Anatomy and application of facies-potential coupling on hydrocarbon accumulation in typical lithologic reservoirs in Jiyang Depression

Oil and gas exploration in the Jiyang Depression showed that lithologic reservoirs were mainly controlled by facies and interfacial potential. As to the facies-controlled effect, the favorable facies with high porosity and high permeability controlled hydrocarbon accumulation. And for the potential-controlled effect, low interfacial potential controlled hydrocarbon accumulation. Only in the coupling region of favorable facies and low interfacial potential, could lithologic reservoirs form. Through typical cases studies of the lithologic reservoirs of the Cheng913 in the Zhanhua Sag and the Niu35-Niu20-Wang70 in the Niuzhuang Sag, results showed that only when the facies-potential coupling index(FPI) was larger than 0.5, could hydrocarbons accumulate in lithologic traps. Besides, the critical condition for hydrocarbon accumulation displayed the characteristics of Two Lows or Two Highs, that was, low or high facies index (FI) and interfacial potential index (PI_S). The larger the FPI was, the higher the oil saturation was, and the easier it was for hydrocarbons to accumulate. Based on the statistics of petroliferous property and the analysis of facies, the potential characteristics of 73 lithologic traps and 54 turbidite lens traps in the Jiyang Depression were concluded, and the quantitative models of the relationship between oil saturation and FPI for two categories of traps were established. Oil saturation of 13 lithologic traps in the Dongying Sag was predicted through this model, and it achieved the accuracy rate of 84.6% for the reservoirs with the deviation rate less than 20%. As a result, this model could be applicable in predicting the oil saturation of lithologic reservoirs.