Abstract: The delineation of reservoir distribution in organic beach reef is significant for reserve estimation and exploitation.In Yuanba area,the organic beach reef in the Changxing Formation is buried over 6 000 m deep,and is featured by lateral deformation and strong heterogeneity.It is difficult to delineate reservoir distribution quantitatively by simple forecasting method.Based on sedimentary facies,the quantitative forecast of phase-controlled reservoir has been carried out with high accuracy.It describes the distribution feature and limit of organic beach reef.The returned ratio of evaluation wells is 100% and the available reservoir thickness is 20-70 m.The gas-bearing area in the Changxing Formation is 155.33 km²,and the gas-in-place is about 1 592.53×10⁸ m³.