Abstract

Deepwater reservoirs continue to provide many new technical challenges for hydrocarbon development and production, where complex environments of deposition and reservoir architectures must be understood to ensure optimal resource development and hydrocarbon recovery. Recent technology advances including higher resolution 4D seismic data coupled with the application of sequence stratigraphic concepts in deepwater reservoir settings has resulted in breakthrough improvement in the understanding of deepwater reservoirs. In the Zafiro Field, such technology-driven learnings have provided a greatly improved understanding of deepwater slope channel systems.

Introduction

Deepwater reservoirs such as the Zafiro Field continue to provide many new technical challenges for hydrocarbon development and production, where complex environments of deposition and reservoir architectures must be understood to ensure optimal resource development and hydrocarbon recovery.

The giant Zafiro Field in Equatorial Guinea was discovered in 1995 and is composed of stacked Pliocene deepwater slope channel deposits that record large scale clastic input into the Gulf of Guinea following partial collapse of the paleo-Niger delta. In this paper we explore the linkage between physical stratigraphy, environments of deposition, reservoir architecture and resulting production performance found in the deepwater slope channel systems of the Zafiro Field.

The paper is divided into two themes, firstly "Reservoir Characterization" where we discuss static aspects of the Zafiro Field, and secondly "Reservoir Modeling and Performance" where we discuss dynamic aspects of the Zafiro Field. The Reservoir Characterization discussion includes stratigraphy and reservoir architectural styles, environments of deposition and lithofacies, lateral continuity and vertical connectivity, and reservoir heterogeneity and permeability anisotropy. The subsequent Reservoir Modeling and Performance discussion will include perched formation water and secondary gas caps, communication within and between reservoirs, and a discussion of reservoir architecture and connectivity as key controls on dynamic reservoir performance. Finally, we will discuss these observations and learnings from the Zafiro Field in the context potential implications for deep-water oil production.

Zafiro Field Location and Dataset

The Zafiro Field in Block B is located in West Africa on the eastern side of the Niger Delta approximately 40 miles offshore Bioko Island in Equatorial Guinea (Figure 1). The staged development at Zafiro started with first oil from the Zafiro Producer Floating Production Unit (FPU) in 1996, the Jade Platform in 2000 and the Serpentina Floating Production Storage and Offloading (FPSO) vessel in 2003 to give a Zafiro Field daily oil production capacity of approximately 300kbd.

The comprehensive dataset used in this study includes high-resolution 3D and 4D seismic surveys that are calibrated by over 75 well penetrations, with >3500ft of conventional core and 8 years of production data. The Zafiro seismic dataset comprises a high quality 1995 3D seismic dataset that was reprocessed in 2000. More recently, a 3D high resolution seismic dataset was acquired in 2003 with a significant increase in bandwidth and peak frequency. Both datasets have been processed for 4D seismic to investigate the time lapse response resulting from 7 years of oil production between 1995 and 2003.

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