Predicting Connectivity and Rock Typing of the Upper Carboniferous Reservoirs in the Southern North Sea (NW Europe): Tackling Mature Reservoirs and Evergreen Challenges with a "Back to the Rocks" Approach

Moscariello, Andrea; van Hoof, Tom; Kunakbayeva, Gulnaz; ten Veen, Johan; Van der Belt, Frank; Davis, Paul; Williams, Huw

Fluvio-deltaic Upper Carboniferous reservoirs in the southern North Sea hold large part of the remaining hydrocarbon resources of north west Europe. Exploration and production activities on those reservoirs began in the early 1960s. Yet these Carboniferous reservoirs still present several challenges mostly releated to connectivity associated both with primary sand body architecture, fault-related compartimantalisation and reservoir properties distribution, the latter affected both by original sediment composition and subsequent diagenesis processes.

A joint industry project has been carried out to provide new guidelines and workflow for establishing a consistent stratigraphical framework across a variety of reservoirs intervals (‘gray' and ‘red' beds) occurring in the Upper Carboniferous.

In particular, key reservoir characteristics and components (e.g. soils, coals-seems, bio-facies content, chemical composition of fine-grained intervals) were identified as tools to predict the overall vertical stacking pattern (e.g. entrenched and amalgamated versus scattered and disconnected channel fill) and thus connectivity. In addition, practical guidelines and learning from a set of outcrops data in eastern Kentucky have been proposed to drive subsurface conceptual geological modeling and in particular to help the understanding of overall vertical and lateral stacking patterns, and ultimately connectivity. The outcrop analogue for the coal-bearing intervals is the Pennsylvanian Pikeville Formation in eastern Kentucky where exceptional exposures allowed us to reconstruct in details the geometry and overall architecture of the reservoir.

Ultimately, the project results provided criteria to distinguish and predict distribution, location and connectivity of different reservoir sedimentary bodies and their reservoir properties (digenesis and rock typing).

This project addresses some of the important outstanding issues faced by southern North Sea operators active in the Carboniferous reservoirs. The results of this study will be used thus to assist them to assess the scope for recovery of additional reserves in existing producing fields and potentially drive further appraisal of this old, but still promising reservoir.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013