The Controlling Effect of Sedimentary Characteristics on the Heterogeneity of Sandstone Conglomerate Reservoir

The internal changes of fan deltas are complex, with differences in sedimentary environments and mineral composition of material sources being important factors affecting reservoir physical properties. There are significant differences in reservoir quality under different sedimentary backgrounds. Compared with other sedimentary types of reservoirs, the study of fan delta reservoirs is still in the exploratory and discussion stage, and classification schemes for internal architecture remain controversial. This paper proposes a new method to characterize the internal architecture patterns and heterogeneity of reservoirs by studying the sedimentary characteristics of fan delta reservoirs. This method utilizes cast thin section data to assist core and logging studies. The research includes four parts: core analysis, log facies study, geological analysis, and remaining oil distribution prediction. Multiple data sources are combined to clarify the controlling effects of fan delta sedimentary characteristics on reservoir heterogeneity. The results show that the Lower Urho Formation in Block 8 was deposited in a fan delta environment. The fan body developed two subfacies: fan delta plain and fan delta front, including seven sedimentary microfacies: braided channel deposits, overbank deposits, debris flow deposits, subaqueous distributary channels, interdistributary channels, clastic flow deposits, and estuary bar deposits, corresponding to seven lithofacies. By integrating macroscopic and microscopic analyses, the controlling factors of reservoir quality were clarified, and a sedimentary model for fan deltas in the study area was established. This research method effectively addresses the challenges of characterizing reservoir heterogeneity in the middle-late development stages of thick sandy conglomerate reservoirs. The research results provide important reference value for the development of similar oil reservoirs.