Petroleum migration pathways through a basin are determined by the three-dimensional distribution of discontinuous sealing surfaces, which are usually parallel to bedding. The petroleum migrates below the sealing surface, taking the structurally most advantageous route. The three-dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper. Application of the model to the Paris and Williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models.

Pathways form a dense network overlying generating areas in the central parts of basins. Toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing-surface morphologies. Eventually, these pathways may reach the surface as seepages. It is important to integrate surface outcrops of migration routes (surface seepages) into migration modeling.

Deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal, fault juxtaposition, or cross-formational seals such as salt intrusions. Deflection of pathways also

©Copyright 1997. The American Association of Petroleum Geologists. All rights reserved.

¹Manuscript received May 8, 1996; revised manuscript received October 1, 1996; final acceptance February 20, 1997.

²Anadarko Algeria Corporation, The Atrium, P.O. Box 576, 1 Harefield Road, Uxbridge, Middlesex UB8 1YH, United Kingdom.

This work was undertaken as part-time research at the Open University, Department of Earth Sciences, Walton Hall, Milton Keynes, England, under the supervision of R. C. L. Wilson, whose support and advice is much appreciated. Particular acknowledgment and thanks to J. T. Hindle (Geofocus Limited) for writing the personal computer program pathways, which forms a central component of the research. My former employer, Texaco Ltd. is also thanked for their support of my research, together with the Texaco graphics department for assisting with the figures. The manuscript benefited greatly from reviews by the following, who are also acknowledged: G. Hampson, P. Waddams, J. W. Lloyd, and S. Blake; and AAPG reviewers D. Schumacher, P. K. Webb, and Elected Editor K. T. Biddle.