A319 Pilot reported engine oil quantity rapidly decreased from 18 quarts to 2 quarts. A diversion and an in flight shut down were performed and a landing was made at a diversion airport.

Narrative

At cruise abeam ZZZ1; engine oil quantity rapidly decreased from 18 quarts to 2 quarts. XA55Z; temp was increasing and oil pressure falling. XB00Z [priority handling was requested] and turn towards ZZZ2 was requested. XB02Z Began planning for precautionary shut down. APU was started; approach briefed; Dispatch was informed; Flight Attendants (FAs) were briefed and passengers informed about 'divert.' Electronic Centralized Aircraft Monitor (ECAM) required inflight shut down; completed at XB35z. All checklists completed by XB40. Flight Attendants were advised about precautionary landing. Approach and landing were completed single engine. All normal. Aircraft Rescue and Firefighting (ARFF) reviewed right engine for oil leaks; none found. Status changed back to normal aircraft; priority handling request was over. Taxi to gate normal. Flight deplaning held for customs/immigration release. Flight deplaned; log book entry made. MX Reports zero oil in engine #2 to Flight Crew; questions if engine was operated without oil pressure. It was never operated above idle below 2 quarts of oil. Chief Pilot and Dispatch debriefed. Additional flying refused; Captain and First Officer proceeded to hotel for rest and down line deadhead to sequence continuation. Debrief of Aircraft X; ZZZ3 to ZZZ4 divert ZZZ2. Date. During Cruise flight at FL380; aircraft at .775 Mach. Captain Flying; First Officer (FO) monitoring over ZZZ1. XA:55 Z (I) Captain noticed that right engine oil quantity (#2 Engine) was rapidly decreasing from approximately 17.5 quarts to 2.0 quarts. I called out the falling oil quantity and assigned the FO as the flying pilot.We discussed the possibility that the engine could fail due to low oil quantity as well as the 'inaccurate instrument indication' possibility. The ACH (Aircraft Hand Book) was consulted and we began to look for increasing temperature and falling pressure. #2 engine temperature began to creep slowly upwards relative to the number 1 engine; quantity remained at 2.0 quarts; pressure in the green. We made note of the minimum oil pressure/ oil quantity requirements and how an ECAM message would be generated/displayed; requiring an inflight shut down. ECAM 1-4 Oil Quantity was consulted. XB00Z We devised the 'best course of action plan' at this time. I began photographing engine parameters for later MX Action. We discussed the best diversion airport; ZZZ5 was below the Aircraft; ZZZ2 was 170 miles away; ZZZ6 was ahead about 50 miles. At a rapid descent; approximately a 3:1 glide ratio it would take approximately 120 miles to reach pattern altitude. We decided that our 'trigger to initiate' a precautionary divert to ZZZ2 was: if any secondary indication became present. ZZZ2 was deemed safer; this due to the superior ARFF; clear weather; and descent positioning outside of mountainous terrain. ZZZ5 and ZZZ6 would have required a steep spiral and descent. The ground below us was not visible and under an overcast layer. At this time we were still unsure if this was an actual or indication problem (No ECAM messages were present yet); or any confirmed secondary indications.XB03Z As oil temp continued to slowly increase; (the oil pressure was stable); we decided nonetheless to begin the divert activation; this after the relative temperature of the engine oil hit my own personal threshold; for being 'symptomatic' and therefore; a secondary indication. At this moment we assumed we had an engine that could be operated safely at idle power. Drift down and one engine cruise QRH was reviewed; as a precaution. ECAM Advisory 1-3 Oil PRESS and 1-4 Oil TEMP were consulted prior to decision. XB05Z I took control of the aircraft and designated the FO as non-flying. The auto throttle was disconnected; speed reduced to green dot +15. We [requested priority handling] with ATC; requested a decent and turn for a direct ZZZ2 routing. When the aircraft was stable; descending and on course; the control was transferred back to the FO. We discussed the 'Engines health'; divert; landing; terrain; and the possibility of doing a preemptive shut down. We decided to follow the ECAM and QRH guidance; and not invent procedures. Dispatch was informed about the precautionary divert and destination intended (ZZZ2) via ACARS. Confirmed at XB18Z via ACARS. Flight Attendant were chimed and told about the divert and to expect a normal landing in ZZZ2. I reiterated that no brief was necessary and this would be a normal landing.Passengers were informed about the need to divert to ZZZ2; due to an 'abundance of caution; related to a cockpit gauge indication'. I estimated landing time and completed the passenger prepare for landing brief. Seat belt sign was now on. During this time the FO was flying and tasked with answering the ATC standard questions. He also showed remarkable composure; securing the weather; landing runway; and programming the approach. We were cleared direct to the fix ZZZZZ on the ZZZ2 ILS XXR. Terrain MEAs were consulted and descents requested; the aircraft was in normal flight with the left engine supplying about 75% max power and the right at Idle. The APU was started. We reviewed and completed checklists; briefed the approach and continued to monitor engine health. Multiple ATC frequency changes were completed. XB35Z At XB36Z the aircraft displayed a 'temporary' Master Caution flash; that self-cleared with no ECAM message associated; it did it again one minute later. We surmised this was the pressure threshold for 'the beginning' of the ECAM directed engine shut down. At XB38Z one minute later. The ECAM message 'ENG 2 OIL LO PR' displayed; and remained steady; as was the Master Caution. Immediate action/ECAM exception logic was followed and FO commanded 'ECAM action'. I shut down the engine following the ECAM prompts as the FO guarded the #1 engine.We [requested priority] with ATC and considered ourselves a priority aircraft at XB40Z; we were approximately 40 miles from ZZZ2. [Company] procedure was consulted after completing the ECAM. Follow ups were concluded and aircraft inoperative systems briefed. I briefed the Flight Attendants (FAs) and Passengers to expect ARFF to be present; again reiterating 'a normal procedure for safety. On interphone I spoke to all the FAs and reaffirmed the 'Precautionary' nature of the briefing. Dispatch was informed we were now: single engine; continuing to ZZZ2 and a Priority Aircraft. CRM: We discussed the situation and decided that the FO would continue to fly the aircraft; I would manage as non-flying pilot. Non Normal routine landing checklist was completed. At every radio frequency change we were asked to restate facts; desires and data points; this became very cumbersome and time consuming. ZZZ2 approach acknowledged our status and cleared us for ILS XXR; we declined the visual approach. Tower cleared us to land.XB58Z We concluded a normal single engine landing to full stop on ZZZ2 XXR; The FOs airmanship was stellar. As we touched down on speed; on center line; in the touchdown zone. I assumed aircraft control and cleared to the right onto taxiway; as ATC directed. Passengers were asked to remain seated. ARFF was contacted; and visual inspection of our right engine and brakes was conducted; this with aircraft parked on taxiway. All engine oil was removed by the air stream and no potential brake fire present. XC10Z We changed our status to 'normal aircraft' and taxi to gate as directed. Debriefs with ZZZ2 ARFF representative; gate agents; station management; ZZZ3 director. Name; and Dispatch Desk were completed; in that order. XC18 Z Engine discrepancy was entered in log book. Engine was found to have zero oil present. Station representative asked us to remain onboard and keep passengers seated until Maintenance has inspected Aircraft. I refused and deplaned Passengers after Immigration clearance received. Additional flying offered was refused. Captain secured hotels and down line sequence continuity."