Characteristics of fissures and their bearings on oil and gas accumulation in the Xujiahe Formation in central Longmen Mountains,western Sichuan

The oil and gas accumulation in the deep-seated strata of the Xujiahe Formation in the frontal areas of the Longmen Mountains tends to be controlled by the fissures that,in turn,are associated with geological structures and faults.The characteristics of fissures are explored with the aid of acoustic emission,homogenization temperature of inclusions,and carbon and oxygen isotope data.The fissures in the Formation include structural fissures and diagenetic fissures.There once occurred multiple phases of tectonic movements in the Formation,including the Indosinian,Yanshanian and Himalayan orogenies,of which the former two were relatively weak and only minor amount of fissures are observed whereas the latter were highly severe and accounted for the formation of numerous faults and structural fissures which may be essential conditions for the enrichment of oil and gas in the dense sandstone reservoirs of the Xujiahe Formation.