Geoscience Reference
In-Depth Information
constitute a 3-D framework, protected from ero-
sion…'' These authors have shown that a quantitative
analysis in term of stress inversion, with the help of
striated faults, permitted to reconstruct the stress
tensor responsible for the brittle deformation in
Rochefort Cave (Namur Province, Belgium). The
study of the longest cave in Britain (Farrant and
Simms
2011
)—Ogof Draenen (70 km), suggests that
''…presence of laterally extensive open joints, ori-
entated perpendicular to the regional neo-tectonic
principal stress field, determines the depth of flow in
the aquifer, rather than fissure frequency.''
The linear segments of surface drainages in the
present Buffalo River landscape (USA, Northern
Arkansas) are parallel to the major joint orientations,
and this correlation indicates that erosion and karst
dissolution are enhanced by regional jointing (Hudson
et al.
2009
). According to these authors ''…Joints
record past stress events, impart fracture permeability,
and
transferred to the depths of the productive oil and gas
reservoirs. Using outcrop data to characterize the
fracture pattern of a reservoir in depth is not accept-
able (Akbar et al.
1993
), because the fracture density
in reservoirs is commonly lower than values recorded
where the same formation outcrops. But, the natural
fractures assumed as a product of the regional tectonic
stresses and their control on the karst networks, can
suggest a preliminary approach when forecasting the
preferential direction for inducing fracturing in the
reservoirs. Induced fractures are expected to have a
preferential orientation subparallel to the natural
fractures, as a general tendency, but not obligatory. In
such a case, the knowledge of the recent stress field,
deduced from the local karst peculiarities, can present
valuable practical information.
For example, the Institute of Karst Geology of
China (Guilin City, Guangxi Province) promoted in
2011 a Project ''Research on the Formation and the
Pattern of Carbonate Fracture Cave System.'' The aim
of this Project has been through detailed description
and comparative study on the typical karst outcrop area
to identify the carbonate fracture cave system in the
area of Tahe Oilfield, to characterize Ordovician karst
landform units of Tarim oil and gas reservoirs, and to
''…launch construction stress field trial in the test area
of Tahe Oilfield, starting from the dynamic mechanism
of structural cracks, adopting brittle rock fracture cri-
teria, to predict the development condition of tectonic
fractures in the test area, to provide theoretical support
for the establishment of fracture prediction model in
the test area of Tahe Oilfield.'' (IKG
2011
).
Thus, the significance of studies on the relationship
between tectonic stress fields, fracturing, and karst
formation has not only scientific importance, but is
also of promising practical interest.
enhance
physical
and
chemical
erosion
that
contributes
to
landscape
evolution,
particularly
in
karst regions.''
Apart from the interest for understanding the tec-
tonic stress field as an important factor for the struc-
tured and not chaotic evolution of the karst systems,
some purely practical issues have raised when
studying the relationship between karst formation and
tectonic stress fields. For example, the paper by
Karfakis and Loupasakis (
2006
) presents data about
the stress field that caused the main neotectonic
structures in the limestone of the Formation Tour-
kovounia (Greece), the distribution and the geotech-
nical characteristics of the karstic fissures, the
orientation and the geometry of the joint sets, and the
geotechnical parameters of the limestones. The paper
proves that the influence of karst structures on the
geotechnical behavior of the limestones is of signifi-
cant importance for construction works.
The most unexpected application of the analyses
on the fracture systems as a product of the tectonic
stress in karst areas is the possibility to determine the
preferential directions of increased permeability in oil
and gas fields. Especially, this approach is useful
when the youngest tectonic stress field is reflected in
the features of the contemporary active karst. Of
course, the results of the studies on outcrops of
karstified carbonate rocks or in the accessible caves
near
References
Akbar M, Nurmi R, Standen E, Sharma S, Panwar P,
Chaturvedi J, Dennis B (1993) Fractures in the basement:
Schlumberger
Middle
East
Well
Evaluation
Review
14:25-43
Angelova D, Benderev A, Shanov S (1999) Tectonic predesti-
nation of the main stages of karst evolution of the Bosnek
Karst Region. In: Proceedings of the Jubilee scientific session
''half century of systematic conditional geological mapping
in Bulgaria'', 25-26 Feb 1999, Sofia, pp 3-5 (in Bulgarian)
the
Earth's
surface
could
not
be
directly
