APPLICATION OF A HIGH RESISTANCE GROUNDING (HRG) UNIT TO AN ESP WITHIN A HAZARDOUS AREA 2014 EUALF

Transcription

1 APPLICATION OF A HIGH RESISTANCE GROUNDING (HRG) UNIT TO AN ESP WITHIN A HAZARDOUS AREA 2014 EUALF

2 INTRODUCTION When conventional attempts to eliminate electrical discharge activity in a zone 1 hazardous area associated with an earth faulted ESP failed, the system was isolated and the back-up system brought online. When the backup system failed an alternative approach to the problem was attempted. This presentation will look at the following: How the fault led to above surface electrical discharge activity How the application of a High Resistance Grounding Unit eliminated the problem 2

3 BACKGROUND Well completed as a dual ESP operated via a Variable Speed Drive (VSD) Primary ESP developed earth fault within first weeks of operation Floating neutral VSD system allowed for continued operation of faulted ESP Gauge of backup ESP connected to maintain downhole data After 16 months operation electrical discharge noticed in wellbay area during routine checks Well taken offline and investigations commenced earlier earth faulted had further degraded Three leg electrical penetrator Electrical discharge from instrument pipework 3

4 CONVENTIONAL SOLUTIONS Tree earthing checked and supplemented Equipotential bonding applied to all extraneous metalwork Backup gauge system isolated (remove alternative power sources) Backup ESP system isolated (removed circulating current paths) Voltage in offline ESP system checked Electrical discharge potential still present measurable as voltage difference between adjacent bonded metalwork 4

5 INTERIM OPERATION Primary ESP mothballed due to discharge Backup ESP brought into operation Well operated for further 22 months until backup ESP failure (suspect motor bearing failure) Opportunity to to re-use primary ESP if electrical discharge potential could be eliminated Sharp increase in amps prior to eventual failure 5

6 FURTHER INVESTIGATIONS Time Domain Reflectrometry employed to determine location of fault Information indicates low impedance earth fault located high in completion (immediately below or within tree) Repair attempted by replacing intermediate connectors but ineffective required completion to be pulled Multiple additional earth bonding jumpers attached to tree and pipework no success Fault location and severity causing capacitive charging of local earth plane Capacitive charge unable to dissipate as supply system (VSD) unearthed 6

7 ALTERNATIVE SOLUTION Fault current requires return path to prevent capacitive charging VSD not suitable for operating with earthed star point High Resistance Grounding Unit (HRGU) being evaluated to extend run life of earth faulted ESP wells Decision to employ HRGU to provide return path for fault current 7

8 HIGH RESISTANCE GROUNDING UNIT HV/LV transformer in Star/Broken Delta configuration HV star point grounded to provide earth fault current return path Open Delta secondary winding closed using high power rating resistor Current flow in primary matched (at transformer ratio) with current flow in secondary Secondary winding resistor limits primary (fault) current 8

9 9 HIGH RESISTANCE GROUNDING UNIT-BETA UNIT

10 10 HIGH RESISTANCE GROUNDING UNIT-METERS WITH GROUND FAULT

11 11 HIGH RESISTANCE GROUNDING UNIT PRODUCTION UNIT

12 INITIAL OPERATION HRGU connected in parallel with VSD output-at VSD VSD operated at low output voltage to determine fault levels HRGU instrumentation indicates earth fault impedance near zero Secondary winding resistor value altered to limit fault current to ~2 Amps VSD run up to operating voltage and frequency Electrical discharge potential voltages still present in well bay area 12

13 REVISED OPERATION Analysis of installation indicates parallel earth paths to HRGU through platform metalwork and supply cable braid Need to provide preferential path for earth fault current Low impedance path provided from close to fault site to HRGU (large diameter earth conductor following path of main conductors) Makes the Tree the New Earth Fault Location No Stray Currents thru Piping! VSD run up to operating voltage and frequency No electrical discharge potential voltages measurable in well bay area 13

14 EXTENDED RUN-LIFE Well brought back online at production rate of ~980 BOPD Well operated for further 10 days Suspect motor failed mechanically (i.e. not directly related to earth fault) Cost of HRGU purchase and installation recouped within first 3 days of additional production HRGU technology and application proven electrical discharge potential from earth faulted ESP eliminated 8.4Mbo additional production 14

15 15 ACKNOWLEDGEMENTS