CENTRAL VALLEY GAS STORAGE (CVGS), LLC

Incident Narrative

WELL CONTROL WAS TEMPORARILY LOST DURING PLANNED MAINTENANCE OF THE C.V.G.S. 1-L (API10: 0401120925), AN UNGSF GAS STORAGE WELL. AT 11:27 AM LOCAL TIME ON JULY 11TH, 2024, 1,478 FEET OF 2-3/8' WORKSTRING WAS EJECTED FROM THE WELL. WITHIN THIRTY SECONDS, THE WELL WAS CONTROLLED AND SECURED BY THE ONSITE CREWS. THERE WERE NO INJURIES. CVGS BEGAN ITS INCIDENT RESPONSE, INCLUDING NOTIFYING THE NRC AND OTHER REGULATORY AGENCIES IN ACCORDANCE WITH CVGS PROCEDURES AND APPLICABLE REGULATIONS. PRIOR TO THE LOSS OF WELL CONTROL AND IN ACCORDANCE WITH THE WELL WORK PROCEDURE, THE WELL HAD A RETRIEVABLE PACKER INSTALLED AT 1,507 FEET MD AND A PLUG SET IN THE PACKER AT 2,424 FEET MD INTENDED TO FUNCTION AS TWO DOWNHOLE ISOLATING BARRIERS BETWEEN THE RESERVOIR AND THE SURFACE. A FEW ELEMENTS OF THE SCADA MONITORING SYSTEM WERE PURPOSEFULLY DISCONNECTED TO ISOLATE HAZARDOUS ENERGY AND ACCESS THE WELL FOR THE PLANNED WORK, AND THE SCADA SYSTEM FOR THE REST OF THE FACILITY WAS OPERATIONAL AND FUNCTIONING. AT SOME TIME PRIOR TO 11:27 AM, POTENTIALLY OVERNIGHT, PRESSURE BUILT BETWEEN THE BARRIERS INSTALLED AT 1,507 FEET MD AND 2,424 FEET MD. AT 11:27 AM, THE WORKOVER CREWS BEGAN TO RELEASE THE RETRIEVABLE PACKER INSTALLED AT 1,507 FEET MD TO RETRIEVE IT FROM THE WELL. AS THE PACKER WAS RELEASED, THE FORCE FROM THE BUILT-UP PRESSURE PUSHED THE WORKSTRING AND RETRIEVABLE PACKER OUT OF THE WELLBORE IN APPROXIMATELY 3 TO 5 SECONDS. THE GAS THAT BUILT UP BETWEEN THE TWO DOWNHOLE BARRIERS WAS RELEASED. IN LESS THAN THIRTY SECONDS, THE ONSITE CREWS SECURED THE WELL WITH MULTIPLE BARRIERS (MASTER VALVE AND BLOWOUT PREVENTER ELEMENTS). THE WORKSTRING CONTACTED THE ELECTRONICS OF AN OFFSET WELL, WHICH SHUT DOWN IN THE INTENDED FAILSAFE CONDITION AND PROVIDED THE INITIAL INDICATIONS OF AN INCIDENT TO THE CONTROL ROOM VIA THE SCADA SYSTEM. THE SURFACE PIPING OF THREE OFFSET WELLS WAS CONTACTED AND THEN TAKEN OUT OF SERVICE UNTIL ASSESSMENTS CONFIRMED THE DAMAGE WAS ONLY COSMETIC. THE WELL WORK PROCEDURE SPECIFIED TO EQUALIZE PRESSURE ACROSS THE RETRIEVABLE PACKER INSTALLED AT 1,507 FEET MD PRIOR TO RELEASING IT. THE PURPOSE OF THIS PROCEDURAL STEP IS TO MITIGATE THE POSSIBILITY OF A FAILURE OF THE ISOLATING BARRIER INSTALLED AT 2,424 FEET MD. THE WELL WORK CREWS SKIPPED THIS STEP. THE FAILURE OF THE ISOLATING BARRIER INSTALLED AT 2,424 FEET MD IS A CONTRIBUTING FACTOR. THE ESTIMATED RELEASE VOLUME WAS CALCULATED USING THE WELL'S INFLOW PERFORMANCE RELATIONSHIP, THE RESERVOIR PRESSURE, AND THE PRESSURE IDENTIFIED AT SURFACE DURING THE RELEASE. AN ALTERNATIVE METHOD RESULTS IN A LOWER RELEASE VOLUME.