Depositional Elements, Control Parameters, and Scaling: A Practical Approach to Turbidite Reservoir Description
Authors: Imbert Patrice , Navarre Jean Christophe 
Published: October 2008

Specific aspects of E&P activities in the GOM include the fast tracking of projects and the scarcity of hard data such as continuous cores or DSTs. As a result, decisions on exploration and production of deep-water accumulations have to rely mostly on seismic data and limited well control only. In order to alleviate the risks, this limited information has to be supplemented by models derived from analogues.

TFE has chosen to develop a practical seismic-based approach based on the recognition of depositional elements. This approach is built first on the availability of a worldwide portfolio of assets in turbidite deposits, providing for instance long-term production data, and also on the outcome of longterm research efforts in the sedimentology of turbidites. Reference data include producing field studies, outcrop examples, shallow parts of 3D surveys and proprietary oceanographic data.

The method consists in relating the seismic morphologies observed in the area of interest to a short list of basic building blocks ("depositional elements"), kept to a minimum number in order to facilitate communication between geoscientists. Channels, levees, lobes, mass transport complexes, and canyon-fills are the main "turbidite" elements, hemipelagic drapes, contourite accumulations and post-burial deformation being the main seismic-scale additions to that list in deep water settings.

The limited number of depositional elements recognized means that the variability in each class is high. The next step consists in relating reservoir properties of depositional elements to their context of deposition. This context is characterized by two main sets of parameters: those related to the sediment source and those describing the basin morphology. The influence of each parameter on reservoir architecture and dynamic behavior is estimated from the inhouse dataset.

The final step consists in downscaling the description so as to get down to the precision needed in each particular case. Outcrop analogues are the best way of approaching the actual complexity of the systems. They help us refrain from believing that the images we see on horizon slices, as beautiful as they may be, are fully representative of the actual complexity of our reservoirs.

Examples of application show how the method and database can help making decisions from a limited dataset, using constraints from analogues to reach the level of precision needed to evaluate the risk on reservoir extension and communication.

1 Introduction

1.1: The problem at issue

Due to technological improvements, exploration for oil and gas took in the last decade a significant step towards deepwater, a domain that was previously considered out of reach of production technology. As a result, more and more fields are now being developed in deep water throughout the world, and in particular in the Gulf of Mexico. The high cost of developments in deep water means that decisions have to be made rapidly, on the basis of limited information only. Moreover, budgetary, technical and legal constraints limit the availability of certain types of data, like full diameter cores and drill stem tests.