Geologic Hazards and Constraints, Federal Oil and Gas Lease Sale 53 Area, Offshore Central and Northern California: ABSTRACT

Abstract

Studies have been completed to assess potential geologic hazards and constraints which could adversely affect safe petroleum resource development in offshore areas of central and northern California. The study includes 243 tracts tentatively selected for the proposed federal Outer Continental Shelf (OCS) Oil and Gas Lease Sale 53. Geologic hazards and constraints are identified in five offshore areas of central and northern California: Santa Maria, Santa Cruz, Bodega, Point Arena, and Eel River. A total of 10,500 line-km of high-resolution data was collected on a 1.0 × 2.0-km grid over the five areas. Geologic hazards are defined for this study as any geologic feature or process that would inhibit the safe development of petroleum resources. Geologic hazards present on the central and northern California continental margins are: (1) mass movement of unconsolidated to semiconsolidated sediments due to earthquakes, overloading, oversteepening, or other End_Page 978------------------------------ causes; (2) steep slopes (> 10°), especially those covered by sediment, and steep-walled submarine channels; (3) faults that intersect or offset the seafloor or Holocene sediments; and (4) areas of high seismic activity. Geologic features considered hazardous in their present state but whose effects can be economically lessened through existing technology and design are referred to as constraints. Constraints identified in offshore central and northern California are: (1) filled or shallow buried channels where load-bearing capacity differs from surrounding sediments; (2) gas seeps, mounds, and craters; (3) zones of unconsolidated to semiconsolidated sediments (3 to 50 m beneath the sea floor) saturated with interstitial gas under normal to near-normal pressures; and (4) possi le pressurized shallow gas identified as bright spots or amplitude anomalies. These geologic hazards and constraints were evaluated for each of the 243 tracts as a basis for recommendation of withdrawal or stipulation prior to the formal announcement of the sale. Further data acquisition and analysis on a more detailed grid will be required of lessees or operators before drilling will be permitted on leases resulting from the sale. End_of_Article - Last_Page 979------------