Identification of High Residual Gas Saturation Zone and Evaluation of its Impact on the Development of the Central-C Gas Condensate Field- Oman

摘要

The active government gas exploration programme inOman has recently added another sizeable gas–condensate discovery that was drilled and tested byCentral-C-1. Destined to unlock the first CA sandstonegas-condensate field, the well results indicated a veryprolific reservoir.In the process of data gathering, a number of challengingaspects were identified and assessed. Residual gassaturation is the most interesting and potentially highimpacting aspect. This paper addresses variations on thegas saturation profile as calculated from thepetrophysical logs, the identification from the specialcore analysis measurement of high residual gassaturation rocks, and all relevant findings inferred fromthe production testing and the static pressuregradient measurement.Despite cautioned applicability of the SCALmeasurement results to reservoir conditions, a potentialevidence for part of the CA reservoir accommodatinghigh residual gas saturation was recorded. Number ofscenarios were modelled to assess the impact of highresidual gas saturation in relation with other reservoiruncertainties normally associated with explorationreserve bookings.These scenarios ultimately studied the impact of theresidual gas saturation uncertainty on the developmenteconomics of the field. This paper explains why major economic measures, such as gas and the condensaterecovery efficiencies, well placements and aquifer influxwere seen sensitive to this uncertainty.For a comprehensive evaluation of its impact, arelationship between rock properties distribution andresidual gas saturation was invisaged as acomprehensive evaluation method. In a deeper conceptthis translates into a relationship between the interpretedoriginal depositional model and the adopted chargemodel. This interesting relationship was evaluated in thesimulator using a special saturation-porosity dependencethat was primarily based on the SCAL measurements.This paper details the analytical and the numericalapproach used to evaluate the impact of the uncertaintyin residual gas saturation. It highlights how thisuncertainty features within the appraisal data gatheringtargets and within the surveillance strategy of this field.