AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
From Dry-Hole to Discovery and Sanction-Ready Development in Less than Three Years: OBS-WAZ Seismic Enables West Boreas and South Deimos Discoveries and Fast-Paced Big Cat Development
(1) Shell Oil Co., New Orleans, LA.
Prestack depth migration of streamer seismic data in early 2000’s led the Deimos discovery, which is a deeper extension of the Mars Field to older sub-salt reservoirs. A highly anticipated follow up exploration well (Boreas) of the updip extent of these reservoirs was drilled in 2004. The Boreas well, had disappointing results: penetrated little sand, and was mostly wet. Furthermore, well results indicated the presence of a previous unimaged major fault which offset the Boreas sub-basin from the prolific Mars Basin. Thus, the Boreas sub-basin became an unattractive candidate for further exploration. In Late 2007, Shell acquired its first Ocean Bottom Seismic-Wide Azimuth (OBS-WAZ) survey to enhance Deimos Field development, which covered a portion of the Boreas sub-basin. The OBS-WAZ was processed and migrated with an existing dual-azimuth anisotropic velocity model and was delivered to interpreters in Q1, 2008. The improvement over the conventional 3D long streamer seismic resulted in a step change in our geologic and stratigraphic understanding and exploration strategy within the Boreas sub-basin. West Boreas and South Deimos stood out as very attractive prospects due to their structure-fitting amplitude anomalies interpreted as direct hydrocarbon indicators. The new survey also showed that the 2004 Boreas well missed a significant HC accumulation, West Boreas, by less than 200 feet and that a fault likely cut out most of a high quality reservoir sand. The OBS-WAZ seismic image and subsequent interpretation were of such high quality that the West Boreas prospect was matured from initial recognition on the newly delivered survey, to a major discovery in approximately one year. Over 280 feet of high quality, oil-bearing reservoir was found just up dip of the original dry hole. The seismic-to-well tie had an excellent match and instilled high confidence in our seismic interpretation and geologic modeling of the sub-basin leading to the rapid maturation of a second prospect within the basin, South Deimos, which was drilled less than one year later. With 3 excellent well ties and calibration to well results, the OBS WAZ survey allowed a detailed structure and stratigraphic interpretation of the sub-basin and the construction of high confidence reservoir models. Thus enabling the combined discoveries to be matured at a fast pace and delivered as a sanction-ready development 2.5 years from when the OBS WAZ seismic was delivered.