Luojiazhai gas field in Lower Triassic Feixianguan Fm is the third largest gas field in Sichuan basin with gas reserves of over 50 BCM.The natural gas is overmature high H

2

S dry gas

with methane content gene-rally in the range of 75.29%-84.95%

ethane content in the range of 0.07%-0.11%

and hydrogen sulfide content in the range of 7.13%-10.49%.Natural gas in Luojiazhai gas field are mainly sourced from the Upper Permian and enriched in the structural traps overlain by the(Lower-Middle)Triassic regional gypsum-halite cap rock

and are controlled by faults.This gas field is of vertical migration and accumulation system with near-normal pressure and allogenetic gas source

i.e.

hydrocarbons have been generated from the source rocks below

accumulated in the reservoirs above and sealed by caprock on the top.It is superior in reservoiring conditions.Bitumens that commonly occur in the reservoirs are the intermediate products resulting from pyrolysis of crude oil into gas in fossil oil reservoirs

and the content of bitumen is positively correlated with porosity and gas deliverability.The gas pool has experienced several processes

such as hydrocarbon accumulating in oolitic rocks and liquid hydrocarbon being deeply buried and pyrolyzed during Late(Indosinian-Early)and Middle Yan-shanian

as well as gas accumulation controlled by structure in the course of structure formation and local adjustment of fluids during Himalayan.(Middle-Late)Jurassic is the main hydrocarbon charging period. The high accumulation efficiency of Luojiazhai gas field has been ensured by the highly efficient carrier system

good reservoir space and favorable sealing conditions.