Abstract: Natural Fracturing Impacts Siliceous Shale Reservoir Development: Cymric Field, California, U.S.A.
JOHNSON, SCOTT J.,
GOPA S. DE, and DONALD F. WINTERSTEINGeophysical data show
pronounced systematic variations in reservoir anisotropy
orientation in
a shallow (< 500 m) Monterey-equivalent reservoir in the Cymric Field
of California. Variations occur over limited areal (< 125 m) and vertical
(< 5 m) distances. Two main orientations are evident: north-northeast
and west-northwest, perpendicular and parallel to anticlinal trends, respectively.
Borehole image data indicate that north-northeast
anisotropy
is regional
maximum horizontal in-situ stress and west northwest
anisotropy
is an oriented
natural fracture system and/or a local stress related to natural fracturing.
Andersonian fault theory accounts for local stress reorientation which
is possible due to the small difference in maximum and minimum horizontal
in-situ stress magnitudes.
Variations in reservoir anisotropy
orientation and type result in significant areal and vertical variations
in depletion geometry patterns. In relatively undeformed portions of the
reservoir where fracture permeability is negligible and regional stress
pervades, cyclic steam injection induces a fracture parallel to regional
maximum horizontal in-situ stress. Where natural fracturing is well-developed,
cyclic steam either induces a fracture of reduced width and height growth
or is injected into the oriented natural fracture system. Oriented fracture
systems in thin, widespread, stratum-bound zones focus injection and facilitate
intrawell communication. Understanding depletion geometry patterns as they
relate to natural fracturing is a key step in optimizing field development.
Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California