CHARACTERISTICS OF IGNEOUS RESERVOIR AND CONTROLLING FACTORS OF RESERVOIR DEVELOPMENT IN THE PERMIAN OF THE SANTANGHU BASIN

The Permian of the Santanghu basin is one of key exploration systems of the region,in which igneous rocks,especially andesite,basalt and their transition types are main reservoir rock types,The storing space are mainly pores and fractures,and,then caves.The types of pores include air pores,residual air pores,in ter-crystal pores in matrix,dissolution pores and residual pore after cement of fractures and caves,etc.Fractures are mainly structural,and then diageneous and weathering in origin.The reservoir spaces experi enced very complex evolution processes,including nine stages:(1)primary pore(air pores and contraction fractures)development;(2)mineral filling up after igneous stage;(3)dissolution near surface;(4)burial filling up in pores;(5)first stage of structural fracture development;(6)cave development;(7)second stage of structural fracture development;(8)later filling up,and(9)dissolution stage.According to the storing space and petrophysical properties,igneous reservoir can be classified into the following three types:reservoir I,porosity 10%~22 %,permeability larger than 10×1O^-3μm²,some up to 100×10^-3μm²,belonging to pore-fracture-carve composite reservoir and partly pore-fractured reservoir,reservoir Ⅱ,porosity larger than 10%,permeability(1~10)×10^-3μm²,belonging to pore-fractured reservoir and partly fractured reservoir,reservoirⅢ,porosity less than 10%,permeability less than 1×10^-3μm²,belonging to pore-type reservoir and partly fractured reservoir.The controlling factors of reservoir development are mainly igneous facies,structure fracturing and dessolution.In addition,hydrocarbon invasion is very impor tant in reservation of storing space.