A Comparative Study of Cambrian Hydrothermal
Dolomite and Associated Dolomite
Reservoirs in Western Canada Sedimentary Basin and Tarim Basin in NW China
Hairuo Qing1, Daizhao Chen2, Zhijun Jin3, and Ping Luo4
¹University of Regina, Regina, SK, Canada
²Institute of Geology and Geophysics, Beijing, China
³SEPRI, Sinopec, Beijing, China
4RIPED, PetroChina, Beijing, China
The process of dolomitization and formation of dolomite reservoirs have been a controversial
topic for a long time. Numerous dolomitizing models of have been proposed to explain the
occurrence of massive dolomite in the rock record. However, if these models were applied
blindly without much scrutiny, a dolomite bandwagon is produced, such as seepage/reflux
model in the 60’s and mixing zone model in the 70’s-80’s. Since late 80’s, a number of
detailed case studies from the Western Canada Sedimentary Basin (WCSB) suggested that
hydrothermal
fluids played a vital role in formation of massive dolomite and associated
reservoirs. In recent years,
hydrothermal
dolomitization has received so much attention and is
becoming a new dolomite bandwagon, which has been applied indiscriminately to some case
studies in China where the differences between these so called
hydrothermal
dolomite were
ignored.
Our comparative study and analyses of Cambrian hydrothermal
dolomites from the WCSB
versa those from the Tarim Basin indicate a fundamental difference between the
hydrothermal
dolomite in these two basins. The
hydrothermal
dolomites from the WCSB
generally occurred in an open system that delivered Mg as well as heat to the reaction site;
whereas most of
hydrothermal
dolomites in the Tarim Basin occurred in a closed or semi
closed system, where Mg is mostly derived via chemical compaction of precursor dolomite.
This fundamental difference resulted in a number of unique petrographic and geochemical
characteristics of
hydrothermal
dolomites in two different basins:
(1) The WCSB is characterized by high water/rock ratio of an open system; the Tarim Basin illustrates low water/rock ratio, typically of closed, semi-closed system.
(2) In the WCSB, hydrothermal
fluids precipitated large amount of dolomite cement and
replaced host precursor limestone; in the Tarim Basin
hydrothermal
fluids mostly
modified earlier dolomites with minor amount dolomite cements.
(3) In the WCSB, the geochemical signatures of hydrothermal
dolomite are distinctly
different from those of host carbonate rocks; in the Tarim Basin the geochemical
signatures of
hydrothermal
are similar to host carbonate rocks.
(4) In the WCSB, hydrothermal
fluids is mostly related to deeply seated fault system; in
the Tarim Basin
hydrothermal
fluids is mostly like linked to the igneous activities.
The fundamental difference of the origin of hydrothermal
dolomite from the WCSB and from
the Tarim Basin requires a different exploration strategy applied to these two basins. In the
WCSB, explorations of
hydrothermal
dolomite should be focused along regional conduit
system along regional faults and reef chains. In the Tarim Basin,
hydrothermal
dolomite
reservoir preferentially occurs around igneous intrusions and/or local fault systems.
AAPG Search and Discovery Article #90175©2013 AAPG Hedberg Conference, Beijing, China, April 21-24, 2013