Reservoir Delineation using 3-D Seismic Data of the Pinghu Field, East China Sea

Qin Wang

Discovered in 1982, Pinghu gas field is the first discovery in the East China Sea. The field is 360 km offshore and sits in 90 m water depth. The structure consists of a series of northeast-trending fault blocks bounded by high angle reverse faults. The reservoir consists primarily of thick (up to 50 m) Eocene-Oligocene fluvial sandstones. Total reservoir thickness is 1200 m, with an oil leg overlying a condensate zone. Amplitude anomalies are common in multiple layers in the reservoir.

Four additional appraisal wells have been drilled. Preliminary field evaluation indicated that this field is marginally economic, primarily because its remote offshore location. Several questions have raised after the preliminary field evaluation. Are there potential undiscovered reserves in fault blocks adjacent to the main block? Where is the best location for another appraisal well? What is the cause of amplitude anomalies? Do they relate to gas-filled reservoirs, coal beds or lithology? Where is the best location for a production platform?

This integrated study uses 3-D seismic data, petrophysical data, seismic modeling and amplitude analysis to address the aforementioned questions. The study shows that the coal beds are the primary causes of amplitude anomalies. Studies of well logs and extracted amplitude maps have helped build depositional environment maps for each of the individual reservoir zones. From these maps, the thickest pay sand locations have been predicted. Structural closure is present in a fault block west of the reservoir, and channel sands have been predicted based on 3-D interpretation, indicating additional reserves may be found in that block.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995