Carbonate Reservoir Characteristics Of Ordovician On The West Margin Of The Ordos Basin

Carbonate rocks are the main of Ordovician formation in the West Margin of the Ordos Basin. It is difficult to effectively distinguish and evaluate reservoir because of its strong heterogeneity and aeolotropy, which result in the difficulty of oil and gas exploration was increased. Since 1986, when the T1 well has produced 16.4×104m3 gas in Ordovician formation lower-paleozoic of Tianchi faults belt, and it reached the Industry Standard. But other regions only have gas showing while drilling, have not to reach Industry Oil and Gas Flow Standard. The total level of exploration is low, especially in the lower-paleozoic.Petroleum geology, sedimentology, solid earth physics, petrology and others are combined for this paper. And the mud logging data, core analysis data, physical properties analysis data, gas testing data are uesd to be the basic data. The characters of Ordovician sedimentary facies and reservoirs are studied with the basic data and logging data. The characters of petrography, physical properties, pore configuration, gas potential were analysised. Last, the reservoir performance was overall evaluated, and the favorable carbonate reservoirs were finded.Results:The western margin Ordovician of Ordos Basin includes the deep-water basin, platform margin slope, platform edge shallow facies, open marine platform facies, restricted oceanic tableland and platform evaporite facies. The restricted oceanic tableland facies and the platform edge shallow facies are the favorable ones.Ordovician reservoir is mainly distributed the Lower Ordovician Series ZhuoZiShan formation (equivalent to Ma6 section) and KeLiMoli formation (the equivalent Ma4 section and Ma5 section), the granular limestone and dolomite are the main reservoir rocks.Type of reservoir space is secondary dissolution pores, holes, fractures as the main reservoir space.The reservoir rocks are effected by dolomitization, partly develop intercrystal pore during the development of quasi-crystals, and during dolomitization of the deep burial, the metasomatism play a greater role in the expansion of the pore space, while the involvement of hydrothermal fluids to enhance the dissolution, the formation of dissolved pore, caverns, but buried authigenic mineral filling, making porosity greatly reduced. By analyzing display features of favorable reservoir rocks and of the gas layers, which show the central paleo-uplift and paleo-uplift to west T1 well-FD 1 well nearby within the favorable reservoir area.