Middle Permian Qixia-Maokou Formation is one of the most important series of strata to explore and develop natural gas in Sichuan Basin.Nanchuan area is located in the southeast of Sichuan Basin.The pilot exploration indicates that there is a great development potential for natural gas in Qixia-Maokou Formation.In order to know its reservoir spaces of carbonate rocks

the test methods

such as thin section identification

SEM and phase analysis of X-ray diffraction

have been taken based on the samples of Well-JY205-2.The reservoir spaces are classified into two categories:pores and fractures.Pores include organic pores and inorganic pores

while fractures include stress fractures

grain edge fractures and shrinkage cracks.The types of reservoir spaces are obviously controlled by lithology.In Qixia-Maokou Formation

the dominant reservoir space types of carbonate reservoirs are the intragranular dissolution pores and the dissolution fractures distributed along the particle edge.These dissolution fractures can connect the pores with the fractures better

and are beneficial to improve the permeability of the reservoir.There are abundant intercrystalline pores of clay minerals in the layers with higher argillaceous content.The surface porosity of intragranular dissolution pores and intercrystalline pores of clay minerals in the layer-① of Mao-1 Member are the highest and in good agreement with the higher porosity and permeability in this layer

which indicates that the layer-① of Mao-1 Member is favorable to natural gas exploration.