A Switch from Verticals to Dual Lateral Producers Accelerate Oil Production and Reduces UTC for Natih Field

摘要

The Natih field in Oman is a densely fractured carbonaternreservoir with a STOIIP of 460 million m3. The displacementrnprocesses active in the Natih reservoir during the productionrnperiod are very complex. Production started in 1967 withrndepletion of the reservoir resulting in production of oil fromrnthe fracture system and oil displacement by fluid expansionrnand solution gas drive. After these processes had ceased, gasrnoil gravity drainage in the secondary gas cap, water oilrnimbibition and water oil gravity drainage by aquifer below thernsecondary oil water contact continued to displace the oil fromrnthe matrix.rnBased on field data available around the early seventies, it wasrndecided in 1972 to arrest further pressure decline by waterrninjection. In the 1980s, field performance reviews improvedrnunderstanding of the displacement processes in the field andrncore analysis data pointed towards a relatively oil wet rock andrna relatively large volume of production was ascribed to thernGOGD process. Following this, further development of thernfield was wholly based on the drilling of GOGD producers inrnthe oil rim and conversion to GOGD producer of suitablyrnlocated wells.rnReservoir simulation work showed that substantial additionalrnreserves could be developed by fracture oil rim lowering to arnlevel close to the original OWC of the field. Through crestalrngas injection and peripheral water production, coming fromrnESP wells placed around the field, this strategy wasrnimplemented. A further feature of this strategy is the drillingrnof multilateral wells with one leg close to the current oil rimrnand one leg in the anticipated final rim position. The upper legrnproduces oil, usually after a short “oiling-in” period. Thernlower leg initially produces water and helps lowering the rim.rnThis paper illustrates the reasons behind each stage of fieldrndevelopment and reviews recent efforts to evaluate therneffectiveness of the Natih oil rim lowering strategy and itsrnfuture production potential through the use of 3D integratedrnmodelling of Natih fracture system.