Sedimentary characteristics of the terminal fan deposits and distribution of residual oil in the upper oil reservoirs of the second member of the Shahejie Formation in the Pucheng Oil Field, Henan

Exemplified by Nos. 2 + 3 sand sets in the upper oil reservoirs of the second member of the Shahejie Formation in the Pucheng Oil Field, the present paper deals with the sedimentary characteristics and model for the terminal fan reservoirs and distribution of residual oil. The terminal fan facies may be subdivided into the proximal fan, middle fan and distal fan subfacies. The distributary channel microfacies of the middle fan subfacies is believed to be the main reservoir sandstones. The residual oil is concentrated to the transitional zones of the flanks of the distributary channel microfacies, proximal overbank, distal overbank and lens which are difficult to be controlled by well spacing patterns. Vertically, the residual oil tends to be enriched in the areas with poor physical properties such as the top of the normal rhythmic successions and base of the reverse rhythmic successions. More precisely, the residual oil occurs in the areas near the gas cap in S₂³ and S₂⁴ beds of No. 2 sand sets, and structural highs of Pu-53 and Wen-17 fault blocks within S₃⁴ and S₃⁵ beds of No. 3 sand sets.