John O. Hastings¹, Mark E. Gregg², Charles T. Bukowski³

(1) Edge Petroleum Corp, Houston, TX
(2) Edge Petroleum Corporation, Houston, TX
(3) Edge Petroleum Corporation, Cypress, TX

ABSTRACT: Developing an Exploration Tool in a Mature Trend: a 3D AVO Case Study in South Texas

Successful exploration for new reservoirs in mature trends often requires trying techniques unproven in the area. The Vicksburg Formation in South Texas has been heavily explored since the 1920's using subsurface geology and structural mapping based on conventional seismic data. There is a scarcity of direct hydrocarbon indicators such as bright spots, which have been key to much of the success in other Tertiary formations in the region.

Our initial exploration efforts in the play met with limited success. In an effort to improve risk assessment, seismic models were generated using dipole sonic data suggesting that Class 2 AVO anomalies would be associated with Vicksburg gas reservoirs. A pilot reprocessing study demonstrated that known gas reservoirs generate Class 2 AVO anomalies and that seismic incident angles greater than about 26 degrees are required to observe them. A large non-exclusive 3D survey was reprocessed using nonhyperbolic moveout to produce usable data at incident angles of over 40 degrees. Resulting angle stacks were visualized on a workstation. Several untested AVO anomalies were identified, including stratigraphic traps.

Wildcat drilling based on this effort has resulted in six commercial discoveries and two dry holes, a success rate significantly higher than was achieved through conventional subsurface geology and structural mapping in this mature play.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado