Reservoir characteristics and development controlling factors of Ordovician weathering crust in Daniudi gas field

Based on cores and thin sections observation,identification and physical properties analysis,the research on reservoir characteristics and development controlling factors of Ordovician weathering crust in Daniudi gas field has been carried out.The results indicate the reservoirs are mainly of3 classes,the mud microcrystalline powder crystal dolomite class,the rock(cream)dissolved breccia dolomite class and the grain dolostone class.There are mainly four types of storage-permeation bodies,the intergranular pore type,the solution pores type,the cracks-holes type and the cracks type,among which the pore type is the most developed,the dissolution pore(hole)and the crack-hole types followed,while the pure fractured-vuggy reservoir is relatively less.The main distribution range of reservoir porosity is less than4%,the permeability distribution range is(0.01~0.32)×10-3μm2 and it belongs to low porosity low permeability reservoir.The reservoirs from Ordovician weathering crust in the lower Paleozoic are mainly controlled by sedimentary and ancient karstification.On the top of the Ordovician,a large number of karst holes,holes and seams have been formed,and then carbonate karst reservoirs have been formed.