Case Study of the Structural and Depositional Evolution Interpretation from Seismic Data

Based on Bally's balanced cross section concept and the sequence stratigraphy theory proposed by Vail, this paper discuss the dynamic interpretation of structural evolution and depositional evolution using 3D seismic data, and by integrated interpretation of the paleo-geomorphology, sedimentation supply with the structural evolution and depositional evolution study results, remaining oil was predicted.

The study field is on a monocline structure in the Jungar basin in western China, with depths between 3230-3480 m. And Jurassic (main producing layer) formation contacts its underlying formation as an angular unconformity. The field has been in production since 1991 with water cut around 60% at the time of 3D seismic acquisition in 2006. Well A situated in the low position outside the oilfield with 5784 tons of accumulative oil production which puzzled reservoir engineers and a 3D seismic is designed to hopefully explain why.

From structural evolution and depositional evolution study on the 3D seismic, in only 260 ms time interval seven quasi-depositional sequences of sedimentation were identified during Jurassic period. Paleo-geomorphologic picture of the Jurassic reservoir sand revealed that the oil field sits on a paleo incised valley fill in Jurarrsic, and interpretation of the flattened section (along bottom of Cretaceous K1tg) in the supply direction indicated that sedimentation supply was from north direction to the incised valley.

With the integrated study of logging and production data to above interpretation results, it is concluded that there is a lithologic variation zone corresponding to weak amplitude in seismic amplitude caused by river channel erosion in later Jurassic, and which separated out well A from the main producing zone to the west. Thus explained why we have high oil and low water production at well A which is situated at structurally low positions. The remaining oil was also predicted and proved by later production.

This case study indicated that structural and depositional evolution interpretation makes the understanding for geologic target intuitive and effective. And by integration with logging and production information, just one 3D seismic measurement could give us the remaining oil prediction result.
 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California