Characteristics of Ordovician Carbonate Reservoirs in Hetian River Gasfield and Its Adjacent Areas

Ordovician carbonate is an important exploration target in the Hetian River Gasfield and its adjacent areas.Natural gas has been found in the region.Controlled by karst,cracks and sedimentary environments,the reservoir pore structure in Ordovician carbonate is very complex,and dissolution caves and cracks are the most important accommodation spaces.The petrophysical properties of various Ordovician stratigraphic units are different.The dolomite in the buried hill of Penglaiba Formation is the best reservoir,and the limestone of Lianglitage Formation is the worst reservoir,and Yingshan Formation is in the between.Three stages of weathering crust karst and five stages of structural fractures developed in the Hetian River Gasfield.Multiple stages of structural fractures(especially the structural fractures developed during the Himalayan movement),posttectonic karst and paleo-weathering crust karst have influenced and spliced each other.These factors and the sedimentary environment controlled the complicated karst system of the Hetian River Gasfield,and they effectively improved reservoir pore space of Ordovician carbonate together.