A Greater Dolphin Area Case Study Part 1: Defining Geological Uncertainty
- Katy Taylor (BG Trinidad & Tobago) | Nik Kalita (BG Trinidad & Tobago) | Joel Frank Dowlath (BG Trinidad & Tobago Ltd.) | Olamide Michael Jegede (BG E&P Ltd.) | Ronnie Arun Ameerali (BG Trinidad & Tobago Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPETT 2012 Energy Conference and Exhibition, 11-13 June, Port-of-Spain, Trinidad
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.5.5 Evaluation of uncertainties, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 5.1.5 Geologic Modeling, 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 5.6.1 Open hole/cased hole log analysis, 3.3.1 Production Logging, 5.1.8 Seismic Modelling, 1.6 Drilling Operations, 2 Well Completion, 1.1 Well Planning, 3.3.6 Integrated Modeling, 4.6 Natural Gas, 1.7.5 Well Control, 2.4.3 Sand/Solids Control, 5.1.2 Faults and Fracture Characterisation, 5.1 Reservoir Characterisation, 1.6.9 Coring, Fishing
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The Dolphin Field is located in the East Coast Marine Area, approximately 60km off Trinidad. It comprises a 5,000 feet succession of stacked, unconsolidated, Pleistocene shoreface-deltaic sandstones and mudstones lying within a three-way dip, fault closure. The field is complicated by poor seismic data due to gas attenuation, fault shadow effects, large velocity variations and noise in the overburden. As a result the use of seismic amplitudes for fluid determination is unreliable and fault interpretation problematic.
Despite over 15 years of production, 5 exploration wells and 13 development wells there remains a high level of subsurface uncertainty. Specific areas of uncertainties include: zones of poor correlation as a result of large-scale sediment deformation; the configuration and sealing properties of both structural and syn-sedimentary faults; the effects of thin-bedded deposits (forming over 50% of the Dolphin reservoir intervals) on reservoir pay and connectivity; and the absence of all but one proven Gas Water Contact (GWC).
Defining the range of these uncertainties has a key impact on the range of GIIP outcomes, the resultant development plan and subsequent reservoir management. This paper will discuss the challenges and impact of these uncertainties on the Dolphin Field. The uncertainties identified on Dolphin form the basis for uncertainty planning in the development of subsequent analogous greenfields also within the Greater Dolphin Area.
Tertiary shallow marine/deltaic provinces form a number of significant reservoirs in many part of the world e.g. Niger, Nile, Orinoco (Dolson et al. 2002, Tuttle et al. 1999, Wood 2000). Despite the extensive published literature in this field there are relatively few examples documented from producing reservoirs where detailed static geological data has been integrated with production data. The Offshore, Plio-Pleistocene sands of the palaeo-Orinoco delta are a well established hydrocarbon province with a number of reservoirs contained within the fluvial-deltaic and shallow marine sands of the Columbus Basin (Leonard 1983, Wood 2000, Hallam & Lum Kin 2003).
The Pleistocene Dolphin Field within the Columbus Basin provides an example of a deltaic/shoreface reservoir with good well control, a detailed static reservoir description and over 15 years of production data. However, even with all this data the Dolphin Field still faces a number of significant technical challenges key to which include uncertainties in the GIIP range and distribution, and dynamic connectivity within the reservoir. The aim of this paper is to summarise these uncertainties and understand how they impact on the future infill drilling campaigns on Dolphin and the development of the neighboring Starfish Field.
Field Setting and History
The Dolphin and Starfish fields lie in the East Coast Marine Area (ECMA) in Blocks 6b and E respectively, 50 miles east of Trinidad in water depths of 350-500ft (Figures 1 and 2). BG Trinidad and Tobago has a 50% working interest in Blocks E, 5a and 6b, and operates them on behalf of venture partner Chevron.
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