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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.

 

Abstract

 

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.

 

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Favorable geological conditions for lithological traps in the Songliao basin.


Case study, Jidong Oil Field: Optimal selection of oil- and gas-rich sags; sag-wide 3D seismic and integrated interpretation.

 


Case study, Jidong Oil Field: Depositional environment reconstruction, reservoir description, lithological trap assesment, and 3D exploration of multiple formations and targets.


Geological controls on formation of lithological traps: Three interfaces control the distribution of major lithological traps.


Case study, synclinal region of Ordos basin: New reserves increased by 460 million tons in 2003-2006.


Exploration results in Bohai Bay and Songliao: Size of field with lithological trap and related reserves have increased significantly since 2003.

 

Conclusions

 

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.