Abstract

One of the most challenging issues within Abu Dhabi onshore fields is the definition, characterization and modeling of the main structural heterogeneities. Integration of structural, geometrical and dynamic understanding is the key to defining what is important from a field development and production viewpoint, since it may affect the economics of the fields.

A consistent analysis and approach is essential to be able to compare the fields taking into account the three different types of fracture (i.e. faults, fracture corridors and diffuse fracturing), and the potential geological events that postdate the fracturing (fluid circulation, diagenesis).

Diffuse fracturing was commonly described across most fields based on core observations and image log interpretation. However, this fracture type alone cannot explain the behavior of many wells.

A new look at the data reveals that several fields exhibit fracture corridors and/or subtle faults. Integrating the well behavior suggests this fracture type may have a significant impact in some fields. Unfortunately, this style of deformation is often below the seismic detection threshold.

The recent acquisition of 3D seismic across most of the Abu Dhabi onshore fields reveals all fields are faulted at the seismic scale. The fault style is often characterized by small throws. Recent improvements in seismic resolution reveal that what was previously interpreted as one fault is in fact made of numerous fault segments separated by relay areas. This new interpretation has obvious implications for the dynamic behavior of these fault zones. Indeed great discrepancies of the fault zone behavior are observed and discussed using six example fields which encompass a wide variety of carbonate reservoirs with varied depositional environments and reservoir properties. Given such a range of reservoir properties, faults and fractures with similar properties might be expected to have very different expressions in the way they affect fluid flow.

Introduction

A number of world-class oil fields have been discovered and under development in Abu Dhabi since the 1960s. Recently 3D seismic surveys have been shot over many of these fields. The seismic data along with extensive core and borehole image data provides an outstanding dataset to allow the study of faulting and fracturing within a regional framework.

With the introduction of 3D seismic, the structural framework changed dramatically for most of the fields where this technology was applied (Figure 1). Likewise, the possibility of obtaining good quality borehole images has raised new challenges in terms of integrating information at different scales and matching dynamic information.

This paper presents the results of an integrated study of six ADCO fields focusing on the varying dynamic impact of faulting and fracturing in differing reservoirs.

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