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Improvements in the Geological Understanding and
Exploration Technology on Lithological
Traps
in China*
By
Wenzhi Z. Zhao1, Chengzao Z. Jia2, and Caineng N. Zou1
Search and Discovery Article #10154 (2008)
Posted October 7, 2008
*Adapted from oral presentation AAPG Convention, San Antonio, TX, April 20-23, 2008
1PetroChina Research Institute of Petroleum Exploration and Development, Beijing, China. ([email protected])
2PetroChina Company Limited, Beijing, China.
The recent
petroleum exploration strategy in China is characterized by a paradigm shift
from structural
traps
to stratigraphic
traps
. Favorable geological conditions
for forming large-scale stratigraphic
traps
exist in many Chinese sedimentary
basins. Significant variations in lithology appear to be the norm in nonmarine
basins and so are gentle structures in small marine cratonic basins. As almost
60% of the remaining petroleum resources in China occur in stratigraphic
traps
,
they have become the focus of current and future exploration activities.
Basic
geological controls for the development of stratigraphic
traps
include six
lines (pinch out, onlap, erosion, change in lithology, variation in fluid
properties and structural contours) and four surfaces (fault planes,
unconformity, flooding surface and over-/underlying beds). Large variation in
the distribution of stratigraphic
traps
has been found in four different
types
of basins (rift, depression, foreland and craton), leading to 14 different
stratigraphic play
types
. Detailed study of the trap elements,
structure-sequence combinations and reservoir filling mechanisms is vital to
the future petroleum exploration in China. This presentation reviews the recent
advances in the geological theory and exploration practices related to
stratigraphic
traps
in China.
Recent exploration success in lithological
traps
has helped China maintain a high rate of reserve growth. With
abundant remaining resources, lithological
traps
have the highest potential in reserve growth, and the growth can
be maintained for at least 10 years.
Advances
in new concept-driven exploration procedures and technology played a key role
in commercial exploration and discoveries in large scale lithological
traps
,
which were made by chance a decade ago. Today, the lithological
traps
contribute
about two-thirds of China’s total proved reserves.
The
currently targeted lithological
traps
in China have self-contained source and
reservoir combinations. A large number of secondary lithologic and
stratigraphic
traps
are dominant in central-western China. Once technology
breakthroughs are made in the future, great discoveries are inevitable.