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ABSTRACT: Seismic delineation of multiple channel geometries using sequence stratigraphy, contribution plots and seismic calibration in Tapti field, India

Ullrich, Laura J., Charles J. Kaiser, Michael Van Horn, and Steven W. Bailey , Enron Global Exploration & Production Inc, Houston, TX

Tapti is one of the largest gas fields in India, discovered in 1978 by ONGC but not developed until 1997, due in part to difficulty in predicting reservoir geometries to assess gas in place. Most of the 13 pay zones are in channel sands. 3D seismic, which was acquired in 1995, indicated that the gas sands had amplitude supported channel geometries. Seismic interpretation of the reservoir horizons required detailed analysis of seismic responses to lateral facies and thickness changes, interference from adjacent pay sands (plus the base of sands), and their variations as they flipped polarity or dimmed at the water contacts. In order to understand the complexities of these variations, synthetic contribution plots were analyzed. Base case synthetics (in-situ, gas and wet) were generated after well bore and gas effect edits of the sonic and density logs were made. Synthetic contribution plots greatly enhanced our understanding of the interference effects from changes in adjacent pay zones and the importance of understanding adjacent zones when interpreting amplitude and AVO data. There are 22 known water contacts in the field. MDT data acquired on the first three development wells established multiple GWCs, and helped determine that several zones shared a GWC. The integration of this information and good velocity control with the synthetic models enabled us to understand the amplitude changes at the contacts. Sequence stratigraphy was utilized to determine which channels were incised valley fills, which had lateral equivalents and which sands were highstand or transgressive.

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia