Mapping of Fracture Zones and Small Faults Using VSP and Cross Dipole Sonic in Eastern Siberia Carbonate Reservoirs, Yurubchansky Field, Russia

Abstract

Zero offset VSP, two Walkaway lines, ultra sonic and cross dipole sonic were used to interpret fracture zones and small faults in the vicinity of a deviated well drilled through carbonate reservoirs of the Yurubchansky giant oil and gas field, Russia. The fractures and small faults are the main flow conduits and storage of the hydrocarbons within mainly low porosity carbonate reservoir of the Proterozoic age. The wells are only successful if they intersect these “sweet spots” in the reservoir. This is a challenge in developing the Yurubchansky field. The 3D seismic over the field has low resolution, strong heterogeneous reservoirs, varying degrees of anisotropy, multiples contamination and therefore cannot be used to map the “sweet spots” reliably.

An incoherency attribute was used to guide fracture and fault interpretation. Two major fault zones and small faults were interpreted from VSPs. One of the fault zones within the reservoir corresponds to fractured core, intensive fracture zones interpreted from the logs and hydrocarbon shows. This demonstrates the effectiveness of high resolution VSP data in mapping fractured zones. Other geological features including unconformity at the top of the reservoir were also interpreted from VSPs.