INTEGRATED PETROPHYSICAL ANALYSIS AND SEQUENCE STRATIGRAPHY OF THE PALAEOCENE INTERVAL, FAROES-SHETLAND BASIN

摘要

Enterprise Oil has developed a sequence stratigraphic framework for the Flett and Erlend sub-basins, West of Shetlands. Three regionally correlatable, unconformity bounded mega-sequences have been identified. These mega-sequences are further subdivided into depositional sequences recognisable at well and seismic scales and form the framework of a detailed playfairway analysis which focuses on the identification of reservoir and seal horizons. Petrophysical data is a key element of the playfairway analysis. The aim of this paper is to present a predictive reservoir effectiveness model that has been developed to aid exploration of the Palaeocene play. The model addresses the distribution of reservoir porosity and net effective reservoir thickness with burial depth, and provides a dataset for reservoir parameter input to exploration prospect evaluation. The model indicates that effective reservoir quality is significantly reduced at burial depths greater than ～10,000 ft. of overburden. In addition, the model identifies a sub-set of wells with anomalously high reservoir quality at burial depths ＞10,000 ft. These high porosity sands have distinctive amplitude versus offset (AVO) and acoustic impedance (AI) signatures. Petrophysical evaluation of the Palaeocene reservoir quality is further complicated by low salinity formation waters giving the potential for low contrast pay zones. Generally, salinities are ＜25,000 ppm NaCl equivalent, and decrease with increasing stratigraphic age and burial depth. Vertical salinity variations are discussed. Log analysis has been calibrated, where possible, to available core data. The development of a predictive reservoir effectiveness model, integrated within a sequence stratigraphic framework, has highlighted the importance of petrophysics and rock physics to the understanding of reservoir quality distribution in the Flett and Erlend Basins. The dataset is currently being used as a tool for acreage evaluation, prospect generation and volumetric modelling of Palaeocene reservoirs, West of Shetland.