We describe the investigative activities and integration of results of four successive geohazard assessments for the Dolphin Field in the Colombus Basin, offshore eastern Trinidad. The initial efforts included a probabilistic seismic hazard analysis, geotechnical studies, and an engineering-geologic assessment to support construction of the Dolphin-A production platform. These studies were followed several years later by a pipeline routing survey and a geohazard assessment to support a phase 2 subsea pipeline tieback from a satellite well.
The later studies included:
comprehensive technical review of existing data and reports;
a GIS-based desktop compilation and analysis of all readily available data;
collection and interpretation of continuous coverage multibeam bathymetry, sidescan sonar, and high-resolution 2D seismic data; and
development of a conceptual model of Quaternary geologic processes at the site.
These studies formed the basis for revision of the initial pipeline route, and also provided additional value by providing a framework within which information from previous reports could be re-interpreted to solve new engineering efforts.
This paper presents the results of successive geohazard assessments for the Dolphin Field, located in the Colombus Basin offshore southeastern Trinidad. We compare the objectives, site investigation methodologies and results of the four studies, and track the cumulative knowledge regarding site geologic and geotechnical conditions. It is our intention to demonstrate the effectiveness of each investigation to satisfying the immediate goals of each site investigation effort, and how the knowledge gained from each study eventually was combined to develop an integrated conceptual geologic model of the active geologic processes at the site.
Each of the investigations represent a very high-quality fit-for-purpose investigation that successfully achieved the goals of the study and provided the basis for that phase of the project development. Even though the earlier reports provided the information necessary to achieve specific project objectives, they were not able to (nor were they intended to) provide a clear picture of the surrounding geological environment. We demonstrate how the information contained in the reporting of the individual investigations was eventually combined to create a robust conceptual geologic model of the site region, and how the model and supporting documents provide extended value to ongoing efforts of site development.
Dolphin Field of the East Coast Marine Area is located within the eastern Columbus Basin on the outer continental shelf of South America, approximately 75 km offshore Galeota Point, southeast Trinidad (Figure 1). The Dolphin Field is in a tectonically active and complex geologic environment. The basin overlies the active tectonic plate boundary between the South American and Caribbean tectonic plates, formed approximately 40 million years ago during late Eocene time (e.g., Babb and Mann, 1999). East-west directed differential plate motion along this boundary of approximately 13 m/ka (meters per thousand years) is accommodated by displacement on relatively narrow fault zones. East and north of the Dolphin Field oceanic crust of the South American plate is subducting westward beneath oceanic crust of the Caribbean plate along the Barbados (Antilles) accretionary prism.