Abstract:

Keluke Formation in the northeast margin of Qaidam Basin was mixed deposits of clastic rock and carbonate rock in transitional facies, in which shales were well developed. The shales’ distribution was studied by observation of the outcrops, and we found that the first section of Keluke Formation was the most beneficial shale exploration target with 60 meters thick in total and 92.6 percent of the ratio shales/stata. The characteristics of mineral composition, lithofacies, reservoir space types and physical properties were studied by detailed description of cores, analysis of thinsection, physical property, Xray diffraction and electron microscopy. The results showed that the mineral composition was dominantly clastic quartz and clay minerals; the main types of lithofacies were dark lamellar siltstone with mediumsized silt, black gray banded siltstone with coarsesized silt, black gray banded siltstone with coarsesized silt and carbonate and dark lamellar siltstone with mediumsized silt, bioclasts, etc. Interlayer lamellation crack, dissolution pores, the intercrystal pores, organicmatter pores and intraparticle pores were well developed in the shales; porosity has the range of 1%3%, permeability ranges between 0.01 and 1 mD. The development of shale reservoirs was affected by the sedimentary environment, mineral composition and diageneses, and the dark lamellar siltstone with mediumsized silt and black gray banded siltstone with coarsesized silt were the good lithofacies for shale reservoirs because of their large thickness, weak cementation of carbonate, high brittleness and good reservoir properties.

Key words: shales, characteristics of reservior, Keluke Formation, the northeast margin of Qaidam Basin