Abstract: 3D Exploitation of Nod Mex Reservoirs in Phase Four Field, Wharton County, Texas

MARK D. McCUEN, and MARK A. WEST
Cox & Perkins Exploration, Inc., Houston, TX

Phase Four field is located in the "Expanded" or "Downdip" Yegua trend in south-central Texas, where reservoirs are developed within the lowstand systems tracts of at least six high-frequency type-one sequences. Phase Four Field is actually a complex of multiple small isolated reservoirs (<200 acres), which are stratigraphically and structurally compartmentalized. Shelf-edge deltaic sand lowstand prograding complexes provide the reservoirs in the Phase Four field complex. These deltaic sands display extreme lateral variations in thickness. Incised valley feeders channeled sediment across the shelf and formed distributary channel complexes within the lower reaches of the valley mouths at the faulted shelf edge.

Field development of Phase Four Field was difficult due to the ineffectiveness of the 2D seismic data in imaging the complex stratigraphy and faulting. Approximately 30 square mi of 3D data was acquired in the Phase Four field area. In addition to the full offset, DMO migrated volume; near-offset, mid-offset, and far-offset migrated volumes were created for AVO interpretation. A comparison of pre- and post 3D interpretations and 2D versus 3D seismic show the effectiveness of the 3D seismic and the 3D AVO method in rapidly analyzing the existing and potential reservoirs. Test wells were targeted in the optimum parts of the reservoirs, resulting in higher sustained rates and quicker payouts. The 19 wells drilled based on interpretation of the 3D data yielded a 79% commercial success rate versus 24% from 21 wells drilled prior to the 3D survey.