Abstract

The Bohai Basin of north east China forms part of the large and prolific North China Basin, with proven reserves of about 3 × 10⁹m³ oil equivalent (20 BBOE). The basin is underlain by Precambrian granitic and metamorphic rocks of the Sino-Korean platform, Cambro-Ordovician shelf carbonates and localised Upper Palaeozoic and Mesozoic sands and shales. Subduction of the Pacific Plate beneath the margin of China - Eurasia commenced in the early Tertiary, causing rifting that led to the formation of the Bohai Basin. The effects of the Himalayan Orogeny, commencing in mid Miocene times and continuing to the present day, caused right-lateral wrenching with an associated phase of volcanicity. Palaeocene to Oligocene syn-rift sedimentation in a deep lacustrine environment deposited up to 2000 m of lacustrine shales with TOCs of 1.5% to 5%, which are the major source rocks for the whole of the North China Basin. The Eocene to Recent sediments record the transition from syn-rift lacustrine to post-rift fluvio-deltaic and alluvial environments, with marine conditions only being established in Pliocene to Recent times. This complex basin evolution has produced a series of sags and intra-basin highs (buried hills) and has created structural and stratigraphic traps for hydrocarbons in a variety of reservoirs ranging in age from Precambrian to Pliocene.

Historically, exploration focussed on shallow clastic reservoirs in structural traps, primarily located in the onshore parts of the basin where significant reserves were discovered in the Shengli, Dagang and Liaohe oilfield complexes. Subsequently exploration expanded into the offshore area and also focussed more towards deeper reservoirs as seismic and drilling technology advanced. Recently, discoveries have been made in deeper Tertiary and pre-Tertiary reservoirs, whilst high resolution 3D seismic and horizontal drilling technology have spurred renewed interest in shallow complex reservoirs. Significant exploration potential still remains in the basin, particularly for stratigraphic traps.