South Marsh Island Block 128 Field, Offshore Louisiana

D. R. Lammlein, J. B. Leedy, D. C. Nester, J. M. Austin

The South Marsh Island Block 128 field is one of the larger producing fields in the Gulf of Mexico. At peak production, this giant field ranked third in annual oil production in federal offshore continental shelf (OCS) waters. The field was discovered by the Pennzoil OCS-G-2587 No. 1 well in 1974. Production commenced in July 1977. Seventy-seven exploratory and development wells have been drilled. Cumulative production from three production platforms is over 81 million bbl of oil and 89 billion ft³ of gas. Estimated ultimate recovery is 101 million bbl of oil and 175 billion ft³ of gas.

The field is a faulted anticline underlain by salt. Production is from 20 Pleistocene sandstones sourced by deeply buried pre-Pleistocene shales. Faulting and permeability barriers separate these sandstones into 93 complex reservoirs.

Because of very favorable geologic conditions and vast improvements in seismic technology since the acquisition of Block 128, the field was selected for an integrated geological and geophysical evaluation. This study used a dense grid of modern and reprocessed 2-D and 3-D GRID^TM data for detailed seismic stratigraphic and structural mapping. Seismic and well data were integrated utilizing synthetic seismograms, seismic modeling, and petrophysical studies.

Following this evaluation, two exploratory and four development wells were drilled. A fourth production platform is being fabricated to develop an extension to the field. Reserve additions from drilling and revisions have significantly increased recoverable reserves. This ongoing evaluation has continually refined our geologic understanding, and although the field is mature, exploration and development continue.

AAPG Search and Discovery Article #91022©1989 AAPG Annual Convention, April 23-26, 1989, San Antonio, Texas.