Understanding Subsurface Pressure Data Signature in a Hydrogeological Context

Arif I. Alkalali
Saudi Aramco
[email protected]

Pressure data are often used to understand the conductive properties of the rock framework, such as compartmentalization and sealing. While using such data is well-justified, the lack of understanding of basinal hydrogeology prevents a more comprehensive and thus accurate interpretation. Using a wealth of pressure data from mature basins and a numerical basin-hydrogeology model, a set of guidelines for understanding the pressure regimes and their implication on the hydrocarbon system are outlined. In subaerially exposed basins, the up-per 10,000 ft or so are usually normally-pressured and dominated by a gravity-driven flow system. In these basins groundwater descends starting at topographic highs and then flows laterally before it ascends at topographic lows. Intermediate and local flow systems also develop at a smaller scale due to local topographic variations. Sometimes the flow may be short-circuited by flow conduits between horizons, such as evaporite or shale layers. The gravity-driven flow system is usually superimposed on a deeper, abnormally-pressured sys-tem whose genesis can be due to multiple aspects. Among those are compaction, hydrocar-bon generation and tectonic compression. The movement of groundwater within these sys-tems and the interaction of such flow systems with the geological framework can generate a multitude of pressure signatures, both on a local and regional scale, which when properly interpreted, can lead to better exploration and development strategies. The developed guide-lines are outlined and applied to flow systems observed in the Arabian Platform and the po-tential implications on understanding the hydrocarbon system is proposed in view of the observed data.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain