Abstract: Using a Prior Knowledge of Natural Fractures for Reservoir Characterization

Atilla Aydin

The objectives of this presentation are three fold: (1) to summarize the state-of-the art knowledge of natural fractures (joints and faults); (2) to classify them in terms of their fluid flow properties; and (3) to propose a methodology for maximizing the benefit of this knowledge in reservoir visualization and characterization.

Over the last century, a significant progress has been made in understanding the orientation, dimension, spacing, connectivity, localization, and fluid flow properties of natural fractures. Each of these parameters is controlled by geological and mechanical processes. The mechanical basis for predicting joint orientation on a local scale is quite reliable but the geological reasons for the variation of the orientation on a regional scale are not well understood. There is a vast amount of data on the orientation of faults but the mechanical basis for fault initiation and propagation is not certain. The dimension and spacing of joints can be linked to mechanical layer thickness, however, the role of the amount and rate of strain remains to be considered. In general, the connectivity of oints and faults is relatively well known whereas the localization of these structures is less known. Because joint and fault zones are important for fluid flow, the geometry and mechanics of these structures are crucial for a sound interpretation and parameterization. The fluid flow properties of natural fractures are perhaps the least known parameters. Here, natural fractures will be classified as either barriers or conduits and factors that enhance or impede their permeability will be discussed.

In conclusion, it is argued that a good understanding of the processes of the formation of rock fractures and their geometry provides a basis for building up a wealth of a priori information about natural fractures. This knowledge provides the cheapest method for reservoir characterization and visualization, and should be considered complementary to other available geophysical, well bore, and stochastic techniques.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994