H-A Wenchang Formation hydrocarbon reservoir (H-A), located in the east of the Pear River Mouth Basin, Northern South China Sea, present a complex characteristics of oil-water distribution. Currently, no reasonable... [ view full abstract ]
H-A Wenchang Formation hydrocarbon reservoir (H-A), located in the east of the Pear River Mouth Basin, Northern South China Sea, present a complex characteristics of oil-water distribution. Currently, no reasonable explanations is proposed to this complicated characteristics, which need further theoretical guidance to explain this phenomenon urgently.
This research give a rational reason to this problem via geostatistic and facies-potential coupling methods. The statistical results show that, petrophysical properties have positive correlation with oil-bearing property, indicating that petrophysical properties control the hydrocarbon distribution to some extent. This controlling effect is determined by the interfacial potential difference between sandstone and surrounding rock, and larger difference causes better oil-bearing property. Therefore, the coupling of petrophysical properties and interfacial potential can effectively analyze the characters of hydrocarbon distribution.
First, we take the fitting formula to calculate facies index (FI), through the relationships between porosity, permeability and oil saturation. The value of FI ranging from 0 to 1, larger value reflects the better reservoir physical property and higher oil-bearing property. Then, based on the conceptual model, we built the potential index (PI) by combining porosity and gas-bearing property dates in study area. The value of PI varying from 0 to 1, smaller value reflects better oil-bearing property. We analyzed the relativities between oil-bearing property and PI, FI, and obtained the weight of PI and FI by using Grey Relational Analysis method. After normalizing the weight coefficients, we acquired the calculation formula of Facies-potential coupling index (FPI). The value of FPI ranging from 0 to 1. Smaller value is, the better oil-bearing property is.
Based on the analysis above, we calculated the FPI of each small layer of the two oil layers N10 and N56, and tested the law of hydrocarbon distribution by using FPI. Result shows that, the layers with FPI value more than 0.5, reflect better oil-bearing property and higher oil saturation. As a contrast, the layers with lower FPI value less than 0.5, are mostly water layer or oil-water layer with bad oil-bearing property. This analysis has preferably applied in H-A, and it has reference for the study of deep reservoir with low porosity and permeability as well as H-A reservoir.
