The gas reservoirs in the Xujiahe Formation

Guang'an area

central Sichuan Basin

are porous-litho-logic tight gas reservoirs.Production test data of 78 wells in the area were analyzed and the following conclusions were obtained.Pore throats in these reservoirs form the main carrier system during the pooling process

and the migration

accumulation and distribution of gas and water is controlled by the physical properties and heteroge-neity of these reservoirs.Gas accumulation is affected by the structures during the later reformation of these reservoirs

and the relatively low amplitude of the structures causes the poor gas-water differentiation

thus water production is common in the gas wells there.The gas reservoirs can be divided into three zones(primary gas zone

secondary gas zone

and gas-water zone) according to the gas and water distribution.Three patterns of gas and water distribution are correspondingly proposed

namely highly permeable zone pattern

single sandbody pattern and micro-fracture-controlling pattern.