Faulting and Fault Interaction in Porous Siliciclastic Reservoirs: Insights from Outcrop Modeling of Analogous Reservoir Rocks in Sinai (Egypt) and Utah (USA)

Atle Rotevatn*, Haakon Fossen, and John Howell
University of Bergen, Norway
*[email protected]

Fault overlap zones are generally considered to have a positive effect on fluid flow across otherwise sealing faults within subsurface hydrocarbon reservoirs. This study’s aim is to assess the validity of this assumption, and to quantify the effects of relay zones on fluid flow. Overlapping faults (relay zones) have been studied and mapped in Arches and Canyonlands National Parks, Utah, using conventional as well as novel (Lidar scanning) techniques. Outcrop models were built and flow simulation was undertaken in order to increase the understanding of the effect of relay zones on fluid flow. Previous studies as well as our own show that overlapping faults commonly are associated with an over-thickened damage zone enveloping the entire overlap zone. As input to the reservoir models, the cores and damage zones of the faults in question were replicated based on detailed studies of tectonic deformation in sandstones in western Sinai (pre-rift Nubian Sandstone) as well as in Utah. Our results indicated that relay ramps nearly always represent a better conduit for flow than a low-permeable fault itself. However, our results also demonstrate that: (1) the presence of very low-permeable damage zone elements (e.g. cataclastic deformation bands) may destroy a relay zone’s capabilities as a conduit to flow. (2) Pressure communication across relay ramps may be poor despite the geometric connectivity created by the ramp. (3) Depositional facies of the affected rocks have a significant bearing on how relay zones influence fluid flow.

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