Complex Karst-controlled Reservoirs in Paleozoic Limestone of the
CIS,
Lapointe, Philippe A.1,
Arnaud Meyer2 (1) TOTAL E&P, 64018 Pau,
France (2) Total Exploration Production, Pau, France
Carbonate karst-controlled
reservoirs are economically interesting. Case histories from CIS,
Detailed examination of cores cut in CIS
and Kazakhstan fields and Europe reveals the karstic
nature, meteoric and coastal/island, of the diagenetic
processes that affected the reservoir and includes the following: cave fills,
locally with shales, fractures enlarged by leaching,
morphologies with erosion overprint and, breccia.
These karsts appear polycyclical, and of wide
extension, but have a low impact on the overall porosity.
The main reservoir enhancement is related
to hydrothermal overprint. The hydrothermal karst
follows the faults and fracture corridor, using the polycyclic meteoric karst and the remnants of the coastal mixing water karst as well as stylolite plans,
bedding and joints. Open conduits and caverns, geodic sparite
cement and other exotic minerals characterize this phase. A low hydrothermal
activity episode corresponds to pulverized zones of the limestone, and creates
high permeability drains.
Mapping of the actual reservoir remains
critical for predicting the best poroperm zone
distribution and the prognosis of future production well locations,
particularly for horizontal or highly deviated wells. The 3-D approach leads to
horizontally-driven and vertically-driven cave developments controlled by all
the existing heterogeneities and particularly those related to the tectonic
events. The resulting complex reservoir is specific. Its identification and
understanding are of paramount importance for reservoir development,
particularly in Paleozoic rocks.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California