Tabor, John R.1, Jay P. Busch2, William F. Dula3, Stephen J.
(1) Shell Oil, Houston, TX
(2) Shell Oil,
(3) Shell Exploration & Production Technology Research, 2280 AB Rijswijk, Netherlands
(4) Shell International Exploration and Production Inc, Houston, TX
Fault-seal capacity can either be enhanced or diminished along critically stressed faults. The dominant mechanisms by which fault seals are enhanced are juxtaposition, fault gouge formation or cementation/diagenesis, whereas geomechanical dilation is believed to diminish the sealing capacity of faults. Most of the oil industry is polarized over which of these mechanisms is the dominant control on hydrocarbon column height in fault-dependent traps. Recent work by Shell in the southern North Sea, suggests that a unified approach to fault seal analysis that integrates these mechanisms best explains observed column heights.
The gas play in the southern North Sea, offshore Netherlands, relies on fault dependent traps in the high (50-85%) net/gross (N/G) Rotliegende reservoir. Juxtaposition leak points appear to control the majority of column heights, however, column heights for several of these traps can also be explained by the sealing capacity of fault gouge. Some of the largest column heights cannot be adequately explained by either juxtaposition or fault gouge, but by a third mechanism that adds to column heights and is impacted by burial history and basin inversion (e.g. cementation and diagenesis). Finally, fault seal destruction by geomechanical dilation appears to not have played a role in this area.
We are attempting to integrate multiple fault seal mechanisms (juxtapostion, fault gouge, cementation/ diagenesis and geomechanical dilation) into a unified workflow for fault seal analysis. A better understanding of the conditions under which these fault seal mechanisms operate will greatly facilitate our ability to predict column heights globally.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.