Features of Sandy Debris Flows of the Yanchang Formation in the Ordos Basin and Its Oil and Gas Exploration Significance

Abstract

Abstract:Sandy debris flow is a new genetic type of sand bodies, which has gained much attention in recent years and its corresponding theory is proved to be a significant improvement and even partial denial to the “Bouma Sequence” and “turbidite fan” deep‐water sedimentary theories to some point. Oil exploration researchers are highly concerned with sandy debris flows for its key role in controlling oil and gas accumulation processes. In this article, by applying sandy debris flows theory and combining a lot work of core, outcrop observation and analysis plus seismic profile interpretation, we recognized three types of sedimentary gravity flows that are sandy debris flows, classic turbidites and slumping rocks in chang‐6 member of Yanchang Formation in the deep‐water area of central Ordos Basin. Among the three types, the sandy debris flows are the most prominent and possesses the best oil bearing conditions. On the contrary, the classic turbidites formed by turbidity currents are limited in distribution; therefore, previous Yanchang Formation deep‐water sedimentary studies have exaggerated the importance of turbidite currents deposition. Further study showed that the area distribution of deep water gravity flow sand bodies in Yanchang Formation were controlled by the slope of the deep‐water deposits and the flows had vast distribution, huge depth and prevalent advantages for oil forming, which make it one of the most favorable new areas for Ordos Basin prospecting.