Abstract:

Dongpu depression is a typical salt-lake basin in Bohai Bay region.Two sets of halites have been deposited in the two Paleogene depositional cycles.The halites in the 3rd member of Shahejie Fm (Es₃) can be divided into three sub-units: the 4th sub-member (Es₃⁴),3rd sub-member (Es₃³),and 2nd sub-member (Es₃²),which mostly distribute near the central uplift belt in northern Dongpu depression. Halites have been compacted and become very tight,which would become barriers and result in higher geotemperature and formation pressure in the underneath stra-ta,and would be favorable to the transformation of organic matters in the underlying source rocks into oil and gas. Meanwhile, halite is also a good cap rock, and would be in plastic state under high temperature and high pressure condition. Because of the barrier and deformation of the halites, multiple reservoir types related to halites have been formed, such as graben-like anticlinal oil and gas reservoirs in the upper part of the halite, oil and gas reservoirs laterally blocked by halite, anticlinal oil and gas reservoirs under the halites and lithological oil and gas reservoirs. As a result of the shifting of halite depocenters during the deposition of Es₃,there are always sandstones under the Es₃⁴, Es₃³ and Es₃² halites, which would become relatively good combination of reservoir and cap rock,and even result in very rich accumulations of oil and gas beneath the halites in central uplift belt. Although the Es 1 halite is thin, its distribution area is large and it would still play the key role in the hydrocarbon accumulation in the 2nd member of Shahejie Fm (Es₂). Much attention should be further paid to those areas, such as deep horst belt under the Es₃⁴ halites in eastern Wenliu,the Es₃² Wen 93 fan between the halites in eastern Wenliu, the Qianliyuan sag in eastern Dongpu depression and Haitongji sag in western Dongpu depression.

Key words: halite, sedimentary characteristics, depositional cycles, Paleogene, lithological reservoir, exploration, Dongpu depression