US oil and gas exploration company ExxonMobil said it is planning a two-pronged development drilling effort at its massive Liza oilDrillship Stena Carrondiscovery off Guyana.This will involve bringing in a pair of offshore rigs for simultaneous operations, according to preliminary development plans filed with Guyanese regulators.During the first phase, the rigs will drill development wells from a pair of drill centres, ExxonMobil said in a supplemental information packet submitted to the Environmental Protection Agency, as part of its application for environmental authorisation for the project. One of the centres is close to the Liza-2 location, which was about 3.6 kilometres west of the Liza discovery. The second lies some 3.9 kilometres north of the Liza-1 well. ExxonMobil, however, cautioned that details of the development programme could change after the filing. Those production centres are paired with corresponding water injection locations set up about 1.6 kilometres east of each of them. There will be a single natural gas injection well at the injection centre closest to the Liza-2 well. Production from the drill centres will be collected via subsea flowlines and sent through subsea manifolds to a Floating Production, Storage and Offloading (FPSO) vessel. Current plans for a FPSO unit call for a conversion of a very large crude carrier with capacity to produce an average of 100,000 barrels per day and store 1.6 million barrels that will be moored 193 kilometres offshore.ExxonMobil said it plans to export the oil to the world market and it has “no current plans” to establish a refinery in Guyana.Engineering works on the FPSO and subsea umbilical, risers and flow line components are ongoing and should be finished in mid-2017.There were previous reports that floater specialists SBM Offshore of the Netherlands and Japan’s Modec have been shortlisted by the US supermajor to provide front-end engineering and design studies on the Liza floater.A six-month FEED process was expected to start in late summer or early autumn, potentially leading on to an engineering, procurement and construction contract.Development drilling is due to begin at the start of 2019 with a pair of yet-unchosen drillships working simultaneously at the two drill centres.“Drillship selection criteria will include historical safety and environmental performance, drillship availability and capability, including well control equipment, operability limits for the Guyana metocean environment, water depth rating and bulk storage capacity,” ExxonMobil said in the planning document.“Based on the water depths in the Liza development area, dynamically-positioned drillships would be used to drill the wells.”First oil for the phase one development will come around the middle of 2020, according to the document.Liza was the largest oil find of 2015, and a successful appraisal at Liza-2 earlier this year, including a drillstem test, led ExxonMobil, along with partners Hess and China National Offshore Oil Corporation subsidiary Nexen, to boost the recoverable resource estimate for the discovery to between 800 million and 1.4 billion barrels.Since that time, Guyana has become a major new focus area for ExxonMobil. The US supermajor snapped up a 50 per cent interest from Israeli explorer Ratio Oil & Gas in the ultra-deepwater Kaieteur block (formerly Block B), north-east of its Stabroek block, where the Liza discovery was drilled last year.In January, it took a 30 per cent operating stake in the Canje block north-east of Liza, along the maritime border with Suriname and now controls 11.4 million acres between the three blocks.ExxonMobil is currently acquiring seismic on Canje and plans to shoot 3D on Kaieteur after the deal is finalised.Meanwhile, the drillship Stena Carron is drilling ahead on ExxonMobil’s Skipjack prospect — its latest wildcat on the play — about 48 kilometres north-west of Liza on the Stabroek block.ExxonMobil secretary Jeff Woodbury said the unit would return to Liza to spud the Liza-3 appraisal after wrapping up Skipjack later this year.