Unlocking Bypassed Oil in Mature PDO South Oilfields by Developing Gharif Low Resistivity Pay

Abstract

Abstract PDO has a large portfolio of mature Gharif fields with significant hydrocarbon potential to be unlocked by efficient well and reservoir management (WRM). In 2016, focussed surveillance on Closed-in Wells (CIW) in a mature PDO South Gharif field, highlighted significant bypassed oil opportunity in Low Resistivity Pay (LoRP) reservoir –"C". Presence of conductive minerals and different clays in the LoRP sands, led to a pessimistic assessment of resistivity based hydrocarbon saturation. As such, histrocially, these oil bearing sands were not perforated. LoRP was production tested in 2 CIW & 3 New Oil (NO) wells in 2015, doubling field's net oil production (Figure1). Insights from historical field production, pressure depletion, core and Nuclear Magnetic Resonance (NMR) data were integrated to update the static subsurface model which led to an increment of 21% in the field STOIIP. Current inventory of high water cut (>95%) and high sand producing oil producers are being converted to dedicated LoRP producers on opportunity basis. This has reduced the frequency of expensive well workovers. Quick screening of LoRP has been initiated for all PDO South fields. Initial results show that similar bypassed oil opportunities exist in other mature brown PDO South fields as well. Broadly speaking, such bypassed oil opportunities can be attributed to one of the following subsurface mechanisms at play i.e. presence of thin sand- shale intercalations which are not vertically resolved on wireline logs, presence of condutive minerals e.g. pyrites or clays and high irreducible water saturation in microporous rocks. With the current low oil prices, re-exploration of mature fields by interpreting and maturing low resistivity pay reservoirs, presents an attractive business proposition.