCS drives. It is important that operators include all required data on the amp-charts, otherwise the use of the amp-charts becomes very limited. Information that should, ideally, be recorded on amp-charts include: mode of VSC operation, operating speed, recorded amps from all three phases, downhole pressure, drive output voltage, transformer ratio, casing and tubing pressure. Many amp-charts are often missing the most important information – location, when it was put on, and when it was taken off!

MONITOR WELL AFTER START-UP - Collect the production data for the first few weeks after installation, as well as for the last few weeks before the failure. It is extremely important that somebody closely monitors the ESP unit following start-up until the well stabilized and then drive settings need to be verified. It is also good practice to test to the separator as often as possible to get an accurate accounting of production. Calculated well production from field data is often misleading, especially in new and dynamic fields. Remember, there can never be too much good-quality production data. The production data from initial weeks is used to verify well information used for application design. Data from the weeks immediately preceding the failure can provide insight to potential changes in well performance or pump wear.

WELL TESTING

MODELING

USE PRODUCTION DATA TO VERIFIED SIZING AND PREDICT FAILURE - Apply collected production data to original design and verify ESP operating conditions. This type of well maintenance can verify the reservoir data used for the original application design. Monitoring the application in this manner can often allow early detection of pump problems, or pending failure, and thereby prevent costly motor failures. Data collected should include operating parameters such as tubing and casing pressure, pumped fluid volume and composition, amps, drive output volts, operating speed, fluid level or BHP, BHT.-

COMPATIBILITY

MATERIALS USED WITHIN ESP WITH CHEMICALS USED FOR TREATMENTS - Verify compatibility between the well treatment chemicals used and the materials used within the ESP, if this was not done before well treatment.

MATERIALS USED WITHIN ESP WITH WELL CONDITIONS - Verify compatibility between downhole conditions and materials used within ESP. Examples of incompatibility include Aflas with condensates; Viton with amine-based well treatments; most stainless steels in a sour environment, etc.

RESULTS

EQUIPMENT TESTING AND DISASSEMBLY - Test, disassembly and inspect failed equipment as required. The dismantle inspection is a critical part of the evidence gathering process necessary to support a successful failure analysis. All evidence should be documented, regardless of its relative importance to the inspector at the time. No interpretation of the evidence should be made during the dismantle inspection so as not to bias the evidence gathering process toward a specific cause of failure. Therefore, it is best to not begin conducting a failure analysis until after the evidence gathering process is complete.

DRIVE REPAIR HISTORY - Examine drive repair history. Faulty drives or low quality incoming power can be the instigators of electrical failures; often the drive at the end of power grid is exposed to the worst operating conditions. Most often, following examination, incoming power problems become very obvious and isolation of these problems can greatly assist in maximizing ESP runlife.

ESP DATA

AMPCHARTS - Perform drive amp-chart analysis, or analysis of data available from data collectors or directly from the drive itself. It is important that operators include all required data on the amp-charts, otherwise the use of the amp-charts becomes very limited. Information that should, ideally, be recorded on amp-charts include: mode of VSC operation, operating speed, recorded amps from all three phases, downhole pressure, drive output voltage, transformer ratio, casing and tubing pressure. Many amp-charts are often missing the most important information – location, when it was put on, and when it was taken off!

OPERATIONAL DATA FROM DRIVE MEMORY - Download of drive history from drive memory prior to attempting the ESP's restart. Often when a unit fails, the first impulse is to attempt a restart, and more often than not, multiple restarts are attempted. If these attempts occur before drive history was download, important information can be lost, especially if the shutdown is actually the reason for pull. Downloading drive history should be a part of operating procedures.

POWER QUALITY