| With the successive breakthroughs in the oil and gas exploration of Middle—Lower Ordovician carbonate
buried-hill in Luosi—Madong area of Tarim Basin, the complexity of carbonate reservoir becomes increasingly
prominent. By analyzing the datum of drilling, seismic, well logging, cores and thin sections, it’s recognized that the
properties of carbonate buried-hill reservoir of the Middle-Lower Ordovician in different settings are significantly
different. First of all, the properties of reservoirs are greatly affected by lithology in vertical. The Penglaiba Formation is
composed of fine-grain dolomite, the Lower Setting of Yingshan Formation is composed of mixed layers of dolomite and
limestone, while the Upper Setting of Yingshan Formation is composed of micrite, and the reservoir properties are getting
poorer from the Penglaiba Formation to Upper Setting of Yingshan Formation. Secondly, the reservoir properties of
carbonate buried-hill between exposed areas and covered areas are different on the plane. The reservoirs in Upper Setting
of Yingshan Formation only develope in exposed areas along the fault belt and the reservoir spare are dominated by
fracture or pore, while reservoirs does not develop in covered areas. The Lower Setting of Yingshan Formation is
characterized with“bead”reservoirs with fractured reservoir developing complementally in the exposed area. Besides, the
Penglaiba Formation is dominated by porous reservoirs which not only develope in exposed areas but also in covered
areas. By analyzing the distribution of reservoirs in Middle—Lower Ordovician, three models are presented: (1) the
Penglaiba Formation is dominated by structural massive reservoirs, (2) the Upper Setting of Yingshan Formation is
dominated by fractured quasi-layered reservoirs, and (3) the Lower Setting of Yingshan Formation is dominated by
fractured-vuggy reservoirs. |
