Research On Characteristics Of Reservoir In Palaeozoic Erathem Of North Rim Of Qaidam Basin

In this thesis, palaeozoic erathem formation is the study object, which located at the North Rim of qaidam basin. Petrology, reservoir quality,diagenesis and pore structure characteristics of clastic rock and carbonate reservoir were described systematically using lithologic character, physical property,mercury penetration,scanning electron microscope and x-ray diffraction datas. Then, a comprehensive reservoir evaluation was made. As a result, the favorable zone for reservoir development in study area was predicted.The stratum of palaeozoic erathem formation is made of Cambrian,Ordovician,upper Devonian and Carboniferous system. Cambrian,Ordovician and Carboniferous system are the emphasis in this rsearch. The Cambrian and lower Ordovician are passive continental margin sedimentary build by a set of carbonate deposition. Tanjianshan group of upper Ordovician is made of volcano rocks. The chuanshangou group to the chengqianggou group of Lower Carboniferous from terrigenous fan delta facies to carbonate platform facies showed transgressive depositional cycle. huaitoutala formation also showed sedimentary cycles of transgression from the littoral tidal flat environment to the carbonate platform facies for the overall performance. The keluke group to zhabusagaxiu group of upper carboniferous is from shore tidal flat, barrier island sedimentary environment to the carbonate platform facies showed sedimentary cycles of transgression.The rock types of Paleozoic carbonate reservoirs in Qaidam Basin are mainly to grainstones and crystalline dolomites. But the crystalline dolomites just developed in lower Paleozoic layers and upper Paleozoic layers. And the clastic reservoir only developed in upper Paleozoic layers including quartzose sandstones, feldspathic lithic sandstones, lithic arkoses, lithic quartzose sandstones and lithic sandstones. There are many diagenesis types in the research area such as compaction, metasomatism, recrystallization and dissolution.The Paleozoic reservoirs in Qaidam Basin came through strong compaction,cementation, complex metasomatism and dissolution on the whole. The research area’s diagenesis has high evolution level, I prefer to set it’s clastic reservoirs as middle A phase and carbonate reservoirs as mesogenetic stage.The porosity of clastic rocks in the reservoir is 0.17~12.56% and the mean value is 4.53%. The permeability is 0.0015~74.0347×10-3μm2 and the mean value is 1.9040×10-3μm2. So, we can put the reservoir as low porosity and low permeability reservoir. And the C2 K has the best reservoir quality, it’s maximum porosity is 12.6%; the porosity of carbonatite in the reservoir is 0.1~14.7% and the mean value is 1.8%. The permeability is 0.0003~76.0915×10-3μm2 and the mean value is 1.0146×10-3μm2. And the C1 h has the best reservoir quality, it’s maximum porosity is 14.7%. It has many kinds of pore spaces, secondary porosity is more developed in clastic reservoir and fractures is more developed in carbonate reservoir.We establish two criterion for the carbonate reservoir and the clastic reservoir. We also classify the reservoir and evaluate it’s quality and get the effective thickness of the reservoir. We think that the glutenites in three-section of C2 k have good reservoir potentiality. It’s thickness is about 33 m. The thickness of reservoirs in other layers is about 330 m.