Abstract:

Various types of fan delta systems have been developed in different evolution stages of faulted basin. Being controlled by the supply rate of sediments, expansion rate of available space and nature of lake basin's boundary fault, four types of fan deltas have been deposited in the 3rd member of Shahejie Fm(Es₃) in Gubei oilfield. Retrograding fan delta has been deposited along with the transgression of the lake in the early and middle Es₃ ;and the prograding fan delta has been deposited during the regression of the lake in late Es₃.There are obviously different sedimentary characteristics, reservoir distribution and reservoir quality between the steep fan delta and the gentle one, the latter has better reservoir quality with an average porosity of 18.2% and average permeability of 293×10^-3 μm², because it has relatively shallow burial depth and weak diagenesis.In addition, the microfacies of sediments would also control the reservoir quality.The glutenites deposited in subaqueous distributary channels in front of the fan delta have the best reservoir quality with an average porosity and permeability of 20.5% and 350×10^-3 μm²,respectively.The deep lacustrine dark-colored mudstones constitutes the major hydrocarbon source and cap rocks, and the glutenites deposited in front of the fan delta are relatively good reservoirs,which would constitute a good combination of source,reservoir and cap rocks. The Es₃ would,therefore,be the target of further exploration.

Key words: fan-delta, steep-slope type, gentle-slope type, sedimentary characteristics, reservoir quality, Gubei oilfield, Zhanhua depression